JPS635015B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for selectively producing bibenzyl from toluene by photoreaction using titanium oxide as a catalyst in a system free of water and dissolved oxygen.

In recent years, research has been active in using semiconductors as catalysts to carry out chemical reactions. This is a method in which electrons and holes are separated by irradiating the semiconductor with light, and a chemical reaction is 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 the conventional dependence on petrochemical energy. Currently, the focus of research is on producing energy such as hydrogen and methanol, rather than using naturally occurring and inexpensive 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 semiconductors as 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 No. 1983-42295). When toluene is used as a compound having an aromatic ring, cresol, bibenzyl, and benzaldehyde are obtained as products. Among these products, bibenzyl is particularly useful as an intermediate raw material for styrene synthesis or as an intermediate raw material for various derivatives. It is a useful product, and selectively producing only bibenzyl has great industrial significance. However, this bibenzyl 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 bibenzyl, the present inventors surprisingly found that
It was discovered that bibenzyl can be obtained with good selectivity when irradiated with light even in a very simple system without water and dissolved oxygen, that is, with only titanium oxide as a catalyst and toluene as a reaction reagent. , we have completed the present invention.

That is, the present invention relates to a method for producing bibenzyl, which is characterized in that toluene is irradiated with light in the presence of titanium oxide as a catalyst in a system free of water and dissolved oxygen.

In the present invention, titanium oxide alone can be used as a catalyst, but for the purpose of increasing its redox ability, titanium oxide, platinum, palladium, gold, nickel, iron, cobalt, silver, ruthenium oxide, palladium oxide, Nickel, cobalt oxide, etc. can also be made to coexist. By utilizing these auxiliary catalysts, it is often possible to generally improve quantum efficiency, reaction rate, etc. Furthermore, in order to advantageously utilize sunlight, a sensitizer such as rhodamine B can also be present.

In carrying out the reaction, a titanium oxide catalyst is generally dispersed in dehydrated toluene, and the reaction is carried out under anoxic conditions.
That is, it is carried out, for example, by irradiating light in an inert gas such as nitrogen. The reaction temperature may be room temperature, or may be carried out at an elevated temperature for the purpose of increasing the reaction rate. However, from the viewpoint of energy saving, it is preferable to carry out the process at around room temperature. As mentioned above, the titanium oxide catalyst is generally used by dispersing it in toluene, but it is not necessarily limited to this method. A so-called photovoltaic reaction, in which a reaction is caused by irradiating a titanium oxide electrode with light, may also be used. The amount of catalyst to be used cannot necessarily be strictly specified, but when the catalyst is dispersed in toluene and reacted,
Generally, the amount is 0.01 to 50 parts, more preferably 0.1 to 10 parts per 100 parts of toluene. When the amount used is small, the reaction rate becomes slow. Further, 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 above reaction is generally 200
~1000 nm is preferred. In addition, in the reaction system,
A form in which only the titanium oxide catalyst and toluene are present is most preferable 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.

As described above, according to the method of the present invention, high value-added bibenzyl can be produced using relatively inexpensive toluene using the energy of light.

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

Example 1 100 c.c. of toluene dehydrated for 24 hours with a molecular sieve (4A type) and powdered titanium oxide (anatase type, manufactured by Rare Metallics) were placed in a 200 c.c. flask made by Pyrex. 1g
I prepared it. While stirring at room temperature, titanium oxide was dispersed in toluene and irradiated with light for 2 hours using a 500W high-pressure mercury lamp. After the reaction, gas chromatography analysis of the toluene solution confirmed the production of 1.1 mg of bibenzyl. Almost no other products were detected.

Example 2 Example 1 except that platinum sodium chloride was used instead of titanium oxide powder, and platinum electrodeposited titanium oxide prepared by electrodeposition on titanium oxide powder by photoreduction was used as a catalyst. As a result of the reaction under the same conditions as above, it was confirmed that 10.1 mg of bibenzyl was produced. As in Example 1, almost no other products were detected.

Claims (1)

[Claims] 1. A method for producing bibenzyl, which comprises irradiating toluene with light in the presence of titanium oxide as a catalyst in a system free of water and dissolved oxygen.