FR2464249A1 - Prepn. of methyl-isocyanate intermediates for insecticides - by passing methyl halide through metal cyanate, catalyst and solvent mixt. at a specified rate - Google Patents

Abstract

Prepn. of methylisocyanate (I) by reaction of an alkali and/or alkaline earth metal cyanate with methyl halides in organic solvents at elevated temps. in the presence of a catalyst such as an iodide or bromide of an alkali(ne earth) metal comprises passing the methylhalide through the reaction mixt. at the rate of 0.5-3 mol/hr. mol. cyanate, so that the reaction time is 1-4 min. Ratio of organic solvent to methyl halide is 3-5:1 and (I) is removed continuously from the reaction zone. (I) is an intermediate in the prepn. of e.g. esters of N-methylcarbamide acids which are strong insecticides. The process gives higher yields of (I) than previous processes, but also has a shorter residence time. Essentially 92-97% of the cyanate is converted to (I).

Description

 The present invention relates to processes for the preparation of isocyanates and, more particularly, to a process for the preparation of methyl isocyanate which is a raw material in the production, for example, of N-methylcarbamic acid ethers having a large spectrum of insecticidal activity.

 Isocyanates are currently widely used in the chemical industry.

Improvements in the processes for preparing isocyanates are directed towards the choice of reagents and of the conditions under which the reactions take place, ensuring a high yield of the desired product.

There is a known process for the preparation of methyl isocyanate (see United States patent No. 3644461) by interaction of phosgene with methylamine or with the hydrochloride of the latter at a temperature of 250 OC followed by the formation N-methylcarbamoyl chloride which is subsequently decomposed to form methyl isocyanate

The treatment of methylamine with phosgene during the first stage is carried out in the gas phase b at temperatures of the order of 350 to 400 OC in a continuous reactor at atmospheric pressure. The reaction gases which are N-methylcarbamoyl chloride and HC1, both in the gaseous state, are brought into a column sprayed with carbon tetrachloride cooled to 10 OC, where they are cooled to 65-70 OC,
The solution obtained of methylcarbamoyl chloride in carbon tetrachloride progresses through the column in order to extract the unreacted phosgene. Then, to obtain methyl isocyanate, the hydrogen chloride is removed from the methylcarbamoyl chloride dissolved in carbon tetrachloride using dimethylamine, at a temperature of 45 to 50 OC. The extraction of methyl isocyanate is carried out in two successive columns. The theoretical yield of methyl isocyanate is approximately 90%.

The methyl isocyanate obtained contains 98% of basic substance of 2% of carbon tetrachloride.

 Although this process guarantees a fairly high yield of methyl isocyanate, it has the drawbacks of requiring several stages and complicated apparatus and of requiring expensive and, more importantly, extremely toxic raw materials. In addition, hydrochloric acid formed during the process of preparing methyl isocyanate causes corrosion of the equipment.

A difficult problem to solve is to regenerate the auxiliary substances that participate in the process.

For example, the waste formed during the regeneration stage of dimethylaniline and carbon tetrachloride must undergo thermal decomposition which leads to pollution of the environment.

Other methods of preparing methyl isocyanate are also contacted, which are carried out, for example, by thermally decomposing N, N'-diphenyl-N'-methylurea at a temperature of 240 to 249 OC (Siejken, Ann ., 1949, 562.75) or by decomposing phenyl methyl methylcarbamate in the presence, as heat carriers, of diaryl carbonates, the operation being carried out at a temperature of 240 to 250 OC (see Japanese patent NO 1653-69).

Methyl isocyanate can also be prepared by interaction of methylamine with diphenyl carbonate at a temperature higher than 200 OC but lower than the boiling temperature of diaryl carbonate (see Japanese patent NO 20534-73) or by interaction of N, Ndimetylurea with a diaryl carbonate, the molar ratio being I / I, 5-I, 4, at a temperature of 200 to 300 OC (see Japanese patent NO I652-73).

 The abovementioned processes however require expensive raw materials, the production of which is in turn linked to the use of phosgene and also expensive amines.

We contact another process for the preparation of organic isocyanates (see the invention patent of the States
Unis NO 3584028) containing 1 to 20 carbon atoms in the carbon group by interaction, at elevated temperature, of an alkali and / or alkaline earth metal cyanate with an organic chlorine compound in an organic solvent medium and presence, as a catalyst, of an iodide or bromide of an alkali or alkaline earth metal.

 To carry out this process, 0.5 to 5 moles, preferably 0.8 to 10 moles, of cyanate are taken per mole of organic chlorine compound; from 0.01 to 10 moles, preferably from 0.5 to 0.25 moles, of catalyst; and from 10 to 100 moles, preferably from 25 to 50 moles, of organic solvent. The reaction temperature is between 250 and 300 ° C., preferably between 50 and 150 ° C., the pressure being between less than 1 kg / cm and 703 kg / cm and the contact time is 50 minutes.

