GB2076802A - Preparation of Isocyanates - Google Patents

Abstract

A method for the preparation of isocyanates of formula R-(NCO)n (I> wherein n is one and R stands for a straight-chained or branched C1-10 alkyl, benzyl, cyclohexyl, phenyl, halophenyl, methylphenyl or methoxyphenyl group, or n is two and R stands for a hexamethylene, phenylene, methylenebis(phenylene), ethylenebis(phenylene) or methylenebis(halophenylene) group, comprises reacting a compound of formula R-(NH2)n with a compound of formula R'-O-CO-Cl (iii> wherein R' stands for chloromethyl, dichloromethyl or trichloromethyl group. The reactants utilized according to the invention are easy to handle, and the required end-products can be obtained with high yields.

Description

SPECIFICATION A Process for the Preparation of Isocyanic Acid Esters This invention relates to a new process for the preparation of isocyanic acid esters of the general formula (I), R(NCO)n (I) wherein n is one and R stands for a straight-chained or branched C,~10 alkyl, benzyl, cyclohexyl, phenyl, halophenyl, methylphenyl or methoxyphenyl group, or n is two and R stands for a hexamethylene, phenylene, methylenebis(phenylene), ethylenebis(phenylene) or methylenebis(halophenylene) group.

Isocyanic acid esters are very important products of modern chemical industry. Large amounts of aromatic isocyanates, particularly toluylene-diisocyanate and diphenylmethane diisocyanate, are utilized for the preparation of polyurethane foams, whereas aromatic monoisocyanates, particularly the halophenylisocyanates, are widely applied as starting substances in the preparation of plant protecting agents. Aliphatic monoisocyanates have a similarly wide industrial use.

A large number of publications deal with the preparation of isocyanic acid esters. The known methods can be classified essentially into two main groups, i.e. methods utilizing phosgene as reactant and those utilizing other reactants.

Several papers and patent specifications are concerned with methods based on the reaction of phosgene with amines, amine salts or diarylureas.

A comprehensive review of these methods is given in the paper of Babad, H. and Zeiler, A.G.

(Chemical Reviews, 73, 75-91/1973/).

The main difficulty in the processes for the preparation of isocyanates by reacting an amine or an amine salt with phosgene is that phosgene, applied as reactant, must not contain chlorine impurity, since otherwise undesired side reactions would occur. Chlorine-free phosgene can be prepared, however, only by liquifying gaseous phosgene and then evaporating the liquid, which requires much energy for cooling.

Several other problems also emerge when performing these reactions on industrial scale.

Upon reacting an amine with phosgene, carbamoyl chlorides always form in the reaction mixture, which can be converted into the respective isocyanates at elevated temperatures only. Furthermore, amine hydrochlorides and urea derivatives may form as well, which do not react with phosgene at all, or even at elevated temperatures an incomplete reaction can be initiated. At these high temperatures, however, phosgene is imperfectly soluble in the solvents applied, making impossible to set the required molar ratio of the reactants.

The introduction of the necessary amount of phosgene at high temperatures involves serious technological problems, too, since a large volume of phosgene gas is to be fed into the reactor. It is also known that at higher temperatures the degree of the thermal dissociation of phosgene increases.

The methods known so far attempted to overcome these difficulties by various means, such as by performing the reaction in many steps at different temperatures, conducting the reaction in vapour phase, applying various catalysts, etc.

Thus e.g. according to the method disclosed in the DL (East German) patent specification No.

88,315 isocyanates are prepared in a continuous process by reacting a primary amine or the hydrochloride thereof with phosgene at 0--250C, in the presence of an acid amide catalyst. This method has the disadvantage that the catalyst has to be separated from the reaction mixture at the end of the conversion, and the recovery of the catalyst is a complicated and expensive operation.

According to the method disclosed in the DE (West German) patent sepcification No.

1,668,109 a primary amine is reacted with phosgene in a mixture of an aqueous solution of an inorganic base and a water-immiscible organic solvent, at temperatures between -300C and +350C.

An improved variant of the above method is described in the DE (West German) patent specification No. 1,809,1 73. According to this method a very short contact time is applied, i.e.

the aqueous phase is contacted for a very short time with the organic phase.

It is generally known from the literature that phosgene hydrolyzes quickly in aqueous alkaline media (thus e.g. phosgene is removed from waste gases by aqueous alkali), therefore the above two processes run with very low yields, or they require very expensive automatic control means.

