DE1768809C3 - Process for the production of aromatic isocyanates - Google Patents

Description

N =

= C-R

il c

15th

ii which R is an aromatic hydrocarbon radical having 1 to 3 aromatic rings, which can be unsubstituted or substituted by non-interfering groups, and m is 0, 1, 2 or 3, is subjected to thermal decomposition.

2. The method according to claim 1, characterized in that that R has 6 to 20 carbon atoms.

3. The method according to claim 1, characterized in that m is 1, 2 or 3 and R is phenyl.

4. The method according to claim 1 to 3, characterized in that the decomposition in the presence an inert solvent is carried out.

30th

The present invention relates to a process for the preparation of aromatic isocyanates, 4as is characterized in that a compound 4 of the general formula

N =

= C-R

C =

= N

(D

45

in which R stands for an aromatic hydrocarbon radical with 1 to 3 aromatic rings, which can be unsubstituted or substituted by non-interfering groups, and m is 0, 1, 2 or 3, is subjected to thermal decomposition. The radical R preferably contains 6 to 20, in particular 6 to 12 carbon atoms. The present invention thus relates, inter alia, to the production of mono-, di-, tri- or tetraisocyanates by decomposition of the corresponding mono-, di-, tri- or tetranitrile carbonates of, for example, toluene, naphthalene, anthracene, phenylbenzene, phenylnaphthalene, diphenylalkylenes such as diphenylmethylene and diphenylethylene (stilbene) and dinaphthylalkylenes.

The monoisocyanates formed can be used to produce urethanes, ureide compounds or other derivatives of compounds containing active hydrogen can be used. Polyisocyanates, such as Diisocyanates are particularly often used in the manufacture of plastics, e.g. B. by Reaction with compounds with terminal active hydroxyl or amine groups.

The decomposition of the nitrile carbonates into the corresponding aromatic mono- or polyisocyanates takes place, for. B. by simply heating the aromatic nitrile carbonates below the decomposition point of the desired aromatic isocyanate. Since the decomposition is exothermic, there is a risk that the reaction temperature will run away. Means should therefore be used to dissipate the heat in order to keep the temperature below the decomposition point of the desired isocyanate. The reaction temperature varies depending on the decomposition temperature of the feed and the decomposition temperature of the isocyanate to be produced. In most cases, it is between about 50 and 200 ⁰ C, preferably between about 75 and 150 ⁰ C. The decomposition is suitably in the presence of an inert solvent such as benzene, xylene, toluene, chlorobenzene etc., or phosgene performed.

The ability of the aromatic nitrile carbonates to form isocyanates on heating is advantageous because the aromatic Nitrilcarbonaie in contrast ζ · ι Isocyanates are stable in the absence of water and are therefore easy to handle and store be able. Since furthermore in the aromatic nitrile carbonates ode · - the decomposition products formed no active hydrogen (e.g. in the form of hydrogen chloride) contributes to the reaction with the isocyanate whose production is available, the new process does not suffer from reduced yields and through Separation and purification problems caused by by-products like the known processes with starting materials that contain active hydrogen. Compared to the known method under The use of azides has the advantage that no explosive substances have to be used and the process is more economical.

The aromatic mono- and polynitrile carbonaie can by reacting an aromatic mono- or polyhydroxamic acid and phosgene can be produced. Aromatic mono- and polyhydroxamic acids, which react with phosgene to form the nitrile carbonates can be obtained by the following Formula can be represented:

HONC —R

CNOH

(ID

in which R and m have the meaning given for formula I. The aromatic hydrocarbon residue R of the hydroxamic acid structure may optionally be substituted as long as the substituents do not interfere with the formation of nitrile carbonate. When using polyhydroxamic acids, it is advisable to that the hydroxamic acid groups are not in o-Siellung stand in the aromatic ring.

According to the invention, for. B. the following mono- or polynitrile carbonates are used:

Tolyl nitrile carbonate,

Xylyl nitrile carbonate.

Trimethylbenzene carbonate,

Ethyl benzene nitrile carbonate,

Hexyl benzene nitrile carbonate.

