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Author: Subject: Building Aromacity
Flip
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[*] posted on 9-5-2006 at 14:54
Building Aromacity


I recently became interested in cyclization reactions...

But what i'd like to know is if there are cyclization reactions that can actually build an aromatic ring from completely aliphatic precursors (unsubstituted or substituted)

Does anyone know of any?
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[*] posted on 9-5-2006 at 18:33


I'm guessing that as long as you form a cyclic molecule with the 'right' number of pi electrons (I'm thinking Hucke's rule: 4n + 2) in the same plane, the aromatic hybrid is thermodynamically favoured and will therefore exist.
Just like when you have -C=C-C=C-C=C... and so on you'll get conjugation I guess, even if you start from scratch and build up the chain, conjugation will occur because it is favoured thermodynamically.
It's a bit of a vitalism/urea type argument really; the 'natural' benzene would be no different to synthetic cyclohex-1,3,5-ene.




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[*] posted on 9-5-2006 at 18:39


One of the reactions for forming benzene involves passing acetylene over some catalyst (or maybe not) at decent temperatures. Benzene becomes one of the important products because it's more stable then other products formed so it's favored in that manner though this isn't specifically a reaction that could form this ring under other conditions.



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[*] posted on 10-5-2006 at 09:09


you can make 1,3,5-trimethylbenzene by heating acetone with a strong acid.
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[*] posted on 10-5-2006 at 09:19


The oxime of glutaraldehyde forma pyridine on heating in acid. Furfural is produced by cooking bran with acid. There are heaps of such syntheses.
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[*] posted on 14-5-2006 at 08:19
citral


Citral can be easily cyclisized into alpha,p-dimethylstyrene

(heating w acid IIRC, this cyclisation also occurs naturally)
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[*] posted on 14-5-2006 at 09:42


Judging from some other Flip's posts I would dare to guess that the info on the kind aromatizations he is looking for is of the type of propylhexedrine to 1-phenylpropan-2-methylamine or similar of the field.

Flip, there was already some discussion on this on some deceased forum. You might do some arHiveology to dig up the old remains of the relevant threads. I remember it was one of the WizardX's favorite ideas so try searching for his posts.




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[*] posted on 4-7-2006 at 15:35
Aromatics from Alkynes


One of Reppe's many innovations in acetylene chemistry was the development of a catalyst, dicarbonyldi(triphenylphosphino) nickel [(CO)2Ni(Ph3P)2] in the presence of which the trimerization of acetylenes to benzenes can be carried out smoothly and efficiently at temperatures of 60-70°. Thus acetylene gives benzene in high yield (80 per cent) while monosubstituted acetylenes furnish either 1 : 3 : 5- or 1 : 2 : 4-trisubstituted benzenes or mixtures of the two isomers, the exact reaction course depending on the nature of the initial acetylene. Use of the catalyst also enables the copolymerization of acetylene with a substituted ethylene in a 2 : 1 or 1 : 2 ratio with the production of cyclohexa-1:3-dienes and cyclohexenes respectively, Another novel Reppe process, hitherto little developed, entails the reaction of acetylene with iron carbonyl hydride, Fe(CO)4H2, in aqueous media, whereby hydroquinone is formed. This reaction has also been applied to mono- and di-substituted acetylenes, the former compounds yielding the 2 : 5-disubstituted hydroquinones; acetylenic hydrocarbons, ethers and amines have been successfully subjected to the procedure.

Seven papers have been uploaded to the Organic Chemistry forum of Wet Dreams, three on the actual syntheses, and four on the catalysts :cool:

[Edited on 4-7-2006 by leu]




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[*] posted on 17-1-2007 at 14:05


Quote:
Originally posted by leu
One of Reppe's many innovations in acetylene chemistry was the development of a catalyst, dicarbonyldi(triphenylphosphino) nickel [(CO)2Ni(Ph3P)2] in the presence of which the trimerization of acetylenes to benzenes can be carried out smoothly and efficiently at temperatures of 60-70°. Thus acetylene gives benzene in high yield (80 per cent) while monosubstituted acetylenes furnish either 1 : 3 : 5- or 1 : 2 : 4-trisubstituted benzenes or mixtures of the two isomers, the exact reaction course depending on the nature of the initial acetylene. Use of the catalyst also enables the copolymerization of acetylene with a substituted ethylene in a 2 : 1 or 1 : 2 ratio with the production of cyclohexa-1:3-dienes and cyclohexenes respectively, Another novel Reppe process, hitherto little developed, entails the reaction of acetylene with iron carbonyl hydride, Fe(CO)4H2, in aqueous media, whereby hydroquinone is formed. This reaction has also been applied to mono- and di-substituted acetylenes, the former compounds yielding the 2 : 5-disubstituted hydroquinones; acetylenic hydrocarbons, ethers and amines have been successfully subjected to the procedure.

Seven papers have been uploaded to the Organic Chemistry forum of Wet Dreams, three on the actual syntheses, and four on the catalysts :cool:

[Edited on 4-7-2006 by leu]


What is this Wet Dreams forum?
Im interested in reading those papers.




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[*] posted on 17-1-2007 at 18:56


"Building Aromaticity"

Sounds like a great title for a two-book 1600pp each set.

Here's some interesting literature, if anyone is interested I also have many papers regarding metal-metal aromaticity and Moebius aromaticity.

I suppose it is all a matter of how far you want to go,

O3

Attachment: Wiberg 2001.pdf (173kB)
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[*] posted on 18-1-2007 at 01:20


Quote:
Judging from some other Flip's posts I would dare to guess that the info on the kind aromatizations he is looking for is of the type of propylhexedrine to 1-phenylpropan-2-methylamine or similar of the field.


In my own defense, only about half of the crazy reaction schemes that I come up with are actually feasible, none of them are practical or of any use to the amateur, and the best of them could inspire the black hats around here to pick up a white coat, as I did long ago. No offense to the following of WX and the like, but I have no interest in that which has already been done. Even as a simple drone I never ventured into that particular forum, and I feel I must have made some error that I could ever be categorized so narrowly. Hell, if anything throw an MD bridge on there.:P

This reply is more than a bit late but i've been busy balancing internships with finishing my degree in Chem.:cool:
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