Several processes were disclosed for the preparation of diisocyanates and various polyisocyanates. The US patent specification No.

3,923,732 describes the preparation of polyisocyanates by reacting the respective polyamines with phosgene in an inert solvent. The disadvantage of this method is that only polyamines can be applied as starting substances, and mixtures of polyisocyanates are formed as products.

In the methods belonging to the second main group no phosgene is applied for the preparation of isocyanates.

According to the method described in the DE (West German) patent specification No.

1,154,090 isocyanates are prepared by reacting a dialkyl urea with diphenyl carbonate.

The US patent specification No. 2,423,448 discloses a method for the preparation of alkyl isocyanates by reacting the respective alkylhydroxamic acids with thionyl chloride.

According to the method described in the US patent specification No.3,017,420 isocyanates are prepared by reacting an alkali cyanate with an alkyl halide in dimethyl formamide as solvent.

According to the method described in the US patent specification No. 3,076,007 ethylene carbonate is reacted with an amine, and the resulting carbamate is converted into the isocyanate at higher temperatures.

The US patent specification No.3,405,159 describes a method for the preparation of aliphatic isocyanates by reacting an aliphatic amine with carbon monoxide at superatmospheric pressure, in the presence of a specially prepared palladium phosphate catalyst.

An alternative method, utilizing carbon monoxide as reactant, is described in the US Patent specification No. 3,523,963. In this method carbon monoxide is reacted with an aromatic nitro compound at superatmospheric pressure, in the presence of a special catalyst.

According to the method disclosed in the US patent specification No. 3,493,596 isocyanates are prepared by oxidixing the respective organic isonitriles with mercury oxide, in the presence of a metal porphyrine or a metal phthalocyanine catalyst.

The US patent specification No. 3,632,620 describes a method for the preparation of phenyl isocyanate by reacting diphenyl carbodiimide with carbon monoxide under superatmospheric pressure and at elevated temperature, in the presence of a catalyst, such as palladium, rhodium, etc.

The majority of these latter methods utilizing no phosgene in the preparation of isocyanates has the disadvantage that they require special compounds with complicated structures as starting substances. Since such compounds are generally not available on the market, they should be prepared in a separate step, which requires extra investments and renders the process less competitive on industrial scale. Moreover, the use of phosgene cannot be eliminated in some of the above processes, since a great number of the starting substances can be prepared only from phosgene.

The yield of the above processes is generally unsatisfactory; thus e.g. when carbon monoxide is applied as reactant, the isocyanate can be prepared with a yield not exceeding 3035%.

Now it has been found that the isocyanates of the general formula (I) can be prepared more easily and more economically than before if the respective amine of the general formula (II), R(NH2)n (II) wherein R and n are as defined above, is reacted with a compound of the general formula (Ill), R'--OO-CCO-CI (III) wherein R' stands for chloromethyl, dichloromethyl or trichloromethyl group, or with a mixture of such compounds, optionally in the presence of phosgene.

The reaction can also be performed under atmospheric or reduced pressure, it is preferred, however, to apply superatmospheric pressure in the process. Depending on the nature of the starting amine, the reaction can be performed at temperatures of-400C to +3000C. According to a preferred method the reaction is performed in the presence of a solvent or a solvent mixture. If desired or necessary, a catalyst can be added to the mixture in order to promote the reaction.

It is preferred to apply a chlorinated hydrocarbon, such as dichloromethane, chloroform, carbon tetrachloride, chlorobenzene, etc., as solvent.

Of the catalyst applicable in the method of the invention activated carbon, metal chlorides (such as iron chloride, zinc chloride, etc.) on activated carbon, furthermore acid catalysts, primarily Lewis acids, are to be mentioned.

The major advantage of the method according to the invention is that the compounds of the general formula (III) are much more easy to handle than phosgene.

As known, phosgene is a gas above 80C, its volume density is low, its solubility in the solvents applied decreases considerably with increasing temperature, furthermore phosgene dissociates at higher temperatures. On the other hand, the compounds of the general formula (III) are liquids, thus their volume densities exceed that of phosgene by orders of magnitude, their boiling points are close to the boiling points of the solvents applied, and their solubilities, even at elevated temperatures, are more favourable than that of phosgene. The compounds of the general formula (III) are more stable thermally than phosgene.It is a particular advantage that the compounds of the general formula (Ill) are good solvents for the isocyanates, thus when applying a compound of the general formula (III) as reactant, isocyanate solutions of higher concentration than the usual 1 7-1 7 W/W% can be prepared, which improves the economy of the process.

