Acetyl bromide additive method

The preparation reported here is based on the method of Christie and Rapoport.4 9-Bromo-9-phenylfluorene has also been prepared by a light-initiated reaction of bromine and 9-phenylfluorene in carbon disulfide,2 by addition of phenylmagnesium bromide to fluorene36 followed by treatment with acetyl bromide,5 and by treatment of 9-phenylfluorene with N-bromosuccinimide.6... 

The addition of HBr to an alkyne can be facilitated by using acetyl bromide (CHsCOBr) and alumina instead of aqueous HBr. Acetyl bromide acts as an HBr precursor by reacting with the alumina to generate HBr. For example, 1-heptyne can be converted to 2-bromo-l-heptene in good yield using this method ... 

In most of the published Merrifield syntheses the peptides are bound to polystyrene by benzyl ester type of linkages, which in analogy to classical methods can be cleaved by HBr/acetic acid. Already in the incipience period of the methodology, however, trifluoroacetic acid saturated with hydrogen bromide was found more efficient, first, because of the increased acidity of the mixture which in addition does not cause proton catalyzed acetylation and, second, since trifluoroacetic acid is more lipophilic than the acetic one, it solvates much better both the polymer and the peptide to be released. 

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