Process for Producing Aniline or Aniline-Derived Products

Abstract

The present invention relates to a method for producing aniline or an aniline-derived product, comprising the steps of: (A) providing aminobenzoic acid; (B) decarboxylating the aminobenzoic acid in a reactor at a reaction temperature in the range of 170° C. to 350° C. to obtain aniline and carbon dioxide, wherein the decarboxylation is carried out at a reaction pressure that reaches or preferably exceeds the boiling point of aniline, so that a liquid first phase, optionally containing solid particles, and a gaseous second phase are formed in the reactor, wherein a gas stream comprising aniline and carbon dioxide is discharged from the reactor; (C) condensing and optionally washing the aniline contained in the gas stream; and (D) optionally converting the aniline obtained in (C) into an aniline-derived product.

Description

[Technical field]

[0001] The invention on which this application is based has been financially supported by the German Federal Ministry of Food and Agriculture as part of the project "Biobasierte Herstellung von Intermediaten für Polyurethane - Phase II (Bio4PURPro)" (funding code 22019918).

[0002] The present invention relates to a process for producing aniline or aniline conversion products, comprising the steps of: (A) providing aminobenzoic acid; (B) decarboxylating the aminobenzoic acid in a reactor at a reaction temperature in the range of 170° C. to 350° C. to obtain aniline and carbon dioxide, wherein the decarboxylation is carried out at a reaction pressure that reaches or exceeds the boiling point of aniline, so that a liquid first phase, possibly containing solid particles, and a gaseous second phase are formed in the reactor, wherein a gas stream comprising aniline and carbon dioxide is discharged from the reactor; (C) condensing and optionally purifying the aniline present in the gas stream; and (D) optionally converting the aniline obtained in (C) into aniline conversion products. [Background technology]

[0003] The preparation of anilines by decarboxylation of aminobenzoic acids is known in principle in the prior art. For example, reference may be made to the international patent applications WO 2005 / 023361 and WO 2005 / 023913 and the documents cited therein. The aminobenzoic acid starting compounds can be obtained chemically or, preferably, fermentatively.

[0004] The chemical preparation of aminobenzoic acids is known. A suitable synthetic route is, for example, the reaction of phthalimide with sodium hypochlorite. Phthalimide itself can be obtained from phthalic anhydride and ammonia.

[0005] The fermentative production of aminobenzoic acids is likewise known and described in the literature, see, for example, the already mentioned applications WO 2005 / 023363 and WO 2005 / 023999 and the publications cited therein.

[0006] US Pat. No. 5,399,433 describes the decarboxylation of fermentatively or chemically produced anthranilic acid and the extraction of the aniline formed in the decarboxylation with an exogenous organic solvent (alcohols, phenols, amides, ethers or aromatic hydrocarbons, in particular 1-dodecanol being highlighted as a suitable solvent).

[0007] US Pat. No. 5,399,366 describes the decarboxylation of fermentatively produced anthranilic acid, inter alia, in water or in an ex situ organic solvent, in particular 1-dodecanol, optionally in a mixture with aniline (see p. 18, lines 28 and 29). Furthermore, this document also describes the option of carrying out the decarboxylation in aniline (without 1-dodecanol, see Figures 35 and 37-38 and the accompanying paragraphs), optionally in the presence of 10% by weight of water (see Figure 36 and the accompanying paragraphs).

[0008] US Pat. No. 5,399,633 describes a process for decarboxylating aminobenzoic acid in a mixture with crude aniline, which originates from the process itself, with part of the product stream not being sent to purification but being recycled to the process. The catalysts described for carrying out the decarboxylation are aqueous acids such as sulfuric acid, nitric acid and hydrochloric acid, solid acids such as zeolites and Si-Ti molecular sieves, solid bases such as hydroxyapatite and hydrotalcite, and polymeric acids such as ion exchange resins (especially Amberlyst).

[0009] US Pat. No. 5,399,633 describes the decarboxylation of aminobenzoic acids in aniline. It is assumed that the aniline itself acts as a catalyst (i.e. has autocatalytic properties). Exogenous catalysts are purposely avoided. The reaction is carried out under conditions in which the aniline is liquid. In certain embodiments, a gas stream is removed from the reactor to discharge the carbon dioxide formed as a co-product. Since this gas stream also entrains small amounts of aniline, it is preferable to selectively condense the entrained aniline and send it to the reaction or work-up.

[0010] Patent document 5 relates to a process for producing aniline or an aniline conversion product, which comprises reacting aminobenzoic acid in the presence of an inorganic heterogeneous metal oxide catalyst containing Al2O3 in a mass proportion of 40.0% to 100% based on the total mass of the metal oxides, where the mass proportion of Al2O3 based on the total mass of the inorganic heterogeneous metal oxide catalyst is 25% to 100%.

[0011] None of the processes described so far is entirely satisfactory in terms of economics, especially with regard to the overall process complexity (actual production of aniline and its subsequent processing by distillation). Likewise, it would be desirable to optimize the yield of aniline (by optimizing the conversion and suppressing the by-product 2-aminobenzanilide). Therefore, improvements were required in the production of aniline or aniline conversion products by decarboxylation of aminobenzoic acids. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] International Publication No. 2015 / 124686 [Patent Document 2] International Publication No. 2015 / 124687 [Patent Document 3] International Publication No. 2018 / 002088 [Patent Document 4] International Publication No. 2020 / 020919 [Patent Document 5] As yet unpublished patent application having reference number EP21177307.2 Summary of the Invention

[0013] In view of this need, the present invention provides a process for producing aniline or an aniline conversion product, comprising the steps of: (A) preparing an aminobenzoic acid; (B) decarboxylating aminobenzoic acid in a reactor, Here, aminobenzoic acid is introduced into the reactor (i) as a solid, (ii) in molten form, or (iii) dissolved or suspended in a solvent, and converted to aniline and carbon dioxide at a reaction temperature in the range of 170°C to 350°C, preferably 185°C to 300°C, more preferably 190°C to 260°C; wherein the conversion is carried out at a reaction pressure which reaches or preferably exceeds the boiling point of aniline, so that a liquid first phase, possibly containing solid particles, and a gaseous second phase are formed in the reactor, and wherein a gas stream containing aniline and carbon dioxide is discharged from the reactor; (C) condensing and optionally purifying the aniline present in the gas stream; (D) optionally converting the aniline obtained in (C) to an aniline conversion product; The present invention provides a method comprising:

[0014] Carrying out the conversion at a reaction pressure that reaches or preferably exceeds the boiling point of aniline means that the reaction pressure and reaction temperature are adjusted to one another so that at the pressure found in the reactor the temperature in the reactor is above or at least equal to the boiling point of aniline. Aniline has a boiling point of 184°C at standard pressure. Therefore, if the conversion is carried out, for example, at standard pressure (1.013 bar) or at pressures that differ only slightly therefrom, a reaction temperature of 184°C or higher should be selected. If the conversion is carried out at reduced pressure, a lower reaction temperature (but not lower than 170°C) corresponding to the pressure reduction can also be selected. If the conversion is carried out at increased pressure, a higher reaction temperature (but not higher than 350°C) corresponding to the pressure increase should be selected.

