JPH07242678A - Production of 2,4,6,8-tetramethylcyclotetrasiloxane - Google Patents

Abstract

PURPOSE:To obtain the subject compound in a stable yield free from polymerization and gelation of a reaction liquid by breakage and cyclization of a polymethylpolysiloxane in the presence of a specific organodisilioxane. CONSTITUTION:A polymethylpolysiloxane selected from a linear polymethylpolysiloxane of formula I [(m)=3-1000; R<1> is methyl or H; R<2> is methyl or when R<1> is H, R<2> is OH] and a cyclic polymethylpolysiloxane of formula II [(n)=5-1000] is subjected to breakage and cyclization in the presence of an organodisiloxane of formula III (R<3> to R<5> are each a 1-10C aliphatic linear hydrocarbon, aliphatic cyclic hydrocarbon, etc.) having a higher boiling point than the objective 2,4,6,8-tetramethylcyclotetrasiloxane, e.g. hexaethylenedisiloxane. Further, a compound of formula III is preferably added in an amount of 1-20wt.% based on a raw material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing 2,4,6,8-tetramethylcyclotetrasiloxane used as a raw material for silicone resins and silicone rubber.

[0002]

2. Description of the Related Art S is used as a raw material for producing a hard polysiloxane polymer used as a silicone resin and a room temperature crosslinkable polysiloxane elastic body used as a silicone rubber.
2,4,6,8-Tetramethylcyclotetrasiloxane containing i-H bonds is used. The hard polysiloxane polymer is obtained by reacting 2,4,6,8-tetramethylcyclotetrasiloxane with a vinyl group-containing polysiloxane in the presence of a platinum-based catalyst and crosslinking. Room temperature crosslinkable polysiloxane elastomers are 2, 4, 6,
It can be obtained by adding various functional groups to the Si-H group of 8-tetramethylcyclotetrasiloxane.

The method for producing 2,4,6,8-tetramethylcyclotetrasiloxane includes the case where a chain polymethylpolysiloxane obtained by hydrolyzing a mixture of methyldichlorosilane and trimethylchlorosilane is used as a raw material. In some cases, one of a chain polymethylpolysiloxane obtained by hydrolyzing methyldichlorosilane and a cyclic polymethylpolysiloxane or a mixture thereof is used as a raw material. The raw material is cleaved and cyclized by heating in the presence of a catalyst such as sulfuric acid, phosphoric acid, activated clay or in the absence of a catalyst.

The Si-H bond contained in the chain polymethylpolysiloxane or cyclic polymethylpolysiloxane has a very high reactivity and is easily decomposed to cause a dehydrogenation reaction with a coexisting silanol group at the terminal of the molecule or a small amount of water. Is hydrolyzed into a silanol group. Another silanol group is Si
Dehydrogenation reaction with -H bond or condensation reaction between silanol groups forms a siloxane bond. By these reactions, the polymethylpolysiloxane containing Si—H bonds becomes three-dimensional and easily gels. These reactions are accelerated by heating, and in the presence of an alkaline substance or an acidic substance, not only gelation but also ring-opening polymerization due to cleavage of siloxane bond occurs, and polymethylpolysiloxane easily becomes high molecular weight. Go.

When industrially producing 2,4,6,8-tetramethylcyclotetrasiloxane, the above reaction occurs during the production, and the reaction liquid has a high molecular weight or gels to lower the yield. There were many Therefore, Si-
There has been a demand for a method of stabilizing polymethylpolysiloxane containing an H bond to produce 2,4,6,8-tetramethylcyclotetrasiloxane in a stable yield.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and in the production of 2,4,6,8-tetramethylcyclotetrasiloxane, polymethyl containing a Si--H bond is used. Stabilize the polysiloxane,
It is an object of the present invention to provide a method for producing 2,4,6,8-tetramethylcyclotetrasiloxane in a stable yield without causing the reaction liquid to have a high molecular weight and gelling.

