Bernard Langlois

Improvement of the synthesis of aryl difluoromethyl ethers and thioethers by using a solid-liquid phase-transfer technique

Abstract A new solid-liquid phase-transfer technique has been used to synthesize aryl difluoromethyl ethers and thioethers. Phenols (or thiophenols) and chlorodifluoromethane, dissolved in a cheap aprotic solvent of low polarity, are contacted with solid sodium hydroxide in the presence of a catalytic amount of tris-(3,6-dioxaheptyl)amine. The work-up of the reaction mixtures is very simple. Although yields are similar in both homogenous and heterogeneous procedures using phenols, improved yields are obtained for thiophenols when using phase-transfer conditions.

Difluoromethanesulfonic acid. I. An improved route to sodium difluoromethanesulfonate

Abstract The synthesis of sodium difluoromethanesulfonate from aqueous sodium sulfite and chlorodifluomethane became productive, more selective and reproducible by adding sodium hydroxide, even in quantities smaller than the stoichiometry. This reaction has been optimized and its carbenic nature unambiguously proved by conducting the reaction in deuterium oxide. “Sodium diflate” could also be formed from sodium sulfite and dibromodifluoromethane by another carbenic process.

Difluoromethanesulfonic acid Part II. A two-step route to the free acid from monohydrated sodium difluoromethanesulfonate

Abstract Anhydrous difluoromethanesulfonic acid (“diflic acid”) can be obtained, in a two-step procedure, from monohydrated sodium difluoromethanesulfonate, a very stable salt not easily dehydrated. In the first step, stable hydronium difluoromethanesulfonate is distilled from a mixture of CHF 2 SO 3 Na,H 2 O and pure sulfuric acid in a 86 % yield. In the second step, diluted oleum (10 % S0 3 ), containing a slight excess of sulfur trioxide, is slowly dropped into hydronium difluoromethanesulfonate and anhydrous difluoromethanesulfonic acid is distilled from the resulting mixture in a 51 % yield. The use of more concentrated oleum and excess of sulfur trioxide causes a rather violent decomposition to gaseous products for which a chain mechanism is proposed. The same process is invoked to explain the more violent degradation of hydronium difluoromethanesulfonate observed with thionyl chloride. This chain reaction seems to be governed by the great ability of the α-acidic hydrogen to form hydrogen bonds

Trifluoromethylation with sodium trifluoromethanesulfinate under oxidative conditions

Abstract Trifluoromethyl radicals ·CF3 can be generated by monoelectronic oxidation (for instance with tertiobutyl hydroperoxide) of sodium trifluoromethanesulfinate (CF3SO2Na). This useful and cheap precursor of triflic acid results from bromotrifluoromethane and sulfur dioxide radical-anion (1). Under these conditions, CF3SO2Na is able to convert mildly organic disulfides into tri-fluoromethyl thioethers (2) and to trifluoromethylate enol esters. In the latter case, additional catalytic amounts of cupric salts are necessary to oxidize the intermediate radical, in order to prevent the formation of by-products. The reaction can be thus considered as a formal electrophilic trifluoromethylation. Aromatic trifluoromethylation can be also performed with the same system and the ratio between mono and his trifluoromethylated products is dependent upon the presence or absence of catalytic cupric salts.

Synthesis of perfluoroalkylthioethers from disulfides

Abstract Perfluoroalkylthioethers are synthesized from disulfides and freons, halons or halogenoperfluoroalkanes according to: 2R F X + 2Red+ RSSR → 2R F SR + 20x This reaction was studied with aliphatic, aromatic and heteroaromatic disulfides Several reductor systems have been used. They behaved as sulfur dioxide-radical anion precursors. The initial step is interpreted by single electron transfer from this radical anion to the halide. The mechanism will be discussed. Halogenoalkylthioethers groups are very lipophilic and interesting as substituents for pharmaceutical drugs and agrochemical compounds.

Improvements in the synthesis of difluoromethanesulfonic acid

Abstract The synthesis of sodium difluoromethanesulfonate from aqueous sodium sulfite and chlorodifluoromethane, known to deliver poor and erratic yields, became more productive, more selective and reproducible when adding sodium hydroxide, even in quantities smaller than the stoichiometry. This reaction has been optimized and its carbenic nature unambiguously proved when operating in deuterated water. “Sodium diflate” has been also produced from sodium sulfite and dibromodifluoromethane. Anhydrous difluoromethanesulfonic acid was distilled from a mixture of hydrated sodium diflate, sulfuric acid and well-controlled quantities of oleum. Violent extensive decompositions occurred when using excess of thionyl chloride or sulfur trioxide. Chain mechanisms will be proposed. ‘Diflic acid’ efficiently catalyzed the condensation of acetic acid on ethylene and has been compared to triflic acid.