Since the compounds of the general formula (III) are liquids, they can be fed easily, with a simple liquid pump, into the reactors operating under superatmospheric pressure, and their concentration can be maintained easily at the value required in the reaction. These tasks cannot be solved in practice when utilizing gaseous phosgene as reactant.

The compounds of the general formula (Ill).

have the further advantage that their hydrolysis rates in alkaline media are substantially lower than that of phosgene, thus they can be applied in a broader pH range.

The non-reacted chlorinated chloroformates, applied in excess, can be decomposed thermally and/or catalytically at the end of the reaction, thus they can be separated easily from the crude isocyanate product.

In the known processes starting from an amine and reacting it with phosgene under superatmospheric pressure the reaction mixture is processed generally so that the mixture is expanded and the individual components are separated from each other under atmospheric pressure. The excess of phosgene and the gaseous hydrochloric acid are removed from the reaction mixture generally by passing an inert gas through the solution of the crude isocyanate, and then the solution is distilled in order to separate the isocyanate from the solvent.

We have found that gaseous hydrochloric acid and phosgene can be removed from the reaction mixture more easily if no pressure release and flushing is applied in the first step of the separation, or if the first step of the separation is performed at a pressure even higher than that applied in the reaction, and only the further steps of purification (and, if required, the recovery of the solvent) are performed at lower pressures.

It has also been found, unexpectedly, that if a mixture of monochloromethyl chloroformate and trichloromethyl chloroformate is reacted with an aromatic amine, diphenylmethane diisocyanate or polyphenyl-methylene polyisocyanates are formed as end-products. These substances are widely used, essential material of the plastics industry.

The process of the invention can be conducted either batchwise or continuously, utilizing apparatuses commonly applied in the chemical industry.

It is preferred to perform the reaction in a continuous way in a pressurized tube reactor, by feeding the reactants into the reactor with a liquid pump.

It is also preferred to use in the reactor a filling with great surface area. As filling e.g. the activated carbon catalyst itself, or a support impregnated with a catalyst (iron chloride, zinc chloride, etc.) can be used.

The process of the invention is elucidated in detail with the aid of the following non-limiting Examples.

Example 1 20 ml/min. of a 31.1 W/W% carbon tetrachloride solution of butylamine and 20.0 ml/min. of a 52 W/W% carbon tetrachloride solution of dichloromethyl chloroform ate are fed simultaneously into a tube reactor operating at 180 C and 50 atm. pressure. The mixture leaving the reactor is fed continuously into a gas/liquid separator connected to the reactor, where 289 ml of a carbon tetrachloride solution containing 24.2 W/W% of butyl isocyanate is separated from the gaseous substances.

After removing the solvent from the solution 94 g of butyl isocyanate are obtained, thus the yield is 95%.

Example 2 20.0 ml/min. of a 31.1 W/W% carbon tetrachloride solution of butylamine and 20.0 ml/min. of a 52 W/W% carbon tetrachloride solution of dichloromethyl chloroformate are fed simultaneously into a tube reactor operating at 1 300C and 5 atm. pressure. 300 ml of a liquid reaction mixture are separated from the gaseous substances in the gas/liquid separator, and the liquid is fed into a column filled with activated carbon at 1 500C under reduced pressure. The carbon tetrachloride solution of butyl isocyanate which leaves the column is separated and purified in the usual manner to obtain 92 g (94%) of butyl isocyanate.

Example 3 20.0 ml/min. of a 31.1 W/W% carbon tetrachloride solution of butylamine and 20.0 ml/min. of a 60.3 W/W% carbon tetrachloride solution of trichloromethyl chloroformate are fed simultaneously into a tube reactor operating at 1 800C and 50 atm. pressure. 280 ml of a carbon tetrachloride solution containing 24.4 W/W% of butyl isocyanate are separated from the gaseous products in the gas/liquid separator connected to the reactor. The solvent is separated from the solute in the usual manner to obtain 93 g (94.5%) of butyl isocyanate.

Example 4 20.0 ml/min. of a 31.1 W/W % carbon tetrachloride solution of butylamine and 20.0 ml/min. of a 60.3 W/W% carbon tetrachloride solution of trichloromethyl chioroformate are fed simultaneously into a tube reactor operating at 1 20OC and 5 atm. pressure. 300 ml of a liquid reaction mixture are separated from the gaseous products in the continuously operating gas/liquid separator, and the liquid mixture is fed into a column filled with activated carbon impregnated with zinc chloride. This column operates at 200 C under atmospheric pressure. The product is separated from the solution leaving the column to obtain 94g (95%) of butyl isocyanate.

