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 , other 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- 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 , as well as , 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 to the lytic condensation reactions and an efficient conver- exterior. sion into the target hexamethyldisiloxane. After heat treatment with acid clay, the hexa- After completion of the condensation and hydro- 20 methyldisiloxane is then brought into contact with lytic condensation reactions, the liquid is neutralized activated carbon in order to completely remove the by removing the catalyst by washing the liquid with microquantities of liberated bad smelling com- water, using the latter at 1-fold to 10-fold based on pounds by adsorption. No specific restriction is the total quantity of the liquid. At this time, placed on the activated carbon in this regard, and it water-soluble solvents will transfer into the aqueous 25 can be granular or microparticulate. With regard to phase, but since hexamethyldisiloxane is almost the procedure for contact with the activated carbon, insoluble in water, this water wash actually provides 0.01 to 5 weight percent activated carbon (based on for the secondary separation of part of the solvent. hexamethyldisiloxane) is added, mixing is carried The water-washed hexamethyldisiloxane is then out at room temperature to 100°C, and this is distilled in order to separate the remaining organic 30 followed by filtration. Alternatively, the hexamethyl- solvent and small quantities of high-boiling com- disiloxane may be continuously passed through an pounds. A packed rectification column can be used activated carbon-packed column maintained In the here, although this will depend on the nature of the above-mentioned temperature range. The second organic solvent present in the hexamethyldisiloxane, method is preferred since activated carbon present and 50 or fewer plates will be satisfactory for the 35 in the hexamethyldisiloxane can then be removed by number of separation stages. Attempts to achieve simple filtration, for example, by a cartridge-type distilled hexamethyldisiloxane purities of, for filter composed of glass fiber or plastic fiber. example, 99 weight percent or greater as the gas The hexamethyldisiloxane produced as above is chromatographic value, will not encounter particular very pure, is colorless and transparent in its external problems since this is merely a problem in the 40 appearance, and has the distinctive fresh odor of the technique of distillation. For the purposes of the hexamethyldisiloxane prepared by the hydrolysis of instant invention, the term "hexamethyldisiloxane of trimethylchlorosilane. Just as for the latter hexa- enhanced purity" refers to a distilled material methyldisiloxane, this former hexamethyldisiloxane significantly increased in hexamethyldisiloxane con- can be effectively utilized as a plasticizer in the tent from the impure hexamethyldisiloxane. That is, 45 production of silicone rubbers, as a starting material the hexamethyldisiloxane of enhanced purity can in the production of silicone compounds, as an have a purity of 99 weight percent or better as agent for treating inorganic materials to impart water compared to the purity of 50 to 60 weight percent of resistance, etc.,. the impure hexamethyldisiloxane. So that those skilled in the art can better While the hexamethyldisiloxane obtained by car- 50 understand and appreciate the instant invention, the rying out the method up to this point has a following examples are presented. The examples are satisfactory purity, the obtained hexamethyldisilox- presented to be illustrative and are not to be ane nonetheless has a distinctly unpleasant smell construed as limiting the claims of the instant due to the presence of microquantities of impurities invention. In the examples, % = wto/o in all cases. which cannot be removed by distillation. Thus, it 55 cannot be used as such in the applications of a Example 1: hexamethyldisiloxane synthesized by the usual A solution recovered as the waste solution from method of hydrolytic condensation of trimethylchlo- silylation contained 56.3% hexamethyldisiloxane rosilane, since the latter does not have this unpleas- and 19.2% dichloromethane, 11.7% trimethylmeth- ant smell. 