DE1901993A1 - Process for the preparation of 4,4'-diphenylmethane diisocyanate and a mixture of di- and polyisocyanates - Google Patents

Description

Badische Anilin- & Soda-Fabrik AG -i ηrH α no

Our reference: 0.Z; 25,968 Ste / Hi

6700 Ludwigshafen, \%. 1. 1969

Process for the preparation of 4,4'-diphenylmethane diisocyanate and a mixture of di- and polyisocyanates

The present invention relates to a method of manufacture of 4,4'-diphenylmethane diisocyanate and a mixture of di- and polyisocyanates by condensation of formaldehyde and Di- and polyamines obtained from aniline.

There is an increasing need in technology for the purest possible 4,4'-diphenylmethane diisocyanate and a mixture of di- and polyisocyanates of the primary di- and polyamines obtained in the condensation of aniline and formaldehyde. It acts the diisocyanates are essentially 4,4'-, 2,4'- and 2,2'-diphenylmethane diisocyanate, while the Polyisocyanates to the isocyanates of higher condensation products the formaldehyde and aniline, z. B. triamines or Tetramines. For example, triamine is the condensation product of 3 molecules of aniline and 2 molecules of formaldehyde.

While the mixture of diamines and polyamines required for the production of a mixture of di- and polyisocyanates obtained relatively easily by condensation of aniline with formaldehyde in the presence of catalytic amounts of hydrochloric acid must be used in the production of the purest possible 4,4'-diaminodiphenylmethane from aniline and formaldehyde Aniline excess and stoichiometric amounts of hydrochloric acid are used will. When using stoichiometric amounts of hydrochloric acid, however, very large amounts of salt are produced during neutralization, the elimination of which causes great difficulties.

From French patent specification 1 487 546 it is known first to produce a mixture of primary diamines and polyamines by condensing aniline and formaldehyde, which is obtained Mixture by phosgenation into a mixture of di- and 689/68 - 2 -

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Transfer polyisocyanates and finally from the obtained Isocyanate mixture by distillation a 4> 4'-Dlphenyiffiethandiisocyanatfraktion and to obtain a mixture of di- and polyisocyanates as residue. However, the 4,4'-diphenylmethane diisocyanate obtained by this process still has a relative high content of isomeric diisocyanates and is therefore for many uses not sufficiently pure.

It has now been found that 4,4'-diphenylmethane diisocyanate and a mixture of di- and polyisocyanates by condensation of formaldehyde with excess aniline in the presence of strong aqueous mineral acids at the beginning of the reaction

^ rigeren and higher temperatures as the reaction progresses, neutralization after the end of the reaction, separation of the resulting mixture of primary di- and polyamines into 4,4'-diaminodiphenylmethane and a mixture of the remaining primary diamines and the primary polyamines, phosgenation of 4,4 ' Diaminodiphenylmethane to 4,4'-diphenylmethane diisocyanate and the mixture of the primary di- and polyamines to form a mixture of di- and polyisocyanates can be advantageously produced if aniline and formaldehyde are used in a molar ratio of 2 to 6 at temperatures of 10 to 90 at the beginning of the reaction ° C and as the reaction progresses from 80 to 150 ⁰ C condenses, from the mixture of primary diamines and polyamines obtained after neutralization, the diamines are completely or partially separated by distillation, from the

Mixture of the separated diamines by crystallization from a solvent 4,4'-Diaminodipheny! Methane wins and that after Separation of the diamines remaining mixture of primary amines after combination with the diamines remaining in the mother liquor during crystallization by phosgenation into a mixture transferred from di- and polyisocyanates.

The process gives a highly pure 4,4'-diphenylmethane diisocyanate, which is ideal for the production of polyurethane elastomers. The obtained mixture of di- and polyisocyanates is a very suitable starting material for the production of rigid polyurethane foams or as a binder suitable for gluing wood.

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The preparation of the mixture of primary diamines and polyamines from aniline and formaldehyde is known per se. Aniline and formaldehyde are used in a molar ratio for the condensation 2 to 6, preferably in a molar ratio of 3 to 5 · The condensation is carried out in the presence of strong aqueous mineral acids such as sulfuric acid and especially hydrochloric acid. In general, 0.02 to 0.3 per mole of aniline. » preferably 0.1 to 0.2 equivalents of the mineral acid used. The formaldehyde can be in polymeric form, for example as trioxane or Paraformaldehyde. However, technical aqueous formaldehyde solutions, for example 20 to 50 percent strength by weight aqueous formaldehyde solutions, used for the condensation.

