JPH03106838A - Production of fluorobenzene - Google Patents

Abstract

PURPOSE:To continuously obtain the subject substance by adding aniline and a nitrous acid donor to anhydrous HF, diazotising at specific temperature, continuously feeding the resultant diazonium salt into a reaction vessel with overflow and pyrolytically decomposing at specific temperature. CONSTITUTION:Aniline and a nitrous acid donor (e.g. NaNO2) are added to anhydrous HF and reacted at 10 deg.C to -40 deg.C (preferably from -10 deg.C to -40 deg.C), then the resultant diazonium salt is pyrolytically decomposed at 30-84.7 deg.C to continuously obtain fluorobenzene. The pyrolytical decomposition is performed for 30-120min using a solution containing fluorobenzene and/or 60-90wt.% HF as a heating medium in a reaction vessel 4 having condenser 6, stirrer 5, overflow pipe 7 and extracting valve 8. Reacting solution is introduced to cooling tank 10 through overflow pipe 7. By said method, the aimed substance is able to be safely mass produced in a low cost without runaway nor clogging, etc., in the reaction.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for producing fluorobenzene.

Furthermore, in recent years, fluorobenzene has been widely used as a starting material for agricultural chemicals, medicines, organic chemicals, dyes, etc. [Prior art] The method for synthesizing fluorobenzene involves adding aniline in an anhydrous hydrogen fluoride solvent, then adding a nitrous acid-imparting agent to diazotize it, producing a diazonium salt, which is then thermally decomposed. So-called diazotization and dediazofluorination reactions have been known for a long time. However, in general, the diazotization reaction is carried out at a low temperature and forms a diazonium salt, and the thermal decomposition reaction of the diazonium salt is carried out at a relatively high temperature.Currently, most of these reactions are carried out using the Basoti method. ing. [Problems to be solved by the invention] Conventional batch production methods are not only disadvantageous in terms of industrial costs but also unsuitable for mass production, so a continuous method is desired. As mentioned above, in the continuous production method of fluorobenzene, since there is a temperature difference between the diazotization reaction and the thermal decomposition reaction of the diazonium salt produced by diazotization, continuous production requires control of the reaction temperature, There were problems with yield, etc., and it was extremely difficult to solve these problems.

One of the conventional continuous methods is a manufacturing method called a pipe reactor. The production method using a pipe reactor includes a method in which diazotization and thermal decomposition of the diazonium salt are carried out continuously, and a method in which only the diazonium salt is produced continuously (Japanese Patent Application Laid-Open No. 62-53935). However, in both methods, it is difficult to control the temperature of the diazotization reaction and thermal decomposition of the diazonium salt, so runaway reactions are likely to occur, and there are problems such as blockage in the pipe. Furthermore, the following method is disclosed as one of the continuous methods. That is, sodium nitrite and aniline are each dissolved in hydrofluoric anhydride to form an aqueous solution of each, and the aqueous solutions are mixed in small quantities and the diazotization reaction and thermal decomposition of the diazonium salt are simultaneously carried out at a reaction temperature of 40°C. There is a method (Japanese Patent Publication No. 53-14057), but the experimental results conducted by the present inventors showed a low yield of 50 to 60%, and the expected results could not be obtained. [Means for Solving the Problems] In order to solve these problems, the present inventors, as a result of intensive studies, added aniline and a nitrite-imparting agent to anhydrous hydrogen fluoride and performed a diazotization reaction. They discovered that diazonium salts can be produced and the diazonium salts can be continuously thermally decomposed, leading to the completion of the present invention. That is, aniline and lI1l1 acid imparting agent are added to anhydrous hydrogen fluoride, and the resulting diazonium salt is reacted at a reaction temperature of 10 to -40°C, and the resulting diazonium salt is continuously fed into a reaction vessel with an overflow. This is a method for producing fluorobenzene by thermally decomposing the temperature of the heating medium at 30 to 84.7°C, and further, the heating medium used in the reaction vessel with an overflow contains fluorobenzene and/or at least The present invention provides a method for producing fluorobenzene, characterized in that the solution contains 60 to 90% by weight of hydrogen fluoride. [Detailed Disclosure of the Invention] The present invention will be explained in more detail. In the diazotization method of the present invention, aniline is added to anhydrous hydrogen fluoride at a reaction temperature of 10 to -40°C to produce aniline hydrofluoride. The molar ratio of aniline and anhydrous hydrogen fluoride in this case is 1
:10 to 1:40, preferably 1:15 to 1:20. Once the aniline hydrofluoride has been used, a nitrite-imparting agent, such as sodium nitrite, is added to diazotize the mixture.

This reaction formula is shown in the following formula.

