Sciencemadness Discussion Board - Ethyl/Isopropyl Bromide preparation

Ethyl/Isopropyl Bromide preparation

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smuv - 2-7-2008 at 15:07

I prepared ethyl bromide last night. The synthesis was quick easy and efficient, so I thought I would post my results.

Procedure
To a 500mL RB flask filled with 42mL of azeotropic ethanol, there was added 45mL of sulfuric acid (rooto drain cleaner) portion-wise with stirring. After the flask had cooled somewhat, 33g of ammonium bromide (reagent grade) was added, as the contents of the flask were swirled. The flask was put into an oil bath and set-up for simple distillation. The receiver was a 150ml beaker which was filled with enough ice water to partially immerse the drip tip of the condenser under water. The flask was rapidly heated and shaken periodically; a nice red-orange hue from Br2 quickly developed. Soon HBr vapors began fuming from the condenser, at which time a damp paper towel was draped over the receiver to absorb any evolved HBr. The fuming ceased after a few minutes and ethyl bromide began coming over. The ethyl bromide was collected for about 25 minutes until only a water miscible distillate could be collected.

Results
In total, 20mL of ethyl bromide was collected, corresponding to a 75% yield based upon the ammonium bromide. This synthesis was quick easy and high yielding. Throughout the reaction not a hint of ethyl bromide could be smelled, although I got a few whiffs of it during clean up.

[Edited on 7-7-2008 by Polverone]

Zinc - 2-7-2008 at 15:17

Very interesting!!

I have heard that nitroethane can be made from EtBr and NaNO2, is that true?

DJF90 - 2-7-2008 at 15:20

Yes, but its not particularly simple, and side product is ethyl nitrite. Method can be found on rhodium IIRC

Zinc - 2-7-2008 at 15:42

Too complicated for me to do those type of synthesizes.

Perhaps could ethyl nitrate be made from EtBr and Pb(NO3)2 or must silver nitrate be used?

497 - 2-7-2008 at 15:59

Do you think this would work with methyl instead of ethyl? I don't see why not. The condenser would have to be much colder to accommodate its lower boiling but other than that it should be simple.

Edit:

@Klute, Yes it boils at 3*C IIRC so I would use dry ice/acetone probably. I like the solvent idea though, I'll have to look in to that. And I just wanted to know if it was possible, I doubt I'll have a chance to try it any time soon. I know it was in wide use for years as a soil sterlilant and fumigant until they figured out it was so very good at destroying ozone, could it be that toxic?

[Edited on 2-7-2008 by 497]

Klute - 2-7-2008 at 16:14

Methyl bromide is a gas under STP. So you cannot condenser it without using dry ice/liq. N2.
You can however dissolove the gas in a suitable solvent, or introduce it as formed in a reaction medium for alkylating purpose, for example. Painkilla succesfully did this, search for his thread in the Org Chem. forum. EDIT: here you go: Asymmetric Etherification of 1,4-dihydroxybenzene

Be carefull, MeBr is nasty stuff, you do not want to breath (cancerigenic). Considering it's a gas, you need a suitable setup and adequate precautions. If you ever consider preparing it, I really advise you to read more on it.

[Edited on 3-7-2008 by Klute]

garage chemist - 3-7-2008 at 01:53

Vanino's book says some water must be added to the H2SO4/ethanol mix before introdution of the bromide salt, otherwise some of the HBr is evolved as gas instead of reacting!
It seems like this is what happened to you.
The ethyl bromide yield can be as high as 90% if you do it right.

smuv - 3-7-2008 at 04:35

The two books I consulted said nothing about adding water; their yields were 80% but on a larger scale. If you factor in the ethyl bromide that was lost to solubility in water the yields are pretty close to 80% even on a small scale.

In the book you quoted were they using azeotropic or anhydrous alcohol?

If I were to do it again I would disolve the ammonium bromide in the ethanol then carefully add the sulfuric acid. Maybe the addition of water could help, but honestly I have never seen that anywhere else; I'll see what vogel says tonight but I dont recall that detail.

EDIT: But I do see how addition of water could help. I was just under the impression that the water in the ethanol should keep the production and loss of anhydrous HBr minimal.

[Edited on 3-7-2008 by smuv]

S.C. Wack - 3-7-2008 at 06:02

Quote:

Originally posted by smuv
Maybe the addition of water could help, but honestly I have never seen that anywhere else

It's also in Mann and Saunders, and the 1937 Gattermann, using the K or Na salts.

garage chemist - 3-7-2008 at 06:45

They are using azeotropic ethanol in Vanino.

Here's the procedure from Vanino, translated from german:

To 1090ml 96% ethanol are added 1090ml conc. sulfuric acid rapidly with stirring.
After the mix has cooled down, 750ml icecold water are added with good stirring.
This mix is then added, with shaking, to 1kg potassium bromide in a 6l-flask and distilled at 110- 125°C oil bath temperature, at the end the bath temperature is increased to 160°C.
The distillate is separated from any water, cooled with ice and salt and mixed dropwise with conc. H2SO4 until the acid layer sinks to the bottom.
The acid layer is discarded and the ethyl bromide washed with water, dried with CaCl2 and fractionally distilled on the water bath. Nearly all passes over from 38-39°C.
Yield: 740g (510ml)

The water addition is very important for the success of the operation, omitting it not only leads to large HBr loss, but also to increased formation of diethyl ether as an unwanted byproduct.
The treatment with H2SO4 removes the ether, the specific gravity of the H2SO4 first becoming lower than that of the ethyl bromide due to the ether uptake until enough H2SO4 has been added for the acid layer to sink down.
The H2SO4 treatment also removes unreacted ethanol more efficiently than washing with water would do.

Pure ethyl bromide has a specific gravity of 1,47- 1,48 g/ml; a lower density of the obtained product would show that it contains diethyl ether.
Pure ethyl bromide also has to react neutral and must leave no trace of a pungent or garlic-like smelling less volatile residue upon rubbing some of the liquid between the hands.

[Edited on 3-7-2008 by garage chemist]

Siddy - 3-7-2008 at 20:29

When i have prepared halides from alcohols, i have used excess HX source and a i utilize a NaOH trap. A rubber tube from the top of the condenser to the a beaker of NaOH solution, no nasty fumes

I suppose in this case, the EtOH is easier to get a cheaper than the Bromide source so thats why you used excess EtOH.

This method works for all primary aliphatic alcohols, even better with aromatic but gets complicated / hindered with secondary and tert. So yes, it works with MeOH, from memory vogel describes the same method for halides.

smuv - 3-7-2008 at 20:39

Quote:

The ethyl bromide yield can be as high as 90% if you do it right.

the procedure you posted has an 80.8% yield on a massive scale....and seems like it would take longer.

But ill give it a try on a smaller scale soon, just to see.

MagicJigPipe - 4-7-2008 at 07:06

I wanted to add that if you are using this for a Grignard Et2O "contamination" might be beneficiary. I assume the ratio of Et2O to EtBr could be determined by density and then more could be added for use in a Grignard.

However, is it difficult to dry Et2O/EtBr mix without loss of Et2O? I never knew that to be the case.

garage chemist - 4-7-2008 at 10:36

I have to admit I didn't calculate the percentage yield of the procedure from Vanino.

But you should really determine the density of the product and the gram yield of your procedure, smuv.

And ethanol contamination of the product is no doubt best taken care of, along with Et2O contamination, by the H2SO4 treatment in Vanino's procedure.
Intentionally leaving Et2O in the product seems to be unpracticable to me- it's really important that no ethanol is in the product, otherwise the grignard won't start.
The temperature of the EtBr procedure is too low for efficient formation of Et2O anyway.

The preparation of methyl bromide is described in Vanino as well.
It is analogous to the EtBr preparation, and uses the proportions:
218ml H2SO4
150ml MeOH
150ml ice water
200g KBr
The resulting MeBr gas is taken off at the top of the reflux condenser, dried with calcium oxide and liquefied by a good ice/NaCl mix.

Vanino also describes the preparation of methyl chloride: A mix of 2 parts MeOH and 1 part anhydrous ZnCl2 is boiled under reflux while a rapid stream of dry HCl gas is passed in.
The MeOH is completely converted into MeCl.
The gas is taken off at the top of the reflux condenser, washed with water to remove HCl and MeOH vapor, dried with CaCl2 and liquiefied with dry ice/ether.
Alternatively, the MeCl can be dissolved into alcohol, which dissolves a large amount of the gas, stored this way, and liberated again by dropping the solution into water, which produces a constant stream of the gas.
This storage method probably also works for MeBr.

