Oxidation

Question 1

Oxidation

Answer 1

Gain of oxygen, loss of hydrogen and loss of electrons

Question 2

Oxidation of alcohols

Answer 2

Primary alcohol to aldehyde to carboxylic acid
Secondary alcohol to ketone
Jones = CrO3, H2SO4/acetone, gives carboxylic acid/ketone
PCC = pyridinium chlorochromate, gives aldehyde/ketone
PDC = pyridinium dichromate, gives aldehyde/ketones, less acidic than PCC so send for acid sensitive FG
Swern = 1. DMSO, o ally chloride at -78 2. Et3N, gives aldehyde/ketone
Dess-Martin = Dess-martin periodinane, selective and mild, gives aldehyde/ketone and highly heat/shock sensitive

Question 3

Oxidation of aldehydes to carboxylic acids

Answer 3

Jones
KMnO4 = selectivity issue as also oxidises alcohols and alkenes
Silver oxide in NaOH = can be used if alkene/alkyne present, strong basic so can’t be used if base sensitive FG present

Question 4

Oxidation of ketones

Answer 4

Baeyer-Villiger = peracid oxidising agent (m-CPBA), forms ester and with unsymmetrical ketones more substituted alkyl C migrates

Question 5

Oxidative cleavage of alkenes

Answer 5

Ozonolysis with O3 or OsO4/NaIO4

Question 6

Ozonolysis mild reductive work up

Answer 6

Me2S or PPh3 or Zn/AcOH forms aldehyde/ketone

Question 7

Ozonolysis hydride reductive work up

Answer 7

LiAlH4 or NaBH4 gives alcohol

Question 8

Ozonolysis oxidative work up

Answer 8

H2O2 or KMnO4 gives carboxylic acid or ketone

Question 9

OsO4 cleavage of alkenes

Answer 9

Concerted reaction forming syn-diol, OsO4 = toxic and expensive but can be used in catalytic amounts with co-oxidant NMO