Organic compounds -- part of the class 532-570 series – Organic compounds – Four or more ring nitrogens in the bicyclo ring system
Reexamination Certificate
2002-03-28
2003-09-09
Rotman, Alan L. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Four or more ring nitrogens in the bicyclo ring system
C544S358000, C546S141000, C546S185000, C546S192000, C546S242000, C548S347100
Reexamination Certificate
active
06617454
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an improved process for the preparation of high quality amine oxides from secondary and tertiary aliphatic amines by Mg—Al—O—t—Bu hydrotalcites using benzonitrile as an additive. More particularly, the present invention relates to an improved process for the preparation of amine oxides from secondary and tertiary aliphatic amines useful in the preparation of hair conditioners, shampoos, toothpaste, laundry detergent powder, fabric softeners, toilet soap bars, cosmetics and surfactants as well as in other applications as synthetic intermediates and excellent spin trapping reagents.
BACKGROUND OF THE INVENTION
Amine N-oxides hold a key position in the chemistry of heterocycles as well as in biomedical area. The tertiary amine oxides are widely used in treatment of fabrics and preparation of hair conditioners, shampoos, toothpaste, laundry detergent powder, fabric softeners, toilet soap bars and cosmetics as well as in other applications. They were also used as stoichiometric oxidants in metal catalysed dihydroxylation and epoxidation reactions of olefins. On the other hand, the oxides derived from secondary amines, called nitrones are highly valuable synthetic intermediates and excellent spin trapping reagents. In particular nitrones are excellent 1,3 dipoles and have been utilized for the synthesis of various nitrogen containing biologically active compounds e.g. alkaloids and lactams.
Conventionally tertiary amine oxides are prepared by oxidation of respective tertiary amines with strong oxidising agent like aqueous hydrogen peroxide in a solvent such as water, lower alcohol, acetone or acetic acid. A dilute or preferably concentrated (30-90% by weight) hydrogen peroxide solution is added in stoichiometric or greater amount to an aqueous solution containing the tertiary amine to obtain amine oxide, (U.S. Pat No. 3,215, 741). The drawback is that the reaction transforms into a gel resembling a thick paste long before completion of reaction, which retards further reaction. The yields are only 30-40% by weight of amine oxide. Later several methods such as incorporation of catalyst and/chelating agent have been developed to in order to increase the quality and yields of the product.
In case of secondary amines, the classical methods involve the condensation of N-monosubstituted hydroxylamines with carbonyl compounds or the direct oxidation of N,N-disubstituted hydroxylamines. Later direct oxidation of secondary amines using several oxidising systems such as R
2
C(&mgr;—O
2
), Na
2
WO
4
—H
2
O
2
, SeO
2
, TPAP-NMO and UHP-M (M═Mo, W), MTO—H
2
O
2
have been developed to accomplish nitrones under homogenous conditions. The drawback in all the above cases is the difficulty in recovering the homogeneous catalyst/reagents from the reaction mixture.
Reference is made to a U.S. Pat. No. 3,283,007 wherein the oxidation of tertiary amines using diethelene trianine penta/tetra acetic acid as chelating agent and sometimes contaminated with heavy metals is recommended to improve the yield. The hydrogen peroxide solution employed has concentration of at least 30-75% by weight. The disadvantages of this process are high reaction temperatures ranging between 40-100° C., longer reaction periods, and lower yields of amine oxides.
Reference is made to U.S. Pat. No. 3,424,780, wherein high yields of tertiary amine oxides are achieved by carrying the oxidation of tertiary amine with 30-70% by weight of aqueous hydrogen peroxide using 0.01 to 2% weight of carbondioxide, in presence of a chelating agent, tetra acetylene diamine, a salt thereof, polyphosphates, stannates, a hydroxy carboxylic acid salts or the salt of poly carboxylic acid. The disadvantages of this process are longer reaction periods and the amine oxide formed is intensively coloured when carbon dioxide atmosphere is used to speed up the reaction and this method necessitates injecting a gas which requires handling facilities. Another disadvantage is more than 30% by weight of hydrogen peroxide is not environmentally friendly.
