JPH0443891B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a novel method for producing aromatic fluorine compounds. More specifically, the present invention relates to a method for producing an aromatic fluorine compound, which comprises reacting a compound having a 1-fluorocyclohexene skeleton in the presence of a dehydrogenation catalyst and an aromatic nitro compound. (Prior art) Conventionally, aromatic fluorine compounds have been produced by thermally decomposing diazonium salts of anilines (Siemann method), or by using alkali metal fluoride to prepare chlorobenzene derivatives having electron-withdrawing substituents. Known methods include fluorine substitution (halogen exchange method), direct fluorination of benzenes with molecular fluorine, and simple dehydrogenation for compounds with relatively complex structures. However, these methods have drawbacks such as the use of expensive raw materials and the low yield of the desired product, an aromatic fluorine compound. In addition, since the Seeman method requires handling of solid diazonium which is unstable and easily decomposed, it is difficult to implement it industrially. The direct fluorination method is not only risky because it uses highly reactive molecular fluorine, but also produces many by-products. A simple dehydrogenation reaction for a relatively complex compound having a 1-fluorocyclohexene skeleton with an electron-withdrawing group as a substituent is known [for example, Petrov et al., Chemical Abstracts, Vol. 51, 7325g] (1957)]. (Problems to be Solved by the Invention) However, conventional dehydrogenation reactions have had problems such as low reaction selectivity. That is,
When a compound having a 1-fluorocyclohexene skeleton is subjected to a simple dehydrogenation reaction using a dehydrogenation catalyst, in addition to the target aromatic fluorine compound, unsaturated hydrocarbons are produced as a result of the cleavage of the carbon-fluorine bond. Compounds and saturated hydrocarbon compounds produced as a result of disproportionation reactions are produced as by-products. Hydrogen fluoride molecules are also generated due to the cleavage of carbon-fluorine bonds. Furthermore, the simple dehydrogenation method requires a high reaction temperature in order to improve the reaction rate, which further reduces the selectivity of the target compound. (Means for Solving the Problems) As a result of intensive research to find a new, homogeneous production method that does not have the above drawbacks, the present inventors have succeeded in producing fluorobenzene from unsubstituted 1-fluorocyclohexene. We have already applied for a patent (Japanese Patent Application No. 60-156949) for a completely new method that allows for In addition, we found that this method can be applied to 1-fluorocyclohexene derivatives having substituents other than 1-fluorocyclohexene, and even if these substituents exist, the fluoro group The inventors have discovered that the corresponding aromatic fluorine compounds can be produced in high yield and high selectivity without causing elimination of fluorine, and have completed the present invention. That is, the present invention provides general formula (I) (In the formula, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ are an alkyl group having 1 to 5 carbon atoms, an acyl group, which may be the same or different,
Indicates an alkoxycarbonyl group, an aryloxycarbonyl group, or a hydrogen atom. General formula () characterized by reacting a compound having a 1-fluorocyclohexene skeleton represented by ) in the presence of a dehydrogenation catalyst and an aromatic nitro compound (In the formula, R ₁ , R ₂ , R ₃ , R ₄ , and R ₅ are the same as above.)
