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Method for Purifying Hexamethyldisiloxane

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Method for Purifying Hexamethyldisiloxane ~" ' MM II II II II II II III II II II II I II J European Patent Office _____ © Publication number: 0 277 825 B1 Office_„. europeen des brevets EUROPEAN PATENT SPECIFICATION © Date of publication of patent specification: 16.03.94 © Int. CI.5: C07F 7/08 © Application number: 88300907.8 @ Date of filing: 03.02.88 © Method for purifying hexamethyldisiloxane. © Priority: 03.02.87 JP 23325/87 © Proprietor: Toray Silicone Company, Ltd. 8, 2-chome Muro-machi @ Date of publication of application: Nihonbashi 10.08.88 Bulletin 88/32 Chuo-ku Tokyo 103(JP) © Publication of the grant of the patent: @ Inventor: Imai, Takeshi 16.03.94 Bulletin 94/11 8-18, 2-chome Sakuradai © Designated Contracting States: Ichihara-shi Chiba Prefecture(JP) DE FR GB Inventor: Suzuki, Masahiko 1-11, 4-chome © References cited: Sakuradai EP-A- 0 059 846 Ichihara-shi Chiba Prefecture(JP) EP-A- 0 223 210 Inventor: Takahashi, Ikuzo US-A- 4 156 689 5-3, 5-chome US-A- 4 210 496 Aobadai Ichihara-shi Chiba Prefecture(JP) Inventor: Toida, Shuzo 22-10, 3-chome Sakuradai Ichihara-shi Chiba Prefecture(JP) © Representative: Lewin, John Harvey et al 00 Elkington and Fife House m Prospect CM 8 Pembroke Road oo Sevenoaks, Kent TN13 1XR (GB) CM Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid (Art. 99(1) European patent convention). Rank Xerox (UK) Business Services (3. 10/3.09/3.3.3) 1 EP 0 277 825 B1 2 Description lowed by a wash with water and distillation to afford a hexamethyldisiloxane of enhanced purity. This The instant invention relates to a method for hexamethyldisiloxane is then heat treated with acid purifying hexamethyldisiloxane. More specifically clay and subsequently brought into contact with the instant invention relates to a purification method 5 activated carbon. which affords a very pure hexamethyldisiloxane, A very impure hexamethyldisiloxane is recov- lacking any unpleasant smell, from the very impure ered in the pharmaceutical sector as a by-product hexamethyldisiloxane ultimately recovered from the from silylation using trimethylchlorosilane or hex- trimethylchlorosilane and hexamethyldisilazane amethyldisilazane; however, even after distillation used as silylating agents in the pharmaceutical io this hexamethyldisiloxane continues to have a dis- industry. tinctly unpleasant smell, which is caused by impuri- Trimethylchlorosilane and hexamethyldisilazane ties. As a consequence, its use in the typical ap- are widely used as silylating agents in the phar- plications of hexamethyldisiloxane is avoided. In maceutical manufacturing industry, such as in the the instant invention's method of hexamethyldisilox- production of antibiotics such as penicillin, 75 ane purification, the yield is substantially improved cephalosporin, etc.,. The hexamethyldisiloxane pro- because distillation is carried out after monofunc- duced and recovered as a by-product from this tional triorganosilane impurities in the hexamethyl- trimethylchlorosilane or hexamethyldisilazane con- disiloxane recovery liquid have been converted into tains large quantities of impurities, such as organic hexamethyldisiloxane by condensation or hydrolytic solvents, since the silyl group protective reaction is 20 condensation. Furthermore, the instant invention conducted in the presence of a low-boiling organic also has the effect of completely eliminating the solvent, as well as trimethylsilanol, trimethyl- disagreeable odor through the joint application of methoxysilane, etc.,. an acid clay treatment and activated carbon treat- Hexamethyldisiloxane no longer functions as a ment after distillation. silylating agent for pharmaceutical manufacture. 25 As a consequence, a very pure, deodorized Also, it is technically difficult to obtain a very pure, hexamethyldisiloxane is readily produced in high deodorized hexamethyldisiloxane from the very im- yields, and it can be used in the typical applica- pure hexamethyldisiloxane recovery liquid. The pri- tions known in the art for hexamethyldisiloxane. mary method of handling this recovery liquid is the Thus, it can be efficiently utilized in the industry, distillative recovery of a major part of the organic 30 making the invention very beneficial to the industry. solvent, with the residue being incinerated as an In accordance with the instant invention there is industrial waste. Even when the hexamethyldisilox- provided a method for purifying hexamethyldisilox- ane is recovered, it has a distinctly unpleasant odor ane under conditions that will be delineated herein. which limits its use (US-A-4 210 496, EP-A-0 059 What is described, therefore, is a method for pu- 846). 