POLARIZATION MEASUREMENTS ON CARBOXYLIC ACIDS IN DILUTE SOLUTION IN NON‐POLAR SOLVENTS

Abstract

The effective use of dielectric polarization measurements in investigating the association of polar molecules in non-polar solvents has been largely confined to a study of the association of alcohols. These show significant changes in their state of aggregation in a range of concentrations sufEiciently high so that the equipment and methods hitherto available for dielectric constant measurements in solutions can be successfully applied to the investigation of their extent of association. The case of the carboxylic acids in non-polar solvents is quite different. Freezing point determinations show that extremely low concentrations must be attained before significant changes in the state of aggregation occur. This range of concentrations in the case of many of the acids lies below 2 X mole fraction. As a consequence it has been difficult to make sufficiently accurate measurements by most of the methods for molecular weight determination in solution to yield quantitative information about the molecular state of these acids in dilute solution in non-polar solvents. While it has been possible to use the freezing point method, this is applicable only a t a single temperature and so gives information about temperature coefficients and energies of association only through the use of estimates made at other temperatures by other methods. In this paper a description will be given of some of the improvements which were made in apparatus and methods in order to carry out dielectric polarization measurements in very low concentrations in non-polar solvents under anhydrous conditions. In view of the low concentrations involved it is necessary to include a comprehensive statement of the errors of the method. A detailed discussion of the methods employed for interpreting and analyzing the results from the standpoint of the association of the solutes is aIso incIuded.