WO1998025888A1

WO1998025888A1 - Process for preparing isocyanates from primary amines which are not readily dissolved

Info

Publication number: WO1998025888A1
Application number: PCT/EP1997/006585
Authority: WO
Inventors: Peter Heitkämper
Original assignee: Bayer Aktiengesellschaft
Priority date: 1996-12-09
Filing date: 1997-11-26
Publication date: 1998-06-18
Also published as: AU5751498A; DE19651041A1

Abstract

Isocyanates are prepared by the 'cold-hot phosgenation' of primary amines which are not readily dissolved in chlorobenzene and/or o-dichlorobenzene. According to this process phosgene is dissolved in a solvent (A) consisting of chlorobenzene and/or o-dichlorobenzene. The amine to be reacted is likewise dissolved, optionally at a high temperature, in a second inert aprotic solvent (B) which is suitable for dissolving the amine, the solvent (B) being miscible with the solvent (A) and having a boiling point which is at least 30 °C higher than that of solvent (A) and a boiling point which is least 30 °C lower than that of the isocyanate to be prepared. The resultant amine solution is mixed with the phosgene solution at temperatures of between 10 and 60 °C, and the mixture reacted in known manner at between 130 and 200 °C by increasing the temperature.

Description

Process for the preparation of isocyanates from poorly soluble primary amines

The present invention relates to an improved process for the preparation of isocyanates by "cold-hot phosgenation" of poorly soluble primary amines.

The production of isocyanates from primary amines by the “cold-hot phosgenation” method is known and is state of the art. Basic descriptions of this method can be found, for example, in (1) Ullmann's Encyclopedia of Industrial Chemistry, Verlag Chemie, 4th edition 1977, Volume 13, pages 347 ff and in

(2) Houben-Weyl, Methods of Organic Chemistry, Georg Thieme Verlag, 4th edition 1983, Volume E4, pages 738 ff.

Chlorobenzene or o-dichlorobenzene are used as solvents in the process carried out in practice (see literature 1, page 351). These solvents have proven their worth, among other things because they are inert, have good solubility and are extremely suitable for recovering excess phosgene and separating it from the hydrogen chloride formed.

In general, there is no need to use solvents other than these. Difficulties arise, however, when the amine to be reacted is sparingly soluble in these solvents.

As literature 2 teaches (page 744), for the phosgenation the amine and phosgene to be reacted should be reacted if possible dissolved in the same solvent. However, many amines are only soluble in very low concentrations in chlorobenzene or o-dichlorobenzene. For example, Japanese Patent 114 726 describes the preparation of tris (4-isocyanatophenyl) thiophosphate, a 3.0% by weight solution of tris (4-aminophenyl) thiophosphate in chlorobenzene heated to 100 ° C. with a solution of phosgene in chlorobenzene

Implementation. Such high dilutions not only result in low space-time yields; they also cause a large amount of energy need and thus high costs in the distillative recovery of the solvent.

One way to circumvent these difficulties could be to dissolve phosgene and the amine to be reacted in a very polar solvent in which the amine is soluble in practical concentrations for phosgenation. Such solvents are known and are mentioned, for example, in literature 2 (page 744). However, they have not proven themselves in practice because the exclusive use of very polar solvents has disadvantages. Above all, their comparatively high solubility of hydrogen chloride is disadvantageous, with the result that excess phosgene and hydrogen chloride formed can only be separated inadequately with their help.

Another possibility for phosgenation of sparingly soluble amines is that the amines are introduced into the phosgene solution in solid form either directly or in suspension in the solvent used to dissolve phosgene and thus brought to reaction. This method is often used in practice for poorly soluble amines (see Literature 1, page 351 and Literature 2, page 744). It is based on the fact that the undissolved arnine particles gradually dissolve in the course of the reaction. The phosgenation of amines in solid form is associated with major disadvantages. For example, the direct addition of solid amine into a phosgene solution requires complex protective measures, especially on an industrial scale, for reasons of occupational safety, so that this method cannot be described as practicable.

