17.5 reactions of aldehydes and ketones: a review and a preview
DESCRIPTION
17.5 Reactions of Aldehydes and Ketones: A Review and a Preview. Reactions of Aldehydes and Ketones. Already covered in earlier chapters: reduction of C=O to CH 2 Clemmensen reduction Wolff-Kishner reduction reduction of C=O to CHOH addition of Grignard and organolithium reagents. - PowerPoint PPT PresentationTRANSCRIPT
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17.517.5
Reactions of Aldehydes and Reactions of Aldehydes and
Ketones:Ketones:
A Review and a PreviewA Review and a Preview
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Already covered in earlier chapters:Already covered in earlier chapters:
reduction of C=O to CHreduction of C=O to CH22
Clemmensen reductionClemmensen reduction
Wolff-Kishner reductionWolff-Kishner reduction
reduction of C=O to CHOHreduction of C=O to CHOH
addition of Grignard and organolithium reagentsaddition of Grignard and organolithium reagents
Reactions of Aldehydes and KetonesReactions of Aldehydes and Ketones
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17.617.6
Principles of Nucleophilic Principles of Nucleophilic
Addition to Carbonyl Groups:Addition to Carbonyl Groups:
Hydration of Aldehydes and Hydration of Aldehydes and
KetonesKetones
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HH22OO
Hydration of Aldehydes and KetonesHydration of Aldehydes and Ketones
CC••••OO ••••
HOHO CC OO HH••••
••••
••••
••••
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compared to Hcompared to H
electronic: electronic: alkyl groups stabilize alkyl groups stabilize reactantsreactants
steric: steric: alkyl groups crowdalkyl groups crowdproductproduct
OHOH
OHOH
RR R'R'++ HH22OO CCCCRR R'R'
OO
Substituent Effects on Hydration EquilibriaSubstituent Effects on Hydration Equilibria
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C=OC=O hydratehydrate KK %%
CHCH22=O=O CHCH22(OH)(OH)22 4141 99.9699.96
CHCH33CH=OCH=O CHCH33CH(OH)CH(OH)22 0.0180.018 5050
(CH(CH33))33CCH=OCCH=O (CH(CH33))33CCH(OH)CCH(OH)22 0.00410.0041 1919
(CH(CH33))22C=OC=O (CH(CH33))22C(OH)C(OH)22 0.0000250.000025 0.140.14
Equilibrium Constants for HydrationEquilibrium Constants for Hydration
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when carbonyl group is when carbonyl group is destabilizeddestabilized
•alkyl groups alkyl groups stabilizestabilize C=O C=O
•electron-withdrawing groups electron-withdrawing groups destabilizedestabilize C=O C=O
When does equilibrium favor hydrate?When does equilibrium favor hydrate?
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RR = CH = CH33: : KK = 0.000025 = 0.000025
RR = CF = CF33: : KK = 22,000 = 22,000
OHOH
OHOH
RR RR++ HH22OO CCCCRR RR
OO
Substituent Effects on Hydration EquilibriaSubstituent Effects on Hydration Equilibria
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Mechanism of Hydration (base)Mechanism of Hydration (base)
CC••••OO •••••••• OO ••••
HH
••••
––
Step 1:Step 1:Step 1:Step 1:
++••••
HOHO CC OO••••
••••
••••••••––
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Mechanism of Hydration (base)Mechanism of Hydration (base)
••••OOHH
HH
••••
Step 2:Step 2:Step 2:Step 2:
++••••
••••OO
HH
••••––
••••HOHO CC OO
••••
••••
••••••••––
••••HOHO CC OOHH
••••
••••
••••
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Mechanism of Hydration (acid)Mechanism of Hydration (acid)
CC••••OO ••••
++
Step 1:Step 1:Step 1:Step 1:
++
••••
HH
OOHH
HH++
CC••••OOHH++
•••• ••••
HH
OO
HH
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Mechanism of Hydration (acid)Mechanism of Hydration (acid)
++
Step 2:Step 2:Step 2:Step 2:
CC••••OOHH++
••••
HH
OO
HH
••••CC OOHH
••••••••
HH
OO
HH
•••• ++
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Mechanism of Hydration (acid)Mechanism of Hydration (acid)
Step 3:Step 3:Step 3:Step 3:
++••••
HH
OO
HH
••••CC OOHH
••••
HHOO
HH
••••
••••
•••• OO
HH
••••CC OOHH
••••
••••
++
HH
HHOO
HH ••••
++
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17.7Cyanohydrin Formation
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++
Cyanohydrin FormationCyanohydrin Formation
••••••••CC OO HCNHCN HHCC OONN CC••••
••••
••••
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Cyanohydrin FormationCyanohydrin Formation
••••••••CC OO
CC––
NN•••• ••••
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Cyanohydrin FormationCyanohydrin Formation
––OONN CC CC••••
•••• ••••••••
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HH
Cyanohydrin FormationCyanohydrin Formation
––OONN CC CC••••
•••• ••••••••
HH
HH
++OO ••••
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HH
Cyanohydrin FormationCyanohydrin Formation
––OONN CC CC••••
•••• ••••••••
HH
HH
++OO ••••
HH
HH
OO ••••••••OONN CC CC••••
•••••••• HH
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2,4-Dichlorobenzaldehyde2,4-Dichlorobenzaldehyde
cyanohydrin (100%)cyanohydrin (100%)
ExampleExample
ClCl
ClCl CHCH
OOClCl
ClCl CHCNCHCN
OHOHNaCN, waterNaCN, water
then Hthen H22SOSO44
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ExampleExample
CHCH33CCHCCH33
OONaCN, waterNaCN, water
then Hthen H22SOSO44
CHCH33CCHCCH33
OHOH
CNCN
(77-78%)(77-78%)
Acetone cyanohydrin is used in the synthesis Acetone cyanohydrin is used in the synthesis of methacrylonitrile (see problem 17.6).of methacrylonitrile (see problem 17.6).