Process for preparation of anilines substituted by chlorine in the meta-position

A process for the dechlorination of aromatic nitro or amino compounds comprising reacting anilines or nitrobenzenes, which are polysubstituted by chlorine, with hydrogen, under the action of heat, in the presence of an excess of chloride ions, in the liquid phase and at low pressure. The process makes it possible selectively to obtain anilines which are chlorine-substituted in the meta-position.

FIELD OF THE INVENTION 
The present invention relates to a process for the preparation of anilines 
substituted by chlorine in the meta-position, by reacting hydrogen with 
nitrogen-containing aromatic compounds which are more highly 
halogen-substituted. 
BACKGROUND OF THE INVENTION 
U.S. Pat. No. 4,085,141, of Mar. 19, 1980, describes the preparation of 
chloroanilines substituted in the meta-position, by reacting 
polychloroanilines with hydrogen. However, the process described in the 
said patent requires the use of high pressures and a very large amounts of 
hydrochloric acid, and this presents serious corrosion problems. 
SUMMARY OF THE INVENTION 
One object of the invention is to provide a process which makes it possible 
to prepare anilines substituted in the meta-position by chlorine, with 
good yields, from nitrogen-containing aromatic compounds which are more 
highly halogen-substituted. 
A further object of the invention is to provide a process for the 
preparation of anilines substituted in the meta-position by chlorine, it 
being possible for this process to use either chlorine-substituted nitro 
compounds (substituted nitrobenzenes and the like) or chlorine-substituted 
amino compounds (polychloroanilines and the like) as the starting 
reactant. 
A further object of the invention is to provide a process for the 
preparation of anilines substituted in the meta-position by chlorine, 
using moderate pressures. 
A further object of the invention is to provide a process for the 
preparation of anilines substituted in the meta-position by chlorine, 
using moderate reaction temperatures. 
Yet another object of the invention is to provide a process for the 
preparation of anilines substituted in the meta-position by chlorine, 
using moderately corrosive conditions. 
Further objects and advantages of the invention will become apparent in the 
course of the description which now follows. 
DETAILED DESCRIPTION OF EMBODIMENTS 
It has now been found that these objects can be achieved by virtue of a 
process for the preparation of anilines substituted in the meta-position 
by chlorine, which process consists in carrying out the catalytic 
hydrogenation of chlorine substituted/nitrogen-containing benzene 
derivatives, in the liquid phase, in an acid medium under the action of 
heat, under pressure and in the presence of noble metals from group VIII 
of the periodic classification, and in which process the benzene 
derivatives have the formula: 
##STR1## 
in which: Y represents the hydrogen atom or the oxygen atom, X' and X", 
which are identical or different from one another, each represent a 
chlorine atom or an optionally substituted alkyl, aryl, aralkyl, alkoxy or 
aralkoxy radical, it being furthermore possible for one of the symbols X' 
and X" to be a hydrogen atom (when preparing monochloroanilines 
(meta-chloroanilines), only one of the substituents X' or X" represents 
the chlorine atom, and when preparing dichloroanilines (disbustituted by 
chlorine in the meta-position), both of the symbols X' and X" represent 
the chlorine atom), and R', R" and R'", which are identical or different 
from one another, each represent a chlorine atom or an optionally 
substituted alkyl, aralkyl, alkoxy or aryloxy radical, at least one of 
these three symbols representing the chlorine atom and it being 
furthermore possible for at most two of the symbols R', R" or R'" to be 
hydrogen, and the reaction is carried out in the presence of chloride ions 
in an amount which is such that the ratio of the concentrations [Cl.sup.- 
]/[H.sup.+ ] is greater than 1.5 and preferably greater than 2. 
As already stated, the reaction is carried out in the liquid phase; in 
practice, it is advantageously carried out in the presence of an inorganic 
or organic solvent which is liquid and inert under the operating 
conditions. The term inert solvent is understood as meaning a solvent 
which does not undergo chemical reaction. In fact, the use of water is 
preferred. 
The acidity of the reaction medium is generally such that the pH (in the 
case of an aqueous medium) is advantageously less than 1.5 and preferably 
less than 1. The concentration of H.sup.+ ions in the medium is generally 
between 0.5 and 10 g.ions/liter and preferably between 1 and 6 g.ions of 
H.sup.+ /liter. 