Bromoethane a la Vanino

smuv - 5-7-2008 at 21:50

I again synthesized ethyl bromide, this time by the procedure from Vanino posted by garage chemist. I scaled the procedure down to use 33g of ammonium bromide so that I could directly compare the two methods. To be clear: the main difference between the two procedures is the addition of water. The hope is, that by adding water less bromide is lost as HBr and less Ether is able to form.

Procedure
A 200mL beaker was filled with 44mL azeotropic ethanol and allowed to cool a little in an ice bath. After a few minutes 44mL of rooto drain cleaner (hopefully conc. H2SO4) was added in two portions with stirring; this solution was again allowed to cool. Next, 30mL of cold water (ca. 5 degrees C) was added in two portions with stirring.

[img]http://i277.photobucket.com/albums/kk55/babygenius814/DSC01423.jpg?t=1215321703[/img]
(the water, ethanol, sulfuric acid solution)

After cooling back to around room temperature, this solution was added to 33g of ammonium bromide in a 500mL round bottom flask. After addition the flask was swirled vigorously.

[img]http://i277.photobucket.com/albums/kk55/babygenius814/DSC01424.jpg?t=1215321846[/img]
(RB just after addition)

The flask was set-up for simple distillation and placed in an oil bath. The outlet of the receiver was immersed in water to minimize exposure to the EtBr and monitor its production (visible oily drops sinking to the bottom). The oil bath temperature was rapidly raised to ~110c and then slowly over the course of about 35-40 minutes brought to ~170c. The flask was swirled from time to time to maintain a steady production of bromoethane. EtBr first started distilling around 105c, peaked around 125c and trailed off from there.

[img]http://i277.photobucket.com/albums/kk55/babygenius814/DSC01426.jpg?t=1215321897[/img]
(the set-up)

[img]http://i277.photobucket.com/albums/kk55/babygenius814/DSC01425.jpg?t=1215322021[/img]
(receiver)

Results
Surprisingly the yield via this method was exactly the same as the previous method (from Campbell and also Cohen); although it is possible that this product contains less ether. Exactly 20mL of crude product was collected representing about a 75% yield.

[img]http://i277.photobucket.com/albums/kk55/babygenius814/DSC01427.jpg?t=1215322082[/img]
(crude product)

Final Thoughts
This alternative method of making bromoethane, in my opinion, is equal to the first. While there was no production of anhydrous HBr the prep took a bit longer; required a solution to be prepared separately, and required a lot of time cooling between each dilution of the sulfuric acid. The Vanino method produced EtBr more smoothly requiring less swirling throughout the process to maintain a steady rate of EtBr production. I don't think the yields came out being any better, because I believe the amount of HBr lost in the previous method was very minor in the grand scheme of things. Also I have found with my experiments preparing 2-bromopropane, that the production of anhydrous HBr in my first method could be greatly minimized with less vigorous heating. The other problem with the Vanino method is that a lot more water comes over with the product, so it is hard to directly obtain a reasonably dry product which can be quickly dessicated and stored (more on this when I talk about isopropyl bromide).

All in all, I think both methods have merits. I just think the method used is up to the chemist. If I were to do it again I would stick to my original method; simply because there is less prep time, and a little HBr 'smoke' doesn't bother me (especially when i replace my broken vac adapter).

P.S. I did not do any further workup because I want to wait until I make some sort of ventilation system/hood before I expose myself to EtBr free from a blanket of water.

P.P.S. I will post my IpBr syntheses tomorrow.

not_important - 5-7-2008 at 22:12

Seems to me you could use CaBr2 to complex the alcohol and water in the crude distilled product, leaving the alkyl bromide and most of the ether behind. Add extra ether and separate liquid phases, or just use plenty of CaBr2 and filter off the complexes.

Panache - 6-7-2008 at 06:18

From a Rhodium thread on nitroalkane preperation
Ethyl Bromide
'1500 ml of concentrated H2SO4 was added to 900 ml H2O, then cooled. Then 1.5 l of absolute ethanol was slowly dripped in, carefully to avoid temperature rise. Cool the mixture and add 1100-1200 g KBr (or equimolar amount of NaBr). Heat the mixture on a sand-bath at the lowest temperature at which the ethylbromide distills over, collect it in water. Wash the ethyl bromide again with water and dry it with CaCl2. Yield 90-96%.'

This works as stated, with quantative yeilds if the reaction is kept as cool as possible. The 'lowest temperature at which ethyl bromide distils', ie the temperature of the reaction matrix is initially 95C slowly creeping up to 105 over 6-8hrs. I have attempted stirring with it but found no effective change in the way the reaction ran, which is unusual as its two phase, however as the ethyl bromide is formed slowly, and is removed slowly as formed, i understand this to be the impediment to a faster reaction not stirring. The reaction time appears to remain constant. One can detect a visual change slowly in the undissolved salts from initially K/Nabr to the sulphates. This reaction produces no HBr vapour as far i i can ascertain.

Now a question i have been meaning to ask for some time. A mixture of ethyl bromide and diethyl ether is a challenging separation, any ideas for this?

smuv - 6-7-2008 at 08:59

it's been covered; wash with H2SO4; it will absorb the ether via multiple reactions; namely formation of an etherate and ethyl sulfates.

Isopropyl bromide -- 2 ways

smuv - 6-7-2008 at 12:49

So yesterday I prepared isopropyl bromide from isopropanol via the two methods previously discussed in this thread. I originally thought elimination to propylene would be a major competing reaction, so I first opted to try the method where the alcohol/sulfuric acid mixture is diluted with water. Surprisingly I found the work up for this method to be a little tricky so next I tried the undiluted method on a large scale, and was pleased with the results.

Isopropyl Bromide: Vanino method

Reagents
33g ammonium bromide
80mL 70% Isopropanol
44mL Sulfuric acid
9mL Water

[img]http://i277.photobucket.com/albums/kk55/babygenius814/DSC01428.jpg?t=1215372221[/img]
(IPA, Sulfuric acid, water solution)

Since 2-bromopropane is less volatile than ethyl bromide I decided to simply collect the distillate in a 100mL rb flask, as opposed to in a beaker under a blanket of water.

[img]http://i277.photobucket.com/albums/kk55/babygenius814/DSC01429-1.jpg?t=1215372349[/img]
(The setup)

Everything seemed to proceed just like the ethyl bromide preparation, except as expected everything kicked in at lower temperatures. From what I could tell during the synthesis elimination did not seem to be much of a problem. As time went on I noticed the receiver was getting pretty full although I could not see a visible aqueous/organic interface. By the end of the run I had collected maybe 60-70mL of a turbid emulsion. I allowed the flask to sit for a few hours, hoping that it would clear up; It didn't. I decided to add a little calcium chloride to get it to clear up, it refused to. I added more with no luck. Surprisingly the calcium chloride did not dissolve within the solution. Next I decided to add some sodium carbonate, and then just distill the damn thing to see if I could remove most of the water. Everything was set up for simple distillation and everything up to 70c was collected (I would have done fractional but working on this scale with 24/40 joints is futile). I now had about 50mL of milky distillate, I added CaCl2, and kept adding CaCl2, the damn thing never cleared up even after sitting for a day. So I momentarily gave up on the workup and tried synthesizing IpBr another way. I am guessing that the workup gave me trouble because probably some isopropanol came over during the synthesis.

[img]http://i277.photobucket.com/albums/kk55/babygenius814/DSC01441.jpg?t=1215377101[/img]
(Full of CaCl2 yet still turbid)

2-bromopropane the other way
After the previous experiment, feeling pretty confident that elimination would not be an issue, I decided to synthesize isopropyl bromide via the undiluted method on a ~1 molar scale.

Everything was done as in the first post of this thread, except, in a 1L flask, w/ a 500mL receiver and I again decided not to collect the distillate under water. Additionally, I decided to heat the oil bath less vigorously and shook the flask more frequently during the synthesis to prevent the loss of HBr.

Reagents
180mL Isopropanol (Gas line antifreeze)
100g Ammonium Bromide
133mL Sulfuric acid

[img]http://i277.photobucket.com/albums/kk55/babygenius814/DSC01433.jpg?t=1215374020[/img]
(Mixed and ready for the oil-bath)

[img]http://i277.photobucket.com/albums/kk55/babygenius814/DSC01435.jpg?t=1215374108[/img]
(The set-up)

Only a puff of HBr 'smoke' came out of the condenser just before isopropyl bromide started coming over; the loss of bromide was trivial. 2-bromopropane was produced very quickly even with gentle heating. The solution frothed a lot and at one point the distillation flask had to be lifted out of the oil bath to prevent a boil over.

