New method for the synthesis of 2-thiophenecarboxylic acids in the presence of V-, Fe-, or Mo-containing catalysts

Abstract

2-Thiophenecarboxylic acid and its derivatives were synthesized by the reaction of thiophenes with the CCl 4 -CH 3 OH-catalyst system in total yields of 44-85%. The probable scheme of the reaction involves successive oxidation of methanol with tetrachloromethane to methyl hypochlorite and formaldehyde. Under the action of the latter, thiophene undergoes oxymethylation, giving rise to 2-oxymethylthiophene, which is oxidized with CH 3 OCl to 2-thiophenecarboxylic acid. In the presence of an excess of CH 3 OH, the latter is subjected to esterification. It was found that Fe(acac) 3 , VO(acac) 2 , and Mo(CO) 6 are the catalysts of choice for this reaction.Keywords: Catalysis, iron, vanadium and molybdenum compounds, methyl hypochlorite, thiophene, 2-thiophenecarboxylic acid, oxidation Results and DiscussionEarlier, we reported 1,2 that the manganese-and vanadium-complexes [Mn(acac) 3 and VO(acac) 2 ] catalyze the oxidation of alcohols (ROH) under the action of CCl 4 giving rise to alkyl hypochlorites (ROCl). Subsequent transformations of ROCl depend on the structure of the radical R. Lower primary alcohols are most readily oxidized. For example, oxidation of methanol with tetrachloromethane in the presence of Mn(acac) 3 affords predominantly methyl formate along with small amounts of formaldehyde. Hydrochloric acid and trace amounts of CH 2 Cl 2 , CH 3 OCH 3 , and water were also found in the reaction mixture. In the course of the reaction, CCl 4 is reduced to CHCl 3 .