KR20010013096A - Method for the Preparation of Organic Isocyanates - Google Patents

Abstract

Method for the preparation of aromatic monomeric or polymeric isocyanates by decomposing aromatic monomeric or polymeric carbamates of the formula R1(NHCOOR2)x wherein x is at least 1, R1is an aromatic radical of valency x and R2is a monovalent organic radical, into aromatic monomeric or polymeric isocyanates of the formula R1(NCO)xand alcohols of the formula R2OH, characterised in that the radical R2is substituted by a group containing at least one halogen group.

Description

Method for the Preparation of Organic Isocyanates

EP-A 611.243 discloses a process for preparing organic isocyanates by pyrolysing carbamate dissolved in a solvent in several separate steps with the corresponding isocyanate and alcohol. In the intermediate stage, the solvent is treated with an inert stripping agent to remove the alcohol produced during the heat treatment and finally recover the isocyanate rich solution.

US-A 5.453.536 discloses pyrolysing polycarbamate in the substantial absence of solvent at temperatures of about 150 to about 270 ° C. under reduced pressure to form the corresponding polyisocyanates and secondary alcohols. Alcohols containing halogen atoms are not mentioned.

In US-A 4.547.322, dinuclear diphenylmethane dicarbamate is prepared by methyleneizing N-phenylcarbamate, which dissolves binuclear diphenylmethane dicarbamate in a solvent having a boiling point of 120 to 350 ° C. Organic hydroxyl compound is prepared by introducing into a pyrolysis process comprising the step of bringing the solution down into the reactor and bringing it back into contact with a carrier introduced upstream into the reactor, recovering the hydroxyl compound as a vapor and the carrier being the upper end of the reactor. It describes a process for preparing MDI from N-phenylcarbamate, which is recovered at and the isocyanate solution is recovered at the lower end.

The method specifically mentions that 2,2,2-trichloroethyl and 2,2,2-trifluoroethyl substituted N-phenylcarbamate can be used, but no such examples are given.

US-A 3.746.689 discloses the use of halogenated alcohols having 1 to 6 carbon atoms as blockers of polyisocyanates.

The present invention relates to a process for the preparation of monomeric or polymeric aromatic isocyanates by thermal decomposition of monomeric or polymeric aromatic carbamate.

An improved process for preparing monomeric or polymeric aromatic isocyanates by thermal decomposition of monomeric or polymeric aromatic carbamates is provided by the present invention.

The present invention relates to an aromatic monomeric or polymeric carbamate of the formula R ¹ (NHCOOR ² ) _x where x is at least ¹ , R ¹ is an aromatic radical having valence x, and R ² is a monovalent organic radical. A process for preparing an aromatic monomeric or polymeric isocyanate by decomposition with an aromatic monomeric or polymeric isocyanate of formula R ¹ (NCO) _x and an alcohol of formula R ² OH, wherein the radical R ² comprises at least one halogen group. It is related with what is substituted by group.

Organic isocyanates can be obtained in high yield in the absence of solvents or from concentrated solutions at low temperatures

R ¹ is an aromatic hydrocarbon radical, optionally substituted, optionally containing a saturated or unsaturated hetero-atom.

R ² is preferably substituted with one or more chlorine or fluorine atoms.

The carbamate composition to be degraded may be a mixture of polymer carbamate compounds of different functionalities, obtaining polymer isocyanates during degradation. In such cases the value of x is the average of the functional groups of all species present in the carbamate mixture. The term "functional group" as used herein is defined as the number of averaged functional groups.

The average value of x is generally 1 to 15, preferably 2 to 10, more preferably 2 to 3.

The term "polymer," as used herein, refers to any functional group greater than one.

Preferred R ¹ is tolylene, methylene diphenylene or polymethylene polyphenylene radicals or mixtures thereof.

Alcohols that may be formed include, for example, 2,2,2-trifluoroethanol, 2,2,2-trichloroethanol, trichloromethanol, 1,1,1,3,3-hexafluoroisopropanol , Monofluoro tert-butanol, fluorophenol, chlorophenol and phenol polysubstituted with halogen.

