Process for producing an iridium solution and use of same as cat

Details Process for producing an iridium solution and use of same as cat Process for producing an iridium solution and use of same as cat

1996-09-27

1998-12-08

Geist, Gary

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

Organic compounds

Carboxylic acids and salts thereof

562517, 562520, 562522, 562591, 502151, 502152, 502161, 502325, C07C 5112, C07C 5114

Patent

active

058472045

DESCRIPTION:

BRIEF SUMMARY
This application is a national stage application under 35 U.S.C. .sctn.371 of PCT/FR94/01542, filed Dec. 28, 1994.
The present invention relates to the preparation of an iridium-based solution and to the use of the latter as catalyst.
Iridium is a well-known catalyst which is used in many types of reactions. Mention may be made, by way of example, of the use of iridium-based catalytic systems in carbonylation reactions of compounds of the alcohol, ether or carboxylic acid eater type with the aim of manufacturing in particular carboxylic acids or carboxylic acid anhydrides. Applications of iridium as catalyst in hydroformylation reactions of olefins to obtain aldehydes are also known. This catalyst can likewise be used to produce acetic acid by isomerization of methyl formate or alternatively in the water gas reaction.
In the more specific case of producing carboxylic acids by carbonylation, American Patent U.S. 3,772,380 describes the use of a catalytic system, which exists in a form which is soluble or insoluble in the reaction medium, based on iridium, one of the ligands of which is a halogen, and on a covalent halide (alkyl halide, for example). The iridium can be introduced into the reaction mixture either directly in the form of a compound comprising a halogen or in the form of two separate compounds constituting precursors of the final compound comprising the iridium and the halogen.
However, the existence is observed of many disadvantages in carrying out the process, as described in this patent, on an industrial scale, and more particularly in the context of a catalysis carried out in a homogeneous phase.
First of all, this patent describes the direct introduction into the reaction medium of a precursor of the catalyst in a solid form. This does not correspond to industrial practice and is the cause of implementational difficulties. The first relates to the fact that the conversion of the solid compound to a catalytically active compound is reflected by an initiation period during which the productivity is not optimum and the formation of by-products very often increased. The second is related to the fact that the conversion to an active compound which is soluble in the reaction medium cannot be monitored. For example, it is not obvious that the said conversion is complete and, if it is not complete, that this does not lead to a fall in activity and is not the cause of a loss of catalyst, by entrainment or other cause.
Moreover, compounds are found, among the precursors mentioned, which contain components foreign to the system which risk contaminating the reaction medium or alternatively disturbing the behaviour of the reaction.
It should also be noted that, in this patent, the conversion to an active compound is carried out under the conditions of the reaction for which the catalyst is subsequently used, that is to say under very severe conditions since the temperature and the pressure are high.
One of the aims of the present invention is therefore to propose an iridium-based solution which can be used directly as catalyst, which can be used on an industrial scale and which does not have the abovementioned disadvantages, whether as regards the preparation of the said solution or its use.
Thus, the present invention makes it possible to obtain an iridium-based solution by implementing a simple process under gentle conditions which do not require in particular use of high pressure and high temperature. For this reason, the necessary equipment in which the conversion takes place is conventional equipment and less expensive than equipment capable of resisting high pressures.
The invention likewise makes it possible to prepare an iridium-based solution which does not comprise components foreign to the subsequent reaction in which it will be employed.
Another aim of the invention is to obtain concentrated iridium solutions. This represents a particularly worthwhile advantage, from an industrial angle, since it makes it possible to reduce the size of the equipment used for preparing the solution or altern

REFERENCES:
patent: 3772380 (1973-11-01), Paulik et al.
patent: 3818060 (1974-06-01), Forster et al.
patent: 4060547 (1977-11-01), Paulik et al.
patent: 5227522 (1993-07-01), Denis et al.
patent: 5420346 (1995-05-01), Denis et al.

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