Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2001-02-28
2001-11-13
Padmanabhan, Sreeni (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S320000, C568S357000, C568S361000, C568S389000, C568S399000
Reexamination Certificate
active
06316676
ABSTRACT:
The invention relates to an improved process for the preparation of ketones of the formula I
where
R
1
and R
2
are a hydrocarbon radical, or
R
1
and R
2
together are an unsubstituted or substituted alkylene group
and X is ═O or 2 alkoxy groups, by catalytic oxidation of the corresponding alcohols of the formula II
and, where necessary, subsequent hydrolysis of the resulting &agr;-diketone monoketals, in particular to an industrially advantageous preparation of diacetyl.
The most important representatives of the ketones of the formula I are, because of their particular olfactory properties, 2,3-butanedione (diacetyl), 1,2-cyclopentanedione, 1,2-cyclohexanedione, 2,3-pentanedione, 2,3-hexanedione and 3,4-hexanedione and the monoketals of said 1,2-cycloalkanediones, but in particular diacetyl.
Due to the large demand for these compounds, in particular diacetyl, there has been no lack of attempts to find suitable preparation processes for these diketones. For example, U.S. Pat. No. 2,043,950 (1936) discloses a process for the catalytic oxidation of ketols in which ketols are reacted with molecular oxygen in the presence of solid oxidation catalysts at elevated temperature. Examples of solid oxidation catalysts are metals, metal alloys, metal salts and metal oxides, preferably elements from Group 3 of the Periodic Table of the Elements, such as Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn and Se, in particular Cu, CuO and Ag. According to the examples, 2,3-butanedione (diacetyl) is obtained from 3-hydroxy-2-butanone (acetoin) on CuO in yields of only 48%, based on reacted acetoin, and on activated copper in yields of from 43 to 82% of theory, depending on conversion. A disadvantage of this process is that, even when the preferred catalysts are used, good yields, e.g. of 82%, are obtained only for low conversions (25%), while in the case of good conversions (e.g. 77%) only low yields (e.g. 43%) are obtained.
The Derwent abstract of SU 825 489 (1979) discloses a process in which diacetyl is obtained in 75% yield by heating acetoin in aqueous solution with iron (III) chloride. Disadvantages of this process are the inadequate yields and the way in which the process is carried out, which is complex on an industrial scale.
Furthermore, DE-A 28 31 229 (1978) discloses a process for the preparation of diketones in which glycols are oxidized using oxygen in the presence of a catalyst consisting of two or more layers of silver and/or copper crystals of specific particle size and under specific conditions of temperature and catalyst compositions. A disadvantage of this process is firstly that the preparation of the 2,3-butanediol required as starting compound for diacetyl is very complex, making 2,3-butanediol very expensive, and secondly that in the reaction of 2,3-butanediol to diacetyl according to Example 3 of this patent, only yields of 76% of theory are obtained.
Furthermore, DE-A 28 31 595 (1978) discloses a process for the preparation of specific carbonyl compounds by oxidation of the corresponding alcohols with oxygen in the presence of silver crystals and/or copper crystals having a particle size of from 0.01 micrometer to 2.5 millimeter at from 450 to 700° C. and a residence time of at most 0.1 second. Essentially aliphatic or cycloaliphatic aldehydes or cycloalkanols are prepared by this process. However, the possibility of using this process to prepare &agr;-ketocarboxylic esters is also described. In the only example in this respect, however, isobutyl &agr;-oxo-isocaprate is only obtained in yields of 81% of theory.
DD 296 274 A (1990) discloses a process for the preparation of &agr;-diketones in which &agr;-acetoxy alkynes are oxidized in a carboxylic acid as solvent at from 0 to 100° C. in the presence of a Pd (II) salt, and the resulting &agr;,&bgr;-unsaturated &agr;-acetoxyketones are converted into &agr;-diketones by subsequent hydrolysis.
Disadvantages of this process are the unsatisfactory yields and the industrially complex way in which the process is carried out.
