Sciencemadness Discussion Board

Dean Stark Trap

FloridaAlchemist - 20-1-2005 at 18:30

Does anyone have any info on making a improvised dean-stark trap for semi-micro scale range? :(

runlabrun - 21-1-2005 at 05:13

rhodium had an interesting glass improv page on the site....

http://rhodium.moppy.net/www.rhodium.ws/chemistry/equipment/...

This has the dean stark your looking for.

-rlr

FloridaAlchemist - 21-1-2005 at 23:15

Thanx for the info.:)
I try to do most of my experimentation on the semi-micro scale and need to remove the water from esters;)

acx01b - 1-12-2005 at 16:48

this is the best cheapest dean stark you can make:




(one flask, one condenser, one pyrex tube, and 2 pierced rubber stoppers)

you can see in red the Trap of the dean stark trap !! lol but it works very well (np rubber stoppers work for H2SO4 200°C temp...)

or, you could use a 2 holes stopper in place of 1hole stopper at the condenser and in one of the hole add an other tube witch would be the trap...

Aubrey - 8-1-2009 at 02:50

i've set up the dean stark a la acx01b's suggestion.
I plan to sytnh ethyl benzoate from benzoic acid and ethanol. i set it up and realised i need sulfuric acid as a catalyst.
There's also a dean stark piece of glassware on ebay, so if i win that before my h2so4 then i might not try this configuration.
The bung doesnt fit that tightly and i've had to invert my reflux condensor.
i'm pretty happy that i discovered that a very small aquarium pump i had in the cupboard from when i kept tropical fish works very well at pumping water through my very long reflux condensor.
sorry about the poor picture quality, i tried with the flash on but the white wall behind reflected it all. I'm considering making a painted background.
does anyone know how much h2so4 is required for a catalyst, and if much of a workup is required after the reflux?

deanstark.jpg - 48kB

stateofhack - 8-1-2009 at 04:50

You might want a second clamp on that..looks like it about to fall to me!

Klute - 8-1-2009 at 12:20

And place the pump in a plastic tube (no breaking :) ), on the top of your improvised stand, so that you have a larger flow of water (no need to force the water up the condenser).

For the esterification, see Vogels etc, or preparation of p-nitroethyl benzoate in the benzocaine synth. You will just need to evaporate part of the ethanol, add brine, extract you ester, wash until neutral, dry and evaporate solvent to get your ethyl benzoate.

Good luck!

Nicodem - 9-1-2009 at 00:31

How is a Dean-Stark trap to be used in the Fischer esterification of benzoic acid when doing it with H2SO4 and EtOH? This does not make any sense to me. Aubrey, are you sure you are not confusing something here like you usually do? What is the reference for the procedure you are following?

DJF90 - 9-1-2009 at 08:16

I thought the dean stark was used to remove water from the reaction mixture as the ester is formed, since fischer esterification is an equilibrium reaction (and the conc. H2SO4 catalyses in both directions) so removing the water shifts the equilibrium to the right [Acid + Alcohol <=> Ester + Water] and also prevents hydrolysis of the ester as it forms (as water is needed for the hydrolysis). At least thats my understanding of it.

gsd - 9-1-2009 at 09:34

The vogel procedure for esterification of benzoic acid by methanol and ethanol (vogel 3rd ed. page 781 & 782) does not use dean-stark trap. BUT it uses very high excess of alcohol and distills excess of it off after 4 hrs of reflux. While doing so the reaction water is also distilled away along with it. However this is far from an ideal way of doing this reaction, as the yield reported for methyl benzoate starting from 30 gm benzoic acid is only 31 gm.

In Preparative Organic Chemistry (by Weygand and Hilgetag - pg 369 onwards)

Authors strongly recommend use of water removing devices. To quote a para from this book :

"Continuous removal of the product water by azeotropic distillation after addition of a carrier such as benzene, toluene, xylene, or a halogenated aliphatic solvent leads to rapid esterification ("azeotropic esterification") and usually also to high yields. The course of the reaction can be followed directly from the amount of water liberated; the apparatus used for this purpose (a water separator) is well known."

gsd

Aubrey - 9-1-2009 at 09:38

Nicodem: Following this
http://courses.chem.psu.edu/chem36/Experiments/Exp84.pdf
but i'm making the ethyl rather than the methyl

it strongly suggests using some kind of dean stark to move the equilibrium.

[Edited on 9-1-2009 by Aubrey]

S.C. Wack - 9-1-2009 at 12:28

No, the use of the trap is suggested in making butyl acetate. And it will work fine there.

