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Method for Purifying Hexamethyldisiloxane

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Method for Purifying Hexamethyldisiloxane turopaiscnes patentamt European Patent Office ® Publication number: 0 277 825 Office europeen des brevets A2 EUROPEAN PATENT APPLICATION (gj) Application number: 88300907.8 © Int. CI.4: C 07 F 7/08 © Date of filing: 03.02.88 Qg) Priority: 03.02.87 JP 23325/87 @ Inventor: Imai, Takeshi 8-18, 2-chome Sakuradai © Date of publication of application : Ichihara-shi Chiba Prefecture (JP) 10.08.88 Bulletin 88/32 Suzuki, Masahiko 1-11, 4-chome Sakuradai @ Designated Contracting States: DE FR GB Ichihara-shi Chiba Prefecture (JP) ® Applicant: Toray Silicone Company, Ltd. Takahashi, Ikuzo 8, 2-chome Muro-machi Nihonbashi 5-3, 5-chome Aobadai Chuo-ku Tokyo 103 (JP) Ichihara-shi Chiba Prefecture (JP) Toida, Shuzo 22-10, 3-chome Sakuradai Ichihara-shi Chiba Prefecture (JP) §) Representative: Lewin, John Harvey et al Elkington and Fife High Holborn House 52/54 High Holborn London WC1V6SH (GB) (§4) Method for purifying hexamethyldisiloxane. (§) A method for purifying impure hexamethyldisiloxane comprising as a major portion hexamethyldisiloxane and as a minor portion a mixture of low-boiling organic solvents, other organosilicon compounds, and odor-producing materials is described. The method comprises (A) first, treating the impure hexamethyldisiloxane with a condensation catalyst to convert the organosilicon compounds to additional hexamethyldisilox- ane; (B) second, washing the treated impure hexamethyldisi- loxane with water; (C) third, separating a water phase from the washed impure hexamethyldisiloxane; (D) fourth, distilling the washed impure hexamethyldisiloxane to yield hexamethyldisi- loxane of enhanced purity; (E) fifth, contacting the hexamethyl- disiloxane of enhanced purity with acid clay at a temperature of greater than about 50° C; and (F) finally, contacting the acid slay treated hexamethyldisiloxane of enhanced purity treated in (E) with activated carbon to yield hexamethyldisiloxane with enhanced purity and minimal unpleasant odor. undesaruckerei Berlin 1 0 277 825 2 Description METHOD FOR PURIFYING HEXAMETHYLDISILOXANE The instant invention relates to a method for in the pharmaceutical sector as a by-product from purifying hexamethyldisiloxane. More specifically the silylation using trimethylchlorosilane or hexamethyl- instant invention relates to a purification method 5 disilazane; however, even after distillation this which affords a very pure hexamethyldisiloxane, hexamethyldisiloxane continues to have a distinctly lacking any unpleasant smell, from the very impure unpleasant smell, which is caused by impurities. As a hexamethyldisiloxane ultimately recovered from the consequence, its use in the typical applications of trimethylchlorosilane and hexamethyldisilazane hexamethyldisiloxane is avoided. In the instant used as silylating agents in the pharmaceutical 10 invention's method of hexamethyldisiloxane purifica- industry. tion, the yield is substantially improved because Trimethylchlorosilane and hexamethyldisilazane distillation is carried out after monofunctional trior- are widely used as silylating agents in the pharma- ganosilane impurities in the hexamethyldisiloxane ceutical manufacturing industry, such as in the recovery liquid have been converted into hexa- production of antibiotics such as penicillin, cepha- 15 methyldisiloxane by condensation or hydrolytic con- losporin, etc.,. The hexamethyldisiloxane produced densation. Furthermore, the instant invention also and recovered as a by-product from this trimethyl- has the effect of completely eliminating the dis- chlorosilane or hexamethyldisilazane contains large agreeable odor through the joint application of an quantities of impurities, such as organic solvents, acid clay treatment and activated carbon treatment since the silyl group protective reaction is con- 20 after distillation. ducted in the presence of a low-boiling organic As a consequence, a very pure, deodorized solvent, as well as trimethylsilanol, trimethylmeth- hexamethyldisiloxane is readily produced in high oxysilane, etc.,. yields, and it can be used in the typical applications Hexamethyldisiloxane no longer functions as a known in the art for hexamethyldisiloxane. Thus, it silylating agent for pharmaceutical manufacture. 