GB2291424A

GB2291424A - Production of isocyanates

Info

Publication number: GB2291424A
Application number: GB9514651A
Authority: GB
Inventors: Simon John Barlow; Brian William Trenbirth
Original assignee: CONTRACT CHEMICALS
Current assignee: CONTRACT CHEMICALS
Priority date: 1994-07-22
Filing date: 1995-07-18
Publication date: 1996-01-24
Also published as: GB9514651D0; GB9414775D0

Abstract

A process for the production of acyl isocyanates comprises reacting a trisubstituted acetyl halide with an alkali metal cyanate or an alkaline earth metal cyanate.

Description

DESCRIPTION PRODUCTION OF ISOCYANATES The present invention relates to the production of acyl isocyanates.

The production of acyl isocyanates by the addition of metal cyanates to acid chlorides has been described in the literature, for example, Tetrahedron 44, 6079-86, 1988. The use of catalysts, for example zinc chloride or tin chloride has also been disclosed.

However, while useful results have been obtained by the use of such catalysts for the production of aroyl isocyanates, such has not always been the case for non-aromatic isocyanates.

Whilst several methods are available for the preparation of isocyanates, the disadvantage is that most of them require relatively expensive or exotic reagents, are difficult to operate on a bulk scale, or use very toxic materials.

The most commercially exploited method for producing acyl isocyanates is the one described in Organic Svnthesis, Coll. Vol 5, 204-6 which outlines the preparation of chloroacetyl isocyanate by the reaction of chloroacetamide with oxalyl chloride. It is suggested therein that such procedure can be extended to other isocyanates, for example, trichloroacetyl isocyanate. Reference is also made therein to another method for producing such isocyanates from the acid chloride and silver cyanate as being described in O.C.Billeter, Ber, 36 3213, (1903) and A.J. Hill and W.M.Degnan, J.Am.Chem.Soc.

62, 1595, (1940). Silver cyanate has the disadvantage of being both highly specialized and commercially unattractive.

At the present time the environmental acceptability of chemical processes is a matter of considerable concern. It is desirable that any process for the production of a chemical product, for example acyl isocyanates, does not produce waste gases, for example hydrogen chloride or carbon monoxide, as has been done by prior art processes.

The present invention overcome such a problem and uses a cheap and readily available cyanate reactant.

According to the present invention there is provided a process for the production of acyl isocyanates which comprises reacting a trisubstituted acetyl halide with an alkali metal cyanate or an alkaline earth metal cyanate.

The trisubstituted compound may be a trihalo compound and is preferably a trichloro compound. Also the halide is preferably a chloride. Thus the particularly preferred compound is trichloroacetyl chloride.

The alkali metal cyanate is preferably sodium cyanate. The alkaline earth metal cyanate may be, for example, calcium or magnesium Whilst the process may be conducted by reacting the trisubstituted acetyl halide with the alkali metal cyanate or the absence of any other substance, it is desirable to conduct the process in the presence of a liquid medium. Such a liquid medium functions as a solvent or partial solvent for the trisubstituted acetyl halide reactant and preferably also for the acyl isocyanate product. It may also function as at least a partial solvent for the alkali metal cyanate reactant.

The liquid medium should, of course, be one which does not react itself with the trisubstituted acetyl halide, the alkali metal cyanate or the acyl isocyanate. It is therefore inappropriate to use alcohols, aldehydes, ketones, amines or acids.

Among liquid media which may be employed are ethers (including aromatic and cyclic ethers), hydrocarbons (including aliphatic, aromatic and cyclic hydrocarbons), chlorinated solvents (including aromatic compounds) and certain nitriles and the acid chloride itself. Particularly useful liquid media which may be employed include 1,2,4-trichlorobenzene, biphenyl, diphenyl ether, hexadecane or trichloroacetyl chloride.

The choice of the liquid medium is, of course, considerably dependent upon its ability to function satisfactorily at the temperature chosen for the process. The temperature at which the process is conducted is usually not above 2500C, being preferably in the range of 100 to 2500C, and more preferably in the range of 115 to 1750C.

The molar ratio of the alkali or alkaline earth metal cyanate to trisubstituted halo acetyl halide is usually in the range of 1:5 to 5:1, more preferably about 1.5:1.

The present invention will now be described with reference to, but in no manner limited to, the following Examples.