[img]http://i277.photobucket.com/albums/kk55/babygenius814/DSC01436.jpg?t=1215374501[/img]
(Out of the bath, and just subsiding)

The synthesis minus workup took about 1 to 1.25 hours; 2-bromopropane just started coming over at around 100c, was most vigorous around 110-115c and was taken all the way to 165c (albeit probably with some propylene gas coming over). Even at 165c an oily flammable liquid, which burned with a sooty flame and produced HBr smoke was being produced.

The contents of the receiver were a little milky with obvious drops of water floating above an organic layer. About .75 grams of sodium carbonate was added with shaking, producing little visible bubbling of CO2. Next, calcium chloride was added and swirled until the solution was transparent; then about 50% more CaCl2 was added and the crude product was allowed to sit over night. The next afternoon the flask was swirled and shaken, the contents remained completely transparent and deemed pure enough. The isopropyl bromide was transfered to a tared amber glass bottle.

[img]http://i277.photobucket.com/albums/kk55/babygenius814/DSC01438.jpg?t=1215375364[/img]
(Straight out of the ice bath, ready for transfer)

Via this method 113.5g of isopropyl bromide was produced representing a 90% yield.

Final thoughts
Via the undiluted method 2-bromopropane was quickly and easily produced without any annoying problems. I am sure a more patient person with a better equipped lab could figure out an easy way to make 2-bromopropane via the other method, but I wont spend any more time with it. In my second attempt I used a hefty excess of isopropanol, I predict this could safely be cut back a little without any impact upon yields.

This series of experiments has been interesting because it demonstrated the differences in reactivity between a primary and secondary alcohol.

[img]http://i277.photobucket.com/albums/kk55/babygenius814/DSC01439.jpg?t=1215376006[/img]
(burning 2-bromopropane absorbed onto a paper towel. Notice the sooty flame and HBr 'smoke').

Panache - 10-7-2008 at 07:31

Quote:

Originally posted by smuv
it's been covered; wash with H2SO4; it will absorb the ether via multiple reactions; namely formation of an etherate and ethyl sulfates.

But what if it was the ether i wanted to keep?
Only joking, have you since found any browning/disscolouration in your ethyl bromide? On one run when i went far too hot i recall that even after fractionation it went brown after several days, a second sulphite wash cleared it up. Nice photo essay, that saucepan has seen better days. did someone large sit on while it was sideways?

[Edited on 10-7-2008 by Panache]

Will It Work?

smuv - 10-7-2008 at 17:39

The ethyl bromide is in a amber glass bottle so it is hard to tell until I use it. The isopropyl bromide from the first run (the one I had trouble with the work up) has been sitting in a clear 100ml rb flask with a cork stopper not too far from a window and there are no signs of bromine.

Just to document on the forum; I tried to make isopropyl chlroide via a similar method (using NaCl though) and as expected it failed; I only produced propylene and anhydrous HCl.

I wonder if preparing ethyl chloride from ethanol, H2SO4 and NaCl would work. The way I see it, the ethyl sulfates formed en situ might posses a good enough leaving group to allow the SN2 reaction to take place. I wonder if the higher temperatures required for elimination to occur on a primary alcohol would allow the chlorination to take place before elimination. I know classically lewis acid catalysts like ZnCl2 should be used but my understanding is that they complex with the alcohol removing electron density from the C-O bond allowing it to become a better leaving group; in the big picture, not too different from the formation of a sulfate.

Anyone have anything that will just blow my self-serving speculation out of the water?

P.S. Panache: Thats not a saucepan, but a very sophisticated rigorously calibrated piece of equipment.

[Edited on 10-7-2008 by smuv]

Panache - 15-7-2008 at 22:08

Quote:

Originally posted by Panache

Quote:

Originally posted by smuv
it's been covered; wash with H2SO4; it will absorb the ether via multiple reactions; namely formation of an etherate and ethyl sulfates.

[Edited on 10-7-2008 by Panache]

Oh my it has been a long time since i revisited that separation, i just went to get the ~1L out of the freezer and realised the difficult separation i had was dichloromethane and ethyl bromide, not ether and ethyl bromide as i had incorrectly remembered it as being.
Does anyone have a non-chromatagraphic (is that a wword?) idea for separating around a 50/50 mix of these two.

497 - 16-7-2008 at 01:15

Maybe freeze with LN2...

EtBr freezes at -119*C while DCM at -97*C... might not work out.

EtBr + Mg ---> EtMgBr maybe.

DCM has a water solubility about 10 times that of EtBr. That would be a pain in the ass though. Good luck.

Nicodem - 16-7-2008 at 03:31

Quote:

Originally posted by smuv
I wonder if preparing ethyl chloride from ethanol, H2SO4 and NaCl would work.

Using the search engine can often give you the answer if you dare using it:
http://sciencemadness.org/talk/viewthread.php?tid=7555
http://sciencemadness.org/talk/viewthread.php?tid=6617
http://sciencemadness.org/talk/viewthread.php?tid=2726

Ethyl Chloride Prep

smuv - 26-7-2008 at 21:10

This procedure is a re-worked methyl chloride preparation and has been adapted to yield ethyl chloride.

Reagents
30mL Ethanol
40mL 31.5% HCl
60mL H2SO4 (Drain cleaner)

The ethanol and hydrochloric acid were mixed in a 500mL rb flask, and cooled in an ice bath. The Ice bath was brought outside and the sulfuric acid was added with the evolution of quite a lot of hydrogen chloride gas, even with slow addition. Next, everything was brought back inside, put on an oil bath and setup for simple distillation with a 100mL receiver. The receiver was half filled with water and the outlet stem of the vacuum adaptor was extended with pvc tubing so it lay just below the water in the receiver (to scrub HCl gas). To the outlet of the vac adaptor where one would normally attach a vacuum pump, a piece of silicon tubing was affixed which connected to an efficient ice condenser.

(Condenser that was used to recover the ethyl chloride. It was made from 1/4" (ID) copper tubing and an old coffee can. The outlet of the spiral is soft soldered to the wall of the coffee can)

(reaction flask and condenser)

(The EtCl condenser. The receiving test tube has an atmospheric vent and is sitting immersed in a basin of ice cold water)

The oil bath was gently heated, I unfortunately neglected to take any temp readings. During heating it was ensured that the contents of the 500mL flask maintained a slow regular ebulation (nothing excessive) and that the receiver had constant flow of bubbles coming out of the extended vacuum adapter stem. The hose from the vacuum adapter was periodically removed and the gas it was emitting cautiously wafted; this helped determine if ethyl chloride was being produced (it smells like you may expect something like a milder chloroform) or if only ether was coming over. The whole operation after setup took about 1.3 hours.

Note: After reading about the toxicity of ethyl chloride and knowing its history as an induction anaesthetic for a long span of time, the wafting operation was judged to be safe.

Results
The yields were not great; I never quantified them but it looks like 2.5mL thereabouts. The recovered ethyl chloride burned with a characteristic greenish-blue flame and emitted HCl gas. I think there was a lot of holdup in my condenser and if that got worked out yields would be better. A fair bit of EtCl seemed to leave uncondensed, and sometimes condensed in and was pushed up the atmospheric vent tube. Also probably setting everything up for reflux as opposed to distillation would increase yields, as unreacted ethanol/ether would not leave the reaction vessel; in retrospect I am not sure what compelled me to setup for distillation.

(recovered EtCl...looks like some copper filings made their way over too.)

(Flame test. Performed by shaking ice cold test tube with my thumb over the outlet; after significant pressure built up my thumb was removed and the effluent gas ignited.)

Conclusion
I am sure the yields for this method could be improved with subtle changes although may never approach those of the standard methods. I believe this could be an efficient way of producing methyl chloride as methyls are more reactive via SN2 mechanisms.

@Nicodem
The only thread you posted that is pertinent to my question was the first one. In this thread 'Per' mixed hydrochloric acid with ethanol and concentrated sulfuric acid and heated everything up; then stopped the operation because HCl gas was being produced; this hardly proved anything.

Maybe for you're reading.

Methyl Chloride prep from which this was adapted

US 2153170 Continuous RCl from ROH HCl + H2SO4

US 2091986

US 2091686 states: 'It is known that ethyl chloride may be produced by various procedures involving the use of ethyl alcohol as a starting material, for example, by a batch process in which dilute sulfuric acid, sodium chloride and ethyl alcohol are heated together. According to such a process, the ethyl alcohol and sulfuric acid are slowly introduced into a mixture of sodium chloride and dilute sulfuric acid, and the ethyl chloride evolved is passed through a reftux condenser which prevents the alcohol from escaping unchanged from the reaction vessel. This type of process has the disadvantage that a considerable time, generally about forty to fifty hours, is required to finish one batch.'

