Nitrosylsulfuric Acid


[7782-78-7]  · HNO5S  · Nitrosylsulfuric Acid  · (MW 127.09)

(nitrosating and diazotizing agent; moderate oxidizing agent)

Physical Data: mp 70 °C.

Solubility: sol sulfuric acid; slightly sol acetic acid, acetonitrile, nitromethane, DMF insol most other organic solvents.

Form Supplied in: pale yellow crystals; commercially available.

Preparative Method: dry SO2 is allowed to pass into a mixture of 98% nitric acid and acetic acid (3:1) at 0 °C; the precipitated NOHSO4 is washed with acetic acid and carbon tetrachloride and dried under vacuum to give the analytically pure reagent.1

Handling, Storage, and Precautions: stable at rt; protect from moisture; use in a fume hood.


Like other nitrosonium salts, namely Nitrosonium Tetrafluoroborate and NOPF6, nitrosylsulfuric acid is an efficient nitrosating agent. It has been reported that NOHSO4 is superior to Nitrosyl Chloride for the nitrosation of N-acylarylamines such as 4-methoxy-3-nitroacetoanilide and 5-acetamido-6-methoxyquinoline (eq 1).2 NOHSO4 has also been shown to be more efficient than other classical nitrosating agents such as Isopentyl Nitrite, phenyl nitrite, and Sodium Nitrite. For example, successful nitrosation of 3-methyl-5-acetamidoisothiazole was achieved by utilizing nitrosylsulfuric acid in DMF, whereas previous attempts using isopentyl nitrite or sodium nitrite in acetic acid had failed (eq 2).3 Nitrosation of thebaine in methanol under different conditions using nitrosyl chloride, phenyl nitrite, and NOHSO4 all gave the oxime together with varying amounts of other bimolecular products.4

The conversion of cyclohexanecarboxylic acid or cyclohexyl aryl ketone to ε-caprolactam by treatment with NOHSO4 in the presence of SO3 (eq 3) may involve the nitrosation of an enol and Beckmann rearrangement.5 Nitrosation of pentamethyleneketene under similar conditions also gives ε-caprolactam.6 Lactams with 11 and 12 carbon atoms in their rings were obtained in good yields by treating cycloundecanoic acid and cyclododecanoic acid with NOHSO4 in chloroform.7

Diazotization and Related Reactions.

Ar-NH2 to Ar-N2+.

Aromatic amines are readily diazotized by NOHSO4 to give the corresponding diazonium hydrogen sulfates. Although solutions of sodium nitrite in concentrated H2SO4, instead of pure NOHSO4, have been used for diazotization, the yields of solid diazonium salts were in some cases relatively poor. For the purpose of preparation of pure diazonium hydrogen sulfates free from other mineral acids and salts, solutions or suspensions of the amines in acetic acid were added to a solution of solid NOHSO4 in acetic acid, then ether was added to precipitate the diazonium salts.8 Nitrosylsulfuric acid is also suitable for the diazotization of weakly basic amines such as nitroanilines (eq 4) and polynitroanilines,8,9 tetrafluoroanthranilic acid,10 aminonaphthoquinones,11 1,4-diaminoanthraquinones (eq 5)12 and 2-cyano-4-nitroaniline.13 In some cases the diazonium salts formed undergo intramolecular coupling with aryl rings to give azo compounds (eq 6).14,15

Ar-NHNH2 to Ar-N3.

Aryl and acyl hydrazines are converted to azides in good yields on treatment with an equimolar amount of NOHSO4 or NOBF4 (eq 7).16

Addition to Alkenes and Dienes.

NOHSO4 adds to trisubstituted alkenes to give b-sulfatooximes (eq 8), which are relatively unstable and react readily with nucleophiles such as Piperidine, MeOH, or AcOK to give the corresponding a-substituted oximes.17 Conjugated dienes react with NOHSO4 at low temperature in liquid SO2, giving 1,4-addition products which spontaneously cyclize to 6H-1,2-oxazine hydrogen sulfates (eq 9).18

Other Applications.

Amides and sulfonamides are converted to the corresponding acids by NOHSO4 and other nitrosonium salts at low temperature in acetonitrile or nitromethane (eq 10).19 Sterically hindered amides also react with ease and good yields, although higher reaction temperatures are needed. A mild cleavage of ethylene dithioacetals to ketones has been achieved with NOHSO4 in methylene chloride or NaNO2 in aq CF3CO2H (eq 11).20

The treatment of 2-amino-4H-pyrans with nitrosylsulfuric acid brings about their transformation into 2-pyridones (eq 12).21

All nitrosonium ions are in principle hydride-abstracting agents, and nitrosylsulfuric acid has occasionally been used as a dehydrogenating agent (eq 13).22

1. Richards, G. W.; Woolf, A. A. JCS 1968, 470.
2. Ahmad, Y.; Qureshi, M. I.; Baig, M. I. CJC 1967, 45, 1539.
3. Taylor, E. C.; Wachsen, E. JOC 1978, 43, 4154.
4. Bentley, K. W.; Kirby, G. W.; Price, A. P.; Singh, S. JCS(P1) 1972, 302.
5. (a) Ogata, Y.; Furuya, Y.; Ito, M. JACS 1963, 85, 3649. (b) Tokura, N.; Kawahara, T.; Sato, T. BCJ 1965, 38, 849.
6. (a) Giuffre, L.; Tempesti, E,; Sioli, G.; Fornaroli, M.; Airoldi, G. CI(L) 1971, 1098. (b) Giuffre, L.; Tempesti, E.; Fornaroli, M.; Sioli, G.; Mattone, R.; Airoldi, G. Hydrocarbon Process 1973, 52, 199.
7. Ziegenbein, W.; Lang, W. AG(E) 1963, 2, 149.
8. Piercey, M. R.; Ward, E. R. JCS 1962, 3841.
9. Röbisch, G.; Süptitz, H. JPR 1978, 320, 1047.
10. Hayashi, S.; Ishikawa, N. BCJ 1972, 45, 2909.
11. Mosby, W. L.; Silva, M. L. JCS 1964, 3990.
12. Law, K.-Y.; Tarnawskyj, I. W.; Kaplan, S. CJC 1991, 69, 1183.
13. Ramdas, S. R.; Ramana, D. V.; Chaudhuri, A. P. IJC(B) 1973, 11, 400.
14. Kolodyazhnaya, S. N.; Simonov, A. M.; Uryukina, I. G. KGS 1972, 1690.
15. Kolodyazhnaya, S. N.; Simonov, A. M.; Zheltikova, N. N.; Pozharskii, A. F. KGS 1973, 714.
16. Pozsgay, V.; Jennings, H. J. TL 1987, 28, 5091.
17. Kisan, W.; Pritzkow, W. JPR 1978, 320, 59.
18. Klamann, D.; Fligge, M.; Weyerstahl, P.; Kratzer, J. CB. 1966, 99, 556.
19. Olah, G. A.; Olah, J. A. JOC 1965, 30, 2386.
20. Olah, G. A.; Narang, S. C.; Salem, G. F.; Gupta, B. G. B. S 1979, 273.
21. Seoane, C.; Soto, J. L.; Zamorano, P.; Quinteiro, M. JHC 1981, 18, 309.
22. Gorelik, M. V.; Lomzakova, V. I. ZOR 1978, 14, 1051.

George A. Olah, G. K. Surya Prakash, Qi Wang & Xing-Ya Li

University of Southern California, Los Angeles, CA, USA

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