That is, CaHsNHz + 20HF + NaNOz →
C, II, NmiNF + NaFHF + 211zO
+ 17HF-・-(1)C6! IsN=NF-DC
611SF + L 1・・−1−−−−−−−−−
1...(2) The above formula (1) is the diazotization reaction when 20 moles of anhydrous hydrogen fluoride is used, and the formula (2) is the formula (1).
This reaction process produces fluorobenzene by thermally decomposing the diazonium salt obtained by the reaction according to the formula. Any ice-free hydrofluoric acid and aniline used here may be used as long as they are normally used industrially. A normal diazotization agent is used as the nitrite imparting agent. For example, sodium nitrite, potassium nitrite, alkyl nitrite, nitrosyl halides, and the like are preferably used. More than one of these groups can be selected and added, but it is preferable to use sodium nitrite and potassium nitrite in terms of cost. The molar ratio of the nitrite-imparting agent and aniline is 1:1 to 1:
1.2 is optimal. The temperature during diazotization is 10 to -40°C, preferably -
A temperature of 10 to -20°C is suitable. When the temperature exceeds 10°C, NOx and N2 gases are generated simultaneously with the addition of the nitrite-imparting agent, making it unsuitable for diazotization.

Further, if the temperature is below -40°C, the nitrite-imparting agent becomes unreacted, which is also not preferable. As described above, in the method of producing a diazonium salt by diazotization, it is also possible to produce it continuously if the reaction temperature and molar ratio meet the above conditions. Thus, the mixed solution of anhydrous hydrogen fluoride, aniline, and nitrite-imparting agent charged in the reaction vessel may be stirred and reacted as is, but in order to prevent oxidation, the anhydrous fluoride charged in the reaction vessel may be stirred and reacted as is. It is more preferable to stir and react while blowing nitrogen gas into the mixture of hydrogen, aniline, and nitrite-imparting agent, or while flowing nitrogen gas into the gas phase of the reaction vessel. Next, thermal decomposition of the diazotized diazonium salt will be explained.

As described above, aniline and a nitrous acid-imparting agent are added to anhydrous hydrogen fluoride and reacted at a reaction temperature of 10 to -40°C to effect diazotization.

The decomposition temperature of the obtained diazonium salt is 30-84.7°C
Thermal decomposition is carried out at a temperature of, preferably 40 to 50°C.

Below 30″C, the rate of dediazo thermal decomposition is slow, and
If the temperature exceeds 84.7°C, the boiling point of the produced fluorobenzene is 84.7°C, which significantly reduces the yield. Therefore, it is preferable to carry out the thermal decomposition at a temperature below the boiling point of the fluorobenzene. Next, regarding the thermal decomposition of diazonium salt, according to Figure 1,
I will explain in detail. The thermal decomposition of the diazonium salt of the present invention uses a reaction vessel 4 having a condenser 6, stirring [5], an overflow tube, and a withdrawal valve 8. In addition, since the reaction vessel 4 needs to be heated, the exterior thereof is of a heating coil type or a jacket type. The heating medium filled in the reaction vessel 4 includes fluorobenzene and/or a 60 to 90% by weight aqueous hydrogen fluoride solution, and hydrogen fluoride (hereinafter referred to as HF) obtained by thermally decomposing the diazonium salt. Also, by-products, fluorobenzene, and mixtures thereof may be used. Here, the heating medium refers to a solution that is added to the reaction vessel 4 before the start of thermal decomposition to facilitate the start of the reaction. In order to thermally decompose the diazonium salt, it is necessary to place a heat medium in the reaction vessel 4 and heat it to 30 to 84.7°C while stirring. The above-mentioned diazonium salt is re-fed into the reaction vessel 4 from the reaction vessel 1 through the feed pipe 3 using the liquid sending pump 2. The average residence time in the reaction vessel 4 varies depending on the feed speed and temperature of the diazonium salt, but ranges from lO to 300
minutes, preferably 30 to 120 minutes. Therefore, depending on the case, it is also possible to connect two or three reaction vessels 4 to increase reaction and residence time.