Notice that the trap is absent when illustrated in the pdf for methyl benzoate: "Place 5.0 g of benzoic acid and 25 mL of methanol in a 100-mL round-bottomed flask, cool the mixture in ice, pour 1.5 mL of concentrated sulfuric acid slowly and carefully down the walls of the flask, and then swirl to mix the components. Attach a reflux condenser, add 3 boiling chips, and reflux the mixture gently for 1 hr. with the set-up shown."

Care to guess why there isn't a trap there?

For making ethyl esters, a good old high-yielding method uses a Soxhlet containing MgSO4 or CaSO4. Using the trap instead will not work here. And the Soxhlet will not work with methyl esters.

DJF90 - 9-1-2009 at 12:53

because methanol is miscible with water, so a trap doesnt help at all... same with ethanol. Am I right?

[Edited on 9-1-2009 by DJF90]

Klute - 9-1-2009 at 14:18

Well, you can make it to work if using enough toluene, or even better lower alkanes. The removal of the water will be longer and incomplete, as the toluene ethanol layer will contain dissolved water, but it will work well enough to displace the equilibrium sufficiently. Then the last water can be removed when the solvents are evaporated. I have used this for condensation involving acetone and MEK, both completly miscible with water. Good results were obtained when using petroleum ether as a co-solvent, with a neat seperation of the water/ketone and alkane/ketone layers.

[Edited on 10-1-2009 by Klute]

DJF90 - 9-1-2009 at 15:17

Yea I know toluene works because we used it in labs when forming a ketal from methyl acetoacetate using ethane-1,2-diol. The separation of toluene and water in the dean stark didnt seem great though, with the toluene layer being rather cloudy (presence of water?) but there was definately two distinct phases.

Nicodem - 10-1-2009 at 04:40

Aubrey, the Dean-Stark trap is not some magical device that dries liquids. It only separates phases during a reflux. If the denser phase happens to be richer in water than the less dense one, Then, and only then, can it be used to remove water from the reaction mixture (there also exist apparatuses for inverse phase removals, but these are a bit more complicated than a Dean-Stark trap). Since in the procedure you are following the distillate is monophasic you can forget about using the Dean-Stark trap, simply because there is nothing to trap. You could use a solvent that forms a ternary azeotrope with water and ethanol and in which the distillate is biphasic with the lower phase richer in water (toluene is one such, and Gsd provided you with one reference about it), but frankly I see no point in complicating what is already a simple esterification.

Aubrey - 10-1-2009 at 05:23

thanks for all the responses, the document i was looking on mislead me a little. i'll look at getting some toluene, and perhaps try it without as well, so i can learn about the different approaches (and because ill have to wait for some toluene) :)

first attempt

Aubrey - 17-1-2009 at 08:29

250ml ethanol
50g benzoic acid
17ml H2So4

I attempted my first experiment, which was this one. I learnt a lot about practical chemistry, although it doesnt appear to have been entirely successful.

Anyway for other interested amateurs, here is what I learnt:

Pouring sulfuric acid into the benzoic ethanol mixture SHOULD be done slowly. it appeared quite violent. I know the instructions said that, but now i know why :)

My water pump could be a little more powerful, it *just* had the capability of pushing water roudn my condensor. Although with this sized rbf, this is not much of an issue since only a small part of it was used.

the stir bar doesnt work when the rbf flask is this height in the sand bath. Perhaps it is better to put the rbf in right against the pan then pour sand around it?

Trying to wedge a rbf into a sand bath is pretty hard. I'm looking forward to my mantle arriving.
The sand bath reached a temp of 130c with no boiling.
a drip appeared the bung in the system, a slight adjustment fixed this... smaller bungs would be better for this.. perhaps with vaseline?
when the sand temp reached about 140c it looked like something began happening to the liquid. A 14/23 thermometer adapter might be worth getting to obtain more accurate temperature. At a sand temp of 170c vig bubbling occurred. the temp reached about 195c and stayed abour there.

My hotplate at least is pretty unresponsive to temp adjustments. it could take like 20 mins / half an hour for a change to take affect.

my reflux condensor is a bit of a monster for that size of rbf, somehting a third of its height would probably have been fine.
a rbf with graduations would have been useful, to see how much water had passed over. during this experiment, i swapped out the beaker / spoon arrangement shown here and put the water tube it into a rbf with two hole stopper and cut the length of the tube so that it didnt coil around.

It was pretty cool watching the water bubbling up the tube and then slowly flowing down the tube and finally seeing something happening after so much reading.

