CH632730A5 - Process for the preparation of branched olefins - Google Patents

Description

The invention relates to a process for the preparation of branched olefins having at least 2 and not more than 3 double bonds. Some of these olefins are important as a base material for more valuable products, some are of interest as chemical flavorings.

The olefins of formula I.

30th

1 t »3

R \ 4 'R

, C = CR - X - C = CII,

(I)

2X

R

7> -CH2

(III)

in which R6 and R7 are each an alkyl radical having 1 to 4 carbon atoms, in the presence of a disproportionation catalyst.

2. The method according to claim 1, characterized in that one uses a compound of formula II in which R5 is the methyl radical.

3. The method according to claim 1 or 2, characterized in that one uses a compound of formula II, in which R1 and R2 are methyl or ethyl radicals and R4 is a hydrogen atom.

4. The method according to any one of claims 1 to 3, characterized in that an isoolefin of the formula III is used, in which Re and / or R7 is the methyl radical.

5. The method according to any one of claims 1 to 4, characterized in that one uses a compound of formula II in which X is the ethylene radical.

6. The method according to any one of claims 1 to 5, characterized in that one uses a heterogeneous disproportionation catalyst.

7. The method according to any one of claims 1 to 6, characterized in that the catalyst used is rhenium oxide on Y aluminum oxide.

8. The method according to any one of claims 1 to 7, characterized in that a catalyst is used which contains 0.1 to 10 percent by weight of potassium oxide as an accelerator.

9. Application of the method according to claim 1 to a compound of formula II, which is obtained by isomerization of the double bond of a compound of formula V.

in which R1 to R4 and X have the meaning given in claim 1 are not readily available. Processes for their preparation, which start from compounds which are more readily available, are often complicated and consist of several process steps, as a result of which a low overall yield is obtained.

It has now been found that the desired compounds of the formula I can be obtained directly by disproportionation of other more readily available olefins with an isoolefin.

The invention thus relates to a process for the preparation of the compounds of the formula I which is characterized in that a compound of the formula II

.1

50

N -4. x - C '= CH-R5 (II>

, 2 /

C »CR

in which R1, R2, R3, R4 and X are as defined in formula I ss and Rs is an alkyl radical having 1 to 4 carbon atoms, with an isoolefin of the formula III

60

, '^ C-CH2

(III)

in which Rö and R7 are each an alkyl radical with 1 to 4 carbon 65 atoms, in the presence of a disproportionation catalyst.

In formulas I and II, R1 and R2 are preferably lower alkyl radicals, e.g. Methyl or ethyl radicals. R4 is ahead

preferably a methyl radical or, particularly preferably, a hydrogen atom.

Specific examples of X are the ethylene, 1,2-propylene, 1,3-propylene and 2,3-propylene radical as well as the 3-methyl-3-hexenylene radical, with the ethylene radical being preferred.

The reaction of the compounds of the formula II and III according to the invention gives rise to 2 disproportionation products, namely a compound of the formula I and a compound of the formula IV,

in which R5, R6 and R7 are as defined above.

You get favorable results especially when

if a compound of the formula II in which Ra is the methyl radical is reacted with more reactive isoolefins of the formula III, in particular with isobutene or methylbutene-1.

In a preferred embodiment of the process according to the invention, 2,6-dimethylocta-2,6-diene is reacted with isobutene to give 2,6-dimethylhepta-1,5-diene (isononadiene) and 2-methylbutene-2.

In another embodiment of the process according to the invention, 2,4,6-trimethylocta-2,6-diene and isobutene are converted to 2,4,6-trimethylhepta-1,5-diene and 2-methyl-butene-2. These methyl-substituted heptadiene are of interest as intermediates for chemical flavors such as hydroxycitroneilal and its homologues. (For the production of hydroxycitroneilal from isononadiene, see DE-OS 2 652 202).