50 oxysilane, 12.2% trimethylsilanol, and 0.6% other " as Accordingly, the present inventors thoroughly impurities. To 1 ,000 g of this solution were added 2 g axamined the elimination of this unpleasant odor, concentrated hydrochloric acid and ion-exchanged and found as a result that merely bringing this water. After mixing for 2 hours at room temperature, distilled hexamethyldisiloxane having a disagreeable the solution was washed 3 times with 1,500 ml Ddor into contact with activated carbon had little 55 ion-exchanged water to neutrality. The oil layer (890 5 0 277 825 6 g) was recovered, and contained 10.0% dichloro- filter. methane and 90.0% hexamethyldisiloxane. This liquid was placed in a 2 1 distillation set-up (equipped with a 30 cm tall glass fractionation column packed with glass Raschig rings), and distilled under 5 Claims ambient pressure to obtain 620 g distillate with a boiling point of 99° C. This was hexamethyldisiloxane 1 . A method for purifying impure hexamethyl- having a purity of 99.830/o as measured by gas disiloxane comprising as a major portion hexa- chromatography, but it had a distinctly unpleasant methyldisiloxane and as a minor portion a smell. 300 g of this hexamethyldisiloxane and 3 g 10 mixture of low-boiling organic solvents, other acid clay (K-500 from Nippon Kassei Hakudo organosilicon compounds, and odor-producing Kabushiki Kaisha) were placed in a 500 ml flask and materials, said method comprising stirred at between 90° and 100°C. for 8 hours. After (A) first, treating the impure hexamethyl- cooling to room temperature, 5 g powdered coconut disiloxane with a condensation catalyst to husk activated carbon (Kanto Kagaku Kabushiki 15 convert the other organosilicon com- Kaisha) was added. After mixing for 3 hours at room pounds to additional hexamethyldisilox- temperature, the liquid was then filtered on a glass ane; filter. A colorless and transparent hexamethyldisilox- (B) second, washing the treated impure ane with a characteristic fresh smell was obtained hexamethyldisiloxane from (A) with water; quantitatively with respect to the amount taken. 20 (C) third, separating a water phase from The bad smelling hexamethyldisiloxane obtained the washed, treated impure hexamethyl- from distillation was also directly treated with the disiloxane; coconut husk activated carbon, omitting the heat (D) fourth, distilling the washed, treated treatment with acid clay but otherwise using the impure hexamethyldisiloxane to yield hexa- same conditions as above. In this case, absolutely 25 methyldisiloxane of enhanced purity; no deodorization of the obtained hexamethyldisilox- (E) fifth, contacting the hexamethyldisi- ane was observed. loxane of enhanced purity with acid clay at a temperature of greater than about 50° C. ; Example 2: and In this example, the waste solution recovered from 30 (F) finally, contacting the hexamethyl- silylation was a hexamethyldisiloxane solution which disiloxane of enhanced purity treated in (E) contained 85% hexamethyldisiloxane, and as im- with activated carbon. purities 10% 1,4-dioxane, 1% dimethylaniline, 1% 2. A method according to Claim 1, wherein trimethylisobutoxysilane, and 3% other. 1 ,200 kg of (A) further comprises adding water to the such a solution, 15 kg concentrated hydrochloric 35 treating of the impure hexamethyldisiloxane acid, and 300 kg tap water were all placed in a 2 with the condensation catalyst. cubic meter reaction kettle, followed by stirring for 2 3. A method according to Claim 1, wherein hours and then standing. After separation, the acidic contacting the hexamethyldisiloxane of en- lower aqueous layer was removed, and the upper hanced purity treated in (E) with activated liquid layer was repeatedly washed with 200 I tap 40 carbon is carried out in a batch mode in which water to neutrality. It was then transferred to a 1 the activated carbon is filtered from the hexa- cubic meter distillation kettle equipped with a methyldisiloxane after contact. packed column (diameter = 30 cm, length = 6 m), 4. A method according to Claim 1, wherein and the hexamethyldisiloxane was then distilled. contacting the hexamethyldisiloxane of en- Hexamethyldisiloxane having a purity of 99.0% or 45 hanced purity treated in (E) with activated better was continuously distilled off (reflux ratio = 5 carbon is carried out in a continuous mode in : 1 to 10 : 1) as the fraction boiling at 99° C. into a 1 which the hexmethyldisiloxane is passed cubic meter treatment kettle. Acid clay (K-500 from through a packed bed of activated carbon. Nippon Kassei Hakudo Kabushiki Kaisha) was added to the treatment kettle at 1% based on the distillate 50 present therein, and the temperature was then raised to 80° to 90° C. with stirring. At this point, the injection of nitrogen gas from the bottom of the kettle into the liquid was initiated at a rate of 1 cubic meter per hour. These conditions were maintained 55 for 9 hours. After cooling, the acid clay was continuously filtered from the hexamethyldisiloxane, which was then continuously passed through a column (diameter = 10 cm, length = 2 m) packed with 12 60 kg activated carbon (Kuraray Coal GL8/48, a granular activated carbon from Kuraray Chemical Kabushiki Kaisha). 950 kg of a purified, deodorized hexamethyldisiloxane was obtained by filtration across a 1 micron polypropylene cartridge-type 65

4