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 filing: 03.02.88

© 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)

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 hexamethyldisiloxane 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 heat treat- condensation and hydrolytic condensation reac- ment of the bad smelling hexamethyldisiloxane with tions and an efficient conversion into the target acid clay, the microquantities of impurities which hexamethyldisiloxane. are the sources of the odor can be liberated from After completion of the condensation and 30 the hexamethyldisiloxane by adding the acid clay hydrolytic condensation reactions, the liquid is neu- at 0.01 to 10 weight percent based on hexamethyl- tralized by removing the catalyst by washing the disiloxane and heating to between 50° and 98 °C. liquid with water, using the latter at 1-fold to 10-fold (the boiling point of hexamethyldisiloxane). An inert based on the total quantity of the liquid. At this gas such as nitrogen can be injected into the time, water-soluble solvents will transfer into the 35 reactor at this time, and in such a case part of the aqueous phase, but since hexamethyldisiloxane is odor will be carried by the inert gas from the almost insoluble in water, this water wash actually treatment reactor to the exterior. provides for the secondary separation of part of the After heat treatment with acid clay, the hex- solvent. amethyldisiloxane is then brought into contact with The water-washed hexamethyldisiloxane is 40 activated carbon in order to completely remove the then distilled in order to separate the remaining microquantities of liberated bad smelling com- organic solvent and small quantities of high-boiling pounds by adsorption. No specific restriction is compounds. A packed rectification column can be placed on the activated carbon in this regard, and it used here, although this will depend on the nature can be granular or microparticulate. With regard to of the organic solvent present in the hexamethyl- 45 the procedure for contact with the activated carbon, disiloxane, and 50 or fewer plates will be satisfac- 0.01 to 5 weight percent activated carbon (based tory for the number of separation stages. Attempts on hexamethyldisiloxane) is added, mixing is car- to achieve distilled hexamethyldisiloxane purities ried out at room temperature to 100°C, and this is of, for example, 99 weight percent or greater as the followed by filtration. Alternatively, the hexamethyl- gas chromatographic value, will not encounter par- 50 disiloxane may be continuously passed through an ticular problems since this is merely a problem in activated carbon-packed column maintained in the the technique of distillation. For the purposes of the above-mentioned temperature range. The second instant invention, the term "hexamethyldisiloxane of method is preferred since activated carbon present enhanced purity" refers to a distilled material sig- in the hexamethyldisiloxane can then be removed nificantly increased in hexamethyldisiloxane con- 55 by simple filtration, for example, by a cartridge- tent from the impure hexamethyldisiloxane. That is, type filter composed of glass fiber or plastic fiber. the hexamethyldisiloxane of enhanced purity can The hexamethyldisiloxane produced as above have a purity of 99 weight percent or better as is very pure, is colorless and transparent in its

