DE2750282A1 - Liq. phase organic isocyanate prepn. - by reacting nitro cpds. with carbon mon:oxide using catalyst supported on heat-modified nitrile polymer - Google Patents

Abstract

Opt. heat-modified nitrile polymers, (I), are used as catalyst supports in organic isocyanate prepn. by liq. phase organic nitro cpd. reaction with CO in the presence of heterogeneous supported catalysts contg. 1 Gp. VIII precious metal cpd. and >=1 Gp. V to VIII base metal cpd. High reaction temps. and pressures are used, pref. 150-250 degrees C and 5-500 bar. Organic monoisocyanates are intermediates for pesticide prodn. Organic polyisocyanates, esp. diisocyanates, are polyurethane raw materials. High prod. yields can be obtd. In an example, replacement of a kieselguhr support by a modified HCN polymer increased isocyanate yield from 38.1-92.8% of theoretical. The modified (I) have high heat-stability and fixing activity for the active precious metal component.

Description

Process for the production of organic isocyanates

The present invention relates to an improved method for Production of organic isocyanates by converting organic nitro compounds with carbon monoxide in the presence of a heterogeneous catalyst system.

Organic isocyanates are important intermediates for a number of syntheses. Organic monoisocyanates provide valuable intermediate products Manufacture of technically valuable pesticides represent while organic Polyisocyanates, especially diisocyanates, are important starting materials for production Polyurethanes are.

They are produced industrially by reacting amines with phosgene, the toxicity of the phosgene necessitates special precautionary measures. The chlorine obtained in the phosgene is converted into worthless hydrogen chloride during the phosgenation about, from which chlorine has to be recovered by electrolysis. For this Basically, the aim is to produce isocyanates by other means than by carry out the technically known phosgenation, and in the patent literature a large number of such phosgene-free manufacturing processes have been described.

From DT-PS 1 815 517, for example, a method is known after which nitro compounds with carbon monoxide in the presence of essentially homogeneously dissolved noble metal halides, heteroaromatic nitrogen compounds and base metal oxides are converted to isocyanates. In this procedure Although high degrees of conversion of the nitro compounds are obtained and when used also obtain useful selectivities from mononitro compounds. A disadvantage however, is the high amount of catalyst required and the difficult work-up of the noble metal complexes dissolved in the reaction medium, which are not without losses and high technical effort can be carried out and the economy of the process questions.

In GB-PS 1 313 199, as well as DT-OS 1 901 202 and 2 165 355 heterogeneous catalysts described, the noble metals on inorganic support materials, such as silica gel or aluminum oxide, which eliminates the costly reconditioning of the catalytic converter is not required. With these heterogeneous catalysts, however, only low conversions obtained, which is particularly evident in the implementation of dinitro compounds makes disturbing noticeable, since practically only the monoisocyanates and not the desired ones Diisocyanates are obtained.

Also the supported catalysts described in DT-OS 2,413,962 based on vinylovridine polymers and those in Japanese application 74 014 731 supported phthalocyanine catalysts give only moderate isocyanate yields and are not suitable for economic implementation. It it has now been found that nitro compounds with carbon monoxide in the liquid Phase at elevated temperature and pressure in the presence of heterogeneous supported catalysts from a noble metal compound of the 8th subgroup of the periodic system, a or several non-precious metal compounds of the 5th to 8th subgroup of the periodic System and an organic carrier material in high yields to convert isocyanates can, if optionally thermally modified nitrile polymers are used as the carrier.

The present invention is therefore a method for Production of organic isocyanates by catalytic conversion of organic Nitro compounds with carbon monoxide in the liquid phase at elevated temperature and elevated pressure in the presence of heterogeneous supported catalysts made from a noble metal compound of the 8th subgroup of the periodic system, one or more non-precious metal compounds the 5th to 8th subgroup of the periodic system and an organic carrier material, characterized in that the carrier optionally modified by the action of heat Nitrile polymers used.

In the context of the present invention are under "nitrile polymers" both any polymerizate of hydrocyanic acid (polymeric hydrocyanic acid) as well as any Polymers or copolymers of olefinically and / or acetylenically unsaturated Monomers containing nitrile groups with themselves or

with other olefinically and / or acetylenically unsaturated compounds to understand.