The highest concentrations of acid can be used but no significant advantage 
is gained. 
The acidity of the reaction medium can be achieved by means of strong 
mineral acids, such as sulphuric, phosphoric or hydrogen halide acids, or 
strong organic acids; however, it is preferred to use hydrogen halide 
acids and more especially hydrochloric acid. In any case, in view of the 
presence of chloride ions, according to the invention, the reaction is in 
fact always carried out, at least in part, in the presence of hydrochloric 
acid. 
The process according to the invention is carried out in the liquid phase 
(with the exception, of course, of the catalyst based on a noble metal, 
which most commonly constitutes a solid phase). The liquid phase can be 
homogeneous and constitute a solution; this is a preferred procedure, in 
particular in the case where Y is an oxygen atom in the formula (I); a 
liquid phase of this type therefore contains the reactants, the reaction 
products and the solvent or solvents which may be present. It is also 
possible to carry out the reaction with 2 liquid phases. 
The pressure at which the reaction is carried out is generally more than 3 
bars (relative pressure) and preferably more than 5 bars. There is no 
critical upper limit for the pressure, but, for economic reasons, it is 
generally advantageous to operate at pressures of less than 100 bars, 
pressures of less than 30 bars being preferred. 
The reaction temperature is generally between 90.degree. and 300.degree. C. 
and preferably between 110.degree. and 200.degree. C. In the case where 
relatively volatile acids are used, an elevated temperature can lead to a 
relatively high partial pressure of the compounds, other than hydrogen, in 
the vapour phase (the term vapour phase is obviously understood as meaning 
the vapour phase above the liquid reaction medium). The operating 
conditions are generally chosen so that the hydrogen partial pressure is 
between 10 and 80% of the total pressure (relative pressure) and 
preferably between 30 and 60%. 
The noble metals constituting the base of the catalysts used in the 
invention are mainly metals from group VIII of the periodic 
classification, such as ruthenium, rhodium, palladium, osmium, iridium and 
platinum; palladium is the preferred metal. The metal can be in the 
metallic form or in the form of a chemical compound; in general, the metal 
is preferably employed in the metallic form because, under the operating 
conditions, the compounds tend to be reduced to the metallic form 
(oxidation state=zero). The catalyst can be supported or unsupported. Any 
support which is in itself known for supporting catalysts can be used as 
the catalyst support, provided that this support is resistant to water and 
acids; activated carbon, silica and barium sulphate may be mentioned as 
being more particularly suitable as supports; activated carbon is a 
preferred support. Both the catalyst and its support are advantageously in 
the finely divided form; specific surface areas of more than 100 m.sup.2 
/g are generally very suitable. 
The amount of catalyst employed in such that the proportion by weight of 
noble metal from the catalyst, relative to the compound of the formula (I) 
to be treated, is generally between 0.05 and 10% and preferably between 
0.5 and 5%. 
The chloride ions employed in the reaction are therefore present in an 
amount which is greater than that of the H.sup.+ ions. The former are 
therefore usually introduced totally or partially in the from of compounds 
of the chloride type. It is generally preferred to introduce these 
chloride ions in the form of an ammonium chloride or a metal chloride or 
in the form of a hydrochloride. The ammonium chlorides can be quaternary 
or non-quaternary ammonium chlorides. They are preferably ammonium 
(NH.sub.4.sup.+) chloride, or alkali metal or alkaline earth metal 
chlorides, such as lithium chloride, sodium chloride or potassium 
chloride. The hydrochlorides are preferably hydrochlorides of a 
substituted aniline such as the amine of the formula (I) (with Y=H) and/or 
the substituted aniline produced according to the invention. The amount of 
chloride ions in the reaction medium is generally between 2 and 15 
g.ions/liter and preferably between 4 and 11 g.ions/liter. 