In the exemplary embodiments, the organic chlorine compound used is benzyl, allyl and n-octyl chlorides.

 This process does not require the use of substances of high toxicity but the yield of isocyanates is between 6.8 and 55%. The other 45 So and more consist of isocyanurates. Isocyanurate formation is mainly due to the excessive contact time (50 'or minutes) of cyanates with organic halogen compounds which allows the isocyanate formed to polymerize.

The process, as indicated in the patent, can also be used for the preparation of an isocyanate containing 1 carbon atom in the carbon group, that is to say methyl isocyanate.

In this case, methyl chloride is used as the organic chlorine compound.

 As the methyl isocyanate is the most sensitive among the isocyanates of alkyl to heat and to the presence of salts which have, for cation, alkali or alkaline-earth metals and, for anion, halogens, OCN, C03 - etc , the yield of methyl isocyanate is even lower.

The invention aims to increase the yield of methyl isocyanate by changing the parameters of the interaction of the halogenated methyl-bearing compound with the reaction medium.

 This problem is solved by the fact that, in a process for the preparation of methyl isocyanate by interaction, at elevated temperature, of an alkali and / or alkaline earth metal cyanate with a methylated halogenated compound in the presence, as catalyst, of an iodide or bromide of an alkali or alkaline-earth metal, the methylated halogenated compound is sent through the reaction mixture at a flow rate of 0.5 to 3 moles of methylated halogenated compound per mole of cyanate per hour, the contact time being 1 to 4 minutes and the rap, port between the organic solvent and the methylated halogenated compound being 3-5 / 1, after which the product is continuously discharged from the reaction zone.

 Methyl isocyanate is sensitive to heat and to the presence of salts which have, for cation, alkali or alkaline-earth metals and, for anion, halogens, OCN-CO3- etc ...

 To obtain a high yield of methyl isocyanate, it is therefore necessary to reduce the contact time of the methylated halogenated compound with the reaction mixture.

 By "reaction mixture" is meant the alkali and / or alkaline earth metal cyanate dispersed in an organic solvent and the catalyst, in the form of an iodide or bromide of alkali or alkaline earth metal, dissolved in this solvent. The contact time is 1 to 4 minutes, which guarantees a high yield of methyl isocyanate and, on the other hand, the continuous evacuation of the product prevents its polymerization.

 The contact time mentioned is provided by the admission flow rate of the methylated halogenated compound through the reaction medium, this flow rate being from 0.5 to 3 moles of methylated halogenated compound per mole of cyanate per hour. This not only ensures a short contact time of the reagents, but also an extension of the contact surface, which in turn contributes to improving the yield of methyl isocyanate.

The method of the invention also makes it possible to reduce the consumption of the organic solvent and to ensure, during the process, a ratio of 375/1 between the organic solvent and the methylated halogenated compound, while the known method provides for 10 to 100 moles of organic solvent per mole of methylated halogenated compound.

 The increase in the ratio of the solvent to the methyl halogenated compound means that the methyl isocyanate is dissolved in the organic solvent and it then becomes impossible to separate it from the solvent, even at a temperature of 150 ° C. and above. The dissolved methyl isocyanate polymerizes and forms methyl isocyanurate, and therefore the yield of methyl isocyanate is reduced to about 50%. The yield of methyl isocyanate is also reduced in the case of a reduction in the ratio between the organic solvent and the methylated halogenated compound.

 Before introducing the methylated halogenated compound it is recommended to heat the reaction mixture, with stirring, to a temperature of 120 to 140 ° C., then to cool it down to a temperature of 600 to 70 ° C. and then introduce an amount of 0.5 to 2 moles of methylated halogenated compound, after which the reaction mixture is heated to a temperature of 1100 to 120 ° C. and the remainder of the methylated halogenated compound is introduced simultaneously.

 The process thus implemented makes it possible to obtain a high yield of methyl isocyanate and a high degree of purity of the product thanks to the fact that before introducing the methylated reagent, the water and the amines which cause l are removed from the reaction mixture. hydrolysis of cyanate and promote the polymerization of methyl isocyanate.

Before introducing the methylated halogenated compound it is recommended to remove the water and the amines by introduction into the reaction mixture of an easily volatile solvent such as petroleum ether, benzene or toluene, followed by a heating the still stirred reaction mixture to a temperature of 1200 to 140 OC and cooling it to a temperature of 600 to 70 OC, after which an amount of 0.5 to 2 moles of reagent carrying is introduced into this mixture methyl, and heating is carried out to a temperature of 110 to 120 ° C. while introducing the remainder of the methylated halogenated compound.

