Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Patent
1992-02-20
1994-03-08
Hollrah, Glennon H.
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
564431, C07C20926
Patent
active
052929574
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an ecologically and economically improved process for the preparation of N-alkylhalogenoanilines by reductive alkylation of nitrohalogenobenzenes, in particular the preparation of N-isopropyl-4-chloroaniline by reductive alkylation of p-nitrochlorobenzene with acetone in the presence of a sulfited platinum catalyst of defined specific activity.
The problem of halogen elimination which occurs in the catalytic hydrogenation of halogen-containing nitro aromatics is also especially important in reductive alkylations of halogen-containing nitro or amino aromatics, in particular in industrial processes.
There has therefore not been a lack of attempts to avoid the disadvantages which occur in reductive alkylation of halogen-containing nitro aromatics or anilines, such as halogen elimination, ring hydrogenation or polyalkylation.
The prior art closest to the process according to the invention is described in German Offenlegungsschrift 2,941,070 A1. The process described there comprises reacting a halogenoaniline or halogenonitrobenzene with 1 to 10 equivalents of an aliphatic carbonyl compound in an inert solvent, but preferably in a solution of the halogenoaniline or of the nitro aromatic in the aliphatic carbonyl compound, using 0.05 to 2.0% by weight of a sulfited platinum/carbon catalyst at temperatures of 70 to 120.degree. C., preferably at 80.degree. to 100.degree. C. The hydrogen superatmospheric pressure employed in this process is 40 to 100 bar. The yields of N-halogenoalkylanilines are about 95% of theory at a purity of mostly over 98%.
"Virtually no halogen elimination is observed" in this process, although no analytical investigations of halogen elimination are mentioned.
The closest prior art furthermore includes the process described in U.S. Pat. No. 3,350,450 for the preparation of aromatic amines by catalytic hydrogenation of aromatic nitro compounds, in particular of N-alkylhalogenoanilines by reductive alkylation of halogenoanilines or halogenonitrobenzenes in a one- or two-stage process, using hydrogen and aliphatic aldehydes or ketones in the presence of palladium, platinum, rhodium, ruthenium or cobalt sulfides.
In the abovementioned U.S. patent, the following reaction conditions for the preparation of N-isopropyl-4-chloroaniline from p-nitrochlorobenzene and acetone are mentioned: reaction temperature 160.degree. to 200.degree. C., hydrogen pressure about 70 to 110 bar. Depending on the metal sulfide catalyst used, the reaction times are 15 minutes to 6.5 hours. The yields of N-alkylhalogenoaniline are 92.5 to 100%.
The two processes of the closest prior art mentioned have in common that the substrate used (halogenonitro aromatic or halogenoaniline) is reacted in a 15- to 10-molar excess of the carbonyl compound. As a result of the drastic reaction conditions employed, a significant portion of the carbonyl compound which is used as solvent is hydrogenated to the corresponding alcohol. This means, on the one hand, increased consumption of hydrogen, and, on the other hand, that the resulting alcohol/carbonyl compound mixture can only be separated by distillation with the use of large amounts of energy. Furthermore, the alcohol formed cannot be reintroduced into the continuous process cycle but has to be disposed of, for example, by introducing it into another process. Both processes have the additional disadvantage that they must be carried out at relatively high reaction temperatures to obtain acceptable reaction times and thus space-time yields.
In contrast, it has now been found that N-alkylhalogenoanilines of the general formula (I) ##STR4## in which X is a chlorine or bromine atom and n is the number 1 or 2, R.sup.1 is a linear or branched alkyl (C.sub.1 -C.sub.4) radical, R.sup.2 a linear or branched alkyl (C.sub.1 -C.sub.6) radical or R.sup.1 and R.sup.2 together with the carbon atom to which they are bound can form a five- or six-membered cycloalkane ring, can be prepared in an advantageous manner, while avoiding the shortcomings of the known processes m
REFERENCES:
patent: 3350450 (1967-10-01), Dovell et al.
patent: 3541153 (1970-11-01), Sandridge
patent: 3803054 (1974-04-01), Habig et al.
Dovell et al. J. Amer. Chem. Soc. 87:2767-8 (Apr. 1965).
Brodt Werner
Papenfuhs Theodor
Burn Brian M.
Hoechst Aktiengesellschaft
Hollrah Glennon H.
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