The process according to the invention can be carried out in the presence of any suitable disproportionation catalyst. A homogeneous catalyst can be used, e.g. if the reaction is carried out batchwise, or preferably a heterogeneous catalyst system. A non-exhaustive number of disproportionation catalysts are described in “Catalyst Reviews”, Volume 3 (1969), pages 37 to 60. Suitable catalysts contain one or more transition metal oxides, e.g. Group VII metal oxides of the periodic table, such as a compound of the formula Re207 on a support, such as aluminum oxide, or tungsten oxide on silica gel. These catalyst systems can also contain one or more accelerators, such as oxides of alkali and alkaline earth metals, e.g. Potassium and cesium oxide. A catalyst is preferred which contains 5 to 70 percent by weight of rhenium oxide on y-aluminum oxide and a small amount, generally 0.1 to 10%, preferably 1 to 2%, of potassium oxide as accelerator.

Suitable reaction temperatures for the process according to the invention are between −20 and 200 ° C. Undesirable side reactions often occur at higher temperatures. When using catalysts containing rhenium oxide, temperatures of 20 to 100 ° C. are very satisfactory, and temperatures of 20 to 80 ° C. are preferred. When using tungsten oxide-containing catalysts, a slightly higher temperature is required, e.g. 120 to 150 ° C. A suitable reaction pressure is between 1 to 150 bar, in particular 1 to 100 bar and preferably between 1 to 25 bar.

The isoolefin of the formula III is advantageously used in a molar excess, based on the olefin of the formula II, in the process according to the invention. Molar ratios up to 50: 1 are suitable, ratios up to 10: 1 are preferred.

632 730

The process according to the invention is advantageously carried out continuously. In a preferred embodiment, the reactants are fed in at one end of a tubular reactor which contains the disproportionation catalyst and possibly additional inert materials, and the product is withdrawn at the other end. Solvents and diluents are not necessary, but they can be used if necessary. Suitable solvents are alkanes with 5 to 14 carbon atoms, e.g. Heptane, cyclic or bicyclic alkanes or alkenes, e.g. Cyclohexane, pinane or l-isopropenyl-2,3-dimethylcyclopentane, aromatic compounds such as toluene, xylene and halogenated benzenes, e.g. Chlorobenzene.

The compounds of formula II, if they are not available, can be easily prepared, e.g. B. you can a compound of formula II in which R5 is the methyl radical,

by isomerizing the double bond of a compound of formula V.

\ A (previous year

2> • C ■ CR - X - CH - CH ■ CH, R 2

in which R1 to R4 are as defined in formula I.

So you can e.g. Prepare dihydroocimene (2,6-dimethylocta-2,6-diene) by isomerizing dihydromyrcene (2,6-dimethylocta-2,7-diene). If R1 and / or R2 is also the methyl radical, the compounds of the formula II can also be prepared from isomers which contain 2 terminal unsaturated bonds. Dihydroocimene can also be obtained from y-dihydromyrcene (2,6-dimethylocta-l, 7-diene).

In a preferred embodiment of the process according to the invention, compounds of the formula II in which R5 is the methyl radical and which have been prepared in situ are reacted, ie the mixture containing these compounds is directly subjected to disproportionation by adding the isoolefin of the formula III without previous isolation of the compound of formula II.

This isomerization of compounds containing 1 or 2 terminal double bonds to compounds of the formula II is preferably carried out in the presence of an alkaline isomerization catalyst. Suitable catalysts are alkali metals on a support, such as potassium and / or sodium on aluminum oxide, and regenerable catalysts, such as aluminum oxide and alkali metal compounds, e.g. Potassium carbonate or sodium oxide, preferably on a support material. The preferred catalyst is potassium oxide on y-aluminum oxide, which contains 1 to 20 percent by weight, preferably 2 to 5 percent by weight, of potassium oxide. However, non-alkaline catalysts can also be used, e.g. Transition metal carbonyl compounds, e.g. Rhodium and iron carbonyl compounds.

This isomerization is expediently carried out at temperatures from 20 to 200 ° C., preferably 50 to 180 ° C., in particular 80 to 150 ° C.

