JPS5980637A - Preparation of p-nitrobenzoic acid - Google Patents

Abstract

PURPOSE:To obtain the titled compound in good hue, by oxidizing p-nitrotoluene with molecular oxygen in acetic acid solvent in the presence of a catalyst constituted of metallic compounds of cobalt, manganese and cerium and a bromine compound. CONSTITUTION:p-Nitrotoluene is oxidized with a gas containing molecular oxygen in acetic acid solvent in the presence of a catalyst constituted of a cobalt compound and a bromine compound as main constituent components and further a manganese compound and/or cerium compound to give the aimed p-nitrobenzoic acid. In the process, a zirconium compound, e.g. zirconium bromide, is further present as the catalyst. The amount of the zirconium compound is preferably 0.5-50wt% based on the cobalt metal used as the catalyst constituent component. The aimed compound in good hue is obtained at a high reaction rate with a small amount of the catalyst with prevented formation of coloring impurities by the above-mentioned oxidative reaction.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing p-nitrobenzoic acid by oxidizing p-nitrotoluene with a molecular oxygen-containing gas.

p-2) Oral benzoic acid is a compound useful as a raw material for agricultural chemicals, medicines, dyes, resins, etc., and it is desired to develop an economical manufacturing method to produce p-2) oral benzoic acid with good purity. There is.

Until now, as a method for oxidizing p-nitrotoluene to p-nitrobenzoic acid in acetic acid with a molecular oxygen-containing gas, a catalyst consisting of bromine, cobalt, manganese and/or cerium has been used, and an all-metal silicone method has been used. manganese and/or
Alternatively, a method of oxidizing cerium at 50 to 150°C with a gram atomic ratio of 0.05 to 15
No. 837) is known.

However, in this method, since manganese and cerium are used together with cobalt to increase the catalytic activity, coloring impurities are produced as by-products, making it difficult to obtain a target product with good color tone.

Therefore, the present inventors conducted the following steps in converting p-nitrotoluene to p-nitrobenzoic acid using a molecular oxygen-containing gas.
We conducted extensive research with the aim of developing a method for obtaining a target product with a good color tone in high yield at a high reaction rate using a small amount of catalyst.
The inventors have discovered that the object can be achieved by making a zirconium compound present in the reaction system in addition to a variable valence metal compound such as manganese or cerium and a bromine compound, and have thus arrived at the present invention.

That is, the present invention provides a method for preparing molecules of p-nitro)/renin in an acetic acid solvent in the presence of a catalyst consisting of a cobalt compound and a bromine compound as main components and a manganese compound and/or a cerium compound added thereto. I)-2) A method for producing p-nitrobenzoic acid, which is characterized in that a zirconium compound is further present in the reaction system.

The method of the present invention will be specifically explained below.

In the method of the invention, p-nitro)tV renin is contacted with a molecular oxygen-containing gas in the presence of a catalyst in an acetic acid solvent.

The appropriate amount of acetic acid to be used is 1 to 7 times the weight of p-nitrotoluene supplied to the reactor. If the amount of acetic acid used is less than 1 times the weight, the oxidation rate is low and the reaction product becomes a highly concentrated slurry or solid that is difficult to handle, making it impossible to achieve a satisfactory level of quality. It is difficult to obtain things stably. On the other hand, if the amount of acetic acid used is 7 times or more by weight, the economic burden due to acetic acid decomposition increases, and the volumetric efficiency of the reactor unnecessarily decreases, which is disadvantageous. Although there is no particular problem if water is present in an amount of about 5% by weight or less, it is preferable that the amount of water in acetic acid is small.

As the catalyst, a cobalt compound and a bromine compound are used as main components, and a manganese compound and/or a cerium compound are used in combination with these to enhance the catalytic activity. In this case, cobalt compounds, manganese compounds, cerium compounds, bromides, hydroxides, carbonates, salts of lower aliphatic carboxylic acids such as acetic acid, salts of aromatic carboxylic acids such as nitrobenzoic acid, and salts of naphthenic acids are used. Compounds that are soluble in the reactants, such as acetylacetonate and do not contain counterions that would interfere with the reaction, are suitable.

Examples of bromine compounds include inorganic bromine compounds such as bromine, hydrogen bromide, cobalt bromide, manganese bromide, ammonium bromide, alkali metal bromides, and tetrabromoethane.
Organic bromine compounds such as bromoacetic acid and benzyl bromide can be used.

