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Course of Applied Chemistry Department of Chemistry and Biotechnology Graduate School of Engineering Tottori University		[Japanese] [English]

If you have learned chemistry in high school or higher educational opportunity, you should know Friedel-Crafts reaction. It is a very useful reaction which introduces a side chain onto an aromatic ring to form a framework of organic compound. Ordinal textbooks state that the catalyst for this reaction is AlCl₃. For example, the reaction is used to produce cumene [isopropylbenzene or (1-methylethyl)benzene in IUPAC rule] from benzene and propylene (propene). This reaction is so-called cumene method for environmental benign way to produce phenol. However, there is a problem. In practice, the liquid reactants are mixed into a solvent, and AlCl₃ is dissolved. In place of it, H₂SO₄ can be used. During the reaction, the catalyst is dissolved to form a homogeneous mixture with the reactant, and therefore it is called "homogeneous catalyst".

There is a serious problem when such a reaction is carried out in an industrial scale. After the reaction, the desired product and catalyst are mixed into the solution, and the separation is difficult. Distillation is effective for separation of organic compounds, but in this case, the catalyst causes side reactions at a high temperature and so that the distillation is difficult. NaOH aq. is added into such a solution to form oil and water layers, where the product, unreacted raw material and solvent are contained by the oil layer, while the salt formed by neutralization of catalyst by NaOH is contained by the water layer. They are easily separated. In the water layer, theoretically, only NaCl, NaAlO₂ and Na₂SO₄ are contained, just like sea water or hot spring. However, waste of such water should cause environmental pollution due to the by-products. It needs a post treatment for decomposition of harmful materials, but it takes energy to increase CO₂. In addition, new catalyst as well as NaOH is necessary for each run of the reaction. Obtaining such resources consumes energy and causes environmental pollution additionally. In other words, a soluble catalyst has a large impact on the environment. Nowadays, it becomes difficult to use the homogeneous catalysts.

Here, let's imagine a solid with acid sites which play a role of acid on the surface. A solid with the surface acid sites is called a solid acid, or a solid acid catalyst when it is utilized as a catalyst. If you pack the solid acid catalyst into a tube, and feed the reactants (for example, benzene and propylene) from the inlet of the tube, you will obtain only the desired product (for example, cumene)!!! Solid catalysts can realize completely harmless chemical plants from a view of environmental protection. Cumene production has been carried out with a solid acid catalyst (zeolite), and replacement of homogeneous catalyst by solid catalyst is strongly demanded in various fields. Suzuki-Miyaura reaction, famous of recent Nobel Prize, requires homogeneous organic Pd complex. Residual of harmful catalyst is a problem in this case. Also this should be solved by using a solid catalyst.