Organic compounds -- part of the class 532-570 series – Organic compounds – Sulfonic acids or salts thereof
Reexamination Certificate
2001-12-12
2003-08-26
Vollano, Jean F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Sulfonic acids or salts thereof
C562S030000, C568S013000
Reexamination Certificate
active
06610881
ABSTRACT:
This application is a 371 of PCT/EP00/03241 filed Apr. 12, 2000 now WO00/64913.
The present invention relates to a process for reducing the sulfur dioxide or sulfite content of solutions of sulfonated arylphosphines, in particular of aqueous solutions of sulfonated arylphosphines.
Complexes which contain a metal of group VIII of the Periodic Table of the Elements as central atom and phosphorus (III) compounds such as phosphines as ligands and in addition possibly further groups capable of complex formation have gained increasing importance as catalysts in recent years. Thus, the industrially widely practiced reaction of olefins with synthesis gas (mixture of hydrogen and carbon monoxide) to give aldehydes (hydroformylation) is carried out in the presence of catalysts made up of cobalt or rhodium and triphenylphosphine. Due to the solubility of these catalysts in organic solvents, the reaction proceeds in a homogeneous phase.
However, instead of in a homogeneous phase, the hydroformylation can also be carried out in heterogeneous reaction systems. The use of catalysts dissolved in water frequently has the particular advantage that these catalysts can be separated simply and gently from the reaction products which are sparingly soluble or insoluble in water and the catalysts can be returned to the reactor.
The use of rhodium-containing aqueous solutions of sulfonated arylphosphines as aqueous catalyst solution for the preparation of aldehydes by reaction of olefins with carbon monoxide and hydrogen (hydroformylation) is known. Such a process is described in DE-A-26 27 354. The rhodium-containing aqueous solution contains, for example, tris(m-sulfophenylphosphine) (TPPTS) as ligand. The use of catalysts dissolved in water has the particular advantage that these catalysts can be separated simply and gently from the reaction products which are sparingly soluble or insoluble in water by means of simple phase separation and can be returned to the reactor. A hydroformylation process carried out in this way is also referred to as a two-phase hydroformylation process.
Sulfonated phenylphosphines are obtained by a process described in J. Chem. Soc. (1985), pp. 281 and 282, by reaction of triphenylphosphine with oleum. In this process, the reaction mixture is firstly heated on a water bath and then hydrolyzed with water. Subsequent neutralization with NaOH forms the corresponding sodium salts of the sulfonated triphenylphosphine.
In the reaction of arylphosphines with a solution of sulfur trioxide in concentrated sulfuric acid, generally referred to as oleum or as “fuming sulfuric acid”, sulfite salts are also formed in small amounts in addition to the desired sulfonated arylphosphines. Furthermore, the reaction solution contains some dissolved sulfur dioxide. In addition, sulfite or sulfur dioxide react further with the sulfonated arylphosphine to form the corresponding phosphine sulfide. In the following, the term sulfite refers to the sulfite or hydrogensulfite anion of sulfurous acid. As is known, sulfur dioxide is present in aqueous solution in physically dissolved form but also reacts with water to form sulfurous acid which is converted by proton abstraction into the hydrogensulfite or sulfite anion.
A serious disadvantage of the known process for preparing sulfonated arylphosphines is the undesirable formation of phosphorus-oxygen compounds which are formed by oxidation of trivalent phosphorus to pentavalent phosphorus by SO
3
dissolved in the oleum. This redox reaction can be reduced in accordance with the teachings of EP-A-0 632 047 by addition of boric acid to the reaction mixture, but in the known process this results in formation of considerable amounts of boron compounds which have to be removed again from the reaction products, which is costly.
In the redox reaction of sulfur trioxide with the phosphine used, sulfur dioxide is formed as reduction product of the sulfur trioxide and the corresponding phosphine oxide is formed from the phosphine. This sulfur dioxide is not removed in the work-up of the reaction mixture with aqueous sodium hydroxide solution as disclosed, for example, in EP-A-0 632 047. Sodium sulfite therefore remains as impurity in the solution of the sulfonated arylphosphine. It is assumed that this sodium sulfite is the source and cause of the contamination of aldehydes with sulfur compounds in the two-phase hydroformylation and that these sulfur compounds are responsible for the poisoning of hydrogenation catalysts in the subsequent hydrogenation of the aldehydes to give alcohols.
It is known that inorganic and organic sulfur compounds, (e.g. butanethiol or thiobutyl butyrate) which are formed in the reaction of the aldehydes formed during the hydroformylation reaction and their downstream products, for example alcohols, with sulfur dioxide or sulfite are responsible for the poisoning of hydrogenation catalysts used for the subsequent hydrogenation of the aldehydes to give the oxo alcohols. Furthermore, the sulfur-containing compounds formed persistently and, in particular, disadvantageously interfere in various chemical reactions and lead, for example, to the formation of undesirable mixed aldols or trimerization products from the aldehydes.
It is therefore an object of the invention to develop a simple process by means of which sulfonated arylphosphines, for example TPPTS, can be prepared reliably and free of sodium sulfite.
This object is achieved by a process of the generic type mentioned at the outset, in which, after reaction of the arylphosphines with oleum, the sulfonation mixture is firstly diluted with water and cooled, an inert gas stream is then passed through the diluted sulfonation mixture until SO
2
is no longer liberated from the diluted sulfonation mixture and the latter is then worked up further in a customary manner.
It has surprisingly been found that as a result of the process of the invention interfering sulfur compounds are no longer detectable in the aldehydes produced by the two-phase hydroformylation. It is particularly surprising that the small amount of sodium sulfite formed sulfur compounds which function as catalyst poisons. They therefore do not come from the sulfur-containing sulfonic acid groups of the sulfonated arylphosphines. If the hydroformylation is carried out using arylphosphines sulfonated by the process of the invention, it is possible to increase the life of hydrogenation catalysts, for example in the hydrogenation of 2-ethylhexenal to 2-ethylhexanol, by a factor of two or more. This lengthening of the life of hydrogenation catalysts results in a considerable economic advantage in the preparation of industrial alcohols.
According to the invention, the sulfonation is carried out in accordance with the teachings of DE-A-26 27 354. After dilution of the sulfonation mixture of arylphosphines and oleum with water to a sulfuric acid content of from 25 to 30% and immediate cooling, an inert gas stream is passed through the diluted sulfonation mixture. The treatment with the gas can be carried out batchwise or continuously.
The amount of inert gas per kg of diluted sulfonation mixture and the time of the treatment with gas depend on the geometry of the gas treatment apparatus. In general, the conditions and the geometry are to be selected so that the diluted sulfonation mixture is largely freed of SO
2
present (at least 90%). In a continuous treatment with gas, for example in a packed column, a mean gas treatment time of from 2 to 100 minutes, preferably from 2 to 20 minutes, is useful. In a continuous gas treatment apparatus, a total amount in the range from 5 to 500 1 of inert gas, preferably from 10 to 200 l, particularly preferably from 20 to 100 l, are required per kg of diluted sulfonation mixture.
In this case, the sulfite content in the sulfonated arylphosphine solution is <0.1% by weight, perferably <0.05% by weight.
The further work-up of the diluted and purified sulfonation mixture is carried out in a known manner in accordance with the teachings of EP-A-0 632 047.
Thus, the diluted sulfonation mixtur
Bahrmann Helmut
Bergrath Klaus
Eckl Robert
Fenske Wilfried
Frohning Carl D
Celanese Chemicals Europe
Muserlian Lucas and Mercanti
Vollano Jean F.
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