[Edited on 26-7-2008 by smuv]

Klute - 27-7-2008 at 05:36

Thanks alot for sharing Smuv, very interesting read. Alkyl halides are very usefull reagents and details several preparations is a very good idea.

Siddy - 28-7-2008 at 00:48

by mixing HCl and H2SO4, are you not creating Cl2 atleast in small concentration?
if so does this mean H2O2 could be replaced for H2SO4? Just and idea since you seem to be listing a few preparation methods.

Nicodem - 28-7-2008 at 05:40

Quote:

Originally posted by smuv
@Nicodem
The only thread you posted that is pertinent to my question was the first one. In this thread 'Per' mixed hydrochloric acid with ethanol and concentrated sulfuric acid and heated everything up; then stopped the operation because HCl gas was being produced; this hardly proved anything.

Actually, in one of those threads there is a study on the EtCl preparation from EtOH where the conditions and acid catalyst were evaluated and optimized, but I had no time to search for the specific post with the file attached. The yields can be increased above 50%, if I remember correctly. Also, if you would have firstly formed ethanolic EtO-SO2-OH from EtOH and H2SO4 and then slowly added this to NaCl or conc. HCl, you might have obtained better yields, at least in theory. Otherwise, nice experiment and pictures (I liked the burning thumb picture). Also, your liquid product is quite probably a mixture containing some EtCl together with other volatiles.

smuv - 29-7-2008 at 12:02

AH! Ok, I interpereted your post much differently. I thought based upon the first link that you posted (I grazed through the others) that you were saying it can't be done.

Yes, I am in the process of making potassium ethyl sulfate (I made the ethyl hydrogen sulfate already via EtOH and NaHSO4) and will try the dry distillation of that with NaCl and possibly other chlorides. I have also been flirting of the idea of distilling ethyl chloride from a slurry of NaCl and Potassium Ethyl sulfate in DMSO, or possibly NaCl, Ethyl hydrogen sulfate and DMSO. I am hoping I could help the reaction out with a good SN2 solvent.

On test tube scale I have already tried the reaction between ethyl hydrogen sulfate with ammonium bromide and Sodium chloride. With ammonium bromide ethyl bromide is produced along with enough bromine to strongly color the mixture; with sodium chloride I got a lot of hydrogen chloride gas and decided the dry distillation might be a more effective method (although I have no good reason to say that it didnt produce some ethyl chloride).

EDIT
The other day I did a run where I added (dropwise very slowly) a mixture of ethanol in a large excess of sulfuric acid to a large excess of sodium chloride in a sury of water. The mixture of ethanol in sulfuric acid was allowed to sit for a day before addition. It didn't really work out, the efluent gas did not smell as strongly like ethyl chloride as the previous run and I was having condensor issues, so I stopped the run after ca 1.2 hours, with no yield. I have more details at home if people are interested.

Also I agree about the impurities; but I first want to make Ethyl chloride on a reasonable scale before I deal with purification. I hate microscale work-ups.

[Edited on 29-7-2008 by smuv]

Panache - 29-7-2008 at 22:28

Quote:

Originally posted by 497

DCM has a water solubility about 10 times that of EtBr. That would be a pain in the ass though. Good luck.

nice one! i have a liquid/liquid extractor, i'll get it going.

Ullmann - 1-8-2008 at 03:43

See at orgsyn:

orgsyn cv1p0025

[Edited on by Ullmann]

[Edited on by Ullmann]

Ethyl Bromide synthesis

Sedit - 7-7-2009 at 18:17

Molar Weights of reactants:

H2SO4 Molar mass 98.08 g/mol

NaBr Molar mass 102.894 g/mol

EtOH Molar mass 46.07 g/mol

Products
----------
C2H5Br Molar mass 108.97 g/mol * .5150 = 56.1195

H2O Molar mass 18.01528(33) g/mol * .5150 = 9.277

NaHSO4 Molar mass 120.06 g/mol

Reaction:

NaBr + H2SO4 = NaHSO4 + HBr
HBr + EtOH = EtBr + H2O

23.67ml or in other terms 30 grams of EtOH was placed into a cold water bath and 130 grams of 44% H2SO4(Liquid Lightning MSDS) was added slowly via dropper syringe over a 10 minute period in order to keep the temperature down.

While waiting for the flask to once again reach ambiant temperatures I weighed out 53 grams of Sodium Bromide(Brom Start MSDS) and prepared for addition.

After evolution of heat some 15 minutes later or so the flask was placed in an ice bath followed by the slow addition of Sodium Bromide. The mixture quickly took on a red orange color with some Sodium Bromide resting on the bottom.

The flask was allowed to set for 15-20 minutes and the arranged for simple distillation.

The reciever flask was filled about a quarter of the way full of cold spring water and as you can see in the picture above the recieving flask was placed in an icebath as to not allow the formed Ethyl Bromide to evaporate.
After reaching 58*C at the still head the formed Ethylbromide started to distill over pretty rapidly and the contents of the flask boiled rapidly. The EtBr droped to the bottom of the reciever with a milky white color. This was sustained for about 25 minutes at which point the rapid frothy boiling stopped and the color of the mixture was not noticebly darker. The sound the boiling made now was completely different and unusual. Everytime a bubble would form it would do so with a sharp tinny sound to it. It sounded as though it was being boiled in a metal container but I think this may due to the EtBr forming and rapidly vaporizing in the solution resulting in the strange sound because the bubbles where forming in the middle of the flask instead of around the sides like normal. It was at this point that the distillate started to take on a slightly orange tinge to it and the distillate took on a dirtier look to it no doubt carrying some EtOH with it as it made the top H2O layer slightly milky looking until more H2O was added to crash the EtBr out. The remainant of the reaction vessle has now lightened to a pale shade of yellow/orange and after cooling the Sodium hydrosulfate crystalized filling up the vessle.

After about 45 minutes to an hour the distilling was stopped because a bad lightning storm was comming and I am working right next to a large open garage door. The distillate was noticed to be only slightly more dirty the the first half of distilling so I just decided to mix both together. This is where one of the notable things happened. When the two distilling flask where added together as soon as the cloudy EtBr hit the air it would release puffs of dense white vapors with the consistancy of smoke. Im pretty sure that its HBr fumes after watching the final product clear up after sitting for an hour.

The yeild prepurification yeilded roughly 30ml or 44.1 grams equaling 78.5% yeilds with more then likely a small amount still in the mother liquid of slightly milky white EtBr with exact weight still to be determined.

I post more tommorow after I am hopefully able to purify it. But the initial conclusion is that this is a very easy synthesis to pull of and the yeilds are not bad either. As smvu said there was no hint of odor until the end and I started to move the contents between flask. After speaking with Arrhenius recently I decided to add excess H2SO4 and EtOH to the mixture to ensure complete digestion of the NaBr.

UnintentionalChaos - 7-7-2009 at 18:50

I spoke briefly with smuv via PM and the problem with my iPrBr synthesis is probably my lack of water in the reaction mixture. I used NaBr which is more or less insoluble in conc. H2SO4, preventing reaction, where smuv used NH4Br. I'll run this again later with some water in the mix and report back with pictures.

Sedit - 7-7-2009 at 18:54

I tryed a small scale run with 98% H2SO4 and did not get really anything of use. The NaBr has poor solubility in Alcohols so I think the H2O helps everything stay mobile also keeping the HBr down in the reaction where it belongs.

jon - 7-7-2009 at 19:27

you know i was wondering could this type of bromination be performed owing to the possibility of aromatic sulfonation side reactions on aklanols bering aryl, indoyl substitutents etc?
wht about lucas reagent? then there's the friedel crafts side reactions so that leaves only pbr3?
input appreciated.
seems like you could get by with just a small amount of h2so4 and nothing bad would happen.
in light of this tosylates seems the route of choice.

[Edited on 8-7-2009 by jon]

DJF90 - 7-7-2009 at 23:33

I dont think a phenyl ring will have side reactions with this method as bromide, dil. H2SO4 and HBr (formed in situ) don't react with benzene. You may encounter problems with activated rings and those with sensitive functionalities. Lucas' reagent forms the chloride, not the bromide. You could also use the appel reaction, which is very mild, and usually works even on sensitive substrates. I would be suprised if the CCl4 used could not be substituted with CBr4 or CI4 to yield the respective alkyl halides.

[Edited on 8-7-2009 by DJF90]

entropy51 - 8-7-2009 at 06:18

Sedit, are you sure you didn't get those images off a DEA website?