Example 5 One proceeds as described in Example 4 with the difference that dichloromethane is applied as solvent. After separating the product from the solvent 91 g (93.5%) of butyl isocyanate are obtained.

Example 6 One proceeds as described in Example 4 with the difference that chloroform is applied as solvent. After separating the product from the solvent 92g (94%) of butyl isocyanate are obtained.

Example 7 One proceeds as described in Example 4 with the difference that chlorobenzene is applied as solvent. After separating the product from the solvent 94g (95%) of butyl isocyanate are obtained.

Example 8 One proceeds as described in Example 4 with the difference that o-dichlorobenzene is applied as solvent. After separating the product from the solvent 94g (95%) of butyl isocyanate are obtained.

Example 9 20.0 ml/min of a 31.1 W/W%carbon tetrachloride solution of butylamine and 20.0 ml/min. of a 41.1 W/W% carbon tetrachloride solution of monochloromethyl chloroformate are fed simultaneously into a tube reactor operating at 1 SOOC and 40 atm. pressure. The reaction mixture exiting the reactor is distilled under superatmospheric pressure. In this step 310 ml of a solution containing 20.9 W/W % of butyl isocyanate are separated from the gaseous substances. The product is separated from the solvent and then purified to obtain 91 g (92%) of butyl isocyanate.

Example 10 20.0 ml/min. of a 31.1 W/W % carbon tetrachloride solution of butylamine and 20.0 ml/min. of a carbon tetrachloride solution containing 30.3 W/W% of phosgene and 30.3 W/W% of trichloromethyl chloroformate are fed simultaneously into a tube reactor operating at 1 8O0C and 50 atm. pressure. The mixture which leaves the reactor is passed through a column filled with activated carbon; this column operates at 2000C and 5 atm. pressure. Thereafter 300 ml of a solution containing 24 W/W% of butyl isocyanate are separated from the gaseous substances in the gas/liquid separator. The product is separated from the sovent and then purified to obtain 93g (94.5%) of butyl isocyanate.

Example 11 A solution of 198 g of trichloromethyl chloroformate in 200 ml of carbon tetrachloride, 73g of butylamine and 200 ml of a 10 W/W% aqueous sodium hydroxide solution are fed into a round-bottomed flask of 1000 ml capacity, equipped with a stirrer, a thermometer, a dropping funnel and a reflux condenser. The reaction mixture is stirred at -2O0C for 2 hours, and then the aqueous phase is separated. The organic phase is dried, evaporated, and the vapours are passed through a column filled with activated carbon, operating at 1 2O0C. The carbon tetrachloride solution of butyl isocyanate is separated then from the gaseous substances, the solvent is distilled off, and the residue is purified in the usual manner to obtain 96.5 g (97.5%) of butyl isocyanate.

Example 12 One proceeds as described in Example 11 with the difference that 270 ml of a 20 W/W% aqueous sodium carbonate solution is substituted for the aqueous sodium hydroxide solution. 96g (97%) of butyl isocyanate are obtained.

Example 13 73g of butylamine, 198 g of trichloromethyl chloroformate and 200 ml of a 10 W/W% aqueous sodium hydroxide solution are fed into a round-bottomed flask of 1000 ml capacity, equipped with a stirrer and a thermometer. The reaction mixture is stirred at -200C for 3 hours, thereafter 101 g of triethylamine are added, and the mixture is stirred at -200C for additional 2 hours. The aqueous phase is separated and the organic phase is distilled. 96g (96%) of butyl isocyanate are obtained.

Example 14 198 g of trichloromethyl chloroformate, 73g of butylamine, 200 ml of o-dichlorobenzene and 200 ml of a 10 W/W % aqueous sodium hydroxide solution are fed into a round-bottomed flask of 1000 ml capacity, equipped with a stirrer, a thermometer and a dropping funnel. The reaction mixture is stirred at -200C for 3 hours, thereafter the organic phase is separated and dried.

10.9 g of tetramethylammonium chloride are added to the organic phase, and the mixture is boiled. When the evolution of phosgene and hydrochloric acid ceases, the solvent is removed from the crude reaction mixture to obtain 96g (96%) of butyl isocyanate.

