Oppenauer oxidation

The Oppenauer oxidation is a name reaction in organic chemistry . It was named after its discoverer Rupert Viktor Oppenauer (1910–1969). The Oppenauer oxidation is a method for the synthesis of ketones from the corresponding secondary alcohols .

It is the reverse of the Meerwein-Ponndorf-Verley reduction . The alcohol is oxidized with aluminum alcoholate in an excess of acetone . This puts the balance on the right.

Overview reaction of the Oppenauer oxidation; R corresponds to a tert -butyl group or an iso- propyl group , R ¹ and R ² denote organic radicals , such as. B. alkyl radicals .

Since the advent of the oxidation methods based on chromates (e.g. PCC ) or dimethyl sulfoxide (e.g. Swern oxidation ), Oppenauer oxidation has been of reduced importance in terms of preparation. Due to the basic reaction conditions, however, it is suitable for the oxidation of acid-sensitive substrates. A variant trichloroacetaldehyde and alumina is used, it selectively allows secondary addition to unchanged primary to alcohols oxidize .

mechanism

In this mechanism, the radical R again represents a tert-butyl group.

Mechanism of the Oppenauer oxidation; R ¹ and R ² denote organic radicals

The mechanism describes how a secondary alcohol 1 is oxidized to a ketone 4 with the help of the Oppenauer oxidation . First, the alcohol reacts with the catalytic aluminum alcoholate to form molecule 2 . The acetone added in excess then acts as a hydride acceptor and thus as an oxidizing agent for the secondary alcohol. The reaction of the aluminum alcoholate 2 with acetone to the desired ketone 4 and molecule 3 proceeds via a six-membered transition state:

Six-membered transition state; Oxidation of the alcohol ( blue ) to the ketone

Finally molecule reacts 3 with the split-off at the start of alcohol to iso -propanol and aluminum alcoholate, which is now again as a catalyst for disposal.

literature

Eberhard Breitmaier, Günther Jung: Organic chemistry. 5th edition, Thieme, Stuttgart 2005, ISBN 3-13-541505-8 . ( limited preview in Google Book search).

Individual evidence

↑ RV Oppenauer: A method of dehydrating secondary alcohols to ketones. I. For the production of sterol ketones and sex hormones. In: Recueil des Travaux Chimiques des Pays-Bas. 56, 1937, p. 137, doi : 10.1002 / recl.19370560206 .
^ The Merck Index: An Encyclopedia of Chemicals, Drugs and Biologicals , 14th Edition, Merck, Whitehouse Station, NJ, USA 2006 , pp. ONR-68, ISBN 978-0-911910-00-1 .
↑ ^a ^b K. Schwetlick et al .: Organikum , 23rd edition, Wiley-VCH, Weinheim 2009 , p. 578, ISBN 978-3-527-32292-3 .
^ H. Höver: Reaction Mechanisms of Organic Chemistry , Verlag Chemie, Weinheim, John Wiley & Sons, Frankfurt am Main 1973 , p. 136, ISBN 3-527-25442-0 .
↑ to: EJ Corey, KC Nicolaou: Strategic Applications of Named Reactions in Organic Synthesis . Elsevier, Inc, 2005 , ISBN 978-7-03-019190-8 .
^ U. Lüning: Organic reactions , 2nd edition, Elsevier Spektrum Akademischer Verlag, Munich 2007 , p. 142, ISBN 978-3-8274-1834-0 .
^ Zerong Wang: Comprehensive Organic Name Reactions and Reagents, Vol. 2 , John Wiley & Sons, 2009 , p. 2089, ISBN 978-0-471-70450-8 .
^ Ivan Ernest: Binding, Structure and Reaction Mechanisms in Organic Chemistry , Springer-Verlag, Vienna-New York 1972 , p. 200, ISBN 3-211-81060-9 .

[1] RV Oppenauer: A method of dehydrating secondary alcohols to ketones. I. For the production of sterol ketones and sex hormones. In: Recueil des Travaux Chimiques des Pays-Bas. 56, 1937, p. 137, doi : 10.1002 / recl.19370560206 .

[Merck-Index_ONR-68-2] The Merck Index: An Encyclopedia of Chemicals, Drugs and Biologicals , 14th Edition, Merck, Whitehouse Station, NJ, USA 2006 , pp. ONR-68, ISBN 978-0-911910-00-1 .

[Schwetlick_578-3] K. Schwetlick et al .: Organikum , 23rd edition, Wiley-VCH, Weinheim 2009 , p. 578, ISBN 978-3-527-32292-3 .

[Höver_136-4] H. Höver: Reaction Mechanisms of Organic Chemistry , Verlag Chemie, Weinheim, John Wiley & Sons, Frankfurt am Main 1973 , p. 136, ISBN 3-527-25442-0 .

[Corey_2005-5] to: EJ Corey, KC Nicolaou: Strategic Applications of Named Reactions in Organic Synthesis . Elsevier, Inc, 2005 , ISBN 978-7-03-019190-8 .

[Lüning_142-6] U. Lüning: Organic reactions , 2nd edition, Elsevier Spektrum Akademischer Verlag, Munich 2007 , p. 142, ISBN 978-3-8274-1834-0 .

[Wang_2089-7] Zerong Wang: Comprehensive Organic Name Reactions and Reagents, Vol. 2 , John Wiley & Sons, 2009 , p. 2089, ISBN 978-0-471-70450-8 .

[Ernest_200-8] Ivan Ernest: Binding, Structure and Reaction Mechanisms in Organic Chemistry , Springer-Verlag, Vienna-New York 1972 , p. 200, ISBN 3-211-81060-9 .