[0015] As a result, in the process according to the invention, the aniline formed by decarboxylation spontaneously evaporates. It is therefore at least very largely transferred into the gaseous second phase and discharged from the reactor by a gas stream containing aniline and carbon dioxide. It cannot be excluded that a small proportion of the formed aniline (in particular up to 5.0%, preferably up to 2.0%, particularly preferably up to 1.0% of the theoretical yield of aniline, where "theoretical yield" is based on 100% conversion of aminobenzoic acid to aniline, in which case 1 mol of aminobenzoic acid is converted to 1 mol of aniline) remains in the liquid first phase, which may contain solid particles, and is then discharged and discarded, for example in a purge stream (see further below for details). This does not depart from the scope of the invention.

[0016] Surprisingly, it has been found that carrying out the decarboxylation under conditions in which the aniline formed passes into the gas phase and is removed in gaseous form represents a simple construction option for a process characterized by high conversion and high selectivity with respect to the target product aniline. In the process according to the invention, the "crude aniline" resulting from the reaction is practically already distilled, which greatly simplifies further purification, if necessary at all.

[0017] The attached drawing shows a reactor suitable for carrying out the process according to the invention continuously. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram showing a stirred tank reactor. [Diagram 2] FIG. 1 shows a rotating tubular reactor. [Diagram 3] FIG. 1 shows a trough reactor (=conveying trough reactor). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] First, a brief overview of various possible embodiments of the invention is provided below.

[0020] In a first embodiment of the invention, which can be combined with all other embodiments, the conversion of aminobenzoic acid is carried out at a reaction pressure (measured in the second phase) in the range from 0.10 bar to 10 bar, preferably from 0.50 bar to 5.0 bar and particularly preferably from 0.90 bar to 1.1 bar (in particular atmospheric pressure).

[0021] In a second embodiment of the invention, which can be combined with all other embodiments, unless these are limited to a discontinuous process mode, aminobenzoic acid is continuously fed to the reactor and aniline and carbon dioxide are continuously discharged from the reactor during the conversion of aminobenzoic acid in step (B).

[0022] In a third embodiment of the invention, which is a specific configuration of the second embodiment, the reactor is a stirred tank reactor with an inlet for aminobenzoic acid, an outlet for a gas stream, and an outlet for a liquid stream that may contain solid particles (so that the conversion of aminobenzoic acid is carried out with (very significant) backmixing).

[0023] In a fourth embodiment of the invention, which is a specific configuration of the third embodiment, the first phase comprises a mass proportion of aniline in the range of 5.0% to 90%, preferably 10% to 70%, based on the total mass of aminobenzoic acid and aniline.

[0024] In a fifth embodiment of the invention, which is another specific configuration of the second embodiment, the reactor comprises a reaction tube with an inlet for aminobenzoic acid, an outlet for a gas stream, and an outlet for a liquid stream that may contain solid particles (so that the conversion of aminobenzoic acid is carried out (to a very large extent) without backmixing).

[0025] In a sixth embodiment of the present invention, which is a specific configuration of the fifth embodiment, the reactor tube rotates about its longitudinal axis (hence this is a so-called rotating tube reactor, in which the reactor tube may be inclined to the horizontal and may optionally be equipped with internals such as lifting strips, flow restrictors or conveying screws), or The reaction tube is arranged in a stationary manner, in which a conveying screw rotates within the reaction tube, which does not completely cover the cross section of the reaction tube (therefore this is a so-called trough reactor or conveying trough reactor).

[0026] In a seventh embodiment of the present invention, which is a specific configuration of the fifth and sixth embodiments, a mixture containing 0.1% to 30% by weight, preferably 1.0% to 7.5% by weight, of aniline based on the total weight of the mixture, is continuously removed from the reactor via an outlet for a liquid stream that may contain solid particles.

[0027] In the eighth embodiment of the present invention, which is a specific configuration of the second to seventh embodiments, the average residence time t from when the aminobenzoic acid molecule enters the reactor to when the aniline molecule formed therefrom is discharged from the reactor via the gas flow is V is set to 1.00 to 500 minutes, preferably 5.00 to 120 minutes.

[0028] In a ninth embodiment of the present invention, which can be combined with all other embodiments, and which is not limited to a continuous process mode, the aminobenzoic acid is discontinuously converted in batches, in which the aminobenzoic acid is initially charged to the reactor and / or is added to the reactor for a period of time t Z After the entire aminobenzoic acid batch is added, the aminobenzoic acid is added to the reactor at the reaction temperature and pressure for a (post) reaction period t R The conversion takes place in the reactor over a period of time.

[0029] In a tenth embodiment of the invention, which is a specific configuration of the ninth embodiment, the reactor is a stirred tank reactor.

[0030] In an eleventh embodiment of the present invention, which is a specific configuration of the ninth and tenth embodiments, the (post) reaction period t R At the start of the reaction, the first phase contains a mass proportion of aniline in the range of 0.1% to 90%, preferably 5.0% to 90%, particularly preferably 10% to 70%, based on the total mass of aminobenzoic acid and aniline.

[0031] In a twelfth embodiment of the present invention, which is a specific configuration of the ninth to eleventh embodiments, 50% to 100% of the total amount of the aminobenzoic acid batch is Z is added (continuously or at intervals) to the reactor over a period of t Z is the total period t Z +t R It is 30% to 70% of the total.

[0032] In the thirteenth embodiment of the present invention, which is a specific configuration of the ninth to twelfth embodiments, R The time is in the range of 1.00 minutes to 500 minutes, preferably 5.00 minutes to 120 minutes.

