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The Dissociation Energy of the C-N Bond in Benzylamine

M. Szwarc
Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences
Vol. 198, No. 1053 (Aug. 15, 1949), pp. 285-292
Published by: Royal Society
Stable URL: http://www.jstor.org/stable/98171
Page Count: 8
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The Dissociation Energy of the C-N Bond in Benzylamine
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Abstract

The kinetics of the thermal decomposition of benzylamine were studied by a flow method using toluene as a carrier gas. The decomposition produced NH3 and dibenzyl in a molar ratio of 1: 1, and small quantities of permanent gases consisting mainly of H2. 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 × 1012 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 ± 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 NH2 radical as 35· 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 NH2 radicals is given.

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