JPH0133451B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for selectively hydrogenating a cyclic polyene using a palladium colloidal catalyst to obtain a cyclic monoene.

The reaction of selectively hydrogenating a cyclic polyene having two or more unsaturated bonds to the stage of a cyclic monoene is a reaction that is expected to have wide application in the field of organic chemistry, but it has not been carried out industrially in the past. This type of hydrogenation method has not been widely used industrially because no hydrogenation catalyst with good selectivity is known. However, since there is no demand for a hydrogenation method with good selectivity, research and development of technology for selective hydrogenation reactions, particularly research on selective hydrogenation catalysts, is active, and various catalysts have been proposed.

Catalyst systems that have been proposed and are said to have relatively good selectivity include solid catalysts and so-called metal complex catalysts poisoned with various poisoning agents, such as metal salts and amines. The above-mentioned solid catalysts are complicated to prepare and generally have relatively low activity, so the reaction must be carried out under harsh conditions, and there are also problems such as a decrease in performance during the reaction. On the other hand, metal complex catalysts have the advantage of catalyzing under relatively mild conditions, but the raw materials for the catalyst are expensive and the manufacturing method is complicated. Many of them are unstable against the like, and there are many problems in process control operations such as difficulty in separating the hydrogenation reaction product from the catalyst, so they are unsuitable for industrial use.

The present inventors have conducted intensive research to develop a hydrogenation method with good selectivity that does not have such problems. When palladium colloid prepared by reductively reacting methanol containing an alkali with palladium is used as a catalyst, cyclic polyenes having two or more unsaturated bonds such as cyclooctadiene and cyclopentadiene can be selected from cyclic monoenes. The present inventors have discovered that hydrogenation can be carried out at a high rate, and have completed the present invention based on this knowledge.

That is, the present invention provides a method for selectively hydrogenating a cyclic polyene, which is characterized by hydrogenating the cyclic polyene in the presence of a palladium colloid catalyst to produce a cyclic monoene.

The palladium colloidal catalyst used in the method of the present invention can be prepared by heating palladium chloride () in methanol in the presence of a protective colloid selected from alkali metal methoxides and synthetic polymer compounds having polar groups. Obtainable.

The alkali metal methoxide used in this case is preferably sodium methoxide, but instead of using sodium methoxide, a compound capable of producing alkali metal methoxide in the reaction system, such as sodium hydroxide, can also be used.

Furthermore, the synthetic molecule having a polar group used as a protective colloid only needs to be soluble in methanol, and any type commonly used as a protective colloid can be used, but polyvinylpyrrolidone is particularly preferably used.

In the present invention, the palladium colloid used as a catalyst can be prepared extremely easily and with good reproducibility, and is stable even when left in air or water, so it is extremely easy to handle. . In the hydrogenation reaction, the palladium colloid may be used as a prepared solution, or may be prepared by evaporating methanol to dryness under reduced pressure and redissolving it in an appropriate solvent. In this case, as the solvent, any solvent used in ordinary hydrogenation reactions can be used as long as it dissolves the polar molecular compound serving as the protective colloid. A mixed solvent can also be used, and the solvent components do not need to be uniformly dissolved in each other.

In the hydrogenation reaction of the present invention, examples of the cyclic polyene that can be selectively hydrogenated include cyclic dienes having 5 or more carbon atoms, trienes, and tetraenes. The catalyst is based on palladium and is used in an amount of less than 1/500th equivalent of the cyclic polyene substrate, sometimes less than 1/1000th of an equivalent, but in terms of reaction selectivity, a particularly effective range is from 1/500th equivalent to 4000th equivalent. The range is 1 equivalent. The reaction temperature is sufficient at room temperature, and the reaction proceeds sufficiently quickly with hydrogen pressure usually at a total pressure of 1 atm.