This variant of the process allows to intensify the process of preparation of methyl isocyanate thanks to the acceleration of the process of elimination of amines and water which are eliminated with the easily volatile solvent at an elevated temperature.

 It is proposed to stir the reaction mixture by introducing an inert gas therein, for example nitrogen.

By stirring the reaction mixture, the inert gas contributes to releasing this mixture of water and amines.

An embodiment of the process of the invention is described below.

To implement the process, a column type reactor is used which has an electric heater and a device for distributing the methylated halogenated compound, placed in the lower part of the reactor.

The process begins with the loading into the reactor of an organic solvent (polar and non-polar solvent), a catalyst (iodide or bromide of an alkali or alkaline earth metal) and an alkali or alkali metal cyanate - earthy.

 The process is carried out with, as non-polar solvents, hydrocarbons having a boiling point of 100 OC and above. One of the effective non-polar solvents is meta-xylene. Mention may be made, as polar solvent, of substituted N, N-dialkylamides, for example dimethylformamide.

 The cyanate used can contain up to 25% carbonates. KCl, which is formed simultaneously with methyl isocyanate, contains K2CO3. The latter can be transformed into KCS by additional treatment with HC t.

 With the reactor loaded, the heater is started and the reaction mixture is started to stir. The stirring is carried out by a stream of nitrogen which is inert to the reaction mixture, or else using a mechanical stirrer, the two methods being able to be used together.

 The reaction mixture being brought to a temperature of 1200 to 140 ° C., one begins to introduce into it chloride, bromide or methyl iodide at a flow rate of 1 to 3 moles (22.4 - 67.2 1) of the compounds indicated per mole of cyanate per hour.

The preparation of methyl isocyanate can be carried out by heating the reaction mixture, still stirred, to a temperature of 1200 to 140 ° C., in order to remove the amines and the water. Then the temperature is lowered to 600 - 70 OC and, the introduction of nitrogen being stopped, in the case of the use of nitrogen to stir the mixture) one proceeds to the introduction of the methylated halogenated compound, in an amount of 0.5 to 2 moles.

 First, the methylated halogenated compound is absorbed by the reaction mixture without the methyl isocyanate or other products being released from the reaction zone. Then the temperature in the reactor spontaneously rises to 900 - 100 OC and there is an intense release of methyl isocyanate which is continuously discharged into a collector through a condenser.

Then the temperature in the reactor is raised to 1200 - 140 OC and the remainder of the halogenated compound born methylated therein.

 The water and the amines can be removed, before the introduction of the methylated halogenated compound by the introduction into the reaction mixture, of an organic solvent (petroleum ether, benzene or toluene or else mixture of benzene and toluene).

Then, the continuously stirred reaction mixture is brought to a temperature of 1200 to 140 ° C. so that the impurities are removed from the reaction medium with the easily volatile solvent. After that, operations take place as described above.

 The process is controlled by gas-liquid chromatography. The process being completed, the reaction mixture is cooled to a temperature of 200 to 25 OC. Then the alkali metal chloride is separated from the solvents and from the catalyst dissolved in the latter, using a centrifuge. The mixture of solvents and catalyst, released from the chloride, can be re-used.

 The yield of methyl isocyanate is 92 to 97% of the theoretical yield calculated relative to the cyanate used. The methyl isocyanate obtained can contain up to 2% of methyl chloride and iodide. However, their presence in methyl isocyanate does not prevent the synthesis of naphthyl ether of N-methylcarbamic acid from methyl isocyanate.

Other characteristics and advantages of the invention will appear on reading the examples of implementation which follow.

EXAMPLE 1
530 g (5 moles) of meta-xy lene, 730 g (10 moles) are charged into a 4 1 capacity reactor, the height of which is 200 cm and the diameter of 5 cm, equipped with an electric heater. of dimethylformamide, 83 g (0.5 mole) of potassium iodide, 300 g of technical potassium cyanate having a granularity less than 0.1 mm and containing 243 g (3 moles) of potassium cyanate and 57 g (0 , 41 mole) of potassium carbonate.

 The mixture is stirred by a stream of dry nitrogen brought into the reactor and simultaneously the heater is started. The temperature in the reactor rises to 1300C, after which 106 g (1 mole) of meta-xylene are extracted in the form of an azeotropic mixture with water and amines. After that, the temperature is lowered to 60 ° C., the nitrogen is stopped and the introduction of methyl chloride in the amount of 151 g (3 moles) begins at a rate of 22.4 (1 mole) per mole of potassium cyanate per hour, the molar ratio "solvent / methyl chloride" being 5: 1. The contact time is 2.5 minutes.

