Kinetic and equilibrium studies of positive halogen compounds

Equilibria in the halogenation of compounds containing C-H, N-H, and O-H bonds have been studied. 1. Electromotive force measurements have been made on cells of the type Pt, X2, X−, (Buffer) / 3.5 N KCl / (Buffer), X−, X2, RH, Pt where X2, X− represent iodine or bromine and the corresponding anion RH an organic compound with a reactive C-H or N-H bond. From these data the thermodynamic equilibrium constants of the reaction RH + X2 = RX + X− + H+ have been obtained for 20 organic compounds, in some cases at several temperatures. 2. From the free energies and heats of halogenation together with other thermochemical data, the differences in the dissociation energy of the C-H and C-X bonds or the N-H and N-X bonds in the compounds RH and RX have been obtained. Their variation in interpreted in terms of the structural changes in the organic compounds. 3. Thermochemical calculations on the hydrolysis of the halogens have yielded dissociation energies of oxygen-halogen bonds. 4. The equilibrium constants of halogenation have also been considered in terms of the ionisation constants of the hydrogen and halogen bonds and of the halogen itself:- Ke = (H+)(X−)(RX)⁄(RH)(X2) = (R−)(H+)⁄(RH) ⋅ (RX)⁄(R−)(X+) ⋅ (X−)(X+)⁄(X2) 5. In this connection the evidence for the existence of halogen cations in aqueous solution is reviewed. Their free energies of formation have been calculated, and their significance in both kinetic and equilibrium problems has been discussed.