Save up for some glassware dude! EtBr is less toxic than MeI, but still...

I'm looking forward to your next installment: the beer bottle Grignard.

[Edited on 8-7-2009 by entropy51]

Sedit - 8-7-2009 at 06:42

LOL, what are you saying entropy.

Brother im a single father with 3 young children that warrent my money much more then a set of glassware. I would have had one sometime ago but a hobby can never take precedence over them.

I started playing with chemistry when I was a kid unable to buy my own stuff so I chose to make what I needed and got pretty good at it. Now that im older its common habit and theres a good chance I would be lost with a good set of glass. The idea of toxicity may play into my favor because I am so worryed about it that someone using proper equipment maynot focus on safety half as much as I do. The synthesis was performed right next to a giant open garage door. Once every thing was running smoothly I kept my distance. Gloves and long sleaves where worn the whole time even though it was 97 degrees outside.

Thats the reason that I have never posted any pictures and such before because people have gotten in there heads that fancy glassware , rotary evaporator, ect... make you a great chemist. I do believe they can make you a better chemist due to ease of use but being able to afford Sigma Aldrich does not make someone a chemist. Being able to perform the work and idealize the synthesis before hand gives someone more of an advantage then money not to mention the amount of fun that you get along the way. Lets face it, Im not the only fellow here that don't have good glassware but I may be the only one that don't mind showing it.

Beer bottle Grignard eh... Hmm now thats an idea

. I got the Ethyl bromide and if im able to get the Grignard to take off in my setting I don't want to here complaints from anyone how hard it is to work with a Grignard reagent.

Reaction note:

Overnight the EtBr cleared up nicely to a very slightly tinted yellow fluid.

entropy51 - 8-7-2009 at 06:55

Just kidding, not dissing. No need to be ashamed if it works! It's taken me over 40 years to accumulate my lab supplies. I'm glad you're trying to ventilate things.

I can't follow your stoichiometry either. Was your EtOH 95%? I think you started with less than 0.4 mol of EtOH, which I think is limiting, and ended up with 0.4 mol of EtBr. Did I mess up my math? And don't forget that you may have water and/or EtOH in your product before purification. Do you plan to dry and distill it?

Sedit - 8-7-2009 at 07:20

Na... no offense taken I knew I was gonna get ragged on before I even posted them pictures. It works good. One of my goals is to give people hope that don't have the best equipment and is scared off by these sort of things.

The EtOH came from window de-icer as it was a by product of extracting the Ethylene Glycol. It was distilled, dryed with MgSO4 and the first few ml and last few that came over where discarded. This was repeated once again until I was satisfied that it was not a mixture of Ethylene Glycol and EtOH. Next time I would use either vodka or Ever clear over this anyday but it was what I had laying around so I used that. In doing so I would also use a more concentrated H2SO4 instead of 45% to help compensate for the H2O in the alcohol.

The total amount of EtOH I used was 30 / 46.07 = .65 mol because I wanted to have excess to ensure completion as much as possible. The limiting reagent was the NaBr so the whole synthesis was based around 53 grams of NaBr or .515 mol. Excess H2SO4 and EtOH where added though for reasons stated above.

I will distill this much slow next time I try it to ensure that HBr is not being lost and to get higher yeilds. Does anyone know how much H2O this reaction can tolerate? It seems that the more there is the more the HBr will stay in solution but im sure there has to be a point where the dilution works against you more then the small amount of HBr loss right?

entropy51 - 8-7-2009 at 09:10

Sedit, you said "23.67ml or in other terms 30 grams of EtOH". But the density of EtOH is only about 0.8, and 23.67 ml x 0.8 gm/mL = 18.9 gms EtOH.

If you have the 95% azeotrope, then I think you had 18.9 x 0.95 = 18 gm EtOH or 0.39 mols EtOH. If so, EtOH is limiting.

Am I missing something?

Speaking of possible losses of EtBr, did you use ice water in your condenser?

Sedit - 8-7-2009 at 09:22

The condenser has a hose that comes streight from the well. It is cold and can handle a heavy flow of water thru it. I had it cranked open pretty well while distilling to make sure the condenser stayed chilled and after a while condensation could be seen on the outside of the condenser.

I am not basing my calculations on the 95% azeotrope because the Ethyl alcohol came from window de-icer and was distilled twice over MgSO4. Possibly Im wrong but im pretty sure this should lead to a much lower percentage of H2O in the EtOH then 95%. When adding the drying agent even the first time it never clumped up and flowed freely so im left to assume that there is little H2O in the EtOH if any at all. So for simplicitys sake I calculated no H2O in the Ethyl alcohol but figured in the H2O from the sulfuric instead.

UnintentionalChaos - 8-7-2009 at 09:23

Quote: Originally posted by Sedit

Does anyone know how much H2O this reaction can tolerate? It seems that the more there is the more the HBr will stay in solution but im sure there has to be a point where the dilution works against you more then the small amount of HBr loss right?

I ran this again last night, and not thinking, used a lot of water. 65g of 90-93% H2SO4 and 95g of water to completely dissolve the NaBr (about 52g IIRC) I was using. There was no bromine evolution at all and the product that distilled is water clear. However, yield appears to be about 50% The distillate was barely acidic, so plenty of HBr is still in the reaction flask. I'm going to add some more iPrOH and reflux for maybe two hours, then redistill to try to salvage some of my bromide.

[Edited on 7-8-09 by UnintentionalChaos]

Sedit - 8-7-2009 at 14:13

After washing with H2O 2x times the water extracts where combined and set aside overnight. I smelled them to see if they contained any Ethyl bromide dissolved but instead was greated with a different smell, Ether. I wounder if as the reaction loses water thru distillation and the concentration of excess H2SO4 goes up the chances of EtO2 formation should go up as well. This is making me rethink the idea of excess H2SO4 a little bit. Maybe a little excess H2SO4 but to much will result in the formation of ether. It can't be a large amount as there is no ether layer on the top but never the lest its there and it more then likely cuts into ones yeilds a bit.

@UC Im not sure refluxing is needed and a slow distill may just suffice. As Arrhenius stated the reaction is not favored as much until the iPrBr distills off. The addition of iPrOH may just push the reaction over to IPrBr by simply distilling it.

entropy51 - 8-7-2009 at 14:53

I used to make alkyl bromides by generating the HBr in situ using NaBr + H2SO4. Then I discovered the preps using HBr. They're much cleaner, just check the literature.

HBr is not hard to make. Here's a prep I posted last week:

https://www.sciencemadness.org/whisper/files.php?pid=156645&...

UnintentionalChaos - 8-7-2009 at 22:27

My question though, is what do the yields look like entropy? Perhaps for a valuable alcohol, HBr may be cleaner, but what if it's something rather cheap like ethanol or isopropanol? That prep you gave produces 85% of azeotropic HBr based on the bromide salt. Then, that percentage yield must be compounded with the percentage yield from the soup of SN1 and SN2 reactions that generate the alkyl bromide. Assuming the bromide salt is our most valuable ingredient, which prep is cheaper and easier?

Also, if I had to guess volumes from looking at a sep funnel, I'd get an F. I was way off from the 50% I guessed before. At any rate, I refluxed the remainder of the reaction mixture with an additional 51mL of dry isopropanol for an hour, then distilled it. Overall yield after washing with NaHCO3 and conc. H2SO4 was 55% with density matching the literature values.

moral of the story- the amount of water when using NaBr is critical.

entropy51 - 9-7-2009 at 14:55

UC, my yields for isopropyl and ethyl bromide run around 80% for the HBr prep, sometimes 90% or so. I never personally achieved those yields with NaBr + H2SO4 when the product was purified and redistilled.

Once you have the HBr prepared there is a lot less futzing aroung with the reaction and workup. I don't think the HBr method produces the ethers that you get with lots of H2SO4 in the mix. I haven't tried to figure out the economics of it. I'm an amateur doing it for fun. But you need an excess of HBr by either method and you can recover the excess HBr by distilling off the azeotrope after the R-Br comes over. I don't think you can do that with NaBr + H2SO4, so the economics might be favorable.

[Edited on 9-7-2009 by entropy51]

Nicodem - 10-7-2009 at 00:24

Isopropanol is way cheaper and more widely available than NaBr, so it would make more sense to use its excess instead of using HBr or NaBr/H2SO4 in excess. My yield of isopropyl bromide using NaBr/H2SO4 was 76% and I think it is not worthy trying to improve its yields given the reaction uses no particularly expensive reagents.

garage chemist - 10-7-2009 at 01:12

Whether the alkyl bromide produced contains any ether can be determined easily by measuring its density and comparing it to the literature value of the density of the pure alkyl bromide.

