Chapter 20: Aldehydes and Ketones

Question 1

H2O with carbonyl

Answer 1

Hydrate Formation

• adds OH to carbonyl and then protenates the O-: results in two OH’s
• Favours reagents
• except for in simple aldehydes like formeldyhyde

Question 2

2ROH, [H+]

With carbonyl

Answer 2

Acetyl formation
on-two moles of alcohol replace the carboxylic acid with acid catalyst
-Acid catalyst is TsOH or H2SO4
-split into two parts:

Question 3

[H+], NH2-R

with carbonyl

Answer 3

Formation of Imine (primary amine)

• produces C=N double bond
• 6 steps in total:
  a) Formation of a cabinolamine
• acid source is protenated amine
• same steps as acetyl
  b) Formation of imine
• pH should be around 4.5

Question 4

[H+] HO-NH2 with Carbonyl

Answer 4

Oxime Formation

Forms primary amine with -OH group in place of carbonyl

Question 5

[H+], NH2-NH2 with carbonyl

Answer 5

Hydrazone Formation

-forms double bond c=N with -NH2 group as R group on primary amine

Question 6

[H+], NH-R2 with carbonyl

Answer 6

tion (secondary amine)Secondary Amines
-acidic conditions of aldehyde and ketones
-forms enamine
-has adjacent C=C bond that delocalizes the N lone pair
A) Formation of carbinolamine
-same as above
B) formation of enamine
-because the N does not have a 2nd proton, the N+ is not stable
-instead the adjacent carbon is deprotenated and the N can take back its electrons from the double bond
-forms a stable , neutral species

Question 7

KOH/H2O, Heat with hydrazone

Answer 7

Wolff Kishner

• can convert hydrazones into alkanes
• two step reduction of carbonyls
• this occurs because it releases N2 gas, which pushes equilibrium foreward
• this is why carbanion can form

Question 8

2RSH, [H+] with Carbonyl

Answer 8

Thioacetyls
-forms a thioacetyl
Exactly the same as ecetyl! With S replacing Oxygen

Question 9

Raney Ni with thioacetyl

Answer 9

Raney Nickel Reduction

• can reduce thioacetyls to yield disulfides and alkanes
• don’t need to know the mechanis

Question 10

R-phosphorane with carbonyl

Answer 10

Wittig Reaction
-uses a phosphorane compound to put a negative charge on the carbon
-there is a charge free resonance structure, but because P and C have different p orbitals, it doesn’t make sense
-the carbanion attacks the carbonyl carbon
-the anion oxygen attack the +P, forms a cyclic intermediate (betaine)
-the oxygen leaves the R group, forms a double bonded C and oxyphosphetane
alkyl group is then deprotenated with strong base
-SN2 reaction so can work for primary/secondary alkyl halides

Question 11

alkyl halide and triphenylphosphine

Answer 11

Forming witting reagent

Question 12

HCN, KCN with Carbonyl

Answer 12

Cyanohydrin formation
The addition of HCN with catalytic amount of base forms cyanohydrine (Cyanide and hydroxyl on same carbon) amount of HCl for protons!
–KCN is safer, but must add small

Question 13

1) LAH

2) H2O with cyanohydrin

Answer 13

Reduction of Cyanohydrins
LAH/ NaBH4
-delivery hydride
-forms c-NH2 and leaves -OH

Question 14

H3O+, Heat with cyanohydrin

Answer 14

Hydrolysis of Cyanohydrins

-forms carboxylic acid from cyanohydrin

Question 15

RCO3H with Carbonyl

Answer 15

Baeyer-Villiger Oxidation of Aldehyde s and Ketones

• treat ketones/aldehydes with peroxy acids to form esters
• peroxy acid is the nuc
• intermolecular proton transfer to the carbonyl in the peroxy from the outer O
• then the carbonyl is reformed and R group moves to peroxy O

Regioselective on which side the peroxy comes onto: migration pattern: H>3>2, Ph>1>methyl