The appropriate amount of the cobalt compound to be used is such that the amount of cobalt metal used is in the range of 0.08 to 0.4% by weight based on the acetic acid solvent. If the amount of cobalt catalyst used is less than 0.608% by weight, a sufficient reaction rate will not be obtained, and if it exceeds 0.4% by weight, the time and effort required to separate the cobalt catalyst from the target product will increase, and coloring impurity by-products will be produced. increases, which is disadvantageous.

In the present invention, a manganese compound and/or a cerium compound are used in addition to the cobalt metal (cobalt metal), and the amount of manganese metal and/or cerium metal used is in the range of 0.1 to 20% by weight based on the cobalt metal. It is desirable to use a manganese compound and/or a cerium compound such that If the amount of the manganese compound and/or cerium compound used is less than the above range, the catalytic activity will decrease, and if it is less than the above range, the by-product of coloring impurities will increase, which is not preferable.

The amount of bromine compound to be used is in the range of 0.2 to 6 times the weight of cobalt metal, especially 0.5
A range of 6 to 6 times the weight is appropriate. No amount of bromine catalyst used
．． When the amount is less than 2 times by weight, sufficient catalytic activity cannot be obtained, and when it exceeds 6 times by weight, the catalyst activity tends to decrease, and contamination of the product by bromine and the burden on the catalyst cost become significant, which is not preferable.

In the present invention, the above-mentioned Coba/L/) compound,
In addition to the bromine compound, manganese compound and/or cerium compound, a zirconium compound is also present in the reaction system. By using zirconium compounds together,
The present inventors have discovered that the catalytic activity is increased and the amount of colored impurity by-products is reduced.

As the zirconium compound, tetratetravalent -)) rheconium compounds, such as zirconium bromide, zirconyl acetate, and zirconium acetate, which are soluble in acetic acid and do not contain counterions that interfere with the reaction, are suitable. The amount of the zirconium compound to be used is such that the amount of zirconium metal used is equivalent to 0.5 to 50% by weight, preferably 1 to 15% by weight, based on the amount of zirconium metal used as a catalyst component. Appropriate. If the amount of the zirconium compound used is less than this range, the effect of addition will be weak, and if it is more than this range, the cost burden and separation effort will increase, but no particular effect will be obtained, which is disadvantageous.

The reaction temperature is suitably in the range of 130 to 180°C. 13
If the reaction temperature is lower than 0℃, the reaction rate will be slow and the by-product of colored impurities will increase, while if the reaction temperature exceeds 180℃, the activity of the catalyst will tend to decrease and the reaction product will be converted to carbon dioxide. decomposition, elimination of nitro groups, and further production of colored impurities as by-products, which are undesirable.

Although pure oxygen or industrial exhaust gas can be used as the molecular oxygen-containing gas used as the oxidizing agent, from an industrial perspective, ordinary air or a mixed gas of air and industrial exhaust gas is suitable.

Regarding the oxygen partial pressure in the reaction system, the total reaction pressure is in the range of 5 to 40 atm, especially in the range of 8 to 60 atm, and the oxygen concentration of the exhaust gas from the reactor is in the range of 1 to 8 by volume. It is preferable to operate. If the reaction pressure exceeds 40 atm, no particular advantage will be obtained, although the equipment cost and the power cost for compressing the molecular oxygen-containing gas will increase, and on the contrary, the decomposition of the reactant into carbon dioxide will decrease. This is a disadvantage as it tends to increase. Furthermore, if the oxygen concentration in the exhaust gas exceeds 8 volumes, there is a strong possibility that the reactor gas phase will form an explosive gas mixture. be.

The reactor used in the present invention is preferably of a forced mixing type rather than a simple bubble column type. That is, in order to achieve good gas-liquid mixing of the molecular oxygen-containing gas and the reaction liquid, to promote dissolution of molecular oxygen into the reaction liquid, and to ensure smooth contact between the reactants in the reactor, It is preferable to use a reactor equipped with a gas inlet consisting of a large number of pores in the lower part of the reactor, and in which forced stirring is performed using a rotating stirring blade or forced circulation is performed using a circulation pump outside the reactor.

