Addition of oxiranes to the acids of phosphorus. Direction of ring opening

The proportion of the α- and β-ring opening in the addition of unsymmetrically substituted oxiranes to P? OH acids namely diethyl phosphoric acid, phosphorous acid, and phosphoric acid, was established. Ring opening of propylene oxide does not depend on the number of the P? OH groups in the acid and, for di- and trifunctional acids, does not depend on the degree of substitution. After this first reaction of addition the formed hydroxyl groups add the oxirane molecules and the phosphorus-containing polyethers are formed. All of the propylene oxide additions exhibit a ratio of α/β-ring openings of 1:1. For the higher substituted oxiranes the proportion of the attack on the least substituted carbon atom increases, reaching for 1,1-dimethyloxirane up to 90% of α-addition (almost exclusive formation of the tertiary alcohol).