Effect of copper salts on hydrothermal oxidative decarboxylation: a study of phenylacetic acid

Abstract

Efficient and selective effects of copper salts on hydrothermal oxidative decarboxylation have been discovered and studied.

Anaerobic oxidation of aldehydes to carboxylic acids under hydrothermal conditions

“…This reaction mechanism is also based on proposed mechanisms in previous studies, where Cu( ii ) has been found as an oxidant for the oxidation of benzylalcohol and benzaldehyde under similar hydrothermal conditions. 17,20 In the present study, however, the electron-donating –CH 3 and –CH 3 O substituted benzaldehyde resulted in a lower conversion than that of the –CF 3 substituted benzaldehyde ( Table 2 ), which does not seem to support the formation of a positively charged intermediate. It is thus more likely that the hydrate formation is the rate-determining step, since the substituent effect on hydrate formation could be opposite to that on oxidation.…”

“…Our recent research on alcohols, carboxylic acids, and amides have shown that organic oxidations can readily occur in the presence of metal salts such as Cu(II) under O 2 -absent hydrothermal conditions. [17][18][19] In those reactions, water serves as a green solvent, while Cu(II) acts as an efficient oxidant. The metal-promoted hydrothermal reactions also mimic natural geochemical processes on Earth, which provides the new "geomimicry" concept of using Earth-abundant metals as the oxidant/reductant for green organic reactions.…”

“…Hydrothermal experiments were conducted in sealed fused silica tubes under an aqueous condition of 200 C and 15 bar (P sat , calculated using SUPCRT92) 22 in the absence of O 2 , following a previously developed method. 17,23,24 We started our investigation by examining the oxidation of benzaldehyde (compound 1) under hydrothermal conditions using various Cu(II) and Fe(III) salts, including CuCl 2 , CuSO 4 , Cu(OAc) 2 , Cu(NO 3 ) 2 , FeCl 3 , Fe 2 (SO 4 ) 3 , and Fe(NO 3 ) 3 (Table 1). In pure water without additives, only 4% of benzaldehyde reacted at 200 C aer 24 h, forming benzoic acid with a yield of 3% (entry 1).…”

Hydrothermal Transformations of Alcohols with Copper(II) and Iron(III) Salts

“…These starting organic and inorganic concentrations were similar to those in our previous copper salt studies. 23,33 After the starting materials were loaded, the oxygen and air inside the tubes were removed by three freeze−pump−thaw cycles prior to sealing with an oxyhydrogen flame under vacuum. The tubes were sealed, while the solution was frozen by liquid nitrogen.…”

“…24 These impressive organic−inorganic interactions not only demonstrate the important roles of minerals and metal ions in organic geochemical transformations in hydrothermal systems, but also bridge geochemistry to green chemistry in a new field of geomimicry. 21,23,25 As shown in Scheme 1, alcohols occupy a central position in the organic functional group interconversions. Previous studies have indicated that dehydration of alcohols is favored under hydrothermal conditions, and formation of alkenes from alcohols can rapidly occur in a temperature range of 200− 350 °C within hours.…”