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Org. Synth. 1922, 2, 61
DOI: 10.15227/orgsyn.002.0061
NITROSO-β-NAPHTHOL
[2-Naphthol, 1-nitroso-]
Submitted by C. S. Marvel and P. K. Porter.
Checked by H. T. Clarke and W. W. Hartman.
1. Procedure
In a 12-l. round-bottomed flask (Note 1) fitted with a mechanical stirrer is placed 500 g. (3.5 moles) of technical β-naphthol dissolved in a warm solution of 140 g. (3.5 moles) of sodium hydroxide in 6 l. of water. The solution is cooled to 0° in an ice and salt bath, and 250 g. (3.5 moles) of powdered technical sodium nitrite is added. Stirring is started, and 1100 g. (833 cc., 4.6 moles) of sulfuric acid (sp. gr. 1.32) is added from a dropping funnel at such a rate that the whole is added in one to one and one-half hours, the temperature being kept at 0°. During the reaction, crushed ice is added from time to time to maintain the temperature at 0°; about 1 kg. is generally used (Note 2). After all the sulfuric acid has been added, the solution should react acid to Congo red paper. The mixture is stirred one hour longer at the low temperature, and then the nitroso-β-naphthol, which has gradually separated during the reaction, is filtered with suction and washed thoroughly with water. The product is at first light yellow in color, but after three to four days it gradually changes to a dark brown. The moisture content seems to have some effect on the color.
After the product has been air-dried for about four days, the yield is about 665 g.; it melts at 97°. A sample of this partially dried product, on drying in a vacuum desiccator over sulfuric acid for twenty hours, loses about 10 per cent of its weight, and the melting point is 106°. By longer drying under ordinary conditions, the melting point of 106° is reached (Note 3). The total yield of dry product is about 595 g. (99 per cent of the theoretical amount).
This product is satisfactory for most purposes. It may be obtained in a crystalline condition, however, by recrystallizing from hot ligroin (b.p. 60–90°). About 2 g. of nitroso-β-naphthol will dissolve in 15 cc. of boiling ligroin. The product is not very soluble in cold ligroin, so that nearly all is recovered.
2. Notes
1. A large vessel is needed for the reaction, as the nitroso-β-naphthol separates in a finely divided condition and there is some tendency to foam.
It has been suggested that instead of a flask there be used a 13–14 l. bottle or crock with an opening of 20–22 cm. and equipped with a stirrer of heavy glass rod having four or five right-angle bends which extend to the top of the bottle and which are just small enough to fit the mouth. If the salt-ice mixture in the cooling bath is stirred well, a temperature of 0° may be maintained without internal cooling (L.F. Fieser, private communication).
2. It is very necessary to keep the temperature near 0° while adding the sulfuric acid, or a tarry product will be obtained. Vigorous stirring and the addition of the sulfuric acid at the proper rate are essential for a good product. Instead of the 1100 g. of sulfuric acid (sp. gr. 1.32) there can, of course, be added an equivalent amount of concentrated acid and sufficient ice to give a cold solution.
3. The final air-dried product is pure except for its moisture content, as is shown by the fact that on drying in a vacuum desiccator it has a very good melting point.
3. Discussion
Nitroso-β-naphthol can be prepared by the action of sulfuric acid upon a solution of potassium or sodium nitrite and the sodium salt of β-naphthol;1 by the action of sodium nitrite upon an alcoholic solution of zinc chloride and β-naphthol;2 by the action of sodium nitrite upon β-naphthol suspended in zinc sulfate solution;3 and electrolytically from β-naphthol.4
This preparation is referenced from:

References and Notes
  1. Fuchs, Ber. 8, 1026 (1875); Groves, J. Chem. Soc. 45, 295 (1884); Lagodzinski and Hardine, Ber. 27, 3076 (1894).
  2. Henriques and Ilinski, Ber. 18, 705 (1885).
  3. Koehler, Ger. pat. 25,469 [Frdl. 1, 335 (1877–87)].
  4. Emi, Repts. Imp. Ind. Research Inst., Osaka (Japan) 15, No. I, 1 (1934) [C. A. 29, 2457 (1935)].

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

ligroin

potassium or sodium nitrite

sulfuric acid (7664-93-9)

sodium hydroxide (1310-73-2)

sodium nitrite (7632-00-0)

β-naphthol (135-19-3)

zinc chloride (7646-85-7)

Nitroso-β-naphthol,
2-Naphthol, 1-nitroso- (131-91-9)

sodium salt of β-naphthol

zinc sulfate (7733-02-0)