The syntheses of these compounds are described, for example, in W. Herrmann and C. Kohlpainter, Angew. If desired, mixtures of two or more different water-soluble ligands can also be used. The water-soluble metal catalyst of the formula I can be synthesized separately or else be prepared in situ by combining a ruthenium, nickel, palladium or rhodium salt, e. If desired, a reducing agent is added. In general, hydrogen is the appropriate reducing agent for preparing the active catalyst species.
Some of the metal complexes of the formula I used according to the invention are known from the literature see, for example, EP-A-0 or J.
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Said catalyst can be easily obtained by a novel process from an aqueous solution of TPPTS and rhodium trichloride and subsequent addition of formaldehyde followed by heating, as is described below in Example 1. This process is significantly simpler than that described in EP-0 Isolation and chromatographic purification of the intermediates is unnecessary.
The carbon monoxide is replaced by the aqueous formaldehyde solution, so that handling in terms of apparatus is also significantly simplified here. The process of the invention is advantageously carried out in an autoclave. Autoclaves are, according to Rompps Chemie Lexikon, closable metal vessels which are tested to a high superatmospheric pressure and have a tightly closed lid which is screwed on and secured by means of a bayonet lock or is pressed on. This autoclave head has, for example, connections for a bursting disk or a safety valve, manometer, thermometer and often also a stirring apparatus which is installed so as to be gastight.
Apart from stationary autoclaves with internal stirring also magnetic stirring there are also shaking autoclaves and rotating autoclaves. In the case of laboratory autoclaves capacity from about ml to a number of liters , the autoclave is usually heated electrically; larger autoclaves in industrial process engineering up to a number of m 3 are usually heated by means of steam.
Autoclaves in which reactions occur with the consumption of gases, e. In most cases, the autoclaves are constructed of high-alloy steel e. V4A , although there are also special autoclaves made of copper, light metal and Monel metal. The catalyst comprising a metal complex of the formula I is preferably used in aqueous solution, with the amount of water being able to be within a wide range.
Since the reaction takes place in the aqueous phase, more nitroaromatic will dissolve in the water, thus accelerating the reduction, if relatively large amounts of water are provided. The amount of water thus has, within certain limits, an influence on the reaction rate. Since the catalyst itself is extremely readily soluble in water, this does not restrict the amount of water.
In addition, account must be taken of the fact that water is formed in the reduction itself. For one mole of substrate and one millimole of catalyst, use is generally made of ml, preferably ml, in particular ml, of water. The molar ratio of the catalyst to substrate is generally from to ,, preferably from to ,, in particular from to The ratios of catalyst to substrate and catalyst to water give a ratio of catalyst to water of from about to ,, preferably from to ,, in particular from to , The respective reaction rate depends on many parameters such as pressure, temperature, the amount of catalyst, the amount of substrate and the amount of water.
However, it also depends critically on the solubility of the substrate in water. Nitroaromatics which contain, for example, an ethoxy or methoxy group are generally more readily water-soluble than alkylated compounds.
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The reaction time is usually, depending on the reaction conditions and the nature of the nitroaromatic, from 30 minutes to 10 hours. The hydrogen uptake generally stops sharply when the reduction is complete. The hydrogen pressure can be bar, preferably bar, particularly preferably bar. After the reduction is complete, the reaction product is separated from the aqueous catalyst solution. The aqueous catalyst solution can be used for further reductions.
No loss in activity is observed on recycling. When the catalyst is recycled a plurality of times, the aqueous catalyst solution is increasingly diluted by the water of reaction formed. The original concentration ratios can be restored, for example, by means of membrane filters or by evaporation under reduced pressure.
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The catalyst system is relatively insensitive to air, but the aqueous solution should nevertheless be handled under inert conditions so as to ensure as long as possible a life and recyclability of the catalyst. In the reduction, it is not necessary to add an organic solvent for the nitroaromatic. The complicated and costly work-up of the solvent is thus also avoided. In addition, the filtration from the catalyst necessary in the heterogeneously catalyzed reduction is not needed either.
However, it is also possible to dilute the nitro compound with an organic solvent, for example with toluene, o-xylene, m-xylene, p-xylene, mixtures of isomeric xylenes, ethylbenzene, mesitylene, chlorobenzene, dichlorobenzene, chlorotoluene, cyclohexane, cumene, decalin, ethyl acetate, butyl acetate or a mixture of two or more of these solvents. Preferred starting materials for the process of the invention are aromatic nitro compounds. Accordingly, particularly preferred products of the process of the invention are amino compounds of the formula XI , STR6 where the symbols and indices are as defined for formula IX.
