Kinetics for Reaction of the Nitrate Radical (NO3.) with aldehydes in Acetone in Acetonitrile

Article abstract of DOI:10.1021/j100347a041

The rate constants for the reactions of NO3^. with RCHO (R: H, CH3, C2H5, CH(CH3)2, and C(CH3)3 and XC6H4CHO (X: NO2, CN, Cl, H, and OCH3) have been measured by following the decay of the transient absorption band of NO3^. generated by photolysis of K2 in acetonitrile.Representative rate constants (in unit of M^-1 s^-1) at 20 deg C in acetonitrile are 2.3E7 for CH3CHO and 2.4E7 for PhCHO.The hydrogen-atom abstraction reaction of NO3^. from the aldehydic C-H was confirmed by the similarity of the above two rate constants and by the higher reactivites than those of acetone and benzene.The rate constants for HCHO and CH3CHO in aqueous solution are smaller than the corresponding values in acetonitrile, because of the hydration.For aliphatic aldehydes, the methyl substitution on the vicinal carbon to aldehydic carbon slightly increase the reactivity of the aldehydic C-H with NO3^..A large negative Hammett reaction constant (ρ=-1.3) for aryl aldehydes indicates the high electrophilicity of NO3^..The polar substituents stronly affect the orientation factors rather than the activation energies, which were obtained by the Arrhenius plots.The rate constants in acetonitrile, however, are ca. 30 times larger than the corresponding ones reported in the gas phase: a polar mediun affects the distribution of an unpaired electron and the polar nature of the reaction.