A Naphthol

Effect of impurities upon the melting point. Let us take a specific example and examine the effect of the addition of a small quantity of naphthalene to an equilibrium mixture of pure solid and liquid a-naphthol at the temperature of the true melting point (95 5°) at atmospheric pressure. 

The naphthalene wUl dissolve in the liquid a-naphthol and, according to Raoult s law, the vapour pressure of the latter will be reduced. Hence a-naphthol will pass preferentially into the liquid phase and, if the external temperature is maintained at 95 5°, the ultimate result will be the complete melting of the solid a-naphthol since melting requires heat and no heat is imparted to the system, the temperature will fall. 

A somewhat different method of plotting the results will help the reader to appreciate the significance of the eutectic temperature. In Fig. 1,11, 2 melting points are plotted against composition. The curve AC portrays the decreasing melting point of a-naphthol as naphthalene is added up to a mol fraction of 0 605. The curve BG represents the... 

Determination of melting points (a-naphthylamine, a-naphthol, benzoic acid, succinic acid and p-nitrobenzoic acid). Use the apparatus shown in Fig. II, 10, 2, a. Construction of calibration curve for thermometer. Determination of m.p. of unknown compound. 

Diazo coupling involves the N exocyclic atom of the diazonium salt, which acts as an electrophilic center. The diazonium salts of thiazoles couple with a-naphthol (605). 2-nitroresorcinol (606), pyrocatechol (607-609), 2.6-dihydroxy 4-methyl-5-cyanopyridine (610). and other heteroaromatic compounds (404. 611) (Scheme 188). The rates of coupling between 2-diazothicizolium salts and 2-naphthol-3.6-disulfonic acid were measured spectrophotometrically and found to be slower than that of 2-diazopyridinium salts but faster than that of benzene diazonium salts (561 i. The bis-diazonium salt of bis(2-amino-4-methylthiazole) couples with /3-naphthol to give 333 (Scheme 189) (612). The products obtained from the diazo coupling are usuallv highly colored (234. 338. 339. 613-616). 

Naphthalenol. 1-Naphthol, a-naphthol, or l-hydroxynaphthalene/P(9-/j5 -iJ forms colorless needles, mp 96°C, bp 288°C, which tend to become colored on exposure to air or light. It is almost insoluble in water, but readily soluble in alcohol, ether, and benzene. 1-Naphthol and 2-naphthol are found in coal tar (56). 

Azoic Dyes. These are used to produce cost-effective heavy yellow, orange, red, maroon, navy blue, brown, and black shades and are ptinted alongside other dye classes to extend the coloristic possibiUties for the designer. Two approaches are adopted. The common method ia the United States is to use both a naphthol derivative and a stabilized color base, usually in the form of a diazo imino compound in the same print paste. This mixture is soluble in dilute caustic soda and no coupling takes place at this stage. The dried prints are passed through steam at 100—105°C that contains acetic and/or formic acid vapor. As neutralization takes place on the print, the coupling occurs rapidly and the insoluble azoic dye is formed. 

B ) Coupling Orange T.—The procedure is the same as in (B) except that the alkaline solution of a-naphthol (Note 4) is cooled to 25 before adding the ice (Note 5). The azo dye in this case does not crystallize but forms a deep purple-red solution. 

The a-naphthol should be free from the /9-isomer if the material is very highly colored it is advisable to purify it by distillation at atmospheric pressure. Material melting at 95-96° is satisfactory. 

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. 

Oxygen -I- Methyl Formamide-1- a—Naphthol = Carbaryl + Water (12.2) which yields an economic potential of 39.99 million per year, and... 

Methyl Amine + a-Naphthol Chloroformate = Carbaryl -I- Hydrogen Chloride,... 

Dime thoxyaniUne Apply sample solution as spots then apply diazonium chloride and a-naphthol solution and develop after 2 min. [61]... 

A mixture of a-naphthol 41 (15.0 g, 0.1 mol), phenylhydrazine 42 (11.0 g, 0.1 mol) and sodium bisulfite solution (36 %, 250 g) was heated at reflux for 15 h. A further 4 g of phenylhydrazine was added and heating continued for 15 h, after which time the majority of the a-naphthol was consumed. After cooling, the mixture was extracted with ether. The oily, ether and aqueous insoluble residue was warmed with cone. HCl until a dark crystalline mass developed. After cooling, the mixture was extracted with ether. The organic extract was dried and concentrated to afford a crystalline residue which was purified by recrystallisation from ethanol to afford the product 43 as a white crystalline solid, mp 225 °C. A reaction yield is not given. 

The Bueherer reaetion is the reversible eonversion of a naphthylamine to a naphthol by the action of aqueous sulfite or bisulfite, see references 2 and 3. 

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