1. Field of the Invention
The present invention relates to a process for preparing trichloroacetic acid from tetrachloroethylene using functional water under irradiation with light and an apparatus for use in such process.
2. Related Background Art
Trichloroacetic acid is a useful compound which is not only used as a raw material for pharmaceuticals, herbicides, caustics, paint removers and deproteinizing agents, but also used for extracting ATP and AMP and separating DNA from protein.
There have been known various processes for preparing trichloroacetic acid. Such processes include, for example, oxidizing chloral with nitric acid, organic percarboxylic acid, hydrogen peroxide, etc.; chlorinating acetic acid, monochloroacetic acid or dichloroacetic acid (Japanese Patent Publication No. 37-4111); hydrolyzing trichloroacetonitrile with hydrochloric acid (Japanese Patent Publication No. 39-2135); hydrolyzing trichloroacetyl chloride; and oxidizing chloral with nitric acid. In particular, Japanese Patent Application Laid-Open No. 5-178786 discloses a process for oxidizing chloral with nitric acid to prepare trichloroacetic acid in which the NO gas produced is oxidized into NO2 in a reactor and condensed, so as to be recycled.
As industrial processes, chlorinating dichloroacetic acid which is produced as a by-product in manufacturing monochloroacetic acid and oxidizing chloral with nitric acid are adopted.
In the industrial processes as described above, however, the reactions require a high temperature and take a long period time. In addition, in the process for oxidizing chloral with nitric acid, a number of processes and a large amount of chemical agents are required for detoxifying a large amount of NO2 and NO gases produced during the oxidation process. Under these circumstances, there have been demands for developing some other process for preparing trichloroacetic acid.
In light of the existing circumstances as described above, the present inventors conducted an intensive investigation of the processes and finally found the fact that functional water such as acidic water obtained by electrolysis of water, which has been reported to have a bactericidal effect (Japanese Patent Application Laid-Open No. 1-180293) and a cleaning effect on the contaminations on semiconductor wafers (Japanese Patent Application Laid-Open No. 7-051675), decomposes tetrachloroethylene into trichloroacetic acid at ordinary temperature and normal pressure in a short time when irradiating it with light. The present invention has been thus achieved.
Tetrachloroethylene used in the present invention as a raw material was once widely and abundantly used in various industries as cleaning solvents for metal parts, semiconductor devices, clothing, etc. and as reactive solvents as well, just like trichloroethylene. However, since the time of the toxicity of these compounds, such as mutagenicity and carcinogenicity, to organisms having been pointed out, there have been strong demands that those stored without having been used and those having leaked out in nature be treated. Viewed in this light, and moreover, in terms of transforming disused articles into useful ones, the present invention is considered to be of great significance.
The present invention is a process for preparing trichloroacetic acid comprising the step of bringing functional water capable of partial oxidizing tetrachloroethylene under irradiation with light or aerated functional water gas which is produced by aerating the above functional water and has a capability similar to that of the above functional water into contact with tetrachloroethylene under irradiation with light.
Further, the present invention is an apparatus for preparing trichloroacetic acid comprising a closable container as a means for bringing functional water capable of partial oxidizing tetrachloroethylene under irradiation with light or aerated functional water gas which is produced by aerating the above functional water and has the capability similar to that of the above functional water into contact with tetrachloroethylene; and means for irradiating the above contact mixture with light.
According to the present invention, trichloroacetic acid can be prepared by the process in which tetrachloroethylene, which is one of the causes of groundwater contamination and soil contamination, is brought into contact with aerated functional water gas at ordinary room temperature and normal pressure under irradiation with light, instead of the prior art processes such as chlorinating dichloroacetic acid at a high temperature for a long period of time and oxidizing chloral with nitric acid in which a number of processes and a large amount of chemical agents are required for detoxifying a large amount of NO2 and NO gases produced.
In other words, according to the present invention, trichloroacetic acid, which is used for the preparation of pharmaceuticals, chemical agents, etc., can be prepared using the compounds which was once contaminants of no utility value as raw materials.