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ChemicalBook CAS DataBase List 2,4,6,8-Tetramethylcyclotetrasiloxane

2,4,6,8-Tetramethylcyclotetrasiloxane synthesis

11synthesis methods
The synthesis process of 2,4,6,8-Tetramethylcyclotetrasiloxane is as follows. A 1-L four-necked flask equipped with a thermometer, stirrer, column packed with cylindrical glass of about 1x1 mm to a height of 500 mm, water-cooled condenser, outlet tube, and distillate receiver was connected to a vacuum pump. To the flask were fed 100 g of trimethylsiloxy end-capped dimethylpolysiloxane having a viscosity of 10,000 centistokes at 25°C and 1.0 g of the catalyst (i) synthesized above, after which agitation was commenced. While the flask interior was kept under a reduced pressure of 50 mmHg, the flask was heated at 250-260°C using a mantle heater. A fraction distilled out for 14 hours was collected (45 g). The residue (31 g) was a clear liquid. yeild= 52%
Yield:- Reaction Conditions:

Stage #1:Dichloromethylsilane;water at 33; under 3863.02 Torr;
Stage #2:dodecylbenzenesulphonic acid in isopar P at 20; for 3 h;


Methyldichlorosilane CH3SICL2 was mixed with a stoichiometric equivalent of water, i. e. 0.5 mole of water per mole of silicon bonded chlorine, in a steam heated continuous hydrolysis reactor. The hydrolysis reactor was maintained at 60 psig and the temperature of the reactor was controlled such that the hydrolyzate exiting the reactor was at a temperature of about 33°C. The hydrolyzate exiting the reactor was analysed by gas chromatography (GC) using a flame ionisation detector (FID) and found to comprise about 95 weight percent linear chlorine end-terminated methylhydrogensiloxane species and about five weight percent cyclic methylhydrogensiloxanes species. The hydrolyzate was diluted to about 20% IN ISOPAR P'hydrocarbon solvent containing 0. 1% dodecylbenzenesulphonic acid catalyst. Excess HC1 gas from the hydrolysis reaction was collected for re-use. [0021] The diluted hydrolyzate containing catalyst was fed through a simple rearrangement reactor tank at ambient temperature and pressure. Residence time of the diluted hydrolyzate in the reactor was about 3 hours. GC-FID analysis of the product exiting the rearrangement reactor showed the siloxane component to consist of about 70 weight percent linear chlorine end-terminated methylhydrogensiloxane species and about 30 weight percent cyclic methylhydrogensiloxane species. [0022] The product from the rearrangement reactor was heated to drive off aqueous HC1, stripped in flash drums under vacuum and then vacuum distilled and the cyclic species and low-boiling linear species taken overhead. The bottom fraction was cooled and recycled to the rearrangement reactor. [0023] Residual chlorine in the overhead fraction from the flash distillation (the crude product) was removed by contact with a calcium carbonate calcium chloride water system. The product was finally dried in a magnesium oxide bed. The recovered cyclic methylhydrogensiloxane fraction was analysed by GC-FID and found to comprise 99.7 weight percent cyclic methylhydrogensiloxanes of the tetramer, pentamer, and hexamer species. The process was run continuously for about 20 days.

References: DOW CORNING CORPORATION WO2005/5441, 2005, A2 Location in patent:Page/Page column 6; 7

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