Fluorinated phosphorus compounds: Part 2. The synthesis of some bis(fluoroalkyl) alkylphosphonates

Twenty bis(fluoroalkyl) alkylphosphonates of structure (RFO)2P(O)R were prepared in 28–69% yields by treatment of alkylphosphonic dichlorides Cl2P(O)R [R=Me, Et, n-Pr, i-Pr] with fluoroalcohols RFOH [RF=CF3CH2, H(CF2)2CH2, C2F5CH2, C3H7CH2, (CF3)2CH] in diethyl ether in the presence of triethylamine. Reactions of isopropylphosphonic dichloride with two molar equivalents of alcohols and fluoroalcohols were compared. After 12 h at room temperature, the alcohols EtOH, n-PrOH, i-PrOH and n-BuOH gave mixtures of monoesters and diesters, except isopropanol, which gave the monoester exclusively. Electronic and steric effects caused by the alkoxy substituents satisfactorily account for the product ratios. With the fluoroalcohols CF3CH2OH, C2F5CH2OH, C3F7CH2OH and (CF3)2CHOH, the diesters predominated. Here the electronic effects of the fluoroalkoxy substituents stabilise the intermediate phosphoranes, eg. Cl2(RFO)P(OH)i-Pr and Cl(RFO)2P(OH)i-Pr, and drive the reactions to completion. Steric effects are clearly much less important in the case of attack by fluorinated alcohols.