Phenyl N-phenylphosphoramidochloridate

However, carboxylic acids are converted almost quantitatively to their corresponding symmetrical anhydride by treatment with 1 equiv of Triethylamine or 1-Ethylpiperidine and 0.5 equiv of phenyl N-phenylphosphoramidochloridate (or Diphenyl Phosphorochloridate) in acetone or dichloromethane, with the product anhydride (10) being obtained by filtration or from evaporation of the solvent after washing with water. The resulting crude products are very nearly pure and the phenyl N-phenylphosphoramidochloridate can be regenerated as the aqueous solutions yield the phosphoramidic acid on acidification, which can be converted to (1) by reaction with Phosphorus(V) Chloride. The proposed pathway for this is through the mixed anhydride (11), which then reacts with a second molecule of acid. The only limitation of this method is the reaction of some of the anhydrides with water, e.g. as observed with trichloroacetic acid. 

Generally, phenyl iV-phenylphosphoramidochloridate and other very similar related organophosphorus reagents e.g. phosphorus oxychloride, phenyl dichlorophosphate, diphenylchlorophos-phate and iV,W -bis(2-oxo-3-oxazolinyl)phosphorodiamidic chloride have been utilised in recent years not only to form symmetrical carboxylic acid anhydrides but also in esterification and thiol esterification reactions although phenyl N-phenylphosphoramidochloridate is not so efficient for the latter two reactions compared to its analogs but is probably the best choice for forming the anhydride. ... 

Phenyl N-Methyl-N-phenylphosphoramidochloridate. Like (1), phenyl A -methyl-7V-phenylphosphoramidochloridate (17) reacts under analogous conditions to give anhydrides and carboxamides (see above). However, phenyl TV-methyl-A -phenylphosphoramidochloridate undergoes one additional reaction which is not observed to any significant degree in (1). It is used for the conversion of imines to a-substituted (J-lactams (eq 11). ... 

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