Sciencemadness Discussion Board - Preparation of Acetyl Chloride

Preparation of Acetyl Chloride

Magpie - 26-8-2014 at 18:09

A. Introduction Back in 2009 I had found a preparation for acetyl chloride in Helvetica Chimica Acta, 1953. Precursors were acetic anhydride (AA) and calcium chloride. The article was in German so I asked garage chemist (GC) to check my Babelfish translation. My translation was OK but he didn’t like the preparation due to poor yield and recommended an alternative. GC’s method reacts dry HCl gas with AA. Acetic acid is a by-product:

1 mole AA + 1 mole HCl ---> 1 mole acetyl chloride + 1 mole acetic acid

Two days ago I finally got around to trying his method.

B. Equipment and Reagents

1. Dry HCl Gas Generator This preparation is a challenge only due to the need to safely produce a controlled flow of dry HCl gas. My method for doing this was to heat an equimolar dry mixture of NaCl (non-iodized, food grade) and NaHSO4 (95%, swimming pool grade). With careful heat modulation using a bunsen burner a steady, prolific stream of HCl was produced. I dried the HCl by sparging it into con H2SO4 using 5cm of submergence of a glass tube with a fritted end. This puts all glassware and connections upstream of this sparge tube under 10 cmH2O gas pressure. The tricky part is the plumbing. Selecting good materials and providing secure connections are critical. Any leak will spew copious amounts of HCl gas. Due to the large thermal mass of the mixed salt in the generator this gas flow will not stop soon even when the heat is removed. (See note 1.)

Generating HCl gas

My tubing was 3/16”ID Tygon, which holds up well to dry HCl. It will even tolerate some minor exposure to con H2SO4 in the event of a foamover (See note 2). Tygon will form a very tight compression seal to glass tubing by using a shrink fit. Heating it in boiling water will facilitate shoving the end onto the glass tubing. Due to different glass tubing sizes I had to use some 3/16” x ¼” adapters. These were made of Nylon which is not a real good choice as they did suffer significant deterioration/partial plugging in dry HCl and even more deterioration in cold con H2SO4 during a foamover. I used some ¼”ID natural rubber to make connections also. This deteriorates (turns brown) in HCl gas but holds up sufficiently for this short term use.

I placed a trap on each side of the H2SO4 absorber: upstream to protect from suckback, and downstream to protect from H2SO4 foamover. Rubber two-hole stoppers were used in each.

Drying HCl gas with H2SO4

2. Reactor My reaction vessel was a 250 ml 2-neck RBF. The center neck was equipped with a reflux condenser topped with a CaCl2 guard tube. In the side neck was placed a sparge tube with a fritted glass end. The reactor was stirred with a magnetic stirrer. The reactor was charged with 102.1g (1 mole) of AA.

Sparging AA with HCl gas

C. Preparation
I made up the salt mix by mixing 100g of NaCl and 216.3g of 95%NaHSO4. This was placed in a 1000 ml RBF generator. I ended up using 2 batches.

The first day I had a massive gas leak right off due to my own negligence and lack of obsevation: I neglected to clamp a glass taper connection at the top of my gas generator. Fortunately the fugitive gas was sucked away by my fume hood. Without a good hood I would have had to evacuate. I sparged for 4 hours, not always under good control as I was recovering from the gas leak and learning how to modulate the heat. When finished I weighed my pre-weighed reactor. Uptake was only 14g. Theoretical requirement is 36.5g (1 mole).

On the next day my gas sparging was very well controlled. I sparged until the salt was producing very little gas, about 5 hours. Total uptake now was 35.9g!

I also noted that the liquid volume had increased significantly in the reactor. The charged volume of AA was 94.4ml. The additive volume of 1 mole of acetic acid and 1 mole of acetyl chloride is 57.25ml + 71.04ml = 128.3 ml, not accounting for any change in volume due to mixing. Also there were droplets of liquid forming on the headspace wall of the reactor even though it had only warmed slightly. I took this as acetyl chloride as it has the relatively low boiling point of 51-52°C compared to AA (140°C) and acetic acid (118.1°C).

