JPS647066B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing regioselective aromatic nitro compounds by reacting an aromatic iodo compound and nitrogen dioxide in a suitable solvent and replacing iodine ions with nitrogen dioxide ions. The feature of this production method is that a regioselective aromatic nitro compound is produced by a combination of a regioselective iodination reaction of an aromatic compound with iodine and a substitution reaction of the aromatic iodo compound with nitrogen dioxide. It is in. The present invention uses an aromatic iodo compound selected from the group of mono- or diiodo compounds of benzenes or bicyclic compounds which may have a methyl group, and nitrogen dioxide in an amount of 5 to 50 times the mole of the aromatic iodo compound. The present invention relates to a method for producing an aromatic nitro compound, which is characterized by carrying out the reaction in a solvent. That is, a method has already been found for regioselectively synthesizing an aromatic iodo compound from an aromatic compound and iodine under mild reaction conditions by using nitrogen dioxide, which is inexpensive and easy to handle, as an oxidizing agent. For example, various aromatic compounds are regioselectively iodized, as shown in the table below.

【table】

[Table] These regioselectively iodinated aromatic compounds react with nitrogen dioxide in an appropriate solvent at low temperatures to give aromatic nitro compounds in which iodine ions are replaced by nitrogen dioxide ions. This heading led to the present invention. In the present invention, since an aromatic nitro compound is obtained by a substitution reaction of an aromatic iodo compound, the position of the nitro group of the produced aromatic nitro compound is maintained. Conventionally, aromatic nitro compounds have generally been synthesized using a mixed acid system of concentrated nitric acid and concentrated sulfuric acid as a nitrating agent, and have been widely adopted industrially. for example,
In the case of nitration of toluene, the composition of mononitrotoluene is 63% o-isomer, 2% m-isomer and 35% p-isomer.
% (Jikken Kagaku Kaiza, Vol. 20, p. 283).
Normally, nitration using a mixed acid system produces a large number of by-products, and it is very difficult to separate and purify them. In addition, a large amount of waste acid is generated, which poses a major problem in terms of pollution. Another method for nitrating aliphatic halides is to use nitrite as a nitrating agent (Org.
Reactions, 1962, 12, 101). However, in this case, several tens of percent of nitric acid esters are produced as by-products, and the nitrating agent is also expensive, so this is not a problem for industrial production. Furthermore, there are examples of nitration reactions of iodized polyalkylbenzenes with concentrated nitric acid (Acta
Chemica Scandinavia A35 (1981) 481). In this case, it is necessary to use a large amount of nitric acid, which is more than 1000 times the mole of the iodo compound, and the product composition is about 30% mononitro and 60% mononitro monoiodo, the latter being better. This is the main product and is considered to be reactively different from that of the present invention. Compared to these conventional methods, in the present invention, aromatic nitro compounds can be selectively obtained, and the amount of nitrogen dioxide used as an oxidizing agent may be several tens of times the molar amount of the iodo compound. Moreover, most of the nitrogen dioxide after the reaction can be recovered and reused, which has great economic advantages. Furthermore, since nitrogen dioxide can be recovered and reused, a large amount of waste acid is not produced as in conventional methods, so there are no environmental or pollution problems. As mentioned above,
The present invention, which produces an aromatic nitro compound via an aromatic iodo compound, is an industrial production method that is superior in both economy and selectivity compared to conventional methods. The present invention is an industry for regioselectively synthesizing aromatic nitro compounds by reacting aromatic iodo compounds and nitrogen dioxide under mild reaction conditions under liquid phase normal pressure and replacing iodide ions with nitrogen dioxide ions. This is a unique manufacturing method. This reaction is a combination of the iodination reaction of an aromatic compound and the iodo substitution reaction of an aromatic iodo compound, but these two reactions may be performed independently, or the two reactions may be performed consecutively. You can do it. That is, the iodination reaction is carried out using a large excess of the aromatic compound as a solvent or a part of the solvent. Since