Preparation and properties of 1-bromo-2,2,3,4,4-pentamethylphosphetan 1-oxide, C8H16P(O)Br, and a comparison with the chloro-compound; hydrolysis of these to the anhydride and acid. Vibrational spectra

Abstract

The title compound can be prepared from the reaction of 2,4,4-trimethylpent-2-ene, phosphorus tribromide, and aluminium bromide in dibromomethane followed by controlled hydrolysis. The inclusion of material containing chlorine results in the production of the well known 1-chloro-analogue, C₈H₁₆P(O)Cl. The bromo-derivative has been fully characterized and its reactivity towards common nucleophilic reagents shows it to be more reactive than the chloro-compound. At room temperature both undergo slow hydrolysis to the corresponding acid, C₈H₁₆P(O)OH, whereas at higher temperatures the initial product is the anhydride, C₈H₁₆P(O)·O·P(O)C₈H₁₆. This compound is relatively resistant to further hydrolysis except by solution of pH > 12. Kinetic studies show that hydrolysis under these conditions is of the first order in both anhydride and OH^–. Other ways of preparing the anhydride as well as its reactions have been studied. Raman and i.r. spectra of the bromide, chloride, acid, and anhydride are analysed; ν_s(POP) is identified.