JPS6219540A - Production of aromatic fluorine compound - Google Patents

Abstract

PURPOSE:To produce the corresponding aromatic fluorine compound in high yield and selectivity, by reacting a compound having the 1-fluorocyclohexene skeleton in the coexistence of an aromatic nitro compound in the presence of a dehydrogenation catalyst. CONSTITUTION:A compound having the 1-fluorocyclohexene skeleton expressed by formula I (R1-R5 are 1-5C alkyl, acyl, alkoxycarbonyl, aryloxycarbonyl or H), e.g. 1-fluorocyclohexene, is reacted in the coexistence of an aromatic nitro compound, e.g. nitrobenzene or nitrotoluene, preferably at 0.2-1 molar ratio based on the reaction raw material in the presence of a dehydrogenation catalyst, particularly preferably at least one selected from compounds containing Pd, Pt or Ru to afford the aimed aromatic fluorine compound expressed by formula II, e.g. fluorobenzene.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a novel method for producing aromatic fluorine compounds.

More specifically, 1-fluorocyclohexene skeleton 'f
The present invention relates to a method for producing an aromatic fluorine compound, which is characterized by reacting a compound represented by v in the presence of a dehydrogenation catalyst and an aromatic nitro compound.

(Prior art) Conventional methods for producing aromatic fluorine compounds include a method of thermally decomposing diazonium salts of anilines (Ziemann method),
A method for substituting chlorobenzene conductors with electron-withdrawing substitution funds with fluorine using an alkali metal fluoride (halogen exchange method), direct fluorination of benzenes with molecular fluorine, or a simple method for compounds with relatively complex structures. Dehydrogenation methods and the like are known.

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, the Zieman method requires the handling of unstable and easily decomposed solid diazonium, which is difficult to implement industrially, while the direct fluorination method is extremely reactive. It is not only dangerous in that it uses highly sensitive molecular fluorine, but also has 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, 7525].
9 (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, there are Saturated hydrocarbon compounds and saturated hydrocarbon compounds produced as a result of disproportionation reactions are produced as by-products. Well, due to the cleavage of the carbon-fluorine bond, hydrogen fluoride molecules are generated. Ninth, the simple dehydrogenation method requires a high reaction temperature 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 production method that does not have the above drawbacks, the present inventors have succeeded in producing fluorobenzene from unsubstituted 1-fluorocyclohexene. As a result of further investigation, we found that by coexisting an aromatic nitro compound in this system, the yield and selectivity of fluorobenzene were dramatically increased. When they found that this method improved, they found that this method could also be applied to 1-fluorocyclohexene derivatives having substituents other than co-K and 1-fluorocyclohexene, and that the corresponding aromatic fluorine compounds could be produced with high yield and high selectivity. This discovery led to the completion of the present invention.

That is, the present invention relates to the general formula 〇) (wherein R1m'R* -Rs 5R4-R1 is an alkyl group having 1 to 5 carbon atoms, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, which may be the same or different. or a hydrogen atom) is reacted with a compound having a 1-fluorocyclohexene + group ab in the presence of a dehydrogenation catalyst and an aromatic nitro compound (wherein Rs mR
s mRs #R4*R1 is 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 a compound having a 1-fluorocyclohexene skeleton is dehydrogenated to produce an aromatic fluorine compound tM.
To:2. t)b When a dehydrogenation catalyst and an aromatic nitro compound coexist in the reaction system, the target compound can be obtained with extremely high selectivity and high yield compared to the conventional simple dehydrogenation method. be.

As the compound having a 1-fluorocyclohexene skeleton used as a raw material, all known compounds having the above general formula (D) can be used.

Examples, jjtf, 1-fluorocyclohexene, methyl-
1-fluorocyclohexene (each isomer), ethyl-1
-Fluorocyclohexene (each isomer), propyl-1
- Monoalkyl-1-fluorocyclohexene (each isomer) such as fluorocyclohexene (each JI isomer), dialkyl-1-fluorocyclohexene (each isomer), trialkyl-1-fluorocyclohexene (each isomer) polyalkyl-1-fluorocyclohexene such as body) a.

Al in is acyl-1-fluorocyclohexene (each isomer) such as 4-acetyl-1-fluorocyclohexene
Flucoxycarbonyl-1-fluorocyclohexenes 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 may be any catalyst that has dehydrogenation ability under the reaction conditions of the present invention, and is not specified in terms of percentage. A catalyst of at least 18I selected from platinum group metals such as , rhodium, osmium, 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 n-mer), nido' ) k
-7 (each n-mer), -) nitrotoluene (each isomer), nitropyridine (each isomer), dinitropyridine (
(isomers), nitronaphthalene (isomers), and dinitronaphthalene (isomers).

Furthermore, in these aromatic nitro compounds, at least 4.1 hydrogen atoms are substituted by other substituents, such as halogen atoms,
b may be substituted with an amino group, a cyano group, an alkyl group, 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 the aromatic nitro compounds.