[0033] In a fourteenth embodiment of the present invention, which can be combined with all other embodiments, the gas stream comprising aniline and carbon dioxide in step (B) is passed through a condenser in order to condense any aminobenzoic acid entrained in the gas stream (thus any entrained aminobenzoic acid is condensed to a large extent, preferably at least 90%, and then returned to the first phase in the reactor, while the aniline passes through the condenser in gaseous form to a large extent, preferably at least 90%, in particular if a further (distillation or rectification) column is arranged between the reactor and the condenser).

[0034] In a fifteenth embodiment of the present invention, an ortho-aminobenzoic acid is provided in step (A). This embodiment can be combined with all other embodiments, as long as another aminobenzoic acid isomer is not provided in step (A).

[0035] In a sixteenth embodiment of the present invention, para-aminobenzoic acid is provided in step (A). This embodiment can be combined with all other embodiments, as long as another aminobenzoic acid isomer is not provided in step (A).

[0036] In a seventeenth embodiment of the invention, which is a particular configuration of the fifteenth embodiment, step (A) comprises (i) the reaction of phthalimide or phthalic acid monoamide with an alkali metal hypohalide, in particular sodium hypochlorite, in a basic medium followed by acid treatment, or (ii) the hydrogenation of 2-nitrobenzoic acid.

[0037] In an eighteenth embodiment of the present invention, which is a specific configuration of the sixteenth embodiment, step (A) comprises (i) the reaction of terephthalic acid monoamide with an alkali metal hypohalite, in particular sodium hypochlorite, in a basic medium followed by acid treatment, or (ii) the hydrogenation of 4-nitrobenzoic acid.

[0038] In a nineteenth embodiment of the present invention, which is a specific configuration of the first to sixteenth embodiments, step (A) comprises fermenting a raw material comprising a fermentable carbon-containing compound and a nitrogen-containing compound in the presence of a microorganism.

[0039] In a twentieth embodiment of the present invention, which is a specific configuration of the nineteenth embodiment, The fermentable carbon-containing compound is selected from starch hydrolysate, sugar cane juice, sugar beet juice, hydrolysate of a lignocellulosic raw material, or a mixture of two or more of the aforementioned carbon-containing compounds; and The nitrogen-containing compound is selected from ammonia gas, aqueous ammonia, (at least) one ammonium salt, soy protein, urea, or a mixture of two or more of the aforementioned nitrogen-containing compounds.

[0040] In a twenty-first embodiment of the invention, which is a specific configuration of the nineteenth and twentieth embodiments, the microorganism is selected from Escherichia coli, Pseudomonas putida, Corynebacterium glutamicum, Ashbya gossypii, Pichia pastoris, Hansenula polymorpha, Kluyveromyces marxianus, Yarrowia lipolytica, Zygosaccharomyces bailii, or Saccharomyces cerevisiae.

[0041] In a twenty-second embodiment of the present invention, which is a specific configuration of the first to twenty-first embodiments, step (B) is carried out without adding a catalyst and without adding aniline.

[0042] In a twenty-third embodiment of the present invention, which is a further specific configuration of the first to twenty-first embodiments, step (B) is carried out in the presence of a catalyst selected from: (a) aqueous mineral acids (particularly sulfuric acid, nitric acid, and hydrochloric acid, etc.); (b) zeolites (particularly Y-type in protonated form (H-form)); (c) Si-Ti molecular sieves; (d) hydroxyapatite; (e) hydrotalcite; (f) ion exchange resins (particularly Amberlyst); and / or (g) inorganic heterogeneous metal oxide catalysts comprising Al2O3 in a mass proportion of 40.0% to 100% based on the total mass of metal oxides, wherein the mass proportion of Al2O3 based on the total mass of the inorganic heterogeneous metal oxide catalyst is 25% to 100%.

[0043] In a twenty-fourth embodiment of the present invention, which is a specific configuration of the twenty-third embodiment, the method comprises step (B)(iii), wherein the solvent comprises aniline (in particular is aniline).

[0044] In a 25th embodiment of the present invention, which is a further specific configuration of the first to twenty-first embodiments, the method comprises step (B)(iii), in which the solvent comprises (in particular is) aniline, and no (external) catalyst is added.

[0045] Twenty-sixth embodiments of the present invention, which can be combined with all other embodiments (as long as aniline is not used as solvent), in particular as they relate to the use of a continuous flow reactor in step (B), comprise a step (B)(iii), in which the solvent remains in the first phase to the extent of at least 90%, preferably at least 95%, particularly preferably at least 99%, at the reaction temperature and reaction pressure.

[0046] In a twenty-seventh embodiment of the present invention, which is a particular configuration of the twenty-sixth embodiment, the solvent is selected from a hydrocarbon (especially having 12 or more carbon atoms), a silicone oil, an ether-based oil (especially triglyme, tetraglyme, or pentaglyme), a molten salt, a sulfolane, a diphenyl ether, a haloaromatic compound (especially trichlorobenzene), or an aniline-based amide (especially 2-aminobenzanilide), where a hydrocarbon or 2-aminobenzanilide is preferred.

[0047] In a 28th embodiment of the present invention, which can be combined with all other embodiments, step (D) is carried out, which comprises the following conversion: (1) The acid-catalyzed reaction of aniline with formaldehyde to form diamines and polyamines of the diphenylmethane series, (2) The acid-catalyzed reaction of aniline with formaldehyde to form di- and polyamines of the diphenylmethane series, followed by reaction of these with phosgene to form di- and polyisocyanates of the diphenylmethane series; or (3) Conversion of aniline to an azo compound, Contains one of the following:

[0048] The above briefly outlined embodiments and further possible configurations of the invention are explained in more detail below: All embodiment and further configuration options can be combined with each other if desired, unless the contrary is clearly evident to a person skilled in the art from the context or unless it is explicitly stated otherwise.

[0049] In step (A) of the process according to the invention, aminobenzoic acid is prepared for conversion. For this purpose, aminobenzoic acid can be produced at the site of decarboxylation or else introduced externally. In the process according to the invention, it is preferred to use ortho- or para-aminobenzoic acid as starting material for decarboxylation, with ortho-aminobenzoic acid (anthranilic acid) being particularly preferred. Aminobenzoic acid can be produced by any method known in the prior art. Both chemical (non-fermentative) and biotechnological (fermentative) routes are known for the production of aminobenzoic acid. Both types of production can be used in the context of the process according to the invention. These are well known and can all be applied without problems in the context of the decarboxylation according to the invention, so they will be only briefly outlined below.