However the so called water which came over tastes pretty much like ethanol so something went wrong. I guess because i didn't use a co solvent (toluene) i was jsut distilling ethanol, because of no heteroazeotrope. ;| So perhaps i can jsut dump the ethanol distillate back in and then dry over CaO or something. The pdf linked to above didnt use any dean stark so i guess i may have had partial success.. wondering whether to get a mel temp off ebay or not, cos its fairly difficult to judge my success.

Well I guess i might have some of my desired product in my rbf
so i might take a small quantity and do the workup, or i could try again with this current mixture when my dean stark arrives.
ho hum

all in all i learnt a lot so it's not a total failure, although obviously i'd like to know what went wrong. because i would actually liek some ethyl benzoate out of this. esp as the ethanol i used in this case is 39 quid for 500ml.

constructive criticism only please. :)
I also took a couple of videos, i could upload to youtube if anyone's interested.

thanks again for all the help i've been given. Klute in particular has been an absolute star :)


[Edited on 17-1-2009 by Aubrey]

SM_grab.jpg - 51kB

Aubrey - 17-1-2009 at 08:34

before heating

[Edited on 17-1-2009 by Aubrey]

ethyl2.jpg - 122kB

crazyboy - 17-1-2009 at 10:53

I made methyl salicylate quite easily without a Dean Strak trap. I am sure the procedures are exactly the same.

Just mix the carboxylic acid and alcohol in a 500ml flask then slowly add the acid catalyst. I suggest a small batch (about 5g carboxylic acid.) Then add several boiling stones and a condenser through which you pump cold water. Reflux gently for 4 hours (I use a heating mantle.) The product does not form crystals of carboxylic acid and no alcohol layer forms indicating almost complete reaction.

This should smell like the desired ester but if you want it purer I'm sure you could wash with bicarb and distill or extract with DCM/ether and dry with MgSO4 or CaCl2.

DJF90 - 17-1-2009 at 12:17

Quote:

However the so called water which came over tastes pretty much like ethanol so something went wrong.


:o You tasted it??

Nicodem - 19-1-2009 at 01:30

This is the longest "write up" of a reaction that I ever read about something as simple as an esterification which actually said about nothing about how the reaction was done. Aubrey, besides again showing you have a terrible death wish you actually said nothing about what you were doing. What distillate? You should have used reflux conditions. Do you even know what the term "reflux" means? What water distilling over? Even if you distilled instead of refluxed there could have been no water distilling over. The distillate should be 96% ethanol and ethanol and water are miscible, surely you know.
What about reading some basic laboratory handbook like Vogel's or something before you go again doing nonsense? Even if you have a reluctance learning the theory behind what you want to do (people with a death wish generally hate theory since it can actually save their life by preventing them to do idiotic things), you still need to know about the practical aspects.

Aubrey - 19-1-2009 at 03:30

i may have little experience of chemistry but what i lack in chemical knowledge you lack in good manners and the ability to relate positive constructive criticism. Each and every one of my posts i make you jump upon, and flame me. I know you're a moderator and all but i feel like i'm being trolled. I'm doing my best to learn and on the one instance when I u2u'd you to ask if i could ask for a reference request, you ignored me, so i guess you must enjoy being spiteful to amateur scientists.

Nicodem - 19-1-2009 at 05:06

Quote:
Originally posted by Aubrey
Each and every one of my posts i make you jump upon, and flame me.

That is true, but I do that on purpose and with a reason.
Quote:
I'm doing my best to learn

That is not true. Up to now you did anything but your best to learn. You do not read chemical literature, instead all you do is internet searches. You are a terrible example for other beginners. You are interested in making ketamine from chinese precursors and you disregard all the rest there is about chemistry as science. You propose and do dangerous things that can lead to self injury and ignore that there are teenagers reading posts on this forum who might imitate your attitude thinking anything goes. Tasting chemicals is dumb! You know nothing about theory, so how do you know that is safe? How do you know you did not ingest some diethyl sulfate that will make you die from cancer in the next ten years?
So either you start reading books or stop doing crazy things (or at least don't post about them!).
Quote:
and on the one instance when I u2u'd you to ask if i could ask for a reference request, you ignored me, so i guess you must enjoy being spiteful to amateur scientists.

