INTERACTION OF 2,4- AND 3,4-BIS(TRIFLUOROACETOXY)BENZOATES WITH SULFUR TETRAFLUORIDE IN ANHYDROUS HYDROGEN FLUORIDE SOLUTION

Abstract

Interaction of methyl 3,4-bis(trifluoroacetoxy)benzoate, methyl and ethyl 2,4-bis( trifluoroacetoxy)benzoates with sulfur tetrafluoride in anhydrous hydrogen fluoride solution has been investigated. On the first stage methyl 3,4-dihydroxybenzoate, methyl 2,4-dihydroxybenzoate and ethyl 2,4-dihydroxybenzoate were obtained by esterification of appropriate acids with respective alcohols using concentrated sulfuric acid as a catalyst. On the second stage obtained dihydroxybenzoates were treated with excess of trifluoroacetic anhydride in autoclave at 150 °C for 5 hours. Then, obtained 2,4- and 3,4-bis(trifluoroacetoxy)benzoates were treated with sulfur tetrafluoride in anhydrous hydrogen fluoride solution at 35 °C for 7 hours under continuous stirring. In such conditions methyl 3,4-bis(trifluoroacetoxy)benzoate transforms into methyl 3,4-bis(pentafluoroethoxy)benzoate with high yield. Unexpectedly, methyl and ethyl 2,4-bis(trifluoroacetoxy)benzoate didn’t undergo similar transformations when treated the same way. Instead of respective bis(pentafluoroethoxy)benzoates, methyl and ethyl 2-hydroxy-4-pentafluoroethoxybenzoates were isolated from the reaction mixture. Obviously, fluorination of trifluoroacetoxy group in the 2 position of benzene ring didn’t take place because of the steric hindrance made by ester group, so 4-pentafluoroethoxy-2- trifluoroacetoxy benzoates were formed. The last compounds were turned to 2-hydroxy-4- pentafluoroethoxybenzoates after quenching the reaction mixture with water. Hydrolysis of obtained methyl 3,4-bis(pentafluoroethoxy)benzoate and methyl and ethyl 2-hydroxy-4-pentafluoroethoxybenzoates with water-alcohol alkaline solution and further acidification of reaction mixture with concentrated hydrochloric acid led to the formation of firstly prepared 3,4-bis(pentafluoroethoxy)benzoic and 2-hydroxy-4-pentafluoroethoxybenzoic acids, respectively. The last one is new fluorine-containing analogue of salicylic acid. The molecular mass of the compounds subject to this study was confirmed by EI-MS and GC/ MS analysis.