14.2 Reactions of Alcohols Flashcards
What types of reactions can alcohols undergo?
COMBUSTION
OXIDATION
SUBSTITUTION
DEHYDRATION
What is the general equation for combustion of an alcohol?
Alcohol + Oxygen ⟶ Carbon Dioxide + Water
Under what conditions does combustion occur?
high temperature
Is combustion exothermic or endothermic?
exothermic
Under what condition do alcohols become oxidised?
acidified potassium dichromate solution
K2Cr2O7 (aq) + H2SO4 (aq)
What is the oxidising agent in oxidation of alcohols/aldehydes?
acidified potassium dichromate ions
During oxidation, are potassium dichromate ions oxidised or reduced?
reduced
What is the colour change during oxidation of alcohols and the formation of what ion is responsible for this colour change?
orange to green
Cr3+
What is the general equation for oxidation of PRIMARY ALCOHOLS?
PARTIAL: Primary alcohol + [O] ⟶ Aldehyde + Water
COMPLETE: Primary alcohol + 2[O] ⟶ Carboxylic acid + Water
What organic product is formed when a PRIMARY alcohol undergoes oxidation under GENTLE HEATING + EXCESS ALCOHOL?
aldehyde
What organic product is formed when a PRIMARY alcohol undergoes oxidation under REFLUX + EXCESS OXIDISING AGENT?
carboxylic acid
What conditions are used in PARTIAL OXIDATION of PRIMARY alcohols?
GENTLE HEATING
EXCESS ALCOHOL - less complete oxidation
(∵ not enough oxidising agent to fully oxidise)
ALDEHYDE DISTILLED OUT - prevents further oxidation into carboxylic acid
What conditions are used in COMPLETE OXIDATION of PRIMARY alcohols?
REFLUX
EXCESS OXIDISING AGENT - make sure all alcohol molecules fully oxidised
What organic product is formed when a SECONDARY alcohol undergoes oxidation?
ketone
What conditions are used in the oxidation of SECONDARY alcohols?
reflux - ensure reaction is complete
What organic product is formed when a TERTIARY alcohol undergoes oxidation?
TERTIARY ALCOHOLS CANNOT UNDERGO OXIDATION REACTIONS
Under reflux:
Primary alcohols oxidise to _____.
Secondary alcohols oxidise to _____.
carboxylic acids
ketones
What compound can be used as a test for the presence of a carboxylic acid?
METAL CARBONATE
CO2 gas released since acid + metal carbonate ⟶ salt + water + carbon dioxide
(Carboxylic) acid + metal carbonate ⟶
salt + water + carbon dioxide
oxidising a primary alcohol ⟶ aldehyde,
what is the change in number of hydrogens and oxygens?
loses 2 hydrogens (oxygen added takes these 2 hydrogens to form water)
Overall no change in oxygen.
the [O] oxygen being added to alcohols causes the formation of what inorganic molecule?
(except aldehyde -> carboxylic acid)
water
O takes 2 hydrogens from the alcohol molecule.
What is the general equation for dehydration of an alcohol?
Alcohol ⟶ Alkene + Water
What are the conditions for dehydration of an alcohol?
PHOSPHORIC ACID catalyst, H3PO4
REFLUX
What is a dehydration reaction?
2 hydrogens + 1 oxygen removed from saturated molecule
forming unsaturated molecule + water
What is a substitution reaction?
reaction where
atom/groups of atoms are REPLACED
by atom/group of atoms.
How many [O] must be added to a primary alcohol to oxidise it to an aldehyde?
1
How many [O] must be added to a primary alcohol to oxidise it to a carboxylic acid?
2
How many [O] must be added to a secondary alcohol to oxidise it to a ketone?
1
Which oxidation reaction involves this:
[O] added to alcohol takes 2 hydrogens from the alcohol, forming water.
primary alcohol ⟶ aldehyde
or
secondary alcohol ⟶ ketone
Which oxidation reaction involves this:
[O] added is incorporated into the molecule by addition.
Aldehyde ⟶ carboxylic acid
