One-step Synthesis of Acetic Acid from Methanol Alone Using Dual Functional Complex Catalysis

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Methanol, produced economically from natural gas, has versatile utilty. Based on the unique idea of synthesizing acetic acid with methanol used as the sole source(instead of conventional carbonylation of reethanol with CO), catalysts possessing this function were investigated. It was found that heteronuclear mixed cluster conlexes of the forms [Ru(SnCl_3)_5L]^<n->(L=MeCN, PPh_3, n=3 ; SnCl_3^-, n=4) were effective for this new reaction. Dependence of the catalytic activity on the kind of lisand (PPh_3 > MeCN >> SnCl_3^-, 65ﾟC) suggests that the presence of neutral ligand is important. During the reaction a small amount of methyl formate was detected, and in a certain case a trace amount of formaldehyde dimethyl acetal(sethylal)was detected. From these results, it is concluded that the reaction proceeds with the sequentialprocesses of (1) methanol -> formaldehyde (dehydrogenation), (2) formaldehyde -> methyl formate (Tischenko-type dimerization), and (3) methyl formate -> acetic acid. I … More n fact acetic acid (methyl acetate) was produced, when either formaldehyde (paraformaldehyde) or methyl formate was given as the reactant. When the reaction was performed under CO atmosphere, . the reaction was retarded considerably(the rate becoming to 1/4), which may be due to the coordination of CO to the catalytically active species(coordinatively unsaturated complex) ; this fact is against the'possibility of acetic acid formation by the reaction of methanol with CO which might be present in a small amount by the decomposition of methanol. Addition of free Cl^- ion changed the main product from acetic acid into methyl formate, and the isomerization of methyl formate to acetic acid with [Ru(SnCl_3)_5(PPh_3)]^<3-> catalyst was inhibited by the addition of free PPh_3. These facts indicate that-the activation of methyl formate occurs with a multi-center interaction consisting of the interactions between RU(II)and C-H bond-(soft Lewis acid and base), and between SN(II)and oxygen atom(hard Lewis acid and base). Less