The following may preferably be mentioned as compounds of the formula (I) 
which can be treated by the process of the invention: 
2,3-dichloronitrobenzene and 2,3-dichloroaniline, 2,5-dichloronitrobenzene 
and 2,5-dichloroaniline, 3,4-dichloronitrobenzene and 3,4-dichloroaniline, 
2,3,4-trichloronitrobenzene and 2,3,4-trichloroaniline, 
2,3,5-trichloronitrobenzene and 2,3,5-trichloroaniline, 
2,3,6-trichloronitrobenzene and 2,3,6-trichloroaniline, 
2,4,5-trichloronitrobenzene and 2,4,5-trichloroaniline, 
3,4,5-trichloronitrobenzene and 3,4,5-trichloroaniline, 
2,3,4,6-tetrachloronitrobenzene and 2,3,4,6-tetrachloroaniline, 
2,3,4,5-tetrachloronitrobenzene and 2,3,4,5-tetrachloroaniline, 
2,3,5,6-tetrrachloronitrobenzene and 2,3,5,6-tetrachloroaniline, and 
pentachloronitrobenzene and pentachloroaniline, but also 
4,5,6-trichloro-2-methylnitrobenzene and 4,5,6-trichloro-2-methylaniline, 
2,5-dichloro-4-methylnitrobenzene and 2,5-dichlor-4-methylaniline, 
2,3,5,6-tetrachloro-4-methylnitrobenzene and 
2,3,5,6-tetrachloro-4-methylaniline, 2,5-dichloro-3,4-dimethylnitrobenzene 
and 2,5-dichloro-3,4-dimethylaniline, 2,5-dichloro-4-ethylnitrobenzene and 
2,5-dichloro-4-ethylaniline, 2,5-dichloro-4-propylnitrobenzene and 
2,5-dichloro-4-propylaniline, 3,4,6-trichloro-2-benzylnitrobenzene and 
3,4,6-trichloro-2-benzylaniline, 
2,2'-dinitro-3,5,6,3',5',6'-hexachlorodiphenylmethane and 
2,2'-diamino-3,5,6,3',5',6'-hexachlorodiphenylmethane, 
2-nitro-3,4,5-trichlorodiphenyl and 2-amino-3,4,5-trichlorodiphenyl, 
4,4'-dinitrooctachlorodiphenyl and 4,4'-diaminooctachlorodiphenyl, 
4,5-dichloro-2-methoxynitrobenzene and 4,5-dichloro-2-methoxyaniline, 
3,4-dichloro-2-methoxynitrobenzene and 3,4-dichloro-2-methoxyaniline, 
3,6-dichloro-2-methoxynitrobenzene and 3,6-dichloro-2-methoxyaniline, 
5,6-dichloro-2-methoxynitrobenzene and 5,6-dichloro-2-methoxyaniline, 
3,4,6-trichloro-2-methoxynitrobenzene and 
3,4,6-trichloro-2-methoxyaniline, 3,4,5-trichloro-2-methoxynitrobenzene 
and 3,4,5-trichloro-2-methoxyaniline, 
3,4,5,6-tetrachloro-2-methoxynitrobenzene and 
3,4,5,6-tetrachloro-2-methoxyaniline, 4,5-dichloro-3-methoxynitrobenzene 
and 4,5-dichloro-3-methoxyaniline, 5,6-dichloro-3-methoxynitrobenzene and 
5,6-dichloro-3-methoxyaniline, 2,5-dichloro-3-methoxynitrobenzene and 
2,5-dichloro-3-methoxyaniline, 4,5,6-trichloro-3-methoxynitrobenzene and 
4,5,6-trichloro-3-methoxyaniline, 
2,4,5,6-tetrachloro-3-methoxynitrobenzene and 
2,4,5,6-tetrachloro-3-methoxyaniline, 2,3-dichloro-4-methoxynitrobenzene 
and 2,3-dichloro-4 -methoxyaniline, 2,5-dichloro-4-methoxynitrobenzene and 
2,5-dichloro-4-methoxyaniline, 2,3,6-trichloro-4-methoxynitrobenzene and 
2,3,6-trichloro-4-methoxyaniline, 2,3,5-trichloro-4-methoxynitrobenzene 
and 2,3,5-trichloro-4-methoxyaniline, 
2,3,5,6-tetrachloro-4-methoxynitrobenzene and 
2,3,5,6-tetrachloro-4-methoxyaniline, 4,5-dichloro-2-phenoxynitrobenzene 
and 4,5-dichloro-2-phenoxyaniline, 
3,4,5,6-tetrachloro-2-phenoxynitrobenzene and 
3,4,5,6-tetrachloro-2-phenoxyaniline, 
2,4,5,6-tetrachloro-3-phenoxynitrobenzene and 
2,4,5,6-tetrachloro-3-phenoxyaniline, 2,5-dichloro-4-phenoxynitrobenzene 
and 2,5-dichloro-4-phenoxyaniline, and 
2,3,5,6-tetrachloro-4-phenoxynitrobenzene and 
2,3,5,6-tetrachloro-4-phenoxyaniline. 