IIF in which the heating medium is obtained by thermal decomposition of a diazonium salt
Stirring is done a little faster so that the mixture of by-products and fluorobenzene becomes uniform. By adding the diazonium salt, the reaction solution passes through the overflow pipe 7 and enters the cooling tank l.
Guided by O. The temperature of the cooling tank 10 is not particularly limited, but is preferably 10"C or less. Also, the generated nitrogen gas is discharged through the cooling pipe 6. [Example] The following is an example. The present invention will be specifically described. Example 1 A jacket-type 3L stainless steel vessel equipped with a stirrer, a cooling condenser, a sample inlet, and a nitrogen gas inlet (hereinafter, other reaction vessels, a cooling condenser, and a stirring All blades, pumps, pipelines, etc. are made of stainless steel) Reaction vessel 1 is used, and jacket and cooling condenser -2 are used.
It was cooled by circulating a 0°C refrigerant. 1,600 g (80 mol) of anhydrous hydrogen fluoride was placed in reaction vessel 1 and heated to -15 with stirring.
Cooled to ℃. Next, 372 g (4 moles) of aniline was gradually added so that the internal temperature did not exceed -10°C to produce aniline fluoride salt. Further, 276 g (4 mol) of dried sodium nitrite powder was added while keeping the internal temperature at -10°C, and diazotization was performed by stirring for about 2 hours. The temperature of the diazotized solution after the reaction is -20
It was kept at ℃. During this time, 30 Id/w of nitrogen gas was added to the gas phase inside the reaction vessel l.
The reaction was carried out while flowing in to prevent oxidation. In order to continuously thermally decompose the diazotized diazonium salt, a 0.52 jacketed reaction vessel 4 equipped with a stirrer 5, a cooling condenser 6, and an overflow pipe 7 is used. The composition of IIF and by-products when diazonium salt is thermally decomposed, i.e. 300 g of HF (
15 mol), 31.5 g (0.75 mol) of NaP, and 27 g (1.5 mol) of Hz0 were added and the mixture was heated using turbine blades to mix the entire liquid uniformly.
Stirred at rpm. The temperature of the heat medium in the reaction vessel 4 is set to 40°C.
I added warm water to the jacket to keep it warm.
In addition, -20°C refrigerant was circulated in the cooling condenser 6. After confirming that the temperature of the reaction vessel 4 has reached 40°C, the above-mentioned diazonium salt is added to the reaction vessel 4 at a rate of 4d/sin.
It was dripped into. About 10 minutes after dropping, overflow began to flow from overflow tube 7. The overflowing liquid was led to a 0.5 ffi cooling tank 10 and cooled. The liquid was extracted from valve 11 every hour and analyzed. The reaction of fluorobenzene reached a nearly steady state in about 1.5 hours after the diazonium salt was dropped into the reaction vessel 4, and the reaction continued for about 7 hours.
Manufacturing was carried out continuously over time. As a result, the yield of fluorobenzene was as high as 82% based on aniline.
Example 2 Everything was carried out in accordance with Example 1, except that the diazotization temperature, the feed amount of diazonium salt, and the temperature of the heat medium were carried out under the conditions shown in Table 1. As a result, the yield of fluorobenzene was as shown in Table 1. Comparative Examples 1 to 2 All procedures were carried out in accordance with Example 1, except that the diazotization temperature, the feed amount of diazonium salt, and the temperature of the heating medium were carried out under the conditions shown in Table 1. As a result, the yield of fluorobenzene was as shown in Table 1. When the diazotization temperature is as high as 20°C (Comparative Example 1)
), or when the temperature of the heating medium was low (Comparative Example 2), the yield was found to be low. [Effects of the Invention] As explained in detail above, the present invention involves adding aniline and a nitrite-imparting agent to anhydrous hydrogen fluoride, diazotizing it at a specific temperature, and continuously transferring the obtained diazonium salt to a reaction vessel with an overflow. fluorobenzene is continuously produced at a specific temperature. This invention overcomes the problems that are most concerning in continuous production, such as runaway and blockage during the reaction in conventional techniques, and makes it possible to obtain fluorobenzene in high yield. In addition, not only is the production cost significantly lower than that of the batch method, but it also enables safe mass production and provides inexpensive fluorobenzene, which is a great industrial advantage, and the present invention has great significance.

[Brief explanation of drawings]

In Figure 1, l 1-11 reaction vessel, 2-...1.Liquid pump, 3---Feed pipe, 4-11...reaction container, 5-.1. Stirring blade, 6.111111 capacitor 7...1 Overflow pipe, 8-----Liquid drain valve, 9-...One-liquid extraction pipe, 10-----Cooling tank, 1l-・1・-・Liquid drain valve, l2, l3-... cooling tank,

Claims (1)

[Claims] 1) Aniline and a nitrite-imparting agent are added to anhydrous hydrogen fluoride, and the resulting diazonium salt is reacted at a reaction temperature of 10 to -40°C, and the resulting diazonium salt is continuously fed into a reaction vessel with an overflow. A method for producing fluorobenzene, characterized in that the temperature of the heat medium in the reaction vessel with an overflow is maintained at 30 to 84.7°C for thermal decomposition. 2) The heat medium used in the reaction vessel with overflow is
Process according to claim 1, characterized in that the solution contains fluorobenzene and/or at least 60 to 90% by weight of hydrogen fluoride.