Example 1 A slurry of sodium cyanate (114.7g, 1.76 mole) in 1,2,4-trichlorobenzene (256.6g, 176.5 ml, 1.41 mole), under nitrogen purge, was warmed to 1750C.

Trichloroacetyl chloride (214.1g, 131.4ml, 1.18 mole) was then added over 2-4h in which time the mixture has started to reflux and the reaction temperature dropped to approximately 1550C. Reflux is continued for a further 1-6-24h until the reaction is deemed complete by chromatographic or other analysis and the trichloroacetyl isocyanate is then recovered by usual means, e.g. fractional distillation. Yield of trichloroacetyl isocyanate, 133.lg, 60%.

Example 2 The method of Example 1 was followed, but using 390.0g (6.0 mole) sodium cyanate, trichloroacetyl chloride 727.3g (430ml, 4.0 mole) and substituting biphenyl (460g, 3.0 mole) for 1,2,4-trichlorobenzene.

On completion of reaction and distillation, trichloroacetyl isocyanate was produced in 42% yield.

Example 3 The method of Example 1 was followed, but using 97.5g (1.5 mole) sodium cyanate, trichloroacetyl chloride 179.2g (110ml, 1.0 mole) and substituting diphenyl ether (161.0g, 0.95 mole) for 1,3,4trichlorobenzene. On completion of reaction and distillation, trichloroacetyl isocyanate was produced in 39.2% yield.

Example 4 Sodium cyanate (35.9g, 0.55 mole) was slurried in trichloroacetyl chloride (91.0g, 56ml, 0.51 mole) and the resultant mixture heated to reflux for 16h. Over the reflux period the reaction temperature rises from 1200C to 1600C. On distillation under reduced pressure was obtained a 27% yield of trichloroacetyl isocyanate b.p. 40-450C/15mmHg.

Example 5 Sodium cyanate (84.5gg, 1.3 mole) was slurried in trichloroacetyl chloride (182g, 110ml, 1.0 mole) and the resultant mixture heated to reflux under nitrogen for 40h. Over the reflux period the reaction temperature rises from 1280C to 1480C. On distillation under reduced pressure was obtained a 53% yield of trichloroacetyl chloride b.p. 1241270C/350mmHg.

Claims

1. A process for the production of an acyl isocyanate which comprises reacting a trisubtituted acetyl halide with an alkali metal cyanate or an alkaline earth metal cyanate.

2. A process as claimed in claim 1, wherein the trisubtituted compound is a trihalo compound.

3. A process as claimed in claim 1 or 2, wherein the trisubtituted compound is a trichloro compound.

4. A process as claimed in any one of claims 1 to 3 wherein the halide is preferably a chloride.

5. A process as claimed in any one of the preceding claims, wherein the trisubtituted compound is trichloroacetyl chloride.

6. A process as claimed in any one of the preceding claims, wherein the alkali metal cyanate is sodium cyanate.

7. A process as claimed in any one of claims 1 to 5, wherein the alkaline earth metal cyanate is calcium or magnesium cyanate.

8. A process as claimed in any one of the preceding claims, wherein the process is conducted in the presence of a liquid medium.

9. A process as claimed in claim 8, wherein the liquid medium is selected from ethers, hydrocarbons, chlorinated solvents, nitriles and the acid chloride itself.

10. A process as claimed in claim 8 or 9, wherein the liquid medium is 1,2,4-trichlorobenzene, biphenyl, diphenyl ether, hexadecane or trichloroacetyl chloride.

11. A process as claimed in any one of the preceding claims, wherein the temperature at which the process is conducted is not above 2500C.

12. A process as claimed in any one of the preceding claims, wherein the temperature at which the process is conducted is in the range of 100 to 2500C.

13. A process as claimed in any one of the preceding claims, wherein the temperature at which the process is conducted is in the range of 115 to 1750C.

14. A process as claimed in any one of the preceding claims, wherein the molar ratio of the alkali metal cyanate to trisubtituted halo acetyl halide is in the range of 1:5 to 5:1.

15. A process as claimed in any one of the preceding claims, wherein the molar ratio of alkali metal cyanate to trisubtituted halo acetyl halides is about 1.5:1.

16. A process for the production of an acyl isocyanate substantially as hereinbefore described with reference to, and as illustrated in any one of the foregoing examples.

17. An acyl isocyanate which is produced by a process as claimed in any one of the preceding claims.