JPH0383959A - Production of aromatic polycarbamate - Google Patents

Abstract

PURPOSE:To produce the subject compound useful as an intermediate for the production of polyurethane in high yield and efficiency by nitrating diphenylmethane and reacting the product with an OH-containing organic compound and CO in the presence of a catalyst. CONSTITUTION:The objective aromatic polycarbamate composed mainly of methylenediphenyldicarbamate can be produced by nitrating diphenylmethane with a nitration agent and reacting the resultant mixture composed mainly of dinitrodiphenylmethane with an OH-containing organic compound and CO in the presence of a catalyst. The dinitrodiphenylmethane used in the reaction is a compound of formula and produced in high yield by the nitration of diphenylmethane.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing aromatic polycarbamate, particularly methylene diphenyl dicarbamate, which is an intermediate in the production of aromatic isocyanate, which is a raw material for polyurethane.

(Prior Art) Aromatic polyisocyanates, especially dinuclear methylene diphenyl diisocyanate (hereinafter abbreviated as MDI), are
It is a useful substance as a raw material for manufacturing polyurethane elastomers and coating materials, and the amount used for this purpose currently exceeds that of tolylene diisocyanate (TDI), which has been problematic due to its high volatility and strong toxicity. It's here,
Mass production is carried out on an industrial scale.

Conventionally, aromatic isocyanates have generally been industrially produced by reducing an aromatic nitro compound with hydrogen to obtain an aromatic amine, which is then treated with phosgene to form an isocyanate. However, this method is complicated, and
Problems include the use of toxic phosgene and the production of large amounts of hydrogen chloride. Therefore, methods for producing aromatic isocyanates that do not use phosgene have been actively researched for the past 20 years.

Methods that do not use phosgene are broadly divided into ∎direct method and ∎carbamate-mediated method.

The first direct method involves reacting aromatic nitro compounds with carbon monoxide in the presence of a palladium-based catalyst in an inert solvent to directly produce aromatic isocyanate compounds, but the reaction conditions are harsh. However, there are drawbacks such as low catalyst productivity and the tendency for side reactions to occur together. Furthermore, fatally, it is difficult to apply this method to the production of polyisocyanates with a polynuclear structure such as MDI.

In the 20th carbamate method, an aromatic nitro compound and an alcohol are reacted with carbon monoxide in the presence of a platinum group metal catalyst or a selenium catalyst to obtain an intermediate aromatic carbamate, and then this carbamate is heated. This is a method to obtain the corresponding aromatic isocyanate by decomposition.

In the production of polyisocyanate via such carbamates, a method for obtaining aromatic carbamates as intermediate products is, for example, as shown in the following reaction formula (a), by combining phenyl carbamate (1) and a substance that generates formaldehyde. There is a method of producing methylene diphenyl dicarbamate (■) (hereinafter abbreviated as MDU) by condensation using an acid catalyst such as sulfuric acid. When this MDU is thermally decomposed, alcohol is eliminated and the corresponding isocyanate MDI (nl
) is generated.

(1) (II) (III) (R: lower alkyl group having 1 to 6 carbon atoms) This method is described in, for example, U.S. Pat. Many proposals have been made. However, in these methods, the following general formula (
It is difficult to simultaneously grow polynuclear bodies such as IV) and obtain the desired product MDU in high yield.

(m: an integer of 1 to 6; R has the same meaning as above) (Issue III to be solved by the invention) As described above, in the conventional method, MDU, which is an aromatic isocyanate and is useful as an intermediate for MDI, is It was difficult to obtain a good yield.

The present invention was made against the background of the above circumstances, and its purpose is to provide an industrially advantageous method for producing aromatic polycarbamates, particularly MDU, in high yield.

(Means for Solving the Problems) The present inventors have discovered that dinitrodiphenylmethane of the following general formula (V) can be easily obtained in high yield through nitration of diphenylmethane, and the dinitrodiphenylmethane thus obtained The present invention has been completed based on the discovery that aromatic polycarbamates, particularly MDU, can be produced in high yield by a known reductive carbonylation reaction from a mixture containing as a main component.