 The introduction of 1.5 moles (75.75 g) of methyl chloride having been completed, the temperature in the reactor rises to 100 ° C., causing the evolution of methyl isocyanate which is removed from the reactor through a kéfrigerant.

The temperature of the solution is gradually raised to 120 ° C. and the remainder of the methyl chloride is introduced. 162.5 g of methyl isocyanate are obtained, which represents 95% of the theoretical yield. The purity of the methyl isocyanate obtained is 98%.

The contents of the reactor are cooled to 25 OC; after which one proceeds to a filtration to separate the mixture of potassium chloride, potassium cyanate and potassium carbonate. The filtrate composed of meta-xylene of dimethylformamide and potassium iodide dissolved in the latter is returned to the reactor for re-use.

EXAMPLE 2
In a reactor like that of Example 1, the following are charged: 530 g (5 moles) of meta-xylene, 730 g (10 moles) of dimethylformamide, 75 g (0.5 mole) of sodium iodide, and 238 , 5 g of technical sodium cyanate at a particle size of 0.1 mm and containing 195 g (3 moles) of sodium cyanate and 43.5 g (0.40 mole) of sodium carbonate.

 The mixture is stirred by a stream of dry nitrogen introduced into the reactor and simultaneously the heater is started to raise the temperature in the reactor to 130 OC.

 A quantity of 106 g (1 mole) of meta-xylene is thus extracted in the form of an azeotropic mixture with water and the amines. After that, the temperature in the reactor is lowered to 60 ° C., the nitrogen is stopped and the methyl chloride is started at the rate of 151 g (3 moles) at a flow rate of 22.4 1 ( 1 mole) per mole of sodium cyanate per hour, the "solvent / methyl chloride" molar ratio being 5/1. The contact time is 2.5 minutes.

The introduction of a quantity of 1.5 moles (75.75 g) of methyl chloride having been completed, the temperature in the reactor gradually rises to 100 ° C., causing the release of the methyl isocyanate which is removed in continuous reaction of the reactor, through a cooler, in a collector. The temperature in the reactor is raised to 120 ° C. and the rest of the methyl chloride is introduced.

 157.3 g of methyl isocyanate are obtained, which represents 92% of theoretical yield. The purity of the methyl isocyanate obtained is 98%. The contents of the reactor are cooled and treated as in Example 1.

EXAMPLE 3
730 g of dimethylformamide, 1060 g (10 moles) of ethylbenzene, 294 g (-i mole) of calcium iodide, and 258 g of technical calcium cyanate are charged to a reactor like that of Example 1. particle size of 0.1 mm and containing 248 g (2 moles) of calcium cyanate and 10 g (0.1 mole) of calcium carbonate. The mixture is stirred by a stream of dry nitrogen introduced into the reactor and simultaneously the heater is started to raise the temperature in the reactor to 140 OC. Thus an amount of 212 g (2 moles) of ethylbenzene is extracted in the form of an azeotropic mixture with water and the amines.

 The temperature is then lowered to 70 ° C., the introduction of nitrogen is stopped and the introduction of methyl chloride in the amount of 151 g (3 moles) is started at a rate of 22.4 1 (1 mole) per mole. of calcium cyanate per hour, the solvent / methyl chloride molar ratio "being 4/1. The contact time is 2.5 minutes. The introduction of an amount of 2.0 moles (101 g) of methyl chloride being finished, the temperature in the reactor gradually rises to 100 OC causing the release of methyl isocyanate which is continuously removed from the reactor through a condenser in a collector. The temperature is gradually raised into the reactor at 120 ° C. and the remainder of the methyl chloride is introduced.

211 g of methyl isocyanate are obtained, which represents 92.5% of the theoretical yield. The purity of the methyl isocyanate obtained is 98.5%.

The contents of the reactor are cooled to 25 ° C. and treated as in Example 1.

EXAMPLE 4
In a reactor like that of Example 1, the following are charged: 300 g (2.5 moles) of mesitylene, 78 g (1 mole) of benzene, 365 g (5 moles) of dimethylformamide, 83 g (0.5 mole ) potassium iodide and 300 g of tectonic potassium cyanate at a particle size of less than 0.1 mm and containing 243 g (3 moles) of potassium cyanate and 57 g (0.41 mole) of potassium carbonate. The mixture is stirred by a stream of dry nitrogen introduced into the reactor and simultaneously the heater is started. The temperature in the reactor rises to 120 ° C. and thus an amount of 75 g (approximately 1 mole) of benzene is extracted in the form of an azeotropic mixture with water and the amines. After this the temperature in the reactor is lowered to 70 OC, the nitrogen is stopped and the methyl chloride in the amount of 151 g (3 moles) is started to be introduced at a rate of 22.4 1 (I mole) per mole of potassium cyanate per hour, the molar ratio "solvent / methyl chloride" being 3/1.

