Process for producing .alpha..beta.-unsaturated carbonyl compound

Disclosed is a process for producing an .alpha.,.beta.-unsaturated carbonyl compound represented by the formula [II]: ##STR1## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 each represents a hydrogen atom or a hydrocarbon residue and may be linear or may form a ring in optional combination thereof and total carbon atom number of R.sub.1, R.sub.2, R.sub.3 and R.sub.4 is 12 or less, which comprises contacting oxygen with an alkenyl compound represented by the formula [I]: ##STR2## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are as defined above and X represents a trihydrocarbylsilyl group or an acyl group in the presence of a platinum group metal-supporting catalyst.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a novel process for producing an 
.alpha.,.beta.-unsaturated carbonyl compound and more particularly, it 
relates to a process for producing an .alpha.,.beta.-unsaturated carbonyl 
compound by reacting an alkenyl compound with oxygen in heterogeneous 
system. 
2. Related Art 
Unsaturated carbonyl compounds such as cyclopentenone derivatives, 
cyclohexenone derivatives and cyclododecenone derivatives are useful 
chemical substances in the field of perfumes, medicines and chemicals. 
As a process for synthesizing of these unsaturated carbonyl compounds, it 
has been known to react an alkenylsilyl ether with palladium acetate 
("Journal of Organic Chemistry", 1978, 43, 1011). However, this process is 
not economical as expensive palladium is used in a stoichiometric amount. 
Moreover, the reaction is carried out in a homogeneous system and so 
recovery of palladium from the reaction system takes trouble and this 
process is inferior in operability. 
SUMMARY OF THE INVENTION 
As a result of the intensive research conducted by the inventors in an 
attempt to solve the above problems, it has been found that unsaturated 
carbonyl compounds can be obtained more economically and with superior 
operability by contacting an alkenyl compound, such as alkenylsilyl ether, 
alkenyl ester or the like, with oxygen in the presence of a platinum group 
metal-supporting catalyst. The present invention has been accomplished 
based on this finding. 
Thus, the present invention provides a process for producing an 
.alpha.,.beta.-unsaturated carbonyl compound represented by the following 
formula [II], characterized by contacting an alkenyl compound represented 
by the following formula [I] with oxygen in the presence of a platinum 
group metal-supporting catalyst. 
##STR3## 
(wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 each represents a hydrogen 
atom or a hydrocarbon residue and may be linear or may form ring in 
optional combination and total carbon atom number of R.sub.1, R.sub.2, 
R.sub.3 and R.sub.4 is 12 or less, and X represents a trihydrocarbylsilyl 
group or an acyl group). 
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
In the present invention, alkenyl compounds represented by the above 
formula [I] are used as starting materials. In the formula, R.sub.1 
represents a hydrogen atom, an alkyl group such as methyl group, ethyl 
group, propyl group, pentyl group or the like, an alkylene group which may 
link to R.sub.2, R.sub.3 or R.sub.4 to form a ring such as cyclopentane 
ring, cyclohexane ring, cyclododecane ring or the like, or an aryl group 
such as phenyl group, trityl group or the like and R.sub.2, R.sub.3 and 
R.sub.4 each represents a hydrogen atom or the same alkyl, alkylene or 
aryl group as of R.sub.1. These R.sub.1, R.sub.2, R.sub.3 and R.sub.4 may 
form ring in optional combination of them such as cycloalkyl group, 
cycloalkenyl, phenyl group, fused ring or the like. The total carbon atom 
number of R.sub.1, R.sub.2, R.sub.3 and R.sub.4 is 12 or less. 
X represents a trihydrocarbylsilyl group such as trimethylsilyl group, 
triethylsilyl group, tripropylsilyl group, tributylsilyl group or the like 
or an acyl group such as formyl group, acetyl group, propionyl group, 
butyryl group, valeryl group or the like. 
As examples of these alkenyl compounds, mention may be made of alkenylsilyl 
ethers such as 1-cyclo-pentenyltrimethylsily ether, 
1-cyclohexenyltrimethylsilyl ether, 2-methyl-1-cyclopentenyltrimethylsilyl 
ether, 1-cyclopentenyltriethylsilyl ether, 1-cyclopentenyltripropylsilyl 
ether, 2-(2-pentenyl)-1-cyclohexenyltrimethylsilyl ether, 
2-propyl-1-cyclopentenyltrimethylsilyl ether, 
2-pentyl-1-cyclohexenyltrimethylsilyl ether, 
2-(2-pentenyl)-1-cyclopentenyltrimethylsilyl ether, 
2-(2-pentynyl)-1-cyclopentenyltrimethylsilyl ether, 
1-pentyl-1-butenyltrimethylsilyl ether, 1-propenyltrimethylsilyl ether, 
1-pentenyltrimethylsilyl ether, 2-methyl-1-butenyltrimethylsilyl ether, 
and 3-phenyl-1-propenyltrimethylsilyl ether, and alkenyl esters such as 
1-cyclopentenyl acetate, 1-cyclohexenyl acetate, 2-methyl-1-cyclopentenyl 
acetate, 2-ethyl-1-cyclopentenyl acetate, 1-cycloheptenyl acetate, 
1-cyclopentenyl propionate, 1-cyclopentenyl butyrate, 1-phenyl-1-butenyl 
acetate, 1-propenyl acetate, 1-hexenyl acetate, 3-methyl-1-butenyl 
acetate, and 3-phenyl-1-propenyl acetate. 
Synthesis of these compounds may be carried out in accordance with 
conventional process. For example, 1-cyclopentenyltrimethylsilyl ether can 
be easily synthesized by reacting cyclopentanone with trimethylsilyl 
chloride in the presence of a base. Furthermore, 1-cyclopentenyl acetate 
can be easily synthesized by reacting cyclopentanone with isopropenyl 
acetate in the presence of an acid or by reacting cyclopentanone with 
acetic anhydride. 
