Amidines. Part 20. Rates of reaction of N,N-dialkylformamide acetals with substituted anilines

Amidines. Part 39.1 Formation of N 1,N 1-dialkylamidines in the reaction between amide acetals and substituted anilines in pyridine. Reaction mechanisms

“…For reactions in neutral solvents a good linear relation for all anilines and acetals studied was obtained, and relative rate constants decreased with a decrease in the electron-donating character of the substituent on the phenyl ring in the aniline molecule. 23 In pyridine, however, relative rate constants for nitroanilines differ markedly from those expected on the basis of the Hammett type relations obtained for other anilines. For p-nitroaniline relative rates are higher than those for p-chloroaniline.…”

“…It was found that in neutral solvents, such as methanol, benzene, THF or chloro- form, the reaction rate depends on the structure of the alkoxy groups. 23 In pyridine, however, a dependence of this kind was not observed. This indicates that in pyridine cleavage of the C-O bond is not involved in the rate-determining step.…”

“…In this study the same set of amide acetals and primary amines as in our previous work 23 were selected so as to obtain results comparable with those for reactions in neutral solvents (benzene or methanol).…”

“…In our previous paper 23 the kinetics of the reaction of N,Ndialkylformamide acetals (R 1 ) 2 N-CH(OR 2 ) 2 with anilines substituted on the phenyl ring were studied in neutral solvents, such as methanol and benzene, commonly used for derivatization with amide acetals. It was found that the reaction is second order and that the reaction rate depends on the solvent, on substitution at the nitrogen and oxygen atoms of the amide acetal molecule as well as on substitution in the amine molecule.…”

Amidines. Part 24. Influences of alkyl substituents at the amidino carbon atom on the sensitivity to substitution at the imino nitrogen atom. pK a Values of N 1 N 1-dimethylamidines

“…Thus, as expected, substitution at this site exerts the strongest influence on the pKa value of amidines. It was shown2-'l that the pKa values of amidines containing a substituent at the imino nitrogen atom obey the Hammett equation (1). It was also found that the pKa values of amidines containing a substituent R, (alkyl, aryl, or aralkyl) at the imino nitrogen atom can be correlated with the pKa values of the corresponding primary amines R,NH, measured under the same conditions, and that equation (2) thus obtained may be used for prediction of the pKa values of amidines.…”