10.2 Alcohols, Aldehydes, and
Carboxylic Acids
BTW- removing a hydrogen is yet another definition of oxidation
• oxidation and reduction can be considered in
terms of…
1. oxidation- substance gains oxygen
reduction- substance loses oxygen
2. oxidation- substance loses hydrogen
reduction- substance gains hydrogen
3. oxidation- the loss of electrons
reduction- the gain of electrons
4. oxidation- the oxidation state/# increases
reduction- the oxidation state/# decreases
Combustion of alcohols
• complete combustion produces carbon dioxide and water
• one mole of methanol…
• CH3OH(l) + 3/2 O2(g) → CO2(g) + 2H2O(g)
• one mole ethanol…
• C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g)
• one mole of butanol…
• CH3CH2CH2CH2OH(l) + 6O2(g) → 4CO2(g) + 5H2O(g)
Oxidation
Primary alcohols
• overview of the two stage process
alcohol
aldehyde
carboxylic acid
https://www.youtube.com/watch?v=OXf447VKj8Q
1. first stage produces an aldehyde from an alcohol
• [O] over the yields arrow indicates an oxidizing agent
• example- ethanol heated with acidified potassium dichromate,
ethanal is produced
• the orange Cr2O72- (Cr6+) is reduced to Cr3+ and turns green in the
reaction
• C2H5OH + heat/H+/K2Cr2O7 → C2H4O
2. second stage produces a carboxylic acid
• if you continue oxidizing the newly formed aldehyde, it
produces a carboxylic acid
• C2H4O (ethanal) => C2H4O2 (ethanoic acid)
• can “interrupt” after the first stage and collect the aldehyde
through a process called distillation to prevent further oxidation
• aldehydes have a lower BP than carboxylic acids due to intermolecular
forces in carboxylic acids (HNOF/hydrogen bonding) and not in
aldehydes
• therefore, they would boil off first and could be collected
• if want to keep going and carboxylic acid is the desired product,
let the oxidation continue in a reflux column
• this is a closed system and prevents the products from escaping/boiling
off and the reaction continues
• Secondary alcohols
• one stage process under the same conditions as
primary alcohols
• oxidized to form a ketone and then done
Esterification
• using sulfuric acid as a catalyst, carboxylic acid and alcohol can react
to yield esters
• esters have a fruity smell and can be synthesized
• called a condensation reaction because water is the other product
H2SO4