PROCESS FOR PREPARING ISOCYANATES CONTAINING ALKOXYSILANE GROUPS

Abstract

The invention relates to a process for preparing isocyanate containing alkoxysilane groups, in which, in the sequence of steps A) to D),

A) haloalkylalkoxysilane is reacted with metal cyanate and alcohol to give alkoxysilanoalkylurethane,
B) alkoxysilanoalkylurethane is freed of low boilers, solids, salt burdens and/or high boilers and optionally purified,
C) alkoxysilanoalkylurethane obtained after B) is thermally cleaved to release isocyanate containing alkoxysilane groups and by-product, leaving bottoms material, and
D) isocyanate containing alkoxysilane groups and by-product are separated from one another and from cleavage bottoms material and collected,
wherein the process regime at least of steps C) to D) is continuous.

Claims

1. A process for preparing isocyanate containing alkoxysilane groups, in which, in the sequence of steps A) to D), A) haloalkylalkoxysilane is reacted with metal cyanate and alcohol to give alkoxysilanoalkylurethane, B) alkoxysilanoalkylurethane is freed of low boilers, solids, salt burdens and/or high boilers and optionally purified, C) alkoxysilanoalkylurethane obtained after B) is thermally cleaved to release isocyanate containing alkoxysilane groups and by-product, leaving bottoms material, and D) isocyanate containing alkoxysilane groups and by-product are separated from one another and from cleavage bottoms material and collected, wherein the process regime at least of steps C) to D) is continuous.

2. The process according to claim 1, wherein in step C) purified alkoxysilanoalkylurethane obtained after B) is thermally cleaved to release isocyanate containing alkoxysilane groups and by-product, leaving bottoms material, while i) the bottoms material is being wholly or partly discharged from the cleavage apparatus, ii) subjected to thermal treatment and/or purification and/or an aftertreatment in the presence of alcohol and iii) the material removed, after thermal treatment and/or purification and/or aftertreatment in A), B) or C), is fed back.

3. The process according to claim 1, wherein the haloalkylalkoxysilane has the formula (1)
R.sup.3.sub.m(OR.sup.2).sub.3-mSiR.sup.1X(1) where R.sup.3, R.sup.2 and R.sup.1 are each independently a linear, branched or cyclic hydrocarbyl radical having 1-6 carbon atoms, m is 0-2 and X=F, Cl, Br or I.

4. The process according to claim 1, wherein the metal cyanate used is an alkali metal or alkaline earth metal cyanate.

5. The process according to claim 1, wherein the reaction is conducted in the presence of an aprotic solvent.

6. The process according to claim 1, wherein a catalyst selected from crown ethers and cryptands is used.

7. The process according to claim 1, wherein in step B) in the sequence of steps i) to iv) i) the product stream A) is filtered or centrifuged, ii) low boilers are removed by distillation, iii) high boilers are optionally removed via thin-film evaporation and iv) alkoxysilanoalkylurethane is purified by distillation and any solvent residues still present are removed.

8. The process according to claim 7, wherein a residue from the thin-film evaporation B) iii) is recycled into the urethane synthesis A) or into the filtration/centrifugation step B) i).

9. The process according to claim 1, wherein the thermal cleavage C) is conducted without solvent and in the presence of a catalyst at a temperature of 150-280 C. and a pressure of 0.5-200 mbar.

10. The process according to claim 9, wherein the catalyst concentration is 0.5-100 ppm.

11. The process according to claim 1, wherein, in step C), an amount of bottoms material corresponding to 1-90% by weight based on the feed is discharged from the bottom and added again in step A), B) or C).

12. The process according to claim 2, wherein the discharged bottoms material is subjected to thermal treatment at a temperature of 150-250 C. over a period of 0.2 to 4 h and/or is distilled under reduced pressure and at a temperature of 150-250 C. and/or is converted in the presence of an alcohol of the formula R.sup.2OH with R.sup.2=linear, branched or cyclic hydrocarbyl radical having 1-6 carbon atoms at 25-100 C. in the presence or absence of a catalyst.

13. The process according to claim 12, wherein no reaction with alcohol is conducted.

14. The process according to claim 13, wherein the distillate obtained is sent to step B) or C).

15. The process according to claim 1, wherein the separation in step D) is a rectification.

16. The process according to claim 2, wherein the haloalkylalkoxysilane has the formula (1)
R.sup.3.sub.m(OR.sup.2).sub.3-mSiR.sup.1X(1) where R.sup.3, R.sup.2 and R.sup.1 are each independently a linear, branched or cyclic hydrocarbyl radical having 1-6 carbon atoms, m is 0-2 and X=F, Cl, Br or I.