In the method of the present invention, when cyclopentadiene and cyclooctadiene are compared, cyclooctadiene is superior in hydrogenation selectivity. This trend is consistent with the generally accepted trend for cyclic dienes excluding _C6 . Moreover, among cyclic dienes of the same size, conjugated dienes are more easily hydrogenated than non-conjugated dienes, and have superior selectivity to monoenes.

In the method of the present invention, since the catalyst used is significantly more active and has better selectivity than conventional catalysts, it is possible to hydrogenate a cyclic polyene to a cyclic monoene with good selectivity using a small amount of catalyst and under mild conditions.

Next, the present invention will be explained in more detail with reference to Examples.

Reference Example 1 Palladium chloride () 5.9 mg (0.33 mmole) and polyvinylpyrrolidone (degree of polymerization 3200) 151 mg (monomer residue amount 1.36 mmole) were each dissolved in 22.5 ml of methanol, mixed, and heated on a water bath for 30 minutes. The mixture was heated to reflux for a minute. Next, while refluxing, 5 ml of a methanol solution containing 6.6 mg (0.17 mmole) of sodium hydroxide was added dropwise, and heating and refluxing was continued for an additional 10 minutes to obtain a blackish brown and uniform palladium colloidal solution.

Also, at this time, the formation of methoxymethanol was observed in the reaction solution, but this was due to the reaction formula PdCl ₂ + CH ₃ OH → Pd + HCHO + 2HCl, where formaldehyde, which was generated as a result of the reductive action of methanol on palladium chloride, reacted with the coexisting methanol. It is thought that this was caused by a reaction.

When a film obtained by evaporating a small amount of this colloidal solution to dryness was observed under an electron microscope at a magnification of 200,000 times, the particle size of the palladium particles in the palladium colloid was distributed from 10 to 80 Å, and the average particle size was 25 Å.

When cyclohexene was hydrogenated with hydrogen at 30°C and 1 atm in methanol using this palladium colloid, the initial hydrogenation rate was 2.0H ₂ mol/Pdg-
It was ATM/sec.

Reference Example 2 Palladium chloride () 5.9 mg (0.033 mmole) and polyvinylpyrrolidone (polymerization degree 3200) 151 mg (monomer residue amount 1.36 mmole) were each dissolved in 22.5 ml of methanol, mixed, and mixed on a water bath. The mixture was heated to reflux for 30 minutes. Next, while continuing to reflux, 5 ml of a methanol solution containing 9.2 mg (0.17 mmole) of sodium methoxide was added dropwise, and heating and refluxing was continued for an additional 10 minutes to obtain a blackish brown and uniform palladium colloidal solution.

The physical properties and activity of this palladium colloid were the same as those prepared in Reference Example 1.

Example 1 Palladium colloidal solution prepared in Reference Example 1
0.3ml (2×10 ^-4 mmole of palladium),
Add to 19.7 ml of methanol deoxygenated by distillation under an argon stream to make a total volume of 20 ml, and at 30.0°C with a total pressure of 1.
The system was saturated with hydrogen by stirring with atmospheric hydrogen for 1 hour. Next, 54 mg of 1,3-cyclooctadiene
(0.5 mmole, 2500 times the equivalent of catalyst palladium) was added to carry out a hydrogenation reaction. Since the same mole of hydrogen as the substrate was absorbed in 2 minutes, the reaction was stopped at this point and the product was immediately analyzed by gas chromatography (PEG + AgNO ₃ , 4 m, temperature increased from 70°C to 90°C). And cyclooctane was not detected, and the content was 100% cyclooctene.

In addition, when the hydrogenation reaction was further continued, the results shown in the attached drawings were obtained. As is clear from this figure, hydrogenation stops in the monoene state,
It's no longer progressing.