[0007]

The method for producing 2,4,6,8-tetramethylcyclotetrasiloxane of the present invention, which has been made to achieve the above-mentioned object, comprises the following formula [I]:

[0008]

[Chemical 4]

(M in the formula [I] is an integer of 3 to 1000,
R ¹ is a methyl group or a hydrogen atom, R ² is a methyl group or a hydroxyl group when R ¹ is a hydrogen atom), and a chain polymethylpolysiloxane represented by the following formula [II]

[0010]

[Chemical 5]

(N in the formula [II] is an integer of 5 to 1000)
When 2,4,6,8-tetramethylcyclotetrasiloxane is produced by subjecting at least one kind of polymethylpolysiloxane selected from the group represented by 4, 6, 8
-The following formula [III] having a higher boiling point than tetramethylcyclotetrasiloxane

[0012]

[Chemical 6]

Organo represented by (wherein R ³ , R ⁴ and R ⁵ in the formula [III] are aliphatic chain hydrocarbon groups or aliphatic cyclic hydrocarbon groups having 1 to 10 carbon atoms, or phenyl groups) React in the presence of disiloxane.

When chain polymethylpolysiloxane, cyclic polymethylpolysiloxane, or a mixture thereof is subjected to a cleavage and cyclization reaction to produce 2,4,6,8-tetramethylcyclotetrasiloxane, the reaction is equilibrium. Since it is a reaction, it is produced while reacting 2, 4, 6, 8
-A method of distilling out low molecular weight polymethylcyclopolysiloxane containing tetramethylcyclotetrasiloxane as a main component (reactive distillation method) is general. The organodisiloxane represented by the formula [III] is 2,4,6,8-
Tetramethylcyclotetrasiloxane (boiling point 135 ° C)
If a compound having a lower boiling point, such as ((CH ₃ ) ₃ Si) ₂ O (hexamethyldisiloxane, boiling point 100 ° C.) is used, the reaction solution is completely distilled out in the reaction distillation system, so that the reaction solution is stabilized. Does not happen.

[0015] 2,4,6,8-than-tetramethylcyclotetrasiloxane as organodisiloxane having a high boiling point is _{((C 2 H 5) 3} Si) 2 O ( hexaethyldisiloxane, boiling point 231 ° C.), _{(C 6 H 13 Si (CH} 3) 2) 2
O (1,1,3,3-tetramethyl-1,3-dicyclohexyldisiloxane, boiling point 290 ° C.), (C ₆ H ₅ S
_{i (CH 3) 2) 2} O (1,1,3,3- tetramethyl -
1,3-diphenyldisiloxane, boiling point 280 ° C.),
_{(C 2 H 5) 3 SiOSi} (CH 3) 3 (1,1,1- trimethyl-3,3,3-ethyl disiloxane, boiling 1
_{71 ℃), t-C 4} H 9 Si (CH 3) 2 OSi (CH 3) 3
(1,1,1,3,3-pentamethyl-3-t-butyldisiloxane, boiling point 155 ° C.). From the viewpoint of stability of the reaction solution, the amount added is 1% by weight based on the raw material.
As described above, 20% or less is preferable in terms of economic efficiency, but it is not limited to this range. Further, among the compounds of the above-mentioned organodisiloxane, the compound having a Si (CH ₃ ) ₃ group forms ((CH ₃ ) ₃ Si) ₂ O during the reaction and distills out. When adding, it is necessary to add a large amount.

[0016]

According to the method for producing 2,4,6,8-tetramethylcyclotetrasiloxane of the present invention, a monofunctional organodisiloxane represented by the formula [III] is always present in the reaction solution. Therefore, the reaction solution is prevented from having a high molecular weight, and even if the Si—H bond is decomposed, the organodisiloxane acts as a sealing agent to prevent three-dimensionalization, so that the reaction solution does not gel. Therefore, stable yields of 2, 4, 6, 8
It is possible to produce tetramethylcyclotetrasiloxane. Furthermore, the kettle liquid after the reaction is not viscous or gelled and is easy to handle.

[0017]

EXAMPLES Examples of the present invention will be described in detail below.

Example 1 (CH ₃ ) ₃ S was added to a round bottom flask equipped with a stirrer and a thermometer.
_{iO (HSiCH 3 O) 25 Si} (CH 3) 3 and 100 g,
_{t-C 4 H 9 Si (} CH 3) 2 OSi (CH 3) 3 10
g and 5 g of concentrated sulfuric acid were charged. While stirring the charged liquid, the pressure of the flask was reduced to 5 mmHg by a vacuum pump via a trap cooled with methanol dry ice,
The temperature was gradually raised.

After 1 hour, when the temperature in the flask reached 50 ° C., the temperature rise was stopped, and after cooling, the pressure in the trap was adjusted to normal pressure and weighed 72 g. Its composition is 2, 4, 6, 8-
It was confirmed to be a low molecular weight polymethylcyclopolysiloxane containing 72% of tetramethylcyclotetrasiloxane. The residue in the flask was a liquid with low viscosity and could be easily extracted.

