Process for the production of 6-methylheptanone

Details Process for the production of 6-methylheptanone Process for the production of 6-methylheptanone

2002-03-08

2003-06-24

Richter, Johann (Department: 1621)

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

Organic compounds

Oxygen containing

C568S392000

Reexamination Certificate

active

06583323

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for the production of 6-methylheptanone or a corresponding homologous methylketone by reacting isovaleraldehyde or a corresponding longer-chain aldehyde and acetone in the presence of an alkali- or earth alkali metal-containing catalyst and a heterogeneous hydrogenating catalyst.
2. Discussion of the Background
Methylketones, in particular 6-methylheptan-2-one, tetrahydrogeranyl acetone and phytone are important intermediates and starting materials for the production of perfumes, pharmaceutical products and feedstuff additives (J. Org. Chem., 32 (1967), 177; J. Org. Chem., 28 (1963), 45; Bull. Soc. Chim. Fr. (1955), 1586), in particular of isophytol which, in turn, is a central compound of vitamin E synthesis.
The production of methylketones, in particular methylheptanone, is described in the relevant literature, various synthesis strategies being used. Thus isoamylhalides and acetic acid esters can be coupled with each other in a nucleophilic substitution reaction in the presence of stoichiometric quantities of a base (Method A). The &bgr;-ketoester that is formed as an intermediate is decarboxylated under separation of the corresponding alcohol and carbon dioxide. The process is uneconomical because it lacks atomic economy, the high quantity of waste CO
2
and alcohol produced and the salt load formed (Wagner et. al., “Synthetic Organic Chemistry”, 327, John Wiley & Sons, Inc.).
A further synthesis strategy begins initially with the production of various unsaturated methylheptanone derivatives, such as 6-methyl-5-hepten-2-one or 6-methyl-3,5-heptadien-2-one (Method B), which are hydrogenated to methylheptanone in a separate reaction step in the presence of heterogeneous catalysts (Izv. Akad. Nauk SSSR, Ser. Khim. 5 (1972), 1052). The disadvantage of this method is the cost of producing the methylheptenone and the necessity of carrying it out as a multi-stage process.
A further possibility is the oxidation of 6-methyl-5-hepten-2-ol (Method C), as disclosed in Recl. Trav. Chim. Pays Bas, 28, 116 (1909), or the treatment of the alkenol with phosphoric acid and phosphor pentoxide (Method D) according to Bull. Soc. Chim. Fr., 1799 (1963). Both methods are unsuitable for the industrial production of methylheptanone, as stoichiometric quantities of the relevant reagents are consumed and the synthesis of the educt is a complex multi-stage process.
A large number of synthesis strategies have dealt with the accessibility of 6-methyl-5-hepten-2-one, from which the corresponding methylheptanone can be produced efficiently by catalytic hydrogenation as illustrated above (Method B). Producers of perfumes, flavorings and vitamins recognized relatively early on that 6-methyl-5-hepten-2-one is a central intermediate on the basis of which various vitamins, including vitamin E and vitamin A, carotenoids and perfumes can be produced. The main processes are explained here by way of example.
In an industrially used multi-stage process (Method E), acetone is converted in a first stage to methylbutinol in ammonia in the presence of basic catalysts. After Lindlar hydrogenation to methyl butenol, it is reacted with diketene and the intermediate formed “in situ” is converted to methylheptenone in a Caroll rearrangement (J. Org. Chem., 23, 153, (1958). Obviously, the large number of stages in the process and the use of diketene and acetylene with the associated high safety requirements, severely restrict the industrial applicability of the process.
A further process for the production of methylheptenone comprises the reaction of 2-methylpropene with formaldehyde and acetone under pressure (Method F). However, the process conditions, which require the use of high temperatures and pressures to achieve good conversions and selectivities, entail 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).
A further route to methylheptenone, which achieves the aim under moderate conditions, is a two-stage process, which has now been adapted for industrial use. In the first step, isoprene is reacted with HCl gas in the presence of a CU—I-halogenide, forming an isomer mixture of the corresponding allyl chlorides. The terminal prenyl chloride is coupled with acetone in a two-phase reaction with aqueous sodium hydroxide solution in the presence of a phase transfer catalyst (Method G). The disadvantage of this process is the stoichiometric formation of salts and moderate yields in the order of 70% (U.S. Pat. Nos. 3,983,175 and 3,984,475).
In view of the cited problems, it seems uneconomical to choose one of the stated synthesis strategies for the production of methylheptanone. In particular, the route known to 6-methylheptan-2-one via 6-methyl-5-hepten-2-one entails a high number of stages and considerable expenditure for equipment.
An alternative process is to access a double-bond isomer of 6-methyl-5-hepten-2-one, i.e. 6-methyl-3-hepten-2-one, by means of crossed aldol condensation of isovaleraldehyde and acetone at moderate temperatures in the presence of an aqueous alkali compound as a catalyst (Nippon Kagaku Kaishi, 59, 224 [1938]).
The lower reaction temperatures, which are set to achieve high selectivities, mean that the reaction also remains at the &bgr;-hydroxyketone stage (Bull. Soc. Chim. Fr., 112 [1957]).
In GB 1,246, 698 acetone and isovaleraldehyde are reacted with each other at temperatures of >200° C. and pressures of >30 bar. Only modest yields of ca. 25% are achieved and acetone is used in a molar excess of 4 equivalents. Aqueous sodium hydroxide solution is used as a catalyst for conversion. In addition, heterogeneous oxides are also disclosed as active aldolizing catalysts.
DE-OS 26 15 308 (see also U.S. Pat. No. 4,146,581) describes the use of catalytic quantities of rare earth alkali oxides and simultaneously of a heterogeneous hydrogenating catalyst (one or more metals of Group VIII of the periodic system) for crossed aldol condensation of symmetrical ketones with low aldehydes (see reaction of acetone with isovaleraldehyde, ex. 12). The reaction is carried out at higher temperatures under hydrogenating conditions (in the presence of hydrogen, preferably at 20-30 bar). According to a variant of this process, a corresponding lipophilic salt (e.g. stearate) is used as aldolizing catalyst rather than a heterogeneous rare earth alkali oxide. The disadvantage of this, substantially good, process is that to achieve good selectivities, the ketone is used in a clear excess (3-5 equivalents in relation to the aldehyde used) and aldehyde conversion is not complete. In addition to the desired methylheptanone, a considerable content of unconverted methylheptenone is also obtained from this procedure. The residence times of the heterogeneous systems used are not discussed.
DE-OS 26 25 541 (corresponds to U.S. Pat. No. 4,212,825) also deals with a method for direct production of higher saturated ketones, in particular 6-methylheptanone, by crossed aldol condensation of acetone with 3-methyl-butanal using a heterogeneous supported contact, which contains zinc oxide as the aldolizing component and nickel, cobalt or copper as the hydrogenating component. The disadvantages of this method are incomplete conversion, unsatisfactory hydrogenation yield and by-products formed by consecutive reactions of methylheptanone with a further equivalent isovaleraldehyde (product mixture contains 2,10-dimethylundecane-6-one and unsaturated precursors). Catalyst preparation is also expensive. No details are given of the long-term activity of the catalyst.
The use of zinc oxide “per se” as an aldolizing catalyst for the production of the corresponding &agr;,&bgr;-unsaturated ketones is disclosed in U.S. Pat. No. 4,005,147. The use of lipophilic zinc salts in the presence of a hydrogenating catalyst is disclosed in U.S. Pat. No. 3,316,303, where, in particular, the use of an unsuitable hydrogenating catalyst (sulfide of the elements Mo, Ni, W or a c

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