Representative monomer isocyanates that may be formed include phenyl isocyanate, 4-chlorophenyl isocyanate, 2-fluorophenyl isocyanate, 3,4-dichlorophenyl isocyanate, tolyl isocyanate and diisopropylphenyl isocyanate.

Examples of difunctional isocyanates which may be formed according to the process include 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane isocyanate, 2,2'-diphenylmethane diisocyanate, diphenylmethane Diisocyanate and mixtures thereof, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, toluene diisocyanate and mixtures thereof, m-phenylene diisocyanate and 1,5-naphthylene diisocyanate.

The process of the present invention can be advantageously used for the preparation of diphenylmethane diisocyanate, toluene diisocyanate, polymethylene polyphenylene polyisocyanate or any mixture thereof.

Tri- and higher functional isocyanates that may be formed include 2,4,6-toluene triisocyanate and polymethylene polyphenylene polyisocyanates.

As mentioned above, any mixture of mono-, di- and polyfunctional isocyanates can be obtained depending on the composition of the starting carbamate mixture.

The reaction can be carried out in an inert solvent, ie any solvent that does not interact with the isocyanate or alcohol under the given reaction conditions. However, the isocyanates formed in the decomposition reaction can also serve as a solvent for the reaction.

Suitable inert solvents that can be used include, for example, aromatic hydrocarbons such as benzene, halogenated aromatic hydrocarbons such as monochlorobenzene, ortho-dichlorobenzene, trichlorobenzene or 1-chloronaphthalene, toluene, xylene, ethylbenzene, Alkylated aromatic hydrocarbons such as cumin or tetrahydronaphthalene, such as anisole, diphenylether, ethoxybenzene, benzonitrile, 2-fluoroanisole, 2,3-dimethylanisole or trifluorotoluene or mixtures thereof Other functionalized aromatic hydrocarbons are included.

Preferred solvents include monochlorobenzene or ortho-dichlorobenzene.

Any of the abovementioned solvents may also be used to produce the carrier gas.

The carrier gas can physically remove any alcohol without forming chemical bonds.

In addition, a mixture of at least one of the above-mentioned solvents and an inert solvent having a lower boiling point used as a carrier gas can be used together.

Examples of such inert solvents having lower boiling points are n-pentane, n-hexane, n-heptane, alkanes such as higher or branched alkanes, cyclic alkanes such as cyclopentane, cyclohexane or derivatives thereof, chloroform, dichloro Halogenated alkanes such as methane, carbotetrachloride, and alkanes having other functional groups such as diethyl ether, acetonitrile, dioxane and the like.

The process can be carried out at atmospheric pressure, preferably under nitrogen.

However, in the absence of solvent, the reaction is preferably carried out under reduced pressure. In such a case, the pressure is preferably reduced to 10 ⁻⁴ to 50 mbar, more preferably 0.1 to 10 mbar.

Depending on the type of solvent used, pressure above atmospheric pressure may sometimes be required.

The reaction time depends on the temperature and the form and quality of the carbamate compound, but generally does not exceed 5 hours. Reaction times of less than 3 hours are common and reaction times of less than 1 hour are used without problems.

The reaction temperature is highly dependent on the presence of the solvent. Generally, it is 50 to 350 ° C. In a solvent free process, the temperature is generally between 350 ° C. at the melting point of the carbamate, while in the presence of solvent it is preferably 100 to 200 ° C., more preferably 120 to 190 ° C. to be.

When using the process of the present invention, yields of more than 90% isocyanate can be readily obtained. At least 95% yield is possible.

The method may be carried out in any suitable apparatus capable of mounting a stirrer and heating and / or cooler, if necessary, to keep the temperature within the desired range. In general, a distillation column is attached to the apparatus.

The process of the invention can be carried out in batch mode or as a semi-continuous or continuous process.

The order of addition of the reactants can be varied to suit the particular apparatus and / or reactants used.

Carbamate compounds and optionally furnaces, in addition to the solvent, generally do not require the presence of any other compounds, such as catalysts or co-reactants.

The isocyanates and alcohols obtained by the process are generally of high purity and do not require any further treatment to further purify the product. If present, only solvent needs to be removed.

