hydrargirum
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Obtaining p-isopropylbenzoic acid
Obtaining p-isopropylbenzoic acid ( cumic acid )
Recently I have prepared cumic acid by the following way:
benzene + isopropyl chloride -------> cumene
AlCl3
cumene ---------------> p-nitrocumene --------------------> 4-isopropylaniline
nitration / reduction
4-isopropylaniline + NaNO2 + HCl ---------------------->isopropylaniline-diazonium chloride
º0 - 5ºC
isopropylaniline diazonium chloride + CuCN -------------------->isopropylbenzonitrile
Sandmeyer reaction
isopropylbenzonitrile + H2SO4/CH3COOH +H2O ---------------------> acid cumic
reflux
After this long chain of reactions is obtained cumic acid and verified by its point fusion around 116 ºC and easy subliming
In addition by esterification with ethyl alcohol and reduction with Na in absolute alcohol, cumic alcohol is obtained of pleasant scent (caraway
odor).
Nevertheless there is a short way to directly obtain it by oxidation of p-cymene in excess with KMnO4 in alkaline solution The several times that I
have tried this one oxidation with KMnO4 al10% in neutral solution, slightly alkaline with Na2CO3 or frankly alkaline with NaOH, even in acetic
solution ,I have only obtained terephthalic acid. (boiling to reflux during several hours, until descoloration of KMnO4 with deposit of MnO2.)
Some suggestions?
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sparkgap
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The reason you got terephthalic acid is that permanganate does not usually give a damn as to whether it's oxidizing a methyl group or an
isopropyl group. As long as the side chain has a benzylic hydrogen, it gets oxidized to -COO<sup>-</sup> after basic permanganate
treatment.
sparky (~_~)
"What's UTFSE? I keep hearing about it, but I can't be arsed to search for the answer..."
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Sergei_Eisenstein
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Have you considered the following reaction pathway:
cumene ---> p-bromocumene
p-bromocumene ---> p-cumylmagnsium bromide
p-cumylmagnesium bromide ---> cuminic acid
The first step is a bromination, which should be straightforward. I expect the p-isomer will dominate over the o-isomer significantly because of
steric hindrance. The second step is the preparation of a Grignard, which should be straightforward too. The benzoic acid can be made by bubbling in
CO2.
Permanganate oxidizes all alkyl side chains as long as their is a benzylic hydrogen present. There is no difference between methyl, ethyl, isopropyl,
isooctyl or undecyl. But t-butyl would be untouched...
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sparkgap
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"...The benzoic acid can be made by bubbling in CO2..."
Wouldn't plunking a few pieces of dry ice be more convenient?
Also, how far away is the BP of p-bromocumene from its ortho isomer?
sparky (~_~)
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Sergei_Eisenstein
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| Quote: | | Wouldn't plunking a few pieces of dry ice be more convenient? |
Yes, adding it in solid form can be more convenient.
I made a trip to the library today to look for some chemistry books and dug up a few refs for the synthesis.
p-Bromocumene has a bp of 218-220°C (760 mmHg), while o-bromocumene has a bp of 208-210°C (760 mmHg).
Out of two handful of references, I'll quote JOC 48 (1983) 3721: Isopropylbenzene (1.2 mol) was treated with Br2 (1.0 mol) in CHCl3 (200 ml)
at 0°C for 2h. Distillation of the reaction mixture gave 4-bromoisopropylbenzene: 110 g (55% based on bromine); bp 214-218°C (756 mm)
Another alternative might be the FC alkylation of bromobenzene. In JACS 61 (1939) 157, they describe a convenient reaction procedure employing
Sciencemadness chemical reagent proportions: 4-Bromocumene - This substance, boiling at 217°, was prepared by Boedtker by the action of propyl
chloride on bromobenzene in the presence of aluminium chloride. In order to be more sure that the product is not contaminated by the n-isomer, which
boils at 220°C, the substance was made by the action of isopropyl chloride on bromobenzene in the presence of aluminium chloride. To a mixture of
2240 g (14.2 mol) of bromobenzene and 110 g of powdered aluminium chloride in a 5 L flask immersed in an icebath was added with stirring 750 g (9.6
mol) of isopropyl chloride. After standing at 0°C for half an hour the reaction mixture was heated on a steambath for 15 min. It was then cooled and
poured on 2 kg of ice. When the dark colour of the complex had disappeared, the lower layer was separated and washed repeatedly with concentrated
sulfuric acid until the acid was only slightly coloured. The material was then washed with water till neutral and was dried with calcium chloride.