Nonyl benzene nitrile carbonate,

Dodecylbenzene carbonate,

Pentadecyl benzene nitrile carbonate, tricosyl benzene nitrile carbonate;
Naphthalene mononitrile carbonates such as 8-naphthalene nitrile carbonate (ie

M-naphthalene nitrile carbonate),

Tetrahydronaphthalenitrile carbonate, 1 -Chlor- ^ benzene nitrile carbonate, 4- bromo-1 -benzenonitrile carbonate, 3-nitrobenzenonitrile carbonate,

Anthracene mononitrile carbonate; Biphenylmononitrile carbonates, such as I - phenyl 4-benzene nitrile carbonate, 1 -BenzyM-benzene nitrile carbonate and! - Phenylethyl 4-benzenonitrile carbonate or m-phenylenedinuril carbonate; Benzotriiiitrilcarbonate, such as
1,3,5-benzene nitrile carbonate;
Benzene tetranitrile carbonates such as pyromellite tetranitrile carbonate and prehneite tetranitrile carbonate; 2,4-dinitrile carbonate-m-xylene,
2,5-dinitrile carbonate-p-xylene,
1 ^ -Dinitrilcarbonat-o-xylene,
2,4-dinitrile carbonate-1-methylbenzene, 2,4-dinitrile carbonate-1-ethylbenzene, 1 ^ S-trinitrile carbonate ^ -ethylbenzene, M-dinitrile carbonate ^ -nonylbenzene, 2,4-dinitrile carbonate-6-tricosylbenzene, 2,4 -Dinitrile carbonate-3-hexylbenzene, 1, SS-trinitrile carbonate-o-hexacosylbenzene, 1,3-dinitrile carbonate-5-benzylben2: ol, 1- [2,4-dinitrile carbonate] -2-phenylpropane, 2,8-dinitrile carbonate naphthalene, 1.3 , 5-trinitrile carbonate naphthalene, 1,3-dinitrile carbonate tetrahydronapluhaline, 2,2-bis [p-dinitrile carbonate phenyl] propane.

Bis- [p-dinitrile carbonate phenyl] methane, l-chloro-3,5-dinitrile carbonate benzene, 4-bromo-1,3,5-trinitrile carbonate benzene, S-nitrile-M-dinitrile carbonate benzene, 2,8-dinitrile carbonate anthracene, 2,5,8-trinitrile carbonate anthracene, 4,4'-biphenyl dinitrile carbonate,

2,2'-biphenyl dinitrile carbonate,

4,4'-Diphenyläthandinitrilcarbonat, 2,2'-Diphenyläthandinitrilcarbonat, 4,4'-stilbenedinitrile carbonate,

2,2'-stilbene dinitrile carbonate.

The temperature for carrying out the reaction of the aromatic mono- or polyhydroxamic acid with the phosgene can vary depending on the particular aromatic hydroxamic acid selected, but it should always be below the decomposition temperature of the desired aromatic nitrile carbonate. It is also possible to use reflux temperatures as long as the reflux temperature of the particular mixture is below the decomposition temperature of the corresponding aromatic nitrile carbonate produced. The reaction temperature is often between a range up to about 90 'C, preferably up to about 50 ⁰ C. The reaction may be up to -30 ° C successfully carried out at temperatures. Usually, the reaction takes place easily at atmospheric pressure, but above or below atmospheric pressures can also be used if necessary Moles of phosgene per hydroxamic acid substituent. A large excess of phosgene is particularly preferred.

The reaction takes place in the liquid phase and in many cases the aromatic hydroxamic acids react in solid form. The aromatic hydroxamic acid is expediently first in an oxygen-containing organic solvents dissolved or slurried. Suitable oxygenated solvents are the phosgene reaction participant itself and usually liquid organic ethers, esters, furans, Dioxanes, etc. The preferred solvent is phosgene and in most cases an excess will dissolve same the aromatic mono- or polyhydroxamic acid easily.

The reaction is often in less than about half an hour, e.g., in 15 minutes, or in about Finished 5 to 20 hours depending on the reaction temperature used and by stopping the evolution of hydrogen chloride is displayed. Usually at least about half an hour required for the completion of a reaction at temperatures which reduce side reactions. the The reaction is usually quite rapid once the aromatic mono- or polyhydroxamic acid is resolved. The aromatic hydroxamic acid usually dissolves at the lower reaction temperatures slowly and may even fall out of solution and redissolve during the reaction.

The aromatic nitrile carbonate can be obtained from the resulting solution by suitable means be done by z. B. the solution obtained first to remove unreacted starting materials filtered and the filtrate to remove unreacted phosgene and any phosgene used inert solvent subjected to reduced pressure to produce the aromatic nitrile carbonate ali> get raw product. Before filtering the solution can also be cooled to crystallize out the product, which is then as described is won. The crude product can be either crystalline or liquid, depending on the particular, produced aromatic nitrile carbonate depends. A purer product can e.g. B. by recrystallization, z. B. from a suitable solvent such as dichloromethane, carbon disulfide, ethyl acetate, Thionyl chloride, etc., or mixtures thereof.