17. The process according to claim 2, wherein the metal cyanate used is an alkali metal or alkaline earth metal cyanate.

18. The process according to claim 2, wherein the reaction is conducted in the presence of an aprotic solvent.

19. The process according to claim 2, wherein a catalyst selected from crown ethers and cryptands is used.

20. The process according to claim 2, wherein in step B) in the sequence of steps i) to iv) i) the product stream A) is filtered or centrifuged, ii) low boilers are removed by distillation, iii) high boilers are optionally removed via thin-film evaporation and iv) alkoxysilanoalkylurethane is purified by distillation and any solvent residues still present are removed.

Description

EXAMPLE 1

Preparation of 3-(trimethoxysilyl)propyl isocyanateReurethanization of the Bottoms Discharge and Recycling into the Urethane Purification

[0068] To a solution of 14.5 kg of chloropropyltrimethoxysilane and 6.0 kg of potassium cyanate and 5 litres of methanol in dimethylformamide were added 20 g of [18]crown-6, and the mixture was stirred under reflux at standard pressure for 9 h. The salt obtained was filtered off, and the solvent and excess methanol were largely removed by flashing-off. The residue was subjected to a fractional distillation at top pressure 2 mbar. The alkoxysilanoalkylurethane was removed at the side draw and run continuously into the circulation of the cleavage column and rectification column, and the deblocking reaction was conducted at a temperature of 192 C. and a bottom pressure of 53 mbar in the presence of a steady-state concentration of tin dichloride of 55 ppm. The cleavage gases IPMS and methanol were condensed out in two successive condensers, it being possible to reuse the methanol obtained as the top product, after further distillation, as raw material, and the IPMS (3-(trimethoxysilyl)propyl isocyanate) was withdrawn at the side draw with a purity of >98% in an amount of 11.7 kg/h, which corresponds to a continuous yield of 77%. To maintain the mass balance within the cleavage column and rectification column, and for avoidance of deposits and possibly blockage of the cleavage apparatus, and for regeneration of values, a substream was continuously discharged from the circuit, cooled down and combined with methanol, and the combined stream (8.0 kg/h) was converted in a tubular reactor at 65 C. until urethanization of all NCO groups was complete. The reurethanizate stream was recycled into the solvent separation.

EXAMPLE 2

Preparation of 3-(trimethoxysilyl)propyl isocyanateThermal Aftertreatment and Separation of the Bottoms Discharge and Recycling into the Urethane Cleavage

[0069] To a solution of 15.8 kg of chloropropyltrimethoxysilane and 6.5 kg of potassium cyanate and 5.5 litres of methanol in dimethylformamide were added 10 g of [18]crown-6, and the mixture was stirred under reflux at standard pressure for 9 h. The salt obtained was filtered off, and the solvent and excess methanol were largely removed by flashing-off. The residue was subjected to a fractional distillation at top pressure 2 mbar. The alkoxysilanoalkylurethane was removed at the side draw and run continuously into the circulation of the cleavage column and rectification column, and the deblocking reaction was conducted at a temperature of 193 C. and a bottom pressure of 54 mbar in the presence of a steady-state concentration of tin dichloride of 28 ppm. The cleavage gases IPMS (3-(trimethoxysilyl)propyl isocyanate) and methanol were condensed out in two successive condensers that were operated at different temperature levels, it being possible to reuse the methanol obtained as the top product, after further distillation, as raw material, and the IPMS (3-(trimethoxysilyl)propyl isocyanate) was withdrawn at the side draw with a purity of >98% in an amount of 13.1 kg/h, which corresponds to a continuous yield of 79%. To maintain the mass balance within the cleavage column and rectification column, and for avoidance of deposits and possibly blockage of the cleavage apparatus, and for regeneration of values, a substream was continuously discharged from the circuit, subjected to thermal aftertreatment at 220 C. with a residence time of 55 min, and then run through a thin film evaporator at 5 mbar. The distillate stream was recycled into the circuit.

COMPARATIVE EXAMPLE

Batchwise Preparation of IsocyanatopropyltrimethoxysilaneBatchwise Deblocking

[0070] To a solution of 15.0 kg of chloropropyltrimethoxysilane and 7.34 kg of potassium cyanate and 5 litres of methanol in dimethylformamide were added 22 g of [18]crown-6, and the mixture was stirred under reflux at standard pressure for 9 h. The salt obtained was filtered off, and the solvent and excess methanol were largely removed by flashing-off. The residue was subjected to a fractional distillation at top pressure 2 mbar, and 15.1 kg of urethane were obtained in this way.

[0071] 378 g of the urethane were heated to a temperature of 192 C. in a 3 l round-bottom flask with distillation apparatus, stirrer and thermometer in the presence of 105 ppm of tin dichloride and at a pressure of 50 mbar. The cleavage gases formed were separated by distillation and condensed out. After 6.5 h, the experiment was stopped after no product stream was obtained any longer in the distillation. A total of 222.3 g of IPMS were obtained with a purity of 97.4% (about 66% yield); 106.9 g of high boilers remained in the round-bottom flask.