That is, the gist of the present invention is characterized in that diphenylmethane is nitrated with a nitrating agent, and the resulting mixture containing dinitrodiphenylmethane as a main component is reacted with a hydrous acid group organic compound and carbon monoxide/element in the presence of a catalyst. This is a method for producing an aromatic polycarbamate containing MDU as a main component.

The present invention will be explained in more detail below.

According to the invention, diphenylmethane is first nitrated.

In the nitration step, diphenylmethane (melting point 26-27°
Although it is preferable to carry out the reaction in a solvent-free liquid phase by gradually dropping the nitrating agent into the melt of C>, other reaction methods can also be adopted.

As the nitrating agent, a mixed acid of concentrated nitric acid and concentrated sulfuric acid is preferred, but fuming nitric acid may be used instead of concentrated nitric acid.The amount of the nitrating agent used is 1.0 molar ratio to diphenylmethane. ~20.0 times.

The reaction temperature is preferably in the range of 20 to 150°C, particularly 40 to 80°C. If the reaction temperature exceeds 150°C, the amount of by-products such as trinitrodiphenylmethane will increase, and the yield of dinitrodiphenylmethane will decrease. Moreover, the reaction progresses rapidly, making it difficult to control the reaction.If the temperature is below 20°C, the reaction will be difficult to proceed, and the reaction time will be too long.

Although the reaction time varies depending on the reaction temperature, the type of nitrating agent, the rate of dropping, etc., the reaction is usually terminated by stirring the reaction mixture for about 10 to 180 minutes after finishing dropping. Nitration is usually carried out without solvent as mentioned above, but
If necessary, an inert solvent such as acetic acid may be used as the nitrating agent.

After the reaction is completed, the reaction mixture is washed with water to remove excess nitrating agent, and the nitrated product is recovered by dehydration and drying.

Preferably, an organic solvent that dissolves the nitration product is added to the reaction mixture to extract the product into the organic phase, and the nitration agent is separated from the aqueous phase by separation. After washing with water as above, drying and evaporation of the solvent, the desired nitrated product is isolated.

The nitration of diphenylmethane produces dinitrodiphenylmethane in high yield and provides a reaction product consisting of a mixture containing dinitrodiphenylmethane as the main component.

2,2′-dinitrodiphenylmethane in the product, 2,
The content of each isomer of 4°-dinitrodiphenylmethane and 4,4°-dinitrodiphenylmethane varies depending on the reaction conditions, but usually the majority is the 4.4°-isomer;
The amounts of the 2'- and 2,4'-isomers produced are small.

The nitrated product obtained from the nitration step is then reacted with a hydrous acidic organic compound and carbon monoxide in the presence of a catalyst to obtain the desired MDU-based polycarbamate product. This reaction can be carried out in the same manner as a conventional similar reaction, for example, by reacting nitrobenzene with ethanol and carbon monoxide to obtain the phenyl carbamate represented by the general formula (1). explain.

As the hydrated acid group organic compound, any of monohydric and polyhydric alcohols and monohydric and polyhydric phenols containing primary, secondary, and tertiary hydroxyl groups can be used. That is, the resulting products may be those in the general formula (I[) above, in which R is not only a lower alkyl group but also a hydroxyalkyl group, an aryl group, or a hydroxyaryl group. However, when producing aromatic polycarbamate as an intermediate for aromatic polyisocyanate, ethanol or methanol is most suitable as the hydrous acid group organic compound because subsequent thermal decomposition to polyisocyanate is easy. .

Since the hydrous acid group organic compound is usually used also as a solvent, it is preferable to use one that is liquid under the reaction conditions. The hydrous acid group organic compound is required for the reaction in an amount equivalent to at least the nitro group, but if it also serves as a solvent, it is used in a large excess amount.

- Carbon oxide is introduced in large excess into the reaction system by conducting the reaction under carbon monoxide pressure.

As the catalyst, a main catalyst made of a platinum group metal is used in combination with a co-catalyst and, if necessary, a ligand.

Main catalysts include palladium, ruthenium, rhodium,
Platinum group metals such as platinum, osmium, and iridium can be used as they are or in the form of metal salts or oxides.

