About The Preparation Of Hexamethyldisiloxane

Update:2020-06-23 11:13

Method 1: Hydrolysis of trimethylchlorosilane, water and sodium hydroxide as raw materials to synthesize hexamethyldisiloxane:

Add a certain amount of water to a 500ml three-necked flask, control the reaction temperature in a water bath, adjust the magnetic stirrer to a certain speed, then slowly add 50mL of trimethylchlorosilane with a syringe, take out the reaction solution after a certain time, after cooling, washing, After separation and vacuum distillation, the purified hexamethyldisilazane is finally obtained. The product composition and purity are analyzed by gas chromatography-mass spectrometry, and the yield is calculated. The optimal process conditions are as follows: adding 0.4mol of sodium hydroxide solid, the reaction temperature is 25℃, the reaction time is 30min, and the volume ratio of water:trimethylchlorosilane is 1:1. The highest yield of prepared hexamethyldisilazane can reach 99.95%, and the purity is as high as 99.876%.



Method 2: The method for preparing hexamethyldisiloxane using trimethylmonochlorosilane includes the following steps:

(A) Add trimethylmonochlorosilane to the enamel reactor, turn on the reactor cooling device and the bottom of the compressed air;

(B) Drip the recovered dilute hydrochloric acid into the reactor and control the temperature of the reactor at 5-35℃;

(C) After the hydrolysis reaction is completed, the hydrolysate is sent to a standing high tank for 30-60 minutes, and the lower concentrated hydrochloric acid is discharged to obtain crude hexamethyldisiloxane, in which: the lower concentrated hydrochloric acid is all exported;

(D) Repeatedly pass appropriate amount of process water to wash to remove the internal hydrochloric acid of crude hexamethyldisiloxane, recover the dilute hydrochloric acid solution generated by washing and use it all in step (A);

(E) After washing, the hexamethyldisiloxane is purified to obtain purified hexamethyldisiloxane.



Method 3: Method for preparing high-quality hexamethyldisiloxane, the steps are as follows:

(1) Add 325g of pure water to a 1L four-necked flask, add 400g of trimethylmonochlorosilane (product of Shandong Dongyue Silicone Material Co., Ltd., purity 99.540%) to pure water, by controlling the drop acceleration and change Keep the reaction temperature at 30 ℃ under hot conditions, and stir vigorously to make the linear velocity of the liquid around the container reach 8m/s. After the dropwise addition, sample and analyze by gas chromatography. Analysis results: Trimethylmonochlorosilane: 5.949%, trimethylsilanol: 0.138%, hexamethyldisiloxane: 93.204%.

2) Gas chromatography analysis results after stirring for 1 h: trimethylmonochlorosilane: 1.093%, trimethylsilanol: 0.162%, hexamethyldisiloxane: 97.890%. The lower acid water was separated and the concentration of hydrochloric acid was determined to be 30.86% by titration.

(3) Add 325g of pure water to the oil phase, wash with high-speed stirring for 0.5h, gas chromatography analysis results: trimethylmonochlorosilane: 0.001%, trimethylsilanol: 0.180%, hexamethyldisiloxane: 98.978%. Total chlorine content: 780ppm. After the water washing process was repeated one more time, the total chlorine content dropped to 17 ppm. The second dilute acid water obtained during the water washing process is used for the first water washing, and the acid water after the first water washing is used for the previous hydrolysis.

(4) The resulting oil phase is transferred to a 5L glass spring packed rectification column for rectification. Hexamethyldisiloxane can be obtained by collecting fractions from 99 to 102°C. Among them, the yield reached 97.5%, hexamethyldisiloxane 99.99%, trimethylmonochlorosilane could not be detected (less than 1ppm), the total chlorine content could not be detected (less than 1ppm), silicon hydroxyl group (trimethyl silicon Alcohol content) 0.01%, moisture content of 38ppm products.



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