KR101318828B1 - Process of preparing xylylene diisocyanates, their reaction intermediates and process of preparing them - Google Patents

Abstract

The present invention provides a method for preparing xylylene diisocyanate, the method comprising: reacting a diamine compound with alkyl chloroformate or dialkyl carbonate to prepare biscarbamate; And it relates to a method for producing xylylene diisocyanate (m-XDI) comprising the step of pyrolyzing the biscarbamate prepared above to decompose the alcohol having a relatively low boiling point. The present invention also relates to certain biscarbamates produced as reaction intermediates in the preparation of such m-XDI and to methods of making such intermediates. By the method of the present invention, m-XDI produced by toxic and highly corrosive phosgene will be able to produce m-XDI of the yellowing type without using phosgene.

Description

Process for preparing xylylene diisocyanate, reaction intermediate thereof and method for producing the reaction intermediate {Process of preparing xylylene diisocyanates, their reaction intermediates and process of preparing them}

The present invention relates to a process for preparing xylylene diisocyanate, and in particular, to react with xylylene diamine with alkyl chloroformate or dialkyl carbonate to produce biscarbamate, and to prepare the biscarbamate by thermal decomposition of alcohol. After decomposing | disassembling and removing m-xylylene diisocyanate (m-XDI), it is related with the manufacturing method which can be used industrially. It also relates to certain biscarbamates produced as intermediates in such a process and to methods of making the intermediates.

Xylylene diisocyanate is a very useful compound as a raw material of polyurethane-based materials, polyurea-based materials and polyisocyanate-based materials in the chemical industry, the resin industry and the paint industry. Among them, meta-xylylene diisocyanate (hereinafter abbreviated as 'm-XDI'; or '1,3-bis (isocinatomethyl) benzene') is added to the benzene core as shown in the following figure. As a specific diisocyanate with methylene group, it has the property of preventing yellowing, which is a disadvantage of aromatic diisocyanates, and is used as a urethane raw material for non-yellowing paints, coatings, leathers and adhesives.

In particular, such meta-xylylene diisocyanate is used as a plastic lens, polyurethane, polyurea, poly-isocyanureate-based raw materials, sulfur-containing compounds and It is a product that is very particularly used for plastic eyeglass lenses that react and exhibit a high refractive index of a polythiourethane system. However, m-XDI has no domestic producers and is supplied by a specific company in Japan (Mitsuke Takeda), and its high refractive index lenses such as MR-6, MR-7 and MR-9 are available. It is a situation that monopolized by manufacturing a urethane spectacle lens.

As a prior art regarding the manufacturing method of such m-XDI, it can be largely divided into (1) phosgene method, (2) non-phosgene method (Metal cyanate method), (3) pyrolysis method (Biscarbamate method).

[Phosgene method]

Such a method is known in various documents, and in particular, Patent Publication No. 1990-0012895 (Korean Application No. 5,196,572, published on Sep. 30, 1990) is present in the presence of an ester as a reaction solvent. A method of preparing xylylene diisocyanate by reacting silylene diamine hydrochloride with phosgene, the first step of reacting xylylene diamine with hydrogen chloride gas at a temperature of 30 ℃ or less, the second step A xylylene diamine hydrochloride produced in step 1 is described with respect to a method characterized by reacting with phosgene at a temperature of 120 to 170 ° C.

This method is the most common method for preparing isocyanates. H-chlorides m-XDA using toxic phosgene gas to protect amine groups and then phosgenation with toxic phosgene to produce m-XDI. After distillation and purification. However, this method has to use the toxic phosgene gas which is toxic and absorbs a large amount of byproduct HCl gas, and the corrosive raw materials and by-products of the device are generated, resulting in a high cost of the device.

Non-phosgene method (Metal cyanate method)

This method is a method of synthesizing xylene dichloride to isocyanate using sodium cyanate in the presence of a catalyst to improve the disadvantage of the phosgene method as shown below. However, this method also requires the use of expensive organic solvents, and the unreacted halogenated raw material remains, which is not easy to separate and purify the product. In addition, the production cost of xylylene dichloride is expensive and not economical.

[Pyrolysis Method (Biscarbamate Method)]

This method produces a carbamate using an alkyl chloroformate (or carbonate) as an amine, and decomposes and removes a relatively low boiling alcohol by pyrolysis using a catalyst and a high temperature solvent. It is a method of manufacturing m-XDI.