If particularly high grades of purity are required, the reaction product formed may use known purification methods such as filtration, extraction, recrystallization or distillation.

The invention is illustrated by, but not limited to, the following examples.

<Example 1>

3 g of diphenylmethane bis (1,1,1,3,3-hexafluoroisopropylcarbamate) were placed in a suitable flask equipped with a condenser. Carbamate was heated to 240 ° C. After the carbamate melted, the pressure was reduced to 0.1 mbar. 1,1,1,3,3-hexafluoroisopropanol was removed from the system as the reaction proceeded. After 25 minutes at 240 ° C., diphenylmethane diisocyanate containing 33.6% by weight of NCO groups remained in the pyrolysis flask.

<Example 2>

Example 1 is repeated, but 4.2 g of polyphenylene polymethylene poly (1,1,1,3,3-hexafluoroisopropylcarbamate) is added to diphenylmethane bis (1,1,1,3, 3-hexafluoroisopropylcarbamate) instead. Carbamate was heated to 220 ° C. After the carbamate melted, the pressure was reduced to 2 mbar. 1,1,1,3,3-hexafluoroisopropanol was removed from the system as the reaction proceeded. After 20 minutes at 220 ° C., diphenylmethane diisocyanate containing 30% by weight of NCO groups remained in the pyrolysis flask.

<Example 3> (Comparative Example)

Example 1 is repeated, but 2 g of diphenylmethane bis (isopropylcarbamate) was used in place of diphenylmethane bis (1,1,1,3,3-hexafluoroisopropylcarbamate). Carbamate was heated to 220 ° C. After the carbamate melted, the pressure was reduced to 1-3 mbar. Isopropanol was removed from the system as the reaction proceeded. After 20 minutes at 220 ° C., diphenylmethane diisocyanate containing 5.7% by weight of NCO groups remained in the pyrolysis flask.

<Example 4> (comparative example)

Example 1 is repeated, but 2.1 g of diphenylmethane bis (1-methoxy-2-propyl carbamate) is added to diphenylmethane bis (1,1,1,3,3-hexafluoroisopropylcarba. Mate). Carbamate was heated to 220 ° C. After the carbamate melted, the pressure was reduced to 1-5 mbar. 1-methoxy-2-propanol was removed from the system as the reaction proceeded. After 25 minutes at 220 ° C., diphenylmethane diisocyanate containing 23.5% by weight of NCO groups remained in the pyrolysis flask.

Comparative Examples 3 and 4 showed that a significantly lower yield was obtained compared to Example 1 when the alcohol formed did not contain a halogen atom.

<Example 5>

In a suitable flask equipped with a condenser and an addition funnel, a dispersion of 5% diphenylmethane bis (1,1,1,3,3-hexafluoroisopropylcarbamate) in chlorobenzene (MCB) was added. The dispersion was heated to about 134 ° C. and the solvent / alcohol mixture distilled off. MCB was added to keep the volume in the pyrolysis flask constant. After 1 hour at 134 ° C., diphenylmethane diisocyanate containing 30.5% by weight of NCO groups was obtained.

<Example 6>

Example 5 was repeated, but a dispersion of 10% polyphenylene polymethylene poly (1,1,1,3,3-hexafluoroisopropylcarbamate) in MCB was used. The dispersion was heated to about 134 ° C. and the solvent / alcohol mixture distilled off. MCB was added to keep the volume in the pyrolysis flask constant. After 1 hour at 134 ° C., polyphenylene polyisocyanate containing 31.2% by weight of NCO groups was obtained.

<Example 7>

Example 5 was repeated, but a dispersion of 5% diphenylmethane bis (2,2,2-trifluoroethylcarbamate) in ortho-dichlorobenzene (ODCE) was used. The dispersion was heated to about 180 ° C and the solvent / alcohol mixture was distilled off. ODCB was added to keep the volume in the pyrolysis flask constant. After 1 hour at 180 ° C., diphenylmethane diisocyanate containing 27.4% by weight of NCO groups was obtained.

