1 -Amino-2-naphthol, preparation

I, 4-benzoquinone.4 Other methods that have been employed include the oxidation of naphthalene with hydrogen peroxide,5 the oxidation of 1,4-naphthalenediamine 6 and naphthylamine sulfonic acid 7 and the oxidation of 4-amino-1-naphthol prepared by electrolytic reduction of 1-nitronaphthalene.8... 

The reduction with hydrosulfite may be carried out in an atmosphere of illuminating gas or hydrogen sulfide. The first precipitate of the free aminophenol is a little lighter in color when prepared in an inert atmosphere but the final amino naphthol hydrochloride has the usual light purple color. 

Liebermann discovered the reaction between nitrous acid and phenols and secondary amines named after him. He prepared amino-naphthols from nitro-naphthols, synthesised the dihydroxyanthraquinones anthrarufin and chrysazin, and studied the reduction of anthraquinone. Another dihydroxy-anthraquinone, quinizarin, was discovered by F. Grimm by heating hydro-quinone with phthalic anhydride. 

The procedure is not usually applicable to aminosulphonic acids owing to the interaction between the amino group and the phosphorus pentachloride. If, however, the chlorosulphonic acid is prepared by diazotisation and treatment with a solution of cuprous chloride in hydrochloric acid, the crystalline chlorosulphonamide and chlorosulphonanilide may be obtained in the usual way. With some compounds, the amino group may be protected by acetylation. Sulphonic acids derived from a phenol or naphthol cannot be converted into the sulphonyl chlorides by the phosphorus pentachloride method. 

The reaction between epoxides and ammonia is a general and useful method for the preparation of P-hydroxyamines. " Ammonia gives largely the primary amine, but also some secondary and tertiary amines. The useful solvents, the ethanolamines, are prepared by this reaction. For another way of accomplishing this conversion, see 10-54. The reaction can be catalyzed with Yb(OTf)3 and in the presence of a-BINOL is l,l -bi-2-naphthol derivative gives amino alcohols with high asymmetric induction. A variation used Yb(OTf)3 at lOkbar or at ambient pressure. Lithium triflate can also be used. Primary and secondary amines give, respectively, secondary and tertiary amines, for example. 

P-Bromonaphthalene. The preparation from p-naphthylamine, which has carcinogenic properties, is avoided by the use of 2-naphthylamine-1-sulphonic acid ( 2-amino-1-naphthalenesulphonic acid ) the latter is obtained commercially by cautious treatment of p-naphthol with sulphuric acid—the SOjH group first enters the 1-position—followed by the Bucherer reaction. Diazotisation and reaction with cuprous bromide yields 2-bromonaphthalene-l-sulphonic acid heating with sulphuric acid eliminates the sulphonic acid group to give 2-bromonaphthalene. 

A totally different picture is presented by 3-phenylazo-2-naphthol. This unusual isomer cannot be prepared by a normal coupling procedure but has been obtained by reaction of 3-amino-2-naphthol with thionyl chloride to give the N-sulphinylamine (4-24), condensation of which with N-phenylhydroxylamine yields the desired product [59]. Here, assumption of a ketohydrazone form would entail loss of aromatic character in both rings of the naphthalene nucleus and the energetic unfavourability of this situation ensures that the compound exists solely in the hydroxyazo form. 

The method has also preparative significance since, ultimately, it is a way of introducing an amino-group. Compare the preparation of aminonaphthols from dyes of which the azo-components are a- or j8-naphthol. 

Routes to benzoxadiazoles are based on approaches to the tautomeric 6-diazo-2,4-cyclo-hexadienones (Scheme 11) <9UST(247)135>. The appropriate 2-aminophenol hydrochloride is diazo-tized using either sodium nitrite or isoamyl nitrite and the diazonium chloride is then carefully neutralized with sodium carbonate or potassium carbonate. An alternative approach is from the monotosylhydrazone of the appropriate o-benzoquinone. Naphthoxadiazole (6) was prepared, in a manner analogous to the first route of Scheme 11, from 3-amino-2-naphthol <91AG(E)1476>. A slightly modified preparation is described in a later paper the method was applied to the synthesis of [9a- C]naphth[2,3-( ]-l,2,3-oxadiazole from 3-amino-[2- C]-2-naphthol <92Mi 403-03>. 