35 rifying impure hexamethyldisiloxane comprising as The object of the instant invention is to provide a major portion hexamethyldisiloxane and as a mi- a purification method which affords a very pure, nor portion a mixture of low-boiling organic sol- deodorized hexamethyldisiloxane from the highly vents, other organosilicon compounds, and odor- impure hexamethyldisiloxane recovery liquid gen- producing materials, said method comprising erated as a by-product in the silylation reaction. It 40 (A) first, treating the impure hexamethyldisilox- is difficult to obtain a deodorized hexamethyl- ane with a condensation catalyst to convert the disiloxane from this recovery liquid by distillation other organosilicon compounds to additional only. The instant invention is a purification method hexamethyldisiloxane; which affords a very pure, deodorized hexamethyl- (B) second, washing the treated impure hex- disiloxane in high yields by virtue of the incor- 45 amethyldisiloxane from (A) with water; poration of relatively simple processes. As a con- (C) third, separating a water phase from the sequence, the hexamethyldisiloxane can be used washed, treated impure hexamethyldisiloxane; as a plasticizer in the manufacture of silicone rub- (D) fourth, distilling the washed, treated impure bers, as a starting material in the preparation of hexamethyldisiloxane to yield hexamethyldisilox- silicone compounds, as an agent imparting water 50 ane of enhanced purity; resistance to inorganic materials, etc.,. (E) fifth, contacting the hexamethyldisiloxane of The object of the instant invention can be enhanced purity with acid clay at a temperature achieved by a method for purifying hexamethyl- of greater than about 50 ° C; and disiloxane which is characterized in that an acidic (F) finally, contacting the hexamethyldisiloxane or basic compound is added to the highly impure 55 of enhanced purity treated in (E) with activated hexamethyldisiloxane. The impurities are, in part, carbon. condensed or hydrolytically condensed at room The hexamethyldisiloxane recovery liquid gen- temperature or with heating. This treatment is fol- erated as a by-product from the silylation reaction 2 3 EP 0 277 825 B1 4 contains large amounts of impurities in the form of compared to the purity of 50 to 60 weight percent low-boiling organic solvent such as, for example, of the impure hexamethyldisiloxane. acetone, dichloromethane, methanol, dioxane, While the hexamethyldisiloxane obtained by isopropanol, or tetrahydrofuran, etc., as well as carrying out the method up to this point has a other organosilicon compounds such as, for exam- 5 satisfactory purity, the obtained hexamethyldisilox- ple trimethylsilanol, trimethylmethoxysilane, etc.,. ane nonetheless has a distinctly unpleasant smell The instant invention seeks to improve the yield by due to the presence of microquantities of impurities means of the addition, prior to distillation of the which cannot be removed by distillation. Thus, it recovery liquid, of a catalyst (an acidic compound cannot be used as such in the applications of a or a basic compound) with subsequent conversion io hexamethyldisiloxane synthesized by the usual of impurities such as trimethylsilanol, trimethyl- method of hydrolytic condensation of trimethylch- methoxysilane, etc., into hexamethyldisiloxane by a lorosilane, since the latter does not have this un- condensation or hydrolytic condensation at room pleasant smell. temperature or with heating. Accordingly, the present inventors thoroughly The condensation catalysts used here are or- is examined the elimination of this unpleasant odor, ganic or inorganic acidic or basic compounds, such and found as a result that merely bringing this as, for example, hydrochloric acid, sulfuric acid, distilled hexamethyldisiloxane having a disagree- acetic acid, para-toluenesulfonic acid, sodium hy- able odor into contact with activated carbon had droxide, potassium hydroxide, or organic amines. little effect. However, it was found that the unpleas- The condensation catalyst is added at between 20 ant smell could be completely eliminated by con- 0.01 to 1.0 weight percent based on the hex- tact with activated carbon after a heat treatment amethyldisiloxane recovery liquid, which is then with acid clay, thus affording a hexamethyldisilox- subjected to condensation or hydrolytic condensa- ane having the fresh smell of a hexamethyldisilox- tion at temperatures between room temperature ane manufactured by trimethylchlorosilane hydroly- and 100°C. The simultaneous addition of water at 25 sis. this point provides for the smooth execution of the With regard to the conditions in the
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