DD217814A1 - PROCESS FOR PREPARING LOW VISCOSES, STORAGEABLE DIORGANOPOLYSILOXANES - Google Patents

Abstract

The invention relates to a process for the preparation of low-viscosity, storable diorganopolysiloxanes with simultaneous recovery of directly usable for synthesis purposes, gaseous hydrogen chloride. This goal is achieved by subjecting diorganodichlorosilanes to a discontinuous or continuous hydrolysis in a solution of ethylene glycol and concentrated hydrochloric acid saturated with hydrogen chloride, followed by a subsequent treatment with gaseous hydrogen chloride or aqueous hydrochloric acid. The recovered diorganopolysiloxanes are intermediates z. B. for the production of silicone oils and silicone rubber.

Description

Ti tel of the invention

Process for the preparation of low-viscosity, storable diorganopolysiloxanerio - '

-Ause of the invention

The invention relates to a process for the preparation of low-viscosity, storable diorganopolysiloxanes with 'simultaneous production of for synthesis purposes directly>. usable, gaseous hydrogen chloride. , The polysiloxanes are Zv ischenprodukte z. B. for the production of silicone gels and silicone rubber *

Characteristics of the acclaimed technical solutions . Diorganopolysiloxanes are preferably selected by hydrolysis of diorganochlorosilanes. Ss are for a variety of process variants, according to a predetermined objective diorganopolysiloxanes are prepared with certain parameters. One of these parameters is the ratio of the linear to cyclic ratio. In his book "Chemistry and Technology of Silicones," NOLL points to a way to increase the proportion of oyclene. "Sr writes that the addition of alcohols, such as ethanol or methanol, to the hydrolysis medium can increase the proportion of cyano. Later, however, this was also the case with the hydroly-

Attention paid to the resulting hydrogen chloride. It has been claimed that it should be obtained in the gas phase with high purity, so that it can be used immediately for post-purification for synthesis purposes. In DE-AS 1? 95 182, such a process is described.

The hydrolysis is carried out at temperatures above the boiling point of the diorganodichlorosilane and of the water so that the hydrogen chloride which forms is gaseous.

Fach ÄP 63 648 is a preparation of diorganopolysiloxanes with simultaneous recovery of gaseous hydrogen chloride possible by using concentrated hydrochloric acid as the hydrolysis medium. However, the diorganopolysiloxanes prepared by this process contain a high proportion of linears, which are short-chained as a result of the low reaction temperature which sets in. As a result, the content of alpha-omega-terminal 0H groups is very high. Diorganopolysiloxane prepared in this way tends to undergo uncontrolled postcondensation which, inter alia, _{results in} an undesirable increase in viscosity during storage,.

Object of the invention _:

The invention is a process for the preparation of low-viscosity diorganopolysiloxanes which do not change their low viscosity during storage for months. At the same time, the hydrogen chloride obtained during the hydrolysis is to be recovered in gaseous form and in such high purity that it can be used immediately as synthesis gas. , .. '. , ; , , Explanation of the essence of the invention

The inventive ZieL is achieved when the manufacture, diorganopolysiloxanes doxane [...] according to the following process. he follows:

Diorganodichlorosilane we./den in a saturated with hydrogen chloride solution of iü to 95% by weight of ethylene glycol and 5 to 90 mass- '' / © of concentrated hydrochloric acid subjected to hydrolysis, The ethylene glycol content is preferably 40 to 60% by mass, öer Content of concentrated hydrochloric acid 60 to 40% by mass * The process can be carried out at 273 to 373 K, the temperature range of -

 ~ 3 -

313 to 333 K, DiorganopOlysiloxanes, which compared to those without ethylene glycol additive, but otherwise under the same experimental conditions produced, have improved characteristics, The Gyclengehalt is substantially increased and the content of OH groups is - in both the sum and the Si-bound - small at low viscosity. "The gaseous hydrogen chloride is not contaminated by the addition of the ethylene glycol uncontaminated surprise" found that when used under the above conditions, ethylene chlorohydrin (01-CH ₂ -CH ₂ -OH) and / or dichloroethane (Cl-CH ₂ -CH ₂ -Cl) does not occur in interfering amounts. When monohydric, lower aliphatic alcohols are added, gaseous hydrogen chloride can not be used for synthesis because it is contaminated by the corresponding alkyl chlorides. "

The diorganopolysiloxanes prepared by the hydrolysis according to the invention are suitable for aftertreatment owing to the low OH group contents at low viscosity. They are carried out in the temperature range from 288 to 373 K with aqueous hydrochloric acid in the concentration range from 15 to 36% by mass or with gaseous hydrogen chloride , In the case of diorganolpolysiloxanes which have been prepared without ethylene glycol additive, the viscosity is increased so much by a similar after-treatment that it makes it difficult or impossible to effect further processing. '·. The diorganopolysiloxanes prepared according to the invention are storage-stable for months. They remain clear with unchanged low viscosity, are thermally stable and can be easily processed into the desired products, such as silicone oils or silicone rubber.

