Preparation of dialkyl ketones

Details Preparation of dialkyl ketones Preparation of dialkyl ketones

2002-07-18

2004-04-20

Wilson, James O. (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

C568S395000, C568S401000, C568S404000

Reexamination Certificate

active

06723882

ABSTRACT:

The present invention relates to a process for preparing dialkyl ketones by reductive carbonylation of &agr;-olefins by means of carbon monoxide and hydrogen in the presence of a catalyst system.
Dialkyl ketones are important solvents and intermediates for organic syntheses. Thus, in particular, 3-pentanone (diethyl ketone) is an excellent solvent for paints. Furthermore, 3-pentanone is used in numerous syntheses, for example the preparation of trimethylphenol and of vitamin E.
Dialkyl ketones are obtainable via a wide variety of synthetic routes, for instance by ketonization of carboxylic acids or aldehydes or by oxidation of secondary alcohols, of olefins or of alkanes. Disadvantages of these synthetic routes are the use of expensive intermediates (carboxylic acids, aldehydes, secondary alcohols, olefins having a central double bond) and often unsatisfactory selectivities and yields in the oxidation of olefins and alkanes.
A further synthetic route is reductive carbonylation of &agr;-olefins (olefins having a terminal double bond) in the presence of hydrogen, water or compounds having a reducing action, e.g. alcohols (cf. Ullmann's Encyclopedia of Industrial Chemistry, 6
th
edition, 2000 electronic release, Chapter “KETONES—Dialkyl Ketones”). A disadvantage of the use of water as hydrogen source is the additional consumption of stoichiometric amounts of carbon monoxide for binding the oxygen. A disadvantage of the use of compounds having a reducing action is the associated coproduction of the corresponding oxidation products.
In the reductive carbonylation of &agr;-olefins in the presence of carbon monoxide and hydrogen to form the corresponding dialkyl ketones, use is usually made of metals of groups 8 to 10 of the Periodic Table. DE-A 2 061 798 discloses carbonylation in the presence of cobalt carbonyl complexes and ammonia, an amine or a nitrile at a pressure of preferably from 4.5 to 140 atmospheres (from 0.45 to 14 MPa abs). U.S. Pat. No. 4,602,116 describes carbonylation in the presence of triruthenium dodecacarbonyl at a pressure of preferably from 1000 to 2500 psig (from 7 to 17.3 MPa abs). GB-A 2 208 480 discloses carbonylation in the presence of a ruthenium compound, a protic acid and a water-soluble solvent at a pressure of preferably from 5 to 7.5 MPa abs. DE-A 1 793 320 teaches carbonylation in the presence of a rhodium-containing catalyst at a pressure of from 200 to 300 atm (from 20 to 30 MPa abs). GB-A 2 202 165 describes carbonylation in the presence of a platinum(II) compound, a diphosphine and a protic acid at a pressure of preferably from 2 to 7.5 MPa abs.
Disadvantages of the abovementioned processes are the unsatisfactory stability of the catalyst systems and the high pressure necessary in carrying out the carbonylation.
EP-A 0 322 811 teaches the reductive carbonylation of &agr;-olefins to form the corresponding dialkyl ketones in the presence of a catalyst system comprising a rhodium complex, a phosphine and a para-substituted benzoic acid having an electron-withdrawing substituent in the para position. Disadvantages of the abovementioned process are the unsatisfactory selectivity (coproduction of aldehyde and ketone) and the (lack of) stability of the catalyst system.
SU-A 813 903 teaches the carbonylation of olefins in the presence of hydrogen to form the corresponding dialkyl ketones in the presence of palladium(II) acetate, triphenylphosphine and trifluoroacetic acid at atmospheric pressure. A selectivity of 50-98% is described for the synthesis of diethyl ketone. A disadvantage of this process is the very low activity of the catalyst system.
It is an object of the present invention to find a process for preparing dialkyl ketones which no longer has the above-described disadvantages, is based on economically attractive and readily available raw materials, avoids the formation of coproducts, utilizes a very stable, active and long-lived catalyst system and makes it possible to prepare dialkyl ketones in high yield even under mild reaction conditions.
