Douchermann
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Sketchy benzyl chloride synth.
This is a synth I got off of rhodium. I was wondering if it works, it seems kinda sketchy though. I'll copy and paste it:
"
Chloromethylation of Benzene [1]
Into a 1-litre three-necked flask, equipped with a reflux (double surface) condenser, a mechanical stirrer (preferably of the Hershberg type, and a
gas lead-in tube extending to near the bottom of the flask, place 200 g (227 ml) of dry benzene, 20g of paraformaldehyde (40% Formalin may also be
used; the proportions are then 200g of benzene, 38g of 40% formalin and 50g of pulverized zinc chloride.) and 20 g of finely powdered anhydrous zinc
chloride. Support the flask on a water bath so arranged that the level of the water in it is about the same height as the reaction. Heat the bath to
60°C and pass in (through an intervening empty wash bottle) a rapid stream of hydrogen chloride until no more gas is absorbed (about 20 minutes):
allow to cool. Transfer the reaction mixture to a separatory funnel, wash it successively with two 50 ml. portions of cold water, two 50 ml. portions
of saturated sodium bicarbonate solution (It is essential to remove all the zinc salts in the washing process, otherwise the product largely
resinifies during the distillation.) and finally with 20 ml. of water. Dry with anhydrous calcium chloride or magnesium sulfate, and distill under
normal pressure from a Claisen flask with fractionating side arm until the temperature rises to 100-110°C. After cooling somewhat, distill under
reduced pressure and collect the benzyl chloride at 63-65°C at 12 mmHg. The yield is 70 g. Some (about 4 g.) p-xylylene dichloride, m.p. 100°, and a
small amount of diphenylmethane are present in the residue in the flask.
"
The first thing that made me question this is that it said "40% Formalin may also be used; the proportions are then 200g of benzene, 38g of 40%
formalin and 50g of pulverized zinc chloride." Benzyl chloride is decomposed by water, so the water in the formaldehyde solution would decompose it
as its formed. Do you think it would work with the paraformaldehyde however? Thanks in advance
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DDTea
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I've heard a blurb or two about a similar synthesis, only the product was diphenylmethane. Sorry I can't offer more info...
Benzyl Chloride can easily be made from Toluene, sunlight, and Chlorine/NaOCl.
I'm thinking you mean Benzoyl Chloride--the acyl chloride, right?
"In the end the proud scientist or philosopher who cannot be bothered to make his thought accessible has no choice but to retire to the heights in
which dwell the Great Misunderstood and the Great Ignored, there to rail in Olympic superiority at the folly of mankind." - Reginald Kapp.
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Douchermann
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Nope, I meant benzyl chloride. I've read about the chlorination of toluene using sunlight. It needs buttloads of anhydrous chlorine gas (half of
which is wasted), and takes forever. I'm trying to find an alternative route to this fairly useful substance.
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Organikum
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TCCA + toluene + light. Use an fair excess of toluene to avoid to much benzal and benzotrichloride being formed.
But that topic is really well coverd here on this board might I suggest to do some search?
/ORG
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Nicodem
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| Quote: | | Benzyl chloride is decomposed by water, so the water in the formaldehyde solution would decompose it as its formed. |
That is not true!
Benzyl chloride takes many days to hydrolyze at a neutral pH. In acidic media and high enough chloride concentration it can not hydrolyze, never. The
equilibrium is way in favor of benzyl chloride or you could never prepare benzyl chloride simply by mixing benzyl alcohol with aqueous HCl.
Read some more literature rather than making bold assumptions that a preparation is faulty even though it uses a reaction that worked for more than a
century for several generations of chemists.
edit:
Using chloromethylation of benzene for something that one can prepare so simply from toluene is rather irrational. You better listen
to Organikum's advice.
[Edited on 31-5-2006 by Nicodem]
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
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unionised
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Anyone for bis chloromethyl ether? One of the nastiest carcinogens, volatile, and easily made by the reaction of formaldehyde and HCl.
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Douchermann
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Look, I was just wondering if that synth would work. I was just browsing rhodium and that looked like a different looking synth instead of the usual
chlorine/toluene based method. I didn't say I wanted to use that as a good synth, but maybe just to try it. I just didn't want to waste benzene and
formaldehyde on it if it wasn't going to work. I did not know that about benzyl chloride however. Thats actually an interesting bit of information.
I just went by what common sources say (such as msds sheets).
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garage chemist
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Benzyl chloride doesn't take days, but rather weeks to hydrolyze at neutral pH (provided good agitation- without agitation, it takes forever), in my
own experience.
Even with aqueous NaOH, several hours of reflux with stirring are necessary for its destruction.
Rhodium also has a synthesis of benzyl chloride by simple mixing of benzyl alcohol and fuming HCl. With high enough HCl excess, the benzyl chloride
yield is nearly quantitative. This reaction yields a product of way superior purity than what can be obtained from TCCA/toluene, Cl2/toluene, and
chloromethylation of benzene.
I suggest you go searching for a source of benzyl alcohol.
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Nicodem
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Actually, by only stirring a benzyl chloride / water mixture the benzyl chloride can never fully hydrolyzes because the pH drops after the initial few
hours (the hydrolysis releases HCl). You would need a buffer in order to hydrolyze at pH 7. On page 86 in this document you can find a table with the kinetics of hydrolysis as well as the appropriate “half life” estimation. For example at 15°C
half of the benzyl chloride hydrolyses in about 3 days and at 30°C in 6 hours. Needless to say this refers to benzyl chloride dissolved in water but
since the solubility is very, very low it will take a very long time to digest a biphasic mixture even with a buffer (and even with NaOH(aq) if no PTC
catalyst or cosolvent is used).
Sorry Douchermann, I always get a bit upset when someone asks if a method, published by the good old chemists in a respectable journal, works and his
doubts are based solely on wrong data. I also often doubt about published methods and consider about 10% of chemistry literature as partially
falsified or at least irreproducible (the peer review system in these days become very inefficient and some chemists can’t see beyond their
ambition). But when it comes to a method that has been used over and over again for such a long time…
I mean, this is not an asymmetric hydrogenation with damn expensive and unavailable Pd ligands that you can be absolutely sure nobody is ever going to
repeat and find out that the reported results were falsified (and even if anybody repeats it, it would just be said that it is irreproducible).
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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S.C. Wack
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Christ, we just had a thread on this. So it must be possible, yes?
https://www.sciencemadness.org/talk/viewthread.php?tid=5658
From vol 1 of Org. React.:
Attachment: chloromethylation.pdf (362kB)
This file has been downloaded 10956 times
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