In contrast, amine suspensions are easier to handle. The conveying and dosing of suspensions is also technically feasible. But this technique presupposes that the suspended amines are sufficiently finely divided. In general, this means that the amines must be ground in a complex process before they are reacted. Another disadvantage is that the phosgenation of suspended amines inevitably requires comparatively long reaction times because the amine concentrations in the liquid phase and thus the reaction rates are low. This also applies if the amines are converted into fine particles. German Patent 1 959 462 describes the preparation of aromatic tetraisocyanates by "cold-hot phosgenation" of the corresponding finely pulverized tetramines, each requiring a total reaction time of about 20 hours. However, long reaction times inevitably mean poor economy of the procedure.

Finally, the phosgenation of suspended amines also has the disadvantage that the isocyanate yields are insufficient. The reason for this is that in the reaction mixtures the isocyanate formed reacts with the free amine at the solid-liquid boundary and can form irreversible by-products. Such side reactions can be minimized in a complex manner by a large excess of phosgene, by a high dilution and by suitable reaction temperatures. For example, Houben-Weyl, Methods of Organic Chemistry, 4th Edition, 1952, Volume 8, page 122 describes the preparation of triphenylmethane-4,4 ', 4 "- triisocyanate by reacting the corresponding triamine in solid form with phosgene, yields of only 70 to 80% of theory are achieved.

It is therefore an object of the present invention to provide a process for the preparation of isocyanates by “cold-hot phosgenation” of primary amines which are sparingly soluble in chlorobenzene or o-dichlorobenzene and which contain the abovementioned

Does not have disadvantages.

The present invention therefore relates to a process for the preparation of isocyanates by “cold-hot phosgenation” of primary amines which are sparingly soluble in chlorobenzene and / or o-dichlorobenzene, which is characterized in that phosgene is obtained in a from chlorobenzene and / or Solves existing o-dichlorobenzene A, the amine to be reacted in a second to dissolve the Amine-suitable inert aprotic solvent B optionally also dissolves at elevated temperature, solvent B being miscible with solvent A and having a boiling point which is at least 30 ° C., preferably 50 ° C., higher than solvent A and an at least 30 ° C., preferably 50 ° C, has a lower boiling point than the isocyanate to be prepared, this amine solution is mixed with the phosgene solution at temperatures of 10 to 60 ° C, preferably 20 to 50 ° C, and the mixture is then preferably in a known manner by increasing the temperature to 135 to 190 ° C.

Examples of the aprotic inert organic to be used according to the invention

Solvents B are tetramethylene sulfone, benzonitrile, 4-tolunitrile, nitrobenzene, 2-nitrotoluene, mixtures of 2- and 4-nitrotoluene, 2, 1,3-benzothiadiazole, 4-methyl-2,1,3-benzothiadiazole, 5-methyl- 2, 1,3-benzothiadiazole, mixtures of 4- and 5-methyl-2, 1,3-benzothiadiazole and other alkyl-substituted 2, 1,3-benzothiadiazoles.

The 2, 1,3-benzothiadiazoles which may be used according to the invention as solvent B are known (see Houben-Weyl, Methods of Organic Chemistry, Volume E8d, pages 170 ff) and correspond to the formula:

in which

the radicals R ¹ , R ² , R ³ , R ^{4 can be the} same or different and have the meaning of a hydrogen atom or a hydrocarbon radical having 1 to 4 carbon atoms. You can, for example, from the corresponding o-phenylene diamines can be prepared by reaction with sulfur dioxide or thionyl chloride.

The solvents B can be used both in a mixture with one another and individually.

The respectively optimal amount of solvents A and B can be determined by appropriate preliminary tests. The optimal amount is usually 1 to 10 times the amount by weight of solvent A, based on the amount of phosgene used, and 1 to 12 times the amount by weight Solvent B, based on the amount of amine used, it is advisable not to use more solvent B than is required to dissolve the amine used

In the process according to the invention, the amount of phosgene used is 1.1 to 10 times, preferably 1.5 to 6 times that stoichiometrically required

Amount based on the amount of amine used.