There is a forum section for requesting references. Don't you think your U2U was a bit arrogant expecting some special treatment? If everybody else uses the Reference section why not you?
I enjoy helping amateur chemists, but you are not one of them, so stop comparing to them. Someone who up to now only posted about how to make ketamine and is even too ignorant to know that many other solvents (of which some can be bought in any hardware shop) besides ethyl benzoate can be used for its production, is not what I consider an amateur chemist. An amateur scientist is someone who is interested in science for the love for science.

Tsjerk - 19-1-2009 at 06:53

To get back on the azeotropic esterfication: I did this one's with hexane-1,6-dicarboxy acid and 3 mol eq. ethanol, H2SO4 as katalyst. Plus about the reaction volume of toluene added. A soxhlet extractor was placed with anhydrous K2CO3 to dry the azeotrope.
A yield of 95% was obtained.

Ps. is there a way to use sub/sup script on this board?

[Edited on by Tsjerk]

[Edited on by Tsjerk]

sparkgap - 19-1-2009 at 08:31

(offtopic) the "sub" and "sup" HTML tags work on this board, like so: <sup>3</sup>H<sub>2</sub>O . ;)

Aubrey,

Nicodem is generally polite. That you have managed to piss him off somewhat is due in part, in all bluntness, some residual ignorance on you. I suggest you look beyond the harsh words and heed his advice. :)

sparky (~_~)

piracetam - 19-1-2009 at 08:52

indeed

I'm somewhat of a n00b here, but no n00b to the art. I have immense respect for those who demonstrate the safe and conscious application of it, and little respect for those who don't.
I think nicodem's tone is pretty lenient. hive mods would've already devoured her (especially with their UTFSE redundancy, the shortest, lazy response to laziness)



there should be a Darwin Awards forum on this board

[Edited on 19-1-2009 by piracetam]

crazyboy - 19-1-2009 at 12:52

Aubrey/FloridaAlchemist, I have no idea how you are having trouble with this. Esterfication is a simple reaction and reflux is a simple process.

5g benzoic acid
50ml 96% ethanol
6ml sulfuric acid

Combine in a 500ml flask with condenser. Add a few boiling stones reflux gently for four hours. That's it. This ester has an intensely fruity smell.

panziandi - 19-1-2009 at 13:00

Aubrey please have a look at this:

http://www.pasynthetics.com/experiments/experiment_pdfs/Expe...

This is my account of making Methyl Benzoate I am unsure what I used as references that is in my lab book but this should be helpful. 50% yield without any removal of water and a work up is written too. I think a Dean Stark is not needed. I would just use excess methanol/ethanol. I would perhaps use Dean Stark etc if you were using an expensive alcohol and wanted maximum yields.

Aubrey - 20-1-2009 at 04:59

thanks for all the replies.
To Nicodem, apologies for saying youire spiteful, i'm sure your intentions were good and i reacted too defensively, which in hindsight i felt bad about. With regard to the reference thing, i didn't realise i was asking for special treatment, because the site specifically says 'Access must be requested of a moderator.', and i couldn't access it without the password, so I asked you

I made a mistake the first time with this experiment, but i learnt a lot. Surely next time i'll get the product i'm aiming for, but it's really a learning process for me. I'm also trying basic college stuff, extraction of caffeine etc.
warmest regards all

panziandi - 20-1-2009 at 05:48

Another very easy ester to make is methyl or ethyl salicylate.

With the methyl or ethyl benzoate you can easily nitrate it and that opens up many doorways.

Manipulating these products will give you skills in washing liquid products, solvent extraction, drying, redistillation, etc.

On my site I describe preparing an ester, nitrating it, saponifying and isolating the acid. You could do something similar.

Aubrey - 20-1-2009 at 08:51

thanks, i just might, now that i've acquired most of the bits and pieces I need ;)

chemrox - 23-1-2009 at 19:57

Aubrey:- your equipment is shit and there's no reason for it. You could use a pyrex bowl and oil for heat and the stirring system would work. You have an ST flask and condenser connected with rubber stoppers and copper tubing.. why? You have too few clamps and you're using a mail caddy in place of stands. I understand working on the cheap but with a little thought you might improvise with a lot more skill than you've shown here.

chemrox - 9-2-2009 at 22:39

Quote:
Originally posted by sparkgap

Aubrey,

Nicodem is generally polite. That you have managed to piss him off somewhat is due in part, in all bluntness, some residual ignorance on you. I suggest you look beyond the harsh words and heed his advice. :)

sparky (~_~)


I'm not sure I entirely agree with that statement either. Nicodem is a moderator now and as such should aspire to a higher level of courtesy and decorum. When the mods lower themselves to flaming it reflects badly on the whole forum. That said, the guy has been a little difficult.