GB1592731A - Production of an n-substituted urethane - Google Patents

Description

(54) PRODUCTION OF AN N-SUBSTITUTED URETHANE (71) We, MITSUI TOATSU CHEMICALS, INC., a Japanese Body Corporate of 2-5 Kasumigaseki 3-chome, Chiyoda-ku, Tokya 100, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a process for producing N-substituted urethanes by reacting nitro compounds, organic compounds containing at least one hydroxyl group (hereinafter referred to as hydroxyl group-containg organic compound) and carbon monoxide under high temperature and high pressure conditions in the presence of a catalyst of a specific type.

As is well known, urethanes have been heretofore produced mainly by reaction if isocyanates and hydroxyl group-containing organic compounds. In recent years, several other processes for producing urethanes have been proposed because of the lack and high cost of starting materials for producing the isocyanates and also the high toxicity of the intermediates derived from the starting materials. However, such recently developed processes have several noteworthy drawbacks and have not been yet put into practice on an industrial scale.

For instance, there has been proposed a process in which an N-aryl substituted urethane is produced from an alcohol, carbon monoxide and an aromatic nitrocompound by use of a rhodium chlorocarbonyl catalyst (United States Patent Specification No. 3,338,956). however, this process is not economically advantageous in producing highly pure N-aryl substituted urethanes since the yield of the urethane product is low even if the reaction is effected in the presence of a large amount of a catalyst for a long period of time.

In order to improve the above process, there has been also proposed another process using a compound containing a carbonyl group of a metal of Group VIII of the Mandeléeff Periodic Table and a metal salt capable of existing in a state of a di- or higher valency such as ferric chloride (German Patent Specification No. 1,543,051). However, this process is not practical since the yield of a urethane product is still low even when a mononitro compound is used as a starting material and use of a dinitro compound will result in lower yield.

There is also known a process using palladium and a Lewis acid as a catalyst (United Kingdom Patent Specification No. 1,246,217). According to the process, even when a dinitro compound is employed as a starting material, a yield of urethane as high as 80 - 90% may be attained. In order to attain such high yield, however, the reaction must be conducted under severe conditions such as of an initial pressure of carbon monoxide of 190 350 kg/cm2 and a reaction temperature of 190 - 200"C. In addition, the process involves an industrially serious problem that a Lewis acid, e.g., ferric chloride, serving effectively as a promoter exerts a considerable corrosive action on a metal material such as iron, stainless steel, or the like. In order to realize the process on an industrial scale, it is accordingly essential to use a glass or tantalum reactor, offering serious economical and technical problems.

There is known a further process using acatalyst composed of a platinum group metal compound and a tertiary amine (United Kingdon Patent Specification No. 1,469,222).

However, this process needs a large amount of the catalyst and is thus economical.

Quite recently, there has been proposed a process in which a ternary catalytic system composed of a substance selected palladium, ruthenium, rhodium and a compound thereof. a Lewis acid, and a tertiary amine is used and the reaction is conducted in coexistence with water, if desired (U.K. Patent Specification No. 1,472,243). However, even this process can hardly produce N-substituted urethanes of high quality and excellent heat stability.

It is an object of the present invention to provide a process for producing N-substituted urethanes in high yield which are thermally more stable and higher in quality than those obtained by prior art processes.

According to the present invention there is provided a process for producing an N-substituted urethane by reacting at least one nitro compound (a) with at least one hydroxyl-group containing organic compound (b) chosen from monohydric alcohols, polyhydric alcohols. monohydric phenols and polyhydric phenols in the presence of (i) a substance chosen from palladium, rhuthenium and rhodium and halides, cyanides, thiocyanides, isocyanides, oxides, sulphates, nitrates and carbonyl compounds of any of the said metals, (ii) a Lewis acid and (iii) ammonia, the reaction being conducted under an initial pressure (in excess of atmospheric pressure) of carbon monoxide of 10 - 500 kg/cm2 and at a temperature of 80 - 260"C, the or each nitro compound (a) being an aromatic, araliphatic or heterocyclic compound having aromatic character. After completion of the reaction, most of the catalyst may be removed from the reaction solution by filtration. The crude N-substituted urethane obtained by drying up the resulting filtrate does not contain any appreciable amounts of catalytic components such as, for example, FeCl2, NH3, PdCl2, etc., so that the crude N-substituted urethane can be immediately thermally decomposed into a corresponding isocyanate. In this respect, when, for example, crude 2,4dinitrotoluene is reacted by use of a known catalytic system composed of palladium, a Lewis acid and a tertiary amine, the purity of the crude N-substituted urethane is lowered to about 30% when thermally treated at 1800C for 1 hour. In contrast thereto, in the case of the process of the invention, the purity of the crude N-substituted urethane can be held to a high level of more than 90%. According to the process of the invention, the purity of a crude N-substituted urethane obtained from an N-substituted the nitro compound(s) of an ordinary quality normally reaches up to 95% and the lowering of the purity after the thermal treatment can be held within a range of several percent.

