WO2008074645A1

WO2008074645A1 - Process for preparing 2-methylpentane 1,5-diisocyanate from methylglutaronitrile

Info

Publication number: WO2008074645A1
Application number: PCT/EP2007/063434
Authority: WO
Inventors: Peter Pfab; Eckhard Stroefer; Carsten KNÖSCHE; Ekkehard Schwab; Matthias KLÖTZER; Gunter Georgi
Original assignee: Basf Se
Priority date: 2006-12-20
Filing date: 2007-12-06
Publication date: 2008-06-26

Abstract

The present invention relates to a process for preparing 2-methylpentane 1,5-diisocyanate, 2-methylpentane 1,5-diisocyanate prepared in this way and its use.

Description

Process for the preparation of 2-methylpentane-1, 5-diisocyanate from methylglutaric dinitrile

description

The present invention relates to a process for the preparation of 2-methylpentane-1, 5-diisocyanate, thus prepared 2-methylpentane-1, 5-diisocyanate and its use.

The preparation of 2-methylpentane-1, 5-diisocyanate from 2-methylpentane-1, 5-diamine is known per se and can phosgene-free (T. Lesiak, K. Seyda, Journal of Practical Chemistry (Leipzig), 1979, 321 ( 1), 161-163) or by reaction with phosgene (eg DE 2625075).

2-methylpentane-1, 5-diamine is industrially produced by hydrogenation of Methylglutarsäu- redinitrile (MGDN, 2-methyl-1, 5-pentenenitrile) and used for example in polyamides, as a curing agent for epoxy resins and for polyurethanes.

The object of the present invention was to provide a further process for the preparation of 2-methylpentane-1, 5-diisocyanate available.

The object was achieved by a process for the preparation of 2-methylpentane-1, 5-diisocyanate, in which a) 1, 3-butadiene with hydrogen cyanide (HCN) to a mixture of Methylglutarsäu redinitrile (MGDN) and adiponitrile (ADN) b) methylglutaronitrile is separated off from the adiponitrile / methylglutaric acid dinitrile mixture thus obtained, c) methylglutaronitrile is converted into 2-methylpentane-1,5-diamine and d) the 2-methylpentane-1,5-diamine thus obtained in 2-methylpentane -1, 5-diisocyanate converted.

The advantage of the process according to the invention is that it optimally utilizes a coproduct and from it makes a high-quality aliphatic isocyanate at minimized production costs, which, in contrast to aromatic isocyanates, can be converted into light-stable polyurethane systems for outdoor applications.

The corresponding method a) to d) can be carried out in combination at a location. However, the intermediate products produced at one location can also be taken from one plant and, via a suitable logistical measure, also be sent to another plant at another location. a) Reaction of 1, 3-butadiene with hydrogen cyanide (HCN) to give a mixture of methylglutaronitrile (MGDN) and adiponitrile (ADN)

The inventive step a) is preferably carried out in two stages in the liquid phase, by initially 1, 3-butadiene, optionally mixed with other C4 alkanes and alkenes, homogeneously catalysed with hydrocyanic acid (HCN) at 10 - 100 bar and 50 - 150 ⁰ C. implements. The resulting isomer mixture of straight-chain and branched-chain pentenenitriles is worked up, preferably by rectification, to give a mixture having the highest possible content, preferably at least 97% by weight, of higher-boiling 3- and 4-pentenenitriles.

The lower-boiling 2-methyl-3-butenenitrile is isomerized and rectified at normal pressure or overpressure up to 5 bar and 80-170 ⁰ C to 3- and 4-pentenenitriles. The thermodynamic equilibrium with the linear nonconjugated pentenenitriles is about 95% on the side of the linear pentenenitriles.

The mixture, which contains predominantly 3- and 4-pentenenitriles, is homogeneously catalyzed at partial conversion of 10 to 50% with further hydrogen cyanide to a mixture of adiponitrile, methylglutaronitrile and ethylsuccinonitrile at 0.5 bar abs to 5 bar overpressure at 40-150 ° C, preferably reacted at 50 - 110 ⁰ C. After separation of unreacted pentenenitriles, extractive separation of the homogeneous catalyst and its constituents, a stream is obtained which contains the dinitriles and is further worked up according to substep b).

Preferred catalysts are Ni (0) -aryl phosphorus complex compounds, where the phosphorus may be present as phosphite, phosphinite, phosphonite or phosphine. As promoters for the isomerization and especially for the addition of hydrogen cyanide to pentenenitrile, Lewis acids, preferably ZnCb or triphenylboron, are used. The homogenate catalysts are prepared after dinitrile preparation and distillative removal of excess pentenenitrile by extraction with low-aromatics (<2% by weight) Cs-Cio alkanes or mixtures thereof, e.g. n-hexane, hexane isomers, cyclohexane, n-heptane, heptane isomers, methylcyclohexane, separated from the dinitriles and recovered by distilling off the extraction agent for the hydrocyanation reactions and the isomerization reaction.

Catalysts used together with selectivities for the formation of the pentenenitrile and dinitrile isomers and process variants for the recovery of dinitriles from butadiene and hydrogen cyanide according to step a) are laid down in detail in the following documents, whose disclosure is expressly referred to in the context of this document: US 3,496,215; US 3,496,217; US 3,496,218; US 3,536,748; US 3564040; US 3773809; US 3853948; US 4,080,374; US 408281 1; US 4328172; US 4330483; US 4339395; US 4539302; US 4705881; US 5512695; US 5512696; WO 99/52632; US 6242633; WO 03/01 1457.

In order to obtain a higher yield of methylglutaric acid dinitrile according to step a), the hydrocyanation of a pentenenitrile mixture which has a high content of 2-methyl-3-butenenitrile is advantageous. These can be obtained by passing only part of the 2-methyl-3-butenenitrile obtained in the hydrocyanation of butadiene (for example 30-65% by weight) over the isomerization. By varying the proportion, pentenenitrile mixtures having a content of 2-methyl-3-butenite.nl of almost 0 to 65% by weight can be adjusted. The 2-Methyl-3-butennit.nl reacts homogeneously catalyzed with hydrogen cyanide with a high selectivity, for example more than 95% to methylglutaric acid dinitrile and ethylsuccinonitrile.

b) separation of methylglutaronitrile from the adiponitrile / methylglutaric dinitrile / ethylsuccinonitrile mixture obtained in a)

The isolation of a adiponitrile and pentennitrilarmen fraction of Methylglutarsäu- can redinitril in several Rektifikationsschritten, wherein the well separation plate columns can be used, be carried out (boiling at 100 mbar: adiponitrile 211 ⁰ C; Metylglutarsäuredinitril 186 ° C; Ethylsuccindinitril 180 ⁰ C, pentenenitriles 55 -77 ° C). Suitably, a fraction of methylglutaric acid dinitrile and 2-ethylsuccinonitrile is obtained, with a proportion of the two last-mentioned dinitriles> 95% by weight and a mixing ratio of 75:25 to 95: 5 in accordance with the selectivities of the reactions from substep a). If desired, the two main constituents can then be separated further by distillation at the stage of the dinitriles or of the secondary products of the diamines (partial step c)) or of the diisocyanates (partial step d)). Of course, they can also be processed as a mixture.

