sonogashira
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Bromobenzene via the Hunsdiecker reaction?
I want to prepare a fairly large amount of bromobenzene for some Grignard experiments. Looking into its preparation it seems like decarboxylation of
sodium benzoate followed by bromination of the benzene would be a suitable route.
I wonder if it could be prepared more easily via the Hunsdiecker reaction?
If anyone has done this I would be most interested in your experiences. I especially wonder whether it would be possible to recycle the silver since
this would obviously reduce the costs considerably. I also wonder if CCl4 can be made by any easy route (Perhaps CHCl3 and HOCl?)
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sparkgap
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These refs look interesting:
http://dx.doi.org/10.1016/S0040-4039(00)98266-2
http://dx.doi.org/10.1016/S0040-4020(01)90307-2
sparky (~_~)
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smuv
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See: Johnson, R. G.; Ingham, R. K. Chem. Rev. 1956, 56, 219
Bromobenzene can be obtained from silver benzoate however between different chemists the yields were extremely variable (ranging from 80 to 14%).
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not_important
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One problem with the Hunsdiecker reaction is getting the silver salt dried well enough. Drying by slow azeotropic distillation of water from the salt
suspended in the solvent (CCl4) just prior to adding the bromine in the dark can be helpful.
The variant using HgO and the free acid
http://www.orgsyn.org/orgsyn/prep.asp?prep=cv6p0179
is less sensitive to water.
Silver recovery can be done by fusion with Na2CO3. If run hot enough so the silver melts it will be recovered as a lump, otherwise it ends up as a
powder that can be annoying to filter (use fritted glass) Dissolving the metal in HNO3, the converting to the carbonate or oxide will recycle almost
all the silver.
The filtrate from that can be evaporated, crushed, mixed with MnO2, treated with H2SO4 and distilled to recover the bromine.
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chemrox
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Is there are a problem getting benzene? Benzene + Fe + Br2. Dibromo products are a minor side reax. Workup is usually steam still followed by still
and dry. Silver salts and HgO would make these suggestions too expensive to compete with just buying the benzene or the ph-Br for that matter.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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LSD25
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There are a number of recent references on the 'Hunsdieker-Borodin-everyone else reaction', some of which use salts other than silver (Lithium Acetate
seems popular), while at least one questions whether metal is necessary at all. Of rather more interest however is the recent move toward the use of
NBS/NCS on its own for this reaction (apart from the rather bizarre metal nitrate decarboxylation via prolonged mixing), anyhow, here are a small
collection of articles on this type of reaction (thanks to Solo who provided a bunch of these)
http://www.4shared.com/dir/5526855/424dc959/Decarboxylation....
Whhhoooppps, that sure didn't work
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smuv
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Since we are sharing
Chem. Rev. article about the Hunsdieker reaction. Very thorough overview of reaction in its classic sense (with metal salts and bromine).
Edit:
Ok nevermind the file is too big, if you would like it see: Johnson, R. G.; Ingham, R. K. Chem. Rev. 1956, 56, 219
[Edited on 31-1-2008 by smuv]
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Mason_Grand_ANNdrews
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In my opinion is the reaction correct only when you have a salt of the carboxylic acid of benzene.
1,2,4-Benzenetricarboxylic acid is easy to get from Fluka and i
don`t no if this right when you mix Benzenetricarboxylic and
a very dilute silver nitrate solution with bromine to make bromrobenzene ?
When you have sodium benzoate, silver nitrate solution and bromine - while giving bromrobenzene ?
~ mol by mol ~
[Edited on 1-2-2008 by Mason_Grand_ANNdrews]
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a new live !
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not_important
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Hunsdieker does not work in the presence of water. The problem with water sensitivity is one reason why the original question of
"decarbox+bromination vs Hunsdieker" likely comes down on the non-Hunsdieker side.
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