2- nitroso-l-naphthol

Cobalt in steel Discussion. An alternative, but less sensitive, method utilises 2-nitroso-l-naphthol, and this can be used for the determination of cobalt in steel. The pink cobalt(III) complex is formed in a citrate medium at pH 2.5-5. Citrate serves as a buffer, prevents the precipitation of metallic hydroxides, and complexes iron(III) so that it does not form an extractable nitrosonaphtholate complex. The cobalt complex forms slowly (ca 30 minutes) and is extracted with chloroform. 

Procedure. Prepare the 2-nitroso-l-naphthol reagent by dissolving 1.0 g of the solid in 100 mL of glacial acetic acid. Add 1 g of activated carbon shake the solution before use and filter off the required volume. 

What about jr-electron donor substituents on nitrosoarenes other than dimethylamino Pedley gives us the enthalpies of formation for three hydroxy derivatives the isomeric 4-nitroso-l-naphthol, 2-nitroso-l-naphthol and l-nitroso-2-naphthol, species 45-47 respectively. Of the three species, only the first cannot have an intramolecular hydrogen bond. By analogy to nitrophenols75 — there being no thermochemical data for the more related and hence relevant nitronaphthols—we expect that species 46 would be less stable than 45. After all, gaseous 2-nitrophenol is ca 20 kJ mol 1 less stable than its 4-isomer. We recall from the discussion of the isomeric naphthylamines that 1- and 2-naphthol are of almost identical stability. This suggests that species 46 and 47 should be of comparable stability. Both expectations are sorely violated by the literature results the enthalpies of formation of species 45, 46 and 47 increase in the order —20.3 4.9, —5.4 6.2 and 36.1 4.7 kJmol-1 respectively. If there is experimental error, where does the error lie ... 

Nitroso-l-naphthol-6-sulphonate iV-(2-Hydroxy-l-naphthalidene) anthranilic acid Riboflavin... 

Nitroso-l-naphthol [132-53-6] M 173.2, m 158 (dec). Purified by recrystn from pet ether (b 60-80°) or by dissolving in hot EtOH, followed by successive addition of small volumes of water. 

Nitroso-l-naphthol-4-sulphonic acid (3H2O) [3682-32-4] M 316.3, m 142-146 (dec). Crystd from dilute HCl soln. Crystals were dried over CaCl2 in a vacuum desiccator. Also purified by dissolution in aqueous alkali and pptn by addition of water. 

Heating o-nitrosophenols with hydroxylamine is reported to give furazans, naphtho[l,2-c]furazan (95) being formed from both l-nitroso-2-naphthol and 2-nitroso-l-naphthol, presumably by oximation of the tautomeric o-naphthoquinone monooximes and subsequent dehydration. Compound (95) has also been prepared by oxidation, using alkaline ferri-cyanide or hypochlorite, of l-amino-2-nitroso- and 2-amino-l-nitroso-naphthalene. This latter approach is suitable for heterocyclic fused furazans thus 4,6-diamino-5-nitrosopyrimidine is converted into the furazanopyrimidine (96) by oxidation with lead tetraacetate (71JOC3211). In a similar reaction alkaline hypochlorite oxidizes o-nitrosoacetaniiide to benzofurazan in quantitative yield. 

Samples are wet digested, cobalt is chelated with 2-nitroso-l-naphthol, solvent-extracted and determined either by FAAS using an air—acetylene flame, or by EAAS. 

NITROSO-l-NAPHTHOL see NLB500 NITROSONIUM BISULFITE see NMJOOO N -NITROSONORNICOTINE see NLD500 N-NITROSOOXAZOUDIN (GERMAN) see NLEOOO... 

The 1-nitroso-2-naphthol and the 2-nitroso-l-naphthol have been studied by H and C NMR. In an early study Vainiotalo and Vepsalainen suggested that l-nitroso-2-hydroxynaphthalene exist at the trans form 51C. For the latter both the oxime and the nitroso (51A) form were suggested based on H and C NMR in CDCI3. However, in a recent study Ivanova and Enchev ° assigned the two different sets of resonances to two different rotamers of the oxime form, i.e. 51B and 51C. They also measured solid... 

