Photoinduced Protocol for Aerobic Oxidation of Aldehydes to Carboxylic Acids under Mild Conditions

Abstract

Herein, a green and practical methodology for the synthesis of carboxylic acids from cheap and available aldehydes is demonstrated. Various aldehydes are well compatible, yielding the corresponding carboxylic acids in moderate-to-good yields. This approach features many advantages, including excellent step-efficiency, using molecular oxygen (O 2 ) as the sole oxidant and water as the main solvent, and performing under room temperature and without any catalyst and additive. Moreover, this strategy not only provides a practical protocol for large-scale synthesis but also can be extended to the facile and efficient synthesis of some valuable compounds such as syringic acid, gemfibrozil, and probenecid, highlighting its application value.

Comment on “Photoinduced Protocol for Aerobic Oxidation of Aldehydes to Carboxylic Acids under Mild Conditions”

“…To meet this demand, several solvent selection guides have been published where the use of water is recommended. , Furthermore, a review and inspiring perspectives − have promoted the switch from organic solvents to water-based reaction mediums. In this context, Li et al recently published the photocatalyzed aerobic oxidation of benzaldehyde into benzoic acid using water as solvent.…”

“…Consequently, benzaldehyde could be included as a guest in benzoic acid crystals, protecting it from oxidation . This phenomenon could explain why total conversion of benzaldehyde could not be obtained even after 30 or 48 h of reaction under 1 atm of O 2 . Li et al further experienced this reactivity when they increased the concentration of benzaldehyde for a gram-scale reaction (Scheme 2b).…”

“…This phenomenon could explain why total conversion of benzaldehyde could not be obtained even after 30 or 48 h of reaction under 1 atm of O 2 . Li et al further experienced this reactivity when they increased the concentration of benzaldehyde for a gram-scale reaction (Scheme 2b). The yield obtained was thus lower for a concentration of 0.5 M than for a concentration of 0.25 M (Table ), i.e., 70% and 86%, respectively.…”

“…Under those conditions, a quantitative yield of benzoic acid was obtained in less than 12 h using a catalyst with an initial concentration of benzaldehyde up to 0.75 M. , The use of water as solvent does not avoid the use of organic solvents and the production of solid waste. The workup procedure used by Li et al requires base and acid treatments and two extractions with EtOAc. Up to 3 kg of solid waste and 50 m 3 of solvent per mole of benzoic acid are produced according to the workup procedure described by Li et al This procedure can be significantly improved.…”

“…The workup procedure used by Li et al requires base and acid treatments and two extractions with EtOAc. Up to 3 kg of solid waste and 50 m 3 of solvent per mole of benzoic acid are produced according to the workup procedure described by Li et al This procedure can be significantly improved. Furthermore, the E-factor could not be the best green metric to compare a new synthetic methodology at the mmol scale (see Supporting Information Tables S1–S3).…”