CH7: Aldehydes + Ketones Flashcards
Aldehyde, Ketone, Alcohol B.P. + Solubility
Aldehydes and Ketones can’t H bond to each other so their B.P. is much lower than the corresponding alcohol
They can, however, H bond with water making them soluble
Aldehydes from primary alcohols
Oxidize with PCC to stop early
How can aldehydes be made from esters, acyl chlorides, C.A. and nitriles?
C.A. can’t do-Convert to acyl chloride with SOCl2
Acyl chloride- 1) LiAH(O-t-Bu)3, Et2O, -78 2) H2O
Ester-DIBAL-H
LiAH(O-t-Bu)3
Used with Et2O, -78 2) H2O to form aldehydes from acyl chlorides…prior to this, we can convert a C.A. to an acyl chloride
DIABL-H
Converts ester to aldehyde
How can ketones be made?
1) Ozonolysis of alkenes
2) Oxidation of secondary alcohols
3) Friedel-Crafts acylation
4) From alkynes through Markovnikov hydration
5) Nitriles + Organolithium/metallic
Ozonolysis of alkenes
1) O3
2) Zn, HOAc
Both are used to split an alkene and form a ketone
Aromatic ketones
Made by Friedel-Crafts acylation
Oxidation of secondary alcohols
With Jones reagent, we form ketones
Vinyl vs allyl
Vinyl is on the carbon of the D.B.
Allyl is one over
Vinylic alcohol
Called an enol, they are relatively unstable, will change to a ketone
Alkyne hydration
When an alkyne reacts with H2O and acid (H2SO4/HgSO4) a vinylic alcohol (enol) forms. This then converts to a ketone
Enol
Vinylic alcohol that interconverts between this form and keto form
Keto-Enol tautomerization
The changing from an enol (vinylic alcohol) to a keto form
Once the vinylic alcohol forms strong acid converts it in an equilibrium
What is needed for keto-enol tautomerization
Strong acid, which has often already been used during alkyne hydration. The D.B. grabs the H
Ketones from nitriles + organometallic/lithium
1) React organometallic with Nitrile (C t.b. N)
2) H3O+ hydrolysis
Hydrolysis of H=N
Turns to H=O every time
Weak vs strong nucleophiles and carbonyl compounds
Weak need a catalys ex Lewis acid H-A to protonate the carbon
Strong ex. R: or H: can attack right away and shift the D.B. up
Aldehyde vs ketone reactivity
Aldehydes are more reactive
1) Less electron pushing “R” groups
2) Less steric-hinderance
Hemiacetal
A ketone or aldehyde in alcohol will form an eq mix with the corresponding hemiacetal. This has -OR and -OH on the same carbon
Ketone and aldehyde in alcohol forms
Hemiacetal
Noncyclic vs cyclic hemiacetals
Non-cyclic aren’t stable 5/6 membered rings are
Hemiacetal formation can be catalyzed by:
Acid or base (alcohol) RO(-) or ROH
Acid is 3 steps
Base is 2 steps
Aldehyde or Ketone + Water
Forms a hydrate (gem diol)…proton transfer occurs
Acetal
Two -OR groups on the same carbon
Acetal formation
An aldehyde or ketone can be reacted with ACID ONLY and excess alcohol to form it. Formation goes through the hemiacetal
How to go away from an acetal
Dilute acid catalyst
What is the key step in hemiacetal –> acetal formation
OR shifts db down to expell H2O+
Acetal formation from ketones vs aldehydes
Aldehydes formation is favored, however ketones can cyclicly form rings with acid catalyst. These cyclic acetals (formed by OH-CH2-CH2-OH are good protecting groups for ketones and aldehydes. Cyclic favors ketones.
Addition of primary and secondary amines + ketones/aldehydes
They form Immines with primary amines
They form Enamines with secondary amines
Immine
Primary amine and ketone/aldehyde. C=N:-R
Have a D.B. and a lone pair
Enamine
Secondary amine and ketone/aldehyde C-N:-R + R’
No D.B. or lone pair. STRONG ACID USED
Immine formation
Primary amine + carbonyl system with H3O+…there is also a proton transfer. The acid makes the OH a good L.G.
Enamine formation
Secondary amine + carbonyl system with HA…key step is removal of an H on the alpha carbon shifting everything back (final step)
Cyanohydrin formation
Carbonyl system + :C t.b.N:
The CN group can be reduced with LAH to a amine group or hydrolyzed to a carboxylic acid
Hydrolysis of a cyanohydrin yields
alpha-hydroxycarboxylic acid
Reduction of a cyanohydrin yields
beta-aminoalcohol
Wittig reaction
Aldehydes and ketones react with a phosphorous ylide to form an alkene with both isomers
Ylide
A neutral molecule with adjacent positive and negative charges
Phosphorus ylide formation
1) (C6H5)3P: attacks a primary or secondary alkyl halide via SN2 forming a salt
2) Base deptotonates this salt
Oxophosphatane
The 4 membered ring formed during the Wittig reaction
Tollen’s test Ag(NH3)2+/H20
Distinguishes aldehydes from ketones
Aldehydes react-Silver
Ketones don’t react-Nothing
Alpha hydroxy ketone-Reacts (Silver)
Alpha hydroxy ketone
OH on alpha carbon