The reaction is initially in the lower temperature range at temperatures between 10 to 90 ⁰ C, preferably 10 to 30 ⁰ C, carried out with the reaction proceeds in the temperature range between 8o and 150 ⁰ C, preferably 80 to l40 ° C to

to

End to be led / be. It can be advantageous here to largely distill off the water from the reaction mixture before the end of the reaction and to keep the remaining mixture at temperatures above 100 ° C., preferably
to undergo reaction.

above 100 ⁰ C, preferably at 120 to 150 ⁰ C, a post

The reaction mixture obtained after the condensation has ended is neutralized, advantageously using alkaline earth metal hydroxides, such as Calcium hydroxide, and especially alkali hydroxides such as sodium hydroxide or potassium hydroxide is used. The hydroxides can be added as such. In general, however, aqueous solutions are used and / or suspensions of the hydroxides are used.

After neutralization, the resulting mixture of primary diamines and polyamines is expediently used as an organic layer from the separated aqueous layer. The organic layer is then distilled, where appropriate initially excess Aniline is obtained. The diamines are then completely or partially through from the remaining residue fractional ».- distillation separated.

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Whether the diamines are completely or partially distilled off depends on the need for 4,4'-diphenylmethane diisocyanate and the Mixture of di- and polyisocyanates. In general, the diamines are only partially separated, usually 40 to 90 percent by weight, based on the total amount of diamines.

The separated mixture of diaminodiphehylmethanes is then separated by crystallization using a solvent, the 4,4'-diaminodiphenylmethane being crystalline is obtained while the isomers such as 2,4-diaminodiphenylmethane and 2,2'-diaminodiphenylmethane in the mother liquor remain. The crystallization can be carried out one or more times. As a rule, one already obtains after a single recrystallization a very pure product. Optionally halogenated solvents are preferably used as solvents for the crystallization aromatic hydrocarbons into consideration. Examples include 1-chloronaphthalene, trichlorobenzene, o-dichlorobenzene, toluene, xylene and especially chlorobenzene. The appropriate weight ratio of solvent and mixture of diaminodiphenylmethanes can be determined in a simple manner determine a preliminary test. In general, 2 to 10 times the amount, in particular 3 to 6 times the amount, is used Solvent, based on the mixture of diaminodiphenylmethanes. It is beneficial to crystallize in such a Make solvent in which the phosgenation to the mixture of di- and polyisocyanates is carried out.

The crystallization is carried out in a manner known per se, for example by removing the diaminodiphenylmethanes by heating, e.g. B. to temperatures between 40 and 80 ° C, dissolves in the appropriate amount of solvent and the solution is ^{cooled to temperatures between 20 and 30 0} C, for example. The 4,4'-diaminodiphenylmethane which has crystallized out is expediently separated off from the solvent by filtration or centrifugation.

The primary amines contained in the mother liquor can before Combination with the mixture of primary amines remaining after separation of the diamines, for example by distillation, to be isolated. However, the mother liquor is preferably used as

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BATH ORIGINAL

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those combined with the mixture of primary amines remaining after the diamines have been distilled off.

The phosgenation of 4,4'-diaminodiphenylmethane to 4,4'-diphenylmethane diisocyanate and the mixture of primary di- and polyamines is carried out in a manner known per se, for example according to the US Pat. No. 2,683,730 in Journal of the Chemical Soc, Volume 117, pages 988 to 992 (1920) and in Ulimann ¹ s Enzyklopadie der Technischen Chemie, Volume 9 (1957), pages 8 ff.

The method according to the invention is illustrated in more detail by the following example. The parts given in the example are parts by weight. Parts by weight and parts by volume are in Ratio of kilograms to liters.

example

465 parts of aniline, 100 parts of 10 weight percent aqueous formaldehyde and 50 parts of 10 weight percent aqueous hydrochloric acid are run into a stirred tank with a reaction volume of 400 parts by volume, with stirring and cooling to about 10.degree. The container is connected by an overflow pipe to a container with a capacity of 800 parts by volume, the content of which is kept ^{at about 100 ° C. with stirring.} The mean residence time of the reaction mixture in this container is about 1 hour. The reaction mixture leaves this container via an overflow and enters a thin-film evaporator, in which the water is drawn off at the top together with azeotropically boiling aniline. The residue remaining after stripping off the water bottom product is held in a Verweilschlange 2 to 3 hours at a temperature of about 130 ⁰ C, wherein the condensation reaction is completed. For neutralization, the reaction product is treated with 100 parts of 20 percent strength by weight aqueous sodium hydroxide solution per hour and the aqueous layer is separated off. The organic layer is washed with water, the water distilled off in a thin-film evaporator being expediently used. The organic layer is then fractionally distilled under reduced pressure, with 290 parts per hour of aniline at 20 torr

