2-naphthol-6-sulfonate

Quantitative studies based on kinetic measurements using strongly electrophilic diazonium ions and, as coupling components, 1-naphthol, 2-naphthol-6-sulfonic acid, and resorcinol in aqueous acid were made by Sterba and coworkers (Kropacova et al., 1970 Kavalek et al., 1970 Sterba and Valter, 1972 Machackova et al., 1972a). In a typical case (2,6-dichloro-4-nitrobenzenediazonium ion and 1-naphthol) the dependence of the logarithm of the measured rate constant (ks) on pH was linear with a slope of 1. At pH < 1, however, a practically constant value of ks was obtained. The measured rate constants therefore correspond to Scheme 12-62, in which the first term relates to the reaction of the naphthoxide ion and the second to that of the undissociated naphthol Ka is the acidity constant of 1-naphthol. 

Bagal et al. (1975) investigated in more detail the role of donor-acceptor complexes in the azo coupling reaction of the 4-nitrobenzenediazonium ion with 2-naphthylamine-3,6-disulfonic acid and that of the 4-chlorobenzenediazonium ion with 2-naphthol-6-sulfonic acid. Their kinetic results are, as would be expected, compatible with the mechanisms shown in Schemes 12-74 or 12-75. 

Micellar catalysis of azo coupling reactions was first studied by Poindexter and McKay (1972). They investigated the reaction of a 4-nitrobenzenediazonium salt with 2-naphthol-6-sulfonic and 2-naphthol-3,6-disulfonic acid in the presence of sodium dodecylsulfate or hexadecyltrimethylammonium bromide. With both the anionic and cationic additives an inhibition (up to 15-fold) was observed. This result was to be expected on the basis of the principles of micellar catalysis, since the charges of the two reacting species are opposite. This is due to the fact that either of the reagents will, for electrostatic reasons, be excluded from the micelle. 

The electrostatic impasse mentioned can be circumvented (Moss and Rav-Acha, 1980) if a cationic surfactant is functionalized with an arenediazonium ion moiety. The azo coupling with the micellar diazonium ion surfactant 12.160 was found to be faster than the azo coupling with the model diazonium ion 12.161 by factors of 122 and 244, in reactions with 2-naphthol and with 2-naphthol-6-sulfonate respectively. 

Schaeffer s salt orgchem HOC oS03Na A light-yellow to pink, water-soluble powder the sodium salt formed from 2-naphthol-6-sulfonic acid used as an intermediate in synthesis of organic compounds. sha-forz, s6lt ... 

Ion-pair HPLC (194,195) was used to separate amaranth from its subsidiary dye l-(4-sulfo-l-naphthylazo)-2-naphthol-6-sulfonic acid disodium salt (fast red E) and from its intermediates 1-naphthylamine 4-sulfonic acid (naphthionic acid) and 2-naphthol-3,6-disulfonic acid disodium salt (R-salt). Ion-pair HPLC was also used for the determination of total free and bound nonsul-fonated aromatic amines in amaranth after diazotization and coupling with R-salt (198). 

In 1985 the FDA published specifications for free amines in FD C Yellow No. 6 (or Sunset Yellow, l-(4 -sulfo-l -phenylazo-)2-naphthol-6-sulfonic acid disodium salt), and FD C Yellow No. 5 (or tartrazine, 4,5-dihydro5-oxo-l-(4-sulfophenyl)-4-[(4-sulfophenyl)azo]-l//-pyra-zole-3-carboxylic acid trisodium salt) and expressed concern about amines in other colors (208). 

It contains 4-aminodiphenylamine-2-sulfonic acid as the diazo component, 1-naphthylamine as the middle component, and 2-naphthol-6-sulfonic acid as the final coupling component. 

Since the transfer of protons is truly contact, this reaction is best suited for comparison with the contact and spinless theory given above. However, the authors who first monitored it in the time domain tried to fit the fluorescence signal as a biexponential one [59]. The similar reaction but of a more reactive photoacid (2-naphthol-6-sulfonate) with an acetate anion has been studied, and its kinetics, which is neither exponential nor biexponential, was fitted to the tme theory of contact quenching [60]. It is especially important that the fluorescence... 

Figure 3.1. Calculated survival probability Ril j of 2-naphthol-6-sulfonate in its reaction with 2 M acetate anion for various solvent compositions (bottom left to upper right) 0, 10, 20, 30, 40, 50, 60, and 70% (vol) of glycerol. (From Ref. 60.)...

The first product formed by the actio of concentrated sulfuric acid on/3-naphthol is 2-naphthol-l-sulfonic acid (page 199). This compound, however, is very unstable and rearranges, even in the cold, in the presence of excess sulfuric acid, to form 2-naphthol-8-sulfonic acid (Bayer acid, croceine acid), and this in turn rearranges, only partially in the cold but completely at higher temperatures, into 2-naphthol-6-sulfonic acid (Schaeffer acid). 

Salting out, 39 Sample dyeing, 375 Sandmeyer reaction, 9, 67,161, 163 Schaeffer acid (and salt), see 2-Naphthol-6-sulfonic add Schultz dye tables, 399 Screw press, 20, 107 Separation reaction products, 27 Silver salt, see Antfaraquinone-2-sulfonic add... 

In practice, the neutral or slightly acid solution of the sodium salts, containing little or no sodium chloride, is evaporated to a definite volume which depends on the composition of the reaction mixture and which is selected so that on cooling only the sodium 2-naphthol-6-sulfonate crystallizes out, but this as completely as possible. The precipitate is removed, and, to the filtrate, usually after further evaporation, is added enough salt to make it an 18 to 20 per cent salt solution. R salt then precipitates when the solution is cooled. Potassium chloride is then added to the mother liquor to precipitate the potassium salt of G acid. 

Quantitative evaluations of kinetic measurements using strongly electrophilic diaa>-nium ions and, as coupling components, 1-naphthol, 2-naphthol-6-sulfonic acid and resorcinol in aqueous acid were made in the seventies by StSrba and coworkers 156-158) jjj typical case (2,6-dichloro-4-nitrobenzenediazonium ion and 1-naph-... 

Halogens as electrofugic leaving groups were studied by Fischer and Zollinger The rates of substitution of the group X in l-X-2-naphthol-6-sulfonic acid by... 

P-SULFOPHENYLAZO-2-NAPHTHOL-6-SULFONIC ACID, DISODIUM SALT see FAG150... 

As the molsidomine case shows, the photodegradation of drugs in the solid state can be enhanced by the use of colorants. Another example of this approach are ethinyl estradiol tablets which can be stabilized by the addition of erythrosine (FD C Red No. 3) but degrade faster if they contain l-p-sulfophenylazo-2-naphthol-6 sulfonate, di-sodium salt (FD C Yellow No. 6) (14). 

Synonyms EllO FD C yellow 6 6-hydroxy-5-[(4-sulfophe-nyl)azo]-2-naphthalenesulfonic acid disodium salt 1-p-sulfophenylazo-2-naphthol-6-sulfonic acid disodium salt yellow orange S. 

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