The homogeneous gas phase reaction between diborane and phosphine at 0deg;C, yielding a solid product of composition BH3PH3, has been observed to give a linear relation between the initial rate of reaction and the pressure of either reactant, provided a certain pressure of each reactant, determined by the equilibrium constant and the pressure of the other gas, is exceeded. The reaction rate is independent of the amount of surface of the solid product or of the wall. When either reagent is in appreciable excess, the ratehyphen;time data obey a pseudo firsthyphen;order equation.These facts are consistent with a ratehyphen;controlling reaction of diborane with phosphine to give BH3PH3and BH3, the borine reacting further with phosphine, and the BH3PH3condensing rapidly to a solid. This mechanism leads to a rate equation which is in good agreement with the experimental evidence. The activation energy of the ratehyphen;controlling step is 11.4plusmn;2.0 kcal molemdash;1.
展开▼