As for the reaction mode, commonly used methods such as fluidized bed type, fixed bed type, or stirred ring type can be used. It may be a continuous method, a flow method, or a batch method.

[L reaction pressure is not particularly limited, and 1-
The compound having a fluorocyclohexene skeleton may be in a liquid phase, a gas phase, or a gas-liquid mixed phase in the reaction system.

A high reaction temperature is advantageous from the viewpoint of equilibrium of the dehydrogenation reaction and to improve the reaction rate, but a relatively high temperature is not preferred due to 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 60%, preferably 200 to 50%.
oC7, and in the case of liquid phase reactions, it is usually room temperature to 4
00C, preferably 50-300C.

In addition, the reaction time varies depending on the reaction temperature, type of catalyst, type of raw materials used, etc., but in the case of a liquid phase reaction, it is usually 0.
．． 05 to 50 hours, preferably 0.1 to 20 hours. In the case of a gas phase flow reaction, the contact time is expressed as 1, usually Q, 1 to 100 seconds, preferably 0.5 to 20 seconds.
Seconds are used.

The quantitative ratio of the reaction raw material to the catalyst can be varied over a wide range of 8, and it also depends on whether the reaction format is continuous or batchwise. For example, in the case of a liquid phase batch method,
Usually expressed as a weight ratio of catalyst to reaction raw materials, 0.
A range of 0001 to 0.5 is used, preferably 00.
It is used in the range of 001 to 0.1.

The quantitative ratio of the reaction raw material to the aromatic nitro compound varies depending on the desired conversion rate of the raw material, but is expressed as the molar ratio of the aromatic nitro compound to the reaction raw material.

Usually 0.05 to 10 is used, preferably 0.1 to 10.
2, more preferably 0.2 to 1.

Additionally, in addition to the reaction raw materials, a compound with a 1-fluorocyclohexene skeleton, an aromatic nitro compound, and a dehydrogenation catalyst, gases such as water vapor, hydrogen, nitrogen, helium, and argon are present in the reaction system as an atmosphere. Alternatively, an organic solvent inert to the dehydrogenation reaction may be present in the reaction system.

(Example) EXAMPLES The present invention will be specifically described with reference to Examples below.

Example 1 1-Fluorocyclohexene 15. Of (0,150
mol ) and palladium black 2. Of, h and 14.8 f (0.120 mot) of nitropenzea were charged into a 75 d capacity stainless steel pressure-resistant reaction tube which had been purged with argon gas in advance, and heated with shaking in a 150 c oil bath for 7 hours. I made it. After cooling the reaction tube, the reaction mixture was analyzed by gas chromatograph 2F method, and as a result, 10.89 (0.112 moA) of fluorobenzene was produced. Further, 5.7 t (0,036 mol) of unreacted 1-fluorocyclohexene remained. Furthermore, 7 nilines were detected along with 1 unreacted nitrobenzene.

The conversion rate of the raw material and the selectivity of fluorobenzene calculated from the above values are shown in Table Is1.

Examples 2 to 10 Dehydrogenation reactions were carried out in the same manner as in Example 1, except that the reaction conditions shown in Table 1 were used. 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.

Example 11 A reaction was carried out in the same manner as in Example 1, except that 25,7 t (0,150 mot) of 4-methoxycarbonyl-1-fluorocyclohexene was used as the raw material and the reaction time was t-2 hours. Analysis of the reaction mixture by gas chromatograph 2F method revealed that 6.9 f (0,048 mol) of methyl 4-fluorobenzoate was produced. Also, 15.8 ? of unreacted 4-methoxycarbonyl-1-fluorocyclohexene? (0,100mot) existed. The conversion rate of the dehydrogenation reaction was 55%, and the selectivity of methyl 4-fluorobenzoate was 96%.

(Effects of the Invention) As in the present invention, a compound having a 1-fluorocyclohexene skeleton represented by the general formula (D) is dehydrogenated to develop an aromatic fluorine compound, a dehydrogenation catalyst, and an aromatic compound. Compared to the conventional simple dehydrogenation method, since nitro compounds are allowed to coexist in the reaction system.

The target compound can be obtained with extremely high selectivity.

Claims (4)

[Claims] (1) General formula (I) ▲There are mathematical formulas, chemical formulas, tables, etc.▼(I) (In the formula, R_1, R_2, R_3, R_4, R_5 are alkyl groups having 1 to 5 carbon atoms, which may be the same or different, acyl group, alkoxycarbonyl group, aryloxycarbonyl group, or a hydrogen atom) in the presence of a dehydrogenation catalyst and an aromatic nitro compound. Formula (II) ▲Mathematical formulas, chemical formulas, tables, etc.▼(II) A method for producing an aromatic fluorine compound represented by a carbonyl group, an aryloxycarbonyl group, or a hydrogen atom. (2) The method according to claim 1, wherein the dehydrogenation catalyst is at least a species 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 a species selected from palladium, platinum, ruthenium, and compounds containing palladium, platinum, and ruthenium. (4) The method according to claim 1, wherein the aromatic nitro compound is nitrobenzene.