Naphthol-coupling

Dihydroxynaphthalene [83-56-7] behaves similarly to 1-naphthol coupling takes place mainly in the 4-position by simple diazonium compounds, and in the 2-position with diazophenols. Diazotized 2-arninophenol-4-sulfonic acid [98-37-3] couples with 1,5-dihydroxynaphthalene to produce the important mordant dye Diamond Black PV [2052-25-7] (see stmcture 53) (Cl Mordant Black 9 Cl 16500). 

Naphthol couples in the more reactive 1-position as in the synthesis of 1-phenylazo-2-naphthol (Expt 6.82). 1-Naphthol couples almost exclusively in position 4 when the diazo component is the p-nitrobenzenediazonium ion the product is Magneson II (Expt 6.83), which is employed as a test reagent for magnesium. 

Phenols, Naphthols (e.g., 39-47). Phenols mainly couple at the 4-position, or at the 2-position if the 4-position is occupied, p-Hydroxybenzoic acid couples with elimination of C02 resorcinol couples twice initially at the 4-position, and with a second equivalent of diazonium compound at the 2-position under acid conditions or at the 6-position under alkaline conditions. a-Naphthols mainly couple at the 4-position, in addition to which varying quantities of 2- and 2,4-coupling products are obtained, depending on the diazo component. p-Naphthol couples at the 1-position. Substituents in the 1-position, such as S03H, COOH, Cl, CH2OH, or... 

Cobalt (II) thiocyanate Diazotization and a-naphthol coupling Ehrlich reagent Fast Blue B Salt... 

Naphthalene, polarographic behavior, 107 o-Naphthol, coupling with, 112 0-Naphthol, coupling with, 112 Narcotic, 146... 

Coupling with phenols is usually effected more easily than coupling with amines, and naphthols couple considerably more readily than hydroxybenzene derivatives. Reactive methylene compounds behave similarly to phenols of the benzene series. Negative substituents (halogen, nitro, sulfo, carboxyl, carbonyl, etc.) accelerate coupling when... 

Reaction with phenols and naphthols are usually carried out in the pH range 8-11, when the coupling species is the phenoxide ion. A cold, acidic solution of the diazonium salt is added to an alkaline solution of the phenol, when a fast electrophilic aromatic substitution occurs at the 4-position (Scheme 8.25). If this position is already occupied, attack occurs at the 2-position. 2-Naphthol couples at the 1-position. 

The azo dyes used in this study were l-phenylazo-2-naphthol-6-sulfonate (2) and seven derivatives with substituents in the meta or para positions of the phenyl ring (3-9). These were selected as representative l-azo-2-naphthol sulfonate dyes and because the substituents on phenyl ring would allow a systematic study of the mechanism of their oxidation by metalloporphyrin-catalysed systems in aqueous solution. Dye 2 is commercially available (as Acid Orange 12) and was purified by reciystallisation whilst the others (3-9) were prepared by standard diazonium ion/2-naphthol coupling reactions. The purities of all the dyes were checked by TLC, MS and H NMR spectroscopy. Table 1 reports the measured pl values of all the azo dyes used in this study. 

Prepare second pad bath naphthol coupling component. 

In naphthalene derivatives, orientation of the entering diazo group is somewhat different. In a/p/ifl-naphthol, the attack is at position 4. If 4 is blocked, the diazo group enters at 2. In heta-naphthol, coupling takes place at 1, never at 3 or 4. The same rules apply to the corresponding naphthylamines. 

Kozlowski and co-workers found that asymmetric cross-coupling between electronically tuned 3-acyl-substituted 2-naphthols was catalyzed by a chiral Cu-diamine complex (Scheme 7.22). The Cu catalyst acts as an oxidation catalyst for naphthol coupling, and the resulting reduced Cu complex is reoxidized by O2 as the sole oxidant. 

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