Synthetic and spectroscopic studies of cyanobiphenyls and related compounds

Abstract

2,2'-, 3,3'- and 4,4'-dicyanobiphenyl have been prepared from the corresponding dihalogenohiphenyls and their nuclear magnetic resonance and ultraviolet absorption spectra observed. 2,2'-dicyanobenzidine has- also been prepared from 2,2'-dibromobiphenyl and its MIR spectrum studied in concentrated and dilute sulphuric acid. The optical resolution of this compound was also attempted but the attempt proved unsuccessful. Two possible routes to 6-nitro-2,2'-dicyanobiphenyl have been investigated, both starting from 6-nitrodiphenic acid. One route involved the conversion of this acid or one of its derivatives into 6-nitro-2,2'-diaminobiphenyl followed by tetrazotisation and reaction with cuprous cyanide. The diamine was successfully prepared and characterised but conversion into the dinitrile proved impossible by any of the methods attempted. The other route was by dehydration of 6-nitrobiphenyl-2,2'-dicarbo-xamide. Several dehydrating agents were tested onbiphenyl-2,2 '-dicarboxaxiide, but the product, where identifiable, was always 4-cyanofluorenone. Similarly, the dehydration of 6-nitrobiphenyl-2,2'-dicarboxamide with thionyl chloride yielded 5-nitro-4-cya.nofluorenone. The ultraviolet and optical rotatory dispersion spectra, of (+)-6-nitrodiphenic acid have been studied both in ethanol and in aquaeous alkali. These spectra are discussed and the optical configuration of the acid is suggested. l-cyanobenzo[c] cinnoline has also been prepared and its UV spectrum observed and compared with those of 1-nitrobenzo [c] cinnoline and benzo [c] cinnoline itself. Both benzo [c] cinnoline and 1-cyanobenzo [c] cinnoline are photochromic in ethanolic solution, and possible reasons for this are suggested.