3 5 EP 0 277 825 B1 6 external appearance, and has the distinctive fresh 3% other. 1,200 kg of such a solution, 15 kg odor of the hexamethyldisiloxane prepared by the concentrated hydrochloric acid, and 300 kg tap hydrolysis of trimethylchlorosilane. Just as for the water were all placed in a 2 cubic meter reaction latter hexamethyldisiloxane, this former hex- kettle, followed by stirring for 2 hours and then amethyldisiloxane can be effectively utilized as a 5 standing. After separation, the acidic lower aqueous plasticizer in the production of silicone rubbers, as layer was removed, and the upper liquid layer was a starting material in the production of silicone repeatedly washed with 200 I tap water to neutral- compounds, as an agent for treating inorganic ma- ity. It was then transferred to a 1 cubic meter terials to impart water resistance, etc.,. distillation kettle equipped with a packed column So that those skilled in the art can better un- io (diameter = 30 cm, length = 6 m), and the hex- derstand and appreciate the instant invention, the amethyldisiloxane was then distilled. Hexamethyl- following examples are presented. The examples disiloxane having a purity of 99.0% or better was are presented to be illustrative and are not to be continuously distilled off (reflux ratio = 5 : 1 to 10 : construed as limiting the claims of the instant in- 1) as the fraction boiling at 99 °C. into a 1 cubic vention. In the examples, % = wt% in all cases. is meter treatment kettle. Acid clay (K-500 from Nip- Example 1 : A solution recovered as the waste pon Kassei Hakudo Kabushiki Kaisha) was added solution from silylation contained 56.3% hex- to the treatment kettle at 1 % based on the distillate amethyldisiloxane and 19.2% dichloromethane, present therein, and the temperature was then 11.7% trimethylmethoxysilane, 12.2% trimethyl- raised to 80° to 90 °C. with stirring. At this point, silanol, and 0.6% other as impurities. To 1,000 g of 20 the injection of nitrogen gas from the bottom of the this solution were added 2 g concentrated hy- kettle into the liquid was initiated at a rate of 1 drochloric acid and ion-exchanged water. After mix- cubic meter per hour. These conditions were main- ing for 2 hours at room temperature, the solution tained for 9 hours. was washed 3 times with 1,500 ml ion-exchanged After cooling, the acid clay was continuously water to neutrality. The oil layer (890 g) was recov- 25 filtered from the hexamethyldisiloxane, which was ered, and contained 10.0% dichloromethane and then continuously passed through a column (diam- 90.0% hexamethyldisiloxane. This liquid was eter = 10 cm, length = 2 m) packed with 12 kg placed in a 2 I distillation set-up (equipped with a activated carbon (Kuraray Coal GL8/48, a granular 30 cm tall glass fractionation column packed with activated carbon from Kuraray Chemical Kabushiki glass Raschig rings), and distilled under ambient 30 Kaisha). 950 kg of a purified, deodorized hex- pressure to obtain 620 g distillate with a boiling amethyldisiloxane was obtained by filtration across point of 99 ° C. This was hexamethyldisiloxane hav- a 1 micron polypropylene cartridge-type filter. ing a purity of 99.83% as measured by gas chromatography, but it had a distinctly unpleasant Claims smell. 300 g of this hexamethyldisiloxane and 3 g 35 acid clay (K-500 from Nippon Kassei Hakudo 1. A method for purifying impure hexamethyl- Kabushiki Kaisha) were placed in a 500 ml flask disiloxane comprising as a major portion hex- and stirred at between 90° and 100°C. for 8 amethyldisiloxane and as a minor portion a hours. After cooling to room temperature, 5 g pow- mixture of low-boiling organic solvents, other dered coconut husk activated carbon (Kanto 40 organosilicon compounds, and odor-producing Kagaku Kabushiki Kaisha) was added. After mixing materials, said method comprising for 3 hours at room temperature, the liquid was (A) first, treating the impure hexamethyl- then filtered on a glass filter. A colorless and trans- disiloxane with a condensation catalyst to parent hexamethyldisiloxane with a characteristic convert the other organosilicon compounds fresh smell was obtained quantitatively with respect 45 to additional hexamethyldisiloxane; to the amount taken. (B) second, washing the treated impure hex- The bad smelling hexamethyldisiloxane ob- amethyldisiloxane from (A) with water; tained from distillation was also directly treated with (C) third, separating a water phase from the the coconut husk activated carbon, omitting the washed, treated impure hexamethyldisilox- heat treatment with acid clay but otherwise using 50 ane; the same conditions as above. In this case, ab- (D) fourth, distilling the washed, treated im- solutely no deodorization of the obtained hex- pure hexamethyldisiloxane to yield hexamethyldisiloxane was observed. amethyldisiloxane of enhanced purity; Example 2: In this example, the waste solution (E) fifth, contacting the hexamethyldisilox- recovered from silylation was a hexamethyldisilox- 55 ane of enhanced purity with acid clay at a ane solution which contained 85% hexamethyl- temperature of greater than about 50 °C; disiloxane, and as impurities 10% 1,4-dioxane, 1% and dimethylaniline, 1% trimethylisobutoxysilane, and

4 7 EP 0 277 825 B1 8

(F) finally, contacting the hexamethyldisilox- Stufe (A) Wasser zusetzt. ane of enhanced purity treated in (E) with activated carbon. 3. Verfahren nach Anspruch 1, wobei man das Hexamethyldisiloxan von hoherer Reinheit in 2. A method according to Claim 1, wherein (A) 5 der Stufe (E) absatzweise mit Aktivkohle in further comprises adding water to the treating Beruhrung bringt und die Aktivkohle nach dem of the impure hexamethyldisiloxane with the Kontakt von dem Hexamethyldisiloxan abfil- condensation catalyst. triert.

