Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
1999-05-13
2001-07-24
Richter, Johann (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S347000
Reexamination Certificate
active
06265617
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application is based on German Application DE 19821379.4, filed May 13, 1998, which disclosure is incorporated herein by reference.
FIELD OF THE INVENTION
This invention relates to a process for the preparation of 3,5,5-trimethylcyclohexa-3-en-1-one (&bgr;-isophorone) by isomerization of 3,5,5-trimethylcyclohexa-2-en-1-one (&agr;-isophorone) in the liquid phase in the presence of a salt-like catalyst containing an inorganic cation.
BACKGROUND OF THE INVENTION
&bgr;-Isophorone is of great interest economically because it is an important synthetic structural unit for the preparation of carotinoids, vitamins and pharmaceutical products. &bgr;-Isophorone in particular is necessary as a precursor for ketoisophorone (=2,6,6-trimethylcyclohex-2-en-1 ,4-dione) and trimethylhydroquinone and hence for the preparation of vitamin E. In addition, it plays a crucial part in syntheses of perfumes and natural substances such as astaxanthin and abscisic acid and derivatives.
Isophorone is prepared by trimerization of acetone, with condensation of the C
3
structural units. &agr;-Isophorone is the main isomer formed because, unlike the &bgr;-isomer, it possesses a double bond conjugated to the keto function. For this reason, the thermodynamic equilibrium lies towards the &agr;-isophorone; the &bgr;-concentration is only about 1-2%, depending upon the temperature, and the equilibrium is established very slowly.
Although there are in principle two different methods of obtaining ketoisophorone, namely, the direct oxidation of &agr;-isophorone → ketoisophorone, and the detour via the isomerization of &agr;-isophorone → &bgr;-isophorone in an initial step and subsequent oxidation of &bgr;-isophorone → ketoisophorone, the latter process is clearly more advantageous. Scheme 1 illustrates these observations on the synthesis of ketoisophorone:
Over the years numerous processes for the isomerization of &agr;-IP have been described, which nevertheless have considerable disadvantages. Aspects such as high consumption of chemicals, poor space-time yield and problems during the working-up have hitherto prevented a practical transfer of the process to a larger scale.
In the processes for preparing &bgr;-IP from &agr;-IP, a distinction can be made between gas-phase reactions and liquid-phase reactions.
Four parallel reactions of &agr;-isophorone in the gas phase are possible in principle. These reactions compete with one another and succeed to a varying degree depending upon the selected temperature range and the surface condition of the catalyst employed.
In the gas phase, isophorone can react on contact in the following ways:
a) isomerization to &bgr;-isophorone
b) reduction to trimethylcyclohexadienes (the hydrogen necessary for this is supplied through the decomposition of IP, which is accompanied by coking phenomena)
c) &bgr;-elimination of methane to 3,5-xylenol
d) formation of mesitylene.
The catalyzed reactions of &agr;-IP in the gas phase on a heterogeneous contact are shown in the following Scheme 2:
EP 0 488 045 B1 discloses an isomerization process in the gas phase (300-450° C.) above a heterogeneous catalyst. The catalysts used are oxides and mixed oxides of Mg (group IIa), AI (IIIa), Si (IVa) and Ni (VIII), which are active per se or are applied to a y-aluminium oxide support (specific surface 1-50 m
2
/g). 1-10 kg &bgr;-IP is used per liter of catalyst; the concentration of the solution obtained as intermediate is 9% &bgr;-IP at most, depending on the catalyst loading; the end concentration after distillation under vacuum is 97% &bgr;-IP. NiO is granulated using 1% Luviskol K90 (- polyvinylpyrrolidone). Under optimal conditions, a catalyst performance of 0.33 liter &bgr;-IP/h/liter
cat
is achieved when this procedure is employed. Based on the volume of educt used, the space-time yield Y
R-Z
=0.09 liter
&bgr;-IP
/h/liter
solution
(Ex. 1).
Moreover, the withdrawal rate is low, which renders the process less attractive on the industrial scale.