Examples of the sparingly soluble amines to be phosgenated according to the invention are 2-chloro-1,4-diaminobenzene, 2,6-dichloro-1,4-diaminobenzene, 2,5-dichloro-1,4-diamino-benzene and 2,5-dimethoxy -l, 4-diaminobenzene, 2,4,6-triaminotoluene, 1,4-diamino-naphthalene, 1,5-diaminonaphthalene, 5-amino-3-phenyl-l, 2,3-benzotriazole, 5-amino-3 - (4-aminophenyl) - 1, 2,3-benzotriazole, 4,4'-diamino-N-methylbenzanilide, 1, 2-bis (4-aminophenoxy) ethane, 1, 4-bis (4-aminophenoxy ) benzene, tris (4-aminophenyl) methane, thiophosphoric acid tris (4-aminophenyl) ester, phenyl bis (5-methyl-2,4-diaminophenyl) methane and tetrakis (4-aminophenoxy )-methane.

The amine solution and the phosgene solution are mixed intensively in the process according to the invention, a mixture having temperatures of 10 to 60 ° C., preferably 20 to 50 ° C. being formed. The mixture is increased to 130 to 200 ° C. by increasing the temperature, preferably 135 to 190 ° C implemented. After the end of

Reaction, the reaction mixture is freed from excess phosgene in the usual manner by distillation and then fractionally distilled, the recovered solvent used. The resulting isocyanate remains as a distillation residue and can optionally also be distilled for purification if it is sufficiently stable thermally.

It must be regarded as very surprising that the phosgenations in the process according to the invention proceed comparatively quickly and with good isocyanate yields, since it was to be expected that when the amine solution was mixed with the phosgene solution, a considerable proportion of the dissolved amine is precipitated or separated out again as free amine by the chlorobenzene or o-dichlorobenzene contained in the reaction mixture. Accordingly, it had to be assumed that a

Phosgenation by the process according to the invention has the same problems as the phosgenation of an amine suspension. However, this is unexpectedly not the case.

Examples

example 1

Production of 1,5-diaminonaphthalene

158 g of distilled 1,5-diamononaphthalene (analytically determined purity 98.7%) were at 90 to 95 ° C in a mixture of 600 g of 4-methyl and 980 g of 5-methyl-2,1,3-benzothιadιazol (solvent B) solved

In a 6-1 phosgenation apparatus, 300 g of phosgene were dissolved in 1,600 ml of anhydrous chlorobenzene (solvent A) at 0 to 5 ° C. With external cooling and vigorous stirring, the approximately 90 ° C. warm amine solution was dissolved in within 15 minutes the phosgene solution metered in. A pulpy but readily stirrable suspension of 35 ° C. was then formed. The reaction mixture was then heated to a rapid rate, the temperature increase being controlled in such a way that the amounts of gas released could be safely removed. From about 80 ° C the initially stormy gas evolution subsided and phosgene was slowly introduced into the reaction mixture (approx. 70 g / h). After heating for a total of 110 minutes, reflux was reached at 140 ° C, and the reaction mixture consisted of a practical, clear solution The mixture was then stirred under reflux for a further 2 hours while introducing phosgene (approx. 70 g / h). The reaction flask was then equipped with a full-body column (Raschig rings, filling height 10 cm) and a distillation bridge. The reaction mixture was distilled off by excess phosgene freed and then fractionally distilled at 19 mbar

3 fractions were obtained, which were weighed and analyzed by gas chromatography

1 fraction (maximum head temperature 87 ° C) 1 198 g

Chlorobenzene with 0.44% = 5.3 g methyl-2, l, 3-benzothiadiazole 2nd fraction (maximum head temperature 131 ° C) 1 565 g:

1,563 g of methyl 2, 1,3-benzothiadiazole with 0, 12% = 1.9 g of 1,5-diisocyanatonaphthalene

3rd fraction (maximum head temperature 192 ° C) 200.8 g: NCO content: calc. 40.0%, found. 39.7%

99.3% = 199.4 g of 1,5-diisocyanatonaphthalene content of hydrolyzable chlorine: 131 ppm.

The total yield of 1,5-diisocyanatonaphthalene was 201.3 g, corresponding to 97.1% of theory. The distillation residue consisted of 6.0 g of dark

Solid.

