TRANSALKYLATION OF PHOSPHONATES - EQUILIBRIUM STUDIES

The reaction between alkylating agents and phosphonates (reactions 1 and 2) was found to proceed at a considerably lower temperature than previously reported. Use of a primary alkyl iodide as the alkylating agent results in a reasonably rapid and clean reaction at 130°, but a temperature as low as 70° can bring about slow interconversion; alkyl tosylates react somewhat faster than the corresponding iodides. Performing the reaction in a sealed tube results in establishment of equilibrium; equilibrium distributions agree closely with calculated values over a rather wide range of initial concentrations. The equilibrium data indicated that phosphonate exchange in the absence of external alkylating agent, reaction 3, should be a random, or entropy-controlled process; this was verified experimentally. The use of transalkylation equilibria as a means of obtaining free energy data for alkyl iodides and tosylates is discussed. Transalkylation can be used as a convenient means of synthesis of phosphonate esters, but the magnitude of the equilibrium constants for the reactions must be considered when planning such syntheses. © 1969, American Chemical Society. All rights reserved.