Diketone
Encyclopedia : D : DI : DIK : Diketone
A diketone is a molecule containing two carbonyl groups.
A diketone is an oxygen nucleophile.
Reactions
Diketones react similarly to ketones or aldehydes.
They also readily undergo enolization, and many 1,3-diketones are thermodynamically stable as conjugated enols or even enolates. One such is ascorbic acid, which is more stable as an enol(ate) rather than a diketone. The enol group gives off a proton, and the charge of the resulting enolate is delocalized along the ketone-enolate system. This delocalization stabilizes the enolate counterion and makes it less likely to regain the proton, which makes ascorbic acid acidic. Also, if a diketone has ketone carbonyls separated only by one carbon, the alcohol hydrogen in the corresponding enol is hydrogen-bonded to the carbonyl oxygen, giving a six-membered ring (-RC=CH-OH..O=CR-).
diketone + nucleophile → tetrahedral carbonyl addition compound
- diketone + alcohol + acid or base ↔ hemiacetal
- *hemiacetal + alcohol + acid catalyst ↔ acetal + water
- *This is a carbonyl-protecting reaction.
Health
EU Commission has declared (see external link), that diketones (for example Pentan-2,4-dion) are like dialcohols and hydroxyketones in that they are in vitro and in vivo genotoxic chemical substances and therefore have been forbidden as nutrition additives since 2005.
External links
- http://europa.eu.int/eur-lex/lex/LexUriServ/site/en/oj/2005/l_128/l_12820050521en00730076.pdf - EU Commission and Diketones
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