Process for the production of 6-methyl heptanone

Details Process for the production of 6-methyl heptanone Process for the production of 6-methyl heptanone

2001-09-10

2002-07-09

Richter, Johann (Department: 1621)

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

Organic compounds

Oxygen containing

C568S390000, C568S392000, C568S396000

Reexamination Certificate

active

06417406

ABSTRACT:

CROSS-REFERENCE TO A RELATED APPLICATION
The present application claims priority to German Application No. DE 100 44 390.7 filed Sep. 08, 2000, the contents of which are incorporated herein by reference
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing 6-methyl heptanone and corresponding methyl ketones, in particular phytone and tetrahydrogeranyl acetone, by aldolization of aldehydes with acetone in the presence of an aldolization catalyst and a heterogeneous hydrogenation catalyst containing a polyhydric alcohol.
2. Background of the Invention
Methyl ketones, in particular 6-methylheptan-2-one, tetrahydrogeranyl acetone and phytone, are important intermediates and starting materials for the production of odoriferous substances, pharmaceutical products and feedstuff additives (J. Org. Chem., 32 (1967), 177; J. Org. Chem., 28 (1963), 45; Bull. Soc. Chim. Fr. (1955), 1586). Furthermore isophytol is a central structural element in vitamin E synthesis.
The production of methyl ketones, in particular methyl heptanone, has been described in the relevant literature employing various synthesis strategies. For example, isoamyl halides and acetic acid esters may be coupled with one another in a nucleophilic substitution reaction in the presence of stoichiometric amounts of a base (pathway A), the &bgr;-ketone ester formed as intermediate is decarboxylated with the elimination of the corresponding alcohol and carbon dioxide. However, this process is not economical due to the disproportionate amount of starting materials required, the amount of CO
2
and alcohol produced as byproducts, and the salts that are formed (Wagner et al., “Synthetic Organic Chemistry”, 327, John Wiley & Sons, Inc., New York)
Another synthesis strategy employed starts with the production of various unsaturated methyl heptanone derivatives, such as 6-methyl-5-hepten-2-one or 6-methyl-3,5-heptadien-2-one (pathway B), which are hydrogenated in a separate reaction stage in the presence of heterogeneous catalysts to form methyl heptanone (Izv. Akad. Nauk SSSR, Ser. Khim. 5 (1972), 1052). The disadvantage of this method is the complicated production of the methyl heptenone and the need to carry out the synthesis as a multistage process. Other pathways that have been described is the oxidation of 6-methyl-5-hepten-2-ol (pathway C) (Recl. Trav. Chim. Pays Bas, 28, 116 (1909)) or the treatment of the alkenol with phosphoric acid and phosphorus pentoxide (pathway D) (Bull. Soc. Chim. Fr., 1799, (1963)). Both methods are unsuitable for industrial production of methyl heptanone because stoichiometric amounts of the corresponding reagents are consumed, the synthesis of the educt involves a multistage process and is complicated.
A large number of synthesis strategies described previously involve the accessibility of 6-methyl-5-hepten-2-one, from which the corresponding methyl heptanone can be produced efficiently by catalytic hydrogenation as illustrated above (pathway B). It was recognized relatively early on by manufacturers of odoriferous substances, aroma substances and vitamins that 6-methyl-5-hepten-2-one represents a central intermediate from which it is possible to produce various vitamins, such as vitamin E and vitamin A, carotinoids and odoriferous substances. Many of these processes are discussed below.
A multistage process starting from acetone (pathway E) is used industrially involving reacting acetone in the first stage in the presence of basic catalysts in ammonia to form methyl butinol. After Lindlar hydrogenation to form methyl butenol, the latter is reacted with diketene to form an intermediate in situ, which in turn is reacted in a Caroll rearrangement to form methyl heptenone (J. Org. Chem., 23, 153, (1958). It is clear that the large number of stages in the process, the use of diketene and acetylene and the associated stringent safety requirements severely restrict the industrial applicability of the process.
Another process for producing methyl heptenone, which has been described, involves reacting isobutene with formaldehyde and acetone under pressure (pathway F). These process conditions, which necessitate the use of high temperatures and pressures in order to achieve good conversions and selectivities, are associated with high apparatus costs and restrict the applicability of the process (DE 12 59 876, DE 12 68 135, U.S. Pat. No. 3,574,773).
Another described pathway for producing methyl heptenone, which under moderate conditions yields the desired product, is a two-stage process that has been adapted for industrial use. In the first stage isoprene is reacted with gaseous HCl in the presence of a Cu—I halide yielding an isomeric mixture of the corresponding allyl chlorides. The terminal prenyl chloride is coupled with acetone in a two-phase reaction with aqueous sodium hydroxide in the presence of a phase transfer catalyst (pathway G). The disadvantages of this process are the stoichiometric amount of salt that is formed and the moderate yields obtained, approximately 70% (U.S. Pat. No. 3,983,175 and U.S. Pat. No. 3,984,475).
In view of the aforementioned problems, the above-described processes are not useful from an economic standpoint in the synthesis of methyl heptanone. In particular, these processes for producing 6-methyl-heptan-2-one via 6-methyl-5-hepten-2-one are associated with a large number of stages, considerable expenditure and apparatus complexity.
Another described process involves the formation of a double bond isomer of 6-methyl-5-hepten-2-one, namely 6-methyl-3-hepten-2-one, by the cross-aldol condensation at moderate temperatures of isovaleraldehyde and acetone, in the presence of an aqueous alkali compound as catalyst (Nippon Kagaku Kaishi, 59, 224 [1938]).
The relatively low reaction temperatures that are used in order to achieve high selectivities mean that the reaction also stops at the &bgr;-hydroxyketone stage (Bull. Soc. Chim. Fr., 112, [1957]).
In GB 1,246, 698 acetone and isovaleraldehyde are reacted together at temperatures of greater than 200° C. and pressures of greater than 30 bar, in which only modest conversions of approximately 25% are achieved and acetone is used in a molar excess of 4 equivalents. In addition to the use of aqueous sodium hydroxide as catalyst for the conversion, heterogeneous oxides are also described as active aldolization catalysts.
DE-OS 26 15 308 (see also U.S. Pat. No. 4,146,581) describes the use of catalytic amounts of rare earth alkaline oxides combined with a heterogeneous hydrogenation catalyst (one or more metals of Group VIII of the Periodic System) for the cross-aldolization of symmetrical ketones with lower aldehydes (see reaction of acetone with isovaleraldehyde, Example 12), whereby the reaction is carried out at elevated temperatures under hydrogenating conditions (in the presence of hydrogen, preferably at a pressure between 20-30 bar). According to a variant of this process no heterogeneous rare earth oxides are used as aldolization catalysts, but instead a corresponding lipophilic salt (for example stearate) is used. The disadvantage of this process is that to achieve good selectivities, the ketone must be used in a substantial excess (3-5 equivalents with respect to the aldehyde that is used) and the conversion of aldehyde is not complete. With this procedure a considerable amount of unconverted methyl heptenone, in addition to the desired methyl heptanone, is obtained. No details of the effective service life of the heterogeneous systems that are used are given.
DE-OS 26 25 541 (corresponding to U.S. Pat. No. 4,212,825) is also concerned with a method for the direct production of higher saturated ketones, in particular 6-methyl heptanone, by cross-aldolization of acetone with 3-methyl-butanal using a heterogeneous supported catalyst that contains zinc oxide as aldolization component and nickel, cobalt or copper as hydrogenation component. The disadvantages of this method are incomplete conversions, unsatisfactory hydrogenation yielda, and second

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