Phenylsulfur trifluoride

Submitted by Wiixiam A. Sheppard 1 Checked by E. S. Glazer and John D. Roberts 

four-necked, round-bottomed flask equipped with reflux condenser, sealed stirrer, thermometer, and solid addition funnel and protected from atmospheric moisture with a Drierite guard tube is carefully dried and flushed with a dry inert gas (Note 1). The flask is charged with 453 g. (3.1 moles) of silver difluoride (Note 2) and 500 ml. of l,l,2-trichloro-l,2,2-trifluoroethane (Note 3), and phenyl disulfide (100 g., 0.458 mole) (Note 4) is weighed into the solid addition funnel. The stirrer is started, and phenyl disulfide is added to the slurry in small portions. An exothermic reaction occurs, and after the addition of several portions the reaction mixture reaches a temperature of 40° (Note 5). By intermittent use of a cooling bath and by adjusting the rate of addition of the disulfide, the reaction temperature may be maintained between 35° and 40°. The addition of the phenyl disulfide requires 45-60 minutes. On completion of the addition the suspension of black silver difluoride has been converted to yellow silver monofluoride, and the exothermic reaction gradually subsides. The reaction mixture is stirred for an additional 15—30 minutes without external cooling and then quickly heated to reflux. 

The reaction mixture is filtered hot through a fluted filter paper 

The equipment should be dried carefully by the techniques normally employed when preparing for a Grignard reaction. Dry nitrogen gas was normally employed to flush the apparatus, but any dry inert atmosphere, or dry air, could be employed. 

A technical grade of silver difluoride (approximately 85%) is available from Harshaw Chemical Company. Better grades of silver difluoride are available and may be employed. It is important that the silver difluoride be a black powder. If the material is light brown and lumpy, a lower yield of product may be obtained. Normally, the contents of a 1-lb. can (approximately 435-470 g.) are employed. 

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A 45-cm. spinning band column was employed by the submitter, but any distillation column with a low holdup may be used. Since the products have widely different boiling points, careful fractionation during distillation is not needed. Because the phenylsulfur trifluoride and benzenesulfinyl fluoride slowly attack glass, all equipment should be rinsed with water and acetone immediately after use to minimize etching. 

Sulfur tetrafluoride provides an inexpensive method for selectively converting a carbonyl to a difluoromethyl group. However, the reactions involving sulfur tetrafluoride, in general, require pressure equipment constructed of fluorine-resistant material such as Hastelloy-C bombs.8 Phenylsulfur trifluoride may be used to advantage for the same reaction, where small amounts are involved, since the reaction may be run at atmospheric pressure in glass, polyethylene, or metal containers. 

Caution Phenylsulfur trifluoride and by-products (e.g., hydrogen fluoride from hydrolysis) are toxic, and all manipulations should be carried out in a good hood. Silva difluoride is a powerful oxidative fluorinating agent and reacts vigorously with many organic materials. These reagents should not be allowed to come in contact with the skin. 

The Freon solvent may be removed under reduced pressure in order to shorten the distillation time. Since phenylsulfur trifluoride attacks glass, the total time involved in the preparation and distillation in the glass equipment should be kept to a maximum of a few hours. It is recommended that the column be changed after distillation of the Freon . If the preparation cannot be completed within a day, the Freon solution of crude phenylsulfur trifluoride may be stored in polyethylene bottles overnight. 

In contact with moisture of glass, phenylsulfur trifluoride develops pink, green, or bluish colors. A small amount of discoloration does not appear to affect the quality. Phenylsulfur trifluoride prepared in glass equipment always contains a few percent of phenylsulfinyl fluoride. The amount of this impurity depends on the care taken to exclude moisture during preparation and manipulation. 

Phenylsulfur trifluoride slowly oozes through polyethylene bottles after storage for several days. However, a sample of phenylsulfur trifluoride has been stored in a bottle of Teflon for several years without decomposition. Storage in a dry atmosphere in a well-ventilated area is recommended. 

Phenylsulfur trifluoride has been prepared only by the present method.8,4... 

Caulionl Phenylsulfur trifluoride is toxic, and this reaction should be carried out in a good hood. The reagent should not be allowed to come in contact with the skin. 

The reaction of aliphatic aldehydes and ketones with organosulfur trifluoridcs is exothermic and is advantageously conducted in dichloromethanc or acetonitrile with a small amount of sodium fluoride added. The reaction with ketones can exhibit an induction period of several hours. Benzaldehyde, when treated with phenylsulfur trifluoride, yields (difluoromethyl)ben-zene (8).26 27... 

These reactions can be carried out at low cost, but require a pressure vessel lined with Hastelloy-C stainless steel, storage vessels of polyethylene or other HF-resistant material, and a specialized technique. For general laboratory use the preferred reagent is phenylsulfur trifluoride. 

PhenylsulfinyIethanol, 475 p-Phenylsulfonylbenzoyl chloride, 849 Phenylsulfur trifluoride, 849,1006,1124 8-Phenyltheophylline, 54 o-Phenyl-o-toluic add, 719 Phenyltolylmethane, 162... 

In 1952, Wittig and Fritz reported that treatment of a triphenylsulfonium salt with phenyllithium afforded directly diphenylsulfide (3) and biphenyl (4). They also showed that treatment of the triphenylsulfonium salt with trityl sodium led to tetraphenylmethane, although in poor yield. Later, in 1962, Sheppard described the reaction of phenyllithium with phenylsulfur trifluoride or with sulfur tetrafluoride at - 80 C, which afforded biphenyl and diphenylsulfide. At the same time, Franzen et al. suggested that a tetracoordinate sulfurane was intermediately formed and collapsed to lead to the ligand coupling products. i... 

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