Orange reduction

The colour sequence already described, for the reduction of van-adium(V) to vanadium(II) by zinc and acid, gives a very characteristic test for vanadium. Addition of a few drops of hydrogen peroxide to a vanadate V) gives a red colour (formation of a peroxo-complex) (cf. titanium, which gives an orange-yellow colour). 

Copperil) oxide, CujO, occurs naturally as the red cuprite. It is obtained as an orange-yellow precipitate by the reduction of a copper(II) salt in alkaline solution by a mild reducing agent, for example glucose, hydroxylamine or sodium sulphite ... 

Reduction to aminophenol. Reduce about 0 5 g. of o-nitrophenol with cone. HCl and tin as described on p. 385. After a few minutes the yellow molten o-nitrophenol disappears completely, the solution becoming homogeneous and colourless due to the formation of 0-aminophenol (which is soluble in HCl). Cool and add 30% aqueous NaOH solution note that a white precipitate is first formed and then redissolvcs in an excess of NaOH, and that the solution does not develop an orange coloration, indicating that the nitro-group has been reduced. 

Sodium hyposulphite (dithionite) NajS O, may also bo employed for the reduction see under Methyl Orange, Section IV,78. 

Reduction of methyl orange to />-aminodimethylaniline. Method 1. Dissolve 2 0 g. of methyl orange in the minimum volume of hot water and to the hot solution add a solution of 8 g. of stannous chloride in 20 ml. of concentrated hydrochloric acid until decolourisation takes place gentle boiling may be necessary. Cool the resulting solution in ice a crystalline precipitate consisting of sulphanilic acid and some p-aminodimethylaniline hydrochloride separates out. In order to separate the free base, add 10 per cent, sodium hydroxide solution until the precipitate of tin hydroxide redisaolves. Extract the cold solution with three or four 20 ml. portions of ether, dry the extract... 

Compounds containing two primary amino groups attached to a benzene ring can be prepared by the reduction of dinitro compounds and of nitroanilines, usually with tin or stannous chloride and hydrochloric acid or with iron and very dilute hydrochloric acid. / ara-diamines may also be obtained by the reduction of aromatic amino-azo compounds (e.g., p-aminodimethylanihne from methyl orange, see Section IV,78). p-Phenylenediamine may also be prepared from p-nitroacetanilide reduction with iron and acid yields p-amino-acetaniUde,.which may be hydrolysed to the diamine. 

Plutonium(III) in aqueous solution, Pu " ( 4)> is pale blue. Aqueous plutonium(IV) is tan or brown the nitrate complex is green. Pu(V) is pale red-violet or pink in aqueous solution and is beUeved to be the ion PuO Pu(VI) is tan or orange in acid solution, and exists as the ion PuO. In neutral or basic solution Pu(VI) is yellow cationic and anionic hydrolysis complexes form. Pu(VII) has been described as blue-black. Its stmcture is unknown but may be the same as the six-coordinate NpO (OH) (91). Aqueous solutions of each oxidation state can be prepared by chemical oxidants or reductants... 

The a2oxy and nitro groups in Direct YeUow 11 are reduced to a2o and amino groups in Direct Orange 15. Direct YeUow 6 (Cl 40006) (14) is a greener and brighter shade of yeUow than Direct YeUow 11 and is made by reductive a2o formation from 4,4 -dinitro-2,2 -stilbenedisulfonic acid to an a2o and a2oxy dye. 

A study of the degradation of two azo disperse dyes. Disperse Orange 5 [6232-56-0] (1) Cl 11100) and Disperse Red 5 [3769-57-1] Cl 11215) showed reduction of the azo linkage into aromatic amines and further dealkylation to -phenylene-diamine [106-50-3] (2) (255). 

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. 

In like manner lodal (VI), on condensation with 6-nitro-3 4-methylene-dioxyphthalide (IV) yields nitro-a -adlumine (I R = NOj . O. CHa. O. at C and C replaced by 20Me), which crystallises from chloroform-methyl alcohol in orange, rectangular plates, m.p. 180-1° dec.), and on reduction yields the corresponding amino-derivative, bundles of minute needles, m.p. 218-9°. 

Nitro-pJienols and Nitro-acids dissolve in ctiustic alkahs as a rule with a deep yellow or orange colour. On reduction with st. innous chloride or zinc dust, as described above, they yield the amino-derivatives. In the case of the amino-phenol, the solution is made alkaline with caustic soda, satuiated with CO.j, salt added and extracted w ith ether. In the case of the amino-acid, the method used is that desciibed under Prep. 91 (p. 201). 

From 13.1 g of N-preduction with Raney-nickel and hydrogen, in which reaction the substance may be suspended in methanol or dissolved in methanol-ethyl acetate at normal pressure and at about 40°C with combination of the theoretical quantity of hydrogen, 12.2 g are obtained of o-emino-N-pfrom aqueous methanol hasaMPof90°C. 

It is a volatile orange-red crystalline solid (m.p. 30°C), stable to over 100°C. On reduction with tertiary phosphines or sodium amalgam, Os(NBu )3 is formed, which is dimeric (ButN)2Os(/x-NBut)2Os(NBu )2. This can be oxidized to the osmium(VII) dication with concomitant shortening in the Os-Os distance from 3.1 to 2.68 A. 

The red tetrasulfide radical anion 84 has been proposed as a constituent of sulfur-doped alkali hahdes, of alkah polysulfide solutions in DMF [84, 86], HMPA [89] and acetone [136] and as a product of the electrochemical reduction of 8s in DM80 or DMF [12]. However, in all these cases no convincing proof for the molecular composition of the species observed by either E8R, Raman, infrared or UV-Vis spectroscopy has been provided. The problem is that the red species is formed only in sulfur-rich solutions where long-chain polysulfide dianions are present also and these are of orange to red color, too (for a description of this dilemma, see [89]). Furthermore, the presence of the orange radical anion 8e (see below) cannot be excluded in such systems. 

The above-mentioned method is useful but metals that form strong M-S bonds (e.g., Hg, Ag, Sn) do not dissolve in W-Melm solutions of sulfur. This problem has been solved by the addition of Mg to the reaction mixture. Metal polysulfides having a variety of metals can be synthesized by the 7 T-Melm/ M-i-Mg/Sg method (Scheme 11) [48]. For example, a mixture of Mg, Sb powder (1 eq.), Sg (15 eq. as S) and W-Melm is heated at 80 °C for 48 h to afford the orange powder of [Mg(N-MeIm)5]Sb2Sj ( x 15) in 88% yield. Rauchfuss et al. proposed the mechanism of these reactions as follows. First, the reduction of Sg with Mg occurs to give the [Mg(W-MeIm)6] salt of Sg , which is probably in equilibrium with Sg, Ss ", Ss" and other species. Independently, the sulfuration of the thiophilic metal takes place. Next, the polysulfide an-... 

Benzene is highly stable to chemical attack. )S-Carotene absorbs visible light and is orange. Both properties are direct consequences of delocalized iz systems. Delocalized n systems also affect the oxidation-reduction... 

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