Halogenation of acids

Drivers for Performing Halogenation of Acids in Micro Reactors... 

Mixed chlorofluorosulfonium salts are prepared by oxidative halogenation of acidic secondary sulfonium salts [Eq. (4.52)] or oxidative fluorination with... 

There is no ambiguity in the halogenation of acids as they can of course enolise on one side only. Reliable methods are bromination with PCI3 and bromine or red phosphorus and bromine. The acid is converted into the acyl chloride with PCI3 or the acid bromide by PBr3, formed in the reaction mixture from red phosphorus and bromine. Bromohexanoic acid 34 can be made in good yield if the reaction mixture is worked up with water.7... 

Halogenation of Acids.—Several facts are of especial importance in connection with the halogenation of the saturated acids. In most cases the introduction of the halogen element into the acid takes place with comparative ease. It may be by the direct action of the halogen. 

There is no ambiguity in the halogenation of acids which can of course enolise n one direction only. A reliable method is bromination with red phosphorus catalyst via the acid bromide. This leads directly to a-bromo esters. 

Give mechanisms for acid-catalyzed and base-promoted alpha halogenation of ketones and acid-catalyzed halogenation of acids (the HVZ reaction). Explain why multiple halogenation is common with basic catalysis, and give a mechanism for the haloform reaction. 

In 2001, Lectka and co-workers [52] adapted their method for catalytic asymmetric a-halogenation of acid chlorides to include bromination reactions (Scheme 13.24). Through use of the same organocatalyst and shuttle-deprotonation strategy, and a polybromoquinone as the bromine source, the catalytic enantioselective... 

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