HOTPLATE
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BENZYL CHLORIDE PROBLEM
I am tring to make Benzyl Chloride by the direct addition of calcium hypo to
Toluene.I realise you don't get much from the reaction.I have done it twice now
and after distilling off the Toluene I am left with a dark brown liquid.I can't work out what it is.Is it better to vacum distill benzyl chloride.Can
the distillation explode. What should I be looking for during the reaction. Would it be better to lead chlorine gas directly into toluene as in Vogels
3rd, and can the distilled off Toluene be reused in another batch.Also how can benzyl chloride and benzaldehyde be seperated having the same bp. and
similar solubilities.
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mantis
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I think your reaction has produced benzoic acid. You have not chlorinated the toluen, hypochlorides are oxi. agents.
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HOTPLATE
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Could it be the calcium hypochlorite or water in the reaction.
What am I doing wrong.
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evil_lurker
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Ok you wanna make some benzyl chloride?
Save yourself a hell of a lot of time and headaches by starting out with benzyl alcohol and esterfy it with hydrochloric alcohol. It can be found on
the net, USP grade from $50-125 per gallon depending on where you look.
The problem with starting from toluene is going to be getting that first hydrogen molecule knocked off the methyl group without chlorinating the ring
or causing the whole methyl group to be chlorinated.
By starting out with the alcohol, you have a nice -OH group to work with and all you have to do is add in HCl.
R-CH2OH +HCl ---------- R-CH2Cl + H20
Very simple huh? The HCl doesnt attach to the ring to produce undesirable by products so the end result is pure product. Plus you don't hav to deal
with producing massive amounts of clorine.
Only one problem, which ain't really much of a problem, is that as with any esterfication, for every mole esterfied a mole of water is generated.
Thats why you reflux at 60C an excess amount of concentrated HCl in with the benzyl alcohol... 6 gram of HCl for ever 2 grams of the other... to keep
the reaction from shifting back to the left.
I don't know if it would work, and I don't see no reason why it would not, but if you had an HCl gas generator set up you could simply bubble HCl
through the alcohol. Any water formed would be immediatly ionized by the HCl keeping the reaction going to the right.
One last word of advice. You better have on a gas mask or damn good respirator when working with the above!
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hydrargirum
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http://www.sciencemadness.org/talk/viewthread.php?tid=4105#p...
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unionised
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"By starting out with the alcohol, you have a nice -OH group to work with and all you have to do is add in HCl.
R-CH2OH +HCl ---------- R-CH2Cl + H20
Very simple huh? The HCl doesnt attach to the ring to produce undesirable by products so the end result is pure product. Plus you don't hav to deal
with producing massive amounts of clorine.
Only one problem, which ain't really much of a problem, is that as with any esterfication, for every mole esterfied a mole of water is generated. "
I suspect that there is indeed only one problem, The reaction doesn't work. It goes backwards.
At the least you would need to spice up the HCl with ZnCl2 or some such.
[Edited on 18-1-2006 by unionised]
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evil_lurker
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Well what does this say about it?
J F Norris, American Chemical Journal 38: 627-642 (1907)
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leu
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You need to give details about the procedure you followed, presumably you're using the Loomis procedure. If so then the dark residual lachrymatory
liquid consists of benzyl chloride, benzyl dichloride, benzyl trichloride and various dimers. Benzyl chloride forms an azeotrope with toluene, so some
of the product is in the distillate if you didn't use a lower boiling azeotrope such as the one formed with isopropanol to remove the toluene from the
chlorination products. The danger from a runaway reaction is during the chlorination, since the reaction is so exothermic. Do not use any type of
steel/iron in the distillation, unless you want to convert the benzyl chloride directly into benzaldehyde/benzyl alcohol/benzoic acid. Benzaldehyde is
most easily separated from benzyl chloride by forming the bisulfite addition product.
[Edited on 19-1-2006 by leu]
[Edited on 20-1-2006 by leu]
Chemistry is our Covalent Bond
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evil_lurker
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Lucas' reagent
From Wikipedia, the free encyclopedia.
Jump to: navigation, search
A solution of zinc chloride in concentrated hydrochloric acid, used to classify alcohols of low molecular weight. The reaction is a substitution in
which the chlorine replaces the hydroxy group. Even though this reaction is normally very unfavorable, the zinc ion complexes with the hydroxy group,
making it a better leaving group.
When Lucas' reagent - ZnCl2 / conc. HCl is added to alkanols, H+ from HCl will protonate the -OH group of alkanol, so that the leaving group H2O,
being a much weaker nucleophile than OH-, hence can be substituted by necleophile Cl-. Lucas' reagent offers a polar medium in which SN1 mechanism is
favoured. In unimolecular nucleophilic substitution, the reaction rate is faster when the carbocation intermediate is more stabilized by greater
number of electron donating alkyl group (R-) bonded to the positively charged carbon atom.
Hence, the rate at which the reaction procedes is indicative of the type of alcohol:
no visible reaction: primary alcohol
solution turns cloudy in 3-5 minutes: secondary alcohol
solution turns cloudy immediately, and/or phases separate: tertiary, allyl, or benzyl alcohol
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HOTPLATE
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I was using the loomis method but I have since read another method using aqueos hypo, toluene and 10% hcl I will give it a try this weekend
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evil_lurker
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Alright preliminary results in on using anhydrous HCl bubbled thru benzyl alcohol:
Setup:
24/40 500ml pressure equalizing funnel
24/40 3000ml RB flask
24/40 Claison adaptor
24/40 gas inlet adaptor
24/40 350ml pyrex gas wash bottle with course frit on bottom
Keck clamps and grease
500ml of ACS (or other non adulterated) sulfuric acid and a stir bar was placed in the 3000ml flask. A Claison adapter was placed on top and the 500ml
funnel charged with 10 molar commercial HCl acid was placed on one of the outlets.