[0050] Suitable chemical synthesis routes include in particular (i) the Hofmann rearrangement of the corresponding imides or monoamides with alkali metal hypohalides (especially sodium hypochlorite) in a basic medium followed by acid treatment, and (ii) the hydrogenation of the corresponding nitrobenzoic acids. Thus, in the first case (i), the starting materials are phthalimides or phthalic / terephthalic monoamides, and in the latter case (ii), 2-nitrobenzoic acid or 4-nitrobenzoic acid.

[0051] Aminobenzoic acids can also be obtained via the fermentative route (see the patent documents cited at the outset). For this purpose, a raw material containing fermentable carbon- and nitrogen-containing compounds is fermented in the presence of microorganisms. In this context: The fermentable carbon-containing compound is selected from starch hydrolysate, sugar cane juice, sugar beet juice, hydrolysate of a lignocellulosic raw material, or a mixture of two or more of the aforementioned carbon-containing compounds; and the nitrogen-containing compound is selected from ammonia gas, aqueous ammonia, (at least) one ammonium salt, soy protein, urea, or a mixture of two or more of the aforementioned nitrogen-containing compounds; is preferred.

[0052] Suitable microorganisms include, in particular, Escherichia coli, Pseudomonas putida, Corynebacterium glutamicum, Ashbya gossypii, Pichia pastoris, Hansenula polymorpha, Kluyveromyces marxianus, Yarrowia lipolytica, Zygosaccharomyces bailii, or Saccharomyces cerevisiae.

[0053] The fermentative route is preferred as it paves the way for a more sustainable and environmentally friendly production of aniline.

[0054] Step (B) of the process according to the invention involves the actual decarboxylation of the aminobenzoic acid to give the desired product (or intermediate), the aniline.

[0055] For this purpose, the aminobenzoic acid prepared in step (A) is introduced into the decarboxylation reactor (i) as a solid, (ii) in molten form or (iii) dissolved or suspended in a solvent. If the aminobenzoic acid is introduced into the reactor in solid form (i), it melts there, since temperatures between 170°C and 350°C, preferably between 185°C and 300°C, particularly preferably between 190°C and 260°C, are found. If the aminobenzoic acid is melted outside the decarboxylation reactor (ii), it should be ensured in particular that decarboxylation has not yet started there. This can be achieved by keeping the residence time as short as possible and the temperature as low as possible. If aniline is used as the solvent (iii), i.e. if an aminobenzoic acid / aniline mixture is fed into the decarboxylation reactor (hereinafter also referred to as reactor for short), the temperature of the solution of aminobenzoic acid in aniline before entering the reactor should be selected between room temperature and 160°C depending on the mixing ratio. Once in the reactor, the mixture is heated to the reaction temperature, where the aniline added to the aminobenzoic acid passes into a second phase, which is very largely gaseous, and is discharged from the reactor by a gas stream containing aniline and carbon dioxide. In parallel with this, the aminobenzoic acid is decarboxylated to further aniline, which also passes into a second phase, which is very largely gaseous, and is discharged from the reactor by a gas stream containing aniline and carbon dioxide. When using a solvent (iii) different from aniline, it should be ensured that these remain very largely, ideally completely, in the liquid phase, i.e. that they have a suitably high boiling point under the selected reaction conditions (this is generally the case when their boiling point at atmospheric pressure is greater than 200° C.), and that at the reaction temperatures and pressures found in the reactor, in particular at least 90%, preferably at least 95%, particularly preferably at least 99%, of these remain in the first phase (liquid phase that may contain solid particles suspended therein).Suitable such solvents are high-boiling compounds that are unreactive under the selected reaction conditions with respect to the functional groups (amine and carboxyl groups) of aniline and aminobenzoic acid, such as long-chain hydrocarbons, especially those with 12 or more carbon atoms (individual compounds or mixtures such as paraffin oil), silicone oils, ether-based oils (e.g. triglyme, tetraglyme, or pentaglyme), molten salts, or high-boiling solvents such as sulfolane, diphenyl ether, halogenated aromatic compounds (e.g. trichlorobenzene), 2-aminobenzanilide, or other aniline-based amides. This embodiment is particularly advantageous when the reaction is carried out in a continuous-flow reactor, since the liquid drainage of the solvent allows the purging of high-boiling impurities such as by-products, thus preventing their accumulation in the reaction chamber.

[0056] The reaction pressure can be selected within a wide range, in particular between 0.10 bar and 10 bar, preferably between 0.50 bar and 5.0 bar, particularly preferably between 0.90 bar and 1.1 bar, provided that an aniline-containing gas phase (second phase) as described above is formed. In the context of the present invention, all pressures reported relate to absolute pressure. Very particularly preferably, the reaction can be carried out at atmospheric pressure, which is a particular advantage of the method according to the invention. To determine the pressure, a pressure measuring device can be installed in the (gaseous) second phase. Of course, measurements in the first phase are also possible, although not preferred. In case of discrepancies between the measured values, the value measured in the second phase is decisive.

[0057] In a preferred embodiment, the gas stream comprising aniline and carbon dioxide removed from the reactor passes through a condenser to (selectively) condense any aminobenzoic acid entrained in the gas stream. The condenser is in particular operated in such a way that most or all of any entrained aminobenzoic acid, preferably at least 90%, is condensed, while the aniline (for the most part) passes through the condenser in gaseous form. The condensed aminobenzoic acid is returned to the first phase (liquid, possibly containing solid particles) present in the reactor. In a preferred embodiment, the condenser is in the form of a plug-in condenser arranged directly above the reactor, so that the condensed aminobenzoic acid can flow out freely. For this purpose, condensers of a type known per se in the specialist field may be used. Particularly suitable designs are characterized by avoiding stagnation of the liquid flow and can be mechanically cleaned. The heat can be dissipated using a secondary circuit of a refrigerant. In a preferred implementation, evaporative cooling by water is implemented, so that the waste heat can be utilized for steam generation. When setting suitable operating conditions, in particular a temperature should be selected that is high enough to prevent crystallization of the aminobenzoic acid and thus to avoid deposits. If necessary, the optimum operating conditions can be determined by simple preliminary experiments.

[0058] In order to minimize the proportion of aniline that is undesirably recycled, a (distillation or rectification) column can be arranged between the reactor and the condenser. It is preferred that at least 90%, preferably (essentially) all, of the aniline passes through the condenser in gaseous form.