D. Fractional Distillation Although the boiling point separation between acetyl chloride and both AA and acetic acid is quite large I decided to use a fractionation column (20cm Hempel, broken glass packing) just to assure a clean cut. I protected the vacuum take-off vent with a CaCl2 guard tube. Just as GC had warned there was a lot of HCl dissolved in the product mix. This revealed its presence by forming a fog on the beaker in which I had placed the guard tube. This also lowered the boiling point of the acetyl chloride distillate. Consequently I captured distillate in the condensation range of 42-49°C. I could likely clean this up by a 2nd distillation.

$fractionating for acetyl chloride.jpg - 88kB$
Fractionating for acetyl chloride

E. Yield Yield of the crude product is 55g. This is a 70.1% yield not considering any dissolved HCl.

F. Conclusions Although quite time consuming I feel that this is an interesting and reasonably productive preparation. However, anyone using it must be confident of his HCl gas generating system and how to control it. Use of a good fume hood is vital as a safety backup.

G. Notes
1. Rhodium’s archive provides a good survey of dry HCl generating methods. His preferred method would eliminate the large thermal mass of my method.
2. I use the term “foamover” to indicate a flow of H2SO4 foam into the downstream trap. It is the result of an excessive HCl gas generation rate.

Questions, comments, and recommendations are welcomed, as usual.

[Edited on 28-8-2014 by Magpie]

Pyro - 26-8-2014 at 19:12

very interesting. again a great writeup!

if you feel like it there is a procedure in vogel's 3rd detailing the synthesis of acetyl chloride with PCl3 and GAA or POCl3 and anhydrous NaAc.
page 367-368
either (or both) would make a nice addition to this as POCl3 or PCl3 might be easier to get/make for some people than AA

DJF90 - 26-8-2014 at 21:45

Congratulations magpie. You may find a reflux period (ice cold water) with CaCl2 guard tube in place suitable for the removal of excess HCl. I too had seen that method using calcium chloride and,acetic anhydride in Feiser 1, but like you on digging out the reference was not best pleased about the 12(?)% yield.

This current method is said to give excellent yield (complete converion IIRC) and you have demonstrated that with a little optimisation it ought to be possible.

I think this deserves a home in prepub, by the way.

Oscilllator - 26-8-2014 at 22:12

Thats an interesting choice of HCl gas generator you have there. Why did you decide to use NaHSO4 instead of H2SO4? I would have thought that slow addition of the sulfuric acid would provide good control of the HCl flow rate, although I don't have any personal experience with that method.

Wonderful write-up though, as always.

aroma princess - 27-8-2014 at 03:17

why not going for instant route? reation of acetic acid with thionyl chloride? Use DMF in catalytic amount as it forms imidochloride complex and accelerates reaction. yield ~ 70%

Magpie - 27-8-2014 at 07:57

Thanks, Pyro.

Quote: Originally posted by Pyro

...either (or both) would make a nice addition to this as POCl3 or PCl3 might be easier to get/make for some people than AA

Unfortunately this is not true for those home chemists who live in "the land of the free."

Thank you DJF90. I remember seeing that you had made acetyl chloride with the CaCl2 method. I used ice-cold water in the condenser and in the bath holding the receiver. That probably just helped keep the HCl in solution. But refluxing like you say should kick that HCl out of solution. For now I'm not going to worry about it. If I find a synthesis in which the HCl would be a problem then I'll expel it.

Thanks Oscillator. I used the salt method as I had some previous experience with it. I looked at the sulfuric acid/muriatic acid method in Vogel and Brauer but it looked cumbersome and I didn't have a long tube at hand. But Rhodium prefers this method and has an equipment modification (he uses a mag stirrer) that would obviate my objections. You do need two mag stirrers, however, which I don't have at this time.

Aroma Princess: This is a forum for home chemists. Thionyl chloride and PCl3 are CWC and are not purchaseable and/or shipable to the US home chemist.

[Edited on 27-8-2014 by Magpie]

[Edited on 28-8-2014 by Magpie]

aroma princess - 27-8-2014 at 22:26

1)absolutely correct oscillator..i always use sulfuric acid for generation of dry HCl...(*caution : very controlled addition is required to avoid runaway situations) and dont forget to put some sodium chloride in HCl).
2) dear magpie : Put a reflux divider over fractionation column and allow self reflux for a while(atleast 20 mins) before you start collecting acetyl chloride.
best of luck..!!