The gas bottle was charged with about 2.5 moles of benzyl alcohol and placed in a hot water bath until the contents reached (unknown temperature, will
try 60 degrees next run). The wash bottle was removed from the water bath and clamped for stability. A short length of vinyl hose connected the inlet
adapter to the wash bottle and the inlet adaptor was fitted onto the claison adaptor.
Gas was then created by opening up the valve on the funnel to a couple drops per second. When the benzyl alcohol begins to absorb the gas, a wadded up
rubber glove is loosely placed in the outlet to keep most of the smaller droplets in.
When the flask stops absorbing the HCl, another 100ml or so of acid is vaporized and run thru the flask for good measure.
The contents of the flask are dumped into a separatory funnel, and the clear layer saved and distilled. Yield as of yet unkown but appears nearly
quantitive. Will find out upon distillation.
Notes:
1. Rooto sulfuric acid SUCKS for making HCl gas. Apparently it is adulterated with buffers or some other shit which results in massive foaming. This
problem does not exist when using ACS grade. (crying, not because of the BzCl but because it is eeexxxpeeensseeeve)
2. Benzyl alcohol will not react with HCl until a certain unknown critical temp is achieved. All of a sudden within a period of 1-2 seconds the clear
benzyl alcohol will turn milky with a slight hint of pink and begin absorbing all the HCl gas bubbled thru it and the flask will get HOT. This means
that no catalyst is necessary, although it might be benificial.
3. Upon completion of the reaction, a milky phase with a slight pinkish tint separates and a clear phase is left on top. Upon pouring into a
separatory funnel, the milky phase is now on top and the clear phase is on bottom. WHAT THE FUCKING HELL? Anyways, by using the separate and sniff
test, it appears the most of the BZCl is in the clear layer which brings me to my next point.
4. BzCL STINKS. You and the laboratory will smell remotely like a hair salon with poor ventilation when a woman is getting her hair permed when the
reaction is completed. I don't how it smells during the reaction because I had on a respirator... but I assume it can't smell too good. BzCL is a
lachyramatic for sure, but it does not disperse very well making it somewhat safe to handle without a respirator on. But stick your nose to the top of
the flask and barely let some waft in and its like chinese hot mustard times 10. Its not as bad as you think really, your eyes won't swell shut and
your nose won't run for 30 minutes, as the effects do not linger. I made the mistake of rinsing out the reaction flask in the kitchen sink... needless
to say I got ran out of the kitchen by the fumes, lol.
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garage chemist
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Hmm, interesting. Using anhydrous HCl gas hasn't been tried before.
The lower layer should be your BzCl, the upper layer the water.
Did you fractionate your product? Some unreacted benzyl alcohol will always remain in the benzyl chloride and has to be removed.
What was the boiling point of your product? Was it constant?
Note that mixing and heating concentrated HCl and benzyl alcohol also produces nearly quantitative yield of BzCl if HCl is used in sufficient excess.
No ZnCl2 is required!
Look here (scroll down):
http://www.designer-drugs.com/pte/12.162.180.114/dcd/chemist...
The BzCl separates as the lower layer, it is separated and fractionally distilled (to get rid of unreacted benzyl alcohol).
[Edited on 7-2-2006 by garage chemist]
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evil_lurker
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Ran the expirement again this morning using the same set up.
Loaded the flask with 325ml (3 moles) benzyl alcohol, heated to 65 degrees and proceeded to gas the shit out of it with HCl (5 moles).
For the first lil bit the contents did not absorb the HCl... then I'd say after the first mole it started soaking it up pretty good. Still no color
change but was getting hot, temp went up to 90C. I was afraid that the alcohol was merely absorbing the HCl and not reacting so at about 2-3 mole mark
of HCl pumped in I dumped in maybe 10-15 grams of solid zinc. Instantly a milky color change and massive amounts of hydrogen was given off for a few
minutes.
Eventually things stabilized and something really weird happened. As the reaction continued to completion most of the zinc did not dissolve! And in
fact, it wasn't even reacting!
This leads me to believet that everthing was about as saturated as it could get and there simply weren't enough H+ atoms floating around to get the
job done.
After pouring off the content into a graduated cylinder, approx 425ml of product was obtained, and a separate layer that looked like milk was on the
bottom of about 75ml.
There should have been 3 moles of water formed, consisting of about 54ml, leaving 21ml to be accounted for. This could theoretically be explained by
the HCl gas having a bit of water in it as I only used 500ml of acid.
It will be interesting to fractionate the product to see what kind of yields are obtained.
I think this run was better because I went out to check the totals and my nose is now burning, lol.
I definatly made something...
Edited to add: I misread the cylinder, the total contents are only about 415ml instead of 425ml. Since I'm using a cheap Bomex cylinder, this leads me
to believe that the product yield is nearly quantitive!
[Edited on 7-2-2006 by evil_lurker]
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evil_lurker
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Ran the reaction one more time, this time using a small amount of zinc, less than 5 grams. Final results were as before, maybe 2 grams of that was
used up. Each time the contents of the flask will start out by not absorbing much gas, then it will absorb quite a bit and stay clear. Somewhere
between the 2-3 mole mark, the flask will turn cloudy in a matter of about a second. About the 4 mole mark the bubbles in the flask will turn to water
droplets (easy to confuse) and then the reaction is done.
I want to run the rxn one more time without any zinc and see what happens. But that will have to happen on another day.
For now, I need to get a coupla cans of propane and hunt down some window screen so I can run my burner (gas camping stove) so I can get it distilled
off and see what I got.
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