Process for producing trifluoromethylbenzylamines

Details Process for producing trifluoromethylbenzylamines Process for producing trifluoromethylbenzylamines

2000-03-07

2001-01-16

Barts, Samuel (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Amino nitrogen containing

C564S389000, C564S390000, C564S391000

Reexamination Certificate

active

06175041

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a process for producing aromatic primary amines having a trifluoromethyl group that are useful in the pharmaceutical and agricultural chemical fields.
Numerous processes for obtaining primary amines by hydrogenation of nitrile compounds have been reported. In addition numerous processes for obtaining primary amines of fluorine-containing aromatics from fluorine-containing aromatic nitrile compounds have also been reported. However, in these known processes, in the case of attempting to obtain primary amines by hydrogenation of nitrile compounds having a trifluoromethyl group, there is a remarkable decrease in selectivity and the following purification steps by distillation and so forth are extremely bothersome, thereby making it difficult to carry out these processes industrially.
Processes for obtaining aromatic primary amines having a trifluoromethyl group from aromatic nitrile compounds having a trifluoromethyl group have problems that remain to be solved, and an industrially useful process for producing aromatic primary amines having a trifluoromethyl group has yet to be established.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a process for producing a trifluoromethylbenzylamine easily and inexpensively.
According to the present invention, there is provided a process for producing a trifluoromethylbenzylamine represented by the following general formula (1). This process comprises hydrogenating a trifluoromethylbenzonitrile represented by the following general formula (2) by hydrogen in an organic solvent in the presence of ammonia, using a Raney catalyst,
where each R independently represents a halogen selected from the group consisting of fluorine, chlorine, bromine and iodine, an alkyl group having a carbon atom number of 1-4, an alkoxy group having a carbon atom number of 1-4, an amino group, a hydroxyl group or a trifluoromethyl group, and n represents an integer from 0 to 4,
where R and n are defined as above. With this process, it is possible to obtain the trifluoromethylbentylamine at an extremely high yield.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The trifluoromethylbenzonitrile represented by the general formula (2) used in the present invention is a benzonitrile having at least one trifluoromethyl group. This benzonitrile may also have a substituent group that is inactive under the conditions of the hydrogenation of the present invention. Examples of such substituent group include halogens (i.e., fluorine, chlorine, bromine and iodine), alkyl groups each having a carbon atom number of 1-4, alkoxy groups each having a carbon atom number of 1-4, amino groups, hydroxyl groups and trifluoromethyl groups. Specific examples of the trifluoromethylbenzonitrile include
2-trifluoromethylbenzonitrile,
3-trifluoromethylbenzonitrile,
4-trifluoromethylbenzonitrile,
2-bromo-5-trifluoromethylbenzonitrile,
2-chloro-5-trifluoromethylbenzonitrile,
2-fluoro-5-trifluoromethylbenzonitrile,
4-iodo-2-trifluoromethylbenzonitrile,
4-iodo-3-trifluoromethylbenzonitrile,
2-methoxy-5-trifluoromethylbenzonitrile,
3-methoxy-4-trifluoromethylbenzonitrile,
4-hydroxy-2-trifluoromethylbenzonitrile,
4-methoxy-3-trifluoromethylbenzonitrile,
2-amino 3-trifluoromethylbenzonitrile,
2-amino-5-trifluoromethylbenzonitrile,
2-amino-6-trifluoromethylbenzonitrile,
3-amino-5-trifluoromethylbenzonitrile,
4-amino-2-trifluoromethylbenzonitrile,
4-amino-3-trifluoromethylbenzonitrile,
2,3-bis(trifluoromethyl)benzonitrile,
2,4-bis(trifluoromethyl)benzonitrile,
2,5-bis(trifluoromethyl)benzonitrile,
2,6-bis(trifluoromethyl)benzonitrile,
3,4-bis(trifluoromethyl)benzonitrile,
3,5-bis(trifluoromethyl)benzonitrile,
2,3,6-tris(trifluoromethyl)benzonitrile,
2,4,6-tris(trifluoromethyl)benzonitrile,
2,3,4,6-tetraquis(trifluoromethyl)benzonitrile,
2-amino-4,6-bis(trifluoromethyl)benzonitrile,