Such a purifying distillation at the stage of the dinitriles can generally give mixtures which have a content of methylglutaronitrile of at least 95% by weight, preferably at least 98% and more preferably at least 99% by weight, the remainder being predominantly adiponitrile, 2-etylsuccindinetrile in addition small quantities, usually <0.5% by weight, of isomeric pentenenitriles and other impurities, such as isomeric nonenitriles, isomeric decendinitriles and phenols.

Ethylsuccinonitrile can also be isolated with a corresponding separation effort in a purity of at least 95%, preferably at least 98% by weight, and particularly preferably at least 99% by weight. The main secondary constituent is methylglutaric acid dinitrile. In an alternative embodiment of the present invention, a mixture of 0.1 to 99.9% by weight of methylglutaronitrile, adiponitrile and ethylsuccinonitrile can be separated and converted into the mixture of the corresponding amines and these in turn into isocyanates. In this case, the term "MGDN" will be used hereinafter for this mixture of nitriles.

The mixtures of 2-methylpentane-1, 5-diisocyanate and hexamethylene diisocyanate and 2-ethyl-1,4-bis (isocyanato) butane formed from such nitrile or after hydrogenation amine mixtures can then be prepared by distillation or another suitable process the pure substances are decomposed or further processed directly as a mixture, for example, be converted into a polyurethane.

c) conversion of methylglutaric acid dinitrile into 2-methylpentane-1,5-diamine

The conversion of methylglutaronitrile into 2-methylpentane-1,5-diamine is preferably carried out by hydrogenation, particularly preferably by catalytic, for example homogeneous or heterogeneously catalyzed hydrogenation, very particularly preferably by heterogeneously catalyzed hydrogenation.

The hydrogenation of organic nitriles can be carried out in any desired manner, for example with Raney catalysts, for example Raney nickel, Raney cobalt or Raney copper, and is frequently additionally carried out in the presence of basic alkali metal or alkaline earth metal compounds, as described in US Pat 3,821,305, US 5,874,625, US 5,151,543, US 4,375,003, EP-A-0316761, EP-A-0913388 and US 6,660,887.

Alternatively, the hydrogenation can also be carried out in a fixed bed, for example on iron- or cobalt-containing catalysts as described for example in US 5,527,946, US 5,756,808, US 5,801,267, US 5,801,268 or US 6,114,567.

As the reducing agent, hydrogen, a hydrogen-containing gas or a hydride ion source can be used, preferably hydrogen or a hydrogen-containing gas.

The hydrogen used for the hydrogenation is generally used in the larger stoichiometric excess of from 1 to 500 times, preferably from 2 to 100 times or stoichiometric amounts. It is usually separated after the reaction and can then be recycled as recycle gas in the reaction.

The hydrogen is generally used technically pure. The hydrogen may also be used in the form of a hydrogen-containing gas, ie in admixtures with other inert gases, such as nitrogen, helium, neon, argon or carbon dioxide. The hydrogenation can also be carried out with a hydride ion source. Suitable hydride ion sources are complex hydrides such as LiAlH ₄ or NaBH ₄

In a process for the preparation of amines by reduction of nitriles, the hydrogenation can preferably also be carried out with the addition of ammonia. As a rule, ammonia is used in molar ratios to the nitrile group in the ratio of 0.5: 1 to 100: 1, preferably 2: 1 to 20: 1. The preferred embodiment is a method in which no ammonia is added.

The hydrogenation can be carried out in the presence of a solvent or solubilizer.

Suitable solvents are, for example, C 1 - to C ₄ -alcohols, C ₄ - to C 12 -dialkyl ethers or cyclic C ₄ - to C 12 -ethers, such as tetrahydrofuran or tert-butyl

Butyl methyl ether or mixtures thereof. The liquid may also be the product of the hydrogenation.

In a preferred embodiment, the hydrogenation is carried out anhydrous.

The catalyst can be freed from the inert liquid or passivation layer before starting the hydrogenation. This is done, for example, by treatment with hydrogen or a gas containing hydrogen, optionally at elevated temperature. The hydrogenation is preferably carried out directly after the reduction of the catalyst precursors in the same reactor in which the reduction also took place.

The hydrogenation is generally carried out at a pressure of from 1 to 300 bar, in particular from 5 to 200 bar, preferably from 8 to 85 bar and particularly preferably from 10 to 65 bar. Preferably, the hydrogenation is carried out at a pressure of less than 65 bar as a low pressure method.

The temperature is usually in a range 40 to 250 ⁰ C, in particular from 60 to 160 ⁰ C, preferably from 70 to 150 ° C, particularly preferably from 80 to 130 ⁰ C.

The hydrogenation may be e.g. in the liquid phase in a stirred autoclave, a bubble column, a circulation reactor, such as a jet loop, or a fixed bed reactor.

The catalyst can be separated from the product by methods known to those skilled in the art, for example filtration or settling. Likewise, the hydrogenation in the gas phase can be carried out in a fixed bed reactor or a fluidized bed reactor. Common reactors for carrying out hydrogenation reactions are described, for example, in Ullmann's Encyclopaedia [Ullmann's Encyclopedia Electronic Release 2000, Chapter: Hydrogenation and Dehydrogenation, Chapter 1.3. and subchapters "Slurry Reactors", "Trickle-Bed Reactors" and "Bubble Column and Ebulliated Bed Reactors"].

The hydrogenation is preferably carried out in suspension.

In a particular embodiment, usually for reasons of simplifying the process, the hydrogenation is carried out in the same reaction vessel in which the catalyst precursor is also reduced.

The hydrogenation processes can be carried out batchwise, semi-continuously or continuously. The hydrogenation processes are preferably carried out semi-continuously or continuously.