Example 15 20.0 ml/min. of a 10.23 W/W % carbon tetrachloride solution of methylamine and 20.0 ml/min. of a 60.3 W/W% carbon tetrachloride solution of trichloromethyl chloroformate are fed simultaneously into a tube reactor operating at 1 600C and 50 atm. pressure. The product is separated from the resulting mixture in the usual way and then purified to obtain 51 .3g (90%) of methyl isocyanate.

Example 16 20.0 mi/min. of a 39.2 W/W% carbon tetrachloride solution of aniline and 20.0 ml/min.

of a 60.3 W/W% carbon tetrachloride solution of trichloromethyl chloroformate are fed simultaneously into a tube reactor operating at 180"C and 50 atm. pressure. The product is separated from the crude reaction mixture in the usual way and then purified to obtain 133.4 g (96%) of phenyl isocyanate.

Example 17 20.0 ml/min. of a 44.2 W/W % carbon tetrachloride solution of m-chloroaniline and 20.0 ml/min. of a 60.3 W/W% carbon tetrachloride solution of trichloromethyl chloroformate are fed simultaneously into a tube reactor operating at 180 C and 60 atm. pressure. 310 ml of a carbon tetrachloride solution containing 33.7 W/W% of m-chlorophenyl isocyanate are separated from the gaseous substances in the gas/liquid separator.

Thereafter the solvent is removed from the mixture to obtain 142.3 g (93%) of m chlorophenyl isocyanate.

Example 18 20.0 ml/min. of a 40 W/W% carbon tetrachloride solution of cyclohexylamine and 20.0 mi/min. of a 60.3 W/W% carbon tetrachloride solution of trichloromethyl chloroformate are fed simultaneously into a tube reactor operating at 1 700C and 50 atm. pressure.

320 ml of a carbon tetrachloride solution containing 33 W/W% of cyclohexyl isocyanate are separated from the gaseous substances in the gas/liquid separator. Thereafter the solvent is removed from the mixture to obtain 136 g (94%) of cyclohexyl isocyanate.

Example 19 20.0 ml/min. of a 42 W/W% carbon tetrachloride solution of hexamethylene diamine and 40.0 ml/min. of a 60.3 W/W% carbon tetrachloride solution of trichloromethyl chloroform ate are fed simultaneously into a tube reactor operating at 1 4O0C and 50 atm. pressure.

430 ml of a carbon tetrachloride solution containing 28.5 W/W% of hexamethylene diisocyanate are separated from the gaseous byproducts. The solvent is removed in the usual way to obtain 1 56 g (94%) of hexamethylene diisocyanate.

Example 20 20.0 ml/min. of a 45 W/W% carbon tetrachloride solution of toluylene diamine (containing 65 W/W% of 2,4-isomer and 35 WADI% of 2,6-isomer) and 40.0 ml/min. of a 60.3 W/W% carbon tetrachloride solution of trichloromethyl chloroformate are fed simultaneously into a tube reactor operating at 1 900C and 50 atm. pressure. 440 ml of a solution containing 29 W/W% of toluylene diisocyanate are separated from the gaseous by-products in the gas/liquid separator. The solvent is removed in the usual way to obtain 1 65 g (95%) of toluylene diisocyanate.

Example 21 10.0 ml/min. (7.3 g/min.) of butylamine and 30.0 ml/min. of trichloromethyl chloroformate are fed simultaneously into a tube reactor operating at 1 500C and 5 atm. pressure. The mixture which leaves the reactor is fed into a column filled with activated carbon, operating at 1 800C and 5 atm.

pressure. Thereafter the gaseous substances are removed in the gas/liquid separator, and the crude product is distilled. 91 g (92%) of butyl isocyanate are obtained.

Example 22 20.0 ml/min. of a 40 W/W% carbon tetrachloride solution of 4,4'-diphenylmethane diamine and 20.0 ml/min. of a 60.3 W/W /O carbon tetrachloride solution of trichloromethyl chloroformate are fed simultaneously into a tube reactor operating at 1 3O0C and 50 atm.

pressure. 320 ml of a solution containing 1 6.6 W/W% of 4,4'-diphenylmethane diisocyanate are separated from the gaseous by-products. The solvent is removed from the solution in the usual way and the product is purified to obtain 70g (74%) of the diisocyanate.

Example 23 20.0 ml/min. of a 39.16 W/W % carbon tetrachloride solution of aniline and 20.0 ml/min.

of a 41.4 W/W% carbon tetrachloride solution of monochloromethyl chloroformate are fed simultaneously into a tube reactor operating at 1 300C and 50 atm. pressure. The gaseous byproducts are separated, and the resulting solution which contains phenyl isocyanate and 4,4'diphenylmethane diisocyanate is distilled. 1 2g (9%) of phenyl isocyanate and 67g (89%) of 4,4'diphenylmethane diisocyanate are obtained.

