Process for preparation of ethylenically unsaturated isocyanates

A process for the preparation of ethylenically unsaturated isocyanates is described, which process comprises silylating an appropriate ethylenically unsaturated urethane precursor at the urethane nitrogen and converting the resulting unsaturated N-silyl-urethane by means of thermolysis at elevated temperature into the desired isocyanate. The unsaturated isocyanates obtainable according to the process are suitable, for example, as monomers or comonomers in the preparation of polymerisates or copolymerisates.

The Examples that follow serve to illustrate the present invention in more 
detail; they are not, however, intended to limit the scope thereof in any 
way. Unless stated otherwise, temperatures are given in degrees Celsius. 
Preparation of the urethanes of formula (3) 
EXAMPLE 1 
608 ml of ethanolamine are dissolved in 13 liters of dry methylene chloride 
under a nitrogen atmosphere in a reaction vessel and then 6.7 g of 
tetrabutylammonium bromide and 2378 g of sodium carbonate are added. The 
mixture is stirred until a homogeneous suspension is formed and it is 
cooled to 10.degree. C. A mixture of 1402 ml of phenyl chloroformate in 5 
liters of dry methylene chloride is then added dropwise within about 11 
hours at a temperature of from 10 to 15.degree. C. and the exothermic 
reaction which commences is controlled by cooling externally using ice. 
When the addition is complete, stirring is continued until the starting 
materials have been reacted completely (about 30 minutes at 25.degree. 
C.). The resulting fine suspension is filtered and then concentrated to a 
volume of about 1 liter using a rotary evaporator. 5 liters of n-hexane 
are added and the resulting suspension is stirred overnight at room 
temperature (25.degree. C.); the suspension is then cooled to 10.degree. 
C. and the solid material is isolated by filtration. The resulting 
crystalline product is washed with two 500 ml portions of n-hexane and 
dried at 30.degree. C. in vacuo. The compound 
N-(2-hydroxyethyl)-phenylcarbamate is obtained in the form of a white, 
crystalline product having a melting point of 79-80.degree. C. 
620.3 g of the N-(2-hydroxyethyl)-phenylcarbamate prepared above and 7.5 
liters of methylene chloride are combined under a nitrogen atmosphere in a 
reaction vessel. 1000 ml of freshly distilled methacryloyl chloride are 
added to the resulting suspension. Heating at 80.degree. C. is carried out 
overnight, with a gentle stream of argon protective gas being passed 
through the reaction vessel. A clear solution is formed, which is cooled 
to 25.degree. C. and freed completely of the solvent using a rotary 
evaporator. The resulting crystalline solid is re-crystallised from a 
mixture of 5 liters of toluene and 3 liters of n-hexane, then washed with 
500 ml of n-hexane and dried at 30.degree. C. in vacuo. The compound 
N-(2-methacryloyloxyethyl)-phenylcarbamate is obtained in the form of a 
white, crystalline product having a melting point of 105-106.degree. C. 
EXAMPLE 2 
In a reaction vessel thoroughly heated under dry nitrogen, 15.56 g of 
2-aminoethyl methacrylate hydrochloride are dissolved in 30 ml of dry 
N,N-dimethylacetamide under a nitrogen atmosphere and the clear, 
light-yellow solution is cooled to about 4.degree. C. Then, at that 
temperature, there are simultaneously added dropwise (a) a solution of 
15.66 g of phenyl chloroformate in 50 ml of dry methylene chloride and (b) 
a solution of 20.5 g of triethylamine in 50 ml of dry methylene chloride. 
After 1.5 hours at about 4.degree. C. the mixture is heated to room 
temperature and stirred for about 12 hours more. 15 mg of 
di-tert-butyl-p-cresol are added and the resulting white suspension is 
freed of most of the solvent using a rotary evaporator. The suspension is 
diluted by adding 200 ml of methylene chloride and extracted three times 
using 200 ml of water each time; the organic phase is then dried using 
sodium sulfate. After concentration by evaporation using a rotary 
evaporator the resulting residue is re-crystallised from diethyl 
ether/methylene chloride in a ratio of 4:1. The compound 
N-(2-methacryloyloxyethyl)-phenylcarbamate is obtained in the form of a 
white, crystalline product having a melting point of 110.degree. C. 
EXAMPLE 3 
Using the procedure described in Example 1,18.1 g of 
N-(2-hydroxyethyl)-phenylcarbamate in dry methylene chloride are reacted 
with 9.05 g of acryloyl chloride and 10.1 g of triethylamine, yielding the 
compound N-(2-acryloyloxyethyl)-phenylcarbamate, which is re-crystallised 
from toluene/hexane. 
Preparation of the isocyanates of formula (1) 
EXAMPLE 4 
400 g of the N-(2-methacryloyloxyethyl)-phenylcarbamate obtained according 
to Example 1 or 2 are suspended in 3 liters of dry toluene under argon 
protective gas with strict exclusion of moisture. After adding 240 g of 
dry triethylamine and 4 g of di-tert-butyl-p-cresol, the reaction mixture 
is heated to 50.degree. C., and 204 g of freshly distilled trimethylsilyl 
chloride are added dropwise over a period of about 20 minutes. After 6 
hours at 50.degree. C., the silylation is complete and a fine suspension 
containing triethylammonium chloride has formed. 
The thermal elimination of the phenoxy-trimethylsilane from the resulting 
N-silylated urethane is carried out by heating the suspension for about 8 
hours under reflux (about 100.degree. C.). The suspension is then stirred 
overnight at room temperature in order to cause the triethylammonium 
chloride to crystallise completely. For working up of the reaction 
mixture, a solution of 2 g of di-tert-butyl-p-cresol in 100 ml of dry 
toluene is added and low-boiling components (excess triethylamine, 
trimethylsilyl chloride) are then removed by distillation at about 
80-100.degree. C. After cooling to 25.degree. C., the triethylammonium 
chloride is separated from the reaction suspension by filtration under an 
argon protective gas atmosphere and washed several times with dry toluene; 
the collected filtrates are concentrated to an amount of about 680 g using 
a rotary evaporator. That residue is first of all rapidly distilled at 
about 4-5 mbar without careful fractionation. The fractions having boiling 
points of between 60 and 80.degree. C. are collected and, after addition 
of a further 2 g of di-tert-butyl-p-cresol, subjected to fractionation 
using a Vigreux column. The compound 2-isocyanatoethyl methacrylate is 
obtained in the form of a colourless oil having a boiling point of 
60.degree. C. at 7 mbar. 
EXAMPLE 5 
In a manner analogous to that described in Example 4, 47.6 g of the 
N-(2-acryl-oyloxyethyl)-phenylcarbamate prepared according to Example 3 
are silylated in dry toluene using 22.8 g of trimethylchlorosilane and 
21.2 g of triethylamine. The process is continued without isolation of the 
intermediate and, after the thermolysis and subsequent fractional 
distillation, the compound 2-isocyanatoethyl acrylate, which has a boiling 
point of 52-54.degree. C. at 5 mbar, is obtained.