The process of the invention has the further advantages that it is possible to raise the percentage of recovery of the catalyst from the reaction solution up to 95% and that the degree of corrosion of a reactor material is normally lower to below 0.001 mm/yr when using a stainless steel (SUS 316).

The starting nitro compounds (a) may be mononitro compounds or polynitro compounds including, for example, nitrobenzene, dinitrobenzenes, dinitrotoluenes, nitronaphthalenes, nitroanthracenes, nitrobiphenyls, bis(nitrophenyl)alkanes, bis(nitrophenyl ethers, bis (nitro-phenyl)thioethers, bis(nitro-phenyl) sulphones, nitrodiphenoxyalkanes, and heter ocyclic compounds such as nitrophenothiazines and 5-nitropyrimidine. Typical of the aromatic nitro compounds are nitrobenzene, o-, m- or p-nitrotoluene, o-nitro-p-xylene, 1-nitronaphthalene, m- or p-dinitrobenzene, 2,4- or 2,6-dinitrotoluene, dinitromesitylene, 4,4'-dinitrobiphenyl, 2,4-dinitrobiphenyl, 4,4'-dinitrodibenzyl, bis(4-nitrophenyl)methane, bis(4-nitro-phenyl)ether, bis(2 ,4-dinitrophenyl)ether, bis (4,-nitrophenyl) thioether, bis(4 nitrophenylsulphone, bis(4-nitrophenoxy)ethane, a,a'-dinitro-p-xylene, a,a'-dinitro-m xylene, 2,4,6-trinitro-toluene, o-.m-, or p-chloronitrobenzene, 2,3-dichloro-, 2,5-dichloro or 3,4-dichloronitrobenzene. 1-chloro-2,4-dinitrobenzene, 1-bromo-4-nitrobenzene, 1fluoro-2,4-dinitrobenzene, o, m- or p-nitrophenylcarbamate, o, m- or p-nitroanisole, 2,4-dinitrophenetole, m-nitrobenzaldehyde, p-nitrobenzoyl chloride, ethyl-p- nitrobenzoate, m-nitrobenzene-sulphonyl chloride, 3-nitrophthalic anhydride, 3,3' dimethyl-4,4'-dinitrobiphenyl,1,5-dinitro-naphthalene and the like. These nitro compounds (a) may be used singly or in combination. Further isomers and homologues of these compounds may be also employed. Of these, 2,4-dinitrotoluene and 2,6-dinitrotoluene are most preferred since the isocyanates obtained by thermal decomposition of N-substituted urethanes prepared from these dinitrotoluenes in accordance with the process of the invention are industrially useful.

The hydroxyl group-containing organic compounds (b) for use in the process of the invention are chosen from monohydric alcohols having a primary, secondary or tertiary hydroxyl group, polyhydric alcohols, monohydric phenols and polyhydric phenols. Suitable alcohols may be expressed by a general formula R(OH)n in which R represents a monovalent or polyvalent aliphatic, cycloaliphatic or araliphatic radical, e.g. a linear or branched alkyl, a cycloalkyl, an alkylene, a cycloalkylene or an aralkyl group and n is an integer. Examples of the alcohols are monohydric alcohols such as methyl alcohol, ethyl alcohol, n- or iso-propyl alcohol, n-, iso- or t-butyl alcohol, linear or branched amyl alcohol, hexyl alcohol, cyclohexyl alcohol, lauryl alcohol, cetyl alcohol, benzyl alcohol, chlorobenzyl alcohol, o-, m- or p- methoxy-benzyl alcohol and the like, dihydric alcohols such as ethylene glycol, diethylene glycol, a propylene glycol, a dipropylene glycol and the like, trihydric alcohols such as glycerine, hexanetriol and the like, and higher polyfunctional polyols. Of these, ethyl alcohol is most preferred from the practical point that the N-substituted urethane obtained therefrom in accordance with the process of the invention can be thermally decomposed to give an isocyanate.