The resulting 2-methylpentane-1, 5-diamine or such a mixture containing, if necessary, be distilled again, so that the degree of purity based on the amine or amine mixture usually at least 98%, preferably at least 99% particularly preferably at least 99.5% and most preferably at least 99.8%.

d) conversion of the 2-methylpentane-1, 5-diamine obtained from c) into 2-methylpentane-1, 5-diisocyanate

Step d) can be carried out without phosgene or in the presence of phosgene. In the latter variant, the phosgenation can be carried out in liquid phase or in gas phase.

Phosgene-free processes for the preparation of isocyanates are known, for example, from EP 18588 A1, EP 28338 A2, EP 27952, EP 126299 and in particular EP 566925 A2.

The phosgene-free processes known in the prior art can be used for the process according to the invention, but preferably the process described below:

To prepare the urethanes, the amine is reacted with urea and at least one, preferably exactly one, alcohol in a molar ratio of amine, urea and alcohol such as 1: 2 to 20: 5 to 40 at temperatures of 50-300 ^° C. and in particular 180 ^° C. 220 ⁰ C under a pressure of 0.1 to 30 bar, preferably 5 - 20 bar to Reaction brought. Under these reaction conditions, the process has average reaction times of fractions of seconds to minutes.

The reaction can conveniently be carried out in the presence of dialkyl carbonates, advantageously in an amount of 0.1 to 30 mol%, preferably 1 to 10 mol%, or carbamic acid alkyl esters in an amount of 1 to 20 mol%, preferably of 5 to 15 mol %, based on the diamine. In particular, mixtures of dialkyl carbonates and alkyl carbamates are used in the stated proportions. Preferred dialkyl carbonates and / or carbamic acid esters are those whose alkyl radicals correspond to the alkyl radical of the alcohol used.

The reaction can also be carried out in the presence of catalysts. These are expediently used in amounts of from 0.001 to 20% by weight, preferably from 0.001 to 5% by weight, in particular from 0.01 to 0.1% by weight, based on the weight of the amine.

Suitable catalysts are inorganic or organic compounds containing one or more cations, preferably a cation of metals of group IA, IB, IIA, IIB, HIB, IVA, IVB, VA, VB, VIB, VIIB, VIIIB of the Periodic Table of the Elements as defined in Handbook of Chemistry and Physics 14th Edition, published by Chemical Rubber Publishing Co., 23 Superior Ave. N.E., Cleveland, Ohio. The cations of the following metals may be mentioned by way of example: lithium, sodium, potassium, magnesium, calcium, aluminum, gallium, tin, lead, bismuth, antimony, copper, silver, gold, zinc, mercury, cerium, titanium, vanadium, chromium, molybdenum, Manganese, iron and cobalt.

The catalyst may further contain at least one anion, for example halides, such as chlorides and bromides, sulfates, phosphates, nitrates, borates, alcoholates, phenates, sulfonates, oxides, oxide hydrates, hydroxides, carboxylates, chelates, carbonates and thio- or dithiocarbamates.

The catalysts can also be used in the form of their hydrates or ammoniaates without noticeable significant disadvantages.

Examples of typical catalysts are: lithium methoxide, lithium ethanolate, lithium propoxide, lithium butanolate, sodium methoxide, potassium tert-butoxide, magnesium methoxide, calcium methoxide, tin (II) chloride, tin (IV) chloride, Lead acetate, lead phosphate, antimony (III) chloride, antimony (V) chloride, aluminum acetylacetonate, aluminum isobutoxide, aluminum trichloride, bismuth (III) chloride, copper (II) acetate, copper (II) sulfate, copper (II) nitrate, bis (triphenylphosphine oxido) copper (II) chloride, copper molybdate, silver acetate, gold acetate, Zinc oxide, zinc chloride, zinc acetate, zinc acetonyl acetate, zinc octoate, zinc oxalate, zinc hexy-lat, zinc benzoate, zinc undecylenate, cerium (IV) oxide, uranyl acetate, titanium tetrabutoxide, titanium tetrachloride, titanium tetraphenolate, titanium naphthenate, vanadium (III) chloride, vanadium ametylacetonate, Chromium (III) chloride, molybdenum (VI) oxide, molybdenum acetylacetonate, tungsten (VI) oxide, manganese (II) chloride, manganese (II) acetate, manganese (III) acetate, Iron (II) acetate, iron (III) acetate, iron phosphate, iron oxalate, iron (III) chloride, iron (III) bromide, cobalt acetate, cobalt chloride, cobalt sulfate, cobalt naphthenate, nickel chloride, nickel acetate and Nickel naphthenate and mixtures thereof.

Examples of preferred catalysts are: lithium butanolate, aluminum acetylacetonate, zinc acetylacetonate, titanium tetrabutoxide and zirconium tetrabutoxide.

The mixing of the educt streams can preferably be carried out in a suitable special mixing device, which is characterized by short mixing times.

The mixed educt stream is then passed to a reaction device which may be backmixed or designed as a tubular reactor or a combination thereof.

The reaction mixture is reacted in the reactor at an average of 10 seconds to 5 hours, preferably 20 seconds to 20 minutes, more preferably 30 seconds to 10 minutes. The temperature is generally between 50 ⁰ C and 300 ⁰ C, preferably between 180 ⁰ C and 220 ⁰ C. The pressure is generally between 0.1 bar abs and 30 bar abs and preferably between 5 and 20 bar abs.

The residence time is chosen so that the conversion, based on amino groups in the amine used to urethane groups, after leaving the reactor is at least 95%, preferably at least 98, more preferably at least 99 and most preferably at least 99.5%.

If the conversion, based on amino groups in the amine used to form urethane groups, is not complete after leaving the reactor and is, for example, less than 95%, then the discharge can be further reacted.

For the separation of the ammonia columns are advantageously used, preferably the ammonia is separated by distillation. This creates a good separation between the alcohol and ammonia. Usually, the separation takes place in a pressure range of 0.01 to 20 bar, preferably 0.04 to 15 bar. The necessary temperatures depend on the alcohol or alcohol mixture used. For n-butanol, the temperature is for example at 60-150 ⁰ C, preferably at 80 to 140 ⁰ C. It has proved to be advantageous to separate the resulting ammonia immediately from the reaction mixture, so that an occupancy by ammonium carbamate, which is formed in minimal amounts of ammonia and carbon dioxide by decomposition of urea, can be avoided.

This distillation unit is of a known type and has the usual installations. In principle, all standard installations are suitable as column internals, for example trays, packings and / or fillings. Of the trays, bubble-cap trays, sieve trays, valve trays, Thormann trays and / or dual-flow trays are preferred; of the trays are those with rings, coils, calipers, Raschig, Intos or Pall rings, Barrel or Intalox saddles, Top-Pak etc. or braids preferred. Floors are preferably used, more preferably bubble trays.

