Aminonaphthols

A fairly general procedure consists in coupling a phenol or naphthol with a diazotised amine, reducing the product to an aminophenol or aminonaphthol, and oxidising the hydroxy compound with acid ferric chloride solution. This method is illustrated by the preparation of (3 (or 1 2)-naphthoquinone ... 

The aminonaphthols are of minor use but the aminohydroxynaphthalenesulfonic acids are intermediates for dyes, eg, fiber-reactive a2o dyes and plain and meta11i2ed a2o dyes (Table 7). 

With the exceptions of 1,4-benzoquiaone and 9,10-anthraquiaone, quiaones are not produced on a large scale, but a few of these are commercially available (see Anthraquinone). The 1995 prices of selected quiaones are Hsted ia Table 4. Most of the compouads are prepared by the methods described hereia. The few large-scale preparatioas iavolve oxidatioa of aniline, pheaol, or aminonaphthols, eg (110), from which (8) is obtaiaed ia 93% yield. 

In disa2o dyes from aminonaphthols, one group exists as a tme a2o group and one as a hydra2o group (17). 

The solution is highly supersaturated, but it will remain so unless allowed to stand for an undue amount of time. It is also a mistake to add the quantity of concentrated hydrochloric acid specified to a suspension of the aminonaphthol, for this may initiate crystallization. 

The only practical method of preparing 1,4-aminonaphthol is from a-naphthol through an azo dye, the nitroso compound not being readily available. The majority of investigators have reduced technical Orange I with stannous chloride Mi.is.is.ir.is by the procedures discussed above, and benzeneazo-a-naphthol has been reduced by the same reagent. In order to make possible the use of crude, technical a-naphthol a method has been developed for the preparation of the benzeneazo compound, its separation from the isomeric dye coming from the d-naphthol present as well as from any disazo compound by extraction with alkali, and the reduction of the azo compound in alkaline solution with sodium hydrosulfite. The process, however, is tedious and yields an impure product. 

The present method is applicable with slight modifications to the preparation of both the ortho and para aminonaphthols and to many homologues, benzologues, and heterocyclic isologues of these substances. The chief feature of novelty is in the use of stannous chloride as an antioxidant in preparing and crystallizing the amine hydrochlorides. 

The only satisfactory method of preparing /3-naphthoquinone is by the oxidation of 1,2-aminonaphthol in acid solution, and the chief problem involved is that of the preparation of this intermediate in suitable yield and purity. This problem and the literature pertaining to it are discussed elsewhere. Most reports of the preparation of the aminonaphthol include some description of its oxidation, but the only particularly helpful comment on the reaction is that ferric chloride is a better oxidizing agent than chromic acid because at a low temperature it docs not attack the quinone, even when present in excess. ... 

Hydrochloride of aminonaphthol, 6, 94 Hydrochloride of 3-bromo-4-aminoto-luene, 6, g... 

Also including aminonaphthols and hydroxy derivatives of higher condensed aromatic systems. 

The major problem of these diazotizations is oxidation of the initial aminophenols by nitrous acid to the corresponding quinones. Easily oxidized amines, in particular aminonaphthols, are therefore commonly diazotized in a weakly acidic medium (pH 3, so-called neutral diazotization) or in the presence of zinc or copper salts. This process, which is due to Sandmeyer, is important in the manufacture of diazo components for metal complex dyes, in particular those derived from l-amino-2-naphthol-4-sulfonic acid. Kozlov and Volodarskii (1969) measured the rates of diazotization of l-amino-2-naphthol-4-sulfonic acid in the presence of one equivalent of 13 different sulfates, chlorides, and nitrates of di- and trivalent metal ions (Cu2+, Sn2+, Zn2+, Mg2+, Fe2 +, Fe3+, Al3+, etc.). The rates are first-order with respect to the added salts. The highest rate is that in the presence of Cu2+. The anions also have a catalytic effect (CuCl2 > Cu(N03)2 > CuS04). The mechanistic basis of this metal ion catalysis is not yet clear. 

In addition to 1,2-, 2,1-, and 1,4-aminonaphthols, sulfonated isomers of 1,7- and 2,6-isomers have also been diazotized, some of this work dating back to the early 1900s (Jacchia, 1902 Cain and Niccol, 1903 Kaufler and Karrer, 1907 Allan and Podstata, 1969). 

Interesting regioselectivities have been known for more than 100 years for azo coupling reactions with aminonaphthol derivatives such as 6-amino-4-hydroxy-2-naphthalenesulfonic acid (12.136, y-acid), 7-amino-4-hydroxy-2-naphthalenesulf-onic acid (J-acid), and 4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid (H-acid). They give two types of isomeric azo compounds depending on the pH-value of the... 

A mechanistic explanation of this selectivity was, however, only given in 1952 (Wittwer and Zollinger). An aminonaphthol coupling component can be considered as a superposition of a naphthol and a naphthylamine. The rates of azo couplings of both these components show the characteristic pH-dependences discussed for naphthols above. For naphthylamines it is the base, and not the ammonium ion, that reacts with the diazonium ion. This pre-equilibrium has a p Ta-value of about 4. Therefore the 1 1 gradient of log A Nh2 against pH is observed only in the range pH <4. 

Freeman et al. (1986) claimed that their experimental results on coupling imply that aminonaphthols are unreactive at pH 5-6. Skrabal and Zollinger (1988) showed that this interpretation is wrong (see Sec. 12.8). 

Aromatic amines and phenols [1-4] e.g. resorcinol, catechol, aminonaphthols Indol m-dinitrobenzene Ruene [2] Sulfapyridine [2, 3] ... 

Oxidation of the aminonaphthols 91 gives the quinone spiroketals 92, analogues of palmarumycin <00TL9105>. The first total synthesis of (+)-diepoxin a 93 has been achieved from a naphthoquinone . 

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