The phenols useful in the present invention include, for example, phenol, cresol, ethylphenols, linear or branched propylphenols, butyl or higher alkylphenols, catechol, resorcinol, 4,4'-dihydroxydiphenylmethane, 2,2'-isopropylidenediphenol, and the like.

The catalyst component (i) used in the reaction of the invention is a substance chosen from palladium, rhodium and ruthenium, and halides, cyanides, thiocyanides, isocyanides, oxides, sulphates, nitrates and carbonyl compounds of the above metals. Component (i) may for instance be in the form of a complex of a halide of Pd, Rh or Ru with ammonia.

These catalyst components (i) may be used as such in the urethanation reaction or may be supported on inert carriers such as alumina, silica, carbon, barium sulphate, calcium carbonate, asbestos, bentonite, diatomaceous earth, Fuller's earth, an organic ionexchange resin, magnesium silicate, aluminium silicate, molecular sieves, and the like. In this connection, the carriers may be placed in a reactor independently of the catalyst component (i).

In the present invention, the Lewis acid (catalyst component (ii)) is employed as a promoter. The Lewis acids useful in the present invention are those described in "Physical Organic Chemistry ", 1962, by Jack Hine and published by McGraw Hill Book Co., New York, including Bronsted acids. The Lewis acids are halides, sulphates, acetates, phosphates and nitrates of metals including tin, titanium, germanium, aluminium, iron, copper, nickel, zinc, cobalt and manganese and may be, for example, ferric chloride, ferrous chloride, stannic chloride, stannous chloride, aluminium chloride, cupric chloride, cuprous chloride or copper acetate. Of these, ferric chloride and ferrous chloride are preferred.

Ammonia (catalyst component (iii)) which is one component of the catalyst system used in the process of the invention may be fed to the reactor separately from the starting materials and the other catalytic components (i) and (ii). Alternatively, ammonia may be used by treatment with part of the other catalyst components to convert it into a suitable compound such as a complex or an adduct. For example, a palladium chloride-ammonia complex typical of which is PdCl2(NH3)2 or PdCl2(NH3)4 may be first prepared and then applied to the reaction system or alternatively ammonia and palladium chloride may be separately added to the reaction system. It will be noted that the amount of the catalyst component (i) such as palladium chloride which is sufficient in the present process is less than that required in known processes, so that the manner of the addition or application of the catalyst components (i), (ii) and (iii) is not so important.

Preferably, ammonia is used in the form of complexes with ferrous chloride or ferric chloride, e.g., those expressed by formulae FeCl2(NH3)n and FeCl3(NH3)m (in which n and m are integers of 1 - 10) or complexes with germanium chloride, e.g., those expressed by formulae GeCl4(NH3)2 and GeCl4(NH3)2. These complexes can be readily prepared without resorting to any specific technique. That is, it is sufficient to agitate catalytic components required to form an intended complex in a suitable solvent such as benzene, monochlorobenzene, dichlorobenzene, ethanol or the like, or to add such catalytic component or components to ammonia under agitation. It should be noted that, in some cases, the preparation in an atmosphere of carbon monoxide results in complexes imparted with stronger activity. If necessary, the solvent or an excess of ammonia employed is removed by distillation.

The amount of ammonia in the reaction system is generally in a range of 0.1 - 5 moles, preferably 0. 2 - 3 moles, per mole of anions of a Lewis acid. Most preferably, approximately equimolar amounts of ammonia and anions are used. Less than 0. 1 mole of ammonia per mole of the anions will have a possibility of producing a crude N-substituted urethane of high quality but does not generally show a satisfactory effect. On the other hand, a larger amount than 5 moles of ammonia is usable but does not offer any particular advantages. As described hereinabove, one of the prominent features of the present invention resides in the use of ammonia as one component of the catalyst system used in the invention. As a matter of course, a tertiary amine may be used in combination with ammonia in such an amount as not to counteract the above-described effects of the present invention.

