Ultrapurification of p-Terphenyl

Abstract

Any attempt to purify a chemical carries with it the need to measure the purity attained. It is often impossible to measure purity directly, so that assay methods for specific impurities are required. In this report, we will describe the application of zone melting to the purification of p-terphenyl and the use of delayed fluorescence measurements to indicate the purity.

In order to provide pure material for spectroscopic studies, p-terphenyl was zone melted. The bottoms of ingots afforded a concentrate from which biphenyl, o-, and m-terphenyl and triphenylene were separated by thin layer chromatography.

Examination of delayed fluorescence along zone melted ingots indicated the presence of impurity with segregation coefficient greater than unity. Repeated zoning gave a fraction in which impurities of molecular weights 304 and 306 were detected by mass spectroscopy. These appear to be 2-phenyl triphenylene and 2,3-diphenyl biphenyl, respectively, present initially at about 5 p.p.m. This finding represents the first use of delayed fluorescence for locating impurities in a zone melted material.