Mechanism Bucherer reaction

The mechanism of the Bucherer reaction amounts to a kind of overall addition-elimination ... 

In the above reaction mechanisms it is noteworthy that the sulphonic acid group introduced has been shown to enter at the 3-position and not the 4-position as previously postulated. A consequence of this situation is that an attempted Bucherer reaction on a naphthol (or a naphthylamine) carrying a sulphonic acid group located meta to the hydroxy (or amino) group would require a second sulphonic acid group to be introduced at this position. Since it is impossible to locate two sulphonic acid groups on the same carbon atom, these compounds cannot undergo the transformation. 

The amino group of naphthylamines can be replaced by a hydroxyl group by treatment with aqueous bisulfite.71 The scope is greatly limited the amino group (which may be NH2 or NHR) must be on a naphthalene ring, with very few exceptions. The reaction is reversible (see 3-7), and both the forward and reverse reactions are called the Bucherer reaction. The mechanism is completely different from any outlined in the first section of this chapter and is discussed at 3-7. 

The naphthylamines may be prepared by reduction of the corresponding nitro compound, but they are readily accessible from naphthois by the Bucherer reaction The naphthol is heated, preferably under pressure in an autoclave, with ammonia and aqueous sodium hydrogen sulfite solution, when an addition-elimination sequence occurs. The detailed mechanism is not completely elucidated, but the Bucherer reaction is restricted to those phenols that show a tendency to tautomerize to the keto form, such as the naphthois and 1,3-dihydroxybenzene (resorcinol). Using 1-naphthol for illustration, the first step is addition of the hydrosulfite across the 3,4-double bond of either the enol or keto tautomer (Scheme 12.9). Nucleophilic attack by ammonia at the carbonyl group... 

The reaction of naphthols with ammonia and sodium bisulfite is called the Bucherer reaction. Primary amines can be used instead of ammonia, in which case A-substituted naphthylamines are obtained. In addition, primary naphthyla-mines can be converted to secondary (ArNH2 + RNH2 + NaS03 ArNHR), by a transamination reaction. The mechanism of the Bucherer reaction amounts to a kind of overall addition-elimination, via 18 and... 

Bisulfite Addition Products and the Bucherer Reaction. The addition of sodium bisulfite to aldehydes and some ketones superficially appears to involve the addition of the elements Na and HS03 to the carbonyl group. Kinetic studies, however, indicate that the reaction is complicated and probably involves sulfite rather than bisulfite ion.10 One possible mechanism is the following ... 

In the presence of aqueous ammonium bisulfite an equilibrium often exists between aromatic amines and aromatic hydroxy compounds. This reaction is called the Bucherer reaction 12 and its mechanism appears to involve the intermediate formation of a bisulfite addition complex. The mechanism which is most widely accepted is that of Fuchs and Stix,13 illustrated here with l-hydroxynaphthalcne-4-sulfonic acid ... 

Bucherer reaction. A procedure for preparation of (i-naphthylamineby heating (i-naphthol with a water solution of ammonium sulfite. A sulfite solution is prepared by saturating concentrated ammonia solution with sulfur dioxide and adding an equal volume of concentrated ammonia solution, (i-naphthol is added and the charge is heated in an autoclave provided with a stirrer or a shaking mechanism. (L. F. Fieser). This reaction is also involved in the preparation of several azo dye intermediates, e.g., Tobias acid. 

The mechanism of the Bucherer reaction has been clarified by Rieche and Seeboth 565 its preparative details, selectivity, and applicability have been reviewed by Drake567 and Seeboth.568... 

Note on Bucherer reaction (BR) The reaction (Figure 2.19) concerns naphthalene compounds and is not applicable to the benzene series. The mechanism of the reaction has been worked out by Rieche and Seeboth (1960) the rate-determining step in the above being considered to be the interconversion of the tetralonedisulphonic acid and imino derivative... 

The above reaction is an example of Bucherer s hydantoin synthesis. Tlie following mechanism has been proposed ... 

Synthesis From Aldehydes and Ketones. Treatment of aldehydes and ketones with potassium cyanide and ammonium carbonate gives hydantoins in a one-pot procedure (Bucherer-Bergs reaction) that proceeds through a complex mechanism. Some derivatives, like oximes, semicarbazones. Iliiosetricarbazones. and others, are also suitable starting materials. 

Fig. 7.12. Mechanism for the formation of hydantoin from 3-(methylthio)propional-dehyde, ammonium hydrogen carbonate and sodium cyanide, the initial reaction of the Strecker/Bucherer synthesis of methionine according to Figure 7.11.

Taillades J, Rousset A, Lasperas M, Commeyras A. Mechanism of the Bucherer-Bergs reaction. Comparison with the basic hydration of a-aminonitriles. Bull. Soc. Chim. Fr. 1986 4. 650—658. Taillades J, Collet H, Garrel L, Beuzelin 1, Boiteau L, Choukroun H, Commeyras A. Ai-carbamoyl amino acid solid-gas nitrosa-tion by NO/NOx A new route to oligopeptides via a-amino acid Ai-carboxyanhydride. Prebiotic implications. J. Mol. Evol. 1999 48. 638-645. 

The Bucherer-Bergs synthesis is of general application to carbonyl compounds, employing potassium cyanide and ammonium carbonate.1,4 Carbonyl derivatives such as semicarbazones, thiosemicarbazones, oximes, azines, phenylhydrazones, imidazolidines, and azomethines also are readily converted directly to the corresponding hydantoins 44 The extent to which the reaction occurs appears unrelated to the hydrolytic stability of the starting material. The proposed mechanism is given in Scheme 1. 

SCHEME 10.1 General Bucherer-Bergs reaction and mechanism. 

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