In this regard, Japanese Patent Laid-Open No. 2001-0013096 published on Feb. 26, 2001 (a domestic patent publication corresponding to PCT / EP1998 / 02733) includes the formula R1 (NHCOOR2) x where x is 1 or more, and R1. Is an aromatic radical having the valence x, and R2 is a monovalent organic radical, wherein the aromatic monomeric or polymeric carbamate is selected from the aromatic monomeric or polymeric isocyanate of formula R1 (NCO) x and the formula R2OH, wherein A method for producing aromatic monomeric or polymeric isocyanates by decomposing with an alcohol of the above) is described.

However, examples of the difunctional isocyanate which may be formed according to the method described in this prior publication are 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane isocyanate, 2,2'-di Phenylmethane 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 Aromatic diisocyanates, such as diisocyanate, are included only.

In addition, the tri- and higher functional isocyanates that can be formed according to this prior invention only include 2,4,6-toluene triisocyanate, polymethylene polyphenylene polyisocyanate and the like. There is no mention in this prior art of the example of m-XDI which is an aralkyl isocyanate.

The inventors of the present invention preliminary experiments on the prior art phosgene method, biphosgene method (Metal cyanate method), pyrolysis method (Biscarbamate method) of the above-described method for producing m-XDI, the thermal decomposition method is industrially applicable It was judged possible.

However, since this pyrolysis method usually requires a reaction at a high temperature of 250 to 350 ° C. or higher, it has been determined that there are still many fields to be improved, and the present inventors preliminary by changing various alkyl groups and pyrolysis catalysts and various solvents. The experiment was performed. In particular, there is a possibility that the reaction temperature can be lowered to 200 ° C. or lower, and a catalyst having good reaction conversion and selectivity was developed to invent a process having economical efficiency.

The problem to be solved in the present invention is a method for producing xylylene diisocyanate,

Reacting a diamine compound of formula (I) with an alkyl chloroformate or dialkyl carbonate of formula (II) to prepare a biscarbamate of formula (III); And

Pyrolyzing the biscarbamate prepared above to decompose and remove the relatively low boiling alcohol;

It can be achieved by a method for producing xylene diisocyanate (m-XDI) comprising a.

Formula (I) Formula (II) Formula (III)

+

(또는

) →

+

(or

) →

→

(Wherein Rx is a halogenated alkyl group)

As a preferred embodiment of the present invention, the pyrolysis process in the process of the present invention can be decomposed without using a solvent, but is preferably performed in the presence of a solvent. The solvent used herein is preferably at least one solvent selected from the group consisting of 1,2-dichlorobenzene, 1,2,4-trichlorobenzene, chlorobenzene.

In another preferred embodiment of the invention, the pyrolysis temperature in the process of the invention is preferably from 120 to 250 ° C. In addition, the pyrolysis process is preferably performed in the presence of an acid or a base catalyst, but more preferably pyrolysis in an acid or non-catalyst. The type of acid catalyst is preferably carried out in the presence of a catalyst selected from toluenesulfonic acid or naphthalenesulfonic acid. In the case of a base catalyst, the decomposition reaction is good, but the resulting isocyanate is not preferable because it tends to be further reacted to dimerize, trimerize and polymerize. In another preferred embodiment of the invention, in the process of the invention, the pyrolysis process is preferably carried out under reduced pressure.

On the other hand, the present invention as an intermediate produced as a novel compound in the process of preparing the xylylene diisocyanate,

It relates to a biscarbamate intermediate of formula (III) prepared by reacting a diamine of formula (I) with an alkyl chloroformate or dialkyl carbonate of formula (II).

Formula (I) Formula (II) Formula (III)

+

(또는

) →

+

(or

) →

(Wherein Rx is a halogenated alkyl group)

Preferred biscarbamate intermediates of the present invention are bis (2,2,2-trichloroethyl) m-xylylenedicarbamate, bis (2,2,2-trifluoroethyl) m-xylylenedica Barmate, bis (2,2,3,3-tetrafluoropropyl) m-xylylenedicarbamate.

In addition, the present invention provides a biscarbamate intermediate of formula (III) prepared by reacting the diamine of formula (I) with alkyl chloroformate or dialkyl carbonate of formula (II) It is about how to.

