Reinvestigating the mechanism of acid-catalyzed cyclization of alkyl biphenyl-2-carboxylate

The strong acid-catalyzed conversion of alkyl esters of biphenyl-2-carboxylic acid to fluorenone derivatives via alcohol elimination is a well-established mechanism in organic chemistry. This reaction typically proceeds through an acid-catalyzed acyl-oxygen cleavage followed by an intramolecular aromatic electrophilic substitution reaction leading to the formation of fluorenone. We became interested to explore the alternate mechanism while quenching the nitration reaction of the methyl ester of biphenyl-2-carboxylic acid; we observed the effervescence of a colorless gas, which was found to be the mixture of H2 and CO2 after the gas chromatography analysis. Later, the same experiment was performed with the ethyl ester of biphenyl-2-carboxylic acid and the evolved gas was checked using gas chromatography. The analysis revealed the presence of both CO2 and CO in the collected gas sample. This unexpected result led us to propose an intriguing parallel mechanism through the formation of alkyl nitrate.