Photoionization of alpha-alkoxybenzyl radicals to yield alpha-alkoxybenzyl cations. Photochemistry of omega,omega-dimethoxy-omega-phenylacetophenone in polar solvents at high light intensities

• Type: Article in International Scientific Journal
• Date: 1997

Authors

Faria, JL (Author) FEUP; Steenken, S (Author) Other

Journal

The Journal is awaiting validation by the Administrative Services.

Title: JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 2

Pages: 1153-1159

ISSN: 1472-779X

Indexing

ISI Web of Knowledge - 9 Citations

Scopus - 9 Citations

Other information

Authenticus ID: P-007-29K

DOI: 10.1039/a607743i

Abstract (EN): On photolysis of the photopolymerization initiator PhC(O)C(OMe)2Ph in aqueous or alcoholic solution with 248 nm laser pulses or with 248 nm followed by 308 nm pulses (two-laser-two-colour technique), the short-lived species PhC.(OMe)2, PhC+(OMe)2 and e- solv were detected by their optical absorptions. The carbocation PhC+(OMe)2 and e- solv are the products of the monophotonic ionization of the radical PhC.(OMe)2 [¿(308 nm) = 0.2 in aqueous solution] generated from the parent, PhC(O)C(OMe)2Ph, by ¿-cleavage [¿(248 nm) ca. 0.5]. PhC+(OMe)2 reacts with water to produce the hemi-orthoester PhC(OMe)2OH and H+ which was identified by time-resolved conductance. PhC(OMe)2OH decomposes to yield PhC(O)OMe and MeOH (identified by GC). The ¿-alkoxybenzyl radicals PhCH.OR, produced by 248 nm photoinduced ¿-cleavage of the benzoin ethers PhC(O)CH(OR)Ph (R = Me, Et, Pri, But), also undergo ionization upon 248 or 308 nm photolysis. The rate constants for reaction of PhCH.OR with the oxidants Fe(CN)6 3-, Ir(Cl)6 2- and PhI2+ are on average 5.9 x 109, 4.2 x 109, 2.8 x 109 and 1.7 x 108 dm3 mol-1 s-1, respectively. From the facile photoionization of the ¿-alkoxybenzyl radicals it is concluded that this process may also take place under the typical high-intensity light conditions used in industrial photocuring, i.e. that the latter may involve cationic polymerization.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 7