P-Toluic anhydride

Fife and Xin (35) found that, under PTC conditions, the reaction between benzoyl chloride and a mixture of 1.0 equivalent of sodium p-toluate and 1.0 equivalent of sodium isobutyrate in the presence of 0,1 equivalent of pyridine 1-oxide gave an anhydride product mixture that contained approximately twice as much benzoic p-toluic anhydride as benzoic isobutyric anhydride on a molar basis (equation 7). Therefore, the process must include an important component that selects for the more lipophilic p-toluate ion. The differential partitioning of the competing carboxylate ions at the di-chloromethane-water interface is a reasonable explanation for this observed selectivity, because product composition correlates with the Hansch (39) hydrophobicity parameters for competing carboxylate ions (40). 

Carboxylic acid anhydrides. A soln. of triflic anhydride in ethylene dichloride added dropwise to a soln. of Ph3PO in the same solvent at 0° under N2 after 15 min a soln. of / -toluic acid in ethylene dichloride added followed by EtjN, and stirred for 15 min - p-toluic anhydride. Y 93%. Redox side reactions are avoided, and ketones, esters and ethers unaffected. F.e. inch ketenes, carboxylic acid esters (incl. aryl esters) and amides, amidines from carboxylic acid amides, benzimidazoles, and intramolecular ar. acylation, also using N-diphenylphosphinyl-N -methylpiperazine (without the need for an additional base), s. J.B. Hendrickson, M.S. Hussoin, J. Org. Chem. 54, 1144-9 (1989) alternative prepn. of reagents cf. D. Crich, H. Dyker, Tetrahedron Letters 30, 475-6 (1989). 

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