Related Experiment Video
Updated: May 23, 2026

Protocol for the Synthesis of Ortho-trifluoromethoxylated Aniline Derivatives
Published on: January 19, 2016
Using heavy atom rare gas matrix to control the reactivity of 4-methoxybenzaldehyde: a comparison with benzaldehyde
Nihal Kuş1, Archna Sharma, Igor Reva
1Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal.
Abstract:
Different patterns of photochemical behavior were observed for 4-methoxybenzaldehyde (p-anisaldehyde) isolated in xenon and in argon matrices. Monomers of the compound isolated in solid Xe decarbonylate upon middle ultraviolet irradiation, yielding methoxybenzene (anisole), and CO. On the other hand, p-anisaldehyde isolated in an Ar matrix and subjected to identical irradiation, predominantly isomerizes to the closed-ring isomeric ketene (4-methoxycyclohexa-2,4-dien-1-ylidene) methanone. Experimental detection of a closed-ring ketene photoproduct, generated from an aromatic aldehyde, constitutes a rare observation. The difference between the patterns of photochemical transformations of p-anisaldehyde isolated in argon and xenon environments can be attributed to the external heavy-atom effect, where xenon enhances the rate of intersystem crossing from the singlet to the triplet manifold in which decarbonylation (via p-methoxybenzoyl radical) takes place. The parent compound, benzaldehyde, decarbonylates (to benzene + CO) when subjected to middle ultraviolet irradiation in both argon and xenon matrices. This demonstrates the role of the methoxy p-anisaldehyde substituent in activation of the reaction channel leading to the formation of the ketene photoproduct.
Related Concept Videos
Reactions at the Benzylic Position: Oxidation and Reduction
Nucleophilic Aromatic Substitution: Elimination–Addition
Benzene to 1,4-Cyclohexadiene: Birch Reduction Mechanism
Ketones with Nonenolizable Aromatic Aldehydes: Claisen–Schmidt Condensation
As the self-condensation of ketones is generally not favored in basic conditions, the self-condensed products do not form in the reaction between ketones and benzaldehyde. The general reaction of Claisen–Schmidt condensation is...
Reactions at the Benzylic Position: Halogenation
Electrophilic Aromatic Substitution: Chlorination and Bromination of Benzene