The distillation column preferably has 10 to 20 theoretical plates.

Alcohol, dialkyl carbonates, if they are formed or present in the reaction mixture, or alkyl carbamates or mixtures of at least two of these components are then removed from the resulting ammonia-depleted reaction mixture and preferably recycled to the reaction stage.

To separate off the components, the reaction mixture is advantageously expanded from the pressure level of the reaction stage to a pressure in the range from 1 to 500 mbar, preferably from 10 to 100 mbar. This gives gaseous vapors containing the predominant amount of alcohol and 0 to 30 wt.%, Preferably 1 to 10 wt.% Dialkyl carbonate and / or 1 to 50 wt.%, Preferably 1 to 20 wt.% Carbamidsäurealkylester, and a liquid discharge consisting essentially of the monomeric diurethane and optionally containing Oligoharnstoff-polyurethanes and high-boiling oligomers.

The resulting vapors are separated in subsequent expedient purification stages, preferably by rectification, and the isolated products of value alcohol and Carbamidsäurealkylester, individually or as a mixture, preferably recycled to the reaction stage to form the monomeric urethanes.

For distillative removal of the alcohol or the alcohol mixture, a so-called flash is often used. This apparatus may be a container or a combination of container and column, preferably a column, wherein in the head of the alcohol or the alcohol mixture and in the bottom, the urethane can be withdrawn. In the top of the column, in addition to the alcohol, more easily than the urethane boiling substances may be included. The separation takes place in a pressure range of 0.001 to 1 bar, preferably 0.02 to 0.5 bar. The obtained after removal of the vapors usually as bottoms liquid, the monomeric diurethanes, and optionally Oligoharnstoff-urethane and high-boiling oligomers containing reaction mixture can either be performed completely in the next stage or is preferably divided into two streams, wherein the weight ratio of the subsets 5 to 50:95 to 50 parts by weight, preferably 10 to 30:90 to 70 parts by weight.

The equal or preferably smaller subset is separated by distillation by means of a conventional distillation unit, preferably a thin film evaporator, at a temperature of 170 to 240 ⁰ C, preferably from 180 to 230 ⁰ C and under a pressure of 0.001 - 1 bar, preferably 0.002 - , 01 bar, into a valuable product containing the diurethanes and the lower-boiling by-products, and non-distillable by-products, which are separated from the production process and usually discarded as non-recyclable residue. The desired product (distillate) is combined with the same or preferably larger other subset and fed the combined diurethane-containing reaction mixture of the thermal cleavage.

By this method measure, the proportion of non-distillable by-products in the reaction mixture, which would form in the successive partial reactions and would constantly accumulate through the recycling recyclable feedstock in the reaction cycle, to a content of 3 to 30 wt.%, Preferably 5 to 20 wt .% limited, thereby ensuring a high-selectivity trouble-free reaction.

Thin-film evaporators or short-path evaporators can be used as distillation devices. The urethane is distilled at pressures of 0.001-1 bar, preferably in the range of 0.002-0.01 bar. The distillate is added to the cleavage.

The high-boiling marsh is preferably discarded or, less preferably, partially re-urethanized.

The resulting diurethane-containing reaction mixture is in a suitable device, preferably solvent-free in the liquid phase in the presence of catalysts at temperatures of 200 to 300 ° C, preferably 220 to 280 ⁰ C and under reduced pressure of 0.01 - 0.6 bar , preferably continuously thermally split in the range of 0.02-0.1 bar. The conversion of diurethane to diisocyanate in the apparatus for thermal cleavage can be chosen largely freely and is expediently in a range of 10 to 98 wt.%, Preferably 40 to 90 wt.% Of the amount supplied. The uncleaved portion of the reaction mixture which contains unreacted diurethanes, oligourea-polyurethanes, high-boiling oligomers and other recyclable and unreachable by-products is separated, continuously discharged from the cleavage apparatus and recycled directly or optionally after reaction with alcohol in the reurethanization in the reaction stage.

As chemical cleavage catalysts, e.g. the aforementioned, the urethane formation catalyzing inorganic and organic compounds use.

Particularly useful and therefore preferably used are dibutyltin dilaurate, iron (III) acetylacetonate, cobalt (II) acetylacetonate, zinc acetylacetonate, zirconium tetra-n-butoxide and tin (II) dioctoate.

As cleavage devices are, for example, cylindrical cleavage reactors, such. Tubular ovens or, preferably, evaporators, for example thin-film or bulk evaporators, e.g. Robert evaporator, Herbert evaporator, caddle-type evaporator, Plattenspalter and preferably Heizkerzenverdampfer.

The separation of the cleavage products takes place in a column, in which usually the isocyanate in the side and the alcohol are taken off at the top.

The crude isocyanate mixture is freed in a subsequent distillation of recombination products, by-products and, if present, the solvent. The by-products are preferably recycled to the thermal cleavage. A part can also be removed.

The cleavage products formed in the thermal cleavage, which are composed mainly of alcohol, diisocyanate, and partially cleaved diurethanes, are then advantageously by means of one or more distillation columns, preferably by rectification at temperatures of 100 to 220 ⁰ C, preferably 120 to 170 ^0th C and a pressure of 1 to 200 mbar, preferably 5 to 50 mbar, in low boilers and especially alcohol and a crude diisocyanate mixture having a diisocyanate content of 85 to 99 wt.%, Preferably from 95 to 99 wt.% Separated. The higher-boiling by-products obtained in the distillative separation and in particular the uncleaved and partially split diurethanes are preferably fed into the cleavage apparatus and / or reurethanization.

The crude isocyanate mixture, preferably obtained by rectification, is purified by distillation at a temperature of from 100 to 180 ^° C. and under a pressure of from 1 to 50 mbar, the individual fractions being recycled or isolated as a pure product. As has already been stated, in the preferred Purification by distillation, the top fraction, which preferably consists of diisocyanate, optionally after reaction of the free isocyanate groups with alcohol in the reaction stage, the side fraction, which consists of pure diisocyanate, preferably with a purity of at least 98 wt.%, In particular more than 99 wt.%, is derived and fed to the storage and the bottoms fraction containing as essential components the partially cleaved diurethanes and diisocyanates, is preferably recycled to the cleavage device for thermal cleavage.

