The Bucherer reaction in

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

is the reversible conversion of a

naphthol Naphthol may refer to: * 1-Naphthol 1-Naphthol, or α-naphthol, is a fluorescent organic compound with the formula . It is a white solid. It is an isomer of 2-naphthol differing by the location of the hydroxyl group on the naphthalene ring. ...

to a

naphthylamine Naphthylamine can refer to either of two isomeric chemical compounds: *1-Naphthylamine 1-Naphthylamine is an aromatic amine derived from naphthalene. It can cause bladder cancer (transitional cell carcinoma). It crystallizes in colorless needles w ...

in the presence of

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...

and

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

. The reaction is widely used in the synthesis of dye precursors

aminonaphthalenesulfonic acids Aminonaphthalenesulfonic acids are compounds with the composition C10H6(NH2)(SO3H), being derived from naphthalene (C10H8) substituted by an amino and sulfonic acid groups. These compounds are colorless solids. They are useful precursors to dyes ...

. :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 (wrongly) 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-aminonaphthalenes.

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 change occurs. A chemical mechanism is a theoretical conjecture that tries to describe in detail what takes place at each stage of ...

proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...

adds to a carbon atom with high electron density therefore by preference to C2 or C4 of

(1). This leads to

resonance stabilized In chemistry, resonance, also called mesomerism, is a way of describing bonding in certain molecules or polyatomic ions by the combination of several contributing structures (or ''forms'', also variously known as ''resonance structures'' or ...

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 crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 ppm by mass. As an aromati ...

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

bisulfite The bisulfite ion (IUPAC-recommended nomenclature: hydrogensulfite) is the ion . Salts containing the ion are also known as "sulfite lyes". Sodium bisulfite is used interchangeably with sodium metabisulfite (Na2S2O5). Sodium metabisulfite disso ...

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 convent ...

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

tautomer 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 relocation of a hydr ...

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 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 additions di ...

follows of the

amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituen ...

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 bo ...

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 th ...

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 The Bucherer carbazole synthesis is a chemical reaction used to synthesize carbazoles from naphthols and aryl hydrazines using sodium bisulfite. The reaction is named after Hans Theodor Bucherer. See also * Borsche-Drechsel cyclization *Buchere ...

is a related reaction.

References

{{DEFAULTSORT:Bucherer Reaction Substitution reactions Name reactions