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

“…Using thiophene as an example, it was demonstrated that the reaction is catalyzed not only by VO(acac) 2 but also by iron-and molybdenum compounds. Of the iron and molybdenum compounds examined in the present study (FeCl 3 , FeBr 2 , Fe(OAc) 2 , Fe(acac) 3 , MoO 3 , MoCl 5 , Mo(CO) 6 ), Fe(acac) 3 and Mo(CO) 6 proved to be most efficient in this reaction.…”

“…However, the reaction starting from 2-methylthiophene 3 and the CCl 4 -CD 3 -VO(acac) 2 system afforded 2-methyl-5-trideuteriomethylthiophenecarboxylate, 4, i.e., the reaction product contained deuterium exclusively in the methoxy group, which argues against the above assumption. …”

“…In the present study, we used the CCl 4 -CH 3 OH-VO(acac) 2 system for oxidation of thiophene and its derivatives. Unexpectedly, the reaction of thiophene 1 with this system gave, along with CHCl 3 and HCl, methyl 2-thiophenecarboxylate 2 as the major product.…”

“…It should be noted that the reaction requires drastic conditions and occurs at 130, 140, and 175 o C in the presence of Mo(CO) 6 , Fe(acac) 3 , and VO(acac) 2 , respectively. Because of high temperature, the reaction was carried out in a sealed tube or a stainless-steel micro-autoclave.…”

“…Under typical conditions (175 o C, 5 h), the reaction in the presence of VO(acac) 2 at concentrations of 0.1, 0.2, and 1.0 mol. % with respect to thiophene afforded product 2 in 25, 31, and 45% yield, respectively.…”