If desired, small amount of water may be added to the reaction system. The presence of water in the reaction system contributes in the acceleration of the reaction velocity to a considerable extent, making it possible to produce an intended product in high yield within a very short period of time. Though the amount of water varies depending on the type of a starting nitro compound (a), the kind and amount of a catalyst, it is generally in the range of 0.01 - 2 moles, preferably 0.01 - 1 mole, per mole of a starting nitro compound. Especially when 2,4-nitrotoluene is used as a starting material for the urethanation reaction in the presence of a catalyst composed of palladium chloride and a ferrous chloride-ammonia complex, it is preferred that the amount of water be in a range of 0.1 - 0.6 mole per mole of 2,4-dinitrotoluene.

The presence of water in the reaction system in the above range does not give any adverse effect on the reactor normally used with regard to the corrosion of the reactor material.

Water may be added to the reaction system by any known means. For example, water may be added to starting materials, a solvent or the like to form a solution thereof or a mixture therewith, or may be added in the form of water of crystallisation or a substance capable of producing water during the reaction.

In the reaction of the present invention, the catalyst components (i), (ii) and (iii) are primarily deposited in the form of solids after completion of the reaction due to presence of the ammonia, it thus being possible to separate and collect the solid catalyst from the reaction solution. The structural form of the thus collected catalyst is not presently known, but it has been found that it may be reused as it is or after treatment by a suitable method such as washing with a solvent.

In the process of the invention, although no specific solvent is required to be added to the reaction system since the hydroxyl group-containing organic compound(s) (b) serve(s) as solvent, a solvent may be used. Examples of solvents include aromatic solvents such as benzene, toluene, xylene, and the like, nitriles such as acetonitrile, benzonitrile and the like, sulphones such as sulpholane and the like, aliphatic halogenated hydrocarbons- such as 1,1,2-trichloro-1,2,2-trifluoroethane and the like, halogenated aromatic hydrocarbons such as monochlorobenzene, dichlorobenzene, trichlorobenzene and the like, ketones, esters, tetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, and the like. It is desired that the reaction is effected at least in equimolar or greater ratios of the hydroxyl group-containing organic compound(s) (b) and carbon monoxide to the aromatic nitro compound(s) (a). Though the amount of the platinum group metal with regard to the nitro compounds) (a) may vary widely depending on the kind of the metal and other reaction conditions, the weight ratio to the nitro compound(s) (a) is generally in a range of 1 - 1 x l0-5, preferably 5 x 10-l - 1 x 10-4 when calculated as elemental metal. For example, when the reaction is conducted by a batch process using dinitrotoluene as a starting material, the weight ratio of the platinum group metal to dinitrotoluene as little as 5 x 10 - 1 x 10-5 calculated as elemental metal is sufficient to make the reaction proceed satisfactorily. In this connection, however, it is preferred that when the reaction is conducted in an industrially advantageous continuous manner, a large amount of the catalyst is used to increase an amount of formation of urethane product per unit time.

The Lewis acid (ii) used as a promoter is generally employed in a weight ratio, to the nitro group(s) of the nitro compound(s) (a), of 2 - 2 x 10-3, preferably 1 - 5 x 10-2.

Although the manner of charging the starting materials is not particularly critical, it is desirable that all or part of the nitro compound(s) (a) and the Lewis acid (ii) are dissolved in the hydroxyl group-containing organic compound(s) (b) or a suitable solvent and then added to the reaction system. The order of addition of the starting materials also is not limited and may be arbitrarily changed within the limitations of the apparatus used. For instance, at least one hydroxyl group-containing compound (b), catalytic components (i), (ii) and (iii), and at least one nitro compound (a) may be introduced altogether into a suitable pressure-resistant reactor such as an autoclave, into which carbon monoxide is further fed under pressure, followed by heating under agitating conditions until the reaction is complete. Carbon dioxide which is formed during the reaction may be exhausted by any suitable means, and the carbon monoxide may be fed either intermittently or continuously.

The reaction may be effected by a batchwise, semi-continuous/or continuous method under urethanation conditions. The reaction is effected under an initial carbon monoxide pressure of 10 kg/cm2 - 500 kg/cm2 gauge. The reaction temperature is in a range of 80" to 260"C., preferably from 140 to 200 C. The reaction proceeds more rapidly at higher temperatures.

