Reactions of Atomic Sodium with Halogenated Hydrocarbons

1 Reactions of Atomic Sodium with Halogenated Hydrocarbons 

The most extensive experimental data on the reaction rate as a function of molecular structure have been obtained [230] for the reaction of atomic sodium with chlorine derivatives of hydrocarbons 

Direct measurements of activation energies for these reactions are sparse. Consequently, to find the approximate dependence of the reactivity (i.e. of the number of effective collisions and of the activation energy) on the molecular structure of RCl in the Na + RCl system, the pre-exponential factors A in the Arrhenius equation have been assumed to be A = 5 10 cm mol- s i for all reactions. The activation energies are then deduced from the measured rate constants and from A (see [511]). 

The collision efficiency k/A for reactions of atomic sodium with chlorinated hydrocarbons of various structures have been calculated from these data. The activation energies for reactions of atomic sodium with hydrocarbons have been found to decrease with the elongation of the hydrocarbon chain CnHan+i, with increasing number of methyl groups, etc. (for details see [230]). 

It also follows from these data that the activation energy gradually decreases with increasing reaction heat Q. This regularity was first noted by Ogg and M. Polanyi [352] (see also [129,130]), who established a linear dependence of E on Q. Lateron, Semenov (see [430]) extended this rule, referred to as the Polanyi-Semenov rule, to exchange reactions of other atoms and radicals. 

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