| Topic: |
Science > Physics |
| User: |
"hanson" |
| Date: |
07 Apr 2006 04:58:39 PM |
| Object: |
Re: benzoate to benzene |
"Jimchip" <jimchip@ifthisisavalidhostname.com> wrote in message
news:123dg48kddrq354@news.supernews.com...
Eric <lucasea@sbcglobal.net> <lucasea@sbcglobal.net> wrote:
It just occurred to me that decarboxylation of benzoate to benzene
is not a redox reaction. Write a balanced equation: [1]
C6H5CO2- + H+ --> C6H6 + CO2
[Jichimp]
Think of a Grignard synthesis of benzoic acid:
C6H5MgX + CO2---> ---> H+
Chemistry can be fun.
I fell on my head as a child and, as it turns out,
Chemistry is the only thing I could learn how to do.
(and I *hated* 'piano lessons' but it made me a better typist :)
[hanson]
..... ahahaha... yeah, yeah, jim, you are right on many counts
especially about line 4... ahahaha...
Eric, afa your comments [1] and [2], you are right and there
are preparative methods for decarboxilations for aromatics,
simply by "cooking" them in 93% H2SO4 or in conc. H3PO4.
IR deCO2ing Pyrazine tetra carboxylic acid into pyrazine
mono carboxylic acid splitting off 3 CO2/mole in a foaming
2 hrs process and the yield was surprisingly good. There is
no discernable reason that this method should not work
for/on C6H6COOH. Naturally for economic reasons it will
never be carried out, except for high school lab demos.
On a related enviro note since so many posters here worry
about the POTENTIAL dangers of benzene first instead of
the issue at hand, ... but most of them being unholy greenies, ...
and certainly being the ones that don't even know how
benzene smells... ahahahaha....
.... I though do agree with them that a constant, long term,
8 hrs/day exposure to C6H6 fumes may cause health issues.
But so does every other aromatic VOC in the long run. But,
their green paranoia is severely overrated because anyone
who forces himself to inhale/stay at a place where there are
these pungent, acrid, cough invoking and migraine producing
fumes of aromatics present, is even more stupid then are the
green shits who try to save them via/with their permit charges,
user fees and enviro surtaxes.... but OTOH do make sure that
the chemical stays available for use... so that these illbegotten
phony green shits can take advantage and make money off
the situation. Case in point:
Long ago, when I visited LA quite often I saw an enviro warning
poster at the gas pump, issued by order of the local Aeolian
enviro agency, signed by chief green fart , named Flatu Lenz,
that said:
=== "This brand of gasoline contains benzene as an octane
enhancing additive from which you may POTENTIALLY get
cancer if you sit 24/7 for 75 (!) seventy-five years next to the
running gas pump nozzle." ===
..... ahahaha... No wonder Eric Gisin said in his memorable post
in news:d8j4df01n0o@enews1.newsguy.com... that
********** "Fucking greens should be shot...." *************
Thanks for the laughs, guys.... ahahahaha....
ahahaha... ahahanson
[Eric]
No reductant needed, just an acid. Mechanism could go something like this:
protonate ipso carbon, and decarboxylate. Having said that, I don't think
I'm familiar with any aromatic decarboxylations like this as synthetically [2]
useful reactions (even with very electron rich arenes that protonate easily
on C). However, that doesn't mean it can't occur as a small side reaction
over a long shelf storage life, to generate low levels of benzene--and all
it requires is the presence of a sufficient concentration of a general acid
catalyst. Since biological (read: food) systems are heavily buffered with
CO2/HCO3-, phosphate and other buffers, (and in fact, fruit juices and pops
even have a pretty high concentrations of specific acids that can act as
catalysts, considering their pH often runs as low as 2 - 3), this provides a
high concentration of a variety of general acid catalysts that could induce
this reaction.
Still, the potential exposure in this case is orders of magnitude lower than
exposure levels in occupational benzene leukemia studies.
Eric Lucas
[snippage]
.
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