The Preparation and Properties of Some Axidobis(ethylenediarnine)cobdt(m) Salts.

The Hammett acidity function in hydrochloric acid-lithium chloride aqueous solutions, at 25.0 "C has been measured at various ionic strengths ( p ) . The H,-value is very sensitive to the ionic strength. H, + log C,+ is not a constant but a plot thereof against CE+ (at constant ionic strength) is linear and a set of such plots, for different p-values, are parallel. At a given acid concentration : H, = L p + constant (the constant is almost zero). Other relationships are presented and discussed.STUDIES have been reported l-l0 which demonstrate that the addition of large amounts of salts to dilute solutions of hydrochloric acid greatly increases the acidity of the solution as measured by the Hammett acidity function. A study at ionic strengths of 1.00 and 3.00 is the only one reported at various ionic strengths involving high concentrations of acid as well as of salt. We were interested in solutions which were much more concentrated and in various relationships over concentration ranges which were as wide as possible. A suitable solvent system is hydrochloric acid-lithium chloride because very high acid and salt concentrations can be used. RESULTSThe acidity function in these solutions has been evaluated by measuring the ionisation ratios of three primary aniline indicators, viz., 4-chloro-2-nitroaniline (pK -1-02), 2,5dichloro-knitroaniline (pK -1-82), and 2,4-dichloro-6t Pvesent address

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The kinetics of the replacement of nitro-and nitrito-ligands from the complexes M(NH,),X2+ (where X = NO, or ON0 and M = Co, Rh, or Ir) a t various temperatures have been studied. The nitro-complexes are hydrolysed in concentrated acid and the logarithm of the corresponding first-order rate constant is proportional to Hammett's acidity function. The nitrito-complexes are hydrolysed in relatively dilute solutions of strong acids. The logarithm of first-order rate constant is proportional to log [H+J2 or ZH,. The Arrhenius parameters and kinetics are interpreted as follows : ( a ) The nitro-complexes are hydrolysed by a loss of NO+ ion from the transition state; water is not involved in the transition state, and ( b ) the nitrito-complexes react via a mechanism involving mono-and diprotonated forms. The equilibria are very sensitive to ionic strength. It is difficult to ascertain from the kinetics whether or not water is involved in the rate-determining step. The similarity of Arrhenius parameters, irrespective of central metal ion, suggests that oxygen-nitrogen bond breaking occurs rather than metal-oxygen.A COMPARISON of the kinetics of the acid-catalysed hydrolyses of azido-and nitro-complexes 2 9 3 demonstrates that, although the first step in both cases is a rapid protonation, the subsequent fates of the two conjugate acids are very different. The overall difference is that azido-complexes lose a molecule of hydrazoic acid whereas the nitro-complexes lose a nitrosonium ion (Scheme 1). However, Jolly et aL4 pointed out that their results did not rule out the possibility of a nitroto nitrito-conversion, before the hydrolysis step, in concentrated acid solutions. The postulate, well supported by experimental evidence, is that nitro-complexes are hydrolysed by a mechanism which has some of the characteristics of the nitrito-nitro rearrangement (Scheme We considered, therefore, that a comparative study of nitro-and nitrito-complexes in acid solutions might be informative.

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