[0059] The decarboxylation can be carried out in the presence of a catalyst. Suitable (ex situ) catalysts include, in particular, (a) aqueous mineral acids (especially sulfuric acid, nitric acid, and hydrochloric acid), (b) zeolites (especially Y-type in protonated form (H-form)), (c) Si-Ti molecular sieves, (d) hydroxyapatite, (e) hydrotalcite, (f) ion exchange resins (especially Amberlyst), and / or (g) inorganic heterogeneous metal oxide catalysts comprising a mass proportion of Al2O3 of 40.0% to 100% based on the total mass of metal oxides, where the mass proportion of Al2O3 based on the total mass of the inorganic heterogeneous metal oxide catalyst is 25% to 100%.

[0060] Such catalytic reactions can be carried out by adding aniline to the aminobenzoic acid to be converted (as described in patent application WO 02 / 06336, but also by using purified aniline instead of crude aniline). However, it is also possible to carry out the decarboxylation without the use of an (ex situ) catalyst, by adding aniline to the aminobenzoic acid to be converted (as described in patent application WO 02 / 06336). It is also possible to add neither aniline nor an (ex situ) catalyst.

[0061] The reaction mode can be discontinuous or continuous.

[0062] In the discontinuous reaction mode, aniline is produced in separate batches, for which the corresponding aminobenzoic acid batches are converted. In the context of batchwise production, the amount of aminobenzoic acid to be converted can be initially charged to the reactor or can be gradually increased over a period t Z Alternatively, a portion of the aminobenzoic acid may be initially charged and the remainder added over a period t Z In either case, after the entire amount of the aminobenzoic acid batch has been added, the aminobenzoic acid is reacted in the reactor at the reaction temperature and pressure for a (post) reaction period t R It is preferred to add 50% to 100% of the total amount of the aminobenzoic acid batch to the reactor continuously or at intervals, where t Z t Z+t R 30% to 70% of the total period of the (post) reaction period t R The value of is preferably 1.00 min to 500 min, more preferably 5.00 min to 120 min. As a reactor for discontinuous aniline production, a stirred tank type reactor is particularly suitable.

[0063] (Post) reaction period t R At the start of the reaction (i.e. after the addition of aminobenzoic acid has ended and the selected conditions of reaction temperature and reaction pressure have been reached), the first phase generally contains a mass proportion of aniline ranging from 0.1% to 90%, preferably from 5.0% to 90%, particularly preferably from 10% to 70%, based on the total mass of aminobenzoic acid and aniline. The exact value depends, inter alia, on the manner of aminobenzoic acid addition. If the aminobenzoic acid is initially charged to the reactor at ambient temperature and melts therein for the first time, naturally a small proportion of the aminobenzoic acid is only converted when the reaction temperature is reached. On the other hand, if the aminobenzoic acid is introduced already in the molten state into a reactor in which the desired conditions of reaction temperature and reaction pressure are already found, then at the end of the addition, significantly more aminobenzoic acid will already have been converted. Of course, the rate at which the formed aniline passes from the first phase (liquid, possibly containing solid particles) to the second (gaseous) phase is also relevant, which again depends on the reaction temperature and reaction pressure.

[0064] In the continuous reaction mode, aniline is produced in a continuous flow reactor, and after a start-up phase, a steady state is established, during which a certain mass flow rate (e.g. reported in kg / h) of aminobenzoic acid is continuously fed to the reactor, and corresponding mass flows of aniline and carbon dioxide are continuously discharged from the reactor. This steady state of continuous conversion of aminobenzoic acid is maintained until production is terminated (e.g. due to necessary maintenance work or simply because aniline is no longer required), unless an interruption in operation occurs. The reactor used must be equally well suited for suspensions (molten solids), which may be highly concentrated, liquids with low viscosity, and liquids (by-products / residues), which may be highly viscous.

[0065] A suitable type of reactor for this purpose is a stirred tank reactor, which, in contrast to the stirred tank reactors further described above in connection with the discontinuous process, is operated such that, over the period of conversion of aminobenzoic acid, aminobenzoic acid is continuously introduced into the reactor and a gas stream (containing aniline and carbon dioxide) is continuously removed from the reactor. The stirred tank reactor must therefore have (at least) one inlet for aminobenzoic acid and (at least) one outlet for the gas stream. Such stirred tank reactors used in a continuous process should also have an outlet for a liquid stream, through which any high-boiling by-products and other impurities that may be present can be discharged in liquid or suspended form. Recovery of reactants or valuable products from this stream can be considered depending on the respective concentrations.

[0066] Such a stirred tank reactor is shown in Figure 1. In this figure, the reference symbols have the following meanings:

[0067] TIFF2025511711000002.tif92170

[0068] When using a stirred tank reactor, the reaction is carried out with significant backmixing. That is, the composition of the reaction mixture taken into account throughout the tank contents is (essentially) constant, in contrast to the continuous flow reactors discussed further below, where the composition of the reaction mixture changes continuously from the reactant inlet to the product outlet (or until maximum conversion is achieved). Preferably, in the process according to the invention, when a stirred tank reactor is used in a continuous process mode, the first phase comprises a mass proportion of aniline in the range of 5.0% to 90%, preferably 10% to 70%, based on the total mass of aminobenzoic acid and aniline. These figures relate to a process in which aniline is not additionally used as a solvent.

[0069] One possible operating configuration for such a stirred tank reactor is described in more detail below.

[0070] A stream of powdered or molten aminobenzoic acid is continuously metered into a stirred tank reactor. The stirred tank is heated and after some time has passed since the start of the metering of the reactants, a liquid level of molten aminobenzoic acid forms at its bottom (establishment of a steady state). The aminobenzoic acid decomposes into aniline and carbon dioxide, the temperature in the tank being selected such that both products become gaseous and leave the stirred tank reactor continuously from there via an outlet at the upper end. A condenser is arranged at the gas outlet, the operating temperature of which is selected such that the entrained gaseous aminobenzoic acid is condensed as selectively as possible and is returned directly to the stirred tank reactor. The remaining gas stream reaches a work-up stage, where the target product aniline is separated from carbon dioxide, water generally present and any low-boiling impurities present. In the lower region of the stirred tank reactor, a small stream of the liquid vessel contents, which may contain solid particles, is continuously removed, thereby avoiding the accumulation of high-boiling impurities in the stirred tank. This stream can optionally be fed to a work-up stage in order to separate the aminobenzoic acid present therein and the aniline present therein from the residue. Depending on the composition of the separated valuable products, these are added either to the reactant stream of aminobenzoic acid or to the product stream of aniline (before or after the work-up). The feed stream of powdered or molten aminobenzoic acid to the reactor must be selected so as to result in partial filling of the stirred tank with liquid, i.e. must be adapted to the residence time required for complete reaction of the aminobenzoic acid and evaporation of the aniline formed. In stationary operating conditions of a continuously operated stirred tank reactor, the liquid level in the stirred tank should be constant. Optionally, a stream of inert gas (e.g. preheated nitrogen) can be passed into the gas space of the stirred tank reactor to reduce the residence time of the gaseous products in the reactor.