Formula (I) Formula (II) Formula (III)

+

(또는

) →

+

(or

) →

(Wherein Rx is a halogenated alkyl group)

The method for producing the biscarbamate intermediate of the present invention can be prepared by conventional methods in the presence of a base such as tertiary amine in an inert organic solvent in the case of using chloroformate, and in aqueous solution when using a base catalyst such as caustic soda. It is preferable to manufacture at room temperature using an organic solvent. In addition, when using dialkyl carbonate, it is preferable to manufacture by organic solvent and a base catalyst.

Since special isocyanates such as m-XDI produced by the method of the present invention are not produced domestically, if these products are economically produced by the present invention, they will greatly contribute to the domestic urethane industry. Currently, only domestic products such as aromatic diisocyanate, TDI (toluene diisocyanate), MDI (methylene diisocyanate), and the like are produced and supplied. Also, the above-mentioned products have a yellowing phenomenon when the polymer resin is exposed to the sun. Accordingly, there will be a need for industrial mass production of products such as HDI (hexamethylene diisocyanate) and IPDI (isophorone diisocyanate) in addition to m-XDI in the form of aliphatic diisocyanate.

In particular, according to the present invention, it will be possible to prepare an isocyanate of the yellowing type without using phosgene, m-XDI produced by toxic and highly corrosive phosgene.

1A is an NMR analysis spectrum of bis (2,2,2-trichloroethyl) m-xylylenedicarbamate obtained in Example 1 of the present invention.
1B is an IR analysis spectrum of bis (2,2,2-trichloroethyl) m-xylylenedicarbamate obtained in Example 1 of the present invention.
2A is an NMR analysis spectrum of bis (2,2,2-trifluoroethyl) m-xylylenedicarbamate obtained in Example 2 of the present invention.
2B is an IR analysis spectrum of bis (2,2,2-trifluoroethyl) m-xylylenedicarbamate obtained in Example 2 of the present invention.
3A is an NMR analysis spectrum of bis (2,2,3,3-tetrafluoropropyl) m-xylylenedicarbamate obtained in Example 3 of the present invention.
3B is an IR analysis spectrum of bis (2,2,3,3-tetrafluoropropyl) m-xylylenedicarbamate obtained in Example 3 of the present invention.
4 is an IR analysis spectrum of m-XDI obtained in Example 4. FIG.

The present invention is prepared by reacting a diamine of formula (I) with an alkyl chloroformate or dialkyl carbonate of formula (II) to produce biscarbamate of formula (III) and pyrolyzing the biscarbamate prepared above. A method of preparing xylylene diisocyanate comprising the step of decomposing and removing a relatively low boiling alcohol.

(Wherein Rx is a halogenated alkyl group and R is an alkyl group)

Xylylene diamines used as diamines (I) in the process of the present invention are m-xylylene diamines, p-xylylene diamines, o-xylylene diamines or mixtures containing these isomers in various fractions. Thus, unless otherwise stated otherwise, the term "xylylene diamine" includes any of the amines described above, and isocyanates made from these amines are referred to as xylylene diisocyanates. In the process of the invention, xylylene diamine can be used as raw material in the form of free amine or hydrochloride.

As the alkyl chloroformate (or dialkyl carbonate) used in the method of the present invention, alkyl chloroformate or dialkyl carbonate substituted with fluorinated or chlorinated alkyl such as trichloro ethyl group, trifluoro ethyl group, tetrafluoro propyl group or the like is used. .

As the reaction ratio of the reactants used in the production method of the present invention, the amount of diamine of formula (I) and alkyl chloroformate or dialkyl carbonate of formula (II) is not particularly limited, but diamine to alkyl chloroformate ( Or dialkyl carbonate) will preferably have 1 mole to 1.96-2.10 moles. Outside this range excess reactants will remain as impurities in the product and will not be economical.

Bis (2,2,2-trichloroethyl) m-xylylenedicarbamate, bis (2,2,2-trifluoroethyl) in biscarbamate prepared as a reaction intermediate in the production method of the present invention m-xylylenedicarbamate, bis (2,2,3,3-tetrafluoropropyl) m-xylylenedicarbamate is considered a novel compound that could not be identified in the prior art. These new intermediate compounds are described in detail in the Examples, and NMR and IR data for them are shown in the figures.