Another suitable method for obtaining a practically chlorine-free, aromatic nitrile carbonate is done by extraction or washing with a hydrocarbon solvent. For extraction any normally liquid hydrocarbon solvent can be used, e.g. B. Alkanes with 5 to 15 or more carbon atoms, aromatic solvents such as benzene, xylenes, toluene, Chlorobenzene etc. The minimum amount of solvent used in extraction is the actual amount Amount depends on the particular aromatic nitrile carbonate. If necessary, a Combination of recrystallization and extraction processes to achieve a practically chlorine-free one aromatic nitrile carbonates are used. The thermal decomposition of the practically chlorine

free product provides improved yields of a purer isocyanate product that is also practical is chlorine free.

Example!

A sample of phenyl nitrile carbonate was dissolved in o-dichlorobenzene dissolved and the solution heated to reflux for 5 minutes. The infrared spectrum of the solution. showed the appearance of a strong isocyanate absorption band at 4.47 microns and the disappearance of the peaks attributed to the carbonate structure (Peaks).

Yield of phenyl isocyanate about 85%.
Kp. = 158 to 162 ⁰ C.

Example 2

350 g of chlorobenzene and 59 g of chlorine-free phenyl nitrile carbonate were placed in a 1 l flask equipped with a stirrer and Künler at room temperature. The heterogeneous mixture was slowly warmed to dissolve the carbonate, then was further heated to about 135 to 140 ⁰ C. After the reaction had ended, carbon dioxide was removed under reduced pressure and a chlorobenzene / benzoisocyanate fraction was collected. Distillation of the fraction gave chlorine-free phenyl isocyanate.

Bp approx. 158 to 162 ° C.

The yield was of the same order of magnitude as in Example 1.

Example 3

p-Methoxyphenyl nitrile carbonate was made by heating decomposed in chlorobenzene according to Example 2 to give chlorine-free p-methoxyphenyl isocyanate.

Yield about 89%.

F. = about -6 to -10 ⁰ C.

40

45

Example 4

p-Nitrophenyl nitrile carbonate was prepared according to Example 2 decomposed to chlorine-free p-nitrophenyl isocyanate.

Example 5

m-nitrophenyl nitrile carbonate was according to example 2 decomposed to chlorine-free m-nitrophenyl isocyanate.

For example, 6

50

A sample of m-phenylenedinitrile carbonate was in Dissolved o-dichlorobenzene and heated the solution to reflux for 5 minutes. The infrared spectrum of this Solution showed a strong isocyanate peak at 4.47 microns and the absence of that for the carbonate structure characteristic tips.

M-phenylene diisocyanate was obtained in a yield of about 85%.

F. = about 135 ° C.

Example 7

A 1-liter flask equipped with a stirrer and condenser was charged at room temperature with 350 g of chlorobenzene and 59 g of chlorine-free mixed m- and p-phenylenedinitrile carbonate obtained by recrystallization of crude mixed m- and p-phenylenedinitrile carbonates. The heterogeneous mixture was slowly warmed. At about 55 ° C, the entire solid dissolved, and it was further heated at about 95 ^C C began a rapid evolution of gas, and the heat would be removed. The exothermic reaction mixture reached a maximum temperature of 125 ° C. Carbon dioxide was removed under reduced pressure and a chlorobenzene phenylene diisocyanate fraction was collected which, after distillation, gave a mixture of chlorine-free m- and p-phenylene diisocyanate.

Yield about 85%.

Example 8

According to Example 7, a sample was made from a mixture of m- and p-phenylenedinitrile carbonate (made by recrystallizing a crude sample in ethyl acetate) to a mixture of chlorine-free Decomposes m- and p-phenylene diisocyanate.

The yield was about as in Example 7.

Example 9

250 ecm of chlorobenzene were placed in a 500 cc round bottom flask equipped with a glass bead column and heated to reflux. A sample of 50 g (0.17 mol) of chlorine-free m-phenylenedinitrile carbonate obtained by pentane washing of crude m-phenylenedinitrile carbonate was introduced into an extraction chamber connected to the reaction device. The chlorobenzene vapors obtained overhead were condensed on a cold finger and the condensate passed through the extraction chamber and further into the heated glass bead column. At this point decomposition occurred and the higher boiling diisocyanate was concentrated in the vessel while gaseous CO _{2 was} removed overhead. This extraction was allowed to continue for about 3 hours. The tank mixture was transferred to a still and the chlorobenzene removed under reduced pressure. After further distillation, chlorine-free m-phenylene diisocyanate was obtained.

The results were as in Example 6.

Example 10

In a similar manner, 12.2 g (0.049 mol) of chlorine-free p-phenylenedinitrile carbonate, obtained c ^! '^"R ch Penta decomposed washing of crude p- Phenylendinilrilcarbonat, in 250 cc of chlorobenzene. The chlorobenzene was removed under reduced pressure, and after further distillation was chlorine-free p-phenylene diisocyanate obtained.

Claims (1)

Patent claims: 1. Process for the production of aromatic isocyanates, characterized in that a compound of the general formula I! c