Upon distillation, the excess bromobenzene was recovered, and the 4-bromocumene boiled at 75-90°C at 9 mmHg. On redistillation, this fraction gave
1300 g (67%) of material boiling from 87-89°C at 9 mmHg (215-216°C at 760 mmHg). From the residue was isolated 240 g (20%) of a substance boiling
from 115-118°C at 9 mmHg. Analysis showed that this material had the composition of a diisopropylbromobenzene.
There is a small article by L Bert about organomagnesiums derived from p-bromocumene: Comptes rendus hebdomadaires des séances de
l'Académie des sciences 177 (1923) 452. He claims an 80% yield of the magnesium bromide and a 40% (from p-bromocumene) of p-cuminic acid
using CO2. The reference can be found on Gallica.
So yields are not stellar, but the syntheses are straightforward and it is only two steps from bromobenzene. Alternatively, you may want to use
chlorobenzene, but preparation of the corresponding organomagnesium will be more difficult. In the CR reference, Bert stated that the organomagnesium
of p-bromocumene is easily formed in ether when a small portion of bromine is added (I suppose a crystal of iodine will do the same).
Please keep us up to date if you decide to follow this route 
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Nicodem
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Actually if one already has cumene and AlCl3, it might be simpler to FC acylate it with acetic anhydride or acetyl chloride and then bleach the
p-isopropyl-acetophenone with NaOCl yielding the desired product (after acidifying the sodium salt).
…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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hydrargirum
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Well, I agree that all the groups alkyl will be oxidized, isopropyl even has priority on metyl; but my attempt of oxidation was impelled by some book
references that speak of the obtaining of cuminic acid by oxidation with KMnO4 of the essence of cumin whose more abundant ingredient is p-cymene
(certainly this essence contains also small amounts of cuminal and cumic alcohol that obvious oxidizes to cuminic acid): by this I have left the
doubt.
I mention¨ General Chemistry, volume II, Organic Chemistry of the Dr. Enrique Calvet/1931 page 566: ¨
¨Cuminic acid: One forms oxidizing the cymene and he abounds in the cumin essence , from which he can obtain itself oxidizing it with KMnO4¨.
Thanks , thanks Sergei_Eisenstein for its indications via Grignard; but I have little Mg in reactive tape quality that is very expensive, which
disables to me to use that method. Very interesting its references, I have selected them and copied in a file
and kept in my chemical directory.
Nicodem: his method(haloform reaction) seems to me very good, practical and short; nevertheless acylation needs amounts equimolar of AlCl3 that I
do not arrange; I generally use catalytic amounts produced ¨in situ¨ with Al and the HgCl2 or iodine to make alkylation of Friedel-Craft that in
general works well.
Other references speak of oxidation of p-cymene with diluted HNO3 forming mixtures of cuminic and p-metilbenzoic acid. Industrial conditions? I
do not know........?.
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Sandmeyer
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| Quote: | Originally posted by hydrargirum
Thanks , thanks Sergei_Eisenstein for its indications via Grignard; but I have little Mg in reactive tape quality that is very expensive, which
disables to me to use that method. |
then swap the aromatic Br with a cyano group using Cu catalysis, followed by hydrolysis of the CN group. I'm at the moment not able to provide
specific references - just an idea if you want to avoid Grignard.
See page 1445 (13 in pdf file) in this review:
http://rapidshare.de/files/4359048/tetrahedron163.pdf.html
[Edited on 1-10-2005 by Sandmeyer]
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