Development of an improved synthetic route to an AB phenylquinoxaline monomer

Abstract

The primary objective of this research was the development of an efficient synthetic route for a previously prepared self-polymerizable PPQ monomer mixture, 2-(4-hydroxyphenyl)-3-phenyl-6-fluoroquinoxaline and 3-(4-hydroxyphenyl)-2-phenyl-6-fluoroquinoxaline. Thus, the intermediate, 4-hydroxybenzil, was synthesized in good yield, starting from phenol with phenylacetyl chloride, followed by oxidation. The other intermediate, 4-fluoro-1,2-phenylenediamine, was also less costly synthesized, starting from 2,4-difluoronitrobenzene with ammonium hydroxide, followed by reduction, giving excellent yield. The overall monomer yield was superior to previous reports. Another research objective involved preparation of various monomer mixtures that could be synthesized even less costly, and attempts on polymerization could generate the same structure of PPQ from an original monomer mixture. Thus, the monomer mixture that had switched functional groups from the original one, 2-(4-fluorophenyl)-3-phenyl-6-hydroxyquinoxaline and 3-(4-fluorophenyl)-2- phenyl-6-hydroxyquinoxaline, was prepared. Various monomers with different functional groups attached on the 6-position of the quinoxaline ring, such as chloro- and nitro-substituted monomers instead of fluoro-substituted ones, were also prepared. Several attempts to build up high molecular weights were not successful. In the case of the switched monomer mixture, weaker nucleophility and less activation on the fluorine atom were to be the reason in the switched monomer. In the cases of chloro- and nitro-substituted monomers, poorer leaving power and side reactions were to be the reasons.