Triethylammonium carboxylate salts

Diphenylphosphoryl azide (DPPA) and triethylamine were formerly employed by Yamada and co-workers in a simple one-pot synthesis of urethanes from carboxylic adds [250]. This procedure involved treatment of a carboxylic acid with triethylamine to produce the triethylammonium carboxylate salt, followed by heating in the presence of DPPA to yield the isocyanate via a Curtius-type rearrangement of the acyl azide. An alcohol was then introduced, functionalizing the isocyanate in situ to yield the urethane. 

D-2-Phenyl-2-aminoacetamido)penicillin-carboxylic acid was reacted with EMME in methylene chloride in the presence of triethylamine at 0-5°C to give the triethylammonium salt of 6- D-2-phenyl-2-[(2,2-diethoxycarbonylvinylamino)-acetamido] penicillincarboxylic acid (35) (74GEP2362978). 

Acyl selenides. The triethylammonium salt of carboxylic acids reacts with C6H5SeCl and Bu3P in THF to form selenoesters in 62-85% yield. These products on reaction with Bu3SnH (AIBN) furnish acyl radicals. 

Methylthiomethyl esters (4, 84-85). These esters can also be prepared by reaction of the triethylammonium salts of carboxylic acids with the Corey-Kim reagent and excess triethylamine initially at —70° and then at 20° for 30 minutes. Yield 80-85%. 

Methylthiomethyl esters have been prepared by reaction of triethylammonium salts of carboxylic acids with chlorodimethylsulfonium chloride or by reaction of the potassium salts of carboxylic acids with chloromethyl methyl sulfide in the presence of sodium iodide and 18-crown-6. ... 

The most secure procedure for the clean preparation of symmetric anhydrides was found in the use of a 10% excess of free carboxylic component over its triethylammonium salt and a 10% excess of this salt over the equivalents of phosgene added at —40 C. 

A reinvestigation of Yamada s method resulted in low yields (10-20%) and isocyanate contaminated by triethylamine (> 30%). These poor results were attributed to the composition of the reaction mixture at the end of the process, i.e. prior to work-up. Reaction of the triethylammonium carboxylate with DPPA yielded a crude mixture of the isocyanate and a triethylammonium phosphate salt 363, which is believed to be in equilibrium with the free acid and base. 

The triethylamine salt of a carboxylic acid, prepared by the reaction of triethylamine and a carboxylic acid 1372, undergoes reaction with one-sixth of an equivalent of triphosgene to give an equimolar mixture of the carboxylate and the predicted intermediate acyl chloroformate 1373 [1042]. Nucleophilic displacement of the chloroformate function by the carboxylate affords the desired anhydride 1374, with concomitant formation of triethylammonium chloride as a precipitate and carbon dioxide gas. The reaction reaches completion in minutes. The solvents of choice have been THF or ethyl acetate, and no evidence for the formation of diacyl carbonates as potential by-products of the reaction has been found. The reaction has been used to prepare the anhydrides from both electron-rich and electron-deficient carboxylic acids (see below) [1042]. 

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