醛酮反应的总结
Key Reactions of Aldehyde & Ketone
[1] Reaction with Grignard Reagents
Treatment of formaldehyde with a Grignard reagent followed by hydrolysis gives a primary alcohol. Similar treatment of any other aldehyde gives a secondary alcohol. Treatment of a ketone gives a tertiary alcohol.
O
H 3C CH 33
OH H 3C CH 3
Ph
[2] Reaction with Organolithium Reagents
Reactions of aldehydes ane ketones with organolithium reagents are similar to those with Grignars reagents.
H 3C C(CH3) 33OH
H 3C C(CH3) 3
[3] Reactions with Anions of Terminal Alkynes
Treatment of an aldehyde or ketone with the alkali metal salt of a terminal alkyne followed by hydrolysis gives
an a-alkynyalchol.
O
CH
[4] Reaction with HCN to form Cyanohydrins
For aldehydes and most sterically unhindered aliphatic ketones, equilibrium favors formation of the cyanohydrin. For aryl ketones, equilibrium favors starting materials, and little cyanohydrin is obtained.
PhCHO + NaCN
Ph CN
H
[5] The Wittig Reaction
Treatment of an aldehyde or ketone with a triphenylphosphonium ylide gives an oxaphosphetane
intermediate, which fragments to give triphenylphosphine oxide and an alkene.
O +
Ph 3CH 2
CH 2+ Ph3PO
[6] Hydration
The degree of hydration is greater for aldehydes than for ketones.
O
+ H2O
H C H
H H OH
(> 99%)
[7] Addition of Alcohols to Form Hemiacetals
Hemiacetals are only minor components of an equilibrium mixture of aldehyde or ketone and alcohol, except where the –OH and the C=O are parts of the same molecule and a five- or six-membered ring can form.
O
CH 3CHCH 2CH 2CH
OH
H 3C
OH
[8] Addition of alcohols to Form Acetals
Formation of acetals is catalyzed by acid. Acetals are stable to water and aqueous base but are hydrolyzed in aqueous acid. Acetals are valuable as carbonyl-protecting groups.
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O + HOCH2CH 2OH
+
+ H2O
[9] Addition of Sulfur Nucleophiles: Formation of 1,3-Dithianes
The most commonly used thiol for preparation of thioacetals is 1,3-propanedithiol. The product is called a 1,3-dithiane.
O
H 3C
H + HSCH2CH 2CH 2SH
3H
+ H2O
[10] A lkylation of Anions Derived from Aldehyde 1,3-Dithianes
Treatment of an aldehyde 1,3-dithiane (pKa 31) with butyllithium gives an anion. This anion can enter into substitution reactions with primary alkyl, allylic, and benzylic halides and addition reactions with the carbonyl group pf aldehydes and ketones.
33Li +22
H 3C CH 2Ph
[11] A ddition of Ammonia and Its Derivatives: Formation of Imines
Addition of ammonia or a primary amine to the carbonyl group of an aldehyde or ketone forms a tetrahedral carbonyl addition compound. Loss of water from this intermediate gives an imine.
O + H2NCH 3
NCH 3+ H2O
[12] A ddition of Secondary Amines: Formation of Enamines
Addition of Secondary amine to the carbonyl group of an aldehyde or ketone forms a tetrahedral carbonyl addition intermediate. Acid-catalyzed dehydration of this intermediate gives an enamine.
O ++
+ H2O
[13] A ddition of Hydrazine and Its Derivatives
Treatment of an aldehyde or ketone with hydrazine gives a hydrazone. Derivatives of hydrazine react similarly.
O + H2NNH 2
NNH 2+ H2O
[14] K eto-Enol Tautomerism
The keto form predominates at equilibrium, except for those aldehydes and ketones in which the enol is stabilized by resonance or hydrogen bonding.
O
H 3C CH CH 3CH 2
[15] D euterium Exchange at the a-Carbon
Acid- or base-catalyzed deuterium exchange at an a-carbon involves formation of an enol or enolate anion intermediate.
H 3C CH 3+ 6 D2O
O
D 3C CD 3+ 6 HOD
[16] H alogenation at the a-carbon
The rate-limiting step in acid-catalyzed a-halogenation is formation of an enol. In base-promoted a-halogenation, it is formation of an enolate anion.