Ether can be removed from the product by shaking it with conc. H2SO4.
It protonates the ether to the oxonium salt, which dissolves in the H2SO4.

entropy51 - 10-7-2009 at 05:42

Yes, a H2SO4 extraction will do that. But it's second on my list of things I rather hate to shake in a sep funnel:

1. NaCN in DMSO

2, Conc. H2SO4

3. BnCl

UnintentionalChaos - 10-7-2009 at 06:39

That's why I used a small stoppered flask with a ST plug and keck clip and then transferred that to a sep. funnel to settle into two layers. Sep funnels have this nasty habit of leaking just a little bit (in my experience) while shaking and I don't trust them with such nasties.

garage chemist - 10-7-2009 at 06:51

Why not? I've shaken bromine with conc. H2SO4 in a sep funnel, it's really no problem.
And besides that, you can simply magnetically stir the two phases in a round-bottom flask instead of shaking them, and then pour the mix into the sep funnel for separation only.

entropy51 - 10-7-2009 at 08:02

"I've shaken bromine with conc. H2SO4 in a sep funnel, it's really no problem."

You get the Great Big Brass Pair award for that GC

Fleaker - 11-7-2009 at 10:09

I've done it too. Just make sure that your bromine isn't horribly wet, and that it and your sulfuric acid are as cold a liquid as can be!!

When I tried this [EtBr via H2SO4/NaBr] reaction, I never had yields better than 50% even on a decent 1 mol scale. Why? Coolant water was not cold enough!

[Edited on 11-7-2009 by Fleaker]

Sedit - 11-7-2009 at 10:16

That was my biggest fear when preparing to perform this but due to the volume of water my condenser handles and the fact that its comming right from a well only a few feat away it proved to be plenty cold enough.

In the very beginning as they started to react wisp of presumably HBr vapors could be seen and if it was heated to distillation temperatures rapidly after that it would all have been lost yeilds. I feel that I pushed the distillation along to fast and next time I will most definitly slow it down to a crawl. I think that in doing so yeilds will be pushed up dramaticly and ether formation may also drop.

entropy51 - 11-7-2009 at 10:27

Sedit, I know well water is cold, but I really think you should try ice water in your condenser, even if not's not constantly flowing, but just changed at intervals.

The reason is the HBr generated in the flask will carry some EtBr out of the condenser unless it contacts a very cold surface.

Try to rig up an adapter to run from the condenser outlet into the water in the receiver. Then the EtBr can't escape even if it all doesn't condense in the condenser.

Sedit - 11-7-2009 at 11:07

Good idea.

I do have a thing for this already as I use it when using the condenser for steam distilling. The issue is its a rubber tube and I do not know the full solvating power of EtBr just yet so I must stay a bit leary of that the first few times.

entropy51 - 11-7-2009 at 11:35

I wouldn't mix rubber and alkyl halides, I get HDPE (?) tubing at the hardward store that might be OK if the stuff wasn't heated. You could test a sample of the tubing in a little EtBr in a test tube maybe.

I'll bet you could get several pieces of glass tubing for a few bucks. If you had some glassware you'd definitely be dangerous.

UnintentionalChaos - 11-7-2009 at 11:39

It's not cheap, but FEP tubing is magical. Resistant to just about everything. I've only seen it ruined by high temperature oleum fumes.

Fleaker will back me up on this :cool:

[Edited on 7-11-09 by UnintentionalChaos]

1-bromobutane

Lambda-Eyde - 8-5-2010 at 10:04

Yesterday I got 4 hours of free access to the school lab. I figured I'd make some 1-bromobutane (butyl bromide).

Pictures:

The setup. The addition funnel contains concentrated sulfuric acid.

You can clearly see the HBr fumes filling the apparatus and the deep red color of bromine, due to oxidation by the acid:

Here the two layers can be seen after the reaction. Top layer: BuBr and bromine along with unreacted 1-butanol. Probably some dibutyl ether too.
Bottom layer: H2SO4, NaHSO4, water.

I didn't have time for the workup, I'll probably do it on tuesday. The reaction mixture is sitting in a separatory funnel in a fume hood over the weekend.

[Edited on 8-5-2010 by Lambda-Eyde]

rrkss - 8-5-2010 at 10:51

Interesting experiment with butyl bromide. Just curious what type of workup do you intend to run?

Lambda-Eyde - 8-5-2010 at 11:00

I'm following Vogel's prep for butyl bromide, which first involves distillation of the crude product. It is then washed with water, concentrated HCl, sodium bicarbonate and then water again. If the color of the bromine persists I'll do a wash with a sodium thiosulfate solution as well. Lastly I'll dry it over some calcium chloride and distill again.

DJF90 - 8-5-2010 at 12:17

Bromine on top?! Thats very odd?!

Lambda-Eyde - 8-5-2010 at 12:24

I figured it would go in the more apolar phase since it's not very water soluble. Also, there's much H2SO4 and NaHSO4 in the bottom, polar phase, decreasing the solubility of Br2.

If you think otherwise, please post what you think. I love to learn!

Sedit - 8-5-2010 at 13:42

When I made EtBr the bottom layer was the EtBr and the reaction mixture appeared abit like your upper layer although much lighter since I did all I could to prevent oxidation of the NaBr by using a more dilute H2SO4 solution.

I may be wrong but assuming the density of BuBr is more then EtBr then I would have to think that your clear layer on the bottom is your BuBr and not the dirty dark upper layer. The bottom layer in the picture also appears to refract light simular to what I experianced.

Lambda-Eyde - 8-5-2010 at 14:02

But that just won't make sense. I used 55 mL 1-butanol in the synthesis, there's no way that would yield ~150 mL of 1-bromobutane!

The density of the 1-bromobutane is ~1,27 g/mL. The bottom layer with a large percentage of H2SO4 and NaHSO4 probably has a higher density.

[Edited on 8-5-2010 by Lambda-Eyde]

Sedit - 9-5-2010 at 00:25

I never said the bottom was pure which given the densitys defined could account for the added bulk. Its easy enough to test. so ...... take it from there and prove me wrong. I more thne likely am... iv mastered being wrong

Lambda-Eyde - 9-5-2010 at 04:15

Quote: Originally posted by Sedit

I never said the bottom was pure which given the densitys defined could account for the added bulk.

But what would the impurities be? BuBr is completely insoluble in water.

But, you're right. I'll do some tests on tuesday prior to the workup; pH, density, smell, flammability etc.

Lambda-Eyde - 10-5-2010 at 00:24

I got about 45 minutes lab time today, enough to do a flammability test. The upper layer was not very flammable, but it definitely burned. The lower layer would not burn at all.

A lot of the NaHSO4 had crystallised in the separatory funnel over the weekend. I decanted the liquid from the funnel and dissolved the NaHSO4 in some water. I saved both solutions. The liquid without the majority of the NaHSO4 was put back in the separatory funnel, and I'll hopefully begin workup tomorrow.

Edit: The upper layer had a very dark purple, almost black color that was visible when I poured it (not bromine?). It had the most peculiar smell (hard to describe), but the smell of unreacted alcohol was also easy to notice. I could not detect the smell of bromine.
The lower layer also had some of that peculiar, hard to describe smell.. Hmm.

I'll see what happens when I react the upper layer with some sodium thiosulfate.

[Edited on 10-5-2010 by Lambda-Eyde]

Sedit - 10-5-2010 at 06:15

It all seems a little complicated to go thru so many steps to try and determine which layer is the BuBr. Wouldn't it be just as easy to take two test tubes filled with chilled water and add a few drops of each layer to different test tubes. The organic phase will sink to the bottom indicating which layer is your BuBr. The aq phase so would just mix in with the water and not be noticed.

Once you got the right one then wash, seperate and distill.

Lambda-Eyde - 10-5-2010 at 06:32

The flammability test along with the volume consideration does it for me. I'll check the densities tomorrow and hopefully do the first distillation.

Propyl Bromide synthesis

mnick12 - 10-5-2010 at 16:21

Well after re-reading this thread and seeing all the good work done I thought I would have a go at n-propyl bromide. My Inspiration for this synthesis was this thread, and it has been a while since I have contributed anything meaningful.

Before I start I feel I should post a brief waring.
Be careful propyl bromide is an alkylating agent, and probably carcinogenic.

