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Author: Subject: Anti-Markovnikov Hydrobromation
VSEPR_VOID
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[*] posted on 15-2-2019 at 19:29
Anti-Markovnikov Hydrobromation


I am doing research into the Anti-Markovnikov hydrobromation of methacrylic acid.

Does anyone have a link, source, or reference to a protocol that goes over something simular? Anything relating to alkenes and Anti-Markovnikov hydrobromation would be useful.




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[*] posted on 15-2-2019 at 20:56


The classic textbook method for an Anti-Markovnikov HBr addition is adding a catalytic amount of an organic peroxide (i.e. benzoyl peroxide, an OTC organic peroxide used for acne treatment), or to irradiate the reaction mixture with UV light. This would work with methacrylic acid, no?



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clearly_not_atara
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[*] posted on 15-2-2019 at 21:45


For methacrylic acid the hydrobromination is always anti-Markovnikov because of the EWG, so no peroxides are required. Instead, just gas HBr through it in acetone or something.



[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 16-2-2019 at 20:42


Can you give me a link to further reading about this? I was doing some more research: Google Scholar led me to some patents about using HBr gas and chloroform.

This is very good information

3-Bromo-2-methylpropionic acid

A. 3-Bromo-2-methylpropionic acid
86 ml (1.01 moles) of methacrylic acid are dissolved in 80 ml of chloroform and hydrogen bromide is bubbled into the solution at -10° C. under stirring. After the absorption of the calculated quantity of gaseous hydrogen bromide, the solution is left to stand at 0° C. for 12 hours. The chloroform is evaporated and the residue is distilled in vacuo.
164.8 g (97.3%) of 3-bromo-2-methylpropionyl chloride are obtained, b.p. 101°-104° C./7 mm Hg. nD 24.5 =1.4753.

From <https://patents.google.com/patent/US4332725A/en>



3-bromo-2-methylpropionic acid 6 HBr gas was bubbled for 2 h in a solution of metacrylic acid (5 ml, 58 mM) at room temperature. The reaction mixture was purified by Kugelrhor distillation under reduced pressure to afford the title compound as a colourless oil; (70%)

From <https://sci-hub.tw/https://onlinelibrary.wiley.com/doi/abs/10.1002/psc.1201>




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[*] posted on 17-2-2019 at 00:40


Yes, I think chloroform would be better than acetone, since acetone might give aldol side products. Dichloromethane should also work. I would avoid ether solvents since HBr might cleave them.



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[*] posted on 19-2-2019 at 04:44


Tetrachloroethane would work as well. It has a higher bp so pruification by evaporation of the solvent would be more difficult.

Chloroform is easy to make for the amateur so it would be a better choice.




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