Kinetics and mechanism of hydroxy group acetylations catalyzed by N-methylimidazole.

Abstract:

:The kinetics of acetylation of alcohols by acetyl chloride and acetic anhydride, with N-methylimidazole as the catalyst, were studied in acetonitrile solution at 25 degrees; some measurements were also made with 4-dimethylaminopyridine as the catalyst. The acetic anhydride-N-methylimidazole system proceeds entirely by a general base catalysis, whereas the acetyl chloride-N-methylimidazole system reacts entirely via a nucleophilic route, with the intermediate formation of the N-acylated catalyst. The reaction of this intermediate with the alcohol is general base catalyzed. The acetyl chloride-4-dimethylaminopyridine system also reacts via the nucleophilic route. In the acetic anhydride-4-dimethylaminopyridine system a small fraction of the intermediate was detected. The acetic anhydride-N-methylimidazole system was studied in n-propanol-acetonitrile solvent mixtures; no spectral evidence for intermediate formation was seen. However, the hydrolysis reaction in acetic anhydride-N-methylimidazole, studied over a wide range of water-acetonitrile mixtures, revealed a change in mechanism from general base in dry acetonitrile to a solely nucleophilic route at high water concentrations.

journal_name

J Pharm Sci

authors

Pandit NK,Connors KA

doi

10.1002/jps.2600710503

subject

Has Abstract

pub_date

1982-05-01 00:00:00

pages

485-91

issue

5

eissn

0022-3549

issn

1520-6017

pii

S0022-3549(15)44155-3

journal_volume

71

pub_type

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