The preparation of biscarbamate prepared as the reaction intermediate is preferably carried out at room temperature in the presence of a base. Bases used herein include metal carbonates or hydroxides, and in particular, bases KOH, Ca (OH) 2, NaOH, Ba (OH) 2, Na 2 CO 3, K 2 CO 3, and the like will be preferred.

The pyrolysis of the biscarbamate prepared in the production process of the invention is carried out in the presence of a catalyst, in particular in the presence of a compound having a catalytic effect on the esterification reaction. Suitable catalysts include carboxylates, metal oxides, and organometallic compounds. In the selection of catalysts, it should be noted that they must be thermally stable and nonvolatile under special reaction conditions, for reasons of product purity and constant pyrolytic activity. Examples of catalysts that meet these requirements are: ferric chloride, cuprous chloride, zinc chloride, zinc bromide, zinc iodide, cadmium iodide, stannous chloride, stannous bromide, stannous iodide; Tintin, zinc, ferric, cobalt, and manganese octanoate and naphthenate; Cuprous oxide, cupric oxide, manganese dioxide, dibutyltin oxide, dibutyltin dilaurate, and titanium 2-ethylhexanoate. Particularly preferred are para-toluenesulfonic acid, naphthalenesulfonic acid, dibutyltin oxide. The catalyst is suitably used at a concentration of 0.0001 to 10% by weight, preferably 0.0005 to 0.05% by weight, particularly preferably 0.001 to 0.02% by weight, based on the biscarbamate to be pyrolyzed.

In the process of the invention the reaction can be carried out in an inert solvent, i.e. any solvent which 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 may be used include, for example, aromatic hydrocarbons such as benzene, halogenated aromatic hydrocarbons such as monochlorobenzene, dichlorobenzene, trichlorobenzene or 1-chloronaphthalene, toluene, xylene, ethylbenzene, cumene or tetra Alkylated aromatic hydrocarbons such as hydronaphthalene, other functionalizations such as anisole, diphenylether, ethoxybenzene, benzonitrile, 2-fluoroanisole, 2,3-dimethylanisole or trifluorotoluene or mixtures thereof Aromatic hydrocarbons are included. Preferred solvents include monochlorobenzene or dichlorobenzene.

The process can be carried out under atmospheric pressure, preferably dried 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 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 biscarbamate, while in the presence of solvent it is preferably 100 to 230 ° C., more preferably 120 to 190 ° C. to be.

The conversion to diisocyanate obtained by the process of the invention is at least 90%, preferably at least 98%.

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.

Alcohols that may be formed by the process of the invention include, for example, 2,2,2-trifluoroethanol, 2,2,2-trichloroethanol, trichloromethanol, 1,1,1,3, Phenol polysubstituted with 3-hexafluoroisopropanol, monofluoro tert-butanol, fluorophenol, chlorophenol and halogen.

It is believed that the diisocyanates and alcohols finally obtained by the process of the invention 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.

First, the manufacturing process of biscarbamate used as a reaction intermediate in the production method of the present invention will be described, and then the manufacturing process of m-XDI prepared from these intermediates will be described.

Example 1

Preparation of bis (2,2,2-trichloroethyl) m-xylylenedicarbamate

2,2,2-trichloroethyl chloroformate (42.g 0.2 mol) was added to a reactor containing m-xylylenediamine (13.6 g 0.1 mol) and NaOH (8.8 g) / H ₂ O (100 ml). The mixed solution dissolved in methane is added slowly using a dropping funnel and stirred at room temperature.

After stirring for 5 hours, the dichloromethane layer was separated using a separatory funnel and distilled under reduced pressure to obtain a white solid material in 95% yield. The melting point of the obtained solid material is 113-115 ° C. The NMR and IR data for this are as follows and these analytical spectra will be shown in FIGS. 1A and 1B.

¹ H NMR (CDCl 3, 300 MHz): δ 4.42 (d, 4H, J = 5.9 Hz), 4.77 (s, 4H), 5.33 (br s, 2H), 7.24 (m, 3H), 7.32 (m, 1H) .

IR (KBr, cm ⁻¹ ): 3315,3056,2950,2262,1708,1541,1251.