3) Acetic anhydride is not restricted? well... in my country it is classified under psychotropic substance category as its main precursor of heroin and is not available.
[Edited on 28-8-2014 by aroma princess]

[Edited on 28-8-2014 by aroma princess]

PHILOU Zrealone - 28-8-2014 at 05:21

In principe, cetene can also add HCl to form acetyl chloride.
CH2=C=O + HCl --> CH2=CCl(OH) <-==> CH3-CCl=O

Magpie - 28-8-2014 at 08:30

Surprisingly enough acetic anhydride is available to the home chemist in the US.

PHILOU: I tried to make AA by making ketene once but my synthesis did not work. Also I was very concerned about ketene's toxicity so decided not to try again.

AvBaeyer - 29-8-2014 at 18:27

Magpie,

Very nice piece of work! Thank you very much.

AvB

Zyklon-A - 29-8-2014 at 19:27

Great write-up, as usual Magpie. I want to try this as soon as I can get some more AA, I'm nearly out.

Quote: Originally posted by Oscilllator

Thats an interesting choice of HCl gas generator you have there. Why did you decide to use NaHSO4 instead of H2SO4? I would have thought that slow addition of the sulfuric acid would provide good control of the HCl flow rate, although I don't have any personal experience with that method.

Yes, I have used 98% sulfuric acid + calcium chloride/sodium chloride to generate dry HCl (g) several times. It's quite simple, all one needs is a pressure-equalized addition funnel, a two-neck RBF, HCl resistant tubing, and the reagents of course.
Although I haven't tried the sodium bisulfate method, I think sulfuric acid makes the job much easier, as the gas comes out completely anhydrous, and no heating is required. Just be sure to keep the acid dripping slowly.

Magpie - 29-8-2014 at 19:53

Thank you both. Zyklon-A could you give a more detailed description of your dry HCl gas generation method? Thanks.

Zyklon-A - 29-8-2014 at 22:26

Sure, although my discription won't be better than Rhodium's or the one I followed, which I have forgotten unfortunately.
To prepare one mole of HCl gas:
58.4 grams (one mole) NaCl is placed in a two-neck RBF (I probably used a 500 mL flask, but I'm unsure). One neck is fitted with a pressure-equalized addition funnel, the other with an adaptor for an HCl(g) resistant rubber tube, which is then fitted on/in.
Then, slightly over one mole (~100 grams IIRC) 98% sulfuric acid is placed in the addition funnel.
The rubber tube is then placed wherever it's needed, and the setup is complete.
Sulfuric acid is added drop by drop on the salt, where this reaction occurs:

H₂SO₄ + NaCl --> NaHSO₄ +HCl (g)

The generated HCl gas shouldn't contain any water, due to the extremely hydroscopic nature of sulfuric acid.
Note: Although I have not, it would, of course, be most economical to use half a mole of sulfuric acid, and then heat the resulting sodium chloride/bisulfate mixture as you have done previously, to harvest all available HCl.
The main reason I tried this method is because I don't have any sodium bisulfate, but I may give it a go when I get some.

[Edited on 30-8-2014 by Zyklon-A]

Magpie - 30-8-2014 at 15:56

Rhodium drops muriatic acid (~31% HCl) onto con H2SO4 but also uses a con H2SO4 bubbler not only to monitor gas flow but to absorb any traces of water that the HCl(g) may contain.

I agree that if you are using dry NaCl and concentrated H2SO4 there should not be any water in the HCl(g). Have you any evidence that this is indeed true?

UnintentionalChaos - 30-8-2014 at 18:46

Quote: Originally posted by Zyklon-A

Although I haven't tried the sodium bisulfate method, I think sulfuric acid makes the job much easier, as the gas comes out completely anhydrous, and no heating is required. Just be sure to keep the acid dripping slowly.

This has not at all been the case for me. Whenever I run one of these generators, the HCl is produced painfully sluggishly and I have to heat after adding all the acid to produce a steady stream of gas.

I always powder the NaCl, so I don't think it's a surface area issue and I use ~95% drain cleaner acid.

With regards to the original post, very nice work. Acyl halides are lovely things, such as for the FC acylation. The anhydrides consume an entire additional equivalent of AlCl3. Acetyl chloride in particular can also halogenate trityl alcohol to the chloride per orgsyn Vol. 23, p.100 (1943).