[0071] Besides stirred tank reactors, tubular reactors (reaction tubes) are also suitable for carrying out the process according to the invention. These reactors have an inlet for aminobenzoic acid at or near the end and an outlet for the gas stream downstream in the upper region. As already mentioned for stirred tank reactors, these reactors also have an outlet for the liquid stream (including high-boiling by-products and any other impurities present), which is suitably arranged opposite the inlet. In such reactors, the reaction proceeds very largely without backmixing. That is, the composition of the reaction mixture flowing through the reactor changes continuously during its passage through the reactor, and at the outlet of the liquid stream the concentration of aminobenzoic acid is at its lowest (=maximum conversion). It is preferable to carry out step (B) as far as possible without backmixing. Depending on the exact configuration of the reactor and the reaction mode, the liquid stream discharged via the outlet may contain solid particles.

[0072] One type of suitable reactor is known as a rotating tube reactor. This is a tubular reactor which rotates about its longitudinal axis during operation. Such a rotating tube reactor is shown in Figure 2. In this figure, the reference symbols already used in connection with Figure 1 have the same meaning as they have in Figure 1. The other reference symbols have the following meaning:

[0073] TIFF2025511711000003.tif14170

[0074] The reactor may also be inclined relative to the horizontal (i.e., the direction of reactant flow) and may optionally be equipped with internals such as lifting strips, flow restrictors, or conveying screws, which are not shown in FIG.

[0075] One possible operating configuration of such a rotating tube reactor is described in more detail below.

[0076] A stream of powdered or molten aminobenzoic acid is metered continuously at the end into a horizontal or inclined rotating tube reactor. The rotating tube reactor is heated and the metered reactants are transported through the tube depending on the rotation speed and inclination of the rotating tube. The aminobenzoic acid decomposes into aniline and carbon dioxide, the temperature in the rotating tube being selected so that both products become gaseous and leave the reactor continuously via an outlet at the downstream end of the rotating tube. In the process according to the invention, the rotating tube is partially filled so that the gaseous products formed during the reaction can pass above the material flowing as a channel at the bottom of the tube to the gas outlet. A condenser is arranged behind the gas outlet, the operating temperature of which is selected so that any gaseous aminobenzoic acid entrained is condensed as selectively as possible, and this condensate stream is returned in an appropriate manner to the inlet of the rotating tube reactor. The remaining gas stream reaches a work-up stage, where the target product aniline is separated from carbon dioxide, water generally present, and any low-boiling impurities present. In the flow path of the material flowing at the bottom in the rotary tube, a composition gradient occurs over the length of the tube as the reaction progresses. In the region of the inlet, the material consists of solid and / or molten aminobenzoic acid, while on the outlet side, the liquid stream, which may contain solid particles, will consist of high-boiling residues (possibly high viscosity) and small proportions of liquid aminobenzoic acid and aniline. This stream can be treated as described above for the stirred tank reactor. The feed stream of powdered or molten aminobenzoic acid to the rotary tube reactor must be selected so that the proportion of valuable products in the liquid residue is as low as possible, i.e. it must be adapted to the residence time required for complete reaction of aminobenzoic acid and evaporation of the aniline formed. The interior of the rotating tube may be empty or may be equipped with internals that may serve to improve transport, mixing and heat transfer, for example in the form of blades, or that may contribute to increasing the amount of reaction mixture present in the rotating tube (so-called hold-up), for example in the form of flow restrictors. Optionally, a flow of inert gas (for example preheated nitrogen) may be added at the inlet of the rotating tube reactor to reduce the residence time of the gaseous products in the reactor.

[0077] A further type of reactor suitable for reaction modes essentially without backmixing is known as a trough reactor (also called a conveying trough reactor). In contrast to rotating tube reactors, this is a fixedly arranged tubular reactor in which a conveying screw rotates and does not completely block the cross section of the reaction tube (it only blocks the lower region of the reactor, only the gas phase is present in the upper region). Such a trough reactor is shown in FIG. 3. In this figure, the reference signs already used in connection with FIG. 1 have the same meaning as they have in FIG. 1. The other reference signs have the following meaning:

[0078] TIFF2025511711000004.tif20170

[0079] The trough reactor can be inclined with respect to the horizontal (i.e., the direction of reactant flow), although this is not shown in Figure 3. One possible operating configuration for such a trough reactor is described in more detail below.

[0080] A stream of powdered or molten aminobenzoic acid is metered continuously at the end into a horizontal or inclined trough reactor. The trough reactor is heated and the metered products are transported through it depending on the rotation speed of the conveying screw and the inclination of the trough. The aminobenzoic acid decomposes into aniline and carbon dioxide, the temperature in the trough reactor being selected so that both products become gaseous and leave the reactor continuously through an outlet at the top of the trough reactor. The trough reactor is partially filled so that the gaseous products formed during the reaction can pass above the material flowing in the bottom of the trough as a channel in the region of the conveying screw to the gas outlet. A condenser is arranged at the gas outlet, the temperature of which is selected so that any gaseous aminobenzoic acid entrained is condensed as selectively as possible and is returned directly to the trough reactor. The remaining gas stream reaches a work-up stage, where the target product aniline is separated from carbon dioxide, water generally present and any low-boiling impurities present. In the flow path of the material conveyed by the screw at the bottom in the trough reactor, a composition gradient occurs over the length of the trough as the reaction progresses. In the region of the inlet, the material consists of solid and / or molten aminobenzoic acid, while at the outlet side, the liquid stream, which may contain solid particles, will consist of high-boiling residues (possibly high viscosity) and small proportions of liquid aminobenzoic acid and aniline. This outlet stream can be further processed as described above for the stirred tank reactor. The feed stream of powdered or molten aminobenzoic acid to the trough reactor must be selected so that the proportion of valuable products in the liquid residue is as low as possible, i.e. it must be adapted to the residence time necessary for complete reaction of aminobenzoic acid and evaporation of the aniline formed. The conveying screw of the trough reactor may be equipped with conveying elements having different geometries over its length, e.g. screw elements of different pitch or conveying direction, to influence the residence time behavior and mass transfer. Optionally, a flow of inert gas (e.g. preheated nitrogen) can be added at the inlet of the trough reactor to reduce the residence time of the gaseous products in the reactor.

