608. The halogen cations in aqueous solution

Abstract

Thermodynamic and other physicochemical data on iodine, bromine, and chlorine have been used in the calculation of several new thermodynamic quantities. These include the free energies of formation in aqueous solution of the halogen cations Xf and H,OX (X = I, Br, Cl).Electrometric measurements have been made on aqueous solutions of iodine in the presence of varying concentrations of silver salts and acid. It has been shown that, under certain experimental conditions, solutions containing considerable concentrations of an iodine cation can be prepared. The free energy of ionisation of iodine a t 25" is found to be 15 kcal./mole, in good agreement with the free energy calculated for the reaction I, + H,O = H,OI + I-.ALTHOUGH the cations of the halogens are now frequently invoked as agents in halogenation reactions, little evidence has so far been produced for their existence in measurable concentration in aqueous solution (Hinshelwood, In this paper theoretical and experimental studies on the halogen cations are presented.Section A . Theoretical Considerations. + + An attempt has been made in this section to calculate the thermodynamic tendency for Throughout this paper, the symbol X In the gas phase the tendency for halogen molecules to ionise with the formation of X+ is various halogen cations to be formed in aqueous solution. stands for I, Br, and C1; all thermodynamic data refer to 25" unless otherwise stated. extremely small. is 195, 231, and 263 kcal./mole for iodine, bromine, and chlorine. These values are obtained from the known free energies of dissociation, ionisation potentials, and electron affinities (National Bureau of Standards, Washington, D.C.) .The tendency to ionisation increases enormously in aqueous solution because of the large heats of solution of the ions. The heats and free energies of solution of ions are obtained by one of the following methods. The free energies of solution of many salts have been obtained directly by experiment. The data for pairs of ions thus obtained can be analysed for single ions if a value for any one ion is assumed. The entropies of solution of ions are referred to the entropy of solution of the proton. The heats of solution of ions of equal charge and size are usually taken as equal. For example, the experimental values for potassium fluoride (radii of Kf and F-are equal) provide a key for the heats of solution of many other single ions. It has, however, been shown theoretically that a negative univalent ion has a heat of solution about 2% higher than a positive ion of equal radius (Bernal and Fowler, J . Chevn. Physics, 1933, 1, 515). The heats and entropies of solution of ions, obtained by this sort of analysis of experimental data, are in good agreement with the results of the a priori calculations by Eley and Evans (Trans. Faraduy SOL., 1938, 34, 1093). The free energies of solution of the ions Xare taken from this paper. I t will be seen later that the free energies of solution of X+ and H,OX can be estimated in a similar manner.We can now consider the t...

Linear Free Energy Relationships.

“…This situation is indistinguishable from that of variations in 2 alone since (15) and the result will be the introduction of another proportionality constant into the g-terms. In other 11. dx + dy + dz + .…”

“…Of 56 reaction series common to both treatments, Bekkum, Verkade and Wepster find 34% having correlation coefficients better than 0.998, 77% better than 0.99 and 89% better than 0.98; while Jaff6, for these reaction series, finds 29% better than 0.99, 59% better than 0.98, but none better than 0.998, in fact only 6% of the 371 reactions covered shorn this high precision. That this marked improvement is due to the removal of deviations due to variable p-substituent influences is shown by the computation of sigmavalues for other m-substituents (Table IV, numbers [11][12][13][14][15][16][17][18][19]. The standard deviations obtained are no larger than might be expected and do not greatly exceed those for substituents "H" and "p-NOn" (Table V) calculated from reaction series correlated using the primary values of these substituents.…”

ÉTUDE CINÉTIQUE DE L'OXYDATION DE LA TRIBENZYLAMINE PAR LA N-BROMOSUCCINIMIDE

“…[4]- [7]) pour ]'ox)-dation de la tribenzylamine par la N-bromosucciniinide (Y = -OR, HOR ou Br-; R = -CH3 ou p H ) .…”

“…[7] est l'ittape de solvolyse et donne lieu aux produits finals (le benzaldkhyde et la dibenzylamine). Sa constante de vitesse (k3) a CtC d6terminCe par la mCthode mentionnke plus haut, et sa valeur est 0.G min-' dans les conditions expitrimentales.…”

Mechanism of Singlet Oxygen Generation by Chemical Reactions.

“…We therefore anticipate that , in equation ( 10 ), k r OtlO 10 sec " with k f determ ined by the difference in base strengths of 11 2 0 and }IOCl 2 (38) .…”