A Publication
of Reliable Methods
for the Preparation
of Organic Compounds
Annual Volume
Org. Synth. 1970, 50, 27
DOI: 10.15227/orgsyn.050.0027
[Propane, 2-diazo-]
Submitted by S. D. Andrews1, A. C. Day1, P. Raymond1, and M. C. Whiting2.
Checked by G. Swift and W. D. Emmons.
1. Procedure
Caution! 2-Diazopropane is volatile and presumably toxic. All operations should be carried out in an efficient hood behind a protective screen.
A 250-ml., two-necked, round-bottomed flask, placed in a room temperature (ca. 20°) water bath, is equipped with a magnetic stirrer, a dropping funnel, and a distillation head carrying a thermometer, and connected via an acetone–dry-ice condenser to a receiver cooled to −78° in acetone and dry ice. In the distilling flask are placed 60 g. (0.27 mole) of yellow mercury(II) oxide (Note 1), 100 ml. of diethyl ether (Note 2), and 4.5 ml. of a 3 M solution of potassium hydroxide in ethanol (Note 3). The pressure throughout the system is reduced to 250 mm., and with vigorous stirring 15 g. (0.21 mole) of acetone hydrazone (Note 4) is added dropwise through the funnel (Note 5). With continued stirring, the pressure is reduced to 15 mm., and ether and 2-diazopropane co-distill and condense in the receiver (Note 6), yielding 70–90% (Note 7), (Note 8), and (Note 9) of product.
2. Notes
1. Laboratory Reagent yellow mercury(II) oxide purchased from British Drug House was used for most runs. The preparation was not apparently improved by the use of freshly precipitated mercury(II) oxide.
2. The quantity of ether can be varied over a wide range (the submitters have successfully used as little as 60 ml.), and is adjusted to yield the desired concentration of 2-diazopropane in the distillate.
3. A stock solution of potassium hydroxide in ethanol was prepared and stored under nitrogen. Old stocks are brown and contain a dark sediment, but are apparently just as effective as the freshly prepared reagent. Methanolic potassium hydroxide has also been used by the submitters; this remains clear and colorless for long periods but offers no other advantage over the ethanolic solution. In absence of the basic solution, the acetone hydrazone is not oxidized by mercury(II) oxide.
4. Org. Synth., Coll. Vol. 6, 161 (1988). Yields are lower if the hydrazone is not freshly redistilled.
5. No special precautions are necessary to keep the reaction mixture cool, since boiling of the ether provides adequate cooling.
6. It is usually unnecessary to dry the distillate, because the water produced in the reaction is largely retained in the distilling flask. That which vaporizes is trapped as ice in the condenser.
7. The solution is ca. 2 M. Yields were determined by nitrogen evolution on adding acetic acid, or spectrometrically from the visible absorption band at 500 nm, which has ε ~ 2 as calculated from the nitrogen evolution. Yields estimated by addition of a standard solution of benzoic acid and titration with alkali were consistently much lower. Both methods underestimate the yield, since decomposition with acid gives tetramethylethylene and some acetone azine in addition to the 2-propyl ester.3 The nitrogen evolution method (and therefore the spectrometric method) probably underestimates the yield by ca. 10–20%. the titration method by more than 50%.
8. The entire preparation is very rapid (ca. 30 minutes) and is easily adaptable to the preparation of larger amounts of 2-diazopropane. Without difficulty, 2–3 M solutions can be obtained (see (Note 2)). The solutions are essentially mercury-free.
9. 2-Diazopropane is an unstable material. The decay is first-order with a half-life of 3 hours at 0°.
3. Discussion
This method4 is an adaptation of that given by Staudinger and Gaule.5 Highly unstable solutions have been obtained by Applequist and Babad5 by use of silver oxide in place of mercury(II) oxide.
Contrary to previous reports,5,6,7 2-diazopropane, as indicated by the present procedure, is neither difficult to prepare nor unduly unstable. The method may be extended to other secondary aliphatic diazo compounds, which have given difficulty in the past.8 The success of the method depends on the use of a basic catalyst for the oxidation. The desirability of a basic catalyst has been recognized previously9,10 and is well illustrated by the contrast between the two preparations of diphenyldiazomethane10,11 (contrast also refs. 9 and 12). Miller has speculated on the role of the basic catalyst.10
2-Diazopropane is a potential source of gem-dimethyl groups. It undergoes 1,3-dipolar addition to acetylenes,13,14 allenes,15,16 and olefins,17 and in all three classes the orientation of addition has been found to be sensitive to steric effects.14,16,17 The adducts with acetylenes14,18 and allenes15,19 give cyclopropenes, and methylenecyclopropanes, respectively, upon photolysis. The adducts with certain acetylenes bearing an α-leaving group, however, are converted photochemically into allenes and conjugated dienes by an ionic mechanism.13

