Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
1999-09-14
2002-01-22
Kumar, Shailendra (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C564S336000, C564S385000
Reexamination Certificate
active
06340773
ABSTRACT:
FIELD OF INVENTION
The present invention relates to the preparation of halogenated amines. More specifically, this invention relates to the preparation of halogenated benzylamines.
BACKGROUND OF THE INVENTION
Halogenated benzylamines, such as bromobenzylamine, are used commonly in the synthesis of fine organic chemicals for use in products in the pharmaceutical, flavor and fragrance, and agricultural fields just to name a few. Halogenated benzylamines are especially useful as stating materials and intermediates given the relatively high reactivity of their halogen group functionality. For example, bromobenzylamine is particularly useful because its bromine functionality acts as a leaving group allowing complex amines to be formed. Therefore, given the desire for halogenated amines, there is a corresponding need for economic and practical methods of synthesizing these compounds. The present invention fulfills this need among others.
DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS
The present invention provides for the preparation of halogenated amines through the catalytic hydrogenation of a corresponding halogenated oxime. Although catalytic hydrogenation of oximes to form amines is well known, traditional reactions tend to be harsh and generally involve the use of highly active catalysts such as palladium. Under these conditions, traditional catalytic hydrogenation results in concurrent dehydrohalogenation and thus is generally inapplicable to the preparation of halogenated amines.
It has been found surprising, however, that using a catalyst based on either noble metals other than palladium or base metals minimizes dehydrohalogenation. Despite being generally less reactive than palladium, these catalysts nevertheless effect commercially-acceptable reaction rates and high yields. Moreover, it has been found that suitable results are obtained under mild, ambient reaction conditions. Such mild conditions not only help to minimize dehydrohalogenation, but also make hydrogenation of the halogenated oxime relatively convenient.
It also has been found surprisingly that the catalyst is reusable in subsequent hydrogenation reactions. Indeed, the effectiveness of the catalyst tends to improve with reuse until reaching a steady state condition.
Accordingly, the present invention provides for a highly-effective, low cost, simple and convenient approach for preparing a wide variety of halogenated amines.
One aspect of the present invention is a method of preparing a halogenated amine using a catalyst based on a suitable non-palladium noble metal or a base metal. In a preferred embodiment, the method comprises hydrogenating a halogenated oxime in the presence of a suitable non-palladium noble metal-based catalyst or base metal-based catalyst and under conditions sufficient to produce a halogenated primary amine.
The catalyst should be adequate to promote the reaction, however, it should not be so active as to break the halogen/carbon bond. It has been found that catalysts comprising a suitable non-palladium nobel metal or a base metal are suitable to effect such a reaction. Preferred non-palladium nobel metals include, for example, iridium, rhodium, ruthenium, platinum, oxides thereof, and combinations of two or more thereof. Preferred base metals include, for example, nickel, cobalt, oxides thereof, and combinations of two or more thereof. More preferably, the catalyst comprises platinum and/or rhodium including alloys therewith or oxides thereof. Even more preferably, the catalyst comprises platinum and/or oxides thereof.
The non-palladium nobel metal and/or a base metal may be used as a catalyst in its pure form, for example, as a wire, although preferably it is deposited on a conventional support. The amount of metal deposited on the support may vary, and suitable results are achievable with a catalyst comprising about 1 to about 10% metal by weight, and, preferably, about 5% by weight.
The material used for the support can vary and are readily-determinable by one skilled in the art. Preferred materials include, for example, charcoal, aluminum, and the like. Preferably, the support is charcoal. Suitable forms of the support include, for example, powders, granules and pellets. Preferably, the catalyst comprises a readily-filterable form, such as, powder.
Suitable commercially-available catalysts are available from Engelhard Corporation (Beachwood, Ohio) as product nos. 781A-15-1 and 781A-15-6-1; and from Johnson Matthey (West Deptford, N.J.) as product nos. B21142-1.5, B21137-3, B21101-5, B21159-5, B21142-5, C21190-5 and C21108-5
Loading of the catalyst in the reaction can be determined readily by one skilled in the art. Generally, a concentration of catalyst metal to starting material of about 0.1 to about 10 wt. % is preferred, and a concentration of about 0.5 to about 4 wt. % is more preferred. At concentrations below 0.5 wt. %, reaction rates tend not to be commercially viable while, at concentrations above 4 wt. %, the amount of catalyst used becomes prohibitively expensive and filtering thereof becomes significant.
The hydrogenation is conducted under conditions sufficient to react a halogenated oxime with hydrogen to produce a halogenated amine. Such conditions are readily achievable since it has been found that the reaction occurs at a sufficient rate and with sufficient selectivity at ambient conditions. Specifically, the reaction may be conducted at or near atmospheric pressure and at about room temperature. Although ambient conditions are preferred from a convenience standpoint, conducting the reaction over a wide range of pressures and temperatures, for example, from about 1 to about 10 atm and from about 5 to about 100° C., is within the scope of invention.
The hydrogen may be supplied to the reaction in any known manner. For example, the reaction mixture may be sparged or blanketed with hydrogen. In any event, the supply of hydrogen should be sufficient to sustain the reaction. It has been found that supplying the hydrogen to the reaction at a pressure of about 1 to about 10 atm.
To improve the selectivity of the reaction, an anhydrous environment is preferred. More specifically, it has been found that water in the reaction mixture tends to result in the formation of secondary and tertiary amines which are undesirable. Accordingly, it is preferred that efforts be taken to establish a substantially anhydrous environment. The term “substantially anhydrous” as used herein means that the reaction mixture contains less than about 0.1 wt. % water and preferably contains less than about 0.05 wt. % water. To this end, it is preferred to use an organic solvent. Suitable organic solvents include, for example: alcohols such as ethanol, methanol, and isopropanol; acidic solvents such as acetic acid and propionic acid; and anhydride solvents such as acetic anhydride. In a preferred embodiment, the organic solvent is an alcohol, more preferably, ethanol.
In addition to using an organic solvent to provide for a substantially anhydrous reaction mixture, it may be necessary to “dry” the catalyst. That is, suitable catalysts are typically available in the form of a wet paste to minimize the risk of fire/explosion. This paste typically contains from about 30 to about 60% by weight water. To dry the catalyst paste, it is preferred to perform a solvent exchange with the water. Solvent exchange is a well-known process and may be performed using an organic solvent as described above.
To render the amine stable and to prevent it from contaminating or “poisoning” the catalyst, it is generally preferred to combine it with another substance. Although one skilled in the art can identify a variety of ways of combining the amine with another substance to stabilize it, forming a salt with a mineral acid is preferred such that its interaction with the catalyst is minimized. For handling convenience, it is generally preferred to maintain the halogenated amine in its combined form to avoid oxidation in air. For example, as a salt, the halogenated amine is a stable solid as opposed to a less-stable
Kocur Michael A.
Martin Mary Frances
Zhang Mingbao
Driscoll Steve
Kumar Shailendra
Szuch Colleen
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