The contact time is 2.5 minutes, the introduction of 1.5 liters (75.75 g) of methyl chloride being completed, the temperature in the reactor gradually rises to 100 ° C., causing the release. of methyl isocyanate which is continuously discharged from the reactor, through a refrigerant, into a collector. The temperature is gradually raised to 120 ° C. and the remainder of CH3Cl is introduced. 165.9 g of methyl isocyanate are obtained, which represents 97% of the theoretical yield. The purity of the methyl isocyanate obtained is 99.0%. The contents of the reactor are cooled to 25 ° C. and treated as in Example 1.

EXAMPLE 5
The following are charged into a reactor like that of Example 1: 335 g (2.5 moles) of diethylbenzene, 505 g (5 moles) of diethylformamide, 92 g (1 mole) of toluene, 0.83 g (0, 5 moles) of potassium iodide and 300 g of technical potassium cyanate with a particle size of less than 0.1 mm and containing 243 g (3 moles) of potassium cyanate and 57 g (0.41 moles) of potassium carbonate . The mixture is stirred by a stream of dry nitrogen introduced into the reactor and simultaneously the heater is started to raise the temperature in the reactor to 130 OC. Thus 92 g (1 mole) of toluene are extracted in the form of an azeotropic mixture with water and the amines.

 Then the temperature is lowered to 70 ° C., the nitrogen is stopped and it begins to introduce methyl chloride in the amount of 151 g (3 moles at a flow rate of 67.2 1 (3 moles) per mole of cyanate potassium per hour, the molar ratio "solvent / methyl chloride" being 3/1.

The contact time is 1 minute. The introduction of a quantity of 1.5 mol (75.75 g) of methyl chloride being completed, the temperature in the reactor gradually rises to 100 ° C. causing the release of methyl isocyanate which is continuously discharged from the reactor, through a condenser, into a collector. The temperature in the reactor is gradually raised to 120 ° C. and the rest of the methyl chloride is introduced.

 164.2 g of methyl isocyanate are obtained, which represents 96% of the theoretical yield. The purity of methyl isocyanate is 98.3%. The contents of the reactor are cooled to 25 ° C. and treated as in Example 1.

EXAMPLE 6
In a reactor like that of Example 1, the following are charged: 530 g (5 moles) of ethylbenzene, 72 g of petroleum ether, 730 g (10 moles) of dimethylformamide, 83 g (0.5 mole) of diiodide of potassium and 300 g of technical potassium cyanate with a particle size less than 0.1 mm and containing 243 g (3 moles) of potassium isocyanate and 57 g (0.41 mole) of potassium carbonate. The mixture is stirred by a stream of dry nitrogen introduced into the reactor and simultaneously the heater is started. The temperature in the reactor rises to 120 ° C., and thus 72 g of petroleum ether are extracted in the form of an azeotropic mixture with water and the amines. Then the temperature in the reactor is lowered to 65 ° C. stops introducing nitrogen and we begin to introduce methyl chloride in an amount of 151 g (3 moles) at a flow rate of 22.4 1 (1 mole) per mole of potassium cyanate per hour, the molar ratio " solvent / methyl chloride "being 5/1. The contact time is 2.5 minutes.

 The introduction of 1.5 moles (75.75 g) of methyl chloride having been completed, the temperature in the reactor gradually rises to 90 ° C., causing the release of methyl isocyanate which is continuously removed from the reactor, through a coolant, in a collector. Then, the temperature is gradually raised in the reactor to 120 ° C. and the rest of the methyl chloride is introduced. 160.7 g of methyl isocyanate are obtained, which represents 94% of the theoretical yield. The purity of the methyl isocyanate obtained is 98%. The contents of the reactor are cooled to 250C and treated as in Example 1.

EXAMPLE 7
In a reactor like that of Example 1, the following are charged: 985 g (5 moles) of diphenylformamide, 265 g (2.5 moles) of meta-xylene, 39 g (0.5 moles) of benzene, 46 g (0.5 mole) of toluene, 83 g (0.5 mole) of potassium iodide and 300 g of technical potassium isocyanate with a particle size of less than 0.1 mm and containing 243 g (3 moles) of potassium cyanate and 57 g (0.41 mole) of potassium carbonate.

The mixture is stirred by a stream of dry nitrogen introduced into the reactor and simultaneously the heater is started. The temperature in the reactor rises to 130 ° C., and thus an amount of 86 g of a mixture of benzene and toluene (0.5 mole of each) is extracted in the form of an azeotropic mixture with water and the amines. .