When the concentration of the nitro compound(s) (a) is high and is likely to be decomposed during the reaction, the reaction may be carried out, by a two-stage process, the first stage reaction being effected in the vincinity of 1600C and the second stage reaction in the vicinity of 1900C.

The reaction time varies depending upon the property of the nitro compound(s) (a), reaction temperature and pressure, kind and amount of catalyst, and kind and type of reaction apparatus and it is generally in a range of 5 minutes to 6 hours.

After completion of the reaction, the reaction mixture may be cooled and the gases in the reactor evacuated therefrom. Then, the thus cooled reaction mixture may be subjected to filtration, distillation or other suitable separation treatments for separating the produced urethane from unreacted materials, by-products, solvent and catalyst.

As will be understood from the foregoing detailed description, the process of the invention can more easily produce crude N-substituted urethanes having excellent thermal stability than processes using known catalytic systems composed of platinum group metals, Lewis acids and tertiary amines. In addtion, crude N-substituted urethanes obtained according to the process of the invention are generally so high in quality that the urethanes can be directly thermally decomposed into corresponding isocyanates without being purified by any specific techniques. This is believed due to a fact that the crude N-substituted urethanes which have been obtained by removing most of the catalyst from the reaction solution by filtration and concentrating the resulting filtrate are contaminated with only small amounts of the catalytic components including a Lewis acid such as Fell2, NH3, a platinum group metal compound such as PdCl2 and a tertiary amine which will be often found in a urethane product obtained by prior art processes. Moreover, the crude N-substituted urethane obtained according to the present invention scarcely contains an unreacted nitro compound since the catalytic system employed is very high in activity, thus leading to the high quality of the urethane product. The above fact that an N-substituted urethane can be produced substantially without being contaminated with the unreacted aromatic nitro compound is very advantageous in that the danger of explosion can be avoided when the N-substituted urethane is subsequently converted into a corresponding isocyanate by thermal decomposition.

The N-substituted urethanes obtained have numerous uses as starting materials for preparing agricultural chemicals, isocyanates and polyurethanes.

The present invention will be illustrated by way of the following examples, which should not be construed as limiting thereto the present invention. In these examples, all the reactions were conducted in a stainless steel ("SUS 316"), electromagnetically agitated autoclave. The degree of corrosion of a metal material was calculated from the weight reduction and surface area of an agitating blade (made of "SUS 316"). The yield indicated in the following examples was calculated on the basis of results of gas-chromatographic and liquid-chromatographic analyses. The thermal stability test was conducted as follows. The reaction solution was filtered at a normal temperature to remove catalyst therefrom. The resulting filtrate was dried and thermally to obtain a crude N-substituted urethane. 1 g of the urethane was placed in a test tube and heated at 1800C for 1 hour in an atmosphere of nitrogen. After cooling, alcohol was added to the test tube to dissolve the urethane therein.

The solution was subjected to gas-chromatographic and liquid-chromatographic analyses from which the purity of the urethane was determined. The purity was compared with that which had been previously determined prior to the heating in a manner similar to the above-described procedure.

Examples 1 - 3 12.3 g of nitrobenzene, 150 ml of ethyl alcohol and a catalytic system indicated in Table 1 were placed in a 500 ml autoclave for reaction at temperatures of 160 - 1700C under an initial carbon monoxide pressure of 100 kg/cm2 (gauge) for different periods of time indicated in the Table. The FeCl2-NH3 complex used was prepared as follows. 36 g of ferrous chloride were suspended in 300 ml of ethanol, into which was blown about 10 g of ammonia gas while agitating. The suspension was filtered and the resulting cake was washed with a small amount of ethanol to obtain 45 g of a ferrous chloride-ammonia complex.