The important products bearing amino substituents in the 6 -position are synthesised from 4-substituted-l-nitroso-2-naphthols (1.14), which are prepared from (1.12) via (1.13). ... 

H-Naphtho[2,l-fe]pyrans (1.19) with an amino or alkoxy residues in the 6-position (1.30) show particularly high colourability. The 1-amino- and l-alkoxy-3-hydroxynaphthalenes (1.28 and 129) required for the synthesis of these compounds are prepared from 2-naphthol as illustrated in Figure 1.9. ... 

In the preparation of 2-phenylazo-3-naphthol it is to be noted that the action of thionyl chloride on 2-amino-3-naphthol results in preferential attack on the amino group. This has been attributed, at least in part, to the fact that the hydroxyl group is in an ortho position. If the reaction is to be extended to aminonaphthols which do not have ortho hydroxyl groups, provisions will probably have to be made for the protection of the hydroxyl group against attack by thionyl chloride. 

Albert S.C. Chun of the Hong Kong Polytechnic University reports (J. Org. Chem. 68 1589, 2003) two important transformations. The three-component (Mannich) condensation of 10 with 11 and 12 proceeds with high diastereoselectivity, to give the amino alcohol 13. Hydroboration of the alkyne 14 followed by transmetalation of the intermediate vinyl borane gives a zinc species, which under catalysis by the easily-prepared 3-naphthol 13 adds to aromatic and branched aldehydes with high . The product allylic alcohols are useful intermediates for organic synthesis. 

The free bases are much less stable than aniline, particularly 2-amino-pyrroles and -furans which are very easily oxidized or hydrolyzed. 2-Aminofurans substituted with electron-withdrawing groups (e.g. N02) are known and 3-amino-2-methylfuran is a relatively stable amine which can be acylated and diazotized. 2-Aminothiophene can be diazotized and the resulting diazonium salt coupled with (3-naphthol. 2,3-Diaminothiophene has been prepared and isolated as the hydrobromide. The free base is not stable (85JCR(S)296). 

Salts of 1,2-naphthoquinone-4-sulfonate have been prepared by the oxidation of 2-amino-i-naphthol-4-sulfonic acid with nitric acid,2 or by the oxidation of the more readily available i-amino-2-naphthol-4-sulfonic acid with the same reagent.3,4 5... 

A similar argument can be applied to the results of later work by Idelson et al.i9 In this they prepared the chromium complex (133) by interaction of the 1 1 chromium complex of 1-phenyl-3-methyl-4-(2-hydroxy-4-cyanonaphth-l-ylazo)-5-pyrazolone and diethylenetriamine and by reaction of the azo compound with [Cr(CO)3dien]. Identical products were obtained and, since the diethylenetriamine occupies9 a facial position in [Cr(CO)3dien], it was concluded that the complex (133) had a facial configuration. Similarly, the reported77 separation of isomeric 2 1 chromium complexes of 2-amino-6-(2-hydroxy-6-nitro-4-sulfonaphth-l-ylazo)-5-naphthol-7-sulfonic acid is... 

The direct replacement of the hydroxyl group in simple phenols by an amino or substituted amino group requires drastic conditions and the method is not suitable for laboratory preparations. With the polyhydric phenols, and more particularly with the naphthols, such replacements occur more readily. Thus 2-naphthol is converted into 2-naphthylamine by heating with ammoniacal ammonium sulphite solution at 150°C in an autoclave. The reaction (the Bucherer reaction) depends upon the addition of the hydrogen sulphite ion to the keto form of the naphthol and the subsequent reaction with ammonia. 

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