the iodination reaction is very fast, an aromatic iodo compound can be obtained in a short period of time, but when the iodo substitution reaction is subsequently performed, the liberated iodine reacts with the aromatic compound to regenerate the aromatic iodo compound. On the other hand, aromatic nitro compounds gradually accumulate in the reaction system, and iodine plays a kind of catalytic role. Typical examples of aromatic iodo compounds used in the present invention include benzenes that may have a methyl group such as toluene and xylene, and mono- and diiodo compounds of bicyclic compounds such as diphenyl and diphenyl ether. Can be mentioned. Nitrogen dioxide used as a nitrating agent may be continuously supplied to the reaction system while being entrained with nitrogen and air, or may be dissolved in a reaction solvent and added dropwise over time. is 5 to 50 times the molar amount of the aromatic iodine compound. Suitable solvents used in this reaction include aromatic compounds, fatty acids such as acetic acid and propionic acid, halogenated aliphatic hydrocarbons such as dichloromethane and chloroform, and mixtures of these various solvents. Note that there is no problem even if nitric acid, sulfuric acid, etc. are present in these solvents. This reaction can be carried out at a temperature range of -10° to 100°C, but a temperature range of 0° to 60°C is optimally desirable. The present invention will be specifically explained based on examples. Example 1 2.96 g (10 mmol) of 4-iododiphenyl ether was mixed with 30 ml of dichloromethane and 0.06 ml of nitric acid in a 100-meter tube equipped with a gas inlet, a cooling tube, and a stirring device.
Transfer to a ml glass container. The reaction vessel is immersed in a 40°C water bath, and nitrogen gas containing 0.43 mmol of nitrogen dioxide is blown into the reaction solution at a rate of 50 ml/min while stirring to initiate the reaction. After reacting for a total of 16 hours, the mixture was allowed to stand at room temperature for an additional 20 hours, and the product was analyzed by gas chromatography. As a result, the product composition was 78% 4,4'-dinitrodiphenyl ether and 22% 2-iodo-4,4'-dinitrodiphenyl ether. Example 2 2.11 g of 4,4'-diiodo diphenyl ether
(5 mmol) in 30 ml of dichloromethane and nitric acid.
Add 0.03 ml to the same reaction container as in Example 1,
50% nitrogen gas containing 0.45 mmol nitrogen dioxide
The reaction was carried out at 20°C for 6 hours while blowing into the liquid at a rate of ml/min. Furthermore, after being left at room temperature for 16 hours, the product was analyzed by gas chromatography, and the results showed that it was 4,4'-
83% dinitrodiphenyl ether and 17% 2-iodo-4,4'-dinitrodiphenyl ether
% selectivity was obtained. Example 3 A reaction similar to Example 2 was carried out at 30°C for 6 hours,
After standing at room temperature for 2 hours, the product was analyzed by gas chromatography and found to be 3% 4-iodo-4'-nitrodiphenyl ether, 78% 4,4'-dinitrodiphenyl ether, and 2-iodo-4 ,4′−
Dinitro diphenyl ether was obtained with a selectivity of 19%. Example 4 4.36 g (20 mmol) of p-iodotoluene and 0.1 ml of nitric acid are placed in a 200 ml three-necked flask along with 60 ml of chloroform. Cool this container to 3℃,
At this temperature, the reaction was carried out for 19 hours while nitrogen dioxide was introduced into the reaction system along with the air. The total supply of nitrogen dioxide is 730 mmol. As a result of gas chromatographic analysis of the reaction product, the conversion rate of p-iodotoluene was 63.2%, indicating a p-iodotoluene conversion rate of 63.2%.
Nitrotoluene, 2,4-diiodotoluene and 2-iodo-4-nitrotoluene were each 36.7
%, 25.9%, and 26.4% selectivity were obtained. Example 5 4.36 g (20 mmol) of iodotoluene, 60 ml of toluene, 25.65 g (557 mmol) of nitrogen dioxide, and 0.04 ml of nitric acid were placed in the same reaction vessel as in Example 4, and air containing 0.68 mmol of NO ₂ was added at 3°C. 50ml/
The reaction was carried out for 15 hours while blowing at a rate of 1 minute. As a result of gas chromatographic analysis of the reaction product, iodotoluene was 19.5 mmol (o:p=
42:58), 24.8 mmol of nitrotoluene (o:
p=41:59) was obtained. This result indicates that iodine liberated by the substitution reaction with nitrogen dioxide reacts with toluene to regenerate iodotoluene.

Claims (1)

[Claims] 1. An aromatic iodo compound selected from the group of mono- or diiodo compounds of benzenes or bicyclic compounds which may have a methyl group and nitrogen dioxide in an amount of 5 to 50 times the mole of the aromatic iodo compound in a solvent. 1. A method for producing an aromatic nitro compound, which comprises reacting with: