chemrox
International Hazard
Posts: 2961
Registered: 18-1-2007
Location: UTM
Member Is Offline
Mood: LaGrangian
|
|
mechanism of benzoic acid formation from butyl lithium
The reaction of 2,3,5-trimethoxy bromobenzene with butyl lithium yielded the corresponding trimethoxybenzoic acid as an intermediate in a synthesis I
read earlier tody. I'm not seeing why.
|
|
|
guy
National Hazard
Posts: 982
Registered: 14-4-2004
Location: California, USA
Member Is Offline
Mood: Catalytic!
|
|
Are you sure those are all of the steps?
The only thing that is possible is the formation of 1-Butyl-2,3,5-trimethoxybenzene. There are no other oxygens to make a benzoic acid. The only way
to get the benzoic acid is to oxidize the butyl side chain.
|
|
|
Nicodem
Super Moderator
Posts: 4230
Registered: 28-12-2004
Member Is Offline
Mood: No Mood
|
|
| Quote: | Originally posted by chemrox
The reaction of 2,3,5-trimethoxy bromobenzene with butyl lithium yielded the corresponding trimethoxybenzoic acid as an intermediate in a synthesis I
read earlier tody. I'm not seeing why. |
The reaction of f BuLi with 1-bromo-2,3,5-trimethoxybenzene in THF at -78°C gives 2,3,5-trimethoxyphenyl lithium trough metal-halogen exchange
metathesis (a SET driven reaction). You omitted which reagent they used to prepare 2,3,5-trimethoxybenzoic acid from 2,3,5-trimethoxyphenyl lithium.
They could have introduced a fast stream of CO2 in the reaction mixture. Other possibilities are to quench the aryl lithium with excess dimethyl
carbonate or methyl cyanoformate, following by hydrolysis of the so formed methyl 2,3,5-trimethoxybenzoate. Direct lithiation of
1,2,4-trimethoxybenzene is no option here, since it would form 2,3,6-trimethoxyphenyl lithium, where lithium is coordinated with two MeO groups –
the reaction would result in the wrong benzoic acid, 2,3,6-trimethoxybenzoic acid. Hence the use of 1-bromo-2,3,5-trimethoxybenzene.
…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!
|
|
|
chemrox
International Hazard
Posts: 2961
Registered: 18-1-2007
Location: UTM
Member Is Offline
Mood: LaGrangian
|
|
woops, yes you're so right. CO2 was mentioned!
Now I have it .. just like the Grignard using CO2..
thanks to Nicodem and Sauron (U2U)
CRX
PS- I just got a book I'm excited about : The Art of Writing Reasonable Reaction Mechanisms by Grossman, UKY, 2002.
|
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