The reaction of the reaction effluent and / or distillation residues are preferably fed back into the process. In this case, the isocyanate groups contained in this mixture and / or allophanates and / or ureas or other reactive constituents are converted to urethanes with alcohol. It is possible, these reactions in separate reactors such. B. mixing reactors or flow tubes or in perform. For the alcoholysis of the residues temperatures of 100 - 250 ⁰ C, preferably 150 - 220 ⁰ C are required. The mean residence times are in the range of a few minutes to hours.

For this purpose, for example, the streams can be combined with alcohol, wherein the molar ratio of NCO groups or their equivalents, ie for example urethane groups, to hydroxy groups up to 1: 100, preferably up to 1: 20, particularly preferably up to 1: 10.

This reaction mixture is in the presence or absence of catalysts within 1 to 150 minutes, preferably 3 to 60 minutes at a temperature of 20 to 200 ⁰ C, preferably 50 to 170 ⁰ C at a pressure of 0.5 to 20 bar, preferably 1 to 15 bar implemented.

The reaction can be carried out in a continuous boiler cascade or in a tubular reactor.

As catalysts, in principle, all compounds in question, which promote the reaction of NCO- with OH groups. Examples which may be mentioned are tin octoate, dibutyltin dilaurate, tin chloride, zinc dichloride, tin (II) dioctoate and triethylamine.

The carrying out of the phosgenation in the liquid phase is likewise known per se and can preferably be carried out as follows:

The 2-methylpentane-1, 5-diamine obtained from step c) is optionally pre-dissolved in free form or optionally as a hydrochloride in a solvent.

The water content of the used in the step c) 1, 5-pentanediamine depends on the nature of the reaction in step c) and should be preferred in the case of phosgenation below 200 ppm by weight, in the case of a phosgene-free implementation preferably below 10% by weight, more preferably below 1% by weight and very particularly preferably below 1000 ppm by weight.

These are chlorobenzene, o- or p-dichlorobenzene, trichlorobenzene, chlorotoluenes, chlorol, chloroethylbenzene, chloronaphthalenes, chlorodiphenyls, methylene chloride, perchlorethylene, toluene, xylene, hexane, decahydronaphthalene, diethyl isophthalate (DEIP) and other carboxylic acid esters, such as No. 5,136,086, column 3, lines 3 to 18, tetrahydrofuran (THF), dimethylformamide (DMF), benzene and mixtures thereof are preferred. Particularly preferred is chlorobenzene and dichlorobenzene.

The content of amine in the amine / solvent mixture is usually between 1 and 50% by mass, preferably between 2 and 40% by mass, more preferably between 3 and 30% by mass.

The phosgene is used as a mixture with the same or another inert solvent, preferably the same, or pure. Particularly preferred as phosgene is at least partially a recycled stream from the workup used, which is supplemented according to the desired stoichiometry by fresh phosgene.

In the process according to the invention, the phosgene can generally be used in the form of 10 to 100, preferably 30 to 95 and in particular 40 to 90% strength by weight, solutions in inert solvents, the phosgene preferably being used for this purpose same solvent as used for the amine.

The temperature of the phosgene solution should be between -35 ⁰ C and 180 ⁰ C, preferably between -30 ⁰ C and 150 ⁰ C.

For example, the temperature of the amine feed to the mixing device may be between 10 and 150 ⁰ C, preferably 15-120 ⁰ C and most preferably 20-100 ⁰ C.

The molar ratio of total phosgene fed into the reaction to amino groups used is generally from 1.1: 1 to 30: 1, preferably from 1.3: 1 to 25: 1.

The mixing of the educt streams is preferably carried out in a suitable special mixing device, which is characterized by low mixing times.

The mean residence time in the reaction after mixing is generally 5 minutes to 15 hours, preferably 10 minutes to 12 hours, more preferably 15 minutes to 10 hours. The temperature in the reaction is generally between 90 ⁰ C and 250 ⁰ C, preferably between 100 ⁰ C and 240 ⁰ C and particularly preferably between 1 10 and 230 ⁰ C.

The pressure in the reaction is generally between 1, 1 bar and 80 bar abs, preferably between 1, 5 and 50 bar abs, more preferably between 2 and 35 bar abs, most preferably between 3 and 10 bar abs, and in particular between 4 and 8 bar abs.

The reaction can be carried out in a back-mixed reactor or in a tubular reactor, or also in a combination of a back-mixed reactor, which is followed by a tubular reactor.

The reaction mixture is then purified by distillation.

For example, it may be a distillation column. This distillation unit is of a known type and has the usual installations. In principle, all standard installations are suitable as column internals, for example trays, packings and / or fillings. Of the soils bell bottoms, sieve trays, valve trays, Thormann trays and / or dual-flow trays are preferred, of the trays are those with rings, helices, calipers, Raschig, Intos or Pall rings, barrel or Intalox Saddling, top Pak etc. or braids preferred. Floors are preferably used, more preferably bubble trays.

The distillation column preferably has 10 to 80 theoretical plates.

In this column, the gas phase from bottom to top and the liquid phase are passed from top to bottom through the column.

The generation of the gas phase in the bottom of the column is carried out by the operation of an evaporator which may be installed in the sump, for example a Robert evaporator, or in circulation with an external evaporator, for. B. tube or plate heat exchanger.

A circulation is then for example a forced circulation or a natural circulation. Preferably, the evaporation takes place in a natural circulation.

A further invention consists in generating a gas stream in the column by blowing in gaseous or superheated phosgene and / or inert solvent and / or inert gases. The average residence time in the column is between 10 minutes and 12 hours, preferably 15 minutes to 11 hours and more preferably 15 minutes to 10 hours.

The bottom temperature in the distillation column is generally between 90 ⁰ C and 250 ⁰ C, preferably between 100 ⁰ C and 240 ⁰ C and particularly preferably between 1 10 and 230 ⁰ C. The top pressure in the distillation column is usually between 1, 1 bar abs and 80 bar abs, preferably between 1, 5 and 50 bar abs, more preferably between 2 and 35 bar abs, most preferably between 3 and 10 bar abs and in particular between 4 and 8 bar abs.

At the bottom of the column, a liquid and / or gaseous stream containing the isocyanate as a product is then removed.

The phosgenation in the gas phase can be carried out, for example, as described in EP 1 275 639 A1, EP 1 275 640 A1, EP 1 449 826 A1, DE 10359627 A1 or in International Patent Application WO 2007/028715 A1.

