Dimethyl(2-oxo-2-phenylethyl)-sulfonium Bromide

(1; X = Br) [5667-47-0] C10H13BrOS (MW 261.18) InChI = InChI=1S/C10H13OS.BrH/c1-12(2)8-10(11)9-6-4-3-5-7-9;/h3-7H,8H2,1-2H3;1H/q+1;/p-1 InChIKey = MOXCZQUDEPYNKM-UHFFFAOYSA-M (2; X = BF4) [24806-57-3] C10H13OSBF4 (MW 268.08) InChI = InChI=1S/C10H13OS.BF4/c1-12(2)8-10(11)9-6-4-3-5-7-9;2-1(3,4)5/h3-7H,8H2,1-2H3;/q+1;-1 InChIKey = NYDZUKNJLPHOOF-UHFFFAOYSA-N Alternate Names: (1) dimethylphenacylsulfonium bromide; (benzoylmethyl)dimethylsulfonium bromide; (2) dimethylphenacylsulfonium tetrafluoroborate; (benzoylmethyl)dimethylsulfonium tetrafluoroborate. Physical Data: (1) hygroscopic colorless plates, d 1.559 g cm−3, mp 145 °C; (2) colorless needles, mp 170–171 °C. Solubility: (1) sol in water, DMSO, EtOH; (2) sol in DMSO, EtOH, MeOH. Preparative Methods: although dimethylphenacylsulfonium bromide can be purchased from several chemical providers, it can be readily prepared via a simple substitution reaction between phenacyl bromide and dimethyl sulfide (eq 1).1 This bromide salt can be transformed to tetrafluoroborate salt by an anion exchange reaction with sodium tetrafluoroborate in acetone.2 (1) Use of highly stench and volatile dimethyl sulfide can be avoided by employing DMSO as a sulfur source.3 DMSO is first reacted with tert-butyl bromide via a SN1 mechanism to give the bromodimethylsulfonium tert-butoxide. Then the anion is exchanged to bromide, which is derived from another t-BuBr molecule. The resulting bromodimethylsulfonium bromide reacts with acetophenone to give α-bromoacetophenone, which is transformed in situ to the title compound by the reaction with the liberated dimethyl sulfide (eq 2). (2) Later, a variant of this method was reported using 3 equiv of hydrogen bromide as a bromine source instead of t-BuBr.4 Here, the title compound is obtained in 69% yield. The corresponding sulfonium chloride can be prepared in the same manner by using HCl; however, the yield is as low as 5%.5 Dimethylphenacylsulfonium iodide is synthesized from phenacyl methyl sulfide and methyl iodide.6 Handling, Storage, and Precautions: proper safety precautions include working in a laboratory fume hood while wearing safety eyewear, appropriate gloves, and a laboratory coat. Compound causes skin and eye irritation. In case of exposure to skin, flush with copious amounts of water for at least 15 min. If irritation persists, seek medical advice.