For comparison, 10.5 mg of palladium supported on activated carbon (manufactured by Nippon Engelhard Co., Ltd., 5% palladium supported activated carbon powder) was used as a catalyst (5×
A hydrogenation reaction of 540 mg (5 mmole, 1000 times the equivalent of the catalyst palladium) of 1,3-cyclooctadiene was carried out using 10 ^-3 mmole), and the progress of the reaction was monitored by gas chromatography. After 4 minutes, the cyclooctadiene disappeared, and the products at this time were 94.1% cyclooctene and 5.9% cyclooctane.

Example 2 Palladium colloid solution prepared in Reference Example 1
A hydrogenation reaction of 54 mg (0.5 mmole, 500 times the equivalent of the catalyst palladium) of 1,5-cyclooctadiene was carried out in the same manner as in Example 1 using 1.5 ml (palladium amount: 1 x 10 ^-3 mmole). During the reaction time of 8 minutes, approximately the same mole of hydrogen as the substrate was absorbed. The product was analyzed in the same manner as in Example 1 and found to be 99% cyclooctene and 1% cyclooctane.

For comparison, 10.5 mg of palladium supported on activated carbon (manufactured by Nippon Engelhard Co., Ltd., 5% palladium supported activated carbon powder) was used as a catalyst (5×
A hydrogenation reaction of 54 mg (0.5 mmole, 100 times the equivalent of the catalyst palladium) of 1,5-cyclooctadiene was carried out using 10 ^-3 mmole). After a reaction time of 7 minutes, cyclooctadiene disappeared, and the products were 91.4% cyclooctene and 8.6% cyclooctane.

Example 3 Palladium colloid solution prepared in Reference Example 2
Using 0.3 ml (palladium amount 2 × 10 ^-4 mmole) 1,
A hydrogenation reaction of 66 mg (1 mmole, 5000 times equivalent to the palladium catalyst) of 3-cyclopentadiene was carried out. During the reaction time of 8 minutes, approximately the same mole of hydrogen as the substrate was absorbed. As a result of analyzing the reaction solution by gas chromatography (PEG + AgNO ₃ , 4m, 50℃),
The composition was 97.3% cyclopentene, 1.9% cyclopentane, and 0.8% cyclopentadiene.

For comparison, palladium supported on activated carbon (manufactured by Nippon Engelhard Co., Ltd., 5% palladium supported activated carbon powder) 10.5 mg (5 × 10 ^-3 mmole of palladium)
33 mg (0.5 mmole,
A hydrogenation reaction of 100 times the equivalent of palladium catalyst was carried out. Cyclopentadiene disappears after 2 minutes,
The product was 86.4% cyclopentene and 13.6% cyclopentane.

Example 4 Using the same amount of palladium colloidal solution as in Example 2, 1,5-cyclooctadiene (540 mg, 5 mmole, catalytic palladium
5000 times equivalent) hydrogenation reaction was carried out. After 1 hour of reaction, the product was analyzed and found that 43.8% of the raw material 1,5-cyclooctadiene remained, 0.5% of cyclooctane, 42.3% of cyclooctene, and 1,4-cyclooctadiene.
-13.4% of cyclooctadiene was produced.
No 1,3-cyclooctadiene was detected.

Furthermore, when the reaction time was increased to 4.5 hours, the products were 1.9% cyclooctane, 84.8% cyclooctene,
%, 1,4-cyclooctadiene 3.1%, 1,5
- 10.2% of cyclooctadiene.

[Brief explanation of drawings]

The drawing is a graph showing the relationship between hydrogen absorption amount and time in the method of the present invention.

Claims (1)

[Claims] 1. A methanol solution of palladium chloride (),
A cyclic polyene is produced using a palladium colloid catalyst obtained by heating in the presence of a protective colloid selected from alkali metal methoxide or a compound capable of producing alkali metal methoxide in the reaction system and a synthetic polymer having a polar group. A method for selectively hydrogenating a cyclic polyene, the method comprising hydrogenating a cyclic polyene to produce a cyclic monoene. 2. The method according to claim 1, wherein the protective colloid is polyvinylpyrrolidone.