Page 1167 - Advanced Organic Chemistry Part B - Reactions & Synthesis

12.5.3. Oxidation with Other Reagents 1143
Selenium dioxide can be used to oxidize ketones and aldehydes to -dicarbonyl SECTION 12.5
compounds. The reaction often gives high yields of products when there is a single Oxidation of Ketones
type of CH group adjacent to the carbonyl group. In unsymmetrical ketones, oxidation and Aldehydes
2
usually occurs at the CH that is most readily enolized. 255
2
O O
SeO 2
O 60% Ref. 256
O O
CCH 3 SeO CCH O
2
Ref. 257
69–72%
The oxidation is regarded as taking place by an electrophilic attack of selenium dioxide
(or selenous acid, H SeO , the hydrate) on the enol of the ketone or aldehyde. This is
2 3
followed by hydrolytic elimination of the selenium. 258
OH O O O OH O
SeO 2 –H O H O –H SeO
2
2
2
RC CHR′ RC CHR′ RC CR′ RC CR′ RC CR′
SeOH Se SeH O
O O O
Methyl ketones are degraded to the next lower carboxylic acid by reaction with
hypochlorite or hypobromite ions. The initial step in these reactions involves base-
catalyzed halogenation. The -haloketones are more reactive than their precursors,
and rapid halogenation to the trihalo compound results. Trihalomethyl ketones are
susceptible to alkaline cleavage because of the inductive stabilization provided by the
halogen atoms.
O O – O O – O
slow – OBr – OH fast
RCCH 3 RC CH 2 RCCH Br RC CHBr RCCBr 3
2
O O –
RCCBr 3 RC CBr 3 RCO H + – CBr 3 RCO 2 – + HCBr 3
2
–
OH OH
O
NaOH
(CH ) CCCH 3 (CH ) CCO H
2
3 3
3 3
Br 2 71–74% Ref. 259
O
KOCl H +
(CH ) C CHCCH 3 (CH ) C CHCO H
2
3 2
3 2
49–53% Ref. 260
255 E. N. Trachtenberg, in Oxidation, Vol. l, R. L. Augustine, ed., Marcel Dekker, New York, 1969, Chap. 3.
256
C. C. Hach, C. V. Banks, and H. Diehl, Org. Synth., IV, 229 (1963).
257
H. A. Riley and A. R. Gray, Org. Synth., II, 509 (1943).
258 K. B. Sharpless and K. M. Gordon, J. Am. Chem. Soc., 98, 300 (1976).
259 L. T. Sandborn and E. W. Bousquet, Org. Synth., 1, 512 (1932).
260
L. I. Smith, W. W. Prichard, and L. J. Spillane, Org. Synth., III, 302 (1955).