[Edited on 8-31-14 by UnintentionalChaos]

AvBaeyer - 30-8-2014 at 20:17

Here is another method for HCl generation using hydrochloric acid and calcium chloride.

AvB

Attachment: Convenient Way To Generate Hydrogen Chloride.pdf (868kB)
This file has been downloaded 1240 times

Zyklon-A - 30-8-2014 at 21:02

Quote: Originally posted by Magpie

I agree that if you are using dry NaCl and concentrated H2SO4 there should not be any water in the HCl(g). Have you any evidence that this is indeed true?

No, I have not. I always used an excess of sulfuric acid, and just assumed it to be dry. If I was doing a delicate reaction which could be ruined by trace amounts of water, I would have done so, or at least bubbled it through sulfuric acid again.
Unintentional Chaos, I think that may have to do with the difference in concentration. Although 95% is quite conc., with this specific reaction, the acid must contain very little water. I heard somewhere that 90% is the minimum for it to produce any HCl(g), that figure may be wrong, but it's pretty close.

Templar - 2-9-2014 at 16:38

guys what was wrong with using cyanuric chloride with ethanoic acid as per the attached patent?

Attachment: TCT acetyl chloride.pdf (952kB)
This file has been downloaded 1030 times

Magpie - 2-9-2014 at 18:07

My guess is that cyanuric chloride is not available to the home chemist, at least not in the US.

Oscilllator - 2-9-2014 at 19:23

I would just like to point out a possible improvement on the H2SO4/NaCl gas generator: Instead of using a pressure-equalising addition funnel, you could just use a normal one. This may seem counter-intuitive, but is has a number of advantages:

-You cannot accidentally add too much sulfuric acid and have a runaway reaction. This is because the faster you add the sulfuric acid, the faster the HCl is generated and this has a feedback loop slowing down the sulfuric acid addition, because the HCl has to come out the same hole the sulfuric acid goes in.

-The HCl is bubbled through the entire column of sulfuric acid, thoroughly drying it. this advantage is lessened the further on the addition goes but it is still a advantage, since it negates the (possible) need to have a separate drying tube.

-Monitoring of flow rate: Since the HCl is being bubble through the H2SO4, it is easy to monitor the flow rate of HCl

I have used this method to generate Chlorine gas with considerable success for a number of experiments, although in this case the normal addition funnel was used out of necessity, not choice.

Dr.Bob - 3-9-2014 at 09:04

I would be afraid that any surge in pressure could cover me with sulfuric acid, using a normal addition funnel. I prefer the idea of a drying tube inline somewhere, and if you add the acid slowly, it should generate gas at a steady rate. And as stated above, 90-90% sulfuric acid will not act nearly as well in dehydrating the HCl, although it should work eventually, but the HCl may just dissolve in the 95% sulfuric acid instead of bubbling off.

CaptainPike - 3-9-2014 at 10:58

First off, like many have already stated REALLY COOL POST! And I like the dry generator – I have a whole bunch of NaHS04 around here, both with the green specks (pool pH modifier) and some "reagent grade product". It's handy stuff, acid in a bag, man!

Also, I have had just awful trouble with gas leakage from my HCL generator – had to leave the room choking, as my makeshift fume hood was inadequate and I had trouble with my gas mask. It seemed like the HCl gas would go ANYWHERE but through my solution (doing a TsOH prep).

Reading magpie's post here has re-enthusiasticiated me! I'm re-rigging my fume hood and going to do this prep (while the weather is still nice LOL). Thank you.

What I want to understand is how the HCl gas exits the generator in Oscillator's version? That is, where does the gas come out of the non-equalizing dropping funnel? Through the top? Or use a 2 neck flask?

Oscilllator - 3-9-2014 at 14:48

It comes out through the top of the addition funnel.

Also @Dr.Bob: One of the advantages is that it's impossible to have a surge of gas. Even if you open the stopcock completely, the flow of gas upwards prevents excessive amounts of sulfuric acid dropping down.

