General Papers ARKIVOC 2006 (i) 119-127
Tetrabutylammonium tribromide mediated condensation of carboxylic acids with alcohols
Sarala Naik, Veerababurao Kavala, Rangam Gopinath, and Bhisma K. Patel*
Department of Chemistry, Indian Institute of Technology, Guwahati-781 039, India E-mail:
[email protected]
Abstract
The direct condensation of various carboxylic acids and alcohols was achieved efficiently at reflux temperature under a solvent free condition using a catalytic amount of tetrabutylammonium tribromide (TBATB). Chemoselective acylation of primary alcohols in presence of secondary alcohols and phenols has been achieved. Steric factors in carboxylic acids played a crucial role during chemoselective acylation of diols. Reaction under a solvent free condition, absence of any dehydrating agent or use of any special techniques for removal of water and higher yields are the important features of this protocol.
Keywords: Catalysis, alcohol, carboxylic acid, tetrabutylammonium tribromide, acylation, chemoselective
Introduction
The acylation of alcohol is one of the fundamental and most consistently used transformation in organic synthesis because of the use of esters as fine chemicals, drugs, plasticizers, perfumes, food preservatives, cosmetics, pharmaceuticals, solvents and chiral auxiliaries.1 In general this can be achieved by treating alcohols with acid anhydrides or acid chlorides in the presence of stoichiometric amounts of amine bases such as tertiary amines,2 4-(dimethylamino)pyridine (DMAP) or 4-(1-pyrrolidino) pyridine (PPY) 3 and Bu3P.4 Acylation of alcohols can also be achieved under an acid catalyzed condition by treating alcohols with acid anhydrides in presence of protic acids5 and Lewis acids.6 Acylations using acid anhydrides work well, but the conversion is inherently wasteful since half of every acid anhydride molecule is lost as carboxylic acid utilizing only one acyl group for acylation. On the other hand acyl chlorides are equally efficient acylating agents but their use is restricted owing to their moisture sensitive, corrosive and lacrymating properties. The use of large amount of acylating reagents and activators should be avoided in order to promote Green chemistry and atom efficiency. To fulfill these requirements direct condensation of alcohols with carboxylic acids is the ultimate choice.
ISSN 1424-6376 Page 119 ©ARKAT