The process of the present invention is carried out by contacting an 
alkenyl compound with oxygen in the presence of a platinum group 
metal-supporting catalyst. 
Oxygen may be supplied in a gaseous form to reaction system or may be 
previously dissolved in reaction system. Furthermore, if necessary, oxygen 
may also be used in admixture with an inert gas such as nitrogen. Amount 
of oxygen used is usually 0.4-5 mols, preferably 0.4-2 mols per 1 mol of 
alkenyl compound. 
Platinum group metal-supporting catalysts used in the present invention are 
those which comprise a carrier on which a platinum group metal is 
supported. The platinum group metals include, for example, palladium, 
platinum, rhodium, iridium, and ruthenium. Carriers include, for example, 
porous materials such as oxides such as silica, alumina, titanium oxide, 
and zeolite or active carbon. 
Platinum group metal is supported on a carrier by conventional method. For 
example, there is a method according to which with an aqueous solution of 
a salt of the above platinum group metal is impregnated a carrier and 
calcined and then reduced. Amount of the platinum group metal supported on 
a carrier is not critical, but usually is 0.1-15% by weight. Amount of 
platinum group metal-supporting catalyst used is usually 0.01-0.5 g atom 
per 1 mol of alkenyl compound. 
Reaction conditions may vary depending on kinds of starting material and 
catalyst, but usually are reaction temperature: 0.degree. C. or higher, 
preferably 20.degree.-100.degree. C. and reaction time: 10 minutes-72 
hours. 
In carrying out the reaction, preferably a diluent is allowed to be used 
for improvement of selectivity. Examples of the diluent are 
N-methyl-pyrrolidone, dimethylformamide, dimethylacetamide, 
tetrahydrofuran and dioxane. These diluents are normally used in such a 
proportion as providing a concentration of starting material of 1-50% by 
weight. 
Since the reaction of the present invention is carried out in a 
heterogeneous system, catalyst can be easily separated by filtration of 
the reaction mixture after completion of the reaction. The filtrate can be 
purified by operations such as distillation and extraction to give a high 
purity .alpha.,.beta.-unsaturated carbonyl compound, namely, 
.alpha.,.beta.-unsaturated ketone or .alpha.,.beta.-unsaturated aldehyde 
as an objective product. Such unsaturated carbonyl compounds are used as 
intermediates for preparation of useful compounds, especially 
intermediates for perfumes and medicines. 
Thus, according to the present invention, .alpha.,.beta.-unsaturated 
carbonyl compounds can be obtained in a high yield in economical and 
superior manner as compared with conventional technique. 
The present invention will be explained in more detail by the following 
non-limiting examples. Parts and percents in examples, comparative 
examples and reference examples are all by weight unless otherwise 
notified. 
Reference Example 1 Preparation of catalyst 
2.5.times.10.sup.-3 mol of tetramminepalladium (II) chloride 
([Pd(NH.sub.3).sub.4 ]Cl.sub.2) was dissolved in 100 ml of 28% aqueous 
ammonia and in the solution was dipped 10 g of silica (trade name Grade 62 
manufactured by Fuji Davidson Co.). Then, the silica was calcined in the 
air for 1 hour at 180.degree. C. and then reduced with hydrogen gas at 
360.degree. C. for 1 hour to obtain 9.6 g of a palladium (0 
valence)-supporting silica catalyst. 
Weight ratio of the supported palladium based on silica was 4.2% which was 
obtained by atomic absorption spectrometry.

EXAMPLE 1 
1.12 mmol of 1-cyclopentenyltrimethylsilyl ether, 0.3 g of the 
palladium-supporting silica catalyst (amount of palladium supported: 4.2% 
by weight of silica), and 4 ml of N-methyl-2-pyrrolidone were charged in a 
vessel and stirred in oxygen atmosphere at 60.degree. C. for 24 hours. 
After completion of reaction, reaction mixture was analyzed by gas 
chromatography to find that 2-cyclopentenone was generated in a yield of 
90.1% and at a selectivity of 99.2%. The reaction mixture was filtered to 
remove catalyst and the filtrate was distilled under reduced pressure to 
obtain 2-cyclopentenone in a yield of 82%. 
Comparative Example 1 
Example 1 was repeated except that nitrogen atmosphere was employed in 
place of oxygen atmosphere. Yield of 2-cyclopentenone in reaction mixture 
was 6.3% and selectivity was 14.6%. 
Comparative Example 2 
Example 1 was repeated except that the catalyst used was prepared in the 
same manner as in Reference Example 1 except that the reduction with 
hydrogen gas was not conducted. Yield of 2-cyclopentenone in the reaction 
mixture was 2.2% and selectivity was 2.9%. Principal product was 
cyclopentanone (yield 72.6%). 
EXAMPLE 2 
Example 1 was repeated except that 1-cyclohexenyltrimethylsilyl ether was 
used in place of 1-cyclopentenyltrimethylsilyl ether and amount of 
supported palladium was 3.9% by weight of silica. Yield of 2-cyclohexenone 
in the reaction mixture was 87.4% and selectivity was 82.3%. 
EXAMPLE 3 
Example 1 was repeated except that 1-cyclopentenyl acetate was used in 
place of 1-cyclopentenyltrimethylsilyl ether. Yield of 2-cyclopentenone in 
the reaction mixture was 64.1% and selectivity was 98.4%. The invention 
being thus described, it will be obvious that the same may be varied in 
many ways. Such variations are not to be regarded as a departure from the 
spirit and scope of the invention, and all such modifications as would be 
obvious to one skilled in the art are intended to be included within the 
scope of the following claims.