TABLE 1 Catalyst reaction Crude urethane net yield purity corrosion time of after rate Classification PdCl2 FeCl2 NH3 FeCl2-NH3 (min) yield nitro urethane aniline others urethane heating (mm/yr) (g) (g) (g) complex (g) benzene (%) (%) (%)c) (%) (wt %) (g) (%) Example 1 0.1 12.7 3.4 0 30 16.0 0 95 3 2 92 92 0.01 Example 2 " 16.6e) " 0 40 16.0 0 93 5 2 90 88 0.02 Example 3 " 0 0 16.1 30 16.3 0 96 2 2 95 93 < 0.001 Reference 1 " 12.7 0 0 60f) 15.8 5 78 7 10 75 50 1.50 2 " 0 3.4 0 60h) 14.0 90 < 1 2 18 < 1 - < 0.001 3 0 0 0 16.1 60h) 13.0 50 0 10 40 0 - < 0.001 4 0.1 0 30k) 0 60h) 14.0 90 < 1 2 18 < 1 - < 0.001 5 " 12.7 16k) 0 30 17.0 0 94 3 3 97 70 0.01 Note c) Tarry matter. d) Determined according to the afore-described thermal stability test. e) FeCl3 f) Slight pressure drop was observed. h) Pressure drop was hardly observed. k) Ammonia replaced by tertiary amine.

After completion of the reaction of Example 1, the reaction solution was cooled down to room temperature. Then, the nitrogen gas was purged from the autoclave and the reaction solution was withdrawn from the autoclave to remove insoluble matter therefrom by filtration. 16.0 g of the solid matter was obtained. The solid matter was analyzed by an atomic absorption method, revealing that 95% of palladium fed to the reactor was recovered.

The advantage of the process using the catalytic systems of the specific type according to the present invention will be understood by comparison with known processes, e.g., a process of Reference 4 using a palladium catalyst and a tertiary amine (such as disclosed in United States Patent Specification No. 3,993,685), a process of Reference 1 using a palladium catalyst and a Lewis acid (such as disclosed in States Patent Specification No.

3,531,512) and a process of Reference 5 using a palladium catalyst, a Lewis acid and a tertiary amine.

Examples 4 - 10 In these examples, different kinds of aromatic nitro compounds indicated in Table 2 were used. 150 ml of ethyl alcohol, 0.1 g of PdC12 and 16.1 g of FeCl2-NH3 complex were placed in an autoclave together with each of the aromatic nitro compounds for reaction at temperature of 160 - 1700C under an initial pressure of carbon monoxide of 100 kg/cm2G for different periods of time indicated in Table 2. The crude urethanes obtained by a series of the experiments were found to contain no unreacted nitro compounds.

TABLE 2 nitro compound Reaction Crude urethane Not yield purity (d) corrosion Classification time of urethane after rate kind amount (min) yield urethane amines others(c) (%) heating (mm/yr) (g) (g) (%) (%) (%) c) (%) Example 4 p-nitrotoluene 13.7 100 17.8 95 3 2 94 91 0.001 Example 5 o-chloronitrobenzene 15.8 120 20.0 93 3 4 93 88 0.002 Example 6 3,4-dichlorobenzene 19.2 120 23.2 94 3 3 93 90 0.002 Example 7 2,4-dinitrotoluene 27.3 210 39.8 91 5 4 91 86 0.001 Example 8 2,6-dinitrotoluene " " 39.8 92 4 4 92 88 0.001 Example 9 crude dinitrotoluene d) " 200 40.5 90 5 5 91(k) 85 0.005 Example 10l) crude dinitrotoluene j) " 230 40.5 86 8 6 87(d) 81 0.010 Reference 6m) Crude dinitrotoluene " 240 39.7 91 4 5 91 50 0.010 note c) and d) : see Table 1. j)Commercial crude DNT containing 2,4-isomer 76 %, 2,6-isomer 19%, ortho isomer 4%. k) Ratio of 2,4-isomer and 2,6-isomer contained in crude dinitrotoluene. l) Instead of using 16.1 g of FeCl2-NH3 complex, 12.7 g of FeCl2 and 3,4 g-of NH3 were employed. m) Instead of using 16.1 g of FeCl2-NH3 complex, 12.7 g of FeCl2 and 16.0 g of pyridine were employed.

Examples 11 - 13 In these examples, water was added to a reaction system to show its effect. That is, Example 1 was repeated using 27.3 g of 2,4-dinitrotoluene, 150 ml of ethyl alcohol and 15 g of FeCl2-NHX complex together with water, with the results shown in Table 3 below.

The purities of the crude urethanes obtained by these experiments were found to be in a range of 90 - 93% and, after heat treatment, were slightly lowered to 87 - 90%.

