Organic compounds -- part of the class 532-570 series – Organic compounds – Fatty compounds having an acid moiety which contains the...
Reexamination Certificate
2002-09-10
2004-02-24
Carr, Deborah (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Fatty compounds having an acid moiety which contains the...
C554S132000
Reexamination Certificate
active
06696582
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 the customary starting materials for obtaining carboxylic acids. The preference for aldehydes for this area of use derives from their manifold availability and the easy oxidative conversion of the carbonyl group into the carboxyl group. In processes applied industrially, the conversion of aldehydes to carboxylic acids mainly takes/place in the presence of catalysts. However, 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. 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 salts have an inhibitory effect, so that the reaction time must be extended 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 molar ratio of manganese to copper being in the range 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 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. 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 catalysts which possibly increase the reaction rate at the mild temperatures which are to be maintained. This is because long reaction times not only are prohibited for economic reasons but may also lead to unwanted side reactions.
DE 29 31 154 C2 discloses the preparation of aliphatic carboxylic acids with 4 to 10 carbon atoms by oxidation of the corresponding aldehydes with oxygen or oxygen-containing gases in the presence of the complex anion [Fe(CN)
5
H
2
O]
3−
as catalyst. The thermal instability of the anion restricts the reaction temperature to a range from 20 to 50° C.
Mixtures of isomeric branched aliphatic or cycloaliphatic carboxylic acids are obtained by the procedure of German patent 1 154 454 from aldehydes which are oxidized in a thin liquid layer at a temperature of 65 to 110° C. with an oxygen-containing gas without use of catalysts. The reaction is carried out in tubes which are empty or packed with inert materials with a large surface area. The proportion of acid in the product of the reaction is between 59 and 80%.
The known processes for preparing carboxylic acids from aldehydes do not yet meet all the technical and economic requirements for modern processes used industrially. The use of catalysts is associated with elaborate purification steps, to which the product of the reaction must be subjected in order to obtain carboxylic acids which can be processed further without problems. Noncatalytic processes are frequently unsatisfactory in terms of the conversion and selectivity for the required product.
The object therefore was to develop a procedure which avoids the disadvantages mentioned and makes it possible to obtain carboxylic acids from aldehydes in high yield with acceptable technical complexity.
This object is achieved by a process for preparing aliphatic carboxylic acids having 4 to 10 carbon atoms by oxidation of the corresponding aldehydes with oxygen or oxygen-containing gases. The process comprises carrying out the oxidation in the temperature range from 0 to 100° C. in at least two stages, with the temperatures increasing from stage to stage.
Deliberate management of the temperature makes it possible to carry out the oxidation of aldehydes to carboxylic acids with oxygen in pure form or as a constituent of gas mixtures, with high conversion, very selectively and without use of catalysts. In this connection, reference must be made in particular to the fact that low reaction temperatures, i.e. temperatures up to about 40° C., lead to unsatisfactory conversions, whereas higher reaction temperatures, i.e. temperatures above about 40° C., distinctly impair the selectivity of the reaction. In these circumstances, it was not to be expected that combining ranges of lower and higher reaction temperature does not lead to a cumulation of the unwanted results but, on the contrary, optimizes both the conversion and the selectivity. It is also noteworthy that the use of different temperatures during the reaction effectively suppresses the formation of peroxy compounds, which may induce uncontrolled oxidation reactions and thus impair the selectivity of the reaction and, moreover, because they are able to decompose easily also require special safety measures.
A very essential feature of the procedure of the invention is the choice of the temperature range in which the reaction takes place, and the control of the changes in temperature during the reaction within this range. It has proved suitable to oxidize the aldehydes in the novel process at temperatures between 0 and 100° C., preferably between 20 and 100° C. and, in particular, between 40 and 80° C. In contrast to previous practice, the reaction is carried out not at a constant temperature or a temperature which is approximately constant within technical possibilities, but in a plurality of stages. The stages differ from one another in such a way that the temperature increa
Heymanns Peter
Springer Helmut
Carr Deborah
Celanese Chemicals Europe GmbH
Muserlian Lucas and Mercanti
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