Organic compounds -- part of the class 532-570 series – Organic compounds – Nitrogen attached directly or indirectly to the purine ring...
Reexamination Certificate
1992-03-16
2001-05-01
Raymond, Richard L. (Department: 1624)
Organic compounds -- part of the class 532-570 series
Organic compounds
Nitrogen attached directly or indirectly to the purine ring...
Reexamination Certificate
active
06225471
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to preparation of pyrazine compounds and/or compositions containing the same.
Pyrazine compositions and derivatives thereof are known to have utility in varieties of applications in various industries as broad-ranging as the pharmaceutical, dyestuff and rubber industries. A plurality of reactant compounds and compositions and reaction mechanisms and conditions have been described, proposed and suggested in the art, including such as those described in U.S. Pat. No. 3,067,199, wherein alkanolamine compounds are disclosed to be reacted with nickel or cobalt hydrogenation/dehydrogenation catalysts at elevated temperature which is said to “favor” pyrazine formation when carried out under sub-atmospheric pressure; in U.S. Pat. No. 3,676,442, wherein acetylene compounds are reacted with an ammoniacal derivative under acid conditions at elevated pressure; in U.S. Pat. No. 4,855,431, wherein pyrazines are prepared by passing an aminoalkyl over a particular crystalline aluminosilicate zeolite composition; and in Japanese Kokai 52-97983, wherein an acyloin compound and an ammonium salt of an acid are heated, as exemplified, with a heat-stable solvent, under neutral or acidic conditions.
As indicated by G. P. Rizzi, in J. Arig. Food Chem. Vol. 36 No. 2, 1988, pp. 349-352, who proceeded to study the nature of pyrazine formation from acyloin compounds and ammonium compounds by reactions which included reflux conditions, although alkyl pyrazines have been widely investigated as trace components in foods, their exact origin remains a mystery.
Rizzi notes that alkyl pyrazines have been found in fermented products, and it also is believed that pyrazine compounds tend to be formed during cooking, roasting, or baking of various foodstuffs and thus have importance as flavor components of such foodstuffs. In particular, it is believed that these compounds impart roast flavor and aromatic characteristics to foodstuffs and also may impart charred notes which are desirable in moderation. Thus, efforts are being made to attempt to prepare such compositions in a food-acceptable manner.
As will be noted from the above-noted art, however, procedures to isolate pyrazine compounds from a reaction mixture are generally complex and, but for one embodiment of U.S. Pat. No. 3,676,442, wherein a filtering and crystallyzation of the desired product is disclosed, that art teaches complex solvent extraction and/or distillation isolation steps.
SUMMARY OF THE INVENTION
The present invention provides processes for the preparation and isolation of alkyl pyrazines, particularly tetra-alkyl pyrazines, and is characterized in that an aqueous medium containing ammonium ions, such as provideed by an ammonium-containing compound, and at least one acyloin compound having the general formula:
wherein R
1
and R
2
are the same or different and are alkyl group of prepared, and the aqueous medium is having from 1 to 3 carbon atoms, are heated and refluxed to obtain a reacted mixture, and an alkylpyrazine compound is isolated from the reacted mixture.
Most advantageously, the reaction is carried out under a pressure less than atmospheric pressure, which has been discovered to increase the yield of the product.
The isolation of the reaction product prepared by heating and refluxing is characterized in that a base is added to the reaction mixture to adjust the pH of the liquid of reacted mixture to an alkaline pH, solid material is separated from the pH-adjusted liquid of the reacted mixture, water is added to dissolve the solid material to form a solution, and the product then is allowed to crystallyze from the solution after which, the crystalline product is recovered from the liquid phase by separating it from the liquid phase. Thus, the isolation, which is particularly useful when R
1
and R
2
of the acyloin are both methyl, avoids inter alia the need for time consuming steps of organic extraction and/or distillation steps known in the arts
The present invention is further particularly characterized in that, in a most advantageous embodiment, an alkylpyrazine reaction product is prepared and isolated from a reacted mixture of an acyloin and an ammonium-containing compound by a simultaneous combination of heating, refluxing and sublimation for collection of the product on a cooled sublimation collection surface.
The products of the present invention provide desirable flavorants which may be added to a variety of foodstuffs to impart at least overall non-species-specific roasted notes. Products of the present invention, therefore, are combined advantageously in food compositions.
DETAILED DESCRIPTION OF THE INVENTION
In the practice of the present inventions, although ammonia gas could be bubbled through an acyloin, with or without water, to provide ammonium ions to effect the reaction, it is most practical to employ an aqueous solution of an ammonium-containing compound including the ammonium salts of organic and inorganic acids, and other equivalent ammonium-containing compounds to provide ammonium ions in the aqueous medium. Employment of ammonium salts of weak acids is preferred since it has been found that such act as a buffer agent against formation of acetic acid and hence, buffer the pH, which decreases during the reaction. Such ammonium salts include ammonium acetate, citrate, formate, lactate, oxalate, succinate and tartrate, and diammonium phosphate, etc., individually or in combination.
Other ammonium salts of stronger acids, while not being particularly effective as buffers, also may be employed to effect the reaction, and such include ammonium chloride and sulfate, etc., and when the pyrazine product is to be employed with a food composition, all such ammonium-containing compounds should of course be deemed to be acceptable in processes related to preparing food products.
The acyloin compositions and the ammonium salts are advantageously employed in a molar ratio of about 1:1 to about 1:3, and preferably, about 1:1.5 to about 1:3, acyloin: ammonium salt, and above. Although it also has been found that the higher the amount of ammonium salt, the better the buffering action and the greater the rate of reaction, amounts of ammonium salt higher than the 1:3 ratio, noted above, have not been found to increase yield significantly, and also have been found to generate less than desirable amounts of ammonia gas. Thus, other basic buffering agents are employed usefully to maintain the reaction mixture weakly acidic, and such has been found to reduce generation of ammonia gas. Such agents may include compounds such as sodium acetate, trisodium phosphate and other alkali salts and the like. Again, if the final product is to be employed in a food application, such agents should be deemed acceptable for use in processes related to preparing food products.
In general, the pH of the reaction mixture will not fall below a pH of about 4.5 to 5 and the buffering agents may be employed to maintain a pH of above 5.
Although the amount of water employed may vary considerably, generally, as the amount of water is increased, the reaction rate decreases. Thus, although the amount of water present may range from about 0.5 to about 100 parts by weight per part of the total weight of acyloin and ammonium salt employed, the amount most advantageously employed is merely that amount sufficient to place the ammonium-containing composition, and any pH-adjusting compositions, in solution at the reaction temperatures.
A dehydrogenating, or aromatization, agent which accepts hydrogen advantageously is employed to increase the reaction rate and yield. Such agents may be employed in an amount of about 1 molar ratio, preferably in a molar ratio from about 0.50 to about 0.70, based on the molar amount of acyloin. Hydrogen peroxide is preferred. However, other dehydrogenation agents, particularly other peroxides, such as peroxyacetic acid, peroxybenzoic acid and m-chloroperoxybenzoic may be employed. In addition, other dehydrogenating agents may include selenium, sulfur and organic disulfides,
Nestec S.A.
Raymond Richard L.
Vogt & O'Donnell, LLP
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