[0081] For all types of reactors in a reaction mode essentially without backmixing, it applies that a mixture comprising 0.1% to 30% by weight, preferably 1.0% to 7.5% by weight, of aniline, based on the total weight of the mixture, is preferably continuously removed from the reactor via an outlet for the liquid stream, which may contain solid particles.

[0082] In all continuously operated process modes of step (B) (i.e., whether or not operation with backmixing is performed), the average residence time t from the time the aminobenzoic acid molecules enter the reactor to the time the aniline molecules formed therefrom leave the reactor via the gas stream is V is 1.00 min to 500 min, preferably 5.00 min to 120 min.

[0083] Step (C) of the process according to the invention comprises condensing and optionally purifying the aniline withdrawn in gaseous form from the reactor. For this purpose, the gas stream withdrawn from the reactor, optionally after passing through a condenser (13 in the figure) as described above to remove any entrained aminobenzoic acid by selective condensation, passes through a condenser (not shown in the figure), which is operated in such a way that the aniline is condensed from the gas stream, while the carbon dioxide (except possibly a small proportion present in dissolved state in the condensed aniline) passes through the condenser in gaseous form. For this purpose, condensers of the type known per se in the specialist field may be used. Particularly suitable designs are characterized by avoiding stagnation of liquid and can be mechanically cleaned. The heat can be dissipated using a secondary circuit of a refrigerant. In a preferred implementation, evaporative cooling by water is implemented, so that the waste heat can be utilized for steam generation.

[0084] Again, as already mentioned above for the condenser 13 which selectively condenses any entrained aminobenzoic acid, a (distillation or rectification) column can be connected upstream of the condenser.

[0085] The aniline thus obtained is already characterized by a high purity, especially if, as described above, a (distillation or rectification) column is connected upstream of the condenser of step (C). If desired, it can be further purified by distillation, especially multiphase azeotropic distillation. The methods for achieving this are sufficiently well known in the art that no further explanation is necessary at this point.

[0086] Step (D) of the process according to the invention relates to any further conversion of the aniline obtained in (C). Possible further conversions include in particular: (1) The acid-catalyzed reaction of aniline with formaldehyde to form diamines and polyamines of the diphenylmethane series, (2) the acid-catalyzed reaction of aniline with formaldehyde to form di- and polyamines of the diphenylmethane series, followed by reaction of these with phosgene to form di- and polyisocyanates of the diphenylmethane series; and (3) Conversion of aniline to an azo compound.

[0087] The further reaction of aniline with formaldehyde to obtain di- and polyamines of the diphenylmethane series (D)(1) is known per se and can be carried out by any prior art method. The continuous or partially discontinuous preparation of di- and polyamines of the diphenylmethane series from aniline and formaldehyde is disclosed, for example, in EP 1 616 890, US 5 286 760, EP 451 442 and WO 99 / 40059. The reaction is carried out under acid catalysis. A suitable acid catalyst is preferably hydrochloric acid.

[0088] The further reaction of the di- and polyamines of the diphenylmethane series thus obtained with phosgene to give di- and polyisocyanates of the diphenylmethane series (D)(2) is also known per se and can be carried out by any prior art method, suitable methods being described, for example, in EP 2 077 150, EP 1 616 857, EP 1 873 142 and EP 0 314 985.

[0089] The conversion of the anilines obtained according to the invention into azo compounds, in particular into azo dyes (D)(3), can also be carried out by any prior art method, for example, reference can be made to the known preparation of aniline yellow (para-aminoazobenzene, CAS 493-5-7) or indigo (2,2'-bis(2,3-dihydro-3-oxomethylidene), CAS 482-89-3).

[0090] The present invention will now be described in more detail with reference to the following examples. EXAMPLES

[0091] Compounds used: Anthranilic Acid (AA, petrochemical): C7H7NO2, purity 98% or higher, Acros Organics Anthranilic Acid (AA, Biological Origin): C7H7NO2, Purity: 98%, Covestro Deutschland AG 2-Aminobenzanilide (AMD): C 13 H 12 N2O, 95% purity, abcr GmbH

[0092] How to explain: HPLC: For the HPLC analysis, an Agilent equipment with UV detection (DAD, measured at 254 nm) was used. For the separation, an Agilent column (Eclipse XDB-C18, 5 μm, 4.6×150 mm) was used. The mobile phase used was a mixture of MeOH and buffer (volume ratio MeOH:buffer=40:60, buffer: 0.7 ml of 85% (analytical grade (pa)) H3PO4 diluted with HPLC water to a final volume of 1 l, where the final loading was performed after setting the pH to 3.0 with aqueous sodium hydroxide). The flow rate was 0.7 ml / min. The column oven temperature was adjusted to 40° C. The injection volume was 0.5 μl. The retention times of the individual components aniline (ANL), anthranilic acid (AA), and 2-aminobenzanilide (AMD) were ANL=2.6 min, AA=5.2 min, amide=14.9 min.

[0093] The peak areas are converted to area percent (Area%). Prior calibration with pure substances allowed the quantification of the individual components in mass percent (wt%) based on the reaction mixture. In addition to the substance composition, these values ​​are used to determine the conversion of anthranilic acid, the yield of aniline formed, the selectivity of aniline formation, and the selectivity towards the formation of 2-aminobenzanilide.