3. A method according to Claim 1, wherein con- 10 4. Verfahren nach Anspruch 1, wobei man das tacting the hexamethyldisiloxane of enhanced Hexamethyldisiloxan von hoherer Reinheit in purity treated in (E) with activated carbon is der Stufe (E) kontinuierlich mit Aktivkohle in carried out in a batch mode in which the Beruhrung bringt, indem man das Hexymethyl- activated carbon is filtered from the hex- disiloxan ein Festbett (packed bed) aus Aktiv- amethyldisiloxane after contact. 15 kohle passieren Ial3t.

4. A method according to Claim 1, wherein con- Revendicatlons tacting the hexamethyldisiloxane of enhanced purity treated in (E) with activated carbon is 1. Un procede pour la purification d'hexamethyl- carried out in a continuous mode in which the 20 disiloxane impur comprenant une majeure par- hexmethyldisiloxane is passed through a tie d'hexamethyldisiloxane et une partie mineu- packed bed of activated carbon. re d'un melange de solvants organiques a bas point d'ebullition, d'autres composes organosi- Patentanspruche licies et de matieres odorantes, ledit procede 25 comprenant : 1. Verfahren zur Reinigung von unreinem Hexa- (A) premierement, le traitement de I'hexamethyldisiloxan, das einen groBeren Anteil He- methyldisiloxane impur avec un catalyseur xamethyldisiloxan und einen geringeren Anteil de condensation pour convertir les autres eines Gemisches aus niedrigsiedenden L6- composes organosilicies en hexamethyldisi- sungsmitteln, anderen Organosiliziumverbin- 30 loxane supplemental ; dungen und Geruch erzeugenden Stoffen ent- (B) deuxiemement, le lavage de I'hexame- halt, bei dem man thyldisiloxane impur traite en (A) avec de (A) erstens das unreine Hexamethyldisiloxan I'eau ; mit einem Kondensationskatalysator behan- (C) troisiemement, la separation d'une pha- delt, urn die anderen Organosiliziumverbin- 35 se aqueuse de I'hexamethyldisiloxane impur dungen in zusatzliches Hexamethyldisiloxan traite lave ; umzuwandeln; (D) quatriemement, la distillation de I'hexa- (B) zweitens das behandelte unreine Hexa- methyldisiloxane impur traite lave pour ob- methyldisiloxan aus der Stufe (A) mit Was- tenir de I'hexamethyldisiloxane d'une purete ser wascht; 40 amelioree ; (C) drittens eine wasserige Phase von dem (E) cinquiemement, la mise en contact de gewaschenen, behandelten unreinen Hexa- I'hexamethyldisiloxane de purete amelioree methyldisiloxan abtrennt; avec de I'argile acide a une temperature (D) viertens das gewaschene, behandelte superieure a environ 50 0 C ; et unreine Hexamethyldisiloxan destilliert, urn 45 (F) enfin, la mise en contact de I'hexame- ein Hexamethyldisiloxan von hoherer Rein- thyldisiloxane de purete amelioree traitee en heit zu erhalten; (E) avec du charbon actif. (E) funftens das Hexamethyldisiloxan von hoherer Reinheit bei einer Temperatur ober- 2. Un procede selon la revendication 1, dans halb von etwa 50 °C mit saurem Ton (acid 50 lequel (A) comprend en outre I'addition d'eau clay) in Beruhrung bringt; und au traitement de I'hexamethyldisiloxane impur (F) schlieBlich das in der Stufe (E) behan- avec le catalyseur de condensation. delte Hexamethyldisiloxan von hoherer Reinheit mit Aktivkohle in Beruhrung bringt. 3. Un procede selon la revendication 1, dans 55 lequel la mise en contact de I'hexamethyldisi- 2. Verfahren nach Anspruch 1, wobei man dem loxane de purete amelioree traite en (E) avec unreinen Hexamethyldisiloxan bei der Behand- du charbon actif est realisee en mode disconti- lung mit dem Kondensationskatalysator in der nu, ou le charbon actif est separe par filtration

5 EP 0 277 825 B1 10 de I'hexamethyldisiloxane apres contact.

Un procede selon la revendication 1, dans lequel la mise en contact de I'hexamethyldisiloxane de purete amelioree traite en (E) avec du charbon actif est realisee en continu, I'hexamethyldisiloxane etant passe au travers d'un lit tasse de charbon actif.