Preferably, the gas phase phosgenation can be carried out as follows:

In the gas phase phosgenation it is by definition desirable to have the

Reaction progress occurring compounds, ie starting materials (diamine and phosgene), intermediates (especially the intermediately formed mono- and Dicarbamoy- chlorides), end products (diisocyanate), and optionally metered inert compounds remain under the reaction conditions in the gas phase. Should these or other components be from the gas phase, e.g. deposited on the reactor wall or other apparatus components, it can be changed by these deposits, the heat transfer or the flow through the affected components undesirable. This is especially true for occurring amine hydrochlorides, which are formed from free amino groups and hydrogen chloride (HCl), since the resulting Aminhydro- chlorides easily precipitate and are difficult to re-evaporate.

The educts, or just one of them, can be metered into the mixing chamber together with at least one inert medium.

The inert medium is a medium which is gaseous in the reaction space at the reaction temperature and does not react with the compounds occurring in the course of the reaction. The inert medium is generally mixed with amine and / or phosgene before the reaction, but can also be metered in separately from the educt streams. For example, nitrogen, noble gases such as helium or argon, or aromatics such as chlorobenzene, chlorotoluene, o-dichlorobenzene, toluene, xylene, chloronaphthalene, decahydronaphthalene, carbon dioxide or carbon monoxide can be used. Preferably, nitrogen and / or chlorobenzene is used as the inert medium. In general, the inert medium is used in an amount such that the ratio of the gas volumes of inert medium to amine or to phosgene is more than 0.0001 to 30, preferably more than 0.01 to 15, particularly preferably more than 0.1 to 5 is.

The starting amines are evaporated before carrying out the process according to the invention and heated to 200 ⁰ C to 600 ⁰ C, preferably 300 ° C to 500 ⁰ C and optionally diluted with an inert gas or with the vapors of an inert solvent supplied by the mixer to the reactor.

The phosgene used in the phosgenation is also heated to a temperature within the range of 200 ° C to 600 ° C, preferably 300 ⁰ C to 500 ° C before carrying out the inventive method optionally diluted with an inert gas or with the vapors of an inert solvent.

According to the invention, phosgene is used in excess with respect to amino groups. Usually, a molar ratio of phosgene to amino groups of 1, 1: 1 to 20: 1, preferably from 1, 2: 1 to 5: 1 before.

The reaction generally starts with contact of the reactants immediately after mixing.

In the mixing device, the educt streams are mixed as completely as possible in a short time.

To carry out the reaction according to the invention, the preheated stream containing amine or mixtures of amines and the preheated stream containing phosgene are passed continuously into the reactor, preferably a tubular reactor.

The reactors are generally made of steel, glass, alloyed or enameled steel and have a length sufficient to allow complete reaction of the diamine with the phosgene under the process conditions.

In general, the reactor types known from the prior art can be used. Examples of reactors are known from EP-B1 289840, Sp. 3, Z. 49 - Sp. 4, Z. 25, EP-B1 593334, WO 2004/026813, S. 3, Z. 24 - P. 6, Z 10, WO 03/045900, page 3, Z. 34 - page 6, line 15, EP-A1 1275639, page 4, line 17 - page 5, line 17 and EP-B1 570799, Sp. 2, Z. 1 - Sp. 3, Z. 42, which are expressly referred to within the scope of this disclosure.

Preference is given to tubular reactors. The reaction of phosgene with amine in the reaction space takes place at absolute pressures of more than 0.1 bar to less than 20 bar, preferably between 0.5 bar and 15 bar and particularly preferably between 0.7 and 10 bar. In the case of the reaction of (cyclo) aliphatic amines, the absolute pressure is very particularly preferably between 0.7 bar and 5 bar, in particular from 0.8 to 3 bar and especially 1 to 2 bar.

In general, the pressure in the feed lines to the mixing device is higher than the above-mentioned pressure in the reactor. Depending on the choice of mixing device drops at this pressure. Preferably, the pressure in the supply lines is from 20 to 2000 mbar, more preferably from 30 to 1000 mbar higher than in the reaction space.

According to the process of the invention, the reaction of phosgene with amine takes place in the gas phase. Reaction in the gas phase is understood to mean that the conversion of the educt streams and intermediates to the products in the gaseous state react with one another and during the reaction during the passage through the reaction space to at least 95%, preferably at least 98%, particularly preferred remain at least 99%, more preferably at least 99.5%, especially at least 99.8 and especially at least 99.9% in the gas phase.

Intermediates are, for example, the monomino-monocarbamoyl chlorides, dicarbamoyl chlorides, monoamino monoisocyanates and monoisocyanato monocarbamoyl chlorides formed from the diamines, and the hydrochlorides of the amino compounds.

In the method according to the invention, the temperature in the reaction space is chosen so that it is above the boiling point of the diamine used, based on the pressure conditions prevailing in the reaction space. Depending on the amine used and pressure, an advantageous temperature in the reaction space of more than 200 ⁰ C yields usually, preferably more than 260 ⁰ C and most preferably greater than 300 ⁰ C. In general, the temperature is up to 600, preferably up to 570 ⁰ C.

The average contact time of the reaction mixture in the process according to the invention is generally between 0.001 seconds and less than 5 seconds, preferably from more than 0.01 seconds to less than 3 seconds, more preferably from more than 0.015 seconds to less than 2 seconds. The average contact time is very particularly preferably from 0.015 to 1.5 seconds, in particular from 0.015 to 0.5 seconds, especially from 0.020 to 0.1 seconds and often from 0.025 to 0.05 seconds. Preferably, the gaseous reaction mixture passes through the reaction space at a flow rate of 10 to 300 meters / second, preferably from 25 to 250 meters / second, more preferably 40 to 230, most preferably 50 to 200, in particular more than 150 to 190 and especially 160 to 180 meters / second.

Due to the turbulent flow close residence times with low standard deviation of usually not more than 6% as described in EP 570799 and good mixing is achieved. Measures such as the constriction described in EP-A-593 334, which is also prone to blockage, are not necessary.

After the reaction, the gaseous reaction mixture is preferably washed at temperatures greater than 130 ⁰ C with a solvent (quench). Suitable solvents are preferably hydrocarbons which are optionally substituted by halogen atoms, such as hexane, benzene, nitrobenzene, anisole, chlorobenzene, chlorotoluene, o-dichlorobenzene, trichlorobenzene, diethyl isophthalate (DEIP), tetrahydrofuran (THF), dimethylformamide (DMF), Xylene, chloronaphthalene, decahydronaphthalene and toluene. The solvent used is particularly preferably monochlorobenzene. The solvent used may also be the isocyanate. In the wash, the isocyanate is selectively transferred to the wash solution. Subsequently, the remaining gas and the resulting wash solution are preferably separated by rectification into isocyanate, solvent, phosgene and hydrogen chloride.