The preferred "nitrile polymers" include a) polymeric hydrocyanic acid (Azulmic acid) as catalyzed by free radicals or preferably basic Polymerization of hydrocyanic acid is accessible in a manner known per se (cf. DT-PS 662 338 or DT-PS 949 060), and generally one over 270, preferably has a molecular weight between 540 and 5400 and b) by radical or base-catalyzed polymerization of olefinically and / or acetylenically unsaturated Nitrile polymers obtained from nitriles. Such polymers are, for example, polyacrylonitrile, Polymethacrylonitrile, poly (2-phenylacrylonitrile) or polycyanoacetylene. These polymers generally above 5000 and preferably between 50,000 to 200,000 lying molecular weight.

Copolymers of olefinically and / or acetylenically unsaturated Nitriles of the type corresponding to the polymers mentioned by way of example are also used suitable. Copolymers are less preferred, but also come into consideration such unsaturated nitriles with other nitrile groups-free olefinic and / or acetylenically unsaturated compounds such as e.g.

Vinyl chloride, styrene, butadiene or acetylene, the weight being Proportion of nitrile group-free monomers in the nitrile polymer up to 50% by weight can make out.

Those are particularly preferred in the process according to the invention Nitrile polymers used, followed by to their production Heating to temperatures above 200 ° C, especially 220-6000C, into structural isomers or derivatives with improved carrier properties have been transferred. These thermal treatment can take place in the absence or presence of molecular oxygen, for example air or a nitrogen-air mixture. In the presence of Molecular oxygen can in the presence of dehydrogenatable hydrogen atoms an oxydehydrogenation to nitrile polymers with a polyene structure or to condensed nitrogen-containing ladder polymers with fused pyridine units that high thermal stability and high activity for the active noble metal component exhibit.

The mode of operation of the nitrile polymer carriers is not detailed known. However, it can be assumed that the nitrogen atoms of the nitrile polymer interact with the active noble metal components of the supported catalyst and besides a favorable influence on the reaction sales, a fixation of the expensive one Effect precious metal on the carrier material.

The halides of palladium, platinum, Rhodium, ruthenium, iridium and osmium in question. The chlorides are preferred used. A particularly preferred noble metal halide is palladium chloride.

An essential component of the noble metal nitrile polymer supported catalysts are in addition to the central polymer inert. and the precious metal compound Non-precious metal compounds of the 5th to 8th subgroup of the periodic system, which, as cocatalysts, essentially accelerate the course of the reaction cause. Halides, in particular chlorides, and / or oxides are used as cocatalysts of the sub-group elements mentioned are suitable. Examples include: vanadium trichloride, Vanadium pentoxide, niobium pentoxide, tantalum pentoxide, tantalum pentachloride, chromium (III) chloride, Chron (III) oxide, chromium dioxide, molybdenum (III) oxide, molybdenum dioxide, molybdenum trioxide, Tungsten oxide, tungsten trioxide, iron (III) chloride, iron (III) oxide, iron spinel. The cocatalysts can be used as pure compounds or in the form of mixtures Carriers are added.

The weight ratio of carrier to noble metal component and cocatalyst can be chosen within wide limits. In general, polynitrile supports are used per part by weight 0.01 to 10 parts by weight of cocatalyst used. In particular, the weight ratio is from noble metal halide to support 0.05: 1 to 3.5: 1, particularly preferably 0.1: 1 to 1: 1 and the weight ratio of cocatalyst to support 0.05: 1 to 5: 1 in particular preferably 0.5: 1 to 2.5: 1.

The nitrile polymer supported catalysts can be used as a fine powder in Reaction medium can be used in suspension. Concentrations are then used from 0.5 to 30% by weight, in particular from 1 to 15% by weight, based on the reaction mixture including any solvent used. Another beneficial one Implementation is, for example, that the catalyst in lumpy Form or in the form of pills is firmly arranged in the reaction space and the input products be passed over the catalyst.

The supported catalyst can be prepared in various ways take place. For example, monomeric starting nitrile or hydrocyanic acid is in a solvent such as water, dioxane, ethylene carbonate, dimethylformamide, dimethyl sulfoxide, chloroform, with a polymerization catalyst (bases such as ammonia or NaOH or radical generator e.g. azodiisobutyronitrile) with stirring, preferably in the temperature range polymerized from 30 to 80 ° C to a powdery polymer, which from the solvent freed, thoroughly dried and optionally by thermal and / or oxidative Post-treatment as already described above, is further modified. The thus obtained Nitrile polymer carrier can now be finely powdered with the appropriate amounts of anhydrous Noble metal halide and base metal compound (cocatalyst) in one inert Solvents or suspending agents such as those mentioned below by way of example, optionally at elevated temperature and optionally under an atmosphere of carbon monoxide. After suctioning off the solvent, the resulting Supported catalyst can be used for the process according to the invention. It is also possible, even during the preparation of the supported catalyst in accordance with the invention Process to use the solvent that is to be used for the supported catalyst or acts as a suspending agent for the individual components of the supported catalyst, and the suspension of the supported catalyst then obtained directly without separating off the Use a supported catalyst as a reaction medium for the process according to the invention. The noble metal halides can also be obtained from aqueous or alcoholic solution soaked on the carrier. The cocatalysts can also be water-soluble links or dissolved in organic solvents on the Nitrile polymer carrier are impregnated.