A reflux condenser is installed at the top of the reactor, and the exhaust gas is discharged through this reflux condenser, and the solvent acetic acid and unreacted nitro)/renin contained in the exhaust gas are condensed and circulated to the reactor. let

As the reaction method, any of a batch method, a semi-continuous method, and a continuous method can be employed, but the target substance of better quality can be obtained in the case of a semi-continuous method or a continuous method.

Note that the method for isolating the target substance p-nitrobenzoic acid from the reaction product mixture obtained by the method of the present invention is to cool the reaction product and optionally further concentrate it.I)
-=) A suitable method is to crystallize benzoic acid and separate it from the mother liquor into solid and liquid. The thus isolated p-nitrobenzoic acid is
If necessary, the product is purified to the desired purity by washing with a solvent and recrystallization if necessary, and then dried to produce a product.

On the other hand, the mother liquor from which p-nitrobenzoic acid is separated contains p-nitrobenzoic acid corresponding to the solubility, reaction intermediates, unreacted raw materials, catalysts, and other organic substances. Alternatively, it can be subjected to appropriate purification treatment and recycled to the reaction system for repeated use.

By the method of the present invention detailed above, it has become possible to economically produce p-nitrobenzoic acid of good quality.

The present invention will be specifically described below with reference to Examples.

Example 1 200 parts of acetic acid (1 part to p-nitrotoluene) was placed in a pressure-resistant titanium reactor equipped with 5 reflux coolers and a rotary vane pump.
．． 54 times the weight), 5 parts of water, 1.3 parts of cobalt bromide hexahydrate
31 parts, cobalt acetate tetrahydrate 1015 parts, cerium acetate -hydrate 1], [+1[38 parts, zirconyl acetate 0.
0237 parts (0.24% by weight of copal to acetic acid, 1.65 times the weight of bromine to cobalt, 1% by weight of cerium to cobalt, 2% by weight of zirconium to cobalt), and the reaction pressure was 14%. Air pressure gauge, reaction temperature 1
At 55°C, while blowing a mixed gas of 7 g of oxygen and 93% of nitrogen, 130 parts of p-nitrotoluene melted in the bath was started to be continuously introduced at a rate that completed the introduction in 4 hours.

Oxygen absorption started 5 minutes after the start of introduction, so the gas to be blown was changed to air, and air was continued to be blown at a flow rate such that the oxygen concentration in the exhaust gas was below 8%, and 4 hours later, p
- The introduction of nitrotoluene was completely stopped, and air blowing was stopped one minute after 5:00.

After the reaction is completed, the product is cooled to room temperature and separated into solid and liquid.
After washing with 400 parts of 0% aqueous acetic acid and drying, the purity is 99.
124 parts of p-nitrobenzoic acid (yield 78 mol%)
)was gotten.

2 g of this p-nitrobenzoic acid was added to 20 g of IN-KOH aqueous solution.
When the light transmittance of 460 parts m was measured in a 1 cm cell, it was 82 cm.

Comparative Example 1 In Example 1, when zirconyl acetate was not added, p
- Yield of nitrobenzoic acid is 111 parts (yield 70 molti)
The light transmittance at 460 nm also decreased to 76 cm.

Example 2 The catalyst used in Example 1 was 0.887 parts of cobalt bromide and large aqueous salt,
Cobalt acetate/shibonsalt Q, 676 parts, cobalt acetate) 0.16% by weight, bromine 1.35 to cobalt
The yield of p-nitrobenzoic acid is 130 parts (yield 82 molti), 46
The light transmittance at 0 nm was 65 cm.

Comparative Example 2 In Example 2, when zirconyl acetate was not added, p
- 130 parts of nitrobenzoic acid was produced, but at 460 nm
The light transmittance decreased to 50%.

Example B In addition to the catalyst of Example 2, cerium acetate-water salt Q, Q
When 57 parts of O (co75 parts by weight relative to cobalt) was added, the yield of p-nitrobenzoic acid was 135 parts (yield: 85 moles), and the light transmittance at 460 nm was 70 moles.

Comparative Example 3 In Example 3, when diμconyl acetate was not added, J) was obtained.

Claims (1)

[Claims] p-Nitrotoluene is oxidized in an acetic acid solvent with a molecular oxygen-containing gas in the presence of a catalyst consisting of a cobalt compound and a bromine compound as main components, to which a manganese compound and/or a cerium compound is added. - A method for producing nitrobenzoic acid, characterized in that a zirconium compound is further present in the reaction system.
Method for producing nitrobenzoic acid.