Example 2

Production of 1,5-diisocyanatonaphthalene

158 g of technical 1,5-diaminonaphthalene (analytically determined purity 94.8%) were phosgenated in the same manner as described in Example 1. The finished reaction mixture was also worked up and fractionally distilled as in Example 1:

1st fraction (maximum head temperature 86 ° C) 1 082 g:

Chlorobenzene with 0.63% = 6.8 g methyl-2, l, 3-benzothiadiazole

2nd fraction (maximum head temperature 125 ° C) 1 569 g:

1,568 g of methyl-2, 1,3-benzothiadiazole with

0.03% = 0.5 g 1,5-diisocyanatonaphthalene

3rd fraction (maximum head temperature 194 ° C) 192.1 g:

NCO content: calc. 40.0%, found 39.3%

98.2% = 188.6 g 1,5-diisocyanatonaphthalene

Hydrolyzable chlorine content: 61 ppm. The total yield of 1,5-di-isocyanatonaphthalene was therefore 189.2 g, corresponding to 95.0% of theory. The residue on distillation consisted of 10.2 g of a dark solid product

170.0 g of the 3 fraction were redistilled at 18 mbar. In addition to 1.6 g

Residue 167.3 g of almost colorless 1,5-diisocyanatonaphthalene (NCO content 39.8%) was obtained

Example 3

Production of 1.5-Diisocvanatonaphthalιn

A solution of 360 g of phsogen in 1,180 ml of anhydrous chlorobenzene (solvent A), cooled to 4 ° C., was placed in a 4-1 phosgene apparatus. With external cooling and vigorous stirring, a solution of approximately 90 ° C. was obtained within 15 minutes 158 g of technical 1,5-diaminonaphthalene (analytically determined purity 94.8%) in 1180 g of benzonitrile (solvent B) were metered into the phosgene solution. A readily stirrable suspension of 40 ° C. was then formed. The reaction mixture was then warmed rapidly, with the temperature increase was controlled in such a way that the amounts of gas released could be safely removed. At about 95 ° C, the initially stormy gas evolution subsided, and phosgene was slowly introduced into the reaction mixture (approx. 70 g / h) after a total of 115 minutes of heating 142 ° C reflux reached, and the reaction mixture consisted of a practically clear solution. The mixture was then stirred under reflux for a further 2 hours while introducing phosgene (approx. 70 g / h)

The reaction flask was then provided with a full-body column (Raschig rings, full height 10 cm) and a distillation bridge. The reaction mixture was freed from excess phosgene by distillation and then fractionally distilled at 18 mbar. 3 fractions were obtained, which were weighed and analyzed by gas chromatography 1 fraction (maximum head temperature 70 ° C) 782 g

Chlorobenzene / 26.7% = 209 g benzonitrile

2 fraction (maximum head temperature 102 ° C) 975 g

Chlorobenzene / 95.6% = 932 g benzonitrile 3 fraction (maximum head temperature 193 ° C) 195.0 g

NCO content over 40.0%, found 39.1% content of hydrolyzable chlorine 195 ppm

The yield of 1,5-di-isocyanatonaphthalene was therefore 190.7 g, corresponding to 95.8% of theory. The distillation residue consisted of 1.4 g of dark solid product

Example 4

Preparation of thiophosphoric acid tπs- (4-isocyanatophenyl) ester

194 g of tri (4-aminophenyl) thiophosphoric ester (analytically determined purity 95.0%) were at 80 to 85 ° C in a mixture of 418 g of 4-methyl and 682 g of 5-methyl-2, l, 3-benzothiadiazole (solvent B) dissolved

In a 4-1 phosgene apparatus, 300 g of phosgene were dissolved at 0 to 5 ° C in 1200 ml of anhydrous chlorobenzene (Solvent A). With external cooling and vigorous stirring, the approximately 80 ° C warm amine solution was dissolved in the Phosgene solution metered in. This gave a readily stirrable suspension of 30 ° C. The reaction mixture was then heated to a rapid rate, the temperature increase being controlled in such a way that the amounts of gas released could be safely removed. From about 85 ° C., the initially stormy gas evolution subsided, and it phosgene was slowly introduced into the reaction mixture (approx. 100 g / h). After heating for a total of 105 minutes, reflux was achieved at 136 ° C., and the reaction mixture consisted of a practically clear solution. The mixture was then stirred for a further 1.5 hours while introducing phosgene ( approx. 100 g / h) on

Reflux stirred The reaction flask was then provided with a full-body column (Raschig rings, full height 10 cm) and a distillation bridge The reaction mixture was freed from excess phosgene by distillation. Finally, the solvents were fractionally distilled off from the reaction mixture at 19 mbar. 2 fractions were obtained, which were weighed and analyzed by gas chromatography.

