Minren Lin

Mechanistic aspects of the oxidative functionalization of ethane and ethanol by platinum(II) salts in aqueous medium. Role of platinum(II) -olefin and platinum(IV) -alkyl intermediates

The relative rate of CH bond activation by the Pt(II) ion decreased in the order HCH2CH3 > HCH2CH2OH > HCH(OH)CH3. The platinum(II)-ethylene complex, [PtCl3(C2H4)]−1, 1, was the key intermediate in the oxidation of ethane, ethanol, and diethyl ether to 1,2-ethanediol by platinum(II) in aqueous medium. In particular, the intermediary of 1 in the oxidation of ethanol to 1,2-ethanediol and 2-chloroethanol was verified through labelling studies. In D2O, 1, upon oxidation with one of a number of oxidants, converted to [PtCl5(CH2CH2OD)]2−, 2. 2 in turn decomposed to a mixture of 1,2-ethanediol and 2-chloroethanol on heating. The rate conversion of 1 was a function of pH, the anions present, and the oxidant used. While the conversion of 1 to 2 involved a nucleophilic attack by water for hydroxide ion), such a step was not observed in the absence of an oxidant. On basic D2O, the sequential replacement of Cl− by OD− in 1 occurred to successively form [PtCl2(OD)(C2H4)]−, [PtCl(OD)2(C2H4)]− and [Pt(OD)3(C2H4)]−. The process was reversed upon acidification. The species [PtCl5(CH2CHO)]2−, 3, appeared to be the source for the small quantities of hydroxy- and/ or chloroacetaldehyde formed during the oxidation of 1. 3 was synthesized independently by the reaction of acetaldehyde with a mixture of PtCl42−, and PtCl62− in aqueous medium. When 1 was oxidized by Cl2 in CD3OD solution, the principal product was [PtCl5(CH2CO2D)]2− 4, when a small amount of water was present, and CD3OCH2CH2OCD3 in the absence of water.

Oxidation and oxidative carbonylation of methane and ethane by hexaoxo-µ-peroxodisulfate(2–) ion in aqueous medium. A model for alkane oxidation through the hydrogen-atom abstraction pathway

In aqueous medium, at 105–115 °C, SO4-˙(generated from S2O82–) was found to abstract a hydrogen atom from methane and ethane to form the corresponding alkyl radicals which could be trapped efficiently by carbon monoxide, the resultant acyl radicals being ultimately converted into the homologous carboxylic acids.

Rhodium(I)-catalyzed alternating co-oligomerization of carbon monoxide with olefins: Synthetic and mechanistic studies

Abstract Rhodium(I) phosphine complexes were found to catalyze the alternating co-oligomerization of ethylene and carbon monoxide in appropriate solvents. In a mixture of alcohol (ROH) and acetic acid, the products were H(CH 2 CH 2 CO) n CH 2 CH 3 and H(CH 2 CH 2 CO) n OR ( n = 1–4). Only the oligomeric polyketones were formed when a mixture of alcohol and water was used as the solvent. The effect of solvent composition and additives on the product distribution was studied extensively. The reactions were initiated by a rhodium-hydride species formed through the water-gas shift reaction. The chain growth involved the alternate insertions of ethylene and carbon monoxide into the initial rhodium-hydride bond. The oligomeric polyketoesters were formed by the alcoholysis of the intermediate rhodium-acyl species, whereas the oligomeric polyketones were generated through a bimolecular reductive elimination from the intermediate rhodium alkyls and a rhodium hydride. The catalyst system was also found to effect the carbonylation of propylene and butene.

Cobalt porphyrin-catalyzed alkane oxidations using dioxygen as oxidant

Abstract In a mixture of trifluoroacetic acid and water, cobalt(II) porphyrin complexes catalyze the oxidation of alkanes by dioxygen. Carbon monoxide is required as a coreductant for the oxidations to proceed. While the turnover rates are slow, the system displays unusual selectivity in that primary CH bonds are more reactive than the weaker secondary CH bonds or CH bonds α to an alcohol functionality.

A broad spectrum catalytic system for removal of toxic organics from water by deep oxidation using dioxygen as the oxidant

In water, metallic palladium was found to catalyze the deep oxidation of a wide variety of functional organics by dioxygen at 80–90°C in the presence of carbon monoxide. Several classes of organic compounds were examined: benzene, phenol and substituted phenols, aliphatic and aromatic halogenated compounds, organophosphorus, and organosulfur compounds. In every case, deep oxidation to carbon monoxide, carbon dioxide, and water occurred in high yields, resulting in up to several hundred turnovers over a 24 h period. Since the heterogeneous catalyst can be removed by simple filtration, simultaneous water purification and contaminant destruction becomes feasible. For those substrates that are insoluble in pure water, a mixture of water and perfluorobutyric acid was successfully employed as the solvent.

The deep oxidation of chemical warfare agent models: facile catalytic oxidative cleavage of phosphorus-carbon and sulfur-carbon bonds using dioxygen

In water, metallic palladium on carbon was found to catalyze the deep oxidation of organophosphorus and organosulfur compounds by dioxygen at 90°C in the presence of carbon monoxide. This system presents the first examples of catalytic cleavage of phosphorus-carbon bonds. Starting with trimethylphosphine oxide, the phosphorus-containing products formed by sequential P-C cleavage were dimethylphosphinic acid, methylphosphonic acid, and phosphoric acid. A similar reaction sequence was also observed for triethylphosphine oxide, except that products formed by partial oxidation of the ethyl groups, such as phosphonoacetic acid, were also seen as intermediates. The deep oxidation of dimethyl and diethyl sulfides proceeded through the intermediacy of the corresponding sulfoxides. For the methyl derivatives, the ease of oxidation decreased in the order: (CH3)2S>(CH3)2S O>(CH3)2SO2 and is consistent with the system acting as an electrophilic oxidant.

NOx-catalyzed partial oxidation of methane and ethane to formaldehyde by dioxygen

At 600 °C, NOx catalyzes the partial oxidation of both methane and ethane by dioxygen to form formaldehyde. The yield of oxygenates from methane is over 11. The yield increases to over 16 when 0.7% of ethane is added to the gas mixture. The yield of oxygenates from ethane is over 24. A catalytic cycle involving NO2 as the C–H activating species is proposed.

A novel hybrid system for the direct oxidation of ethane to acetic and glycolic acids in aqueous medium

A combination of platinum(II) ion and metallic platinum is found to oxidise ethane to a mixture of acetic and glycolic acids in aqueous medium in the presence of oxygen; the platinum(II) ion is responsible for the initial C–H activation step leading eventually to the formation of ethanol and ethylene glycol, while metallic platinum catalyses the subsequent air oxidation of the alcohols to the corresponding acids.