JPS6232736B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for selectively producing benzaldehyde from toluene by photoreaction using titanium oxide as a catalyst.

In recent years, research has been active in conducting chemical reactions using semiconductors as catalysts. This is a method in which electrons and holes are separated by irradiating the semiconductor with light, and chemical reactions are also performed using the redox ability of the semiconductor.

Currently known examples of chemical reactions that utilize this principle include (a) an example of decomposing water to generate hydrogen, and (b) an example of synthesizing methanol from carbon dioxide gas and water. etc. These examples are characterized by the fact that the energy source for the reaction can be obtained directly from sunlight, and is an epoch-making technology that makes it possible to break away from conventional dependence on petrochemical energy. Currently, the focus of research is on producing energy such as hydrogen and methanol, rather than using inexpensive naturally occurring raw materials. However, to date, there have been few examples of its application to organic synthesis reactions that utilize inexpensive petroleum products and convert them into high value-added products through photoreactions using semiconductor catalysts.

It will be extremely important in the direction of solving future energy problems to directly utilize the infinite amount of solar energy to carry out reactions that have conventionally been carried out at high temperatures and high pressures at room temperature and normal pressure. It has a meaning.

From the above point of view, the present inventors first produced (1) phenol or a phenol derivative, and/or by irradiating a compound having an aromatic ring with light using a semiconductor as a catalyst and in the presence of oxygen and water. or (2) filed a patent application for a method for producing biphenyl, bibenzyl, or their derivatives, and/or (3) aromatic aldehyde or ketone compounds (Japanese Patent Application Laid-Open No. 158731/1983). When toluene is used as a compound having an aromatic ring, cresol, bibenzyl, and benzaldehyde are obtained as products. Among these products, benzaldehyde is a product useful as an intermediate in the synthesis of dyes, fragrances, medicines, etc. Therefore, selectively producing only benzaldehyde has great industrial significance. However, this benzaldehyde could not be selectively obtained by conventional reactions in the coexistence of oxygen and water.

As a result of intensive research into a method for selectively producing benzaldehyde, the present inventors surprisingly found that when toluene is irradiated with light using titanium oxide as a catalyst in a system where water does not coexist, that is, in the presence of oxygen, benzaldehyde The present invention has been completed based on the discovery that this can be obtained with good selectivity.

That is, the present invention relates to a method for producing benzaldehyde, which is characterized by irradiating toluene with light in the coexistence of a catalyst containing titanium oxide and oxygen.

When using titanium oxide as a photocatalyst, titanium oxide alone can of course be used as a catalyst, but in order to increase its redox ability, for example, platinum, palladium, gold, nickel, iron, cobalt, silver, etc. , ruthenium oxide, palladium oxide,
Nickel oxide, cobalt oxide, etc. can also be present. By utilizing these auxiliary catalysts, quantum yield, reaction rate, etc. can generally be improved in many cases. Furthermore, in order to advantageously utilize sunlight, a sensitizer such as rhodamine B can also be present.

The reaction is generally carried out by dispersing titanium oxide in dehydrated toluene and irradiating it with light in an oxygen-rich atmosphere such as oxygen or air. It may be carried out at elevated temperature. However, from the viewpoint of energy saving, it is preferable to carry out the process at around room temperature. As mentioned above, titanium oxide is generally used by being dispersed in toluene, but the method is not necessarily limited to this method. A so-called photovoltaic reaction, in which a titanium electrode is irradiated with light to cause a reaction, may also be used. The amount of catalyst to be used cannot necessarily be strictly regulated, but when dispersing it in toluene and reacting, it is generally used per 100 parts of toluene.
The amount is 0.01 to 50 parts, more preferably 0.1 to 10 parts. When the amount used is small, the reaction rate becomes slow.
Furthermore, when a large amount is used, although the reaction rate is high and desirable, problems may occur in terms of mechanical stirring and light transmission. The wavelength of the light irradiated during the reaction is generally preferably around 200 to 1000 nm. In addition, it is most preferable to have only titanium oxide and toluene present in the reaction system from the viewpoint of subsequent product separation and removal, but it is also possible to coexist other solvents, etc., as long as they do not interfere with the reaction. be.

As described above, according to the method of the present invention, the energy of light makes it possible to
It is possible to produce benzaldehyde with high added value.

The present invention will be explained below with reference to Examples.

Example 100 c.c. of toluene dehydrated for 24 hours with a molecular sieve (4A type) and 1 g of powdered titanium oxide (anatase type, manufactured by Rare Metallic Co., Ltd.) were placed in a 200 c.c. flask made by Pyrex. I prepared it. While dispersing titanium oxide in toluene under stirring at room temperature, 2
Irradiated with light for a period of time. After the reaction, the toluene solution was subjected to gas chromatography analysis, and it was confirmed that 18.6 mg of benzaldehyde was produced. No other products were detected.

Claims (1)

[Claims] 1. A method for producing benzaldehyde, which comprises irradiating toluene with light in the coexistence of titanium oxide and oxygen.