The present invention relates to a method for producing an aromatic fluorine compound represented by: The feature of the present invention is that when dehydrogenating a compound having a 1-fluorocyclohexene skeleton to produce an aromatic fluorine compound, by coexisting a dehydrogenation catalyst and an aromatic nitro compound in the reaction system, it is possible to produce an aromatic fluorine compound by dehydrogenating a compound having a 1-fluorocyclohexene skeleton. Compared to the elementary method, the target compound can be obtained with extremely high selectivity and high yield. The compound having a 1-fluorocyclohexene skeleton used as a raw material has the general formula ()
Any known compound satisfying the above conditions can be used. For example, 1-fluorocyclohexene, methyl-1-fluorocyclohexene (each isomer),
Monoalkyl-1-fluorocyclohexene (each isomer) such as ethyl-1-fluorocyclohexene (each isomer), propyl-1-fluorocyclohexene (each isomer), dialkyl-1
- Polyalkyl-1-fluorocyclohexenes such as fluorocyclohexene (each isomer), trialkyl-1-fluorocyclohexene (each isomer), or acyl-1-fluorocyclohexene such as 4-acetyl-1-fluorocyclohexene Cyclohexene (each isomer), alkoxycarbonyl-1-fluorocyclohexene such as 4-methoxycarbonyl-1-fluorocyclohexene, and aryloxycarbonyl-1-fluorocyclohexene are preferably used. More preferably, 1-fluorocyclohexene and alkyl 4-fluorocyclohexene-3-carboxylate are used. The dehydrogenation catalyst used in the present invention is not particularly limited as long as it has dehydrogenation ability under the reaction conditions of the present invention. Preferably, at least one catalyst selected from platinum group metals such as palladium, platinum, ruthenium, nickel, cobalt, rhodium, osmium, and iridium and compounds containing platinum group elements is used. More preferably, at least one catalyst selected from palladium, platinum, ruthenium, and compounds containing palladium, platinum, and ruthenium is used. Examples of aromatic nitro compounds include nitrobenzene, dinitrobenzene (each isomer), nitrotoluene (each isomer), dinitrotoluene (each isomer), nitropyridine (each isomer), dinitropyridine (each isomer), Examples include nitronaphthalene (each isomer) and dinitronaphthalene (each isomer). In addition, in these aromatic nitro compounds,
At least one hydrogen has another substituent, such as a halogen atom, an amino group, a cyano group, an alkyl group,
It may be substituted with an alicyclic group, an aromatic group, an aralkyl group, an alkoxy group, a sulfoxide group, a sulfone group, a carbonyl group, an ester group, an amide group, or the like. Preferably, nitrobenzene and nitrotoluene (in each isomer) are used as aromatic nitro compounds. As the reaction mode, commonly used methods such as fluidized bed type, fixed bed type, or stirring type can be used. Further, either a flow method or a batch method may be used. Further, the reaction pressure is not particularly limited, and the compound having a 1-fluorocyclohexene skeleton used as a raw material may be in any of a liquid phase, a gas phase, or a gas-liquid mixed phase in the reaction system. As for the reaction temperature, a high temperature is advantageous from the viewpoint of safety of the dehydrogenation reaction and to improve the reaction rate, but a too high temperature is not preferable from the viewpoint of problems such as side reactions. In the present invention, the reaction temperature varies depending on the type of catalyst used and the reaction method used, but in the case of a gas phase reaction, it is usually 100 to 600
℃, preferably 200 to 500℃, and in the case of liquid phase reaction, usually room temperature to 400℃, preferably 50 to 50℃.
Performed at 300℃. The reaction time varies depending on the reaction temperature, type of catalyst, type of raw materials used, etc., but in the case of liquid phase reaction, it is usually 0.05 to 50 hours, preferably 0.1 to 20 hours.
Time is used. In the case of gas phase flow reaction,
Expressed in terms of contact time, usually 0.1 to 100 seconds, preferably 0.3 to 20 seconds is used. The quantitative ratio of the reaction raw materials to the catalyst can be varied over a wide range, and will also vary depending on whether the reaction format is continuous or batchwise. For example, in the case of a liquid phase batch system, the weight ratio of the catalyst to the reaction raw material is usually in the range of 0.0001 to 0.5, preferably in the range of 0.001 to 0.1. Although the quantitative ratio of the reaction raw material to the aromatic nitro compound varies depending on the desired raw material conversion rate, it is usually expressed as a molar ratio of the aromatic nitro compound to the reaction raw material, and is preferably 0.05 to 10. is 0.1
-2, more preferably 0.2-1 is used. Furthermore, even if gases such as water vapor, hydrogen, nitrogen, helium, argon, etc. are present in the reaction system as an atmosphere in addition to the reaction raw materials, such as the compound having a 1-fluorocyclohexene skeleton, the aromatic nitro compound, and the dehydrogenation catalyst. Often, an organic solvent inert to the dehydrogenation reaction may be present in the reaction system. (Example) Examples are shown below to specifically describe the present invention. Example 1 1-fluorocyclohexene 15.0g
(0.150 mol), 2.0 g of palladium black, and 14.8 g (0.120 mol) of nitrobenzene were placed in a 75 ml stainless steel pressure-resistant reaction tube that had been purged with argon gas in advance, and heated with shaking in an oil bath at 150°C for 7 hours. The reaction was allowed to take place. After cooling the reaction tube, the reaction mixture was analyzed by gas chromatography, and 10.8g (0.112mol) of fluorobenzene was found.