Example 24 20.0 ml/min. of a 39.16 W/W% carbon tetrachloride solution of aniline and 20.0 ml/min.

of a carbon tetrachloride solution containing 20.52 W/W% of monochloromethyl chloroformate and 30.15 W/W% of trichloromethyl chloroformate are fed simultaneously into a tube reactor operating at 1 3O0C and 50 atm. pressure. The gaseous byproducts are removed in the gas/liquid separator, and then the solvent is removed from the resulting carbon tetrachloride solution of phenyl isocyanate and 4,4'-diphenylmethane diisocyanate. The residue is purified in the usual way to obtain 14 g (10%) of phenyl isocyanate and 64.7g (85%) of 4,4'-diphenylmethane diisocyanate.

Example 25 20.0 ml/min. of a carbon tetrachloride solution containing 12.1 W/W% of butylamine and 36 W/W% of aniline and 22.0 ml/min. of a solution containing 69 W/W% of trichloromethyl chloroformate and 29 W/W% of monochloromethyl chloroformate are fed simultaneously into a tube reactor operating at 1 7O0C and 50 atm. pressure. The gaseous byproducts are removed in the gas/liquid separator to obtain a solution which contains butyl isocyanate, phenyl isocyanate and 4,4'diphenylmethane diisocyanate.

The solvent is evaporated, and the isocyanates are separated from each other by distillation. 34g (94%) of butyl isocyanate, 9g (10%) of phenyl isocyanate and 92g (86%) of 4,4'diphenylmethane diisocyanate are obtained.

Example 26 20.0 ml/min. of a 31.1 W/W% carbon tetrachloride solution of butylamine and 20.0 mi/min. of a 60.6 W/W% carbon tetrachloride solution of trichloromethyl chloroformate are fed simultaneously into a tube reactor operating at 1 500C and 5 atm. pressure. The mixture which leaves the reactor is passed through a column filled with activated carbon, operating at 1 800C and 5 atm. pressure. Thereafter the mixture is fed into a gas/liquid separator operating at 800C and 5 atm. pressure, and 73g of pure, dry, gaseous hydrochloric acid are lead off from the separator in every 10 minutes. The liquid phase is expanded and distilled at atmospheric pressure, and the phosgene-containing carbon tetrachloride solution is recirculated into the column filled with activated carbon.The product is purified to obtain 93g (94%) of butyl isocyanate.

Example 27 One proceeds as described in Example 26 with the difference that o-dichlorobenzene is applied as solvent. 92g (93%) of butyl isocyanate are obtained.

Example 28 One proceeds as described in Example 26 with the difference that the reactants are fed directly into the column filled with activated carbon, operating at 1 8O0C and 5 atm. pressure. 92.5g (93.5%) of butyl isocyanate are obtained.

Example 29 One proceeds as described in Example 26 with the difference that 20.0 ml/min. of a 31 W/W ib carbon tetrachloride solution of butylamine, 20.0 ml/min. of a 30.3 W/W% carbon tetrachloride solution of trichloromethyl chloroformate and 20.0 ml/min. of a 30.4 W/W % carbon tetrachloride solution of phosgene are fed simultaneously into the tube reactor operating at 1 5O0C and 5 atm. pressure. After one hour the feeding of the phosgene solution is cut off, and the carbon tetrachloride solution of phosgene, obtained in the distillation at atmospheric pressure, is recirculated into the tube reactor. 94g (95%) of butyl isocyanate are obtained.

Example 30 20.0 ml/min. of a 10.23 W/W% carbon tetrachloride solution of methylamine and 20.0 ml/min. of a 60.3 W/W% carbon tetrachloride solution of trichloromethyl chloroformate are fed into a tube reactor operating at 1 5O0C and 5 atm.

pressure. The mixture which leaves the reactor is fed into a reactor filled with activated carbon, operating at 1 800C and 5 atm. pressure.

Thereafter the mixture is fed into a separator operating at 800C and 5 atm. pressure, and 22 g (6.6 litres) of dry, gaseous hydrochloric acid are led off from the separator. The mixture is then expanded and distilled at atmospheric pressure.

The phosgene-containing carbon tetrachloride solution is recirculated into the reactor filled with activated carbon, and the product is purified.