In the case of 2-nitrosophenols, the main issue is the question of whether the species exist as an nitrosophenol (71) or as the quinone-monooxime tautomer (72). Both forms are stabilized by intramolecular hydrogen bonding. A similar tautomerism, but without intramolecular hydrogen bonding, is relevant for 4-nitrosophenols. According to IR spectroscopic data , 2-nitrosophenol is present in the quinonoid form while 4-nitrosophenol exists in equilibrium between both tautomeric forms. l-Nitroso-2-naphthol exists in quinonoid form only, while the existence of both forms has been suggested for 2-nitroso-l-naphthol. For recent reviews, see the publications by Ivanova and Enchev and Krzan and coworkers . 

In the reaction with nitrosonaphthols, cobalt is oxidized by atmospheric oxygen to the (III) oxidation state. The complex of cobalt with l-nitroso-2-naphthol is orange, whereas that with 2-nitroso-l-naphthol is brown-pink. The absorption spectra of the two chelates in chloroform solutions are shown in Fig. 18.1. 

Fig. 18.1. Absorption spectra of cobalt complexes with 1-nitroso-2-naphthol (1) and with 2-nitroso-l-naphthol (2)...

Chloroform is the most popular solvent, although carbon tetrachloride, benzene, toluene, and isoamyl acetate are also used. The reaction between cobalt ions and nitroso-naphthols takes place in weakly acidic medium and proceeds rather slowly. For this reason, the sample solution is allowed to stand for about 30 min after the reagent is added, before the complex is extracted. The reaction with cobalt is done at pH 3 with l-nitroso-2-naphthol, and at pH 4 with 2-nitroso-l-naphthol. 

Nitroso-l-naphthol, 0.5% solution in glacial acetic acid. Purify the solution as for 1-nitroso-2-naphthol. 

To a solution containing not more than 30 pg of Co, add 1 ml of the 1-nitroso-2-naphthol (or 2-nitroso-l-naphthol) solution with stirring, adjust the pH of the solution with ammonia to 4 (or 5 in the case of 2-nitroso-l-naphthol), and allow to stand for 30 min. Transfer the solution to a separating funnel and extract with two portions of CHCI3. Shake the combined extracts with 2 M HCl, followed by two portions of 2 M NaOH, and finally wash with water. Transfer the extract to a 25-ml standard flask, make up to the mark with chloroform, and measure the absorbance of the solution at 415 nm (in the case of 2-nitroso-l-naphthol, at 365 nm), using the solvent as the reference. 

Related reagents, such as 2-nitroso-l-naphthol-4-sulphonic acid [31,32], 1-nitroso-naphthol-6-sulphonic acid, and 2-nitroso-l-naphthol-6-sulphonic acid [33] have also been recommended for determination of cobalt. The complexes with these reagents can be extracted into CHCI3 in the presence of amines [31,33]. 

The dyes Rhodamine 6G [55] and Crystal Violet [56] form extractable ion-associates with the anionic complexes of nickel with chloro-oxine [551 and 4-chloro-2-nitroso-l-naphthol [56], (e = 7.7-10 - 8.2-10 ). The ion associate of Rose Bengal with the cationic nickel complex with 1,10-phenanthroline, extractable into nitrobenzene, is also the basis of a sensitive method (e > 1-10 ) [57]. Hydroxynaphthol Blue has been applied for determination of Ni in the presence of Cu by the derivative spectrophotometry method [58]. 

A group of methods for determining Ru is based on nitroso compounds such as 1-nitroso-2-naphthol and 2-nitroso-l-naphthol (e = 1.8-10" ) [9,48], 3-nitroso-2,6-pyridinediol (49], and isonitrosoacetophenone [50]. 

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