In a 1 1 glass reactor with stirrer ^ contact thermometer, reflux condenser and .Gasableitungsrohr 430 ml of saturated hydrogen chloride solution of 45% by weight of ethylene glycol and 55% by mass of concentrated aqueous hydrochloric acid were presented at constant temperature within 60 minutes 240 ml of dimethyldichlorosilane and 35 ^ iL

10 V / ater was added to the vigorously stirred hydrolysis "The liberated during the conversion of hydrogen chloride was so pure," that he a, B could be ₆ used immediately for the synthesis of tfrichlorsilan ,, The dimethylpolysiloxanes formed were after a short separation time from the almost clear Hydro -Iysemedium separated j which is reusable for further hydrolyses,

The characteristics of the clear, colorless dimethylpolysiloxanes »• For different hydrolysis temperatures in Table 1 lr _? 1 to 5 compiled

§ C comparative example)

dimethylpolysiloxanes without the addition of ethylene glycol, ie, _4f, in aqueous hydrochloric acid solution saturated with hydrogen chloride, were prepared under the same conditions as in Example 1.

The characteristic values of the dimethylpolysiloxanes thus obtained have been compiled for different hydrolysis temperatures in Table 1 Iir "7 to 9".

In a circulation apparatus consisting of a container without internals, a centrifugal pump ₉ a heat exchanger and a separation vessel ₉ , the container was filled with a saturated with hydrogen chloride solution of 4-5% by weight of ethylene glycol and 55% by mass of aqueous hydrochloric acid and heated to 333 K. In the means of centrifugal pump constantly in flow

- · 5 -

held solution, the hydrolysis medium, 21 kg of dimethyldichlorosilane per hour and 3 kg of water per hour were fed continuously. The liberated, pure hydrogen chloride is discharged. After an immediate separation of the biorganopolysiloxane, the recirculation of the

_t Hydrolysis medium into the reaction vessel. The characteristics of the clear, colorless dimethylpolysiloxanes are given in Table 1 Hr. 6 to remove _e

Example 4- (Comparative Example )

According to the prior art dimethy! Polysiloxanes were prepared in concentrated aqueous hydrochloric acid solution as Hy'drolysemedium and without external heat, d, h., At 273 K according to the otherwise described in Example 3. The characteristics of the thus obtained dimethylpolysiloxanes are the table 1 Ur. 10 to remove.

A comparison with the characteristic data f obtained in Example 3 shows the superiority of the method according to the invention over the prior art.

20 ' . '. '·

Example 5 *

200 g of dimethylpolysiloxane, prepared as described in Example 3, were prepared in a 500 ml round-bottomed flask with a biotrider, thermometer and contact thermometer (for characteristic values see

.25 Table 1 No. "6), heated to 333 K with 200 g of aqueous hydrochloric acid and dispersed by rapid stirring with each other for 20 minutes.

Subject of the neutralization, the characteristic values listed in Table 2 Nos. 1 and 2 were determined. , .-

Be itpiel 6

A gas washing bottle was filled with 100 g of dimethylpolysiloxane, prepared as described in Example 3, and sprayed through a frit with hydrogen chloride gas. After a gassing time of 30 minutes, the dimethylpolysiloxane was neutralized, characteristics are given in Table 2 no _e 3

· - 6

Table 1 ;'

Characteristic values of the dimethylpolysiloxanes after the hydrolysis

Sr. Glo-%. _: HCl- # TV ₂₀ Cyol .- ^ ± _QH

, 1 45 55 373 10.5 69 0.35 0.12 2 45 55 353 15.9 62 0.32 0.13 ^V -3 ' 45 55 333 12.9 61 0.42 0.14 4 45 55 313 _i .9,6 68 "* 0.19 10 5 45 55 273 18.3 53 0.87 0.24 6 ^X ' 45 .55 333 .19,1 62 0.63   0.14 7 0 100 3> 3 163 36 0ί, 31 0.12 8th 0 100 333 109 27 0 ^ 43 0.12 ^: .-;. '9: 0 \ 100 273 30.6 41 1.07 > 0.3 15 10 ^x ^ 0 100 273 31 1.60 > 0.25 Table 2

Characteristic values of the dimethylpolysiloxanes after the aftertreatment

α-hydrochloric acid V ₂₀ Σ oh

1 20 20.1 0.28 2 ' 25 ': .22,6 0.23 25  3 - gasi'o HCl 111 0.30

/ = continuous production

Gl, - ^ s Glycolanteil in the hydrolysis medium in mass% 3Q HCl-% as proportion conc. Hydrochloric acid in the hydrolysis medium in mass%

T =: temperature in K ^

Vp ₀ s viscosity at 293 K in mm / s cycle -Φ S content of cyclen ^ in mass%

1. _οίίs sum of all OH groups in mass ~% Odβi = OH groups bonded to Si in mass% ^ hydrochloric acid a HCl content of aqueous hydrochloric acid in mass%

Claims (2)

The invention s.sn sy> ru c h, ..: 1. A process for the preparation of low-viscosity, storable diorganopolysiloxanes while gaining gaseous hydrogen chloride of high purity, '} characterized in that the preparation by hydrolysis of a Diorganodichlorsilans in.einer with chlorine -; hydrogen saturated solution solution of 10 to 95% by weight. Ethylene glycol and 5 to 90% by mass of concentrated hydrochloric acid in the temperature range from 273 to 373 K, followed by a post-treatment of the diorganopolysiloxane. xcjis with hydrochloric acid; a concentration of 15 to 36; Mass% or gaseous hydrogen at 2S8 to ^: 373 K is performed, 2 »method according to item 1, characterized in that the content of ethylene glycol is 40 to 60% by mass _o β - .. Method according to item 1, characterized in that the Temperature range for the hydrolysis between 313 .20. 333 K lies ο , ' ,