title: The free-radical chemistry of polyethylene glycol: organic reactions in compressed carbon dioxide.
abstract: The thermal oxidative degradation of polyethylene glycol (PEG) is known to occur in an oxygen atmosphere at elevated temperatures. In this study, PEG radicals assumed to result from thermal oxidative degradation are successfully applied, in combination with compressed CO(2), to initiate a range of free-radical reactions, such as selective formylation of primary and secondary aliphatic alcohols, oxidation of benzylic alcohols, benzylic C==C bond cleavage, and benzylic sp(3) C--H oxidation, demonstrating enormous synthetic potential in a cost-efficient, practically useful, and environmentally friendly manner; not requiring any catalyst or additional free-radical initiator. We find that both PEG and molecular oxygen are prerequisites in order to perform these reactions smoothly. Given that dense CO(2) is immune to free-radical chemistry; it is an ideal solvent for such reactions. As a result, compressed CO(2) allows reactions initiated by PEG radicals to be tuned by subtly adjusting reaction parameters such as the CO(2) pressure, thereby enhancing the product selectivity. By attaining a high selectivity towards the desired products this methodology is practical for organic syntheses.
authors: Institute of Elemento-Organic Chemistry, Nankai University, Tianjin, PR China.
authors: Jin-Quan
authors: JQ
authors: Wang
authors: Liang-Nian
authors: LN
authors: He
authors: Cheng-Xia
authors: CX
authors: Miao
authors: Jian
authors: J
authors: Gao
mesh_terms: D000438:Alcohols / Q000737:chemistry; D002245:Carbon Dioxide / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry; D055772:Green Chemistry Technology; D008970:Molecular Weight; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry*; D011312:Pressure
chemical_list: D000438:Alcohols; D005609:Free Radicals; D002245:Carbon Dioxide; D011092:Polyethylene Glycols; D010100:Oxygen