1 fraction (maximum head temperature 90 ° C) 1 127 g

Chlorobenzene with 0.64% = 7.2 g methyl-2, l, 3-benzothiadιazol

2 fraction (maximum bottom temperature 150 ° C, maximum head temperature 1 1 PC) 1 097 g 1.06% = 1 1.6 g chlorobenzene / 98.9% = 1 085 g methyl-2, 1,3-benzothiadiazole

229.1 g of dark product remained as the crude isocyanate

NCO content above 27.1%, found 25.5% hydrolyzable chlorine content 0.15%

Example 5

Preparation of thiophosphoric acid tris (4-isocvanatophenyl ester

A solution of 320 g of phosgene in 1,035 ml of anhydrous chlorobenzene (solvent A), cooled to 5 ° C., was placed in a 4-1 phosgene apparatus. With external cooling and with vigorous stirring, a solution of about 40 ° C. was obtained within 10 minutes 194 g of thiophosphoric acid tris (4-aminophenyl) ester (analytically determined purity 95.0%) in 1 100 g of benzonitrile (solvent B) were metered into the phosgene solution. This gave a readily stirrable suspension of 40 ° C. Subsequently, the The reaction mixture was heated briskly, the temperature increase being controlled in such a way that the amounts of gas released could be safely removed. At about 55 ° C, the initially stormy gas evolution subsided, and a practically clear solution was formed. Then phosgene was slowly introduced into the reaction mixture (approx. 100 g / h) After heating for a total of 75 minutes, reflux was achieved at 133 ° C. The mixture was now left for 1 hour stirred while refluxing phosgene (approx. 100 g / h). The reaction flask was then provided with a full-body column (Raschig rings, full height 10 cm) and a distillation bridge. The reaction mixture was freed from excess phosgene by distillation - Mix the solvent fractionally evaporated at 18 mbar. 2

Fractions obtained, which were weighed and analyzed by gas chromatography

1 fraction (maximum head temperature 65 ° C) 838 g

Chlorobenzene / 23.5% = 196.9 g benzonitrile 2 fraction (maximum bottom temperature 150 ° C, maximum head temperature 123 ° C) 841 g

2.4% = 20.2 g chlorobenzene / 97.6% = 820.8 g benzonitrile

226.3 g of dark product remained as the crude isocyanate. NCO content above 27.1%, found 25.4%.

Hydrolyzable chlorine content 0.15%

Example 6

Production of Tπs- (ιsocvanatophenyl-methane

145 g of technical Tπs- (amιnophenyl) methane (analytically determined purity 93.4%, content of 4,4 ', 4 "-Trιamιno-tπphenylmethane 81%) were at 95 ° C in a mixture of 400 g of 4-methyl and 660 g of 5-methyl-2, l, 3-benzothιadιazol (solvent B) dissolved

In a 4 1-phosgene apparatus, 600 g of phosgene were dissolved at 0 to 5 ° C. in 1300 ml of anhydrous chlorobenzene (solvent A). With external cooling and vigorous stirring, the approximately 90 ° C. warm amine solution was introduced into the phosgene within 10 minutes Solution metered in. A readily stirrable suspension of 38 ° C. was then formed. The reaction mixture was then warmed to a high temperature, the temperature increase being controlled in such a way that the amounts of gas released were dangerous. After 1.2 hours of heating, a practically clear solution was obtained at 73 ° C. After a total of 2 hours of heating, reflux was achieved at 136 ° C. The reaction flask was then removed using a full-body column (Raschig rings, full height 10 cm). and a distillation bridge. The reaction mixture was freed from excess phosgene by distillation. Finally, the solvents were fractionally distilled off from the reaction mixture at 20 mbar. 2 fractions were obtained, which were weighed and analyzed by gas chromatography

1 fraction (maximum head temperature 80 ° C) 905 g

Chlorobenzene with 2.4% = 21.7 g methyl-2, l, 3-benzothiadiazole 2 fraction (maximum bottom temperature 140 ° C, maximum head temperature 114 ° C) 1042 g 1.8% = 18.4 g chlorobenzene / 98, 2% = 1023 g methyl-2,1,3-benzothiazole