The compounds of the formula I prepared in the process according to the invention can be isolated in a known manner. In general, distillation of the desired product from the mixture is preferred, but other methods can also be used, e.g. the chemical separation.

The examples illustrate the invention.

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632 730

4th

example 1

a) 2,6-Dimethylocta-2,6-diene (starting material) 25 g of y-aluminum oxide are cal-cinated for 2 hours at 500 ° C., then stirred with 0.25 g of sodium metal at 200 ° C. under nitrogen protection. The impregnated aluminum oxide is cooled to 20 ° C. and 75 ml of 2,6-dimethylocta-2,7-diene are added.

According to gas-liquid chromatography, the starting material is completely isomerized within 5 minutes after the addition, the selectivity to the desired 2,6-dimethylocta-2,6-diene being 85%. The diene can be purified by distillation, bp 172 to 173 ° C at atmospheric pressure.

b) 2,6-dimethylhepta-l, 5-diene (isononadiene) y-aluminum oxide is first impregnated with an aqueous potassium carbonate solution, dried at 120 ° C. and treated with a rhenium heptoxide solution. After drying at 120 ° C. for 3 hours, the catalyst is calcined at 500 ° C. for 3 hours. The catalyst then contains 14 percent by weight rhenium heptoxide and 1.3 percent by weight potassium ions. Before use, the catalyst is activated by heating in a stream of pure nitrogen at 500 ° C for 3 hours.

10 g of this catalyst, 25 g of 2,6-dimethylocta-2,6-diene, 50 g of isobutene and 25 g of n-heptane are 3 hours at 30 ° C.

stirred in an autoclave. After this time, the conversion of starting material is 85%, the selectivity to the desired product is 90%, determined by gas-liquid chromatography. Fractional distillation gives pure 2,6-dimethylhepta-l, 5-diene, bp 139 ° C. at atmospheric pressure.

Example 2

a) 2,6-Dimethylocta-2,6-diene (Dihydroocimen) io A tubular reactor which is equipped with a holder for a thermocouple is charged with 5 g of a fixed bed catalyst. This catalyst consists of spherical y-aluminum oxide, which has been impregnated with 4 percent by weight of potassium carbonate and calcined at 15 575 ° C. for 16 hours.

In a continuous experiment, 2,6-dimethylocta-2,7-diene is fed into this reactor at an hourly weight-space velocity of 1.0. The temperature is kept at 165 ° C, the pressure is atmospheric-20 spherical. After a reaction time of 24 hours, the conversion is 93%, the overall yield of isomerized products is 90% and the selectivity to 2,6-dimethyl-octa-2,6-diene is 77%.

25 b) The disproportionation of the dihydroocimene formed is carried out according to the procedure of Example 1b.

Claims (5)

632730 2nd PATENT CLAIMS 1. Process for the preparation of branched olefins of formula I. R \ u 2 ^ C - CR - X - C = CII2 (I) R in which R1, R2 and R3 are each an alkyl radical with 1 to 4 carbon atoms, R4 is an alkyl radical with 1 to 4 carbon atoms or a hydrogen atom and X is a divalent aliphatic hydrocarbon radical with a maximum of 8 carbon atoms, where X is saturated or contains a double bond, provided there is no conjugation with the double bonds indicated in formula I and an alkyl radical is attached to at least one of the. carbon atoms involved in the double bond, characterized in that a compound of formula II R N / A C - CR - X - A c = CH - R " R R 2 / CR - X - CH R. (V) - CH = CH " 10th in which R1 to R4 and X are defined according to claim 1. 10. Application according to claim 9, to a compound of the formula II obtained in the isomerization in the form of the crude reaction mixture. 11. Use according to one of claims 9 and 10, characterized in that one uses an alkaline isomerization catalyst. 12. Application according to one of claims 9 to 11, characterized in that a potassium compound is used containing catalyst. (II) in which R1, R2, R3, R4 and X are as defined above and R5 is an alkyl radical having 1 to 4 carbon atoms, with an isoolefin of the formula III