Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Patent
1983-04-22
1984-10-02
Raymond, Richard
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C07P20908
Patent
active
044749694
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention relates to a process for preparing indole from aniline and ethylene glycol.
2. Background Art
This invention relates to an improved preparation process of indole using aniline and ethylene glycol as raw materials.
More specifically, this invention relates, upon preparing indole from aniline and ethylene glycol in the presence of a catalyst, to a feeding method of ethylene glycol which is one of the starting materials.
Indole is known as a raw material for the chemical industry. Notably in recent years, it has become an important material as a raw material for the syntheses of various fragrant compounds and amino acids.
Several attempts have heretofore been made to synthetically obtain indole. Many of such attempts resulted in the occurrence of lots and/or many by-products and required costly starting materials. In addition, they involved many steps to reach indole, and were irksome to practice. However, a preparation process of indole from aniline and ethylene glycol has recently been developed as a one-step preparation process of indole using inexpensive starting materials.
As reaction catalysts for the synthesis of indole from aniline and ethylene glycol, a variety of solid acid catalysts and metallic catalysts have been proposed.
To the knowledge of the present inventors, it seems to be essential, in order to obtain indole with a good yield, to feed a very excess amount of aniline relative to ethylene glycol to the catalyst bed when indole is prepared from aniline and ethylene glycol using various catalysts proposed so far. When preparing indole in the above manner, it is necessary to separate and recover a large amount of aniline contained in the resulting reaction mixture, leading to a problem that the above preparation process requires a very large separation/recovery unit and lots of energy.
The present inventors have carried out an extensive research on the relationship between the molar ratio of aniline to ethylene glycol, both charged into a reactor, and the yield of indole. As a result, it has been found, as described later in a referential example, that the yield of indole on the basis of ethylene glycol increases as the molar ratio of aniline to ethylene glycol becomes greater. Analyses of liquid reaction products and gaseous reaction products have also uncovered that aniline and ethylene glycol are converted into indole in accordance with the following chemical equation (1) but a reaction represented by the following chemical equation (2) also takes place, thereby causing ethylene glycol to undergo a decomposition reaction. ##STR1## The reaction (2) takes place more violently as the molar ratio of aniline to ethylene glycol decreases, thereby leading to a poor yield of indole.
When the molar ratio of aniline to ethylene glycol is small, the reaction (2) is promoted whereas the reaction (1) is suppressed. The following explanation may be given as causes for the above tendency. First of all, the reaction (1) pertaining both aniline and ethylene glycol and the reaction (2) pertaining ethylene glycol only are governed by the partial pressure of each of the reactants. When the molar ratio of aniline to ethylene glycol is small, the partial pressure of aniline in the reaction system becomes smaller and, instead, the partial pressure of ethylene glycol increases and the reaction (2) is more encouraged to take place than the reaction (1). Secondly, as a more important cause than the aforementioned first cause, the reaction (1) is an exothermic reaction of 40-50 Kcal under reaction conditions, while the reaction (2) is an endothermic reaction of 40-50 Kcal. Thus, when the molar ratio of aniline to ethylene glycol is small, heat is produced in accordance with the reaction (1) at an inlet portion of the catalyst bed where the concentration of ethylene glycol is high, leading to the development of a localized high-temperature region (i.e., so-called heat spot). As a result, the reaction (2), which is an endothermic reaction, seems to be promoted at such a he
REFERENCES:
patent: 2438721 (1948-03-01), Sensel et al.
patent: 2618660 (1952-11-01), Payne et al.
patent: 3656911 (1972-04-01), Hobbs
Honda Tadatoshi
Terada Kazuhiro
Mitsui Toatsu Chemicals Incorporated
Raymond Richard
Springer D. B.
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