50707-43-2

A kinetic study of the reaction between 3-alkyl-1-aryltriazenes and substituted acetic acids has been made in solvent acetone over the temperature range 21-37 deg C.Ea is 17.3 +/- 0.3 kcal mol-1 and log A is 10.3 +/- 0.1.Influence of the substituents on the reaction rate has been analyzed.The Hammett correlation with ? gave a ρ value of -0.96 for para-aryl substituted triazenes and +0.35 for meta- and para-substituted phenylacetic acid.The rate of decomposition of triazenes is also affected by changing the alkyl group.From these results a duality in mechanism is proposed; first, a simultaneous protonation and alkyl group expulsion to be the rate-determining step when R is tertiary, benzylic and possibly secondary.Secondly, a concerted mechanism for the protonation of nitrogen and cleavage of the N-R bond for primary alkyl groups.

Both tautomers of propyl-p-nitrophenyl-, -p-cyanophenyl-, -3,5-dichlorophenyl-, and -p-chlorophenyl-triazenes are directly observable by 1H n.m.r. at 200 MHz in CD3CN at 25 deg C.In addition, lower temperature studies enable the two tautomers of propyl-p-methylphenyl- and -p-methoxyphenyl-triazenes to be quantitated.At -45 deg C rotamers about the N-N bond of the conjugated tautomers are also separately observable. 13C N.m.r. studies of the p-nitro- and p-chloro-compounds suggest tautomerisation involves the less abundant rotamer of the conjugated tautomer and the unconjugated tautomer.The position of equilibrium at 25 deg C is described by log (/) = (0.67 +/- 0.13) - (0.31 +/- 0.04)pKa (ArNH3+). 13C, as well as 1H n.m.r. studies indicate that change of solvent to (CD3)2SO, CD3CN-(CD3)2SO, or CD3CN-(CD3)2SO-H2O has little effect.Neither, in the p-nitrophenyl case, does change of the propyl group for benzyl.