Substituted Aromatic Aldehyde Decomposition under Hydrothermal Conditions

The reaction kinetics and product formation from a range of hydroxy (-OH) and methoxy (-OCH3)-substituted aromatic aldehydes were determined under hydrothermal conditions between 280 and 360 degrees C. The presence of methoxy functionalities in the aromatic aldehyde led to hydrolyticdemethylation reactions, whereas hydroxy moieties-including those generated by hydrolytic demethylation-enhanced cleavage of the formyl group. The effect was most prominent with-OH substitution at the ortho-positions. Ahypothetical reaction pathway in which H2O plays a role in the aldehyde cleavage from the aromatic ring is proposed. Aldehyde rearrangement was identified experimentally at high temperature and long reaction times, consistent with a high energy barrier predicted by density functional theory. Importantly, the decomposition of aldehydes following a Cannizzaro pathway, involving the disproportionation of an aldehyde to an equimolar mixture of an alcohol and a carboxylic acid, was not observed.

Automated summary

The reaction kinetics and product formation of hydroxy and methoxy-substituted aromatic aldehydes under hydrothermal conditions were investigated. The presence of methoxy groups resulted in hydrolytic demethylation reactions, while hydroxy groups enhanced the cleavage of the formyl group. The ortho position substitution with hydroxy groups showed the most prominent effect. The study proposed a hypothetical reaction pathway involving water in the aldehyde cleavage from the aromatic ring. Importantly, the aldehydes did not decompose following a Cannizzaro pathway.