The dissociation energy of the C-N bond in benzylamine

The kinetics of the thermal decomposition of benzylamine were studied by a flow method using toluene as a carrier gas. The decomposition produced NH$_{3}$ and dibenzyl in a molar ratio of 1: 1, and small quantities of permanent gases consisting mainly of H$_{2}$. Over a temperature range of 150 degrees (650 to 800 degrees C) the process was found to be a homogeneous gas reaction, following first-order kinetics, the rate constant being expressed by k = 6 $\times $ 10$^{12}$ exp (59,000/RT) sec.$^{-1}$. It was concluded, therefore, that the mechanism of the decomposition could be represented by the following equations: $ \matrix\format\l \\ \quad \text{C}_{6}\text{H}_{5}.\text{CH}_{2}.\text{NH}_{2}\rightarrow \text{C}_{6}\text{H}_{5}.\text{CH}_{\boldsymbol{2}}\boldsymbol{\cdot}+\text{NH}_{2}\boldsymbol{\cdot}, \\ \text{C}_{6}\text{H}_{5}.\text{CH}_{3}+\text{NH}_{2}\boldsymbol{\cdot}\rightarrow \text{C}_{6}\text{H}_{5}.\text{CH}_{2}\boldsymbol{\cdot}+\text{NH}_{3}, \\ \quad \quad \ 2\text{C}_{6}\text{H}_{5}.\text{CH}_{2}\boldsymbol{\cdot}\rightarrow \text{dibenzyl}, \endmatrix $ and the experimentally determined activation energy of 59 $\pm $ 4 kcal./mole is equal to the dissociation energy of the C-N bond in benzylamine. Using the available thermochemical data we calculated on this basis the heat of formation of the NH$_{2}$ radical as 35$\cdot $5 kcal./mole, in a fair agreement with the result obtained by the study of the pyrolysis of hydrazine. A review of the reactions of the NH$_{2}$ radicals is given.