Example 2

Preparation of bis (2,2,2-trifluoroethyl) m-xylylenedicarbamate

In a flask containing m-xylylenediamine (13.6 g 0.1 mol) and NaOH (8.8 g) / H ₂ O (80 ml), 2,2,2-trifluoroethyl chloroformate (32.4 g, 0.2 mol) was added. The mixed solution dissolved in dichloromethane (100 ml) is stirred using a dropping funnel at room temperature. After stirring for 4 hours, the dichloromethane layer was separated using a separatory funnel and distilled under reduced pressure to obtain a white solid material in 96% yield. The melting point of the obtained solid material is 122-124 ° C. The NMR and IR data for this are as follows and these analytical spectra will be shown in FIGS. 2A and 2B.

¹ H NMR (CDCl ₃ , 300 MHz): δ 4.38 (d, 4H, J = 6.1 Hz), 4.47 (q, J = 8.5 Hz), 5.31 (brs.2H), 7.20 (m, 3H), 7.32 ( m, 1 H).

IR (KBr, cm ⁻¹ ): 3319, 3066, 2974, 2264, 1708, 1550, 1253.

Example 3

Preparation of bis (2,2,3,3-tetrafluoropropyl) m-xylylenedicarbamate

A mixture of dichloromethane and 2,2,3,3-tetrafluoropropyl chloroformate (57.0 g 0.29 mol) was added dropwise to a reactor in which m-xylylenediamine (20.0 g, 0.14 mol) and NaOH / H ₂ O were mixed. Stir at room temperature while adding using a funnel.

After stirring for 5 hours, the dichloromethane layer was separated using a separatory funnel and distilled under reduced pressure to obtain a white solid material in 93% yield. Melting | fusing point of the obtained solid substance is 86.8-88.2 degreeC. The NMR and IR data for this are as follows and these analytical spectra will be shown in FIGS. 3A and 3B.

¹ H NMR (CDCl ₃ , 400 MHz): δ 4.36 (d, 4H, J = 6.1 Hz), 4.52 (t, 4H J8.5 Hz) 5.27 (br s, 2H), 5.87 (m, 2H), 7.20 (m, 3H), 7.32 (m, 1H)

IR (KBr, cm ^-1 ): 3324, 3062, 2928, 1696, 1538, 1267, 1105, 966, 703

(Example 4)

Preparation of m-XDI by Intermediate Obtained in Example 1

Bis (2,2,2-trichloroethyl) m-xylylenedicarbamate (100 g, 0.205 mol) in 1,2-dichlorobenzene (ODCB) (1 L) in a reactor equipped with a distillation apparatus (including dean-stark) After stirring), 2-naphthalenesulfonic acid (1.5 g) is added as a catalyst, and the temperature is adjusted so that the amount of the solvent distilled at 180 ° C. for 6 hours while gradually heating is about 300 ml. During the reaction, the reaction product was collected little by little from the reaction flask every hour to check the production of m-XDI using GC. While taking the sample, supplement the ODCB by the amount of the distilled solvent to maintain a constant water level.

After the reaction was completed, the ODCB used at atmospheric pressure to distill the m-XDI was distilled off about half, cooled, and the residual ODCB solvent was removed under reduced pressure (about 2 torr) (internal heating temperature was 80 ° C). Keep below). After cooling the reactor, the remaining reactants were dissolved in 300 ml of MC (methylene chloride), and then a small amount of solid material was filtered off, and the filtrate was concentrated to remove the used MC, followed by m-XDI 35 g (Y = 91%, purity). 99.3 area% by GC). An isocyanate group (-NCO) was confirmed at 2264 cm ^-1 by infrared spectroscopy (IR) of the obtained product, and is shown in FIG. 4.

IR (KBr, cm ^-1 ): 2264 (-NCO), 1698, 1444, 1352, 784, 579

(Example 5)

Preparation of m-XDI by Intermediate Obtained in Example 2

Bis (2,2,2-trifluoroethyl) m-xylylenedicarbamate (77.6 g, 0.2 mol) was dissolved in ODCB (1 L) and heated to proceed with the reaction. After heating up to reflux (180 ℃) proceeded for about 20hr, by-product trifluoroethanol was removed with azeotropic ODCB using dean stark.

