1. Field of the Invention
The present invention relates to a process for producing 2,4-dihydroxyacetophenone. The 2,4-dihydroxyacetophenone obtained by the present invention is useful both as an intermediate for producing 2,4-dihydroxy-3-propylacetophenone which is a starting material for medicines to treat allergic diseases and as a starting material for photosensitive materials and anti-suntan cosmetics.
2. Related Art of the Invention
Many processes have been reported for producing 2,4-dihydroxyacetophenone. Typical processes include, for example:
(1) processes wherein resorcinol and acetic acid are reacted in the presence of zinc chloride (see Japanese Patent Laid-open Nos. Sho 61-176548 and Sho 59-65039, and Organic Synthesis Coll., Vol. III, page 761);
(2) a process wherein resorcinol and acetyl chloride are reacted in the presence of zinc chloride (see Japanese Patent Laid-open No. Sho 61-180738);
(3) a process wherein resorcinol and acetic anhydride are reacted in the presence of zinc chloride (see Japanese Patent Laid-open No. Hei 2-11536);
(4) a process wherein resorcinol and acetic anhydride are reacted in the presence of aluminum chloride (see RO 53277 (Rumanian Patent)); and
(5) processes wherein resorcinol and acetic anhydride are reacted in the presence of sulfuric acid (see J. S. African Chem. Inst. 26, 41 (1943) and Japanese Patent Laid-open No. Sho 60-248642).
However, these processes have several problems to be solved when carried out on an industrial scale. More particularly, the processes (1) to (4) mentioned above need to use Lewis acids, such as zinc chloride and aluminum chloride, in stoichiometric amounts relative to resorcinol. Therefore, in order to put the processes into practice on an industrial scale, it is necessary to use, in large amounts, these Lewis acids unstable in the presence of water. In addition, these processes involve a problem on the treatment of waste water, because the Lewis acids are a kind of metal-containing catalyst. Further, the processes (2) to (5) are disadvantageous in that these processes need to use chemicals, such as acetyl chloride and acetic anhydride, unstable in the presence of water and difficult to handle. With the process (5), it has also been pointed out that the obtained 2,4-dihydroxyacetophenone is highly colored.
In view of the above facts, the known processes for producing 2,4-dihydroxyacetophenone are not suitable for industrial applications.