82.55 g of a product consisting of 70 W/W% of methylcarbamoyl chloride and 30 W/W% of methyl isocyanate are obtained, thus the conversion is 97.6%.

Example 31 20.0 ml/min. of a 43 W/W% carbon tetrachloride solution of hexylamine and 20.0 ml/min. of a 60.3 W/W% carbon tetrachloride solution of trichloromethyl chloroformate are fed simultaneously into a tube reactor operating at 180 C and 50 atm. pressure. 300 ml of a mixture of n-hexyl isocyanate and carbon tetrachloride are obtained after separating the liquid from the gaseous substances in the liquid/gas separator.

This mixture is distilled to obtain 101.9 g (91%) of n-hexyl isocyanate.

Example 32 20.0 ml/min. of a 23.4 W/W% carbon tetrachloride solution of isopropylamine and 20.0 ml/min. of a 60.3 W/W% carbon tetrachloride solution of trichloromethyl chloroformate are fed simultaneously into a tube reactor filled with granular activated carbon, operating at 220 C and 50 atm. pressure. The mixture which leaves the reactor is fed continuously into a gasiliquid separatol, where 260 ml of a carbon tetrachloride solution containing isopropyl isocyanate are obtained. This solution is distilled to obtain 68.4 g (94%) of isopropyl isocyanate.

Example 33 A solution of 44.6g of 4-chloro-4'-aminobiphenyl in 200 ml of dichloromethane and 200 ml of a 20 W/W% dichloromethane solution of trichloromethyl chloroformate are fed continuously, within 10 minutes into a tube reactor operating at 1 200C and 5 atm. pressure.

The mixture which leaves the reactor is subjected to separation, and the 350 ml of the solution obtained is distilled. 23 g (90%) of 4-chlorobiphenyl-4'-isocyanate are obtained.

Example 34 20.0 ml/min. of a 37.8 W/W% chlorobenzene solution of p-toluidine and 20.0 ml/min. of a 41 W/W% chlorobenzene solution of trichloromethyl chloroformate are fed continuously into a tube reactor filled with activated carbon, operating at 1800 C. The mixture which leaves the reactor is fed into a gas/liquid separator, and the separated 360 mi of liquid are distilled. 98.6 g (93%) of 4methylphenyl isocyanate are obtained.

Example 35 20.0 ml/min. of a 46 W/WO/o o-dichlorobenzene solution of 4-ethylaniline and 20.0 ml/min. of a 60.3 W/W% o-dichlorobenzene solution of trichloromethyl chloroform ate are fed simultaneously and continuously into a tube reactor operating at 1 5O0C and 5 atm. pressure.

The mixture which leaves the reactor is expanded and fed into a gas/liquid separator to obtain 380 ml of a solution, which is then distilled. 102 g (88%) of 4-ethylphenyl isocyanate are obtained.

Example 36 20.0 ml/min. of a 22.9 W/W% carbon tetrachloride solution of p-anisidine and 20.0 ml/min. of a 60 W/W% carbon tetrachloride solution of trichloromethyl chloroformate are fed simultaneously and continuously into a reactor operating at 1 800C and 50 atm. pressure. The mixture which leaves the reactor is separated, and the solution is distilled to obtain 102.6 g (86%) of 4-methoxyphenyl isocyanate.

Example 37 20.0 ml/min. of 43.2 W/W% chlorobenzene solution of m-phenylene diamine and 30.0 ml/min. of a 65 W/W% o-dichlorobenzene solution of trichloromethyl chloroformate are fed simultaneously and continuously into a tube reactor operating at 1 500C and 5 atm. pressure.

460 ml of a liquid are separated in the gas/liquid separator, and then the liquid is distilled to obtain 106 g (91.6%) of m-phenylene diisocyanate.

Example 38 400 ml of o-dichlorobenzene and 130 ml of trichloromethyl chloroform ate are introduced into a round-bottomed flask of 2500 ml capacity, equipped with a stirrer, a reflux condenser and a thermometer. Thereafter 1000 ml of a 21 W/W /O o-dichlorobenzene solution of 4,4'diaminodibenzyl are added to the mixture with stirring, whereupon the temperature of the reaction mixture rises above 1 O00C. The resulting mixture is stirred at 1 300C for 4 hours and then processed by fractional distillation. 201 g (94.8%) of 4,4'-dibenzyl diisocyanate are obtained.

