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Selective oxidation of alcohols in the presence of hindered amine light stabilizers (HALS)

IP.com Disclosure Number: IPCOM000243072D
Publication Date: 2015-Sep-11
Document File: 6 page(s) / 201K

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Abstract

The invention deals with an oxidation process of alcohol having a high selectivity. The alcohol is oxidized in the presence of hindered amines. This yields in a decrease of the amount of undesired by-products. One potential process is a low cost modification of nitroxy radical mediated oxidations of alcohols (e.g. Anelli-oxidation).

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Selective oxidation of alcohols in the presence of hindered amine light stabilizers (HALS)

Abstract:

The invention deals with an oxidation process of alcohol having a high selectivity. The alcohol is oxidized in the presence of hindered amines. This yields in a decrease of the amount of undesired by-products. One potential process is a low cost modification of nitroxy radical mediated oxidations of alcohols (e.g. Anelli-oxidation).

Description:

The selective oxidation of alcohols to corresponding carbonyl compounds is one of the most important reactions in the organic chemistry. In common oxidation processes, toxic or sensitive agents (e.g. MnO2, chromium salt or Dess-Martin agent) are used or formed in large scale, since the agents has to be used in stoichiometric quantities.

An alternative route is the oxidation catalyzed by stable nitroxy radicals. 2,2,6,6- tetramethyl piperidine-N-oxyl (TEMPO) is a commercial available, stable nitroxy radicals which is commonly used in controlled free-radical polymerizations or as a standard for ESR. Nevertheless, TEMPO and its derivates are very expensive compounds.

Our invention is a low price modification of the nitroxy radical mediated oxidation of alcohols. Instead of high price nitroxy radicals (200 - 500 US$/kg), hindered amines (5-10 US$/kg) can be used. Hindered amines are used in large scale as light stabilizer of thermoplastic materials like polyethylene. Hindered amines are excellent reduction agents and can be easily oxidized into nitroxy radicals.

Our experiment shows that the oxidation of alcohols (phenols) is controlled by presence of hindered amines. It is assumed that the catalyzing compound is generated in the course of the oxidations process. The number of undesired side-products is reduced and the yield of the product is increased.

An in situ formation and consumption of TEMPO like material is unknown up to now. Usually, TEMPO and similar compounds are synthesized in a separate manufacturing step and added to the final reaction. In our invention a catalytic amount of TEMPO is formed and catalyses the oxidation reaction. This leads to low content of TEMPO in the reaction mixture, so that none or only traces of these compounds can be detected.

A suitable method to generate the TEMPO like compounds is a reaction of HALS with benzoylperoxide. The reaction of benzoylperoxide with steric hindered amines is a common way for the formation of radical at ambient temperature (for example the curing reaction of unsaturated polyester resins).

An interesting process can be the oxidation of DONOL, a precursor of ADONA which is used as an emulsifier in many fluoropolymer polymerizations at Dyneon. Patents describing the nitroxyl mediated oxidation of DONOL has been filed (US2012184770).

The in situ formed nitroxy radical can have an impact on many free radical reactions. This invention allows for low price method of nitroxy radical mediated oxidations. While most nitroxy radical compound...