Patent Watch

November 9, 2009

Here’s a safe and inexpensive route to arylsulfur pentafluorides. T. Umemoto discloses the production of a wide range of compounds that can be used to introduce SF₅ groups into organic molecules. The product molecules are useful for preparing liquid crystals and bioactive chemicals such as fungicides, herbicides, and insecticides.

The inventor claims that the known methods for producing arylsulfur pentafluorides are impractical. For example, they involve expensive reagents such as XeF₂, use toxic materials, and give low product yields.

The figure summarizes one of the methods used to prepare arylsulfur pentafluorides. In the first of two stages, chlorination of disulfide 1 with chlorine gas in the presence of KF gives chlorofluorosulfur compound 2. In the case of Ar = Ph, the product is obtained as an oil in 88% yield. In the workup of this stage, dry solid KF is added to the filtrate to prevent possible decomposition of the product. Yields of other aryl products range from 60% for Ar = p-C₆H₄NO₂ to 86% for Ar = C₆F₅. Compound 2 has the trans configuration, as confirmed by ¹⁹F NMR.

In the second stage, 2 is heated with ZnF₂, and desired product 3 is recovered by vacuum distillation. For Ar = Ph, the yield is 75%; yields for other derivatives vary from 36% for p-C₆H₄NO₂ to 79% for p-C₆H₄Br. An alternative for the second stage is the use of HF in pyridine. For Ar = Ph, the reaction is carried out at room temperature for 1 h, then at 50 °C for 3 h. ¹⁹F NMR shows that product 3 is produced in 93% yield.

Arylsulfur pentafluorides can be prepared from thiophenols instead of disulfides by using the same procedure. Chlorination of PhSH gives 2 in 83% yield. The inventor also describes procedures for the second stage that use fluorides other than ZnF₂. Examples are given for the use of SbF₃, SbF₅, TiF₄, SnF₄, and CuF. The yields are lower, ranging from 33 to 57%. The use of BF₃ with 2 (Ar = Ph) gives a polymeric residue and no detectable 3, but HBF₄·OEt₂ gives 3 in 40% yield.

The patent contains more than 30 examples. ¹⁹F NMR data are provided for all of the prepared compounds. The process avoids the use of expensive or toxic reagents and can be applied to a wide range of substrates. (IM&T Research [Denver]. US Patent 7,592,491, Sept. 22, 2009; Keith Turner)

View patent information from CAS.

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