Furthermore, C.A. 123:285011X (Abstract of Stud. Surf. Sci. Catal. 1994, 82, pages 853-60) discloses the preparation of diacetyl by partial oxidation of methyl ethyl ketone on a vanadium oxide catalyst. A disadvantage of this process is that relatively large amounts of acetic acid, acetaldehyde, methyl vinyl ketone, propionaldehyde and CO
2
are formed as byproducts.
In more recent experiments for the oxidation of acetoin with Ce(IV) in aqueous HClO
4
, no diacetyl at all was isolated since it reacted further to give acetic acid (cf. Acta Chem. Scand. (1991), 45(5), pages 543-5).
Furthermore, WO 96/04229-A1 discloses the oxidation of diols with gaseous fluorine to give 1,2-hydroxy-carbonyl compounds or to give 1,2-diones. A disadvantage of this process is that fluorine is a relatively expensive and dangerous-to-handle oxidizing agent.
EP 658 533 (1994) describes the oxidation of diols with o-iodoxybenzoic acid in dimethyl sulfoxide at from 40 to 50° C. A disadvantage of this process is that the oxidizing agent is difficult to prepare and is therefore very expensive.
Furthermore, EP 430 406 discloses the fermentative preparation of diacetyl and acetoin from sugars using lactic acid bacteria. A disadvantage of this process is that the yields which can be achieved are still inadequate.
It is an object of the invention to develop a highly advantageous process for the preparation of &agr;-diketones from the corresponding ketols or ketals of these ketols, which permits the preparation of &agr;-diketones, in particular diacetyl, even on an industrial scale in very good yields and space-time yields from relatively readily available starting compounds using low-cost oxidizing agents and on catalysts which are stable over a long period, with good sensory properties.
Relatively readily available starting compounds which have proven useful are ketols and ketals of ketols. For the preparation of diacetyl, which is in demand in particular as a butter aroma, these are acetoin, which is readily available by electrochemical oxidation of 2-butanone, and in particular 3,3-dialkoxy-2-butanols, which are very readily available, even on an industrial scale, by the process, described in EP 460 451, by electrochemical oxidation of methyl ethyl ketone (2-butanone) in the presence of alkanols, water and an auxiliary electrolyte.
The invention thus provides a process for the preparation of carbonyl compounds of the formula I
where
R
1
and R
2
are a saturated or unsaturated, branched or unbranched aliphatic, cycloaliphatic, aromatic-aliphatic or cycloaliphatic-aliphatic radical having from 1 to 10 carbon atoms, preferably an alkyl group having from 1 to 4 carbon atoms, in particular a methyl group or ethyl group, or
R
1
and R
2
together are an alkylene group having from 3 to 10 carbon atoms which is unsubstituted or substituted by lower alkyl groups, preferably a propylene or butylene group,
and X is ═O or 2 alkoxy groups —OR
3
, where R
3
is a saturated or unsaturated, branched or unbranched aliphatic radical having from 1 to 6 carbon atoms, preferably an alkyl group having from 1 to 4 carbon atoms, in particular a methyl group or ethyl group, or the two R
3
together are an alkylene group having from 3 to 6 carbon atoms which is unsubstituted or substituted by lower alkyl groups, in particular by methyl or ethyl groups,
which comprises oxidizing alcohols of the formula II
where R
1
to R
3
and x are as defined above,
with oxygen in the gaseous phase
a) at temperatures of from 270 to 600° C., preferably from 300 to 550° C., on silver coated catalysts which comprise an abrasion-resistant coating of metallic silver on a core of inert support material, or
b) at temperatures of from 450 to 750° C., preferably from 480 to 600° C., on silver crystals and/or copper crystals, preferably on silver crystals, having a particle size of from 0.1 to 2.5 mm for a residence time of at most 0.1 second.
Suitable starting materials of the formula II for the novel process are thus compounds in which X is ═O, i.e. ketols. In general,
Aquila Werner
Botzem Jorg
Brunner Melanie
Fuchs Hartwig
Krause Wolfgang
BASF - Aktiengesellschaft
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Padmanabhan Sreeni
LandOfFree
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