The Bucherer reaction in

organic chemistry Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic matter, organic materials, i.e., matter in its various forms that contain ...

is the reversible conversion of a naphthol to a naphthylamine in the presence of

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

and

sodium bisulfite Sodium bisulfite (or sodium bisulphite, sodium hydrogen sulfite) is a chemical mixture with the approximate chemical formula NaHSO3. Sodium bisulfite is not a real compound, but a mixture of salts that dissolve in water to give solutions compose ...

. The reaction is widely used in the synthesis of dye precursors aminonaphthalenesulfonic acids. :C₁₀H₇-2-OH + NH₃ C₁₀H₇-2-NH₂ + H₂O The French chemist Robert Lepetit was the first to discover the reaction in 1898. The German chemist Hans Theodor Bucherer (1869–1949) discovered (independent from Lepetit) its reversibility and its potential especially in industrial chemistry. Bucherer published his results in 1904 and his name is connected to this reaction. The

organic reaction Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions, mechanistic organ ...

also goes by the name Bucherer-Lepetit reaction or (incorrectly) the Bucherer-Le Petit reaction. The reaction is used to convert 1,7-dihydroxynaphthalene into 7-amino-1-naphthol and 1-aminonaphthalene-4-sulfonic acid into 1-hydroxynaphthalene-4-sulfonic acid. It is also useful for transamination reactions of

2-aminonaphthalene 2-Naphthylamine or 2-aminonaphthalene is one of two isomeric aminonaphthalenes, compounds with the formula C10H7NH2. It is a colorless solid, but samples take on a reddish color in air because of oxidation. It was formerly used to make azo dyes, b ...

Mechanism

In the first step of the

reaction mechanism In chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical reaction occurs. A chemical mechanism is a theoretical conjecture that tries to describe in detail what takes place at each stage ...

proton A proton is a stable subatomic particle, symbol , Hydron (chemistry), H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an e ...

adds to a carbon atom with high electron density therefore by preference to C2 or C4 of naphthol (1). This leads to resonance stabilized adducts 1a-1e. De-aromatization of the first ring of the

naphthalene Naphthalene is an organic compound with formula . It is the simplest polycyclic aromatic hydrocarbon, and is a white Crystal, crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 Parts-per notation ...

system occurs at the expense of 25 kcal/mol. In the next step a bisulfite

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...

adds to C3 through 1e. This results in the formation of 3a which

tautomer In chemistry, tautomers () are structural isomers (constitutional isomers) of chemical compounds that readily interconvert. The chemical reaction interconverting the two is called tautomerization. This conversion commonly results from the reloca ...

izes to the more stable 3b to the

sulfonic acid In organic chemistry, sulfonic acid (or sulphonic acid) refers to a member of the class of organosulfur compounds with the general formula , where R is an organic alkyl or aryl group and the group a sulfonyl hydroxide. As a substituent, it is kn ...

of tetralone. A

nucleophilic addition In organic chemistry, a nucleophilic addition (AN) reaction is an addition reaction where a chemical compound with an electrophilic double or triple bond reacts with a nucleophile, such that the double or triple bond is broken. Nucleophilic addit ...

follows of the

amine In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...

with formation of 4a and its tautomer 4b loses water to form the resonance stabilized

cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

5a. This compound is deprotonated to the

imine In organic chemistry, an imine ( or ) is a functional group or organic compound containing a carbon–nitrogen double bond (). The nitrogen atom can be attached to a hydrogen or an organic group (R). The carbon atom has two additional single bon ...

5b or the

enamine An enamine is an unsaturated compound derived by the condensation of an aldehyde or ketone with a secondary amine. Enamines are versatile intermediates. The word "enamine" is derived from the affix ''en''-, used as the suffix of alkene, and the r ...

5c but an equilibrium exists between both species. The enamine eliminates sodium bisulfite with formation of naphthylamine 6. : It is important to stress that this is a

reversible reaction A reversible reaction is a reaction in which the conversion of reactants to products and the conversion of products to reactants occur simultaneously. : \mathit aA + \mathit bB \mathit cC + \mathit dD A and B can react to form C and D or, in the ...

. The reaction is summarized as follows: : The Bucherer carbazole synthesis is a related reaction.

References

{{DEFAULTSORT:Bucherer Reaction Substitution reactions Name reactions