Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2002-09-05
2004-10-05
Trinh, Ba K. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S534000, C554S137000
Reexamination Certificate
active
06800783
ABSTRACT:
The present invention relates to a novel, noncatalytic process for preparing aliphatic carboxylic acids from aldehydes by oxidation with oxygen or oxygen-containing gases.
Aldehydes are used on a large scale as starting materials for obtaining carboxylic acids. The preference for aldehydes for this use derives from their ready availability by a number of processes, which are also used in industry. Moreover, the carbonyl of the aldehydes can easily be converted into the carboxyl group characteristic of carboxylic acids. In processes applied industrially, the conversion of aldehydes to carboxylic acids often takes place in the presence of catalysts. However, there is no lack of warnings about employing catalysts because they promote the occurrence of side reactions, e.g. decarbonylation of the aldehydes employed to hydrocarbons. Accordingly, various processes in which the use of catalysts is dispensed with are also known. To avoid side reactions, both the catalytic and the noncatalytic processes employ temperatures which are as low as possible, and in general the reaction temperature does not exceed 100° C. Suitable catalysts are mainly salts of transition metals, in particular salts of cobalt and of manganese, and of chromium, iron, copper, nickel, silver and vanadium. Nevertheless, the formation of carboxylic acids from aldehydes is frequently associated, even if optimal temperature conditions are maintained, with side reactions and degradation reactions. This applies equally to reactions in the presence and in the absence of catalysts. In such cases, the selectivity of the conversion can be considerably improved by adding alkali metal salts of weak acids to the reactants. However, the disadvantage of this variant of the process is that the alkali metal salts have an inhibitory effect, so that long reaction times are necessary for complete conversion of the starting materials.
In the process described in DE-A 30 29 700, the appropriate aldehydes for preparing aliphatic monocarboxylic acids having 6 to 9 carbon atoms are oxidized with oxygen in pure form or with air. A combination of manganese and copper compounds which are soluble in the acid acts as catalyst. The metals are each present in an amount of about 10 to about 2000 ppm, preferably 200 to 600 ppm, manganese and copper, based on the weight of the liquid reaction mixture. The molar ratio of manganese to copper is from 5:1 to 0.5:1. The conversion of the starting materials takes place in liquid phase at temperatures of about 50 to 80° C. and pressures in the range from about 1.4 to 10.3 bar. The main difficulty of this process is described, in the description of the process, as being the presence of copper compounds, and manganese compounds, in the reaction product, i.e. in the carboxylic acid. Elaborate purification measures are necessary to remove the metals, for example precipitation thereof with aqueous oxalic acid.
The process disclosed in U.S. Pat. No. 4,487,720 for preparing C
5
to C
9
monocarboxylic acids by oxidizing aldehydes with the same number of carbon atoms using pure oxygen or air likewise operates with copper and manganese compounds as catalysts. The total amount of the metals extends over a range from 10 to 200 ppm, based on the total weight of the solution consisting of aldehyde, acid and catalyst. Manganese and copper are employed in a molar ratio of about 3:1 to about 1:1. The disadvantage described for this procedure is the formation of copper films which appear on purification of the acid by distillation and result in mechanical damage to the distillation apparatus. To avoid this problem, it is recommended that the distillation be carried out in the presence of oxygen.
Another catalytic process for reacting aldehydes with oxygen to form carboxylic acids is disclosed in the published international application WO 97/14668. The catalysts used are substituted or unsubstituted alkylamines, alkylamine N-oxides, aromatic amines, aromatic N-oxides, heterocyclic amines, heterocyclic amine N-oxides and mixtures thereof in an amount ranging from about 0.001 or less to about 10 or more mole equivalents, based on the aldehyde. About 0.005 to about 2 mole equivalents are preferably employed, in particular about 0.005 to about 1.2 mole equivalents of the amine or of the amine N-oxide, based on the aldehyde. It is expressly pointed out that the nitrogen compounds with catalytic activity must have a higher boiling point than the product of the reaction in order to suppress contamination of the acid by the catalyst.
According to the teaching of the published Japanese patent application 53-105413, &agr;-branched aliphatic aldehydes are oxidized with oxygen in the presence of lithium or alkaline earth metal compounds, which are employed in amounts of from 0.01 to 10% by weight (based on the complete reaction system), in order to prepare &agr;-branched aliphatic carboxylic acids.
The procedure described in the French patent application 2 769 624 is characterized by maintaining low reaction temperatures, namely temperatures between 0 and 25° C. The process likewise requires the presence of alkali metal or alkaline earth metal compounds as auxiliaries. It is not disclosed what specific effects these compounds display, i.e. whether they merely improve the selectivity of the conversion, as known, or else possibly also increase the rate of reaction at the chosen low temperatures.
The published German patent application 26 04 545 relates to the preparation of alkylcarboxylic acids of general formula C
n
H
2n+1
COOH, in which n has a value from 2 to 18, by hydroformylation of an olefin C
n
H
2n
and direct oxidation of the reaction mixture resulting from the hydroformylation. Direct means in this connection that there is no previous workup of the hydroformylation product. The process is used in particular for preparing mixtures of isomeric C
9
to C
16
fatty acids. Suitable starting olefins are preferably dimers and trimers of propene and the butenes, including in particular the dimeric isobutene (2,4,4-trimethyl-1-pentene). Both individual reactions in the two-stage process, i.e. both the hydroformylation and the oxidation, are catalyzed by rhodium in the form of its compounds. The rhodium concentration in the reaction mixture subjected to the oxidation is therefore determined by the relatively high rhodium content in the hydroformylation product. In order to ensure that the overall process is economic, it is necessary to recover as completely as possible the noble metal from the final product of the process, the carboxylic acid, by suitable measures. In addition, it cannot be precluded that unwanted side reactions are favored by rhodium at the concentration present during the oxidation process, since the carboxylic acid yield is, as shown by the examples, inadequate for industrial exploitation of the process.
Larkin reports in J. Org. Chem. 1990, 55, pp. 1563 et seq. that the presence of catalysts in the commercially implemented oxidation of aldehydes to carboxylic acids is regarded as necessary because traces of metal salts are present in the reaction mixture and may catalyze the side reactions. The formation of the metal salts is attributed to corrosion of metallic parts of the system. The task of the catalysts is to overcompensate the effect of the corrosion products.
Ullmanns Encyclopadie der technischen Chemie, 4th edition 1972 et seq., volume 9, also refers to repeatedly to the adverse effect of metallic impurities in the initial aldehydes employed for the oxidation. Thus, for example, iron and cobalt salts dissolved in butyraldehyde lead, on oxidation thereof to butyric acid, to an increased production of by-products (loc. cit., page 142, left-hand column) and in the oxidation of 2-ethylhexanal to 2-ethylhexanoic acid the carbonylation of the initial aldehyde to heptane is promoted by heavy metal ions (loc. cit. page 144, left-hand column).
The known processes for preparing carboxylic acids from aldehydes do not yet meet to the full extent the requirements for modern processes used industrially. The use of
Lappe Peter
Springer Helmut
Celanese Chemicals Europe GmbH
Muserlian Lucas and Mercanti
Oh Taylor Victor
Trinh Ba K.
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