The amount of ODCB removed was added to the reactor to maintain a certain amount of solvent, and the progress of the reaction was confirmed by using GC. After cooling, unreacted intermediates (mono-carbamate and di-carbamate) precipitated as solids. Filtered off. The filtrate was concentrated to remove the solvent used to obtain 36.8 g (Y = 84%, purity 86 area% by GC) of m-XDI, this material was vacuum distilled to give a product of 99% GC purity.

(Example 6)

Preparation of m-XDI by Intermediate Obtained in Example 3

Bis (2,2,3,3-tetrafluoropropyl) m-xylylenedicarbamate (91 g, 0.2 mol) was dissolved in ODCB (1 L) and heated to proceed with the reaction. Heating was raised to reflux (180 ℃) and proceeded for about 20hr, by-product trifluoroethanol was removed with azeotropic ODCB using dean -stark.

The amount of ODCB removed was added to the reactor to maintain a certain amount of solvent, and the progress of the reaction was confirmed by using GC. After cooling, unreacted intermediates (mono-carbamate and di-carbamate) precipitated as solids. Filtered off. The filtered filtrate was concentrated to remove the solvent used to obtain 36.5 g (Y = 93%, purity 96 area% by GC) m-XDI.

Example 7

Preparation of m-XDI with the intermediate obtained in Example 3 under nonsolvent

Bis (2,2,3,3-tetrafluoropropyl) m-xylylenedicarbamate (200 g, 0.442 mol) is melted above the melting point without using a solvent, and then 2-naphthalenesulfonic acid ( After adding 2 g), the vaporized tetrafluoropropanol was removed using Dean-stark while raising the temperature directly to 120 ° C to 180 ° C.

The reaction was terminated after stirring and warming until no vaporized substance appeared in the liquid state. The conversion rate was 98%, the obtained product was 96% GC analysis, and vacuum distillation yielded 67.3g (yield 81%) of more than 99%.

IR (KBr, cm ^-1 ): 2264 (-NCO), 1698, 1444, 1352, 784, 579

By the method of the present invention, m-XDI produced by toxic and highly corrosive phosgene will be able to produce diisocyanate of non-yellowing type without using phosgene, thereby being eco-friendly and on an industrial scale. The preparation of diisocyanates will be industrially available.

Claims (10)

As a method for producing xylylene diisocyanate,
Reacting a diamine compound of formula (I) with a halogenated alkyl chloroformate or halogenated dialkyl carbonate of formula (II) to prepare a biscarbamate of formula (III); And
Decomposing and removing the halogenated alcohol obtained by pyrolyzing the biscarbamate prepared above;
Method for producing xylylene diisocyanate (m-XDI) comprising a.

Formula (I) Formula (II) Formula (III)

+

(or

) →

→

Wherein Rx is an ethyl halide or propyl group
The process of claim 1 wherein said pyrolysis is carried out in the presence of a solvent.
The method of claim 2, wherein the solvent is at least one solvent selected from the group consisting of 1,2-dichlorobenzene, 1,2,4-trichlorobenzene, chlorobenzene.
The method according to any one of claims 1 to 3, wherein the pyrolysis temperature is 120 to 230 ° C.
The process of claim 1 wherein said pyrolysis is carried out in the presence of an acidic catalyst of toluenesulfonic acid or naphthalenesulfonic acid.
The process according to claim 1 or 5, wherein said pyrolysis is carried out under reduced pressure.
A biscarbamate intermediate of formula (III) prepared by reacting a diamine of formula (I) with a halogenated alkyl chloroformate or halogenated dialkyl carbonate of formula (II).
Formula (I) Formula (II) Formula (III)

+

(or

) →

Wherein Rx is an ethyl halide or propyl group
8. The intermediate of claim 7, wherein said biscarbamate intermediate is any one selected from the following compounds:
Bis (2,2,2-trichloroethyl) m-xylylenedicarbamate;
Bis (2,2,2-trifluoroethyl) m-xylylenedicarbamate; And
Bis (2,2,3,3-tetrafluoropropyl) m-xylylenedicarbamate.
A process for preparing a biscarbamate intermediate of formula (III) prepared by reacting a diamine of formula (I) with an alkyl chloroformate or dialkyl carbonate of formula (II).
Formula (I) Formula (II) Formula (III)

+

(or

) →

(Wherein Rx is a halogenated alkyl group)
The method of claim 9, wherein said reaction is prepared in the presence of a base.

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