Carbodiimide-intermediated esterification of the inorganic phosphates and the effect of tertiary amine base

Detailed analysis of appropriate 31P nuclear-magnetic-resonance spectra shows that under the usual laboratory conditions, carbodiimide-induced condensation of orthophosphoric acid in a number of solvents leads to condensation only slightly beyond the metaphosphate composition in the presence of strong tertiary amines; whereas in the absence of amine, the condensation proceeds into the ultraphosphate region about halfway between the metaphosphate and phosphoric anhydride compositions. With amine, the principal product consists of the cyclic trimetaphosphate anion, with one of the nonbridging oxygen atoms substituted by the urea resulting from hydration of the carboiimide, i.e., (O2-) P-O-P(O2-) -O-P(O) [N[CH(CH3)2] see article [C(O)NHCH(CH3)2]] for the condensation with diisopropylcarbodiimide. Without amine, the major product is the 1,5-mu-oxotetrametaphosphate anion see article. The well-known carbodiimide-mediated phosphorylation of alcohols with orthophosphoric acid is shown to be directly attributable to the high reactivity of the phosphate branch groups of the carbodiimide-generated ultraphosphates.