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be recovered, which are used again for the condensation. 100 parts per hour of the mixture of the diaminodiphenylmethanes, which has a boiling range of 220 to 230 ^° C. at 2 torr, are then separated off from the residue. The separated diaminodiphenylmethanes are dissolved in 400 parts of monochlorobenzene in the heat, and the resulting solution is then cooled to 20 ° C., the 4,4'-diaminodiphenylmethane crystallizing out. The crystals are separated off in a pressure cell filter and washed with 100 parts of cold chlorobenzene. This gives 50 parts of 4,4'-diaminodiphenylmethane with a melting point of 92 ⁰ C. The mother liquor and the wash-chlorobenzene are combined and used to dissolve the remaining in the thin-film evaporator after the Abdestiüieren diaminodiphenylmethanes the bottom product. The resulting solution of the primary di- and polyamines is then phosgenated.

The phosgenation of the 4,4'-diaminodiphenyl methane or the mixture of di- or polyamines consists of a cascade of three stirred vessels which are operated at 5-10 ⁰ C, 6O-8O ° C and 110-130 ⁰ C. (Cf. . Fig.)

While boiler I has a filling volume of 1000 parts by volume, boiler II has a volume of 15ΟΟ parts by volume and boiler III of 2500 parts by volume. Closes to the phosgenation apparatus a stripping column (1), in which phosgene and part of the solvent are distilled off, and after cooling in (2) via a Wash column (3) is returned to reactor I. In (3) the waste gas from boilers II and III is also washed to remove phosgene to be removed from the exhaust gases and returned to the reaction circuit. The remaining solvent is in a further column (4) removed, that for dissolving the di- or di- and polyamine feed is used in the boiler I, and the isocyanates in (6) win as the crude product. Every hour, to the one shown in Fig. sketched apparatus 80 parts by weight of di- or di- and polyamines and 330 parts by volume of chlorobenzene added (at 7), while about 95 parts by weight Phosgene can be introduced into boiler I at (8) in gaseous or liquid form. The stripping column is heated with so much steam that about 600 parts by volume of phosgene and chlorobenzene evaporate and Reach the reactor I via the wash column to remove the

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To keep the reaction mixture fluid. In the bottom of the stripping column, about 100 parts per hour of isocyanates are obtained, which, dissolved with 330 parts by volume of chlorobenzene, are freed from solvent in the distillation column. In the case of a mixture of di- and polyisocyanates, the bottom product can be taken off directly from (6) and processed further. If, however, highly pure 4,4'-diphenylmethane diisocyanate is produced, this is again distilled off overhead in a further evaporation plant. The yield of 4,4'-diphenylmethane diisocyanate and the mixture of di- and polyisocyanates is in each case almost 100 %, based on the primary amine used for the phosgenation.

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Claims (1)

- 8 - O.Z. 25th Claim Process for the preparation of 4,4'-diphenylmethane diisocyanate and a mixture of di- and polyisocyanates by condensation of formaldehyde with excess aniline in the presence of strong aqueous mineral acids at lower temperatures at the beginning of the reaction and higher temperatures as the reaction proceeds, neutralization after the reaction has ended, Separation of the resulting mixture of primary di- and polyamines in 4,4'-diaminodiphenylmethane and a mixture of the remaining primary diamines and the primary polyamines, phosgenation of 4,4'-diaminodiphenylmethane to 4,4'-diphenylmethane diisocyanate and the mixture of the primary di - And polyamines to form a mixture of di- and polyisocyanates, characterized in that aniline ^ and formaldehyde in the molar ratio 2 to 6 at Temper "'" uren from the beginning of the reaction 10 to 90 ⁰ C and with the progress of the reaction from 80 to 150 ⁰ C condensed, from the mixture of primary diamines and polyamines obtained after neutralization the diamines are completely or partially separated off by distillation, 4,4'-Diaminodiphe ^ vlmethane is obtained from the mixture of the separated diamines by crystallization from a solvent and the mixture of primary amines remaining after separation of the diamines is combined with the crystallization in the. The diamines remaining in the mother liquor are converted into a mixture of di- and polyisocyanates by phosgenation. Badische Anilin- & Soda-Fabrik AG drawing. η r- t ·· -