Anhydrides of Carboxylic Acids The word anhydride literally means without water,and an acid anhydride is the combination of two molecules of carboxylic acid with the elimination of one molecule of water 0 0 R-C-O-H H-O-C-R R C-O-C-R' +H2O Anhydrides are also considered as activated forms of carboxylic acids,although anhydrides are not as reactive as acid halides The anhydride group also inductively withdraws electron density from the carbonyl carbon,and the carboxylate anion serves as a good leaving group. RCO Q-C-R R-C :0-C-R Nuc: carboxylate leaving group Half of the anhydride is'lost'as the leaving group,and if the carboxylic acid is very precious(expensive or limited quantity)then this is an undesirable way of making an activated carboxylic acid,and the acid chloride route would be more desirable. Ch21 Carboxylie acid Derivatives(landscape) Page 10 Ch21 Carboxylic acid Derivatives(landscape) Page 10 Anhydrides of Carboxylic Acids The word anhydride literally means without water, and an acid anhydride is the combination of two molecules of carboxylic acid with the elimination of one molecule of water. Anhydrides are also considered as activated forms of carboxylic acids, although anhydrides are not as reactive as acid halides. The anhydride group also inductively withdraws electron density from the carbonyl carbon, and the carboxylate anion serves as a good leaving group. Half of the anhydride is 'lost' as the leaving group, and if the carboxylic acid is very precious (expensive or limited quantity) then this is an undesirable way of making an activated carboxylic acid, and the acid chloride route would be more desirable. R C O O-H C R O H-O R C O O C O R' + H2O