Naphthylamines, reduction

In naphthylamines reduction with sodium in refluxing pentanol affected exclusively the substituted ring, giving 51-57% of 2-amino-l,2,3-4-tetrahy-dronaphthalene [715]. 

In the naphthalene series, a-naphthylamine is easily obtained by the reduction of the readily accessible a-nitronaphthalene ... 

Naphthaleneamine. 1-Naphthylamine or a-naphth5iamine/7i5 -i2- can be made from 1-nitronaphthalene by reduction with iron—dilute HCl, or by catalytic hydrogenation it is purified by distillation and the content of 2-naphthylamine can be reduced as low as 8—10 ppm. Electroreduction of 1-nitronaphthalene to 1-naphthylamine using titania—titanium composite electrode has been described (43). Photoinduced reduction of 1-nitronaphthalene on semiconductor (eg, anatase) particles produces 1-naphthylamine in 77% yield (44). 1-Naphthylamine/7J4-J2-. can also be prepared by treating 1-naphthol with NH in the presence of a catalyst at elevated temperature. The sanitary working conditions are improved by gas-phase reaction at... 

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... 

Although El-Bayoumy and Hecht (84) did not detect the reduction of 1-nitronaphthalene to 1-naphthylamine in their S9 incubations, Poirier and Weisburger (125) did find reduction under... 

Absorptive cathodic stripping voltammetry has been used [151,152] to determine nanomolar levels of nitrite in seawater. The nitrite is derivatised by diazotisation with sulfanilamide and coupled with 1-naphthylamine to form an azo dye. The dye adsorbs onto a mercury drop electrode and its reduction is fully reversible. The concentration of dye is linearly related to concentration of nitrite in the range 0.3-200 nM. Down to 0.3 nM nitrite can be determined in seawater for an adsorption time of 60 seconds. 

Reduction of a nitro compound to the corresponding naphthylamine proceeds exactly as in the benzene series. A batch process using iron and hydrochloric acid is traditional but has been somewhat superseded by catalytic hydrogenation. 

In all the above sequences, single isomers are produced by careful control of the reaction conditions combined with purification by selective isolation at various points in the synthesis. Occasionally two isomers are produced which give dyestuffs that have very similar properties in these cases it is often quite acceptable and economically beneficial not to separate the individual components but to use the total mixture in dye preparation. An example is the mixture of l-naphthylamine-6- and 7-sulphonic acids (4.46 mixed Cleve s acids), which arises by nitration and reduction of naphthalene-2 Sulphonic acid (Scheme 4.30). 

The reduction of aromatic nitro-compounds is of exceptionally great interest, not only scientifically, hut also technically. The conversion of the hydrocarbons of coal tar into useful products began with the discovery of the nitration process the conversion, on the technical scale, of the nitro-group of nitrobenzene into the amino-group gave aniline, the starting material for the preparation of innumerable dyes and pharmaceutical products to aniline were added the homologous toluidines, xylidines, naphthylamines, and so on. 

Naphthylamine and also its sulphonic acids are likewise employed technically for the manufacture of azo-dyes. In the same way a-naph-thol is made from naphthalene-a-sulphonic acid by fusion with sodium hydroxide although on a smaller scale than /3-naphthol. a-Naphthyla-mine, on the other hand, is obtained by the reduction of a-nitronaph-thalene (analogy to aniline). The fusion of alkali salts of arylsulphonic acids with alkali also serves technically for the production of pure phenol and of many phenol derivatives. 

Reduction of naphthols, naphthyl ethers, naphthylamines and naphthoic acids are discussed on pp. 80, 82, 93 and 140, respectively. 

Reductive desulphonation of naphthalenesulphonic acids is also observed [84]. The 1-sulphonic acid substituent in a wide range of sulphonated naphthylamines is removed by reduction at mercury in aqueous sodium hydroxide [85], Reductive... 

Nitrate is of interest as a possible indication of watering. Many potable water supplies contain 30 mg/liter of nitrate whereas normal wines contain about 4-5 mg/liter on the average (46,47,48). The present recommended procedure (49) is reduction of nitrate to nitrite followed by colorimetric determination with sulfanilic acid and a-naphthylamine. 

The initial product, nitrosobenzene, is so easily reduced to N-phenylhydroxyl-amine that it has not been isolated from the reduction medium, but its presence has been established by reaction in solution with hydroxylamine to yield a benzenediazonium salt, which couples readily with 1-naphthylamine to form the dyestuff 2-phenylazo-1 -naphthylamine. 

