Carbonic acid esters mixed

Carboxylic acids can be activated in situ as mixed anhydrides B (Figure 6.14) that are mixed anhydrides of a carboxylic acid and a carbonic acid half ester. As can be seen from Table 6.1, in anhydrides of this type the C=0 double bond of the carboxylic acid moiety is stabilized less by resonance than the C=0 double bond of the carbonic acid moiety. Therefore, a nucleophile chemoselectively reacts with the carboxyl carbon of the carboxylic and not the carbonic acid ester moiety. 

Crossed Claisen condensations can be chemoselective even when the nonenolizable ester is not a better electrophile than the enolizable ester. This can be accomplished by a suitable choice of reaction conditions. The nonenolizable ester is mixed with the base and the enoliz-able ester is added slowly to that mixture. The enolate of the enolizable ester then reacts mostly with the nonenolizable ester for statistical reasons it reacts much less with the noneno-lized form of the enolizable ester, which is present only in rather small concentration. Carbonic acid esters and benzoic acid esters are nonenolizable esters of the kind just described. 

The first (3-thiolactone was prepared according to Scheme A by Knunyants and co-workers. A mixed anhydride of )3-mercaptocarboxylic acid and carbonic-acid ester is obtained by treatment of a salt of the mercapto acid with a chlorocarbonate ester.Cyclization to the 3-thiolactone occurs during the reaction this synthetic method is exemplified by the preparation of 302 from 301. A mixed carboxylic-sulfonic acid anhydride is involved in the formation of the thiolactone ring in 303. ... 

In the second step, a mixed carbonic acid ester is formed from the carbonic acid ester chloride and the alcohol moiety formed in the first step. 

Mixed from active carbonic acid esters... 

Triazolelbenzyltrimethylammonium salt Urethans from mixed carbonic acid esters N-Carbo-ferf-butoxylation... 

The reaction proceeds in stages, first producing a carbonochloridic ester (chloroformate), and then a carbonic acid diester (carbonate). When a different alcohol is used for the second stage, a mixed radical or unsymmetrical carbonate is produced. 

Ca.rboxyhc Acids. Esters are the main products in the reaction of chloroformates with carboxyHc acids. The intermediate mixed carboxyhc—carbonic anhydrides are very active acylating agents (25—27) but these agents may be isolated in cold temperatures for producing useful products (28). 

A soap-based powder can be produced in combination with ester sulfonates. Thirty-five percent of a sodium soap mixture (5% lauric acid, 5% myristic acid, 52% palmitic acid, 21% stearic acid, 12% oleic acid, and 5% linoleic acid) is mixed with 15% sodium a-sulfo palm oil fatty acid methyl ester, 3% lauric acid ethoxylate, 5% sodium silicate, 17% sodium carbonate, 20% Na2S04- 10H2O, and 5% water [79]. 

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