Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Patent
1998-09-21
2000-07-11
Killos, Paul J.
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C07C24100
Patent
active
060875348
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for the synthesis of arylhydrazine or a derivative thereof by reduction of a diazo derivative. The invention relates more particularly to a bisulphite-type reduction.
The most direct route of access to hydrazines substituted with an aryl derivative is, in most cases, the diazotation of an aniline, followed by a reduction, generally a hydrogenation.
Besides being relatively expensive, this route has many difficulties, among which mention may be made of the often prohibitive number of steps and the formation of heavy by-products, resulting, ipso facto, in very mediocre overall yield and purity. On top of all this, the reduction techniques give erratic results, depending on the substituents on the rings. The problem is particularly pronounced in the case of electron-poor aromatic rings.
Thus, in the course of the study which led to the present invention, it has been shown that the most standard technique for reducing "diazo" compounds, i.e. the use of tin, gives results which, at best, can only be described as mediocre.
Accordingly, one of the aims of the present invention is to provide a process which makes it possible to obtain arylhydrazine from a diazo derivative.
Another aim of the present invention is to provide a process which is suitable for electron-poor or moderately electron-poor rings.
Another aim of the present invention is to provide a process which allows a good yield.
Another aim of the present invention is to provide a process which allows the one-step production of arylhydrazines which can readily be purified or which can even be obtained directly in high purity.
These aims and others which will become apparent hereinbelow are achieved by means of a process for reducing a diazo derivative, this process including at least the following step: pH is at least equal to 7.
The reason for this is that the use of sulphite has proved to be particularly advantageous as a reducing agent provided that it is at a sufficiently basic pH. This is particularly surprising since the reduction reaction requires the presence of acidic ions.
Advantageously, in order to avoid the presence of a coloured product which would impair the purity and colour of the hydrazine, and thus in order to avoid a rigorous purification step, it is desirable to work at a pH of between 7.2 and 11, preferably between 7.5 and 10.
In order to avoid the presence of tars and heavy products, it is preferable for the temperature at which step c) is carried out to be at most equal to 100.degree. C., advantageously to 50.degree. C.
Although this cannot be fully explained, the best results are obtained when the pH of the sulphite/bisulphite solution is buffered with a nitrogenous base (such as amines, including anilines) whose pKb is between 6 and 11; preferably, the pH is buffered with a nitrogenous base whose pKb is between 7 and 10.
For economic reasons, the said nitrogenous base is aqueous ammonia.
According to a particularly advantageous embodiment of the present invention, step c) is carried out by addition of the said diazo derivative to an initial charge of reductive bisulphite solution.
It is desirable for the pH to be adjusted during step c) such that it is always close to a preselected value and above 7 and below 11, advantageously below 10.
The process advantageously also includes a step a) of synthesis of the diazo derivative, in particular in order to avoid having to insert the diazo derivative to be reduced.
This step a) of synthesis of the diazo derivative is generally carried out by the action of a nitrite, advantageously an alkyl or metal nitrite, on an aniline.
Advantageously, the said nitrite is an alkaline nitrite.
In general, the said diazo derivative is a diazonium salt.
The results are more predictable if the aromatic ring bearing the diazo function is a benzene ring.
The process is particularly advantageous when the said benzene ring, not taking the diazo function into account, has substituents such that it is electron-poor overall, or, preferably and, when the benzene ring, n
REFERENCES:
Chemische Berichte, vol. 93, 1960, Weinheim DE, pp. 540-544, XP002014817, R. Huisgen et al, "Zum Mechanismus der Phenylhydrazinsynthese nach E. Fischer".
Mas Jean-Manuel
Rochin Christophe
Killos Paul J.
Rhodia Chimie
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