JPH0584289B2 - - 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 aromatic fluorine compounds, which comprises oxidatively dehydrogenating a compound having a 1-fluorocyclohexene skeleton in the presence of a dehydrogenation catalyst and molecular oxygen. (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. Furthermore, the Seeman method requires the handling of solid diazonium salts that are unstable and easily decomposed, making it difficult to implement 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 various 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 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 for a completely new method that allows for this, but after further investigation, we found that by coexisting an aromatic nitro compound in this system, the yield and selectivity of fluorobenzene were dramatically improved. Along with discovering things,
They also discovered that this method can be applied to 1-fluorocyclohexene derivatives having substituents other than 1-fluorocyclohexene, and that the corresponding aromatic fluorine compounds can be produced in high yield and high selectivity, and have previously applied for a patent. The present inventors conducted further research on this new reaction that can produce the corresponding aromatic fluorine compound from a compound having a 1-fluorocyclohexane skeleton. We have discovered a method that can produce the desired aromatic fluorine compound with high yield and high selectivity, and have completed the present invention. That is, the present invention provides at least one compound selected from platinum group metals and compounds containing platinum group elements.
In the presence of a species dehydrogenation catalyst and molecular oxygen, the general formula ()

[Formula, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ are alkyl groups having 1 to 5 carbon atoms, acyl groups, which may be the same or different,
Indicates an alkoxycarbonyl group, an aryloxycarbonyl group, or a hydrogen atom. ) General formula () characterized by dehydrogenating a compound having a 1-fluorocyclohexene skeleton represented by

The present invention relates to a method for producing an aromatic fluorine compound represented by the following formula: (wherein R ₁ , R ₂ , R ₃ , R ₄ , and R ₅ are the same as above). A feature of the present invention is that aromatic fluorine compounds are produced by oxidatively dehydrogenating a compound having a 1-fluorocyclohexene skeleton with molecular oxygen. Although this method was completely unknown until now, it is characterized by the ability to obtain the target compound with extremely high selectivity and high yield compared to conventional simple dehydrogenation methods. be. The compound having a 1-fluorocyclohexene skeleton used as a raw material may be any compound as long as it satisfies the above general formula (). For example, monoalkyl-1-fluorocyclohexene, methyl-1-fluorocyclohexene (each isomer), ethyl-1-fluorocyclohexene (each isomer), propyl-1-fluorocyclohexene (each isomer), etc. Cyclohexene (each isomer), dialkyl-1-fluorocyclohexene (each isomer),
Polyalkyl-1-fluorocyclohexenes such as trialkyl-1-fluorocyclohexene (each isomer), or acyl-1-fluorocyclohexene (all isomers) such as 4-acetyl-1-fluorocyclohexene, 4- Alkoxycarbonyl-1-fluorocyclohexenes such as methoxycarbonyl-1-fluorocyclohexene and aryloxycarbonyl-1-fluorocyclohexene are preferably used. More preferably, 1-fluorocyclohexene and alkyl 4-fluorocyclohexene-3-carboxylate are used. Such a compound having a 1-fluorocyclohexene skeleton may be produced by any method. The dehydrogenation catalyst used in the present invention includes palladium, platinum, ruthenium, nickel,
At least one catalyst selected from platinum group metals such as cobalt, rhodium, osmium, and iridium and compounds containing platinum group elements is used. Preferably, at least one catalyst selected from palladium, platinum, ruthenium, and compounds containing palladium, platinum, and ruthenium is used. In addition, these catalyst components include activated carbon, graphite, silica, alumina, and silica.
Alumina, silica-titania, titania, zirconia, barium sulfate, calcium carbonate, asbestos, bentonite, diatomaceous earth, polymer, ion exchange resin, zeolite, molecular sieve,
It may be supported on a carrier such as magnesium silicate or magnesia. As platinum group elements in the metallic state, for example, metals such as palladium, rhodium, platinum, ruthenium, iridium and osmium;
Catalytic components containing these metal ions are supported on the above-mentioned carrier and then reduced with hydrogen, formaldehyde, hydrazine, etc., and alloys or intermetallic compounds containing these metals are used. Further, the alloy or intermetallic compound may be one of these platinum group metals, or may be one of these platinum group metals, or may contain other elements such as selenium, tellurium, sulfur, antimony, bismuth, copper, silver, gold, zinc,
It may contain tin, vanadium, iron, cobalt, nickel, mercury, lead, thallium, chromium, molybdenum, tungsten, and the like. On the other hand, examples of compounds containing platinum group elements include halides, sulfates, nitrates, phosphates,
Inorganic salts such as borates; acetates, oxalates,
Organic acid salts such as formates; cyanides; hydroxides; oxides; sulfides; metal acid salts containing anions such as nitro groups, cyano groups, halogens, oxalate ions, and ammonia, amines, Examples include metal complex compounds such as salts or complexes containing phosphines, carbon monoxide, chelate ligands, etc.; organometallic compounds having organic ligands or organic groups; and the like. Further, the molecular oxygen used in the present invention is pure oxygen or a substance containing oxygen, and may be air, or other gases that do not inhibit the reaction with air or pure oxygen, such as nitrogen, argon,
It may be diluted by adding an inert gas such as helium or carbon dioxide. In some cases, the gas may also contain gases such as hydrogen, carbon monoxide, hydrocarbons, and halogenated hydrocarbons. 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. When the reaction is carried out in a liquid phase, it may be carried out in the presence of a solvent inert to the reaction. Particular preference is given to carrying out the reaction in the gas phase. The reaction temperature is determined from the viewpoint of equilibrium of the dehydrogenation reaction, and
Although high temperatures are advantageous in order to improve the reaction rate, too high temperatures are 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 80 -
It is carried out at 500°C, preferably 90 to 400°C, and in the case of liquid phase reaction, it is usually carried out at room temperature to 400°C, preferably 50°C.
Performed at ~300°C. 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 as a contact time, usually 0.01 to 600 seconds, preferably 0.1 to 200 seconds is used. The quantitative ratio of the compound having a 1-fluorocyclohexene skeleton used as a raw material and the catalyst can be set over a wide range. For example, in the case of a liquid phase batch system, the weight ratio of the catalyst to the reaction raw materials is usually used, and is preferably in the range of 0.0001 to 10.
Used in the range 0.001 to 0.5. Also, for example,
In the case of a gas phase flow reaction, the reaction is carried out using a catalyst amount and a flow rate such that the contact time as described above is satisfied. The reaction of the present invention is represented by the following formula.

