Bohn-Schmidt reaction

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The Bohn-Schmidt reaction is a reaction in organic chemistry in which a hydroxyl group is introduced on an anthraquinone system. The anthraquinone must already have at least one hydroxyl group. The reaction was first described in 1889 by René Bohn (1862–1922) and in 1891 by Robert Emanuel Schmidt (1864–1938), two German industrial chemists. René Bohn is one of the few industrial chemists after whom a reaction is named. In 1901 he made indanthrone from 2-aminoanthraquinone and thus laid the basis for a new group of dyes.

Overview reaction

In this reaction, a hydroxyanthraquinone is made into a polyhydroxyanthraquinone with the help of sulfuric acid and boric acid.

Bohn-Schmidt reaction ÜV5

mechanism

The postulated reaction mechanism is explained below using the example of 2-hydroxyanthraquinone:

Bohn-Schmidt reaction mechanism

A ketone of the anthraquinone is protonated by the sulfuric acid at 1 . This leads to a shift of the electrons to the oxonium ion at 2 . As a result of this shift, the sulfuric acid in 3 can attack a carbenium ion that is formed . The sulfuric acid present oxidizes the resulting hydroxyanthracenone 5 , which is then attacked by a proton and the reaction starts all over again. At the end you get polyhydroxyanthraquinones with different numbers of hydroxyl groups.

The reaction proceeds best at 25–50 ° C and takes up to several weeks to proceed. The presence of a catalyst such as selenium or mercury accelerates the reaction.

By adding boric acid , sulfuric acid can be used instead of fuming sulfuric acid . If boric acid is used, it has a regulating effect, as ester formation occurs, which prevents further oxidation.

Atomic economy

This reaction is ideal for the general production of polyhydroxylated anthraquinones. The sulfuric acid can continue to be used as it is split off at the end. The reaction is therefore used in many dye manufacturing processes. The only disadvantage is that when boric acid is used, esterifications occur which then have to be removed again.

Individual evidence

  1. ↑ a b c d e Zerong Wang: Comprehensive Organic Name Reactions and Reagents, 3 Volume Set . John Wiley & Sons, Hoboken, New Jersey 2009, ISBN 978-0-471-70450-8 , pp. 459-460.
  2. ↑ Wolfgang Girnus, Horst Remane: Milestones in Chemistry 2012 . In: Nachrichten aus der Chemie : Zeitschrift der Gesellschaft Deutscher Chemiker , Volume 60, No. 1, January 3, 2012, p. 16, doi : 10.1002 / nadc.201290036 .
  3. ↑ Eckart, A .: On the knowledge of the Bohn-Schmidt reaction in the benzene series and on the determination of nitrogen according to Kjeldahl in nitro compounds . In: Monatshefte für Chemie - Chemical Monthly , Volume 34, No. 10, October 1913, pp. 1957-1964, doi : 10.1007 / BF01518987 .
  4. ↑ Helmut Krauch, Werner Kunz: Reactions of organic chemistry . John Wiley & Sons, 2009, ISBN 3-527-62512-7 , pp. 127 .
  5. ↑ Max. Phillips: The Chemistry of Anthraquinone. In: Chemical Reviews . 6, 1929, pp. 157-174, doi : 10.1021 / cr60021a007 .