Temperature dependent photochemical cleavage of 2,5-dimethylphenacyl esters

Author: Literík Jaromír   Relich Stanislav   Kulhánek Petr   Klán Petr  

Publisher: Springer Publishing Company

ISSN: 1381-1991

Source: Molecular Diversity, Vol.7, Iss.2-4, 2003-01, pp. : 265-271

Disclaimer: Any content in publications that violate the sovereignty, the constitution or regulations of the PRC is not accepted or approved by CNPIEC.

Previous Menu Next

Abstract

The study of the temperature-sensitive photochemical release of a carboxylic acid from 2,5-dimethylphenacyl ester is reported. Quantum yields of the benzoate ester degradation in benzene increased from 0.22 at room temperature to 0.28 at 50 °C whereas a more significant increase (nearly by a factor of 3) was observed in methanol and ethanol, reaching a high reaction efficiency (0.25) typically found in non-polar solvents. The reaction proceeds predominantly via the triplet pathway and the E-photoenol in the whole temperature range in methanol solution. A higher quantum efficiency in heated methanol is explained by enhancing the E-photoenol population. This picture was partially confirmed by the quantum chemical calculations. The 2,5-dimethylphenacyl chromophore is proposed as an efficient photoremovable protecting group for carboxylic acids in solutions under conventional or microwave-assisted heating for applications in organic synthesis, such as the solid-phase synthesis.