Sciencemadness Discussion Board

xylene to benzene: HCl + al

zaltar - 12-12-2014 at 09:57

I want to de-methylate xylene to toluene
and toluene to benzene. Iv'e have some
source information and tryed to do it
by bubbeling hcl gas (made from salt and
h2so4) and put in some aluminium as the
method discribed. But the reaction of
the aluminium wont start because i think
is anhydrous, because when I add a bit
water the reaction starts and the xylene
mixture starts to stink (:-) assuming
this is benzene.Is it impossible to
dissolve hcl in the xylene mixture ?

Attachment: The Friedel-Crafts reaction Part III.pdf (287kB)
This file has been downloaded 312 times

DraconicAcid - 12-12-2014 at 10:25

The paper you cite shows the reaction of alkylbenzenes with anhydrous aluminum chloride. I don't think benzene or xylene will be a good solvent to try to react HCl with aluminum. If I was to try to make anhydrous aluminum chloride, I think I would try reacting chlorine gas with aluminum in a solvent such as dichloromethane or chloroform (with a reflux condenser!) or reacting aluminum with anhydrous CuCl2 or FeCl2 in a halogenated version of the thermite reaction. I'd also hit up a search engine *well* before trying either of these reactions.

zaltar - 12-12-2014 at 12:35

yeah ok, i dont want to use chlorine in my house :-)

CuReUS - 13-12-2014 at 00:56

this would be a really bad method ,but if you really want benzene from xylene
why dont you oxidise both the methyl groups to COOH using KMnO4 and then decarboxylate that

also,dealkylation using AlCl3 works best with tert-butyl group

they use tert-butyl to protect the para position and at the end it is removed using AlCl3 :)

blogfast25 - 13-12-2014 at 06:03

Quote: Originally posted by CuReUS  
this would be a really bad method ,but if you really want benzene from xylene
why dont you oxidise both the methyl groups to COOH using KMnO4 and then decarboxylate that

also,dealkylation using AlCl3 works best with tert-butyl group

they use tert-butyl to protect the para position and at the end it is removed using AlCl3 :)


Neither are practical options for a beginner. Oxidising xylene to phthalic acid with KMnO4 is very skilful. Isolating the phthalic acid isn't easy either. Nor is decarboxylating it.

FC reactions aren't for the faint of heart and require large amounts of AlCl3.

OP's best bet for benzene is the decarboxylation of sodium benzoate with NaOH, as described in great detail in the relevant OC sticky thread:

http://www.sciencemadness.org/talk/viewthread.php?tid=325

[Edited on 13-12-2014 by blogfast25]

macckone - 13-12-2014 at 12:16

The oxidation is the hard part. It uses a lot of permanganate.
The decarboxylation is basically the same for benzoic acid
and phthalic/terphthalic acids.

CuReUS - 14-12-2014 at 03:47

Quote: Originally posted by blogfast25  

Neither are practical options for a beginner. Oxidising xylene to phthalic acid with KMnO4 is very skilful. Isolating the phthalic acid isn't easy either. Nor is decarboxylating it.


by it being skillful,are you talking about completely oxidizing both the methyl groups ,instead of only one of them oxidising to COOH

also as you say ,the extraction will be difficult ,as partially oxidized xylene(only one methyl group becomes COOH) would also precipitate out when you use NaOH

Quote:
FC reactions aren't for the faint of heart and require large amounts of AlCl3.


IIRC F.C reactions are common in undergrad chem course
but i agree that the yields are shitty and require large amounts of catalyst
Quote: Originally posted by macckone  
The oxidation is the hard part. It uses a lot of permanganate.
.


maybe not as much as we think ;)

in the mechanism of KMnO4 oxidation of toluene ,benzaldehyde is formed as an intermediate .
benzaldehyde can convert to benzoic acid by air oxidation alone

so if enough KMnO4 was used to convert both the groups to benzaldehdye then it could be left in an open beaker for one week to get the pthallic acid
(there may be a chance of polymerisation though )

the problem with KMnO4 oxidation is the solubility
you could use a 54.2 w/v acetic acid-water mixture

or you could use methylene chloride
https://books.google.co.in/books?id=bga3xjLVCo0C&pg=PT60...

or another organic solvents
http://chemistry.stackexchange.com/questions/540/what-organi...

zaltar - 16-12-2014 at 10:05

but xylene H2 (or H donor) and a cth catalyst such as NiCl2 works ?!!

blogfast25 - 16-12-2014 at 10:43

However you look at it, converting something like Xylene to benzene is folly, when sodium benzoate is readily available and can be decarboxylated fairly easily.

zaltar - 16-12-2014 at 11:14

where can you find sodiumbenzoate ,in the grossery store, i mean witch products contains sodiumbenzoate ?

Furboffle - 26-12-2014 at 11:10

I work part time in grocery store while finishing grad school and I've never seen it or benzoic acid. (I keep an eye out for these types of products...) though I would recommend checking out your local brewing shop. They usually have a small but nice selection of chemicals, granted they all pertain to brewing, winemaking, or cheesemaking... I'm not positive that sodium benzoate is typically sold there, but being a food related chemical I would have high hopes of finding it there. otherwise hit up ebay. its like $6 for a pound.

Mabus - 27-12-2014 at 06:29

Sodium benzoate is sold as a food preservative, usually in small bags. You should look in hypermarkets, in the seasonings section.

Bert - 27-12-2014 at 07:42

Member names zaltar and lyserisc are apparently the same person...

Both profiles have the same birthday, they post from the same IP address while asking similarly ignorant organic chemistry synthesis questions. Quite like member names phendrol and ewel.

https://www.sciencemadness.org/whisper/viewthread.php?tid=51...


[Edited on 27-12-2014 by Bert]