After adding a binder, e.g. graphite, the supported catalysts become pilled. You can already pill with the possibly modified Carry out nitrile polymer support and only then the other catalyst components apply e.g. by soaking.

Starting compounds for the process according to the invention are any organic nitro compounds, i.e. containing any nitro groups, otherwise organic compounds which are inert under the conditions of the process according to the invention with at least one aliphatically, cycloaliphatically and / or aromatically bound Nitro group.

For example, the following aromatic nitro compounds can be used be: nitrobenzene, o-dinitrobenzene, m-dinitrobenzene, p-dinitrobenzene, o-chloro-nitrobenzene, m-chloro-nitrobenzene, o-chloro-nitrobenzene, o-nitrotoluene, m-nitrotoluene, p-nitrotoluene, 2,3-dinitrotoluene, 2,4-dinitrotoluene, 2,5-dinitrotoluene, 2,6-dinitrotoluene, 3,4-dinitrotoluene, 3-nitro-xylene, 4-nitro-o-xylene, 2-nitro-m-xylene, 4-nitro-m-xylene, 5-nitro-m-xylene, Nitro-p-xylene, 3,4-dinitro-o-xylene, 3,5-dinitro-o-xylene, 3,6-dinitro-o-xylene, 4,5-dinitro-o-xylene, 2,4-dinitro-m-xylene, 2,5-dinitro-m-xylene, 4,5-dinitro-m-xylene, 4,6-dinitro-m-xylene, 2,3-dinitro-p-xylene, 2,6-dinitro-p-xylene, 1-nitronaphthalene, 2-nitronaphthalene, Dinitronaphthalenes, nitroanthracenes, nitrodiphenyls, bis (nitrophenyl) methanes, Bis (nitrophenyl) thioether, bis (nitrophenyl) sulfones, nitrodiphenoxyalkanes, nitrophenothiazines.

The following are mentioned as cycloaliphatic nitro compounds: Nitrocyclobutane, Nitrocyclopentane, nitrocyclohexane, 1,2-dinitrocyclohexane, 1,3-dinitrocyclohexane, 1,4-dinitrocyclohexane, bis (nitrocyclohexyl) methane.

Examples of the group of nitroalkanes are: nitromethane, Nitroethane, 1-Nitropropane, 2-Nitropropane, Nitrobutane, Nitropentane, Nitrohexane, Nitrodecanes, nitrocetanes, 1,2-dinitroethane, 1,2-dinitropropane, 1,3-dinitropropane, Dinitrobutane, Dinitroentane, Dinitrohexane, Dinitrodecane, Phenylnitromethane, Bis- (nitromethyl) -cyclohexane, Bis- (nitromethyl) -benzenes, <9 -nitrocarboxylic acid nitriles.

Particularly preferred starting materials for the inventive Processes are aromatic nitro compounds such as in particular nitrobenzene, 1,3-dinitrobenzene, 2,4-dinitrotoluene, 2,6-dinitrotoluene, dinitronaphthalenes such as 1,5-dinitronaphthalene or 2,4'- or 4,4'-dinitro-diphenylmethane.

Foil conversion of the nitro compounds with carbon monoxide takes place in the liquid phase at elevated temperature and pressure according to the following general reaction equation: In general, 5 to 30 moles of carbon monoxide are added per mole of nitro group to be converted.

The implementation of the nitro compounds with carbon monoxide can in principle can be carried out without solvents. Because of the high exothermic heat release However, it is advisable to use a solvent for the technical implementation of the reaction to use. Useful solvents are aromatic, cycloaliphatic and aliphatic Solvents which may optionally be substituted by halogen, such as, for example Benzene, toluene, xylene, chlorobenzene, dichlorobenzene, trichlorobenzene, chloronaphthalene, Cyclohexane, methylcyclohexane, Cn'orcyclohexane, methylene chloride, carbon tetrachloride, Tetrachloroethane, trichlorotrifluoroethane, etc. Links. Chlorinated aromatic Hydrocarbons are preferred.