4-amino-3,5-bis(trifluoromethyl)benzonitrile and
4-chloro-3,5-bis(trifluoromethyl)benzonitrile. These trifluoromethylbenzonitriles having trifluoromethyl groups can be produced by various processes. For example,
2-trifluoromethylbenzonitrile can be obtained by fluorinating
2-trifluoromethylbenzonitrile with antimony trifluoride, while
4-trifluoromethylbenzonitrile can be obtained by heating
4-trifluoromethylaniline diazoate with Ka[Cu(CN)
4
].
Raney nickel or Raney cobalt can be used as the Raney catalyst in the process of the present invention. Raney catalyst refers to a porous, sponge-like metal catalyst. Although it can be prepared in accordance with routine methods, commercially available catalysts may also be used. Examples of commercially available Raney catalysts include Raney nickel NDT-90 of Kawaken Fine Chemicals Co. and Raney cobalt OFT-55 of Kawaken Fine Chemicals Co. The method for preparing the Raney catalyst is as described in detail in the literature (Kubomatsu, A. and Komatsu, S.: “Raney Catalysts”, Kyoritsu Publishing Co.(1971)), and Raney catalysts prepared in accordance with this method can be used in the process of the present invention. In the case of Raney nickel, the catalyst is prepared by adding aluminum, and depending on the case manganese, chromium and/or molybdenum, to nickel (normal content: 40-50 wt %) and developing the alloy with aqueous sodium hydroxide to elute the aluminum. The conditions for development may include a temperature on the order of −20° C. to +120° C., a weight ratio of sodium hydroxide to the nickel-aluminum alloy of 1/1 to 1.5/1, and a treatment time in the range of about 50 minutes to about 12 hours, and these conditions can be suitably combined. In the case of Raney cobalt, the catalyst is prepared by adding aluminum, and depending on the case manganese, chromium and/or molybdenum, to cobalt (normal content: 40-50 wt %) and developing the alloy with aqueous sodium hydroxide to elute the aluminum. The conditions for development may include a temperature on the order of −20° C. to +120° C., a weight ratio of sodium hydroxide to the cobalt-aluminum alloy of 1/1 to 1.5/1, and a treatment time in the range of about 50 minutes to 12 hours, and these conditions can be suitably combined. The amount of Raney catalyst used in the process is preferably 1 to 200 parts by weight, more preferably 5 to 50 parts by weight, to 100 parts by weight of the reaction substrate (i.e., the trifluoromethylbenzonitrile). If the amount is less than 1 part by weight, the reaction may not proceed sufficiently. If the amount exceeds 200 parts by weight, the catalyst may be wasted too much thereby making this undesirable.
The hydrogenation of the present invention preferably uses a non-polar solvent. Examples of non-polar solvents that can be used in the reaction include toluene, xylene, ethylbenzene, tetralin, n-hexane, n-octane, cyclohexane and methylcyclohexane. Although there are no restrictions on the amount of solvent used, the use of roughly 0.1 to 20 parts by weight to 1 part by weight of the trifluoromethylbenzonitrile is preferable in terms of manipulation of the reaction. Deviation from this range, however, does not result in any problems with respect to the reaction.
In general, polar solvents such as methanol have been used for the nitrile hydrogenation solvent. In that case, ammonia is frequently added for the purpose of inhibiting secondary amines formed as a by-product in nitrile hydrogenations. Since the solubility of ammonia is high in these polar solvents, they are also used for reasons of easier workability during charging. However, in the case of the trifluoromethylbenzonitriles of the present invention, polar solvents such as alcohol cause an addition reaction to the trifluoromethylbenzonitriles, and since, for example, methoxyimine is generated in the case of methanol, the use of such polar solvents may result in a significant decrease in yield. Moreover, the reaction products (e.g., methoxyimine) of this addition reaction may turn into dimers and trimers, due to heating and so forth during distillation in following isolation procedures. In contrast, when

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