· (MW 431.79)
(mild oxidizing agent for oxidizing benzyl alcohols and secondary alcohols to benzaldehydes and ketones;1 selectively oxidizes sulfides to sulfoxides;2 oxidizes monothioacetals to aldehydes3)
Alternate Name: DABCO.2Br2; 1,4-diazabicyclo[2.2.2]octane, compound with Br2.
Physical Data: mp 155-160 °C (dec).
Solubility: insol most organic solvents and water.
Form Supplied in: yellow amorphous solid (not commercially available).
Preparative Method: prepared by adding excess Bromine to solutions of 1,4-Diazabicyclo[2.2.2]octane in benzene, carbon tetrachloride, or water1-4 (95% yield obtained on 50 mmol scale).4
Handling, Storage, and Precautions: thermally stable in neutral or basic media; decomposes in acidic media. Nonhygroscopic and stable to air, water, and light. This reagent should be handled in a fume hood.
DABCO.2Br2 is one of several complexes of halogens with amines, such as Chlorine-Pyridine5 and bromine/quinoline,2 that are used as oxidants for organic molecules. This reagent is more convenient to use because it is readily prepared and is very stable to air, water, light, and basic media.1-4 Acidic media decompose it. This stable complex allows for the more accurate measuring of active bromine, especially for small scale reactions. X-ray studies of DABCO.2Br2 show that it exists as a novel complex of multiple DABCO and bromine units.6 Hudlický has reviewed this reagent and alternative oxidation reagents.7
Selective Oxidation of Alcohols.
DABCO.2Br2 oxidizes benzyl alcohol and secondary aliphatic alcohols (eq 1) to benzaldehyde (97%) and ketones (36-71%) in acetonitrile or refluxing methylene chloride.1 Primary alcohols are oxidized less readily (ca. 10%). Optimum yields are obtained after 3-6 h. Superior yields (62-100%), better selectivity, and shorter reaction times (2-60 min) are observed when bromine/HMPA is used as an oxidant.8
Oxidation of Sulfides to Sulfoxides.
DABCO.2Br2 oxidizes sulfides to sulfoxides in 70% aqueous acetic acid without over-oxidation to sulfones.2 Yields for substrates ranging from dibutyl sulfide to thianthrene (eq 2) varied between 70 and 95%. The reaction is fast enough to be used as a method to prepare 18O-enriched sulfoxides from sulfides.2 Sulfides can also be oxidized to sulfoxides with Dipyridine Chromium(VI) Oxide, Manganese Dioxide,9 and Sodium Periodate.10
DABCO.2Br2 oxidizes monothioacetals to aldehydes (eq 3) in 40-83% yield.3 No aldehydes were obtained when 3-chloroperoxybenzoic acid, sodium periodate, and selenium dioxide-hydrogen peroxide were used as oxidants.
- 1. Blair, L. K.; Baldwin, J.; Smith, W. C., Jr. JOC 1977, 42, 1816.
- 2. Oae, S.; Ohnishi, Y.; Kozuka, S.; Tagaki, W. BCJ 1966, 39, 364.
- 3. Otera, J.; Niibo, Y.; Nozaki, H. JOC 1989, 54, 5003.
- 4. Herrick, E. C. U. S. Patent 2 964 526, 1960 (CA 1961, 55, 11 446b).
- 5. Wicha, J.; Zarecki, A. TL 1974, 3059.
- 6. Allwood, B. L.; Moysak, P. I.; Rzepa, H. S.; Williams, D. J. CC 1985, 1127.
- 7. Hudlický, M. Oxidations in Organic Chemistry, ACS Monograph 186; ACS: Washington, 1990; Chapters 1 and 3.
- 8. Neirabeyeh, M. A.; Ziegler, J.-C.; Gross, B.; Caubère, P. S 1976, 811.
- 9. Edwards, D.; Stenlake, J. B. JCS 1954, 3272.
- 10. Leonard, N. J.; Johnson, C. R. JOC 1962, 27, 282.
M. P. Moon
DuPont Agricultural Products, Newark, DE, USA
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