Reactants

n-propyl alcohol 60.10gr
sulfuric acid 98.08gr
potassium bromide 119.00gr

So first I added the KBr to a 3 neck 500ml rbf. The KBr was really lumpy so I added 20ml of tap water to help break it up. Next I added all the n-propanol to the mix, next I took a 125ml addition funnel and placed it in the middle neck of the flask. I poured the H2SO4 into the funnel and adjusted it so that it took 1hr to add all of the H2SO4 into the mix. Once the acid was mixed in the solution sat for about an hour. Then I stoppered off two of the necks, and in the third I placed a 200cm vigreaux column. I only had time to run it for an hour which normally would be enough, but it was super super windy so the column got cooled really easily. Anyway the I ended up with 50ml of liquid, and I think there is about 2ml of water in it. So I may try see if I can distill any more propyl bromide from the original mix, but I doubt that will yield anything more.
So in conclusion I would say this works pretty well, but the yields are kind of low. It would probably work better with pure HBr, but that would require another step which can complicate things.
And now for the pics!

Propyl bromide reagents.jpg - 24kB

Here are the reactants from left to right, sulfuric acid, potassium bromide, and n-propyl alcohol.

finished Propylbr.jpg - 23kB

Here is the finished product.

Sorry I dont have any other pictures, I actually took alot but for some reason they wont load into the attachment thing. These two were the only ones that worked. So use you imagination to get the rest.

UnintentionalChaos - 10-5-2010 at 19:30

My guess would be not enough water and needing of longer reflux.
A vigreux!? That's....a bizarre choice. That, the wind and the volatility of your product probably lead to significant losses. An efficient reflux condenser would be recommended here.

See: http://www.orgsynth.org/orgsyn/orgsyn/prepContent.asp?prep=c...

Sedit - 10-5-2010 at 19:58

When I made the EtBr I added the H2SO4 first which forms an exothermic reaction with the alcohol atfirst then after this calmed down and I had EtSO4 <=> H2O IIRC I slowly added the NaBr after chilling the -OH acid mixture. I know there was a reason for me adding the acid first but I can not for the life of me remember exactly what the mechanics behind it was but perhaps others could review my post or explain there own reason for why I did this

Sorry my memory these days is short lived to say the lest.

Arrhenius - 10-5-2010 at 20:40

Dissolving concentrated acids in anything will be exothermic. You're correct, there is an equilibrium between sulfuric acid, the alcohol, the monoalkyl sulfate ester and the dialkyl sulfate ester. Surely there are competing mechanisms leading to the same product. I suspect the bromide displacing the monoalkyl sulfate ester is the predominant reaction, though directly displacing water via the protonated alcohol may become dominant as the reaction progresses (more water, Le Chatelier favors free alcohol + sulfuric acid). Regardless, the order of addition will not affect the reaction, though it's probably safest to add the sulfuric acid to cold alcohol.

Panache - 11-5-2010 at 02:25

Quote: Originally posted by mnick12

Then I stoppered off two of the necks, and in the third I placed a 200cm vigreaux column.

thats a pretty tall column!!

Lambda-Eyde - 11-5-2010 at 03:02

I did a simple distillation of the product today. Passing over from 82 to about 104 degrees celcius was a milky organic liquid and some water. It did not even have the slightest hint of the dark compound, earlier assumed to be bromine, that was left in the distillation flask. Some passed over from 112 to 124 degrees, which I didn't add together with the other batches for the workup.

The distillate collected at 82-104*C was put in a separatory funnel and separated into two phases: One lower, organic layer with a milky appearance and a small aqueous phase above.

I'll do the workup and hopefully a final distillation of the product in about an hour. Report with numbers and pictures are to follow later today.

Lambda-Eyde - 11-5-2010 at 12:17

Finally got done with the synthesis today. The result what somewhat disappointing, but not surprising.

Here's the reaction mixture in a separatory funnel after standing over the weekend. Note the large amount of crystals and the dirty upper (!) organic layer.

A picture of the first distillation setup.

Two of the receiving flasks.

Seems like I forgot to take any more pictures. They wouldn't have been any spectacular anyways.

Before beginning workup of the crude distillates I decided to add the batch that came over at 112-124*C to the total distillate anyways in hope of extracting any BuBr present.
The distillate was first washed with 100 ml of water, then 100 ml 36% HCl, 100 ml water again, then 100 ml sodium carbonate solution, and 100 ml water again. This was done according to Vogel's recommended workup method for BuBr synthesis.

To the thoroughly washed organic layer was then added about a teaspoon (I feel like a briton

) of CaCl2. It was dried for about twenty minutes with occasional swirling; no clumping was observed. It was then filtered straight into a 100 ml round bottom flask and distilled in a dry, clean distillation setup into a 50 ml flask. The first distillate came over at 99-102*C. The distillation was stopped when the temperature rose to about 110*C, and it was cut off before any of it could contaminate the previous batch.

The distillate was perfectly clear and didn't smell too strongly. It was vaguely remniscient of methylene chloride, but had a more sickening smell. Not very sweet.

The distillate occupied 19 ml and weighed in at 23,5 grams, giving a specific gravity of 1,24. This is close enough to the specific gravity of 1-bromobutane; 1,27 (Wikipedia).

The yield, however, was rather lousy. Basing the calculations on the amount of 1-butanol used, 55 ml, or 0,6 moles, gives a yield of 29 %, not very spectacular. Vogel quotes a yield of 95 % for the same synthesis, although at a 2x scale.

I can already see a number of reasons for the bad yield. Firstly, I used equimolar amounts of 1-butanol and HBr (NaBr). I should have used an excess of NaBr when taking in consideration the losses due to evaporation of HBr during the synthesis and oxidation of the bromide ion. I rushed the synthesis too much. I was kinda in a hurry when I did it and used much heat and refluxed the reaction mixture for only 70 minutes. The addition of the sulfuric acid was done all to quickly during the synthesis due to the time strain, causing oxidation of bromide which could be observed. This probably resulted in some dibutyl ether too.

I had to rush the synthesis somewhat because neither leaving the setup hot nor missing my bus home were options I wished to go for.

[Edited on 11-5-2010 by Lambda-Eyde]

[Edited on 11-5-2010 by Lambda-Eyde]

Ethyl Bromide

rrkss - 11-5-2010 at 12:25

I just ran vanino's prep for ethyl bromide. I ultimately intend to use it in a grignard reaction with ethyl acetate to prepare 3-methyl-3-petanol.

In a 500 mL roundbottom, I added a magnetic stirbar and 38 mL of H2O + 55 mL of 95% ethanol. This flask was submerged in a beaker with icewater and using an addition funnel I added 55 mL of concentrated H2SO4 with constant magnetic stirring. Upon completion I added 98g of NaBr. The flask turned orange upon the addition of the NaBr. I setup for simple distillation using a seperatory funnel containing about 20 mL of H2O as a receiver. I cooled my condenser with Ice Water.

IMG_1012.JPG - 92kB

I set my variac to 25% power and started to distill my product.

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At the end of the distillation my flask filled up with a white gas (SO2?) and I dropped the mantle at this point.

IMG_1016.JPG - 50kB

Here is my seperatory funnel with a cloudy Ethyl Bromide on the bottom layer and H2O on the top.

IMG_1017.JPG - 54kB

Next step is a 3 step workup involving a shake with 10% NaOH solution, followed by a shake of 10% Sodium Thiosulfate solution and then a dry on CaCl2 to remove water and any ethanol that might have distilled over. I don't care about any ether as I am using this for a grignard and thus I am eliminating the concentrated H2SO4 workup described in Vanino.

Will report my yield when I finish the workup.

[Edited on 5-11-10 by rrkss]

rrkss - 11-5-2010 at 17:43

Did a large portion of my workup. The cloudy ethyl bromide turned clear and colorless almost immediately upon the addition of 30 mL of 10% NaOH solution to the Sep Funnel. I agitated the funnel and drained the lower organic layer into a seperate container. Then after emptying the upper aqueous layer, I put the organic layer back into the sep funnel and rewashed with 30 mL of sodium thiosulfate solution. The organic layer which appears to be about 50+ mL was then drained into a 250 mL roundbottom filled with 10 grams of anhydrous CaCl2. It is sitting outside overnight in this flask to ensure good drying but so far, I see no clumping of the CaCl2.

rrkss - 12-5-2010 at 12:31

Done with my workup. I got 52.54g of product after distillation or a 48% yield. Not a great yield but the product seems to be very pure. The boiling point range during the simple distillation from CaCl2 was 38.5 - 39.0 degrees which is very narrow and very close to the literature value of 38.4 degrees.

redox - 12-6-2011 at 05:28

I performed the bromethane synthesis about two weeks ago, and as of now it has all evaporated. It turns out my bottle didn't have a good seal. Damn! :mad:

[Edited on 12-6-2011 by redox]

spong - 12-6-2011 at 06:29

The same happened to my EtBr even though the bottle had a seal

I wouldn't store it unless the bottle has a pretty hefty cap/seal, the seal on mine was a normal seal coated in teflon tape because I was worried about it dissolving the seal. I'll use all of it next time I make it, EtBr isn't something I want leaking into the air, even if it does smell awesome

redox - 12-6-2011 at 10:07

You like the smell of bromoethane? It smells odd/bad to me.

smuv - 12-6-2011 at 17:23

Store it under a layer of water.

redox - 16-6-2011 at 14:13

I find storing under water doesn't work well. It still has a vapor pressure under water, doesn't it?

