smaerd
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Friedel Crafts with Ring Deactivating Functional Groups
I have always read this was impossible. Even in an organic text-book circa 1994(half priced book-store hehe).
Anyways I'm looking for two articles, the one seems to imply it's a menial task with the right catalyst. I know there is a whole subforum dedicated to
this, however I am not permitted inside. Not sure if this is against the board rules, if it is ban me  .
The first Friedel-Crafts reaction of nitrobenzene
Yusheng Shen, Hongxia Liu, Yiqiu Chen
J. Org. Chem., 1990, 55 (12), pp 3961–3962
DOI: 10.1021/jo00299a051
Publication Date: June 1990
Friedel-Crafts alkylation of benzenes substituted with meta-directing groups
Yusheng Shen, Hongxia Liu, Ming Wu, Wuqin Du, Yiqiu Chen, Nianping Li
J. Org. Chem., 1991, 56 (25), pp 7160–7162
DOI: 10.1021/jo00025a037
Publication Date: December 1991
Same team of people 1 year apart, pretty interesting stuff in my undereducated opinion.
Thank you, if take the time to scoop these up for me, it means a lot.
[Edited on 6-8-2011 by smaerd]
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Nicodem
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I would very much prefer if you stick to the forum convention and do literature requests where everybody else does it (access can not be an excuse
because you know what you need to do to gain it), but for the sake of possible discussion arising from your request, I will let it stay here. Also, if
you really need the papers, you can always force yourself to physically go in a real world scientific library. I haven't done this for a while, but
from experience I can tell you it can actually be interesting.
Both references were previously cited in this post, but I don't think the articles were ever uploaded. In essence, the authors explain their hypothesis on why only Friedel-Crafts
ethylations of nitrobenzene in H2SO4 are possible:
- hydride shift is symmetrical (gives the same carbocation) and irreversible decomposition or fragmentation nearly impossible;
- the substrate (nitrobenzene) does not get deactivated by protonation with H2SO4 (check pKa of PhNO2) while it gets deactivated by stronger
non-protic acids such as AlCl3;
- ethanol is borderline in the formation of an extremely reactive carbocation (while methanol, being primary, can not form carbocations at such
conditions).
All in all, the Friedel-Crafts ethylation of nitrobenzene in H2SO4 is a very exceptional case.
The meta methylenations, chloromethylations and amidomethylations of 4-alkylnitrobenzenes are also possible (using paraformaldehyde,
bis(chloromethyl) ether, or acetamide/paraformaldehyde correspondingly; see J . Org. Chem. 1983, 48, 2938-2939). However, I can't remember if
any of these were ever done on the considerably less reactive plain nitrobenzene. Due to the nature of the carbocation involved, I would not be
terribly surprised if it turns out possible (particularly for methylenation and amidomethylations). Such reactions are also considered as a special
cases of Friedel-Crafts alkylations, but are not plain alkylations in the basic sense as the above described ethylation is.
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smaerd
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Ah yes somehow I didn't read the ask polverone thing. Took care of that, my apologies. I'll have to make a day-trip to a library or something once I
can scratch up a big list of fun looking articles. My school doesn't have access I don't think.
On-topic:
So in theory longer chain alcohols could work as well, say for instance n-butanol, etc. So long as the alcohol has a secondary carbocation when
ionized?
It's a really interesting variant in my opinion as it does not require anhydrous conditions. Also granted the diversity of reactions for phenolic
amines(sandmeyer for halogens, phenols, etc), which of course nitro groups are easily reduced to. I'd really love to see the experimental data though
to get a basic idea of the heat energy, selectivity, etc.
I'd imagine a lot of stirring would be necessary to increase the interfacial area of the bi-phasic mixture. Though nitrobenzene is slightly soluble in
water, it's hard for me to guess(need to learn thermo).
Thanks for the information and helping me to understand in premise what is going on. Very, very, very, cool. Definitely an experiment worth
recreating, unless the article pulls out some voodoo reagents or equipment.
[Edited on 6-8-2011 by smaerd]
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Nicodem
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Quote: Originally posted by smaerd  | | So in theory longer chain alcohols could work as well, say for instance n-butanol, etc. So long as the alcohol has a secondary carbocation when
ionized? |
n-Butanol would give isobutyl derivatives if used in Friedel-Crafts alkylations, but due to the reasons mentioned in my previous post, I can't see how
could it work in such an alkylation of nitrobenzene. I already explained that ethanol is a special case and the reasons the article authors offer.
Their reasoning sounds reasonable to me.
| Quote: | | It's a really interesting variant in my opinion as it does not require anhydrous conditions. |
The conditions are essentially anhydrous except for the equivalent of water that forms during the reaction, which is however put out of play by a
nearly complete protonation anyway. But that is the general case for any Friedel-Crafts alkylation with an alcohol and nothing specific for this
method (see the recent thread on the topic). Besides, the reaction has little to no preparative use as separation of products would be quite tedious and
yields poor due to poor selectivity (neglecting also that it is only useful for ethylations).
| Quote: | | I'd imagine a lot of stirring would be necessary to increase the interfacial area of the bi-phasic mixture. Though nitrobenzene is slightly soluble in
water, it's hard for me to guess(need to learn thermo). |
As far as I know, nitrobenzene is well soluble in conc. H2SO4. I'm not sure it is miscible in all proportions, but soluble it is. The reaction mixture
should be monophasic at the beginning, but might become biphasic toward the end.
| Quote: | | Definitely an experiment worth recreating, unless the article pulls out some voodoo reagents or equipment. |
Concentrated H2SO4 and ethanol are no voodoo reagents, though they can just as well kill you or make you appear like a zombie.
…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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smaerd
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Ah sorry, this is why I wanted to read the articles rather than only the abstracts.
Well shoot, I'll have to figure something else out than. It's lovely to see the theory applied though and have the expected result, though I need a
preparative approach. Thanks for chiming in here. It means a lot.
Ethanol and sulfuric acid don't trouble me  , unless it's the di-ester  .
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