25 can be efficiently utilized in the industry, making the Also, it is technically difficult to obtain a very pure, invention very beneficial to the industry. deodorized hexamethyldisiloxane from the very In accordance with the instant invention there is impure hexamethyldisiloxane recovery liquid. The provided a method for purifying hexamethyldisilox- primary method of handling this recovery liquid is the ane under conditions that will be delineated herein. distillative recovery of a major part of the organic 30 What is described, therefore, is a method for solvent, with the residue being incinerated as an purifying impure hexamethyldisiloxane comprising industrial waste. Even when the hexamethyldisilox- as a major portion hexamethyldisiloxane and as a ane is recovered, it has a distinctly unpleasant odor minor portion a mixture of low-boiling organic which limits its use. solvents, other organosilicon compounds, and odor- The object of the instant invention is to provide a 35 producing materials, said method comprising purification method which affords a very pure, (A) first, treating the impure hexamethyldisi- deodorized hexamethyldisiloxane from the highly loxane with a condensation catalyst to convert impure hexamethyldisiloxane recovery liquid gener- the other organosilicon compounds to addi- ated as a by-product in the silylation reaction. It is tional hexamethyldisiloxane; difficult to obtain a deodorized hexamethyldisiloxane 40 (B) second, washing the treated impure from this recovery liquid by distillation only. The hexamethyldisiloxane from (A) with water; instant invention is a purification method which (C) third, separating a water phase from the affords a very pure, deodorized hexamethyldisilox- washed, treated impure hexamethyldisiloxane; ane in high yields by virtue of the incorporation of (D) fourth, distilling the washed, treated relatively simple processes. As a consequence, the 45 impure hexamethyldisiloxane to yield hexa- hexamethyldisiloxane can be used as a plasticizer in methyldisiloxane of enhanced purity; the manufacture of silicone rubbers, as a starting (E) fifth, contacting the hexamethyldisiloxane material in the preparation of silicone compounds, of enhanced purity with acid clay at a tempera- as an agent imparting water resistance to inorganic ture of greater than about 50° G.; and materials, etc.,. 50 (F) finally, contacting the hexamethyldisilox- The object of the instant invention can be ane of enhanced purity treated in (E) with achieved by a method for purifying hexamethyldisi- activated carbon. loxane which is characterized in that an acidic or The hexamethyldisiloxane recovery liquid gener- basic compound is added to the highly impure ated as a by-product from the silylation reaction hexamethyldisiloxane. The impurities are, in part, 55 contains large amounts of impurities in the form of condensed or hydrolytically condensed at room low-boiling organic solvent such as, for example, temperature or with heating. This treatment is acetone, dichloromethane, methanol, dioxane, iso- followed by a wash with water and distillation to propanol, or tetrahydrofuran, etc., as well as other afford a hexamethyldisiloxane of enhanced purity. organosilicon compounds such as, for example This hexamethyldisiloxane is then heat treated with 60 trimethylsilanol, trimethylmethoxysilane, etc.,. The acid clay and subsequently brought into contact with instant invention seeks to improve the yield by activated carbon. means of the addition, prior to distillation of the A very impure hexamethyldisiloxane is recovered recovery liquid, of a catalyst (an acidic compound or 2 o 0 277 825 4 a Dasic compound j wan suDsequent conversion or effect. However, it was found that the unpleasant impurities such as trimethylsilanol, trimethylmeth- smell could be completely eliminated by contact with oxysilane, etc., into hexamethyldisiloxane by a activated carbon after a heat treatment with acid condensation or hydrolytic condensation at room clay, thus affording a hexamethyldisiloxane having temperature or with heating. 5 the fresh smell of a hexamethyldisiloxane manufac- The condensation catalysts used here are organic tured by trimethylchlorosilane hydrolysis. or inorganic acidic or basic compounds, such as, for With regard to the conditions in the heat treatment example, hydrochloric acid, sulfuric acid, acetic acid, of the bad smelling hexamethyldisiloxane with acid para-toluenesulfonic acid, sodium hydroxide, potas- clay, the microquantities of impurities which are the sium hydroxide, or organic amines. The condensa- 10 sources of the odor can be liberated from the tion catalyst is added at between 0.01 to 1 .0 weight hexamethyldisiloxane by adding the acid clay at 0.01 percent based on the hexamethyldisiloxane re- to 10 weight percent based on hexamethyldisiloxane covery liquid, which is then subjected to condensa- and heating to between 50° and 98° C. (the boiling tion or hydrolytic condensation at temperatures point of hexamethyldisiloxane). An inert gas such as between room temperature and 100°C. The simulta- 15 nitrogen can be injected into the reactor at this time, neous addition of water at this point provides for the and in such a case part of the odor will be carried by smooth execution of the condensation and hydro- the inert gas from the treatment reactor
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