After the reaction mixture has been reacted in the reaction space, it is passed into the workup device with quench. This is preferably a so-called scrubbing tower, the isocyanate formed being separated off from the gaseous mixture by condensation in an inert solvent, while excess phosgene, hydrogen chloride and optionally the inert medium pass through the work-up device in gaseous form. The temperature of the inert solvent above the solution temperature of the carbamoyl chloride belonging to the amine is preferably maintained in the selected quench medium. In this case, the temperature of the inert solvent is particularly preferably kept above the melting temperature of the carbamyl chloride belonging to the amine

In general, the pressure in the workup device is lower than in the reaction space. The pressure is preferably 50 to 500 mbar, more preferably 80 to 150 mbar, lower than in the reaction space.

The laundry can be carried out, for example, in a stirred tank or in other conventional apparatus, for example in a column or mixer-settler apparatus. Technically, all known extraction and washing processes and apparatus can be used for a wash in the process according to the invention, for example those described in Ullmann's Encyclopedia of Industrial Chemistry, 6th ed, 1999 Electronic Release, Chapter: Liquid - Liquid Extraction - Apparatus are. For example, these may be one-stage or multistage, preferably single-stage extractions, as well as those in cocurrent or countercurrent mode, preferably countercurrent.

A suitable quench is known, for example, from EP-A1 1403248, Sp. 2, Z. 39 - Sp. 3, Z. 18, to which reference is expressly made in the scope of this disclosure.

Further possibilities for designing the quench are known, for example, from the unpublished European patent applications with the file numbers EP 06123629.5 and 06123621.2 with the filing date 07.1 1.2006, to which reference is expressly made in the scope of this disclosure.

In this quench zone, the reaction mixture, which consists essentially of the isocyanates, phosgene and hydrogen chloride, is mixed intensively with the injected liquid. The mixing takes place in such a way that the temperature of the reaction mixture is lowered from 200 to 570 ^° C. to 100 to 200 ^° C., preferably to 140 to 180 ^° C., and the isocyanate contained in the reaction mixture passes completely or partially into the sprayed liquid droplets by condensation, while the phosgene and hydrogen chloride remain substantially completely in the gas phase.

The proportion of the isocyanate contained in the gaseous reaction mixture, which passes into the liquid phase in the quench zone, is preferably from 20 to 100% by weight, more preferably from 50 to 99.5% by weight and in particular from 70 to 99% by weight, based on the isocyanate contained in the reaction mixture.

The reaction mixture preferably flows through the quench zone from top to bottom. Below the quench zone, a collecting container is arranged, in which the liquid phase is separated off, collected and removed from the reaction chamber via an outlet and subsequently worked up. The remaining gas phase is removed via a second outlet from the reaction space and also worked up.

The quench can be carried out, for example, as described in EP 1403248 A1, or as in international application WO 2005/123665 A1. The liquid droplets are for this purpose by means of single- or Zweistoffzerstäuberdüsen, preferably Einstoffzerstäuberdüsen generated and produce depending on the embodiment, a spray cone angle of 10 to 140 °, preferably from 10 to 120 °, particularly preferably from 10 ° to 100 °.

The liquid that is injected via the atomizer nozzles must have a good solubility for isocyanates. Preferably, organic solvents are used. In particular, use is made of aromatic solvents which may be substituted by halogen atoms.

The work-up of the diisocyanate thus obtained can be carried out in a manner known per se, for example as described above in liquid phase phosgenation.

The 2-methylpentane-1, 5-diisocyanate prepared in this way contains no aromatic groups in contrast to the otherwise industrially produced isocyanates MDI and TDI.

Another object of the present invention is 2-methylpentane-1, 5-diisocyanate, which additionally has a total chlorine content below 50 ppm by weight and a content of hydrolyzable chlorine below 10 ppm by weight. Such 2-

Methylpentane-1,5-diisocyanate is obtainable by carrying out step d) phosgene-free.

The inventively prepared 2-methylpentane-1, 5-diisocyanate is particularly suitable for the production of polyisocyanates containing isocyanurate, polyisocyanates containing uretdione, polyisocyanates containing biuret groups, polyisocyanates containing urethane or allophanate groups, oxadiazinetrione groups or iminoxadiazinedione groups containing polyisocyanates and / or uretonimine-modified polyisocyanates.

Such polyisocyanates are used, for example, in the production of urethane, isocyanurate, amide and / or urea group-containing plastics by the polyisocyanate polyaddition process. Such polyisocyanate mixtures are used in particular for the production of light-resistant polyurethane coatings and coatings.

The polyisocyanates thus obtained based on the 2-methylpentane-1, 5-diisocyanate prepared according to the invention are generally used in the paint industry. The mixtures according to the invention can be used, for example, in coating compositions for 1K or 2K polyurethane coatings, for example for primers, fillers, basecoats, unpigmented topcoats, pigmented topcoats and clearcoats Industrial, in particular aircraft or large vehicle paint, wood, automotive, especially OEM or car refinish, or decorative paint can be used. The coating compositions are particularly suitable for applications in which particularly high application safety, outdoor weathering resistance, appearance, solvent and / or chemical resistance are required. The curing of these coating compositions is not essential according to the invention. In the automotive industry, in particular, multilayer curing, for example of clearcoat and basecoat, (so-called two-in-one), or of filler, clearcoat and basecoat (so-called three-in-one) are increasingly being carried out.

Furthermore, the 2-methylpentane-1, 5-diisocyanate according to the invention can be used for the production of thermoplastic polyurethanes (TPU), as for example in the Plastics Handbook, Volume 7 "Polyurethane", Carl Hanser Verlag Munich Vienna, 3rd edition 1993, pages 455 to 466 is described.

They are prepared by reacting diisocyanates with compounds having at least two isocyanate-reactive hydrogen atoms, preferably difunctional alcohols.

As isocyanate-reactive compounds, generally known polyhydroxy compounds having molecular weights of 500 to 8,000, preferably 600 to 6,000, especially 800 to 4,000, and preferably an average functionality of 1, 8 to 2.6, preferably 1, 9 to 2.2 , in particular 2, for example polyesterols, polyetherols and / or polycarbonate diols. Preference is given to using polyesterdiols obtainable by reacting butanediol and hexanediol as diol with adipic acid as dicarboxylic acid, the weight ratio of butanediol to hexanediol preferably being 2: 1. Also preferred is polytetrahydrofuran having a molecular weight of 750 to 2500 g / mol, preferably 750 to 1200 g / mol.

