Process for preparing isocyanates containing alkoxysilane groups
The invention relates to a process for preparing isocyanate containing alkoxysilane groups, in which, in the sequence of steps A) to D), A) alkoxysilano(cyclo)alkylamine is reacted with dialkyl carbonate in the presence of a basic catalyst to give alkoxysilano(cyclo)alkylurethane, B) simultaneously or successively, the catalyst is removed and/or deactivated, and low boilers, solids, salt burdens and/or high boilers are removed, C) alkoxysilano(cyclo)alkylurethane 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 bottoms material and collected, wherein the basic catalyst is a guanidine base.
1. A process for preparing isocyanate containing alkoxysilane groups comprising the sequence of steps A) to D),
A) alkoxysilano(cyclo)alkylamine is reacted with dialkyl carbonate in the presence of a basic catalyst to give alkoxysilano(cyclo)alkylurethane,
B) successively
removing and/or deactivating the basic catalyst, and then
removing low boilers by distillation,
removing solids and salt burdens by filtration or centrifugation
removing high boilers by thin-film evaporation,
C) alkoxysilano(cyclo)alkylurethane 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 bottoms material and collected,
wherein the basic catalyst is a guanidine base.
2. The process according to claim 1 , wherein in step
C) purified alkoxysilano(cyclo)alkylurethane obtained after step 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 step A), B) or C), is fed in again.
3. 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 2 OH with R 2 =linear, branched or cyclic hydrocarbyl radical having 1-6 carbon atoms at 25-100° C. in the presence or absence of a catalyst.
4. The process according to claim 3 , wherein no reaction with alcohol is conducted.
5. The process according to claim 3 , wherein the distillate obtained is sent to step B) or C).
6. The process according to claim 2 , wherein the alkoxysilano(cyclo)alkylamine has the formula (1)
R 3 m (OR 2 ) 3-m Si—R 1 —NH 2 (1)
where R 3 , R 2 and R 1 are each independently identical or different hydrocarbyl radicals having 1-6 carbon atoms, where these may be linear, branched or cyclic, and m is 0-2.
7. The process according to claim 2 , wherein the dialkyl carbonate used is selected from the group consisting of dimethyl, diethyl, dipropyl and dibutyl carbonate.
8. The process according to claim 2 , wherein the guanidine base in uncharged form has the following structural formula (I):
wherein R 1 , R 2 , R 3 , R 4 and R 5
are each independently selected from an optionally substituted C 1 -C 14 -alkyl radical and/or
R 1 and R 2 and/or R 3 and R 4 together are an optionally substituted C 2 -, C 3 -, or C 4 -alkylene radical or an optionally corresponding, preferably N- or O-substituted, heteroalkylene radical and/or
R 5 =H.
9. The process according to claim 2 , wherein the guanidine base is selected from the group consisting of
a. Barton's base, Murphy's guanidine, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), pentamethylguanidine, tert-butyltetramethylguanidine (BTMG), and
b. reaction products
i. of oligocarbodiimides or polycarbodiimides with amines or
ii. of polyamines with carbodiimides.
10. The process according to claim 1 , wherein the alkoxysilano(cyclo)alkylamine has the formula (1)
R 3 m (OR 2 ) 3-m Si—R 1 —NH 2 (1)
where R 3 , R 2 and R 1 are each independently identical or different hydrocarbyl radicals having 1-6 carbon atoms, where these may be linear, branched or cyclic, and m is 0-2.
11. The process according to claim 1 , wherein the dialkyl carbonate used is selected from the group consisting of dimethyl, diethyl, dipropyl and dibutyl carbonate.
12. The process according to claim 1 , wherein the guanidine base in uncharged form has the following structural formula (I):
wherein R 1 , R 2 , R 3 , R 4 and R 5
are each independently selected from an optionally substituted C 1 -C 14 -alkyl radical and/or
R 1 and R 2 and/or R 3 and R 4 together are an optionally substituted C 2 -, C 3 -, or C 4 -alkylene radical or an optionally corresponding, preferably N- or O-substituted, heteroalkylene radical and/or
R 5 =H.
13. The process according to claim 1 , wherein the guanidine base is selected from the group consisting of
a. Barton's base, Murphy's guanidine, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), pentamethylguanidine, tert-butyltetramethylguanidine (BTMG), and
b. reaction products
i. of oligocarbodiimides or polycarbodiimides with amines or
ii. of polyamines with carbodiimides.
14. The process according to claim 1 , wherein, in step B) in the sequence of steps i) to iv),
i) the catalyst is removed and/or deactivated,
ii) low boilers are removed by distillation,
iii) solids and/or salt burdens are optionally filtered or centrifuged off, and
iv) high boilers are removed via thin-film evaporation.
15. The process according to claim 14 , wherein the residue from the thin-film evaporation is recycled into the urethane synthesis A) or into the optional filtration step B) iii).
16. 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.
17. The process according to claim 16 , wherein the catalyst concentration is from 0.5[H] to 100 ppm.
18. The process according to claim 16 , 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 2 OH with R 2 =linear, branched or cyclic hydrocarbyl radical having 1-6 carbon atoms at 25-100° C. in the presence or absence of a catalyst.
19. 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).
20. The process according to claim 1 , wherein the separation in step D) is a rectification.