 Then the temperature in the reactor is lowered to 70 ° C., the nitrogen is stopped and the methyl chloride in the amount of 151 g (3 moles) is started to flow at a rate of 22.4 1 (1 mole) per mole of potassium cyanate per hour, the “solvent / methyl chloride” molar ratio being 3/1. The contact time is 2.5 minutes. The introduction of 1 mole (50.5 g) of methyl chloride having been completed, the temperature in the reactor gradually rises to 90 ° C., causing the release of methyl isocyanate which is continuously evacuated from the reactor, at through a refrigerant, in a collector. The temperature is gradually raised in the reactor to 120 ° C. and the remainder of the methyl chloride is introduced. 160.3 g of methyl isocyanate are obtained, which represents 92% of the theoretical yield. The purity of the methyl isocyanate obtained is 98 1. The reactor content is cooled to 25 ° C. and treated as in Example 1.

EXAMPLE 8
In a reactor like that of Example 1, the following are charged: 600 g (5 moles) of ethyltoluene, 92 g (1 mole) of toluene, 870 g (10 moles) of dimethylacetamide, 83 g (0.5 mole) potassium iodide and 300 g of technical potassium cyanate with a particle size of less than 0.1 mm and containing 243 g (3 moles) of potassium cyanate and 57 g (0.41 mole) of potassium carbonate. The mixture is stirred by a stream of dry nitrogen introduced into the reactor and simultaneously the heater is started. The temperature in the reactor rises to 120 OC and thus a quantity of 92 g (1 mole) of toluene is extracted in the form of an azeotropic mixture with water and the amines. Then the temperature in the reactor is lowered to 70 OC , one ceases to introduce nitrogen and one begins to introduce methyl chloride in an amount of 151 g (3 moles) at a rate of 22.4 1 (1 mole) per mole of potassium cyanate per hour, the "solvent / methyl chloride" molar ratio being 5/1.

The contact time is 2.5 minutes.

 The introduction of 1.5 moles (75.75 g) of methyl chloride having been completed, the temperature in the reactor gradually rises to 100 ° C., causing the release of methyl isocyanate which is continuously removed from the reactor , through a refrigerant, in a collector. The temperature is gradually raised in the reactor to 120 ° C. and the remainder of the methyl chloride is introduced. 159 g of methyl isocyanate are obtained, which gives 93% of the theoretical yield. The purity of methyl isocyanate is 98%.

 The contents of the reactor are cooled to 25 ° C. and treated as in Example 1.

EXAMPLE 9
In a reactor like that of Example 1, the following are charged: 530 g (5 moles) of meta-xylene, 730 g (10 moles) of dimethylformamide, 60 g (0.5 mole) of potassium bromide and 300 g of technical potassium cyanate with a particle size less than 0.1 mm and containing 243 g (3 moles) of potassium cyanate and 57 g (O, 41 moles) of potassium carbonate. The mixture is stirred by a stream of dry nitrogen introduced into the reactor, and simultaneously the heater is started. The temperature in the reactor rises to 1300C and thus 106 g (1 mole) of meta-xylene are extracted in the form of an azeotropic mixture with water and amines. Then we stop introducing nitrogen and we start to introduce methyl chloride in an amount of 151 g (3 moles) at a flow rate of 22.4 1 (1 mole) per mole of potassium cyanate per hour, the molar ratio "solvent / methyl chloride'1 being 5/1 The contact time is 2.5 minutes.

 The methyl isocyanate which is released is continuously discharged from the reactor, through a condenser, into a collector.

The introduction of 3 moles of methyl chloride being completed, the contents of the reactor are cooled to 25 ° C. and treated as in Example 1.

 137 g of methyl isocyanate are obtained, which represents 80% of the theoretical yield.

 The purity of methyl isocyanate is 98%.

EXAMPLE 10
In a reactor like that of Example 1, are charged: 530 g (5 moles) of meta-xylene, 730 g (10 moles) of dimethylformamide, 51.5 g (0.5 mole) of sodium bromide and 238 , 5 g of technical sodium cyanate with a particle size of less than 0.1 mm and containing 195 g (3 moles) of sodium cyanate and 43.5 g (0.40 mole) of sodium carbonate. The mixture is stirred by a stream of dry nitrogen brought into the reactor and simultaneously the heater is started.

The temperature in the reactor is 130 ° C. and thus 106 g (1 mol) of meta-xylene are extracted in the form of an azeotropic mixture with water and the amines. One ceases to introduce nitrogen and one begins to introduce methyl chloride in an amount of 151 g (3 moles) at a rate of 15 1 (0.7 mole) per mole of sodium cyanate per hour, the ratio "solvent / methyl chloride" molar being 5/1.

 The contact time is 4 minutes.

The methyl isocyanate which is released is continuously discharged from the reactor, through a condenser, into a collector. The introduction of methyl chloride being complete, the contents of the reactor are cooled to 25 ° C. and treated as in Example 1. The yield of methyl isocyanate is 128.3 g, which represents 75% of the theoretical yield.

