Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
1997-08-15
2003-02-04
Stockton, Laura L. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S593000, C562S580000, C562S600000, C562S554000
Reexamination Certificate
active
06515171
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for separating an oxidation reaction product or its salt, and an oxidation catalyst from a reaction mixture, the reaction mixture being obtained by oxidation of a substrate with using an imide compound such as N-hydroxyphthalimide as the oxidation catalyst.
BACKGROUND OF THE INVENTION
N-hydroxyphthalimide and other imide compounds are known as oxidation catalysts, such oxidation being conducted by allowing a substrate such as a hydrocarbon, an alcohol, an aldehyde, a ketone, an amine and a heterocyclic compound to contact with molecular oxygen (Japanese Patent Application Laid-open No. 38909/1996 (JP-A-8-38909)). An oxidation reaction by means of this catalyst, which can be conducted under mild conditions without any exhaust gas treatment, can provide an oxidation reaction product including an alcohol, an aldehyde, a ketone and an organic acid at a high conversion rate and selectivity. Such an oxidation reaction product is separated from a reaction mixture commonly by distillation.
Distillation, however, is not always an advantageous process for separation of an oxidation reaction product from a reaction mixture. When both of the oxidation reaction product and the substrate have low boiling points (e.g. 50 to 150° C.), distillation results in deterioration of purity and yield owing to the substrate with a low boiling point. On the other hand, when the oxidation reaction product is a compound with a high boiling point (e.g. 150 to 500° C.), the oxidation catalyst might be decomposed during distillation which is carried out at a high temperature with heating. The imide compound has a low decomposition temperature, for example, 230° C. in the case of N-hydroxyphthalimide. Thus, distillation, as a process for separating a high-boiling-point oxidation reaction product, has a risk of thermal decomposition of the oxidation catalyst, failing to reutilise the oxidation catalyst and raising the cost. Besides, the thermally decomposed product of the oxidation catalyst might degrade the quality of the reaction product. As mentioned above, it is not wise to choose distillation for separation of an oxidation reaction product having any boiling point from a reaction mixture without any consideration.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a process for separating an oxidation catalyst such as N-hydroxyphthalimide or other imide compounds from a reaction mixture obtained by oxidation of a substrate such as a hydrocarbon in order to make effective use of the oxidation catalyst.
It is another object of the present invention to provide a process for efficiently separating the imide compound to be reutilised while preventing decomposition thereof, even when the oxidation reaction product is a compound with a high boiling point.
It is yet another object of the present invention to provide a process for efficient separation of the oxidation reaction product and the oxidation catalyst from the reaction mixture obtained by oxidation of the substrate, the process not being affected by the boiling point of the reaction product.
A further object of the present invention is to provide a process for separating the oxidation reaction product and the oxidation catalyst from the oxidation reaction mixture by an easy operation under mild conditions.
After intensive works for achieving the above objects, the inventor of the present invention has found that, in an oxidation reaction using an imide compound such as N-hydroxyphthalimide as the oxidation catalyst, use of an aqueous solvent at least containing water and a non-water-soluble solvent helps efficient distribution of the oxidation reaction product into an aqueous solvent layer and efficient distribution of the oxidation catalyst into a non-water-soluble solvent layer, each solvent acting as an extracting solvent. The present invention is based on the above findings.
The separation process of the present invention is a process for separating an oxidation reaction product and an oxidation catalyst from a reaction mixture obtained by oxidation of a substrate in the presence of an imide compound shown by the formula (1) as the oxidation catalyst, which process comprises using an aqueous solvent containing at least water and a non-water-soluble solvent separable from the aqueous solvent, thereby efficiently distributing the oxidation reaction product into the aqueous solvent layer and the oxidation catalyst into the non-water-soluble solvent layer,
wherein R
1
and R
2
independently represents a hydrogen atom, a halogen atom, an alkyl group, an aryl group, a cycloalkyl group, a hydroxyl group, an alkoxy group, a carboxyl group, an alkoxycarbonyl group or an acyl group; R
1
and R
2
may together form a double bond, or an aromatic or nonaromatic ring; X stands for an oxygen atom or a hydroxyl group; and n denotes an integer of 1 to 3.
The imide compound includes, for instance, N-hydroxyphthalimide and other N-hydroxyimide compounds. As the substrates, there may be mentioned hydrocarbons, alcohols, aldehydes, ketones, amines and heterocyclic compounds. Use of the above substrate provides a corresponding oxidation reaction product (e.g. an alcohol, an aldehyde, a ketone, a carboxylic acid). Water can be used as the aqueous solvent containing at least water (hereinafter it may be referred to as “hydrophilic solvent” or “aqueous solvent”). As the non-water-soluble solvent (hereinafter it may be referred to as “hydrophobic solvent” or “hydrophobic organic solvent”), use can be made of hydrocarbons, ketones, esters and nitriles.
DETAILED DESCRIPTION OF THE INVENTION
[Imide Compound]
In the compound of the formula (1), the halogen atom as the substituents R
1
and R
2
includes iodine, bromine, chlorine and fluorine atoms. Examples of the alkyl group include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, t-butyl, pentyl, hexyl, heptyl, octyl, decyl groups and other straight chain or branched chain alkyl groups each having about 1 to 10 carbon atoms. A preferred alkyl group includes an alkyl group having about 1 to 6 carbon atoms, and, in particular, a lower alkyl group having about 1 to 4 carbon atoms.
The aryl group includes, for example, a phenyl group and a naphthyl group. The cycloalkyl group includes cyclopentyl, cyclohexyl, and cyclooctyl groups. As the alkoxy groups, there may be mentioned, for instance, methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, t-butoxy, pentyloxy, hexyloxy and other alkoxy groups each having about 1 to 10 carbon atoms. Among them, alkoxy groups each having about 1 to 6 carbon atoms, in especial, lower alkoxy groups each having about 1 to 4 carbon atoms are desirable.
Examples of the alkoxycarbonyl group include methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, isopropoxycarbonyl, butoxycarbonyl, isobutoxycarbonyl, t-butoxycarbonyl, pentyloxycarbonyl, hexyloxycarbonyl and other alkoxycarbonyl groups each having about 1 to 10 carbon atoms in the alkoxy moiety. A preferable alkoxycarbonyl group includes an alkoxycarbonyl group having about 1 to 6 carbon atoms, above all, a lower alkoxycarbonyl group having about 1 to 4 carbon atoms.
As examples of the acyl group, there may be mentioned formyl, acetyl, propionyl, butyryl, isobutyryl, valeryl, isovaleryl, pivaloyl and other acyl groups each having about 1 to 6 carbon atoms.
The substituents R
1
and R
2
may be the same, or be different from each other. Further, R
1
and R
2
in the formula (1) may bond together to form a double bond, or an aromatic or nonaromatic ring. A preferred aromatic or nonaromatic ring has about 5 to 12 members, in particular about 6 to 10 members. The ring may be a heterocycle or condensed heterocycle, but it may practically be a hydrocarbon ring. Such a ring includes, for example, nonaromatic alicyclic rings (e.g. a cyclohexane ring and other cycloalkane rings, each of which may have a substituent, a cyclohexene ring and other cycloalkene rings, each of which may have a substituent), nonaromatic bridged rings (e.g.
Birch & Stewart Kolasch & Birch, LLP
Daicel Chemical Industries Ltd.
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