Magpie - 3-9-2014 at 18:08

Thank you for the kind words Captain. I have spent some time since working on the problems I identified in my plumbing for this experiment - I too hate gas leaks! I think I have now selected materials for the plumbing that will provide reliable leak free gas production for both HCl and Cl2. Once I test this system I will post the details.

hanjo - 19-9-2014 at 08:51

Can the same thing be made with another anhydride for example benzoic anhydride or other

Scr0t - 19-9-2014 at 09:20

Quote: Originally posted by hanjo

Can the same thing be made with another anhydride for example benzoic anhydride or other

Presumably that would give benzoyl chloride. That could then be reacted and distilled with acetic acid to make acetyl chloride.

hanjo - 21-9-2014 at 10:56

So basically if i follow you reasonement if you have an Carboxylic Acid Anhydride you can virtually make any other Anhydride or Chloride of any carboxylic acid.

Exemple ( ??) : Acetic anhydride + Sodium butyrate --> Butyryl Cloride + Sodium Acetate

And is this reaction possible Benzoic anhydride + Glacial acetic Acid ---> Anhydride Acetic + Benzoic acid ????

Is this possible ?Someone had any Documents to share about these reactions

Thanks

[Edited on 22-9-2014 by hanjo]

[Edited on 22-9-2014 by hanjo]

[Edited on 22-9-2014 by hanjo]

Scr0t - 22-9-2014 at 03:56

Quote: Originally posted by hanjo

So basically if i follow you reasonement if you have an Carboxylic Acid Anhydride you can virtually make any other Anhydride or Chloride of any carboxylic acid.

Exemple ( ??) : Acetic anhydride + Sodium butyrate --> Butyryl Cloride + Sodium Acetate

No.
https://www.sciencemadness.org/whisper/viewthread.php?tid=77...

plante1999 - 22-9-2014 at 04:25

Best way for benzoyl chloride is to reflux benzotrichloride with benzoic acid, which can be made with toluene and chlorine, benzoic acid can also be made with toluene. This process is not only cost efficient, but toluene can be extracted from many paint stripper in most country to a cost of about 10$/100 ml of toluene.

Dr.Bob - 22-9-2014 at 11:15

Quote: Originally posted by hanjo

No, in most cases you reach an equilibrium, in that some proportion (you can approximate half, for a starting point) will be on each side of the arrow. At that time, unless there is some driving force, like a way to remove one of the materials from the reaction, say by distillation, precipitation, volatilazation, or some other means, the reaction will stay a mixture of many things.

But for every reaction there may be a way to shift the equilibrium to one side or the other of the reaction, by using a specific solvent, temperature, etc to try to remove one material from the reaction. This is why having a product precipitate from the reaction will drive the reaction forward. But other ways are possible as well. That is why most people use oxalyl or thionyl chloride to make acid chlorides, as both create volatile compounds when they react with the acid, so the reactions are pretty much one way only. If you start with an excess of one reagent, that can also help push the reaction towards the other side of the reaction.

hanjo - 23-9-2014 at 14:12

Ok thanks for explanations

CuReUS - 27-9-2014 at 05:10

magpie ,really amazing write up .
can we make acetyl chloride like this https://www.erowid.org/archive/rhodium/chemistry/anhydrides....

under the title Acetic anhydride from sodium acetate, using S2Cl2
sodium acetate is reacted with S2Cl2 to get that beautiful symmetric molecule which decomposes to give acetic anhydride upon heating.
now instead of heating why cant we chlorinate it or use some strong chlorine donor(aqua regia or hypochlorite,even electrolysis) or chlorine free radicle(UV)

6 chlorine atoms participate in the reaction totally

1.first the S-S bond breaks to give free radicle S

2.then the C-O bonds on both sides of the S breaks(to try to fulfill S valency),O being more electronegative than S pulls the electron towards itself.

3. finally the Cl simultaneously adds to the S as well as the C

so we get acetyl chloride and thionyl chloride

could someone validate my idea or point out the mistakes :cool:

hcl gas generation

MARXYZ - 28-9-2014 at 04:46

Try 85% phosphoric acid and damp rid.

Produces steady stream of gas. No need to worry about suck back. It won't happen.

1/4 inch phosphoric on bottom of Erlenmeyer. Fill to neck with CaCl2. Insert stopper with hose. Voila!

Chemosynthesis - 8-10-2014 at 16:24

Quote: Originally posted by CuReUS

under the title Acetic anhydride from sodium acetate, using S2Cl2
sodium acetate is reacted with S2Cl2 to get that beautiful symmetric molecule which decomposes to give acetic anhydride upon heating.
now instead of heating why cant we chlorinate it or use some strong chlorine donor(aqua regia or hypochlorite,even electrolysis) or chlorine free radicle(UV)

I am having a very difficult time envisioning where your electrons all go. Could you work out a pictorial mechanism on something like chemsketch next time? It is free.