Examples 14 - 19 In these examples, different types of monohydric alcohols indicated in Table 4 were used as hydroxyl group-containing organic compound. 12.3 g of nitrobenzene, 150 ml of the alcohol indicated in Table 4, 0.02 g of PdCl2, 15.0 g of FeCl2-NH3 complex and 0.8 g of water were placed in an autoclave for reaction at temperatures of 160 - 17() C under an initial pressure of carbon monoxide of 100 kg/cm2G for different periods of reaction time indicated in the Table 4.

Example 20 - 21 In these examples, RhCl2 and RuCl2 were used instead of PdCl2. That is, 27.3 g of 2,4-dinitrotoluene, 150 ml of isobutyl alcohol, 0.05 g of the primal catalyst indicated in Table 5, 20 g of FeCl3-NH3 complex and 1.2 g of water were placed in an autoclave for reaction at tcl cratures of 160 - 1700C under an initial pressure of carbon monoxide of 100 kg/cm2G for different periods of reaction time with the results shown in the Table 5.

TABLE 3 water PdCl2 reaction reaction net yield corrosion Example No. temperature time of urethane rate (g) (g) ( C) (min) (%) (mm/yr) 7 0 0.1 160 - 170 210 91 0.001 11 1.2 " 160 - 220* 10 80 0.005 12 " 0.01 170 - 180 180 91 0.001 13 2.4 " " 100 89 0.01 Note: * Because of the considerable generation of heat, the temperature of the system was hard to control and was raised up to 220 C.

TABLE 4 Crude urethane Example No. Alcohol Reaction Net yield Purity after Corrosion time yield urethane amine others of urethane heating rate (min) (g) (%) (%) (%)c) (%) (%)d) (mm/yr) 14 methyl 120 14.5 94 4 2 90 91 0.005 15 ethyl 90 16.0 93 4 3 93 90 0.010 16 n-propyl 100 17.0 96 3 3 91 91 0.010 17 iso-propyl 150 17.0 95 3 2 90 89 0.005 18 n-butyl 150 19.0 91 5 4 90 85 0.005 19 iso-butyl 160 19.0 95 3 2 91 89 0.001 note c) and d) see Table 1.

Claims (10)

1. TABLE 5 Not yield Example No. Main catalyst Reaction time of urethane (min) (%)

   3 PdCl2 90 90

   20 RhCl2 120 80

   21 RuCl2 150 75 WHAT WE CLAIM IS: 1. A process for producing an N-substituted urethane by reacting at least one nitro compound (a) with at least one hydroxyl-group contaning organic compound (b) chosen from monohydric alcohols, polyhydric alcohols, monohydric phenols and polyhydric phenols in the presence of (i) a substance chosen from palladium, ruthenium, and rhodium and halides, cyanides, thiocyanides, isocyanides, oxides, sulphates, nitrates and carbonyl compounds of any of the said metals (ii) a Lewis acid, and (iii) ammonia, the reaction being conducted under an initial pressure (in excess of atmospheric pressure) of carbon monoxide of 10 - 500 kg/cm2 and at a temperature of 80 - 260"C, the or each nitro compound (a) being an aromatic, araliphatic or heterocyclic compound having aromatic character.
2. 2. A process according to Claim 1, wherein the Lewis acid (ii) and ammonia (iii) are premixed to form a complex.
3. 3. A process according to Claim 1 or Claim 2, wherein the amount of ammonia (iii) in the reaction system is in a range of 0.1 - 5 moles per mole of the anions of the Lewis acid (ii).
4. 4. A process according to any preceding claim, wherein the reaction is conducted in the presence of water.
5. 5. A process according to Claim 4, wherein the amount of water present is in a range of 0.01 - 2 moles per mole of the or each nitro compound (a).
6. 6. A process according to preceding claim, wherein the nitro compound(s) (a) is/are nitrobenzene, nitrotoluene, a dinitrobenzene and a dinitrotoluene, or a mixture of two or more thereof.
7. 7. A process according to any preceding claim, wherein the compound(s) (b) is/are methyl alcohol, ethyl alcohol, n- and iso-propyl alcohol, and n-, iso- and t-butyl alcohol, or a mixture of two or more thereof.
8. 8. A process according to any preceding claim, wherein the Lewis acid (ii) is ferric chloride or ferrous chloride.
9. 9. A process according to Claim 1 substantially as herein described and exemplified.
10. 10. A N-substituted urethane which has been produced by the process claimed in any preceding claim.