The following may preferably be mentioned amongst the anilines which are 
substituted in the meta-position by a chlorine atom and which can be 
prepared by the process according to the invention: meta-chloroaniline and 
3,5-dichloroaniline, but also: 5-chloro-2-methylaniline, 
5-chloro-3-methylaniline, 3-chloro-4-methylaniline, 
3,5-dichloro-4-methylaniline, 5-chloro-3,4-dimethylaniline, 
3-chloro-4-ethylaniline, 3-chloro-2-benzylaniline, 
4,4'-diamino-2,6,2',6'-tetrachlorodiphenyl, 3-chloro-2-methoxyaniline, 
5-chloro-2-methoxyaniline, 3,5-dichloro-2-methoxyaniline, 
3-chloro-4-methoxyaniline, 5-chloro-3-methoxyaniline, 
3,5-dichloro-4-methoxyaniline, 3-chloro-2-phenoxyaniline, 
5-chloro-2-phenoxyaniline, 3,5-dichloro-2-phenoxyaniline and 
3,5-dichloro-4-phenoxyaniline. 
The process according to the invention can be carried out continuously or 
discontinuously. At the end of the reaction, the catalyst can be separated 
off, if necessary, by filtration or by equivalent means such as draining; 
the amine prepared, which is chlorine-substituted in the meta-position, 
can be separated off by any means which is in itself known, e.g. by 
solvent extraction and/or by distillation; before carrying out this 
separation, it is generally appropriate to convert the amine (salified in 
an acid medium) back into the form of an (unsalified) amine by rendering 
the reaction mixture neutral or alkaline with the aid of an alkaline 
agent. 
The process according to the invention is very advantageous because of its 
good selectivity with respect to the amine which is chlorine-substituted 
in the meta-position, and because of the relatively mild conditions under 
which it can be carried out. The amines produced in this way, which are 
chlorine-substituted in the meta-position, can be used, in particular, for 
manufacturing pesticides.

The following example, which is given without implying a limitation, 
illustrates the invention and shows how it can be put into effect. 
EXAMPLE 
2,3,4,5-Tetrachloroaniline (0.83 g), a catalyst consisting of palladium 
deposited on activated carbon (specific surface area of the activated 
carbon 1,100 m.sup.2 /g; proportion of palladium by weight: 10%) (0.07 g), 
an aqueous solution of hydrochloric acid having a concentration of 4 
mols/liter (95 cc) and lithium chloride (37.5 g) are introduced into a 225 
cc autoclave coated on the inside with tantalum. 
The autoclave is closed and purged first with argon and then with hydrogen. 
The temperature is then raised to 170.degree. C., whilst allowing the 
autogenous pressure to increase, and then, when this temperature has been 
reached, hydrogen is introduced until the total (relative) pressure is 21 
bars, the hydrogen partial pressure being 8 bars. 
The reaction is allowed to proceed under these conditions for 4 hours 10 
minutes. 
After cooling, the liquid reaction mixture is rendered alkaline with an 
aqueous solution of sodium hydroxide (NaOH); the palladium catalyst is 
filtered off; 3,5-dichloroaniline is extracted from the aqueous phase 
using methylene chloride; the methylene chloride solution thus obtained is 
dried over sodium sulphate; the solvent is evaporated off in vacuo; the 
degree of conversion of the tetrachloroaniline was 100%. The yield of 
3,5-dichloroaniline was 95.4%.