Kinetics of the reaction of pentacyanonitrosylferrate(II) with aliphatic amines

The reactions of pentacyanonitrosylferrate(II) with ethyl-, n-propyl-, n-butyl-, cyclohexyl- and benzylamines were studied in dilute aqueous solution at 8.6–9.6 pH and 15–35 °C. Nitrosation, diazotation and deamination processes take place in the reactions resulting in alcohols and N₂ gas as final products. On the basis of spectrophotometric and gasvolumetric experiments the rate law was determined as follows.v = kRNH₂]Fe(CN)₅NO^2?] The dependence on pH was interpreted by the protonation equilibria of the amines. From the function of the logarithm of rate constants vs. reciprocal temperature, relatively small activation enthalpies (15–70 kJ mol^?1) and extremely high negative activation entropies (?80) ? (?240) J K^?1 mol^?1] were found. The mechanism was interpreted by the analogy with nitrous acid diazotation.A parallel trend was observed between the rate constants at 25 °C and the basicity constants of the amines.