I think I misunderstand your reaction. I am actually not sure I am reading the products correctly. Ideally, you could look up bond enthalpies or dissociation energies and get an idea of what kind of energy you would need input or released for your reaction, and that can give you an idea of the likelihood of how exergonic or endergonic a reaction is.

Okay, let me answer what I think is your question as best I can as I understand it. First, for the sake of argument, what prevents alpha halogenation of your chloride, ala the HVZ reaction?

Now, my real answer: no, I find that highly improbable and would expect a Zincke cleavage of the disulfide bond to be far more reasonable than your proposal, as I understand it.

Magpie - 27-2-2015 at 14:32

Not yet having any use for my homemade acetyl chloride and wanting to do something simple in my lab I decided to do the 3 qualitative tests in Brewster (1960). I used a large (20mm x 150mm) test tube for all tests. Here's the results:

(1) Hydrolysis. Carefully poured 1mL in 5mls of water. There was some immediate bubbling and the tube got very hot.

CH3-COCl + HOH --> CH3-COOH + HCl

(2) Esterification. Cautiously poured 1 mL in 2 mL of 95% ethanol. Same as above only the reaction was more vigorous. I could only add a portion at a time. More bubbles and the tube got very hot. Poured into 50mL of water and smelled the ethyl acetate.

CH3-COCl + CH3-CH2-OH --> CH3-C-OOCH2-CH3 + HCl

(4) Reaction with Aniline. Slowly mixed 1mL with 1mL of aniline. This reaction was downright violent. I could only add a drop or two at a time. Purified the acetanilide and determined its mp to be be 114-115°C.

C6C5-NH2 + CH3-COCl --> C6H5- NH-COCH3 + HCl

The only reason I'm posting these results is to comment on the remarkable reactivity of this compound. It is much greater than that of acetic anhydride. I know that chloride is a good leaving group, and that one product is a gas (HCl), but does anyone know what else contributes to this compound's remarkably high reactivity?

[Edited on 27-2-2015 by Magpie]

blogfast25 - 27-2-2015 at 14:51

With those two 'electron pullers' (O= and -Cl) that C-Cl bond must be highly polarised. I'm not sure, reactivity wise, there's all that much more to say, really.

Over to the real experts.

Magpie - 27-2-2015 at 15:53

Blogfast - what you are saying is that the carbon of -COCl is highly electropositive. Therefore it is also highly electrophilic. Is that your point?

Because of the heat generated on hydroysis and esterification I was curious what I would calculate for heats of reaction for the acetyl chloride. Here's what I found:

(1) hydrolysis: -21.7 kcal/mole

(2) esterification: -18.1 kcal/mole

(3) rx with aniline: -31.09 kcal/mole

These results seem unremarkable.

If someone missed this

franklyn - 28-2-2015 at 01:21

http://www.sciencemadness.org/talk/viewthread.php?tid=9&...

qeezur - 4-3-2015 at 07:47

i used to activate acids with better leaving groups back in my benchwork days ... we used SOCl2 ... i know its banned ... but it was the best way if yield is to be considered ... i can write up my settled methodology if someone is interested ...

Magpie - 31-8-2016 at 19:03

Today I used the remaining 32g of acetyl chloride that I had made almost exactly 1 year ago. It was tainted a dark brown. On cleanup of the glass bottle I had stored it in (Qorpak Thermoset F217 cap with ptfe liner) I noticed that the cap threads were black with a wipeable corrosion product. So I am assuming that this is the source of the brown coloration. I do not know what Thermoset 217 is but I would guess it is some kind of phenolic. I think this is Qorpak's best cap.

clearly_not_atara - 2-9-2016 at 00:16

It just has very low barriers to reaction. Acetate is a much weaker leaving group than chloride.

chem.yu.edu.jo/rawash/chem%20611/homeworks/h17.pdf

[Edited on 2-9-2016 by clearly_not_atara]

The jersey rebel - 24-1-2017 at 07:04

acetonitrile, dry HCl and acetic acid can also be used to make acetyl chloride. chem player made a video about it