In L. F. Korzhova, Y. V. Churkin and K. M. Vaisberg, Petrol. Chem Vol. 31, 1991, 678 the reaction of &agr;-IP at 300-800° C. in the presence of heterogeneous catalysts is described. The catalytic systems considered are &ggr;-aluminum oxide, magnesium oxide and quartz. The range of products is examined in relation to temperature and catalyst. The formation of &bgr;-IP, trimethylcyclohexadiene, 3,5-xylenol and of mesitylene are compared with one another (see Scheme 2: routes a., b., c.; d.). Thus the thermal decomposition of &agr;-IP at above 550° C. on a less developed catalytic surface (quartz) yields a mixture having the composition c>>a>>d and b=0. The reaction on the MgO contact at 400° C. shows a similar range of products at a significantly lower temperature, namely c>>a>d>b. In the presence of an aluminium oxide catalyst having a marked basic-acidic surface structure, the reaction takes place at 300° C. with a clear preference for the cyclohexadiene products, namely b>>c>d.
Altogether, it can be assumed that a catalytic gas phase isomerization as several quite definite disadvantages: in general, it can be said that these processes are disadvantageous because either the formation of the product is accompanied by a considerable accumulation of secondary products, or the space-time yield (absolute &bgr;-IP-formation/h/kg
cat
) is too low.
There are also a number of publications which deal with the isomerization in the liquid phase. The closest prior art is represented by the following documents:
D1=A. Heymes et al., Recherches 1971, 18, 104
D2=FR-A-1 446 246
D3=DE-OS-24 57 157
D4=U.S. Pat. No. 4,005,145
D5=EP-A-0 312 735
D6=JP87-33019 eq. to HEI-1-175954 v. 12.07.1989
D1 discloses the isomerization of (&agr;-IP to &bgr;-IP using stoichiometric quantities of MeMgX (X=halogen-), a Grignard compound. In the presence of catalytic quantities of FeCl
3
, 73% &bgr;-IP is obtained, with release of methane. Mechanistic concepts assume that the Grignard compound reacts as a base and does not function as the carrier of a carbanion. Excess Mg leads to the formation of mixtures of dimers, which are the result of a reducing metallic dimerization. However, the reaction of &agr;-isophorone with molar quantities of methylmagnesium iodide in the presence of catalytic quantities of FeCl
3
, the subsequent hydrolysis and the working-up by distillation is a complicated procedure as well as being expensive as regards chemicals.
D2 relates to the isomerization of &agr;-IP to &bgr;-IP in the presence of catalytic quantities of p-toluenesulfonic acid and aromatic sulfonic acids generally, in particular anilinesulfonic acid. The quantity of the catalyst used is 0.1-0.2%, based on the &agr;-IP used. However, a lower degree of conversion and a greater accumulation of secondary products prevents an industrial application of the process in D2.
According to D3, &bgr;-IP is prepared by boiling &agr;-IP for several hours in triethanolamine, fractionating and then washing the distillate with tartaric acid and common salt solution. Again, the consumption of chemicals and the labor expended in the process are considerable.
In D4, acids having a pK=2-5 and a boiling point higher than that of &bgr;-IP (bp &bgr;-IP=186° C./760 mm Hg) are used as catalyst. The patent claim explicitly protects the following compounds in the liquid phase:
aliphatic and aromatic amino acids, adipic acid, p-methyl-benzoic acid, 4-nitro-m-methylbenzoic acid, 4-hydroxy-benzoic acid, 3,4,5-trimethoxybenzoic acid, vanillic acid, 4-trifluormethylbenzoic acid, 3-hydroxy-4-nitrobenzoic acid and cyclohexanecarboxylic acid and derivatives.
The quantity of catalyst used is 0.1-20 mol.%. The yield of &bgr;-IP (based on &agr;-IP used) and therefore the selectivity is 74.5%. Under the given conditions this corresponds, converted to the quantity of catalyst used and time, to a yield Y=0.218 liters &bgr;-IP per kilogram of catalyst per hour.
The h
Hahn Rainer
Hasselbach Hans-Joachim
Huthmacher Klaus
Kretz Stephan
Krill Steffen
Degussa-Huls Aktiengesellschaft
Parsa J.
Pillsbury & Winthrop LLP
Richter Johann
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