Anyway, I now store my freshly made bromoethane inside of one of these bottles:

http://www.eandkscientific.com/product.php?productid=31329&a...

The smallest one on the right.

I also wrap teflon tape on the threads and sealing tape around the cap.

bahamuth - 16-6-2011 at 17:09

Haloalkanes should be stored dry in my experiance, makes it so much easier to use is one thing.

Usually store them with a piece of silver wool or precipitate copper powder (after prolonged drying with CaCl2 and redistillation) to capture any free halognes, atleast the alkyl iodides (which is all those I have), as I have seen heavy decomposition if left without silver or copper metal for prolonged periodes, even as I store them at -20 all the time.

redox - 16-6-2011 at 18:03

Quote: Originally posted by bahamuth

Haloalkanes should be stored dry in my experiance, makes it so much easier to use is one thing.

Usually store them with a piece of silver wool or precipitate copper powder (after prolonged drying with CaCl2 and redistillation) to capture any free halognes, atleast the alkyl iodides (which is all those I have), as I have seen heavy decomposition if left without silver or copper metal for prolonged periodes, even as I store them at -20 all the time.

This seems wise. My collection of alkyl halides (bromoethane, 1-bromopropane, 2-bromopropane, 1-bromobutane) are obviously all bromides, and I have found that they don't decompose very much. I plan to make some iodides by the finklestein reaction sometime in the near future.

spong - 18-6-2011 at 02:11

Quote: Originally posted by redox

You like the smell of bromoethane? It smells odd/bad to me.

Ohh it smells so sweet! Like the sweet smell from methanol or chloroform but stronger.

redox - 19-6-2011 at 11:08

Quote: Originally posted by spong

Quote: Originally posted by redox

You like the smell of bromoethane? It smells odd/bad to me.

Ohh it smells so sweet! Like the sweet smell from methanol or chloroform but stronger.

I love the smell of chloroform, but I cannot smell methanol. Bromoethane does smell sweet, but an overpowering, acrid kind of sweet.

Hazel - 7-7-2011 at 02:39

Hi, small question: could allyl alcohol be successfully substituted for those alkyl alcohols?

Thanks.

Cloner - 7-7-2011 at 04:05

It has been described as high yielding and succesful. (http://www.erowid.org/archive/rhodium/chemistry/tcboe/chapte...)

[Edited on 7-7-2011 by Cloner]

Dr.Bob - 11-7-2011 at 10:39

For those interested in preparing alkyl halides, the father of some of this chemistry was Max Gergal, who wrote a great book about his company, Columbia Organics, which is hard to find, but sometime available via Amazon or other sources. He describes some of his experiences making them along with the joys or running a small company. It's a hoot.

http://www.amazon.com/Excuse-Would-Like-Isopropyl-Bromide/dp...

Thor - 11-7-2011 at 12:21

Quote: Originally posted by Dr.Bob

For those interested in preparing alkyl halides, the father of some of this chemistry was Max Gergal, who wrote a great book about his company, Columbia Organics, which is hard to find, but sometime available via Amazon or other sources. He describes some of his experiences making them along with the joys or running a small company. It's a hoot.

http://www.amazon.com/Excuse-Would-Like-Isopropyl-Bromide/dp...

There is a copy in the forum library, a really great read.

rodanid88 - 9-9-2012 at 12:51

I tried to synthesize BuCl from BuOH, 32% HCl and 96% H2SO4. At the end of the distillation i got black tarry remainder in the RBF. Anyway the yield was very low (~30%), but it is not the main problem, because the process was not the best. I can only imagine that the H2SO4 was not pure enough.
Thanks

Magpie - 9-9-2012 at 16:03

I was just reading about this. For the conversion of primary alcohols to alkyl halides use of PX3 is usually recommended. The yields are much higher than with HX acids. There are no rearrangements with the PX3.

When making alkyl iodides formation of the PI3 in situ from P and I2 is recommended due to instability of PI3.

ref: Bruice's textbook

Heuteufel - 11-9-2012 at 02:47

I did the synthesis of 1-Bromobutane recently: Synthesis of 1-Bromobutane
The yield was 63 %, which is not astonishing, but the product is quite pure as a Grignard I performed with it started very readily. In my opinion the washing with (a sufficient amount!) of concentrated sulfuric acid is very important. If it is ommited, the yield may seem high, but the product is impure and useless for most reactions.

gsd - 11-9-2012 at 09:39

Quote: Originally posted by rodanid88

I tried to synthesize BuCl from BuOH, 32% HCl and 96% H2SO4. At the end of the distillation i got black tarry remainder in the RBF. Anyway the yield was very low (~30%), but it is not the main problem, because the process was not the best. I can only imagine that the H2SO4 was not pure enough.
Thanks

The procedure for making alkyl chlorides is different from that of bromides.

Procedure for Preparation of n-Butyl Chloride

http://www.orgsyn.org/orgsyn/pdfs/CV1P0142.pdf

gsd

UnintentionalChaos - 16-11-2012 at 01:34

I ran a prep of Ethyl Bromide today based on the orgsyn.org prep (http://www.orgsyn.org/orgsyn/orgsyn/prepcontent.asp?prep=cv1...)

Instead of HBr, I substituted NaBr with excess H2SO4. A 1L RBF was charged with 241ml of 80 proof vodka (equivalent to 1.65mol of anhydrous ethanol). With stirring, 154.34g of NaBr (1.5mol) was added. A standard distillation apparatus was assembled with ice water supplied to the condenser and the recieving flask (250ml) sitting in an ice-salt bath. In place of a thermometer adapter, a pressure-equalizing addition funnel was added containing 330g of ~92% drain cleaner sulfuric acid (~3.1mol). This was slowly added to the ethanol/water/NaBr mixture with occasional cooling by an ice bath. A lot of fumes were produced in the flask initially, but did not pass over into the condenser. The reaction mixture became fairly warm and turned orange, but no distillate formed. A considerable amount of NaHSO4 was formed, but the stirring was able to keep it in suspension.

After the sulfuric acid addition was complete, the addition funnel was replaced with a thermometer adapter. Distillation was carried out on a fairly low heat setting (3 on my Corning PC-351). The upper portion of the flask was insulated with a sheet of aluminium foil since the ambient temperature was fairly low. Distillate initially came over fairly rapidly in the low 40C range. When flow slowed, the heat was gradually increased to 4. Distillate came over in the 40-50C range for 3 1/2 hours. Heat was increased to 5 when the stillhead temp was near 55C. Distillate (showing droplets of an organic phase) continued to be collected up until the stillhead reached 80C and flow came essentially to a halt.

The distillate consisted of a large organic phase with a thin aqueous phase on top. The entire contents was transferred to a 250ml sep funnel and washed with about 40ml of ice cold saturated sodium bicarbonate solution containing a very small amount of sodium sulfite. No apparent CO2 was formed on shaking indicating absolutely minimal or no HBr contamination. This wash should be considered extraneous or be replaced with a wash of ice cold distilled H2O.

The organic phase was removed, the funnel cleaned and dried, and the organic phase returned to it. 30g of concentrated H2SO4 was added and shaken with the EtBr repeatedly. This caused an unusual faint cloudiness in the organic phase which split light and made it very colorful when illuminated.

The lower H2SO4 layer was drained off and the organic phase was immediately washed with a large portion of ice-cold saturated sodium bicarbonate solution. Initial CO2 release is dramatic from H2SO4 adhering to the sep funnel's walls. Agressive shaking and venting is needed to expel CO2 from solution. When the upper aqueous phase still produces bubbles with some dilute acid, enough NaHCO3 has been used.

The lower phase was drained into an RB flask and dried over CaCl2 for a few hours. The dry product weighed 147.54g (1.35mol), a 90% yield from NaBr.

[Edited on 11-16-12 by UnintentionalChaos]

chucknorris - 17-11-2012 at 19:21

Can you do this process non-stop by mixing the goods beforehead and then continuously flowing them into the reactor and distill over crude bromoethane?

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