Substituted 1,3-dithianes with phosphorus-based secondary antioxidant activity
Publication Date: 2000-Oct-16
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Substituted 1,3-dithianes with phosphorus-based secondary antioxidant activity are described. Antioxidant activity results from the thioalkyl and phosphorus functionality, providing novel self-synergized compositions of matter.
1,3-dithianes contain two sulfur atoms each with adjacent carbon atoms containing hydrogen atoms. Various compounds with thioalkyl substituents are known to be good free radical scavengers. In addition, phosphites are known to be good secondary antioxidants as a result of their ability to form the corresponding phosphate while destroying a peroxy radical or peroxide molecule. Substituted dithianes, 3, possess all of the above features, and therefore are expected to show antioxidant properties.
Structures 1, 2, and 3 refer to structures shown in the attached figure. Anion, 1, is prepared by treating 10 mmol of 2-vinyl-1-3-dithiane in 20 mL THF/4-8 mL HMPTA (caution highly toxic) at -78 centigrade with 11 mmol of n-butyllithium, then raising the temperature to 20 centigrade within 2-3 hours. The resulting dark red solution of anion 1 is treated dropwise with 10 mmol of phosphorus trichloride in 1 mL of THF to afford intermediate 2. After stirring for 1 hour at room temperature, 22 mmol of a substituted phenol (ArOH) are added and the mixture is allowed to stir for an additional 2 hours, with heating if necessary to complete the reaction, as indicated by thin layer chromatography. The mixture is worked up by performing ether/water extractions to afford crude antioxidants, 3, which can be purified by conventional means.
ArOH is phenol with C1 through C10 alkyl groups in the 2 and 4 positions, such as 2,4-di-tert-butyl phenol. The alkyl groups in the 2 and 4 positions may be the same or different. The compositions of matter, 3, are good antioxidants for oil or plastic.