The Bohn–Schmidt reaction, a named reaction in chemistry, introduces a

hydroxy group In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydrox ...

at an

anthraquinone Anthraquinone, also called anthracenedione or dioxoanthracene, is an aromatic organic compound with formula . Isomers include various quinone derivatives. The term anthraquinone however refers to the isomer, 9,10-anthraquinone (IUPAC: 9,10-dioxoan ...

system. The anthraquinone must already have at least one hydroxy 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 Indanthrone blue, also called indanthrene, is an organic compound with the formula . It is a dark blue solid that is a common dye as well as a precursor to other dyes. Preparation The compound made from 2- aminoanthraquinone treated with potass ...

from 2-aminoanthraquinone and thus laid the basis for a new group of dyes.

Reaction mechanism

The postulated reaction mechanism is explained below for the example of 2-hydroxyanthraquinone: Bohn-Schmidt_Reaktion_MV7

The sulfuric acid protonates the keto group of the

1. This causes a shift of the electrons to the

oxonium ion In chemistry, an oxonium ion is any cation containing an oxygen atom that has three bonds and 1+ formal charge. The simplest oxonium ion is the hydronium ion (). Alkyloxonium Hydronium is one of a series of oxonium ions with the formula R''n'' ...

in molecule 2. This shift enables the sulfuric acid to attack the carbenium ion 3 which is formed. The sulfuric acid oxidizes the resulting hydroxyanthracenone 5, which is then

protonated In chemistry, protonation (or hydronation) is the adding of a proton (or hydron, or hydrogen cation), (H+) to an atom, molecule, or ion, forming a conjugate acid. (The complementary process, when a proton is removed from a Brønsted–Lowry acid ...

and the reaction starts all over again. Finally, polyhydroxyanthraquinones with different numbers of hydroxy groups are obtained. The reaction proceeds best at 25–50 °C and takes up to several weeks to complete. The presence of a catalyst such as selenium or mercury accelerate 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.

Atom economy

The reaction is ideally suited for the general production of multi-hydroxyated anthraquinones due to the good

atom economy Atom economy (atom efficiency/percentage) is the conversion efficiency of a chemical process in terms of all atoms involved and the desired products produced. The simplest definition was introduced by Barry Trost in 1991 and is equal to the rati ...

. Sulfuric acid can be reused, as it is split off at the very end. The reaction is therefore used in many dye production processes.. The only disadvantage is that in case boric acid is used,

esterification In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glyceride ...

occurs, which must then be reverted (

hydrolyzed Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysis ...

References

{{DEFAULTSORT:Bohn-Schmidt reaction Name reactions Organic redox reactions

Reaction mechanism

Atom economy

See also

References