[0094] General Procedure (GP) 1: Decarboxylation of anthranilic acid with complete reflux of the formed aniline (comparison) The setup consists of an 80 ml four-neck flask equipped with a stir bar, a jacketed dropping funnel, a reflux condenser and an inert gas connection (Ar). First, the dropping funnel is charged with the desired amount of solid AA at room temperature and the entire apparatus is inerted with a constant Ar flow of 20 standard l / h. The apparatus is operated open at atmospheric pressure. The reflux condenser is cooled to 5°C. After inerting, the dropping funnel thermostat is set to 155°C and a waiting period of 25 minutes follows until the AA is completely melted. At the same time, the reaction vessel is heated to 210°C and the transitions (reaction vessel-dropping funnel, reaction vessel-reflux condenser) are insulated. Then AA is added for a defined period (t Z) into the reaction vessel. After the continuous metering, the reaction mixture is added at a specific time (t R Stirring is continued for 30 min, and then the system is shut down. The mass of the reaction vessel product is determined and characterized in terms of AA, ANL, and AMD composition via HPLC analysis.

[0095] GP2: Decarboxylation of anthranilic acid with gaseous release of the aniline formed (according to the invention) The equipment consists of an 80 ml four-neck flask equipped with a stir bar, a jacketed dropping funnel, a distillation bridge with a distillation vessel and an inert gas connection (Ar). First, the dropping funnel is charged with the desired amount of solid AA at room temperature and the whole apparatus is inerted with a constant Ar flow of 20 standard liters / h. The apparatus is operated open at atmospheric pressure. The distillation vessel is cooled to 5°C. After inerting, the thermostat of the dropping funnel is set to 165°C and a waiting period of 25 minutes follows until the AA is completely melted. At the same time, the reaction vessel is heated to 210°C and the transitions (reaction vessel-dropping funnel, reaction vessel-distillation bridge) are insulated or trace heated. Then, AA is added for a defined period (t Z ) into the reaction vessel. After the continuous metering, the reaction mixture is added at a specific time (t R Stirring is continued for 30 min, then the system is shut down. The product masses in the reaction vessel and product vessel are determined and the fractions are characterized for AA, ANL, and AMD composition via HPLC analysis.

[0096] The experiments are summarized in the following table, in which the following abbreviations are used: C=Comparative example ANL = aniline AA = anthranilic acid AMD = 2-aminobenzanilide

[0097] TIFF2025511711000005.tif158170

[0098] Table Notes: [a]t=t tot (where ttot =t Z +t R ) Mass distribution of the reaction mixture in the reaction vessel or distillation vessel (numbers are mass%) [b] Mass fraction (%) of the product mixture based on the total mass of the products in the reaction vessel and distillation vessel; [c] Chemical conversion of anthranilic acid, [d] chemical yield of aniline, [e] selectivity for aniline or 2-aminobenzanilide; [f] Chemical yield of aniline in the distillation vessel (%); [g] Purity of aniline (t = t in the container under consideration) R (Determined from the mass distribution of ANL, AA, and AMD at [h] Final mass from the reaction vessel or the combination of the reaction vessel and distillation vessel.

[0099] As shown by the examples, the process according to the invention allows the conversion of aminobenzoic acid with high conversion and low formation of by-products, resulting in high yields of aniline.The process according to the invention shows many advantages over processes without separation of distillation products.With the same reaction time, a higher conversion of AA and therefore a higher yield of ANL can be observed when the product is continuously removed by distillation.With the same conversion of AA, an increase in the selectivity of ANL and therefore a higher yield of ANL can be observed when the product is continuously removed by distillation.A further advantage is that with the process according to the invention, ANL is already obtained in high purity, so that there is less tendency towards post-reaction or continuous loss of yield in subsequent process steps.

Claims

1. A method for producing aniline or aniline conversion products, (A) The process of preparing aminobenzoic acid, (B) A step of decarboxylating the aminobenzoic acid in a reactor, Here, the aminobenzoic acid is introduced into the reactor in (i) as a solid, (ii) in a molten state, or (iii) dissolved or suspended in a solvent, and is converted to aniline and carbon dioxide at a reaction temperature in the range of 170°C to 350°C. Here, since the conversion is carried out at a reaction pressure that reaches or exceeds the boiling point of aniline, a first liquid phase and a second gaseous phase, which may contain solid particles, are formed in the reactor, and a gaseous stream containing aniline and carbon dioxide is discharged from the reactor. The process, (C) A step of condensing the aniline present in the gas stream and purifying it as desired, (D) Optionally, a step of converting the aniline obtained in (C) into an aniline conversion product, Methods that include...

2. The method according to claim 1, wherein the aminobenzoic acid is continuously supplied to the reactor and aniline and carbon dioxide are continuously discharged from the reactor during the period of conversion of the aminobenzoic acid in step (B).

3. The method according to claim 2, wherein the reactor is a stirred-tank type reactor having an inlet for the aminobenzoic acid, an outlet for the gas flow, and an outlet for a liquid flow that may contain solid particles.

4. The method according to claim 2, wherein the reactor comprises a reaction tube having an inlet for the aminobenzoic acid, an outlet for the gas flow, and an outlet for a liquid flow that may contain solid particles.

5. The reaction tube rotates around its longitudinal axis, or The method according to claim 4, wherein the reaction tube is positioned in a fixed manner, and a transfer screw that does not completely block the cross-section of the reaction tube rotates inside the reaction tube.

6. The aminobenzoic acid is converted in a discontinuous batch, and here, the aminobenzoic acid is initially packed into the reactor, and / or for a period of t Ｚ The aminobenzoic acid is added to the reactor over a period of time, and after the entire batch of aminobenzoic acid is added, the aminobenzoic acid is reacted at the reaction temperature and reaction pressure for a period of time t. Ｒ The method according to claim 1, wherein the conversion occurs within the reactor over a certain period of time.

7. The method according to claim 6, wherein the reactor is a stirred tank type reactor.

8. The gas stream containing aniline and carbon dioxide in step (B) is passed through a condenser, The method according to claim 1 or 2, wherein any aminobenzoic acid entrained in the gas stream is condensed.

9. (α) Prepare orthoaminobenzoic acid in step (A), or The method according to claim 1 or 2, wherein para-aminobenzoic acid is prepared in step (A) (β).

10. Step (D) is performed, which results in the following transformation: (1) Formation of diphenylmethane series diamines and polyamines by acid-catalyzed reaction of aniline and formaldehyde, (2) Formation of diamines and polyamines of the diphenylmethane series by an acid-catalyzed reaction between aniline and formaldehyde, followed by the formation of diisocyanates and polyisocyanates of the diphenylmethane series by reaction between them and phosgene, or (3) Conversion of the aniline to an azo compound, The method according to claim 1 or 2, comprising one of the following.

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