Organic compounds -- part of the class 532-570 series – Organic compounds – Nitriles
Reexamination Certificate
1996-06-14
2001-06-19
Higel, Floyd D. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Nitriles
C558S311000
Reexamination Certificate
active
06248917
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a process for the preparation of 2-hydroxybenzonitrile by dehydration of 2-hydroxybenzamide in the gas phase.
DESCRIPTION OF THE BACKGROUND
2-Hydroxybenzonitrile is an important intermediate for the preparation of biologically active substances.
The preparation of 2-hydroxybenzonitrile from 2-hydroxybenzamide is known in principle. However, only expensive reagents are described as dehydrating agents, which, moreover, must further be used in stoichiometric or superstoichiometric amounts.
Japanese patent application JP 12 301/66 discloses the reaction of, for example, 2-hydroxybenzamide with phosphorus chloride nitrides at 100 to 600° C.
DE-A 25 33 245 teaches the preparation of 2-hydroxybenzonitrile by reaction of the amide with phosgene in a nonpolar solvent. The nitrile is obtained in this reaction in a yield of >90%. Apart from the fact that phosgene must be used here in superstoichiometric amounts, the use of phosgene in industrial processes is associated with considerable difficulties because of its extreme toxicity.
The use of thiophosphoric diamide (Bull. Soc. Chim. Belg. 86, 4 (1977)), thionyldiimidazole (Heterocycles 12, 1285 (1979)) and trichloromethyl chloroformate (Tetrahedron Lett. 2203 (1986)) as dehydrating agents is also known for the preparation of 2-hydroxybenzonitrile from 2-hydroxybenzamide.
All of the methods described supra are only suitable for preparation of dehydrated products on the laboratory scale, since the reagents required are expensive and, furthermore, must be used in stoichiometric or superstoichiometric amounts.
Another reaction which is known is the catalytic reaction of methyl 2-hydroxybenzoate with ammonia to give 2-hydroxybenzonitrile (Izv. Akad. Nauk. Kaz. SSR, Ser. Khim. 1987 (2), 62). The catalyst used in this case is boron phosphate. A problem in this process is the formation of methylamine from ammonia and methanol which originates from the methyl ester. In addition, 2-hydroxybenzonitrile has the tendency to convert irreversibly at temperatures of >100° C. in the liquid phase into a high-melting triazine. That is, the 2-hydroxybenzonitrile which is formed reacts further in the hot reactor predominantly to give triazine. The product yield is therefore poor. Furthermore, this procedure is not suitable as an industrial process, since the reactor clogs within a short time. A need therefore continues to exist for an improved, industrially acceptable method of dehydrating amide compounds to the corresponding nitrites.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a simple and economical process of dehydrating 2-hydroxybenzamide to 2-hydroxybenzonitrile in good yields.
Briefly, this object and other objects of the invention as hereinafter will become more readily apparent can be attained in a method of preparing 2-hydroxybenzonitrile by passing 2-hydroxybenzamide in the gas phase over a solid catalyst, thereby effecting dehydration of the 2-hydroxybenzamide to the corresponding nitrile product.
REFERENCES:
patent: 2 020 866 (1971-11-01), None
patent: 710973 (1954-06-01), None
Patent Abstracts of Japan, vol. 13, No. 49 (C-565), Feb. 3, 1989, JP-A-63 243064, Oct. 7, 1988.
Masaru Ogata et al, “Reaction Of N,N'-Carbonyldiimidazole and N,N'-Thionyldiimidazole With Amides: An Imidazole Transfer Reaction”, Heterocycles, vol. 12, No. 10, 1979, pp. 1284-1289.
Chemical Abstracts, published by the American Chemical Society, vol. 108, 1988, Abstract No. 74939h.
Khuong Mai et al, “Facile Conversion Of Carboxamides To Nitriles”, Tetrahedron Letters, vol. 27, No. 20, 1986, pp. 2203-2206.
Higel Floyd D.
Huels Aktiengesellschaft
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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