The excess acidity of aqueous HCl and HBr media. An improved method for the calculation of X-functions and H₀ scales

Abstract

. Can. J. Chem. 59,2116Chem. 59, (1981. Excess acidity (X-function) scales for 0-40% wlw aqueous HCI and 0-60% wlw aqueous HBr solutions are derived, using ionization ratio data for 29 and 9 weak bases, respectively; in these media the resulting ~K B H + values are quite similar to those obtained by standard acidity function treatments. A generalized derivation of the excess acidity enables the determination of pKR+ values for protonation-dehydration processes, some of which are given, and the study of partially dissociated acids. An improved computer program was used, applicable to smaller data sets (up to 50 bases); this program permitted adetermination of the inherent precision of the derived functions, and a more rigorous evaluation of previously derived X-functions and the whole excess acidity method. ROBIN A. COX et KEITH YATES. Can. J. Chem. 59,2116Chem. 59, (1981. En se basant sur des donnees de rapport d'ionisation respectivement pour 29 et 9 bases faibles, on a dkduit des echelles d'acidite en exces (fonction-X) pour des solutions aqueuses de HCI a 0-40% wlw et de HBr a 0-60% wlw; dans ces milieux les valeurs de pKBH+ obtenues sont tout a fait identiques a celles que donnent les fonctions d'acidite normale. Une derivation generale de I'acidite en exces permet de determiner les valeurs de pKR+ pour des reactions de protonation-deshydration, dont quelques-unes sont connues, et d'etudier les acides partiellement dissocies. On a utilise un programme d'ordinateur ameliore, applicable a des ensembles de donnees (jusqu'a 50 bases) plus petites; ce programme a permis de determiner la precision inherente des fonctions derivees et d'evaluer d'une f a~o n rigoureuse les fonctions-X derivees anterieurement ainsi que la methode totale d'aciditk en e x c b .[Traduit par le journal]

Thermodynamics of protonation of weak bases in H2SO4-H2O media, determined using the excess acidity method

“…2, Table l), but not that given by the Ho acidity function (7). It is also reasonable that AS' for the triphenylmethanols should be negative, since the reaction is bimolecular attack of water on a carbocation (reaction [3] in reverse), and that for the anilines should be positive, since the reaction is an acid dissociation (reaction [I] in reverse). Previous work gives positive AS0 values in the latter case (35), but also mostly positive values for the former (9,10).…”

“…Ionization ratios 1 of a weak base B are measured as a function of acid concentration, and these, with the proton concentration CH+ and the excess acidity X (2, 3), give the intercept protonation acidity constant pKsH+ defined for reaction [I]. [2] log I -log CH+ = PKBH-+ m*X KR + [3] ROH + H' % R+ + Hz0…”

“…For the protonation-dehydration reaction [3] (HR compounds (1)) the corresponding equation is eq. [4].…”

“…[4]. Here I is CR+/CROH and the 1.743 is included because definitions of KR+ customarily do not include the water concentration (3); values of m* of about 1.8 have been found for triarylcarbinols in aqueous HCl (3). The method has found widespread use for these equilibria, as has the corresponding method applied to reaction rates; many references are collected in ref.…”

Hydrolysis mechanisms for acylhydrazines in aqueous sulfuric acid, determined using the excess acidity method

“…[3]. X = log (fB* f H + / f B e H + ) for a standard base B*; values of X and log CH+ in H2SO4 (13), HC104 (13), and HCl (14) are available. Suitable manipulation of eqs.…”