We have found that this object is achieved by a process for preparing dialkyl ketones by reductive carbonylation of &agr;-olefins by means of carbon monoxide and hydrogen in the presence of a catalyst system comprising
(a) palladium or a palladium compound;
(b) a phosphine;
(c) a protic acid having a pK
a
of ≦4.5, measured in aqueous solution at 25° C.; and
(d) a solubilizable carboxamide.
The presence of a solubilizable carboxamide is essential for the stability, activity and longevity of the catalyst system.
The carboxamides to be used in the process of the present invention are solubilizable in the reaction mixture and are also present in solubilized form under the reaction conditions. For the purposes of the present invention, the term “solubilized” refers to a largely homogeneous distribution of the carboxamide in the reaction mixture, which is able to stabilize the catalyst system sufficiently. In general, the carboxamide is homogeneously dissolved in the reaction mixture or at least colloidally dispersed.
The carboxamides to be used in the process of the present invention have at least one carboxamide group of the formula —CO—N< the molecule. The molar mass of the carboxamides can vary within a wide range from low molecular weight carboxamides having one carboxamide group in the molecule through to high molecular weight, polymeric carboxamides having a molecular weight of a few hundred thousand g/mol and a few hundred or a few thousand carboxamide groups in the molecule.
The chemical structure of the carboxamides to be used in the process of the present invention plays a minor role. Thus, the carboxamides can be, for example, saturated or unsaturated, aliphatic, aromatic or araliphatic compounds. Furthermore, the carboxamide can contain one or more heteroatoms such as oxygen, nitrogen, sulfur or phosphorus, for example —O—, —S—, —NH—, —NR—, —CO—, —CO—O—, —N═, —CO—N<, —SiR
2
—, —PR— and/or —PR
2
and/or be substituted by one or more functional groups containing, for example, oxygen, nitrogen, sulfur and/or halogen atoms.
As carboxamides having one carboxamide group of the formula —CO—N< in the molecule, preference is given to carboxamides of the formula (II)
where the radicals R′, R″ and R′″ are each, independently of one another,
hydrogen;
an acyclic or cyclic alkyl radical having from 1 to 30 carbon atoms which may contain one or more heteroatoms such as oxygen, nitrogen, sulfur or phosphorus, for example —O—, —NH—, —NR—, —CO— and/or —CO—O—, and/or may bear one or more functional, aromatic or heteroaromatic groups containing, for example, oxygen, nitrogen, sulfur and/or halogen atoms, for example —OH, —CHO, —NH
2
, —COOH, —F, —Cl, —Br and/or —CN, as substituents, for example methyl, ethyl, 1-propyl, 2-propyl (sec-propyl), 1-butyl, 2-butyl (sec-butyl), 2-methyl-1-propyl (isobutyl), 2-methyl-2-propyl (tert-butyl), 1-pentyl, 2-pentyl, 3-pentyl, 3-methyl-2-butyl, 2-methyl-2-butyl, 1-hexyl, 1-heptyl, 1-octyl, 2-ethyl-1-hexyl, 1-nonyl, 1-decyl, 1-dodecyl, 1-tetradecyl, 1-hexadecyl, 1-octadecyl, 1-eicosyl, cyclopentyl, cyclohexyl, cyclooctyl, phenylmethyl (benzyl), 2-phenyl-1-ethyl; or
an aromatic radical having 1 or 2 aromatic rings and from 3 to 30 carbon atoms which may contain one or more heteroatoms, for example nitrogen, and/or may bear one or more functional or aliphatic groups containing, for example, oxygen, nitrogen, sulfur and/or halogen atoms, for example —OH, —CHO, —NH
2
, —COOH, —F, —Cl, —Br and/or —CN, as substituents, for example phenyl, 2-methylphenyl (2-tolyl), 3-methylphenyl (3-tolyl), 4-methylphenyl (4-tolyl), 2,4-dimethylphenyl, 2,6-dimethylphenyl, 2,4,6-trimethylphenyl, 1-naphthyl, 2-naphthyl.
Particularly preferred carboxamides having one carboxamide group of the formula —CO—N<in the molecule are carboxamides (II) in which the radicals R′, R″ and R′″ are each, independently of one another,
a C
1
-C
10
-alkyl radical, for example methyl, ethyl, 1-propyl, 2-propyl (sec-propyl), 1-butyl, 2-butyl (sec-butyl

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