The minimum amount of solvent to be used depends on the amount of heat to be dissipated; the amount of solvent increases limited economic considerations.

In general, the concentration of the nitro compound in the solvent is 5-50 total%; Concentrations of 10-30% by weight are particularly advantageous.

The reaction temperature is generally between 100 ° C. and about 30O0C, in particular between 1500C and 2500C and particularly advantageous in the range from 1700C to 2000C. The pressure must be such that there is always a liquid phase is ensured and is generally in the range from 5 to 500 bar, particularly advantageously in the range from 50 to 300 bar at the reaction temperature. Depending on the nitro compound used and the reaction conditions, the for quantitative conversion required reaction time between a few minutes and several Hours.

The reaction of the nitro compounds with carbon monoxide can be discontinuous or be carried out continuously.

The discontinuous reaction can be carried out in a high-pressure autoclave with fine distributed catalyst can be carried out with vigorous guidance. The heat of reaction is advantageous through built-in cooling units or by pumping the reaction mixture above removed by an external heat exchanger. After finished Reaction is the catalyst, for example by filtration or centrifugation, separated from the liquid reaction mixture and converted into a new reaction of nitro compounds returned with carbon monoxide. The reaction mixture is in the usual way, e.g. by fractional distillation, into pure isocyanates, solvents and, if necessary separated small amounts of by-products.

The continuous reaction is advantageous in a tube bundle reactor carried out with a fixed catalyst. The dissipation of the heat of reaction takes place in the usual way by means of a liquid cooling medium or evaporating water. The liquid reaction product withdrawn from the reactor can after relaxation in usually worked up immediately by distillation.

The procedure is illustrated by the following examples, without thus to restrict the invention to the conditions given in the examples.

Example 1 A catalyst system was used as the supported catalyst from 7.5 parts by weight of anhydrous palladium chloride, 5 parts by weight through 5 hours Modified polymeric hydrocyanic acid is heated to 200 ° C under a nitrogen atmosphere (prepared according to Angew. Chem. 72, No. 11, page 30R ('960)) and 5 parts by weight Vanadium pentoxide used by intimately mixing the finely powdered Components had been made in boiling chlorobenzene.

11.7 g of the supported catalyst and a solution of 30 g of nitrobenzene 200 g of chlorobenzene are placed in a 0.7 l VA autoclave and carbon monoxide is added to 120 bar pressed on. The mixture is then heated to 180 ° C. for 3 hours with vigorous stirring. After cooling to room temperature and releasing the pressure, the catalyst is filtered off and the filtrate is analyzed by gas chromatography. From the analysis it was calculated a nitrobenzene conversion of 98.8% and a phenyl isocyanate yield of 92.8% of theory. Th.

Example 2 A catalyst system was used as the supported catalyst consisting of 7 parts by weight of anhydrous palladium chloride, 4.8 parts by weight pyrolyzed polyacrylonitrile (produced by J.Amer.Chem.Soc, 87, 2676) and 4.8 Parts by weight of vanadium pentoxide. The catalyst was prepared as in Example 1 described.

Under the same experimental conditions as in Example 1, nitrobenzene converted quantitatively and phenyl isocyanate in a yield of 72% of theory obtain.

Example 3 The supported catalyst used was a catalyst system that consists of 7 parts by weight of anhydrous palladium chloride, 4.8 parts by weight pyrolyzed polyacrylonitrile (prepared as in Example 2) and 4.8 parts by weight Composed of molybdenum oxide. The catalyst components were mixed as in example 2.

Under the conditions given in Example 1, the nitrobenzene conversion was 98 X and the phenyl isocyanate yield 65% of theory

Scisniel 4 A catalyst system was used as the supported catalyst, which was prepared as folet: 7 parts by weight of palladium chloride were diluted in Dissolved hydrochloric acid and the palladium from the hydrochloric acid solution at room temperature 5 parts by weight of finely powdered pyrolyzed as prepared in Example 2 Impregnated with polyacrylonitrile. The palladium-containing carrier was. at 1000C and 200 Torr and dried with a boiling suspension of 4.8 parts by weight of vanadium pentoxide treated in chlorobenzene. After 1 hour of intensive stirring, the mixture was brought to room temperature cooled and sucked off by the catalyst. The finished catalyst was at 1000C and dried overnight at 200 torr.