As chain extenders it is possible to use generally known compounds, for example diamines and / or alkanediols having 2 to 10 C atoms in the alkylene radical, in particular ethylene glycol and / or butanediol-1, 4, and / or hexanediol and / or di- and / or Tri-oxyalkylene glycols having 3 to 8 carbon atoms in the oxyalkylene radical, preferably corresponding oligo-polyoxypropylene glycols, it also being possible to use mixtures of the chain extenders. As chain extenders it is also possible to use 1,4-bis (hydroxymethyl) benzene (1,4-BHMB), 1,4-bis (hydroxyethyl) benzene (1,4-BHEB) or 1,4-bis (2 -hydroxyethoxy) -benzene (1, 4-HQEE) are used. Preferred chain extenders are ethylene glycol and hexanediol, particularly preferably ethylene glycol.

Usually, catalysts are used which control the reaction between the NCO groups of the diisocyanates and the hydroxyl groups of the synthesis components for example, tertiary amines such as triethylamine, dimethylcyclohexylamine, N-methylmorpholine, N, N'-dimethylpiperazine, 2- (dimethylaminoethoxy) ethanol, diazabicyclo- (2,2,2) -octane and the like, and in particular organic metal compounds such as Titanium acid esters, iron compounds such as iron (Ml) - acetylacetonate, tin compounds such as tin diacetate, tin dilaurate or Zinndialkylsalze aliphatic carboxylic acids such as dibutyltin diacetate, dibutyltin dilaurate or the like. The catalysts are usually used in amounts of 0.0001 to 0.1 parts by weight per 100 parts by weight of polyhydroxyl compound.

In addition to catalysts can be added to the structural components to also conventional auxiliaries. Mention may be made, for example, of surface-active substances, flame retardants, nucleating agents, lubricants and mold release agents, dyes and pigments, inhibitors, stabilizers against hydrolysis, light, heat, oxidation or discoloration, protective agents against microbial degradation, inorganic and / or organic fillers, reinforcing agents and plasticizers.

The preparation of the TPU is usually carried out by conventional methods, such as by belt systems or reaction extruder.

To produce expanded TPU, the TPUs are preferably mixed with expandable microspheres and thermoplastically processed to the desired shaped articles. This can be done for example by injection molding sintering or by extrusion. The temperature during the thermoplastic processing leads to an expansion of the expandable microspheres and thus to the formation of the expanded TPU. Preferably, the melt is introduced into molds and cures there.

Expanded TPUs can be used, for example, as films, tubes, profiles, fibers, cables, shoe soles, other shoe parts, ear tags, automobile parts, agricultural products, electrical products, damping elements; armrests; Plastic furniture elements, ski boots, bumpers, wheels, ski goggles, Powderslushoberflächen be used.

It is an advantage of the present process that a particularly colorless 2-methylpentane-1, 5-diisocyanate can be obtained with this method, preferably this has a color number of not more than 15 APHA according to DIN ISO 6271 on.

Claims

claims

1. A process for the preparation of 2-methylpentane-1, 5-diisocyanate, in which a) 1, 3-butadiene with hydrogen cyanide (HCN) to a mixture of methylglutaric acid dinitrile (MGDN) and adiponitrile (ADN) and optionally 2-

B) methylglutaronitrile is separated off from the adiponitrile / methylglutaric acid dinitrile mixture obtained in this way, c) methylglutaronitrile is converted into 2-methylpentane-1,5-diamine and d) the 2-methylpentan-1, 5-diamine thus obtained in 2 -Methylpentane-1, 5-diisocyanate converted.

2. The method according to claim 1, characterized in that in step a)

1, 3-butadiene homogeneously catalyzed with hydrocyanic acid (HCN) at 10 - 100 bar and 50 - 150 ⁰ C to a mixture of isomers of pentenenitriles.

3. The method according to claim 2, characterized in that separating the obtained according to claim 1 isomer mixture of pentenenitriles by distillation, optionally with isomerization of 2-methyl-3-butenenitrile, in a predominantly 3- and 4-pentenenitriles-containing fraction and these homogeneously catalysed with further hydrocyanic acid to a mixture of adiponitrile, methylglutaronitrile and ethylsuccinonitrile at 0.5 bar abs to 5 bar overpressure at 40 - 150 ⁰ C reacted.

4. The method according to any one of the preceding claims, characterized in that in step b) the reaction mixture obtained from step a) is purified by distillation so that the content of methylglutaric acid and ethylsuccinonitrile is at least 95% by weight.

5. The method according to any one of claims 1 to 4, characterized in that in step b) the reaction mixture obtained from step a) is purified by distillation so that the content of the distillate 0.1 to 99.9% by weight of methylglutaric acid, adiponitrile and ethylsuccinonitrile which is used as a mixture in step c).

6. The method according to any one of the preceding claims, characterized in that the discharge from stage b) on a catalyst selected from the group consisting of Raney nickel, Raney cobalt, Raney copper, iron and cobalt-containing catalysts in the presence of Hydrogen is hydrogenated to the corresponding amines.

7. The method according to any one of the preceding claims, characterized in that one carries out the step d) by reacting the amine with urea and at least least one alcohol in a molar ratio of amine, urea and alcohol such as 1: 2 to 20: 5 to 40 at temperatures of 50 - 300 ⁰ C under a pressure of 0.1 to 30 bar for the reaction and the resulting urethane at temperatures from 200 to 300 ⁰ C and under reduced pressure of 0.01 - 0.6 bar thermally splits.

8. The method according to any one of claims 1 to 6, characterized in that amine and phosgene optionally in the presence of an inert solvent in a molar ratio of phosgene to amino groups of 1, 1: 1 to 30: 1 with a mean residence time of 5 min to 15 h and a temperature between 90 ⁰ C and 250 ⁰ C and a pressure between 1, 1 bar and 80 bar abs in the liquid phase to the corresponding isocyanates.

9. The method according to any one of claims 1 to 6, characterized in that amine and phosgene in a molar ratio of phosgene to amino groups of 1, 1: 1 to 20: 1 at a temperature between 200 ⁰ C to 600 ° C and a pressure between 0.1 bar and 20 bar abs in the gas phase to the corresponding isocyanates.

10. 2-methylpentane-1, 5-diisocyanate obtainable according to one of claims 1 to 9, characterized in that it has a color number of not more than 15 APHA according to DIN ISO 6271.

1 1. Use of 2-methylpentane-1, 5-diisocyanate, optionally in admixture with isomeric hexane diisocyanates according to any one of claims 1 to 9 for the preparation of polyisocyanates or thermoplastic polyurethanes.