The purity of the methyl isocyanate obtained is 98%.

EXAMPLE 11
530 g (5 moles) of ethylbenzene, 730 g (10 moles) of dimethylformamide, 199.8 g (1 mole) of calcium bromide and 258 g of calcium cyanate are charged into a reactor as in Example 1 technique with a particle size less than 0.1 mm and containing. 248 g (2 moles) of calcium cyanate and 10 g (0.1 mole) of calcium carbonate. The mixture is stirred by a stream of dry nitrogen brought into the reactor and simultaneously the heater is started. The temperature in the reactor rises to 130 ° C. and, thus, 106 g (1 mole) of ethylbenzene are extracted in the form of an azeotropic mixture with water and the amines. Then we stop introducing nitrogen and we start to introduce methyl chloride in an amount of 151 g (3 moles) at a flow rate of 15 l (0.7 mole) per mole of calcium cyanate per hour, the molar ratio "solvent / methyl chloride being 3 / 1'3
The contact time is 4 minutes.

 The methyl isocyanate which is released is continuously discharged from the reactor, through a condenser, into a collector. The introduction of methyl chloride in an amount of 5 moles having been completed, the contents of the reactor are cooled to 25 ° C. and treated as in Example 1.

178 g of methyl isocyanate are obtained, which represents 78% of the theoretical yield.

The purity of the methyl isocyanate obtained is 98%.

EXAMPLE 12
In a reactor like that of Example 1, the following are charged: 530 g (5 moles) of ethylbenzene, 730 g (10 moles) of dimethylformamide, 166 g (1 mole) of potassium iodide and 150 g of cyanate of technical potassium with a particle size less than 0.1 mm and containing 121.5 g (1.5 mole) of potassium cyanate and 28.5 g (0.20 mole) of potassium carbonate and 129 g of calcium cyanate technique with a particle size less than 0.1 min and containing 124 g (1 mole) of calcium cyanate and 5 g (0.05 mole) of calcium carbonate.

The mixture is stirred by a stream of dry nitrogen introduced into the reactor and simultaneously the heater is started. The temperature in the reactor is 130 ° C. and thus 106 g (1 mole) of ethylbenzene are extracted in the form of an azeotropic mixture with water and the amines.

 Then the temperature in the reactor is lowered to 60 OC, the nitrogen is stopped and the methyl chloride is started to be introduced in an amount of 151 g (3 moles) at a flow rate of 22.4 1 (1 mole ) per mole of mixture of cyanates of alkali metal (K) and alkaline earth metal (Ca) per hour, the molar ratio "solvent / methyl chloride" being 5/1. The contact time is 2.5 minutes.

The introduction of 1.5 moles (75.75 g) of methyl chloride having been completed, the temperature in the reactor gradually rises to 100 ° C., causing the release of methyl isocyanate which is continuously removed from the reactor , through a refrigerant, in a collector. The temperature is gradually raised in the reactor to 120 ° C. and the remainder of methyl chloride is introduced.

 183 g of methyl isocyanate are obtained, which represents 92.8.1 of the theoretical yield (the calculation having been made for the mixture of potassium cyanates and calcium).

The purity of the methyl isocyanate obtained is 98.2%.

 The contents of the reactor are cooled to 25 ° C. and treated as in Example 1.

EXAMPLE 13
In a reactor like that of Example 1, the following are charged: 530 g (5 moles) of meta-xylene, 730 g (10 moles) of dimethylformamide and 300 g of technical potassium cyanate containing 243 g (3 moles) of cyanate of potassium and 57 g (0.41 mole) of potassium carbonate at a particle size of less than 0.1 min. By respecting the conditions described in Example 1, 285 9/3 moles of methyl bromide are passed through the suspension (reaction mixture) to obtain 150.4 g of methyl isocyanate, which represents 89% of the theoretical yield. the purity of the methyl isocyanate obtained is 98.1%.

EXAMPLE 14
In a reactor like that of Example 1, the following are charged: 530 g (5 moles) of meta-xylene, 730 g (10 moles) of dimethylformamide and 300 g of technical potassium cyanate containing 243 g (3 moles) of cyanate of potassium and 57 g (0.41 mole) of potassium carbonate at a particle size of less than 0.1 min. By respecting the conditions described in Example 1, 426 g (3 moles) of methyl iodide are passed through the suspension to obtain 163 g of methyl isocyanate, which represents 95.2% of the theoretical yield.

The purity of the methyl isocyanate obtained is 98%.