(In the formula, R ₁ , R ₂ , R ₃ , R ₄ , and R ₅ are the same as above.) Therefore, it is possible to use molecular oxygen in an amount equal to or more than the amount of the compound having a 1-fluorocyclohexene skeleton. Although necessary to increase the reaction rate,
Of course, it may be less. Additionally, the reaction system should be operated so that it is outside the explosive limits. In addition to the compound having a 1-fluorocyclohexene skeleton, molecular oxygen, and dehydrogenation catalyst as reaction raw materials, a gas such as water vapor, hydrogen, nitrogen, helium, or argon may be present in the reaction system as an atmosphere. An organic solvent inert to the dehydrogenation reaction or its vapor may be present in the reaction system. (Example) Examples are shown below to specifically describe the present invention. Example 1 Pellets of Pd/SiO ₂ 10 supporting 1% palladium were placed in a glass tubular reactor with an inner diameter of 1.5 cm.
g and heated. 1-fluorocyclohexene was introduced into the reactor at a flow rate of 8 g/h. At the same time, air was introduced at a flow rate of 90 ml/min and nitrogen at a flow rate of 180 ml/min. The reaction was carried out at a temperature range of 140-150°C. After reaching a steady state, the reaction products were collected with a dry ice trap and analyzed by gas chromatography. As a result, the reaction rate of 1-fluorocyclohexene was 100%, and the yield of fluorobenzene was 85%. It was generated at a rate of 85%. The product was identified by gas chromatography and GC-MS. Example 2 A reactor similar to Example 1 was filled with 5 g of Pd/SiO ₂ supporting 1% palladium and heated. 8 1-fluorocyclohexene was added to this reactor.
Oxygen and nitrogen each at a flow rate of 31 g/h
ml/min and a flow rate of 200 ml/min. The reaction was carried out at a temperature range of 155-160°C. The reaction result is that the reaction rate of 1-fluorocyclohexene is 100
%, fluorobenzene yield 88%, selectivity 88%
It was generated with . Example 3 The reaction was carried out in the same manner as in Example 2, except that the amount of catalyst was 2.5 g and the reaction temperature was 180 to 190°C. As a result, the reaction rate of 1-fluorocyclohexene was
At 95%, fluorobenzene yield was 87% and selectivity was 92.
It was generated in %. Example 4 The dehydrogenation reaction of 1-fluorocyclohexene was carried out in the same manner as in Example 2 except for using 5 g of Pt/C in which 2% platinum was supported on activated carbon.
-The reaction rate of fluorocyclohexene was 48%, and fluorobenzene was produced with a yield of 41% and a selectivity of 85%. Example 5 Ru/2% ruthenium supported on alumina
The reaction was carried out in the same manner as in Example 2 except that 10 g of Al ₂ O ₃ was used. As a result, the reaction rate of 1-fluorocyclohexene was 35%, and the yield of fluorobenzene was 35%.
28%, with a selectivity of 80%. Example 6 23.7 g of 4-methoxycarbonyl-1-fluorocyclohexene and 1 g of palladium black were placed in a flask and heated to 140 to 150°C. A mixed gas of nitrogen and oxygen containing 5% oxygen is added to the liquid at the bottom of this reactor.
It was introduced at a flow rate of 250 ml/min. Analysis of the reaction solution after 6 hours revealed that 4-methoxycarbonyl-1-
The reaction rate of fluorocyclohexene was 35%, and 4-
Methyl fluorobenzoate yield 31%, selectivity 90%
It was generated with . Example 7 The reaction was carried out in the same manner as in Example 1 except that 1-fluoro-2-methylcyclohexene was used instead of 1-fluorocyclohexene. As a result, 2-fluorotoluene was produced in a yield of 82% and a selectivity of 88.
Obtained in %. Example 8 A reaction was carried out in the same manner as in Example 6, except that 20 g of 4-acetyl-1-fluorocyclohexene was used instead of 4-methoxycarbonyl-1-fluorocyclohexene. As a result, 4-fluoroacetophenone was produced. Obtained with a yield of 40% and selectivity of 89%. Example 9 4-phenoxycarbonyl- instead of 4-methoxycarbonyl-1-fluorocyclohexene
The reaction was carried out in the same manner as in Example 6 except that 30 g of 1-fluorocyclohexene was used. As a result, phenyl 4-fluorobenzoate was produced in a yield of 30%.
A selectivity of 85% was obtained. (Effect of the invention) As is clear from the examples, according to the present invention,
The desired aromatic fluorine compound can be produced with high yield and high selectivity.

Claims (1)

[Scope of Claims] 1. In the presence of at least one dehydrogenation catalyst selected from platinum group metals and compounds containing platinum group elements and molecular oxygen, ₁ , R ₂ , R ₃ , R ₄ , and 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. ) [Formula] (where R ₁ , R ₂ , R ₃ , R ₄ , R ₅ are the same as above) .)
A method for producing an aromatic fluorine compound shown in