The compounds prepared according to the invention have a wide variety of uses, for example as intermediates for preparing active compounds, polymers and dyes. Diazonium salts serve, for example, as intermediates for preparing active compounds, polymers and dyes and in particular as diazo copying precursors. The documents cited in the description, which, for example, illustrate the technical field of the invention or describe the preparation of compounds used according to the invention, are expressly incorporated by reference into this application.
The disclosure of the German Patent Applications The solution changed color from dark red to yellow. In a 2 l autoclave fitted with gas-introduction stirrer, a two-phase system comprising g 1. After 8 hours, the aniline content was The aqueous catalyst solution was separated off in a separating funnel. The aniline content was After 8.
The reaction was complete after one hour. According to GC, the solution after phase separation contained Using the aqueous catalyst solution recovered from Example 5, g 1. After 3 hours 40 minutes, the compound was completely converted into 3-methylaniline. Starting material could no longer be detected in the solution. A mixture of g 0. GC analysis of the product solution indicated a 3,4-dimethylaniline content of In a 2 l autoclave, g 0. A catalyst solution comprising 0.
After 7 hours, the conversion was The catalyst phase was separated off by filtration of the product and reused. The catalyst solution from Example 8 was added at the beginning of the reaction. After 10 hours, the conversion was The catalyst solution from Example 9 was added at the beginning of the reaction. After 5.
The catalyst solution from Example 10 was added at the beginning of the reaction. After 9. The catalyst phase was separated off by filtration of the product. After 2. The catalyst solution from Example 12 is added at the beginning of the reaction. After 6. The catalyst solution from Example 13 was added at the beginning of the reaction. The catalyst solution from Example 14 was added at the beginning of the reaction. Effective date : The invention concerns a process for the reduction of nitro groups to amino groups, characterized that a nitro compound is reacted with hydrogen in the presence of an aqueous solution of a water-soluble metal catalyst of the formula M L n Y m wherein M is ruthenium, rhodium, nickel, or palladium; L, is a water soluble ligand; Y is a further ligand or an alkaline earth ion; n is 1, 2, 3, or 4; and m is 0, 1, or 2.
The invention accordingly provides a process for reducing nitro groups to amino groups, which comprises reacting a nitro compound with hydrogen in the presence of a water-soluble metal catalyst of the formula I , M L. M is preferably rhodium, ruthenium or palladium.
In particular, by employing palladium iodide-based catalysts, many carbonylation reactions have been developed, under oxidative as well as non-oxidative conditions. We have previously reviewed our efforts on oxidative carbonylations and carbonylative synthesis of heterocycles [ 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ]. In this personal account, we will describe our achievements on PdI 2 -catalyzed carbonylations leading to various carbonyl compounds under oxidative as well as non-oxidative conditions.
Particularly in the case of oxidative carbonylations, more emphasis will be given to the most recent results and applications. According to the literature [ 26 ], in organic synthesis, oxidative carbonylation is a process in which carbon monoxide CO is inserted into an organic substrate s SH 2 to yield a carbonylated product [S CO ], under the promoting action of a metal species [M X ], which is reduced to M X -2 at the end of the process Scheme 1 a. A catalytic version of this reaction is achieved when operating in the presence of a suitable external oxidant OX , able to reoxidize M X -2 back to M X , with the formation of OXH 2 Scheme 1 b [ 26 ].
At the beginning of the nineties, we reported that a very simple palladium-based catalytic system, consisting of PdI 2 in conjunction with an excess of KI, was a very efficient catalyst for promoting the oxidative dialkoxycarbonylation of terminal alkynes, carried out with oxygen as the external oxidant, with the formation of maleic diesters and their cyclic tautomers in high yields and excellent TONs Scheme 2 [ 31 , 32 ]. Later on, we found that, using water as the nucleophile under suitable conditions, it was also possible to effectively synthesize maleic anhydrides or acids [ 33 ].
The main reason for the high efficiency shown by this complex was related to a very efficient reoxidation of Pd 0 , through a mechanism involving the initial oxidation of the 2 equiv of HI ensuing from the carbonylation process to I 2 followed by the oxidative addition of the latter to Pd 0 Scheme 3 ; in this and in all the following Schemes in this account, unreactive iodide ligands are omitted for clarity. The PdI 2 -catalyzed oxidative carbonylation of the triple bond described in Section 2.