The hydrolysis of the borohydride ion according to the equation (i) is catalysed by nickel-boron and cobalt-boron alloys. The metal-catalysed hydrolysis has been studied a t 22.0 "C by measurement of the hydrogen gas evolved.Arialysis of the gas evolved when the reaction is carried out in deuterium oxide shows that approximately half the hydrogen evolved originates from the borohydride and half from the solvent. The deuterium content of the gas increases with reaction time. In mixtures of H 2 0 and D20, preferential hydrogen evolution occurs and isotope separation factors of 8.5 (for a nickel-boron catalyst) and 9.2 (for a cobalt-boron catalyst) have been derived. BH,-+ 3H20 -W H2B0,-+ 4H2 (i)ALTHOUGH numerous studies have been made l4 of the solvolysis of the borohydride ion in aqueous solution, the metal-boron alloy-catalysed solvolysis has received relatively little a t t e n t i ~n . ~ Both the homogeneous acidcatalysed solvolysis and the heterogeneous alloy-cat alysed solvolysis follow the same stoicheiometry expressed by equation ( 1).BH,-+ 3H,O -w H,BO,-+ 4H, A study of the metal-boron alloy-catalysed solvolysis was undertaken as a part of a wider study concerned with the ' electroless ' or autocatalytic deposition of nickel and cobalt films. It is well-known that reaction (1) occurs concurrently with metal deposition when the borohydride ion is employed as reducing agent in such systems6 This work is also relevant to studies 7-9 of the anodic oxidation of the borohydride ion. EXPERIMENTAL AND RESULTSSolution Preparation.-Sodium borohydride (Koch-Light Pure ') was purified by recrystallisation from diglyme according to the method of Brown, Mead, and Subba Rao.10 The diglyme was first dried (CaC1,) and then distilled under nitrogen. The sodium borohydride produced by this method was determined by the method of Lyttle, Jensen, and Struck l1 to be 99.60,/,. Sodium hydroxide solutions were prepared from AnalaR sodium hydroxide and distilled water, and sodium deuteroxide solutions were prepared by dissolving sodium wire in deuterium oxide (99.6%) under nitrogen.Kinetic Studies.-Afiparatus.The apparatus consisted of a three-necked reaction vessel (25 ml) equipped with a nitrogen inlet and a thermometer. The third neck was connected through a water-condenser to a gas-burette to measure the volume of hydrogen evolved a t atmospheric pressure. The reaction vessel was immersed in a thermo-

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