<Example 8>

Example 5 was repeated, but a dispersion of 5% polyphenylene polymethylene poly (2,2,2-trifluoroethylcarbamate) in the MCB / ODCE mixture was used. The dispersion was heated to about 180 ° C. ODCB was added to keep the volume in the pyrolysis flask constant. After 1 hour at 180 ° C., polyphenylene polyisocyanate containing 27.4% by weight of NCO groups was obtained.

<Example 9> (Comparative Example)

Example 5 was repeated, but a dispersion of 5% diphenylmethane bis (isopropylcarbamate) in the MCB / ODCE mixture was used. The dispersion was heated to about 180 ° C. ODCB was added to keep the volume in the pyrolysis flask constant. After 2 hours at 180 ° C., diphenylmethane diisocyanate containing 8.6% by weight of NCO groups was obtained.

Compared with Example 5, this comparative example showed that a lower yield was obtained than when an alcohol containing no halogen atom was separated.

<Example 10> (Comparative Example)

Example 5 was repeated, but a dispersion of 10% polyphenylene polymethylene poly (1-methoxy-2-propylcarbamate) in ODCE was used. The dispersion was heated to about 180 ° C. ODCB was added to keep the volume in the pyrolysis flask constant. After 2½ hours at 180 ° C., polyphenylene polymethylene polyisocyanate containing 9% by weight of NCO groups was obtained.

Compared to Example 6, Comparative Example 10 showed that the yield was significantly lower when alcohols not according to the invention were formed during decomposition.

<Example 11>

In a suitable flask equipped with a condenser and an addition funnel, a dispersion of 10% toluene 2,4 bis (2,2,2-trifluoroethylcarbamate) in ortho-dichlorobenzene (ODCB) was added. The dispersion was heated to about 180 ° C and the solvent / alcohol mixture was distilled off. ODCB was added to keep the volume in the pyrolysis flask constant. Toluene diisocyanate was obtained after 90 minutes at about 180 ° C. containing more than 43% by weight of NCO groups (corresponding to 89% yield).

<Example 12>

In a suitable flask equipped with a condenser and an addition funnel, a dispersion of 10% toluene 2,4 bis (1,1,1,3,3-hexafluoroisopropylcarbamate) in ortho-dichlorobenzene (ODCB) Put in. The dispersion was heated to about 180 ° C and the solvent / alcohol mixture was distilled off. ODCB was added to keep the volume in the pyrolysis flask constant. Toluene diisocyanate was obtained after 90 minutes at about 180 ° C. containing more than 47% by weight of NCO groups (corresponding to 99% yield).

Claims (12)

The general formula R ¹ (NHCOOR ²⁾ _x formula an aromatic monomeric or polymeric carbamates (where, x is 1 or more and, R ¹ is the valence x of the aromatic radical, R ² is a monovalent organic radical Im) R ¹ A process for producing aromatic monomeric or polymeric isocyanates by decomposition with an aromatic monomeric or polymeric isocyanate of (NCO) _x and an alcohol of formula R ² OH, wherein the radical R ² is substituted by a group comprising at least one halogen group Characterized in that the method. The method of claim 1, wherein R ² is substituted with one or more chlorine or fluorine atoms. The process according to claim 1 or 2, wherein R ¹ comprises methylene diphenylene or polymethylene polyphenylene radicals or mixtures thereof. The method of claim 1, wherein R ¹ comprises a tolylene radical. The process of claim 1, wherein the decomposition is carried out in the presence of a solvent. The method of claim 5 wherein the solvent comprises monochlorobenzene or ortho-dichlorobenzene. The process according to claim 5 or 6, wherein the decomposition temperature is 100 to 200 ° C. 8. The method of claim 7, wherein the decomposition temperature is from 120 to 190 ° C. The process according to claim 1, wherein the solvent is mixed with a solvent having a lower boiling point used to produce the carrier gas. The process according to any of claims 1 to 4, wherein the decomposition is carried out in the absence of a solvent. The process of claim 10 wherein the decomposition is carried out at a temperature between 350 ° C. and the melting point of the monomeric or polymeric carbamate. The process according to claim 10 or 11, wherein the decomposition is carried out under reduced pressure.