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Org. Synth. 1945, 25, 80
DOI: 10.15227/orgsyn.025.0080
NITROSOBENZENE
[Benzene, nitroso-]
Submitted by George H. Coleman, Chester M. McCloskey, and Frank A. Stuart.
Checked by W. E. Bachmann, N. C. Deno, and R. F. Edgerton.
1. Procedure
A mixture of 250 ml. (2.44 moles) of nitrobenzene (Note 1) and (Note 2) and a solution of 150 g. of ammonium chloride in 5 l. of water in a 5-gal. crock (Note 3) is stirred vigorously (Note 4), and 372 g. (5.15 moles) of zinc dust (90% zinc) is added in small portions over a period of 5 minutes. About 5 minutes after the addition of the zinc, the main reaction occurs and the temperature rises. When the temperature reaches about 65°, enough ice is added to the stirred mixture to bring the temperature down to 50–55° (Note 5). Twenty minutes after the addition of zinc was started, the solution is filtered through a 24-cm. Büchner funnel and the zinc oxide residues are washed with 3 l. of boiling water. The filtrate and washings are combined in a 6-gal. crock (Note 6) and cooled immediately (Note 7) by the addition of enough ice to bring the temperature to 0° to −2° and leave at least 1 kg. of ice unmelted.
To this cold solution or suspension of β-phenylhydroxylamine, a cold solution of sulfuric acid (750 ml. of concentrated acid and sufficient ice to bring the temperature down to −5°) is added with stirring. An ice-cold solution of 170 g. of sodium dichromate dihydrate in 500–750 ml. of water is added as rapidly as it can be poured into the mixture, which is stirred or swirled (Note 8). After 2 to 3 minutes, the straw-colored precipitate of nitrosobenzene is collected on a Büchner funnel and washed with 1 l. of water (Note 9).
The crude nitrosobenzene is steam-distilled (Note 10), and the distillate is collected in a receiver cooled by ice (Note 11). The nitrosobenzene is finely ground in a mortar, transferred to a Büchner funnel, and washed with water until the washings are no longer brown. After it has been sucked as dry as possible on the filter the nitrosobenzene is pressed between layers of filter paper (or other porous paper). One or two changes of paper may be necessary. The yield of nitrosobenzene melting at 64–67° is 128–138 g. (49–53%) (Note 12) and (Note 13). If a purer product is desired, the crude nitrosobenzene can be recrystallized from a small amount of ethanol with good cooling, and the product dried over calcium chloride at atmospheric pressure.
2. Notes
1. Commercial nitrobenzene of good quality is satisfactory.
2. Contact with nitrobenzene, phenylhydroxylamine, and nitrosobenzene or prolonged breathing of the vapors should be avoided.
3. The checkers used a 12-l. round-bottomed flask.
4. Vigorous stirring is necessary in order to prevent the zinc dust from caking on the bottom of the crock. The submitters employed two mechanically driven stirrers in order to keep the zinc dust in suspension. The checkers used a single paddle stirrer successfully.
5. At higher temperatures secondary reactions take place.
6. The checkers used a 22-l. round-bottomed flask.
7. Since β-phenylhydroxylamine decomposes on standing, the filtrate should be cooled as soon as the filtration is completed, and the oxidation to nitrosobenzene should be carried out immediately. An excess of ice should be present since the oxidation reaction is exothermic and the temperature of the solution should still be near 0° after the oxidation. At higher temperatures oxidation products other than nitrosobenzene are produced.
8. It is important to add the dichromate solution rapidly in order to obtain a good yield of easily filterable product. In a run in which the dichromate solution was added over a period of 25 minutes, only a 10% yield of nitrosobenzene was obtained.
9. This product is stable for about a week if kept at 0°.
10. Connections should be of glass since cork and rubber are attacked readily. Since nitrosobenzene decomposes at the elevated temperature, it should be steam-distilled as rapidly as possible. If several runs are made, not more than four or five should be combined for distillation. A Hopkins still head is effective for preventing contamination.
The nitrosobenzene condenses to a green liquid which solidifies to a white solid. Care should be taken that the solid does not clog the condenser. Distillation is stopped when yellow oily material appears in the condenser.
11. Cooling of the receiver is necessary because the nitrosobenzene has a very high vapor pressure at room temperature.
12. Yields as high as 65–70% have been obtained in smaller runs.
13. Nitrosobenzene can be kept at room temperature in a closed container for 1–2 days. Over longer periods it should be stored at 0°.
3. Discussion
Nitrosobenzene can be prepared by the oxidation of aniline with permonosulfuric acid1 or peracetic acid2 and by the oxidation of β-phenylhydroxylamine,3 which is prepared by the reduction of nitrobenzene. Purification by sublimation has been recommended.4
This preparation is referenced from:

References and Notes
  1. Caro, Z. angew. Chem., 11, 845 (1898).
  2. D'Ans and Kneip, Ber., 48, 1144 (1915).
  3. Bamberger, Ber., 27, 1555 (1894); Parsons and Bailar, J. Am. Chem. Soc., 58, 268 (1936).
  4. Robertson and Vaughan, J. Chem. Education, 27, 605 (1950).

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

β-Phenylhydroxylamine

ethanol (64-17-5)

calcium chloride (10043-52-4)

sulfuric acid (7664-93-9)

ammonium chloride (12125-02-9)

aniline (62-53-3)

zinc (7440-66-6)

Nitrobenzene (98-95-3)

Phenylhydroxylamine (100-65-2)

zinc oxide

sodium dichromate dihydrate (10588-01-9)

peracetic acid (79-21-0)

Nitrosobenzene,
Benzene, nitroso- (586-96-9)