title: Photochemical acetalization of carbonyl compounds in protic media using an in situ generated photocatalyst.
abstract: Carbonyl compounds are conveniently converted into their corresponding dimethyl acetals in good yields and short reaction times by means of a photochemical reaction in methanol with a catalytic amount of chloranil (2,3,5,6-tetrachloro-1,4-benzoquinone, CA) as the sensitizer. Using aldehydes gives better results than using ketones, which also tend to form enol ethers as side products. These results are similar to those of simple acid-catalyzed acetalization reactions, suggesting the involvement of a photochemically generated acid. On the basis of steady state and laser flash photolysis data the reaction is proposed to involve the in situ generation of a photocatalyst (2,3,5,6-tetrachloro-1,4-hydroquinone, TCHQ) via reaction of CA with the solvent. The acetalization process is initiated by ionization of TCHQ, followed by loss of a proton to the solvent or the carbonyl, which starts a catalytic reaction. The photocatalyst is regenerated via a disproportionation reaction.
authors.affiliation: Department of Chemistry and Biochemistry, California State University Fullerton, Fullerton, California 92834-6866, USA. pdelijser@fullerton.edu
authors.forename: H J Peter
authors.initials: HJ
authors.lastname: de Lijser
authors.forename: Natalie Ann
authors.initials: NA
authors.lastname: Rangel
mesh_terms: D000080:Acetals / Q000737:chemistry*; D000447:Aldehydes / Q000737:chemistry; D002384:Catalysis; D002703:Chloranil / Q000737:chemistry*; D006841:Hydrocarbons, Aromatic / Q000138:chemical synthesis* / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007659:Ketones / Q000737:chemistry; D008027:Light; D015394:Molecular Structure; D010777:Photochemistry; D010782:Photolysis; D012997:Solvents / Q000737:chemistry*
chemical_list: D000080:Acetals; D000447:Aldehydes; D006841:Hydrocarbons, Aromatic; D007659:Ketones; D012997:Solvents; D002703:Chloranil