Abstract
The single-pot efficient oxidation of ethane to acetic acid catalysed by Au(I) or Au(III) compounds, chlorotriphenylphosphinegold(I) (1), chlorotrimethylphosphinegold(I) (2), 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidenegold(I) chloride (3), dichloro(2-pyridinecarboxylato)gold(III) (4), homogenous and supported on different carbon materials: activated carbon (AC), multi-walled carbon nanotubes (CNT) and carbon xerogel (CX), oxidised with nitric acid followed by treatment with NaOH (-ox-Na), is reported. The reactions were performed in water/acetonitrile. The materials were selective for the production of acetic acid, with no trace of by-products being detected. The best homogenous catalysts were complexes 2 and 3 which showed the highest ethane conversion and an acetic acid yield of ca. 21%, followed by 4 and 1. The heterogenised materials showed much better activity than the homogenous counterparts, with acetic acid yields up to 41.4% for 4@CNT-ox-Na, and remarkable selectivity (with acetic acid being the only product detected). The heterogenised catalysts with the best results were reused up to five cycles, with no significant loss of activity, and maintaining high selectivity for acetic acid. 4@CNT-ox-Na showed not only the best catalytic activity but also the best stability during the recycling runs.
Highlights
Direct ethane oxidation is difficult to achieve due to the low reactivity of the C-H bond
The kinetic labile products increase the difficulty of this potentially rewarding reaction [1]. Speaking, this reaction is important, as several bulk chemicals rely on the ethane oxidation products
Methanol carbonylation is responsible for 65% of the world capacity, the remaining 35% being distributed between oxidation of n-butane, acetaldehyde, naphtha and fermentation of hydrocarbons [4]
Summary
Direct ethane oxidation is difficult to achieve due to the low reactivity of the C-H bond. The kinetic labile products increase the difficulty of this potentially rewarding reaction [1]. Speaking, this reaction is important, as several bulk chemicals rely on the ethane oxidation products. Acetic acid is the most sought product [2]. It is commercially produced mainly from methanol carbonylation [3], which gives rise to several environmental problems. Methanol carbonylation is responsible for 65% of the world capacity, the remaining 35% being distributed between oxidation of n-butane, acetaldehyde, naphtha and fermentation of hydrocarbons [4]
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