The present invention relates to aqueous tertiary di-.beta.-hydroxy amine oxides and particularly to their stabilization against phase separation.
Wieland [Ber., 54, 2353 (1921)] first proposed the oxidation of tertiary amines with hydrogen peroxide. He assumed that the hydrogen peroxide added first to the amine to form an ammonium peroxide compound which then decomposed to amine oxide and water. This intermediate ammonium peroxide complex formation has been substantially by Oswald et al [J. Org. Chem., 28, 657 (1963)]. Trialkylaminehydrogen peroxide adducts have been isolated from reactions using 90+% H.sub.2 O.sub.2 at low temperatures (e.g. -50.degree. C.). These complexes are unstable, colorless liquids at room temperature and have been shown by infrared spectroscopy to be hydrogen bonded polar complexes. These complexes are thermally unstable and decompose to yield trialkylamine oxides and water. This decomposition is quite rapid at 50.degree. C.
The most obvious method for the direct oxidation of tertiary amines is to use concentrated hydrogen peroxide sans solvent. However, Hoh et al [J.A.O.C.S., 40, 268 (1963)] has shown that oxidation of dimethyldodecylamine without added solvent at 60.degree. C. using 90% H.sub.2 O.sub.2 proceeds only to 40% completion in 3 hours reaction time. With 70% aqueous H.sub.2 O.sub.2 at 50.degree. C., a 45% completion was realized in 3 hours; however, the completion leveled off at 60% oxide in 10 hours reaction time. Using 35% aqueous hydrogen peroxide, the reaction proceeds more rapidly to yield 50% amine oxide in less than 2 hours reaction time and about 85% amine oxide at the completion of the reaction.
The preferred method determined by Hoh et al was the addition of 35% aqueous hydrogen peroxide to the tertiary amine with stirring at 60.degree. C. over a 1 hour period during which time the mixture became gelatinous. Sufficient water was added to keep the reaction mixture fluid. Upon completion of peroxide addition, the proportion of water required to yield a 30%-40% amine oxide solution was added and the temperature was raised to 75.degree. C. A conversion approaching 100% then was realized in 2 hours reaction time. The incremental addition of water was found to give rapid oxidation initially and a quick completion of the reaction. Alternatively, when all of the water was added at the commencement of the reaction, the initial rate of reaction was slow and excessive reaction times were experienced. Hoh et al determined that the optimum reaction temperature for their reaction procedure was about 60.degree.-65.degree. C. They noted that at higher temperatures some decomposition apparently occurred (a yellow color developed) and at lower temperatures the reaction rate decreased. Present day commercial manufacturing of aqueous tertiary amine oxides typically involves the incremental addition of aqueous hydrogen peroxide to the tertiary amine and water.
Aqueous trialkyl, ether dialkyl and polyoxyalkylene amine oxides (e.g. 35%-50% amine oxide solids) appear to provide stable, one phase systems upon storage. However, it has been determined that aqueous tertiary di-.beta.-hydroxy amine oxides are not storage stable but split into two layers upon standing. Many of these hydroxy amine oxides cannot be produced by the noted oxidation reaction without added aqueous solvent and are hygroscopic so that removal of water therefrom is difficult if not impossible. Thus, a great need exists for stabilizing such aqueous amine oxide systems.