Comparative Example 1 Using the same apparatus as in Example 1, t-C ₄ H ₉ Si was added to the charged liquid.
The reaction was carried out under the same conditions except that the formulation was such that (CH ₃ ) ₂ OSi (CH ₃ ) ₃ was not added.

The liquid accumulated in the trap was weighed to be 56 g, and the composition was the same as in Example 1. The residue in the flask was a highly viscous liquid, and the viscosity increased with time and gelled.

Example 2 A round-bottomed flask equipped with a stirrer, a thermometer, a dropping funnel, a reflux condenser and a water-cooled condenser capable of taking out distillate (
CH ₃ ) ₃ SiO (HSiCH ₃ O) ₂₅ Si (CH ₃ ) ₃ 100 g, ((C ₂ H ₅ ) ₃ Si) ₂ O 5 g, activated clay 1
g prepared. The temperature of this charging liquid was raised and the mixture was stirred in a temperature range of 130 to 140 ° C., and a dropping funnel was used to 2.
48 g of water was added dropwise over 5 hours to distill a low molecular weight polymethylcyclopolysiloxane together with water. 2 for distillate
The layers were separated and 76 g of low molecular weight polymethylcyclopolysiloxane layer was recovered along with 46 g of the aqueous layer. The composition of the low molecular weight polymethylcyclopolysiloxane layer was confirmed by gas chromatography to contain 58% of 2,4,6,8-tetramethylcyclotetrasiloxane. The residue in the flask was a liquid with low viscosity and could be easily extracted.

Comparative Example 2 The same apparatus as in Example 2 was used to prepare ((C ₂ H ₅ ) ₃ S in the charged liquid.
i) Reaction was carried out under the same conditions except that the formulation was such that ₂ O was not added.

60 g of the low molecular weight polymethylcyclopolysiloxane layer was recovered together with 47 g of the water layer, and the composition of the low molecular weight polymethylcyclopolysiloxane layer was the same as in Example 2. The residue in the flask was a highly viscous liquid, and the viscosity increased with time and gelled.

Example 3 A round-bottomed flask equipped with a stirrer, a thermometer, a dropping funnel, a reflux condenser, and a water-cooled condenser capable of removing distillate,
100 g of a mixture of a chain polymethylpolysiloxane obtained by hydrolyzing methyldichlorosilane and a cyclic polymethylpolysiloxane, and (C ₆ H ₁₃ Si (CH ₃ ) ₂ ) ₂ O
0 g and 1 g of activated clay were charged. 48 g of water was added dropwise by a dropping funnel over 2.5 hours while stirring the charged liquid in the temperature range of 130 to 140 ° C. to distill a low molecular weight polymethylcyclopolysiloxane together with water. The distillate was separated into two layers, and 70 g of a low molecular weight polymethylcyclopolysiloxane layer was recovered together with 47 g of an aqueous layer. The composition of the low molecular weight polymethylcyclopolysiloxane layer was 2,4, by gas chromatography.
64% of 6,8-tetramethylcyclotetrasiloxane
It was confirmed that it included. The residue in the flask was a liquid with low viscosity and could be easily extracted.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuo Wakai 28-2 Nishifukushima, Kubiki Village, Nakakubiki District, Niigata Prefecture 1 Shinetsu Chemical Industry Co., Ltd.

Claims (1)

[Claims] 1. The following formula [I]: (M in the formula [I] is an integer of 3 to 1000, R ¹ is a methyl group or a hydrogen atom, R ² is a methyl group or a hydroxyl group when R ¹ is a hydrogen atom) And the following formula [II] At least 1 selected from cyclic polymethylpolysiloxanes represented by (n in the formula [II] is an integer of 5 to 1000)
When 2,4,6,8-tetramethylcyclotetrasiloxane is produced by subjecting two kinds of polymethylpolysiloxane to a cleavage and cyclization reaction, a higher The following formula [III] having a boiling point (R ³ , R ⁴ and R ⁵ in the formula [III] have 1 to 1 carbon atoms.
0, an aliphatic chain hydrocarbon group, an aliphatic cyclic hydrocarbon group, or a phenyl group).
A method for producing 8-tetramethylcyclotetrasiloxane.