Cetonas y Aldehídos Ejemplos, Diapositivas de Química

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ALDEHÍDOS Y CETONAS

Oxidation of Primary Alcohols to

Aldehydes

 (^) Pyridinium chlorochromate (PCC) is selectively used to oxidize primary alcohols to aldehydes.

Ozonolysis of Alkenes

 (^) The double bond is oxidatively cleaved by ozone followed by reduction.  (^) Ketones and aldehydes can be isolated as products.

Hydration of Alkynes

 (^) The initial product of Markovnikov hydration is an enol, which quickly tautomerizes to its keto form.  (^) Internal alkynes can be hydrated, but mixtures of ketones often result.

Hydroboration–Oxidation of

Alkynes

 (^) Hydroboration–oxidation of an alkyne gives anti-Markovnikov addition of water across the triple bond.

Alkylation of 1,3-Dithiane

 (^) Alkylation of the dithiane anion by a primary alkyl halide or a tosylate gives a thioacetal that can be hydrolyzed into the aldehyde by using an acidic solution of mercuric chloride.

Ketones from 1,3-Dithiane

 (^) The thioacetal can be isolated and deprotonated.  (^) Alkylation and hydrolysis will produce a ketone.

Ketones from Nitriles

 (^) A Grignard or organolithium reagent can attack the carbon of the nitrile.  (^) The imine is then hydrolyzed to form a ketone.

Aldehydes from Acid

Chlorides

 (^) Lithium aluminum tri( t -butoxy)hydride is a milder reducing agent that reacts faster with acid chlorides than with aldehydes.

Nucleophilic Addition

 (^) A strong nucleophile attacks the carbonyl carbon, forming an alkoxide ion that is then protonated.  (^) Aldehydes are more reactive than ketones.

Hydration of Ketones and

Aldehydes

 (^) In an aqueous solution, a ketone or an aldehyde is in equilibrium with its hydrate, a geminal diol.  (^) With ketones, the equilibrium favors the unhydrated keto form (carbonyl).

Cyanohydrin Formation

 (^) The mechanism is a base-catalyzed nucleophilic addition: Attack by cyanide ion on the carbonyl group, followed by protonation of the intermediate.  (^) HCN is highly toxic.

Formation of Imines

 (^) Ammonia or a primary amine reacts with a ketone or an aldehyde to form an imine.  (^) Imines are nitrogen analogues of ketones and aldehydes with a C═N bond in place of the carbonyl group.  (^) Optimum pH is around 4.