EXAMPLE 15 (Comparative)
In a reactor like that of Example 1, the following are charged: 530 g (5 moles) of meta-xylene, 730 g (10 moles) of dimethylformamide, 83 g (0.5 mole) of potassium iodide and 300 g technical potassium cyanate with a particle size of less than 0.1 mm and containing 243 g (3 moles) of potassium cyanate and 57 g (0.41 moles) of potassium carbonate.

The mixture is stirred by a stream of dry nitrogen introduced into the reactor and simultaneously the heater is started.

 The temperature in the reactor is 130 OC and thus 106 g (1 mole) of meta-xylene are extracted in the form of an azeotropic mixture with water and amines. Then the temperature in the reactor is lowered to 60 ° C., the introduction of nitrogen is stopped and the introduction of methyl chloride in an amount of 151 g (3 moles) is started at a flow rate of 7.6 1 (0.35 mole) per mole of potassium cyanate per hour.

The "solvent / methyl chloride" molar ratio is 5/1.

 The contact time is 8- minutes.

The introduction of 1.5 mole (75.75 g) of methyl chloride having been completed, the temperature in the reactor gradually rises to 100 ° C., causing the release of methyl isocyanate which is continuously removed from the reactor , through a refrigerant, in a collector. The temperature in the reactor is gradually raised to 120 OC. The yield of methyl isocyanate is 96 g, which represents 56% of the theoretical yield. The purity of the methyl isocyanate obtained is 98%.

Thus the increase in contact time above the limit indicated for the process of the invention causes a reduction in the yield of methyl isocyanate.

EXAMPLE 16 (Comparative)
In a reactor like that of Example 1, the following are charged: 530 g (5 moles) of meta-xylene, 730 g (10 moles) of dimethylformamide, 83 g (0.5 mole) of potassium iodide and 300 g technical potassium cyanate with a particle size of less than 0.1 mm and containing 243 g (3 moles) of potassium cyanate and 57 g (0.41 mole) of potassium carbonate.

The mixture is stirred by a stream of dry nitrogen introduced into the reactor and simultaneously the heater is started. The temperature in the reactor is 130 ° C. and thus 106 g (1 mol) of meta-xylene are extracted in the form of an azeotropic mixture with water and the amines. After that the temperature in the reactor is lowered to 70 ° C., the nitrogen is stopped and the methyl chloride is started to be introduced in an amount of 50.5 g (1 mole) at a flow rate of 22.4 1 '(1 mole) per mole of potassium cyanate per hour, the molar ratio "solvent / methyl chlowre" being 15/1. The contact time is 2.5 minutes. The introduction of 0.5 mole (25.25 g) of methyl chloride having been completed, the temperature in the reactor gradually rises to 90 ° C., causing the release of methyl lisocyanate which is removed from the reactor, through a refrigerant, in a collector. The temperature in the reactor is gradually raised to 120 C.

 The yield of methyl isocyanate is 90 g, which represents 52.5% of the theoretical yield. The purity of the methyl isocyanate obtained is 98%.

 With the increase in the amount of solvent above the limit indicated for the process of the invention the yield of methylisocyanate decreases.

Claims (4)

 1 - Process for the preparation of methyl isocyanate by interaction, in an organic solvent medium, of an cyanate of an alkali and / or alkaline-earth metal with a methylated halogenated compound in the presence, as catalyst, dsiodide or bromide of an alkali or alkaline earth metal at high temperature, characterized in that the methylated halogenated compound is introduced at a flow rate of 0.5 to 3 moles of this compound per mole of cyanate per hour, the contact time being 1 to 4 minutes and the ratio of the organic solvent to the methylated halogenated compound being 3 to 5/1, and the product is continuously removed from the reaction zone.  2 - Process according to claim 1, characterized in that, before introducing the methylated halogenated compound, the reaction mixture is brought, while stirring, to a temperature of 1200 to 140 OC and then cooled to a temperature from 600 to 70 OC, then an amount of 0.5 to 2 moles of methylated halogenated compound is introduced therein and the mixture is heated to a temperature of 110 to 120 OC by simultaneously introducing the remainder of the methylated halogenated compound. 3 - Process according to claim 1, characterized in that, before introducing the methylated halogenated compound, the reaction mixture and the amines are eliminated from the reaction mixture by introduction into the reaction medium of an easily volatile solvent, such as ether of petroleum, benzene or toluene or a mixture of benzene and toluene, followed by heating the reaction mixture to a temperature of 1200 to 140 ° C., and cooling of said mixture to a temperature of 60 ° C. to 700 ° C., 0.5 to 2 moles of methylated halogenated compound are then introduced and the reaction mixture is heated to a temperature of 1100 to 120 ° C. while introducing the remainder of the methylated halogenated compound. 4 - Process according to claim 2 or 3, characterized in that the reaction mixture is stirred by introducing an inert gas, such as nitrogen.