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Br
O
3+ Br2
Br
O
2Br + HBr
[17] T he haloform Reaction
The haloform reaction oxidizes a methyl ketone to a carboxylic acid.
CH 3CH 3O + CHCl3
CH 33CH CHCH CHCOH 32. H3O
[18] O xidation of an Aldehyde to a Carboxylic Acid
The aldehyde group is among the most easily oxidized functional groups. Oxidizing agents include KMnO4,
K 2Cr 2O 7, Tollens’ reagent, H2O 2, and O2.
CHO OH
2. H3O CO 2H OH
+ Ag
[19] O xidation of a Ketone to an Ester: The Baeyer-Villiger Rearrangement
Oxidation of a ketone by a peroxyacid involves nucleaophilic addition to the carbonyl group of the ketone to form a tetrahedral carbonyl addition intermediate followed by molecular rearrangement to give an ester.
O
CH 3+ CF3CO 3H
O
CH 3+ CF3CO 2H
[20] C atalytic Reduction
Catalytic reduction of the carbonyl group of an aldehyde or ketone to an alcohol group is simple to carry out and yields of alcohol are high. A disadvantage of this method is that some other functional groups, including carbon-carbon double and triple bonds, may also be reduced.
O
OH
[21] M etal Hydride Reduction
O
2
Both LiAlH4 and NaBH4 are selective in that neither reduces isolated carbon-carbon double or triple bonds.
OH
[22] C lemmensen Reduction of an aldehyde or ketone
Reduction of the carbonyl group of an aldehyde or ketone using amalgamated zinc in the presence of concentrated hydrochloric acid gives a methylene group.
OH O
C (CH2) 5CH 3OH H
2
C (CH2) 5CH 3
[23] W olff-Kishner Reduction of an Aldehyde or Ketone
Formation of a hydrazone followed by treatment with base, commonly KOH in diethylene glycol or potassium tert -butoxide in dimethyl sulfoxide, reduces the carbonyl group of an aldehyde or ketone to a methylene group.
CH 3
CH 2CH 3+ N2 + H2O
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[24] T he Cannizzaro Reaction
This reaction takes place by nucelophilic addition of OH- to an aldehyde to give a tetrahedral intermediate, which expels hydride ion as a leaving group.
2PhCHO
2Na + PhCH2OH
PhCHO +CH 2PhCH 2OH +HCO 2H
[25] R eactions of a,b-Unsaturated Carbonyl Compounds
a,b-Unsaturated aldehydes and ketones often react with nucleophiles to give the product of conjugate
addition. Particularly useful is the reaction of organocopper reagent.
Nu OH
43
21
O
43
2
1
H R CH 2COCH 3CH 3CH CH 3
33O
321
21
43
H
[26] A ldol Reaction
Aldehydes and ketones with an a-hydrogen dimerize.
2 CH3CHO
CH 3CH=CHCHO
-Ph C CHCHO + CHCHO 3PhCHO
H
[27] M eerwein-Ponndorf –Verley reaction
This reaction involes reduction of a carbonyl by treatment with an excess of aluminum triisopropoide. Its
reverse reaction is called Oppenauer Oxidation.
R R'(H)
Meerwein-Ponndorf Reduction
[(CH) CHO]Al
O + (CH3) 2CHOH
R R'(H)
Oppenauer OxidationOH + CH3COCH 3
[28] B eckman Rearrangement
This reaction is a reaction of an oxime to produce an amide, proceeding via an 1,2-sigmatropic rearrangement to an electron-deficient nitrogen.
R R
O + NH2OH
N Oxime
OH
+5
O
R NHR Amide
[29] R eduction by Metals
This reactions include single molecular reduction and two molecular reduction.
R R'(H)
O
R R'(H)
R
OH
R'
O
+
R' R' R R OH OH
[30] T he Benzoin Condensation
When certain aromatic aldehydes are treated with cyanide ion, benzoins are produced.
O 2N
Acceptor
CHO +CH 3O
Donor
CHO
-CH 3O
O OH H
NO 2
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