Industrially, palladium and ruthenium are preferred. As a co-catalyst, a Lewis acid containing an element selected from Group I of the Periodic Table and subgroups TB-VB can be used. Among the ligands, halides such as ferrous and ferric chlorides, stannous and stannic chlorides, and cupric and cupric chlorides are particularly preferred.
Nitrogen-containing heteroaromatic compounds such as pyridine, quinoline, O-phenanthroline and derivatives thereof can be used.

The reaction can be carried out batchwise, semi-continuously, or continuously.The reaction conditions are generally a reaction temperature of 130 to 190°C, a reaction time of 0.5 to 10 hours, and an initial pressure of carbon oxide of Approximately 50 to 300 kg/dG is preferable.

As the solvent, a hydrous acid group organic compound can be used as both the reaction substrate and the solvent, but it is also possible to use an inert solvent such as a hydrocarbon solvent in combination.

The separation of the 0 reaction product in which the corresponding MDU isomer is produced in a high yield of over 90% from each isomer of dinitrodiphenylmethane by the above carbonylation reaction can be carried out by a conventional method. For example, separating the platinum group metal catalyst from the reaction mixture and then evaporating the hydrous acid group compound from the organic layer will isolate the polycarbamate product as a solid.

The product thus obtained can be used for the production of polyisocyanates by pyrolysis (generally liquid-phase pyrolysis), usually as is or, if necessary, after a purification or isomer isolation step; As a result, high quality MD
An aromatic polyisocyanate containing I as a main component is obtained.

(Example) The present invention will be explained below with reference to Examples.

10 g of diphenylmethane was charged into a 300-capacity flask equipped with a reflux condenser, a thermometer, and a dropping funnel.
Warmed to 0°C. While stirring, add mixed acid (70 wt% nitric acid/96 wt% sulfuric acid = 8/11 (wt/
wt) 35g was gradually added dropwise so that the reaction temperature was in the range of 50 to 60°C.
After heating and stirring at 0°C, toluene 1001
d was added, the aqueous layer was separated, the organic layer was washed with water and dried, and the toluene solution was analyzed by high performance liquid chromatography. As a result, unreacted diphenylmethane was not detected, and 2.2°-dinitrodiphenylmethane, 2,4
What is the yield of each isomer of °-dinitrodiphenylmethane and 4,4゛-dinitrodiphenylmethane? , 6.1
It was 0.3.68.8 a+o1%. Trinitrodiphenylmethane and mononitrodiphenylmethane were detected as by-products.

M (Carbonylation reaction) Toluene was recovered from the toluene solution obtained in Example 1 using an evaporator to obtain a solid. 2.0 g of this solid, 15 d of ethanol, 0.6 g of pyridine, 0 of anhydrous ferric chloride
．． 6 g and 0.16 g of 5% palladium-carbon were charged into a 60-volume Hastelloy alloy T magnetically stirred autoclave, and after the atmosphere was sufficiently replaced with carbon monoxide, the initial pressure was set to 80 k.
Carbon monoxide was charged to g/cd-G. 50
The temperature was raised while stirring at 0 rpm, and the reaction was carried out at 160°C for 3 hours. After the completion of the 0 reaction, the 0 reaction solution was cooled to room temperature and replaced with nitrogen. When analyzed by high performance liquid chromatography, it was found that 2.2'-MDU , 2,4°-MDU, 4.4'-
The yield of MDU was 92.92.91 mo1%, based on each dinitrodiphenylmethane isomer contained in the toluene solution used.

In addition, when the catalyst was filtered from the reaction solution and ethanol was removed, the MDU content in the obtained solid was 90 wt.
%Met.

(Effects of the Invention) According to the method of the present invention, by nitrating and carbonylating diphenylmethane, an aromatic polycarbamate containing MDU as a main component can be efficiently obtained in high yield. Compared to the conventional aromatic polycarbamate manufacturing method described above, there is almost no production of polynuclear polycarbamate, and substantially dinuclear aromatic polycarbamate (MD
Since only U) can be produced, a polycarbonate "-) useful as a raw material for producing high-quality polyisocyanate can be obtained.

Claims (1)

[Claims] The main component is methylene diphenyl dicarbamate, which is characterized by nitrating diphenylmethane with a nitrating agent and reacting the obtained mixture mainly consisting of dinitrodiphenylmethane with a hydrous acid group organic compound and carbon monoxide in the presence of a catalyst. A method for producing an aromatic polycarbamate.