Example 39 400 ml of o-dichlorobenzene and 100 ml of trichloromethyl chioroformate are introduced into a round-bottomed flask of 2500 ml capacity, equipped with a stirrer, a reflux condenser and a thermometer, 1000 ml of a 27 W/W% odichlorobenzene solution of methylenebis-(ochloroaniline) are added to the mixture with stirring, whereupon the temperature of the reaction mixture raises above 1000C. At the end of the addition the mixture is stirred at 1 300C for 4 hours and then distilled. 230 g (90%) of 3,3'dichloro-diphenylmethane-4,4'-diisocyanate are obtained.

Example 40 210 g of ignited sodium carbonate and 100 ml of o-dichlorobenzene are introduced into a round bottom flask of 2500 ml capacity, equipped with a stirrer and a thermometer. 100 ml of a 30 W/W% o-dichlorobenzene solution of trichloromethyl chloroformate are added to the mixture under continuous stirring and intense cooling (at40 C) within one hour. The reaction mixture is stirred then for one further hour at O- 200 C, thereafter the mixture is filtered and the filtrate is distilled to obtain 26 g (92%) of methyl isocyanate.

Example 41 One proceeds as described in Example 4 with the difference that activated carbon impregnated with 0.5 W/V\P/O of ferric chloride is applied as catalyst. 91 g (92%) of butyl isocyanate are obtained.

Example 42 One proceeds as described in Example 4 with the difference that activated carbon impregnated with 0.5 W/W% of aluminium chloride is applied as catalyst. 89 g (90%) of butyl isocyanate are obtained.

Example 43 One proceeds as described in Example 1 5 with the difference that the reactor is operated at 250"C under a pressure of 5 atmospheres. 53 g (93%) of methyl isocyanate are obtained.

Example 44 20.0 ml/min. of a 31.1 W/W% o-dichlorobenzene solution of butylamine and 20.0 ml/min.

of a 60 W/W% solution of trichloromethyl chloroformate are fed simultaneously and continuously, through a pre-heater, into a tube reactor filled with activated carbon, operating at 3000 C. The mixture which leaves the reactor is passed through a separator, and the separated liquid is distilled. 83 g (85%) of butyl isocyanate are obtained.

Example 45 20.0 ml/min. of a 36.8 W/W% odichlorobenzene solution of benzylamine and 20.0 ml/min. of a 30 W/W% solution of trichloromethyl chloroformate are fed simultaneously and continuously, by means of a high-pressure liquid pump, into a tube reactor operating at 1 800C and 200 atm. pressure. The mixture which leaves the reactor is expanded, passed through a gas/liquid separator, and the separated liquid is distilled. 92 g (86%) of benzyl isocyanate are obtained.

Example 46 20.0 ml/min. of a 33.6 W/W /O o- dichlorobenzene solution of aniline and 20.0 ml/min. of a 60.5 W/W% o-dichlorobenzene solution of trichloromethyl chloroformate are fed simultaneously and continuously into a reactor operating at 1 2O0C and 0.2 atm. pressure. The product is removed continuously from the reactor by distillation, and the crude product is purified by fractional distillation. 120 g (86%) of phenyl isocyanate are obtained.

Claims (3)

Claims

1. A process for the preparation of isocyanate esters of the general formula (I), R--(NCO), (I) wherein n is one and R stands for a straight-chained or branched C,~10 alkyl, benzyl, cyclohexyl, phenyl, halophenyl, methylphenyl or methoxyphenyl group, or n is two and R stands for a hexamethylene, phenylene, methylenebis)phenylene), ethylenebis(phenylene) or methylenebis(halophenylene) group, from amines of the general formula (II) R(NH2)n (II) wherein R and n are as defined above, at a temperature of-400C to +3O00C under a pressure of 0.2 to 200 atmospheres, optionally in the presence of a chlorinated hydrocarbon solvent or a solvent mixture containing a chlorinated hydrocarbon and/or in the presence of an activated carbon catalyst impregnated optionally with 0.1 to 5 W/WO/o of a metal halide and/or optionally in the presence of an inorganic base or a tertiary amine, wherein one or two amines of the general formula (II) are reacted with a compound of the general formula (III), R'-O-CO-Cl (Ill) wherein R' stands for chloromethyl, dichloromethyl or trichoromethyl group, or with a mixture thereof, fed into the reaction mixture in liquid state.

2. A process for the preparation of isocyanate esters as claimed in Claim 1 substantially as hereinbefore described in any one of the Examples.

3. An isocyanate ester when produced by d process as claimed in Claim 1 or Claim 2.