The crude isocyanate left 183.6 g of dark product which was viscous in the cold

NCO content 32.7%

Hydrolyzable chlorine content 0.15%

Example 7

Production of tris (isocvanatophenvD-methane

The reaction described in Example 6 was repeated, using only 300 g of phosgene instead of 600 g. By adding the amine solution within 10 minutes, a readily stirrable suspension of 45 ° C. was formed. When heated, a practically clear solution was obtained after 1.3 hours at 80 ° C. The heating up to reflux (136 ° C.) was a total 1.8 hours Then 70 g of phosgene were refluxed into the reaction solution for a further 1 hour. The reaction mixture was then worked up as described in Example 6 1st fraction (maximum head temperature 70 ° C) 816 g:

Chlorobenzene with 0.84% = 6.9 g methyl-2, l, 3-benzothiadiazole

2nd fraction (maximum bottom temperature 130 ° C; maximum head temperature

113 ° C) 1 126 g:

7.8% = 87.8 g chlorobenzene / 92.2% = 1038 g methyl-2, 1,3-benzothiadiazot

The crude isocyanate left 184.1 g of dark, viscous product in the cold: NCO content: 32.8% content of hydrolyzable chlorine 0.39%.

Example 8

The reaction described in Example 7 was repeated, with 145 g of amine at room temperature in 1,266 g of benzonitrile (solvent B) instead of at 95 ° C. in 1,060 g

Methylbenzothiadiazole were solved. By adding the 20 ° C cold amine solution within 10 minutes, a readily stirrable suspension of 25 ° C was formed. When heated, a practically clear solution was formed after 45 minutes at 65 ° C. The total heating time to reflux (136 ° C) was 1.8 hours. Then 70 g were refluxed in the reaction solution for 1 hour

Phosgene introduced. The reaction mixture was then worked up as described in Example 6:

1st fraction (maximum head temperature 70 ° C) 1,161 g:

Chlorobenzene / 27, 1% = 315 g benzonitrile

2nd fraction (maximum bottom temperature 130 ° C; maximum head temperature

108 ° C) 961g:

Chlorobenzene / 97.1% = 933 g benzonitrile

184.3 g of dark, viscous product in the cold remained as crude isocyanate;

NCO content: 33.1% content of hydrolyzable chlorine 0.17%.

Claims

claims

Process for the preparation of isocyanates by "cold-hot phosgenation" of primary amines which are sparingly soluble in chlorobenzene and / or o-dichlorobenzene, characterized in that phosgene is dissolved in a solvent A consisting of chlorobenzene and / or o-dichlorobenzene, the amine to be reacted in a second inert aprotic solvent B suitable for the amine solution, if appropriate also at elevated temperature, whereby the solvent B is miscible with the solvent A and has a boiling point at least 30 ° C higher than the solvent A and a boiling point at least 30 ° C lower than has the isocyanate to be prepared, the amine solution thus prepared is mixed with the phosgene solution at temperatures of 10 to 60 ° C. and the mixture is reacted in a known manner by increasing the temperature at 130 to 200 ° C.

A method according to claim 1, characterized in that the solvent B 2, 1,3-benzothiadiazoles of the general formula

in which

the radicals R ¹ , R ² , R ³ , R ^{4 can be the} same or different and have the meaning of a hydrogen atom or a hydrocarbon radical having 1 to 4 carbon atoms,

used. 3 Process according to claim 2, characterized in that the solvent B used is 4-methyl-2, l, 3-benzothiadiazole or 5-methyl-2, l, 3-benzothiadiazole or mixtures of these two isomers

4 The method according to claim 1, characterized in that tetramethylene sulfone is used as solvent B.

5 The method according to claim 1, characterized in that nitrobenzene is used as solvent B.

6 The method according to claim 1, characterized in that benzonitrile is used as solvent B.

7 Process according to claims 1 to 6, characterized in that chlorobenzene is used as solvent A.

8 Process according to claims 1 to 7, characterized in that 1,5-diaminonaphthalene is used as the amine

9 Process according to claims 1 to 7, characterized in that tris (4-aminophenyl) methane is used as the amine

10 Process according to claims 1 to 7, characterized in that tπs- (4-aminophenyl) ester is used as the amine thiophosphoric acid