It was generating. Furthermore, 3.7 g (0.036 mol) of unreacted 1-fluorocyclohexene remained.
Furthermore, aniline was detected along with unreacted nitrobenzene. Table 1 shows the raw material conversion rate and fluorobenzene selectivity calculated from the above values. Examples 2 to 10 Example 1 except that the reaction conditions shown in Table 1 were used.
The dehydrogenation reaction was carried out in the same manner. The results are shown in Table 1. Comparative Example A dehydrogenation reaction was carried out under the same reaction conditions as in Example 6, except that no aromatic nitro compound was used. The results are shown in Table 1.

【table】

[Table] Example 11 Using 23.7 g (0.150 mol) of 4-methoxycarbonyl-1-fluorocyclohexene as a raw material,
The reaction was carried out in the same manner as in Example 1, except that the reaction time was 2 hours. Analysis of the reaction mixture by gas chromatography revealed that 6.9 g (0.048 mol) of methyl 4-fluorobenzoate was produced. In addition, unreacted 4-methoxycarbonyl-1
-15.8 g (0.100 mol) of fluorocyclohexene were present. The conversion rate of the dehydrogenation reaction was 33%, 4-
The selectivity for methyl fluorobenzoate was 96%. Example 12 4-Methyl-1-fluorocyclohexene 11.4
The reaction was carried out in the same manner as in Example 3, except that 4-fluorotoluene was used as the raw material. As a result, the addition rate of the raw material was 90%, the yield of 4-fluorotoluene was 88.2%, and the selectivity was 98%. Obtained with. Example 13 2-acetyl-1-fluorocyclohexene
The reaction was carried out in the same manner as in Example 3 except that 14.2 g (0.1 mol) was used as the raw material. As a result, the addition rate of the raw material was 95%, and the yield of 2-fluoroacetophenone was 91.2%. A rate of 96% was obtained. Example 14 The reaction was carried out in the same manner as in Example 1 except that 10.2 g (0.05 mol) of 2-phenoxycarbonyl-1-fluorocyclohexene was used as the raw material. As a result, the addition rate of the raw material was 40%. , phenyl 2-fluorobenzoate was obtained in a yield of 36% and a selectivity of 95%. (Effect of the invention) By the method of the present invention, 1-fluorocyclohexene having a 1-fluorocyclohexene skeleton,
and 1-fluorocyclohexene compounds having substituents, fluorobenzene and aromatic fluorine compounds having corresponding substituents can be produced in high yield,
It has become clear that high selectivity can be obtained.

Claims (1)

[Claims] 1 General formula (I) (In the formula, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ are an alkyl group having 1 to 5 carbon atoms, an acyl group, which may be the same or different,
Indicates an alkoxycarbonyl group, an aryloxycarbonyl group, or a hydrogen atom. General formula () characterized by reacting a compound having a 1-fluorocyclohexene skeleton represented by ) in the presence of a dehydrogenation catalyst and an aromatic nitro compound (In the formula, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ are an alkyl group having 1 to 5 carbon atoms, an acyl group, which may be the same or different,
Indicates an alkoxycarbonyl group, an aryloxycarbonyl group, or a hydrogen atom. ) A method for producing an aromatic fluorine compound represented by 2. The method according to claim 1, wherein the dehydrogenation catalyst is at least one selected from platinum group metals and compounds containing platinum metal elements. 3. The method according to claim 2, wherein the dehydrogenation catalyst is at least one selected from palladium, platinum, ruthenium, and a compound containing palladium, platinum, and ruthenium. 4. The method according to claim 1, wherein the aromatic nitro compound is nitrobenzene.