The iV-methylamine (160) (R = Me) gives a complex mixture of products when treated under the same conditions.186 It was shown subsequently that prior reduction of the anils used as starting materials is, in fact, unnecessary since in the presence of potassamide in liquid ammonia (o-chlorobenzylidene)aniline forms phenanthridine in excellent yield, and the analogous anils from p-toluidine and a-naphthylamine undergo ring closure under similar conditions. In view of the known trans geometry of the anils and the unlikelihood of trans-cis equilibration under these conditions this reaction deserves further study.187 Potassamide in liquid ammonia also converts 2-bromo-iV-ethyl-3 -hydroxybenzanilide (162) into a mixture of iV-ethyl-3-(164) and N-ethyl-1 -hydroxyphenanthridone (165), probably via the aryne (163).188... 

The easiest preparation of naphthylamines involves the catalytic reduction of the nitronaphthalenes. 

Nitrates and nitrites in water are frequently estimated together, e.g. by reduction to ammonia,1 which can be determined m the manner described below alternative processes are based on the reduction of these salts to nitric oxide which may be measured volumetrically, and on reduction of the nitrate to nitrite when the total nitrite may be estimated eolonmetncaUy by the addition of sulphanihc acid and a-naphthylamine.3 For the estimation of nitrites and mtrates separately, organic colorimetric methods are usually applied.4... 

Similarly, (V-ethyl-l-naphthylamine was prepared in 88% yield, and (V-ethyl-, N-bu-tyl- and (V-benzyl-2-naphthylamine, and (V-ethyl- and (V-butyl-/ -toluidine were prepared in 50-64% yields.34 In the alkylation of / -toluidine and / -anisidine with butyraldehyde, N,N-dibutyl derivatives were also produced in 19 and 25% yields, respectively. The Emerson-Waters procedure was also applied to the reductive alkylation of 2-phenylpropylamines and 2-phenylisopropylamines with C1-C3 aldehydes (amine aldehyde ratio = 1 3).35 With higher aldehydes the monosubstituted products were isolated in good yields (in 48-94% yields with acetaldehyde), while with formaldehyde (V.N-dimethyl derivatives were obtained in 51-85% yields. 

TABLE 6.6 Reductive Amination of a-Oxo Acids with Chiral Benzyl- and Naphthylamines"... 

The reduction is repeated four times with 20 g. of /3-naph-thylamine so that altogether 100 g. of naphthylamine has been reduced (Note 5). The isoamyl alcohol solutions from all five portions are combined and concentrafed hydrochloric acid is added until the solution is just acid to litmus. For this purpose usually about 40-50 cc. is needed (Note 6). The greater part of the isoamyl alcohol is now distilled from a large flask (about 900-1100 cc. is recovered). The distillation is continued until a crust of crystals starts to form, and the residue is then cooled and treated with 200-300 cc. of water and about 300 cc. of 50 per cent potassium hydroxide solution. The base which separates is extracted in the separatory funnel with four 400-500 cc. portions of ether and the ether extracts combined in a flask with a wide neck. 

Up to the present the only method used for the reduction of 0-naphthylamine for obtaining the tetrahydro base has been with sodium and alcohol. This method was first described by Bamberger and Muller.2 It is possible to substitute ethyl alcohol for amyl alcohol but the yield is distinctly lower. The base has been resolved into its optically active components.3... 

Reduction to nitrite test Nitrates are reduced to nitrites by metallic zinc in acetic acid solution the nitrite can be readily detected by means of the sulphanilic acid-a-naphthylamine reagent (see under Nitrites, Section IV.7, reaction 11). Nitrites, of course, interfere and are best removed with sulphamic acid (see reaction 3 above). 

Sulfurous acid and its salts are inexpensive reducing agents which are, however, usable only in special cases. These reagents frequently give sulfonation simultaneously with reduction (cf. the preparation of l-naphthylamine-2,4-disulfonic acid from 1-nitronaphthalene, and of l-amino-2-naphthol-4-sulfonic acid from nitroso- -naphthol, pages 178 and 201). Also, in the reduction of diazobenzene to phenylhydrazine, a N-sulfonic acid is formed first and this must be split by vigorous treatment with hydrochloric acid (see pages 96 and 128). 

The reaction mixture can also be worked up in the following way. When the reduction is complete, the mixture is neutralized with soda and all of the water is evaporated under vacuum. The residue is then extracted three times with benzene, and the extract is distilled at atmospheric pressure to remove the benzene. The a-naphthylamine is then distilled under reduced pressure. 

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... 

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