23.7 g of this catalyst, 60 g of nitrobenzene and 200 g of chlorobenzene were placed in a 0.7 l autoclave and 120 bar of carbon monoxide were injected. The contents of the autoclave were heated to 1800 ° C. while stirring vigorously. It posed a maximum pressure of 163 bar. After 2 h, the mixture was cooled to room temperature and the reaction product is separated off from the catalyst by suction filtration. The gas chromatographic Analysis showed quantitative conversion of the nitrobenzene and a phenyl isocyanate yield from 67 X d.Th.

Example 5 (for comparison, without nitrile polymer): As a supported catalyst was made of 3.1 parts by weight of palladium chloride, 8.8 parts by weight of silica gel and 8.8 parts by weight of vanadium pentoxide existing inorganic supported catalyst used. Under the conditions given in Example 1, nitrobenzene became quantitative implemented; However, the phenyl isocyanate yield was only 38.1 of theory.

Example 6 (for comparison, without nitrile polymer) As a supported catalyst a palladium chloride on an organic carrier catalyst system was used consisting of 7.3 parts by weight of palladium chloride and 92.7 parts by weight of one Copolymer prepared as follows: 32 parts by weight of styrene, 3 parts by weight 4-vinylpyridine, 3.2 parts by weight divinyibenzene and 0.4 part by weight benzoyl peroxide are added to 160 parts by weight of water, 1.6 parts by weight of a 5 ¢ ' aqueous solution of polyvinyl carboxyethyl cellulose as a dispersant and stabilizer unfolded. The dispersion obtained is stirred for 3 hours at 900 ° C. under nitrogen polymerized as a protective gas. Then the copolymer with water, acetone and washed with hot chloroform and dried at 1100C for 5 hours.

The palladium chloride was applied to the copolymer as a palladium chloride 'pyridine complex in the form of a 1, Jigen solution in chloroform (10 Hours of stirring at room temperature). The supported catalyst filtered off was with Washed chloroform thoroughly and dried at 1000C for 3 hours.

7.5 g of the organic supported catalyst thus prepared were a solution of 20 g of nitrobenzene and 70 g of chlorobenzene added and the reaction mixture in a 0.3 l VA autoclave with vigorous stirring with carbon monoxide reacted at 180 ° C and 170 bar for 3 hours. One obtained with a: Nitrobenzene conversion of 5% only a phenyl isocyanate yield of <4% d. Th.

Claims (13)

Process for the production of organic isocyanates through 'catalytic conversion of organic nitro compounds with carbon monoxide in the liquid phase at elevated temperature and pressure in the presence of heterogeneous supported catalysts made from a noble metal compound of the 8th Subgroup of the periodic system, one or more non-precious metal compounds the 5th to 8th subgroup of the periodic system and an organic carrier material, characterized in that the carrier is optionally by the action of heat modified nitrile polymers are used. 2. The method according to claim 1, characterized in that the nitrile polymer polymeric hydrogen cyanide is used. 3. The method according to claim 1, characterized in that the nitrile polymer polymeric acrylonitrile is used. 4. The method according to claim 1, characterized in that the nitrile polymer polymeric methacrylonitrile is used. 5. The method according to claim 1 to 4, characterized in that the Nitrile polymers modified by thermal treatment in the range of 200 - 6000C will. 6. The method according to claim 1 to 5, characterized in that one the nitrile polymers in the presence of molecular oxygen in the range of 200 - 6000C thermally treated. 7. The method according to claim 1 to 6, characterized in that <: hnet that the reaction of the nitro compounds with carbon monoxide in the presence of 0.5 to 30 wt .-% suspended catalyst is made. 8. The method according to claim 1 to 6, characterized in that the Reaction of the nitro compounds with carbon monoxide over a fixed catalyst is made. 9. The method according to claim 1 to 8, characterized in that as Nitro compound nitrobenzene is used. 10. The method according to claim 1 to 8, characterized in that as Nitroverbinduna Dinitrotoluol is used. 11. The method according to claim 1 to 10, characterized in that chlorinated aromatic hydrocarbons are used as solvents. 12. The method according to claim 1 to 11, characterized in that the reaction of the nitro compounds with carbon monoxide at temperatures of 150 - 2500C performs. 13. The method according to claim 1 to 12, characterized in that the reaction of the nitro compounds is carried out at pressures of 5 to 500 bar.