Kinetic study of the reactions of various types of C-acids with amine bases in acetonitrile. An unusual effect of common BH⁺ cation on the rate constants

The rates of proton transfer reactions between C-acids of different types such as 1-(4-nitrophenyl)-1- nitroalkanes, 4-nitrophenylcyanomethanes, and 2,4,6-trinitrotoluene, and organic bases such as 1,1,3,3- tetrametylguanidine, 7-methyl-1,5,7-triazabicyclo(4.4.0)dec-5-ene (MTBD), and tri- n-butylamine have been measured in acetonitrile at pseudo-first-order conditions. A general equation for the rates of proton transfer reactions between C- acids and bases with product existing in two forms, ions and ion pairs, has been derived and its applicability tested. The equation works well except for reactions of 1-(4-nitrophenyl)-1-nitroalkanes with guanidines for which the second- order rate constant is diminished with concentration of guanidinium cation, while tetrabutylammonium salts accelerate the reactions. Possible reasons for this are discussed.