Transition metal ion-assisted photochemical generation of alkyl halides and hydrocarbons from carboxylic acids

TitleTransition metal ion-assisted photochemical generation of alkyl halides and hydrocarbons from carboxylic acids
Publication TypeJournal Article
Year of Publication2012
AuthorsCarraher JM, Pestovsky O, Bakac A
Journal TitleDalton Transactions
Volume41
Pages5974-5980
Date Published05/21
Type of ArticleArticle
ISBN Number1477-9226
Accession NumberWOS:000303166800031
KeywordsAQUEOUS-SOLUTION, CHLORIDE, complexes, ethyl, iron(iii), kinetics, oxidation, photo-decarboxylation, RADICALS, relative reactivities, sh2 attack
Abstract

Near-UV photolysis of aqueous solutions of propionic acid and aqueous Fe3+ in the absence of oxygen generates a mixture of hydrocarbons (ethane, ethylene and butane), carbon dioxide, and Fe2+. The reaction becomes mildly catalytic (about five turnovers) in the presence of oxygen which converts a portion of alkyl radicals to oxidizing intermediates that reoxidize Fe2+. The photochemistry in the presence of halide ions (X- = Cl-, Br-) generates ethyl halides via halogen atom abstraction from FeXn3-n by ethyl radicals. Near-quantitative yields of C2H5X are obtained at >= 0.05 M X-. Competition experiments with Co(NH3)(5)Br2+ provided kinetic data for the reaction of ethyl radicals with FeCl2+ (k = (4.0 + 0.5) x 10(6) M-1 s(-1)) and with FeBr2+ (k = (3.0 + 0.5) x 10(7) M-1 s(-1)). Photochemical decarboxylation of propionic acid in the presence of Cu2+ generates ethylene and Cu+. Longer-chain acids also yield alpha olefins as exclusive products. These reactions become catalytic under constant purge with oxygen which plays a dual role. It reoxidizes Cu+ to Cu2+, and removes gaseous olefins to prevent accumulation of Cu+(olefin) complexes and depletion of Cu2+. The results underscore the profound effect that the choice of metal ions, the medium, and reaction conditions exert on the photochemistry of carboxylic acids.

URL<Go to ISI>://WOS:000303166800031
DOI10.1039/c2dt30210a
Alternate JournalDalton Trans.