Solid + liquid phase equilibria and solid-compound formation in mixtures of phosphorus oxychloride with a Group IVA tetrachloride

Abstract

Solid + liquid phase diagrams have been obtained from cooling and warming curves for binary mixtures formed from POCl 3 + SnCl 4, + GeCl 4, + SiCl 4, and + CCl 4. A congruently melting compound of empirical formula SnCl 4 · 2POCl 3 forms. The other mixtures show no compound formation. Solid solutions form over a considerable part of the composition range for POCl 3 + CCl 4. Exploratory measurements show no compound formation between SnBr 4 and POCl 3 or Sn(CH 3) 4 and POCl 3. A comparison is made between the experimental freezing curves for SiCl 4 and GeCl 4 in POCl 3 with the curves calculated assuming ideal-mixture behavior. Both mixtures show positive deviations from Raoult's law. The deviations are larger for SiCl 4 + POCl 3 suggesting less attraction between unlike molecules than in GeCl 4 + POCl 3. The lack of compound formation of phosphorus oxychloride with all the tetrachlorides except that of tin and the deviations from ideal-mixture behavior are explained in terms of steric effects and the electron-accepting ability of the Group IVA elements.