Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2003-02-20
2004-09-14
Trinh, Ba K. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S598000, C562S606000
Reexamination Certificate
active
06790987
ABSTRACT:
The present invention relates to a catalytic process for the preparation of carboxylic acids by catalytic cleavage of lactones over catalysts derived from metals of group VIII of the Periodic Table of the Elements. In contrast to the known cleavage of lactones by saporification, in which carboxylic acids having hydroxyl groups originating from the lactone group, or functions formed from these form, in the cleavage according to the invention a carboxyl function is formed from the lactone function present in the molecule, although no hydroxyl function or functional group derived therefrom is formed.
Lactones play an important role, for example, in the fragrance and flavor industry. By contrast, as a starting material for the preparation of other products, lactones have hitherto only appeared to a minor degree. This is due, firstly, to the reactivity of the lactones. In the simplest reaction of lactones, hydrolysis, hydroxycarboxylic acids or derivatives thereof are formed. It is generally necessary to reduce the hydroxyl function; firstly to provide carboxylic acids or also esters with a broad potential field of use, and secondly, of course, also to avoid the back-formation of lactone. The otherwise known reactions of lactones virtually always lead only to products which are of no or only low industrial importance and/or can be prepared more favorably by another method.
It is also a factor here that, in addition to the frequently undesired reactivity pattern, lactones are generally expensive products. This is due to the comparatively complex preparation process. Of the processes for lactone preparation, the telomerization of butadiene with CO
2
and optionally further starting material compounds has recently become the focal point. As the starting materials are low in cost and present in large amounts, some lactones at least have become accessible at low cost and are available as starting substances for secondary reactions, some of which have still to be developed, to give products which are of potential interest for certain fields of application.
One example of a readily accessible lactone which may be mentioned is the &dgr;-lactone 2-ethylidene-6-heptenolide, which is prepared in a telomerization reaction from two molecules of butadiene and one molecule of CO
2
. Organophosphine-modified palladium complexes are used as catalysts. The process can be modified in various ways. Using modem process variants, yields of 95% with regard to the lactone are possible, and even the problem of catalyst recycling has meanwhile been solved in a number of ways. According to the process disclosed in WO 98/57745, this is possible, for example, by immobilizing the catalyst on a polystyrene support, or by extracting the resulting lactone when the reaction is complete and returning the catalyst which is insoluble in the extractant. This last process is disclosed in Chemie-Ingenieur-Technik 72 (2000), pages 58 to 61.
Hitherto known secondary reactions which have been carried out on this lactone are alkaline cleavage, which produces, as product, 2-ethylidene-5-hydroxy-6-heptenoic acid, and acid-catalyzed cleavage in the presence of methanol, which produces a mixture of the methoxy derivatives and the methylester of the abovementioned acid, see Z. Chem. 25 (1985), pages 220 to 221. Also known is the synthesis of the corresponding &ggr;-lactone from 2-ethylidene-6-heptenolide.
It is an object of the present invention to provide a process with which lactone cleavages can be carried out which produce, as secondary products, carboxylic acids which do not have hydroxyl groups or substituents derived therefrom. The process should be easy to carry out, produce high yields and leave intact other functional groups present on the lactone, such as, for example, olefin functions.
We have found that this object is achieved by a process for cleaving lactones optionally having functional groups to give carboxylic acids, this process comprising reacting the corresponding lactone with hydrogen under catalysis by a compound of a metal of group VIII of the Periodic Table of the Elements which has been modified with organophosphines.
The process according to the invention permits, as a result of the cleavage of lactones, the preparation of carboxylic acids which no longer have hydroxyl groups originating from the lactone function, but in which other functional groups are generally still present.
This is a transition-metal-catalyzed process in which catalytically active complexes of metals of group VIII of the Periodic Table of the Elements which have been modified with phosphine ligands are used. The metals are preferably chosen from the group consisting of Ru, Os, Pd, Pt, Rh and Ir. In particular, the metals are chosen from the group consisting of Rh and Ir.
The type of phosphine ligands which are used varies depending on the method by which the process according to the invention is carried out. This process can be carried out homogeneously in an organic phase, optionally with the addition of a solvent, heterogeneously in organic phase using an insoluble catalyst fixed to a support, optionally with the addition of an organic solvent, or in a two-phase system having one aqueous phase and one organic phase, optionally with the addition of an organic solvent.
If the homogeneous reaction method is chosen, the customary organophosphines are generally suitable; these may be mono-, bi- or else polydentate. In general, mono- or bidentate phosphines are used. These may be chosen from the known organophosphines soluble in the customary solvents. These are, for example, triarylphosphines, trialkylphosphines and alkylene- and arylene-bridged diphosphines which carry alkyl or aryl substituents. Examples include trimethylphosphine, triisopropylphosphine, tricyclohexylphosphine, triphenylphosphine, diphenylphosphinoethane and -methane, dimethylphosphinoethane and -methane, and the phosphines known under the name BINAP.
If the abovementioned phosphines are used, the reaction is carried out without the addition of a solvent or with the addition of a customary solvent, for example heptane, toluene, diethyl ether, dioxane or methanol or else mixtures thereof.
The resulting carboxylic acid is isolated by, for example, removing it from the reaction mixture by distillation, or extracting it therefrom, for example by acid-base extraction or using a suitable solvent.
Simple isolation and separation of the product from the catalyst is, according to one variant of the present invention, possible using phosphine ligands fixed to supports. All of the abovementioned phosphine ligands suitable for use in the process according to the invention can be fixed to suitable supports. These are, firstly, organic polymers, for example polystyrene, which may optionally be modified (Merrifield resin, Wang resin, aminomethyl-substituted polystyrene), Tentagel and polyamide resins. It is also possible to use inorganic supports, such as silicon dioxide and pulp.
In this process variant in which organophosphines fixed to supports are used, the reaction mixture can, when the reaction is complete, be separated off simply by decantation from the catalyst, which can then be reintroduced into the reaction. The reaction mixture separated off from the catalyst is then isolated and purified using customary methods, for example removal of the solvent by distillation followed by purification of the product by distillation.
In a preferred embodiment of the present invention, the process is carried out in a water/organic solvent two-phase system, in which case water-soluble phosphine ligands are used. These phosphine ligands may be mono- or bidentate and have the customary organic groups known to a person skilled in the art on the organic substituents bonded to the phosphorous, as a result of which the solubility in water is effected. Examples of such groups which effect solubility in water include carboxyl functions, hydroxyl functions, alkoxylated hydroxyl functions, phosphonato functions and sulfonyl functions, preferably sulfonyl functions.
One group of suitable water-s
Behr Arno
Brehme Volker
BASF - Aktiengesellschaft
Keil & Weinkauf
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