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The Bohn–Schmidt reaction, a
The sulfuric acid protonates the
named reaction
A name reaction (or named reaction) is a chemical reaction named after its discoverer(s) or developer(s). Among the tens of thousands of organic reactions that are known, hundreds of such reactions are typically identified by the eponym. Well-known ...
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 hydroxy ...
at an anthraquinone
Anthraquinone, also called anthracenedione or dioxoanthracene, is an aromatic hydrocarbon, aromatic organic compound with formula . Several isomers exist but these terms usually refer to 9,10-anthraquinone (IUPAC: 9,10-dioxoanthracene) wherein th ...
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 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:
The sulfuric acid protonates the keto group
In organic chemistry, a ketone is an organic compound with the structure , where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond C=O). The simplest ketone is acetone ( ...
of the anthraquinone
Anthraquinone, also called anthracenedione or dioxoanthracene, is an aromatic hydrocarbon, aromatic organic compound with formula . Several isomers exist but these terms usually refer to 9,10-anthraquinone (IUPAC: 9,10-dioxoanthracene) wherein th ...
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 chemical bond, 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 fo ...
in molecule 2. This shift enables the sulfuric acid to attack the carbenium ion
The carbenium ion is a kind of cation, positive ion with the structure RR′R″C+, that is, a chemical species with carbon atom having three covalent bonds, and it bears a +1 formal charge. Carbenium ions are a major subset of carbocations, whic ...
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), usually denoted by H+, to an atom, molecule, or ion, forming a conjugate acid. (The complementary process, when a proton is removed from a Brà ...
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 goodatom 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 acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...
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 hydrolysi ...
).
See also
*Wolffenstein–Böters reaction The Wolffenstein–Böters reaction is an organic reaction converting benzene to picric acid by a mixture of aqueous nitric acid and mercury(II) nitrate.
The reaction, which involves simultaneous nitration and oxidation, was first reported by the Ge ...
References
{{DEFAULTSORT:Bohn-Schmidt reaction Name reactions Organic redox reactions