Comparison of Carboxamides Reactivity with Respect to Benzoyl Chloride and Diphenyl Chlorophosphate in Acetonitrile

For amides belonging to series RCONH₂ (I), RCONHMe (II), RCONHPh (III), and RCONMe₂ (IV) rate constants k₁ (l mol^-1 s^-1) were determined (in acetonitrile at 25°C) specifying the nucleophilic reactivity of the oxygen atom in amides toward benzoyl chloride and diphenyl chlorophosphate. The lack of substrate selectivity in the reactions in question was established. For equal values of inductive constants ^* of the R substituents the reactivity sequence of amides with respect to both substrates is the same (I >> IV > II, and III > II), and it does not follow the corresponding sequence of basicities. A conclusion was drawn that both groups of reactions proceed through cyclic transition states resembling reagents: six-membered with amides I and III, and five-membered with amides II and IV.