jizmaster
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God damn nitro-aldol
Hi everyone, i had to register and ask this before i go completely nuts! I'm trying to make phenyl-2-nitropropene to use in a catalyst synth.
I've tried the cold MeOH w/aqueous base method and on workup i get a yellow oil containing mostly unreacted benzaldehyde.
Tried a dean-stark in toluene, (Et3N as base) no water was observed to come over and an orange oil was obtained on removal of solvent. Again mainly
unreacted benzaldehyde.
Refluxing for 6h in ipa or gaa (Et3N again) gives a dark, dark reddish brown oil (from piperonal this time). I managed to get yellow crystals after
many recrystallisations but it was more trouble than its worth.
Any ideas are very welcome, im stumped.
NB. the aldehydes looked pure by NMR, same with the nitroethane (i was kind of suspicious because it was from an old looking bottle). the nitroethane
dissolves in aqueous hydroxide and IR shows the nitro group.
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Darkfire
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I've heard the nitroethane nitroaldol is really low yeild. With trimethoxybenzaldhyde and nitromethane, the reaction worked very well for me.
TMBA and MeNH2 go into methanol, then at low temps NaOH in methanol is slowly added and HCl is used to dehydrate it to the beta nitro styrene.
\"I love being alive and will be the best man I possibly can. I will take love wherever I find it and offer it to everyone who will take it. I
will seek knowledge from those wiser and teach those who wish to learn from me.\" Duane Allman
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Synopsis
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Dean-Stark in toluene with triethylamine, eh? The boiling point of triethylamine is 88°C, at the reflux temperature of toluene this means your base
is in the gaseous phase. Also, if water gets out, Et3N is soluble in it and will be removed from the reaction from this pathway as well.
Primary amines usually reacts better, find some ethylene diamine for the toluene reflux (gives roughly 70-80% yield with benzaldehyde) and, as
Darkfire states, you need an acidic work-up to dehydrate the beta-hydroxy nitroalkane in order to get good yields from the base/methanol method.
Your theory is crazy, but it\'s not crazy enough to be true. - Niels Bohr
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jizmaster
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Yeah i dont know whats up with the cold alcohol method. i know about the acidic workup, the colour changes when its poured into acid, it fizzes with
yellow foamy precipitate floating on the surface and when its cooled it sinks to the bottom as an oil with benzaldehyde and a yellow solid with
piperonal. recrystallise and its still yellow but it melts at about 30o.
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jizmaster
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Synopsis, some phenethylamine was added to the dean stark expt after a couple of hours had passed and no water formed in the receiver.
Darkfire, all reports ive seen of nitroethane aldol have ~65%+ yields, theres a procedure on rhodiums site for MDP2NP with methylamine.hcl and Na2CO3,
leave in a dark place for 2 weeks, 90% yield.
Tried again with benzaldehyde, refluxed 24h in ethanol gave an orange oil with very little aldehyde remaining. nmr was a bit of a mess and it didnt
crystallise so its now being reduced with borohydride. hopefully the nitroalkane dissolves in aqueous hydroxide and it can be purified that way. (i
need 50+ grams of this so a column is not an option)
[Edited on 3-2-2005 by jizmaster]
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Darkfire
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Aldol reactions are typicly low yeild anyways so 65% is on the high side. The MeNH2 reaction works very well as you have read, certain substituted
aldahdye wont work with that reation tho, tri-methoxy being one of them.
\"I love being alive and will be the best man I possibly can. I will take love wherever I find it and offer it to everyone who will take it. I
will seek knowledge from those wiser and teach those who wish to learn from me.\" Duane Allman
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jizmaster
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might try dissolving the nitroethane in aqueous base to deprotonate it then add that to the aldehyde in cold methanol.
think u can make the lithium enolate with LDA? seems ok to me
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