Reference is made to another U.S. Pat. No. 4,889,954 wherein the tertiary amines are reacted in high yields to give the corresponding amine oxides with a low content of nitrosamine, the oxidation of tertiary amine being carried out in the presence of a dialkyl carboxylic acid ester as catalyst and if appropriate, ascorbic acid as a co-catalyst using 45-70% by weight of hydrogen peroxide. The drawbacks in the above process are the requirement of frequent addition of water to avoid gel formation, high reaction temperatures, longer reaction periods and difficulty in separation of the catalyst from the reaction mixture.
Reference is made to another U.S. Pat. No. 4,565,891 wherein octacyano molybdate or iron salts are used as catalysts and molecular oxygen for oxidation of tertiary amines at high pressures and temperatures. The main drawback of this process is the need of very high temperature of 90-130° C. and low yields of amine oxide reporting 11-52% of conversion.
Reference is made to a U.S. Pat. No. 5,130,488 wherein the solid amine oxide can be prepared by reacting a tertiary amine with hydrogen peroxide using carbon dioxide in presence of acetate and cooling to precipitate the product. This process is superior to previously known methods of preparing amine oxides. However, its use can sometimes lead to cleavage of the solvents, plating on the walls of the vessel used for the precipitation, contamination of the product with residual peroxide, and or discoloration of the product.
Reference is made to a publication by Walter W. Zajac et al., J. Org. Chem.; 53, 5856, 1988 wherein the oxidation of secondary and tertiary amines using 2-sulfonyloxyaziridines (Davis Reagents) were reported. The drawback of the above process is, the reagent was used in stoichiometric amounts.
Reference is made to a publication by Shun-Ichi Murahashi et al., J. Org. Chem.; 55, 1736, 1990 wherein the sodium tungstate was used as catalyst for the oxidation of secondary amines. The drawback is difficulty in recovery of the catalyst from homogeneous conditions.
Reference is made to publication by Murraay et al., J. Org. Chem.; 61, 8099, 1996 wherein methyltrioxorhenium was used as a catalyst in oxidation of secondary amines. The drawback is the difficulty in recovery of the catalyst.
Reference is made to publication by Choudary et al., Chem. Commun.; 2001, 1736 wherein tungstate-exchanged Mg—Al—LDH was used as a catalyst in oxidation of tertiary amines. The time taken for the reaction is 3-4 h.
OBJECTS OF THE INVENTION
The main object of the present invention is to provide an eco-friendly and simple process for N-oxidation of secondary and tertiary amines using layered double hydroxides exchanged with anion of alkoxides as a catalyst which is cheaper, non-corrosive and recyclable catalyst utilising only lower percentage of hydrogen peroxide at moderate temperatures to give high yields of product.
Another object of the present invention is to provide an improved process for the preparation of tertiary amine oxides and secondary amine oxides (nitrones), widely used in detergents, shampoos, fabric softers and biomedical area.
Another object of the present invention is the use of non-corrosive and low cost heterogeneous catalysts i.e. layered double hydroxides exchanged with anion of tert-butoxide, isopropoxide, ethoxide and methoxide.
SUMMARY OF THE INVENTION
The present invention describes a recyclable heterogeneous catalyst, i.e. layered double hydroxides exchanged with anion of tert-butoxide, isopropoxide, ethoxide or methoxide that catalyses the oxidation of secondary and tertiary amines in presence of an additive selected from benzonitrile, propionitrile, acetonitrile, isobutyronirtile, benzamide, isobutyramide. The advantages such as low cost of the catalyst, reusability for several times and its ability to oxidise the amines at 10-65° C. in a shorter period make the present invention as a promising candidate for a clean and efficient industrial route to amine oxide preparation.
Bharathi Balagam
Choudary Boyapati Manoranjan
Kantam Mannepalli Lakshmi
Prakash Billakanti Veda
Reddy Chinta Reddy Venkat
Council of Scientific and Industrial Research
Covington Raymond
Morgan & Finnegan , LLP
Rotman Alan L.
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