References and Notes
  1. Dyson Perrins Laboratory, University of Oxford, Oxford, England.
  2. Department of Chemistry, University of Bristol, Bristol, England.
  3. D. E. Applequist and H. Babad, J. Org. Chem., 27, 288 (1962).
  4. A. C. Day, P. Raymond, R. M. Southam, and M. C. Whiting, J. Chem. Soc., C, 467 (1966).
  5. H. Staudinger and A. Gaule, Ber. Dtsch. Chem. Ges., 49, 1897 (1916).
  6. G. M. Kaufman, J. A. Smith, G. G. Vander Stouw, and H. Shechter, J. Am. Chem. Soc., 87, 935 (1965).
  7. J. R. Dyer, R. B. Randall, and H. M. Deutsch, J. Org. Chem., 29, 3423 (1964); D. W. Adamson and J. Kenner, J. Chem. Soc., 286 (1935).
  8. K. Heyns and A. Heins, Justus Liebigs Ann. Chem., 604, 133 (1957), and ref. 6.
  9. C. D. Nenitzescu and E. Solomonica, Org. Synth., Coll. Vol. 2, 496 (1943); P. D. Bartlett and L. B. Gortler, J. Am. Chem. Soc., 85, 1864 (1963).
  10. J. B. Miller, J. Org. Chem., 24, 560 (1959).
  11. L. I. Smith and K. L. Howard, Org. Synth., Coll. Vol. 3, 351 (1955).
  12. L. I. Smith and H. H. Hoehn, Org. Synth., Coll. Vol. 3, 356 (1955).
  13. A. C. Day and M. C. Whiting, J. Chem. Soc. B, 991 (1967); Chem. Commun., 292 (1965).
  14. A. C. Day and R. N. Inwood, J. Chem. Soc. C, 1065 (1969).
  15. A. C. Day and M. C. Whiting, J. Chem. Soc. C, 464 (1966); Proc. Chem. Soc. London, 368 (1964).
  16. S. D. Andrews, A. C. Day, and R. N. Inwood, J. Chem. Soc. C, 2433 (1969); S. D. Andrews and A. C. Day, Chem. Commun., 902 (1967).
  17. S. D. Andrews, A. C. Day, and A. N. McDonald, J. Chem. Soc. C, 787 (1969).
  18. A. C. Day and M. C. Whiting, J. Chem. Soc. C., 1719 (1966).
  19. S. D. Andrews and A. C. Day, J. Chem. Soc. B, 1271 (1968); Chem. Commun., 667 (1966).

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

ethanol (64-17-5)

acetic acid (64-19-7)

diethyl ether (60-29-7)

silver oxide (20667-12-3)

nitrogen (7727-37-9)

Benzoic acid (65-85-0)

mercury(II) oxide (21908-53-2)

acetone (67-64-1)

potassium hydroxide (1310-58-3)

tetramethylethylene (563-79-1)

Diphenyldiazomethane (883-40-9)

Acetone hydrazone (5281-20-9)

Acetone azine (627-70-3)

Propane, 2-diazo- (2684-60-8)