Author Topic: Problems distilling benzyl chloride, HCL gas!!!!  (Read 1165 times)

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abacus

  • Guest
Problems distilling benzyl chloride, HCL gas!!!!
« on: July 28, 2004, 09:41:00 AM »
SWIM made some benzyl chloride via benzyl alcohol and about 3 molar excess of 32% w/w HCL solution.

Basically stirred at room temp for 24 hours, then heated to 70DegC for 30 minutes which aided the layer seperation.

Removed benzyl chloride, and distilled quantitative yield of benzyl chloride at 179DegC at atmospheric pressure, with absolutely no problems.

Now comes the problem,  decided to re distill.

So changed glassware and placed freshly distilled benzyl chloride in a new flask (washed and oven dried) and reheated at around 170DegC, as soon as distillation was starting something very nasty happened and HCL gas started pouring from the receiver adaptor hose outlet filling the lab with HCL gas.

Once the situation was under control, SWIM vacuum distilled about half of the benzyl chloride and was left with a sticky mess that seems to react with air releasing HCL gas.

TFSE was used, SWIM was totally unprepared for this, and can anybody explain what went wrong.

Abacus

Organikum

  • Guest
You cannot get quantitative yields from this...
« Reply #1 on: July 28, 2004, 10:15:00 AM »
You cannot get quantitative yields from this reaction - it is an equilibrium established between HCl - BzCl and BzOH.

Probably you distilled a mixture of these three compounds (BzCl forms some odd azeotropes btw.) and thats what you got in the receiving flask. ANd so the reaction goes on - in one or another direction.

The Gattermann has a good chapter on halogenation with halo-acids - mechanism and more...
... another workup perhaps? Removal of all HCl before distillation?

but this I would have to look up myself.

hope this helps
ORG


abacus

  • Guest
Sorry if i posted in the wrong forum SWIM...
« Reply #2 on: July 30, 2004, 01:46:00 AM »
Sorry if i posted in the wrong forum

SWIM needs to practice his UTFSE skills :-[

After a tip from Org, i found a thread in the stimulant section on this topic.

such as

Post 508542

(ning: "by the way", Stimulants)


I guess it was just luck that it didn't happen during the first distillation.

Abacus

armageddon

  • Guest
I would guess that during the first...
« Reply #3 on: July 30, 2004, 04:22:00 AM »
I would guess that during the first distillation, the reactands were present in the right proportions, so everything went fine - only that the separation of BzCl through distillation was not very good (use vigreux perhaps?).

During the second distillation, the proportions HCl/BzCl/BzOH weren't the same (but still all three were present), this caused your HCl accident. Vacuum distillation (with several NaOH containing washing flasks between dist.setup and pump!! Or use a NOISY aspirator - ZZZSHHHHHHHH...) might be the solution, together with using a column when distilling BzCl out of the reaction.

And drying organic liquids before distilling them is always a good idea BTW!!

Greetz A