Author Topic: Failure to purify benzyl chloride  (Read 1966 times)

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  • Guest
Failure to purify benzyl chloride
« on: August 05, 2004, 08:16:00 PM »
Swig is sharing his failures in this reaction in hope that other bees will avoid the pain and torture that swig has endured. 
First Swig would like to express that this was not a failed reaction, which is evident by the stale burning odor of benzyl chloride. This reaction is one of the most elementary reactions in the subject, even a monkey could be trained to mix benzyl alcohol and hydrochloric acid together.  With that being said, swig can now express the problems encountered when one tries to purify benzyl chloride.  Swig ran into many problems which can be lead to one or two shortcomings.

Problem 1.

According to the literature (Which can be found at, one should mix a 1:3 ration of benzyl alcohol and hydrochloric acid, and then slowly heat until 60c, which then two layers separate.  Swig made the big mistake because he failed to appreciate all the factors that take part in this reaction.  Swig did not want to waste his time with a measly 2 grams of reactant; he wanted to go for the big gun, one whole mole of benzyl chloride.  However the reaction does not work so well for scaled-up reactions, why?, because it takes time, and a lot of it. You can’t just put a mole of benzyl chloride in a flask and mix hydrochloric acid and expect that the reaction will take place in an hour.  It seems that one would have to wait at least 24-48 with low heat to achieve this goal.  This leads swig to his next failure.

Problem 2. 

A person can expect to wait at least 24 hours before distillation is complete, that is of course if that person lacks a vacuum, and uses an efficient column.  It seemed that oxidization took over completely by the time enough heat was generated.

Swig did try the reaction with hydrobromic acid, and the speed of the reaction seemed to be much faster.  A person needs to choose which hydrogen halide to used according to which will be safer for their lab set up.  Benzyl bromide has to be the most awful smell swig has encountered in the lab, seriously, benzyl chloride does not even come close to the pain of being exposed to benzyl bromide, however benzyl chloride seems to be a lot more harmful to the body then benzyl bromide. 

Even though swig has not yet successfully purified either halogen compound, Swig has some good advice that should be taking into consideration.

1.   Don’t get greedy, do small reactions.
2.   Distill in small portions unless one has a vacuum and good heat source.
3.   Wear protection gear.
4.   Wear goggles, inhalation mask, and 1-2 pair of nitrile gloves, when cleaning glassware, for some reason when water is added, the shit hits the fan., also if doing the reaction inside, cover all nearby food. It will absorb though your Doritos bag.

I hope this information has helped, please give feedback that would help make this reaction (purification) more successful.

P.S. If Zinc is dissolved in the hydrochoric acid the reaction would happen much faster.


  • Guest
Deceiving Eyes????
« Reply #1 on: August 06, 2004, 12:10:00 AM »
Are my eyes deceiving me here???
ADDkid: Don't get me wrong here but the majority of the threads I've read eminating from your circle are all riddled with a patronizing attitude and telling us how things should be done in regards to rxns and chemistry.
Now I'm all for a confident "off the beaten path" attitude.
It's the arrogance and grandiosity I have a hard time digesting.
I cite the above post for example.
You are telling us where you went wrong and telling us how it can be fixed and in the very next breath you post a request for feedback that will help with your purification steps/processes.
Maybe it's just me but for the life of me, I just don't think things work that way around here.
If your having problems...ask for help like ya need it and not like you are too smart to be on the receiving end.
A little gratitude goes a long way! And a little humility unlocks a treasure trove of information and knowledge you never knew existed.
And like I said...don't get me wrong...I appreciate your trying to help the collective with your insight when  you see others struggling...
But maybe your delivery could use some brushing UP some so it doesn't come across in such a condescending way.
Just tryin to help man! Nothing evil!
I understand you are learning as we all are. Some more advanced than others. Nobody is better than the next regardless of what they know.
I think you would receive a ton more collaboration with others if you'd leave room for others to feel as if they are helping you arrive at solutions.
Just my unsolicited two cents!
Carry On!


  • Guest
I really don't mean it to be in arrogant ...
« Reply #2 on: August 06, 2004, 01:49:00 AM »
I really don't mean it to be in arrogant nature, in the above post I just stated the things that I believe were big mistakes on my part, and how they might be prevented.  For example, I failed to recognize the fact that all reactions take time and the larger the scale the more time it may take.  For some reason I though the times would be proportion to the literature as long as an 1:3 ratio mixture were applied.  In my experience I notice that the biggest mistakes are those simple concepts that I don't take into consideration.  As with this reaction, I was just providing my results, and gave my theories, while at the same time encouraging feedback or suggestions.  I don’t see how this could be arrogant when I am clearly giving all of my shortcomings of this reaction.  If in previous post if I sounded arrogant, it was probably because I, (at that time) was on the defense.
            Sincerely, ADDkid


  • Guest
Chlorination Methods
« Reply #3 on: August 06, 2004, 02:39:00 AM »
This study of the chlorination of alcohols by Clark and Streight, from Transactions of the Royal Society of Canada Section III, pp 77-89 (1929) states that the best yields for the chlorination of benzyl alcohol aren't when heating is used, but quantitative yields can bee achieved in the cold, using a ratio of 1 BzOH / 2 ZnCl2 / 2 HCl  ;)


Now as far as your problems in purifying halide compounds, first you must consider the nature of the reaction. The organic halide is probably going to contain some of the acid used to produce it, thus washing with a basic solution to remove these acidic impurities is in order  :P  Many metals are destructive to these halides, so you must prevent exposure; vacuum distillation is the recommended technique for final purification  :)


  • Guest
How vunerable do you think benzyl chloride is...
« Reply #4 on: August 06, 2004, 03:49:00 AM »
How vunerable do you think benzyl chloride is when speaking in terms of polymerization?


  • Guest
Tar Formation Equals Polymerization
« Reply #5 on: August 06, 2004, 03:54:00 AM »
If you read the table in the article just uploaded, you will see that tar was the only product of one method, this is the result of polymerization  ::)  Acidic impurities are rather likely to cause such a difficulty, though there are many other ways to create tar  ;D


  • Guest
Swig forgot some very valuable information,...
« Reply #6 on: August 06, 2004, 04:31:00 AM »
Swig forgot some very valuable information, well at least it seems very valuable now.
Swig did get a fraction at 165-185C, which he planned to redistill, but made the mistake of mixing it with another reaction that swig attempted. When the two were put together and redistilled he got the same results that had been reported with a fraction coming over at 98-101C, which eventually caused the remaining liquid in the flask to change from a clear color into a dark orange color. Also previously to that swig did another reaction with about 50ml of benzyl alcohol. This reaction was allowed to sit for about two hours, and then dried with CaCl2.When this dry mixture had been allowed to stay put with CaCl2 still present, swig obtain his biggest findings.  The CaCl2 reacted with the mixture and absorbed most of the mixture.  I can’t help to think that this happened because the reaction did not even come close to finishing, because CaCl2 and alcohols form alcohols of crystallation.  I think that ZnCl2 is only important when the reaction mixture exceeds .5 mol of benzyl alcohol; however the mixture should be slowly heated and allowed to sit for at least 24 hours, and distilled shortly after.  I still don’t know what compound came over at 98-101C, this is interesting, because it remains there for long period of time even when the fraction has come over.