alcohols: content Flashcards
(23 cards)
comment on the boiling points of alcohols
alcohols can form hydrogen bonds and so have higher boiling points than alkanes of similar mass/Mᵣ
are alcohols miscible in water? why
yes
they are polar and so alcohol molecules can form hydrogen bonds with H₂O molecules
how can alcohol miscibility change?
(think molecule size)
the bigger the molecule, the less soluble
only the OH bit is polar. as the hydrocarbon chain increases, the influence of the OH group is reduced (makes up a smaller proportion of the molecule) and the insolubility of the longer hydrocarbon chain becomes more dominant
how are alcohols classified
primary (1°) - the carbon to which the carbonyl group is bonded is bonded to one other carbon
secondary (2°) - the carbon to which the carbonyl group is bonded is bonded to two other carbons
tertiary (3°) - the carbon to which the carbonyl group is bonded is bonded to three other carbon
name the alcohol reactions required by the OCR spec
combustion
dehydration (elimination)
substitution
esterification
oxidation
dehydration of alcohols
use concentrated H₂SO₄ under reflux
products of combustion of alcohols
carbon oxides and water
why can alcohols undergo substitution reactions
OH is a nucleophile
(nucleophilic substitution)
conditions for nucleophilic substitution
typically done under reflux
conditions of esterification reactions of alcohols
concentrated sulphuric acid
(elimination reaction)
how can carboxylic acids be formed
heating aldehydes under reflux
reagent: acidified potassium dichromate (VI)
how are aldehydes formed
distillation of 1° alcohols
reagents: acidified potassium dichromate (VI)
equation to form carboxylic acids from alcohols
alcohol + 2[O] -> carboxylic acid
(primary alcohols)
oxidation of secondary alcohols
ketones
reagents: acidified potassium dichromate (VI)
conditions: reflux
oxidation of tertiary alcohols
tertiary alcohols cannot be oxidise by acidified potassium dichromate (VI)
describe the colour change during alcohol oxidation reactions
K₂Cr₂O₇/H⁺ is orange
when it acts as an oxidising agent, it is reduced to green chromium (III) ions
- used to distinguish primary/secondary alcohols from tertiary
how to test for aldehydes
tollen’s reagent
describe the process of simple distillation (alcohols, aldehydes and carboxylic acids)
- 1° alcohol and K₂Cr₂O₇ dipped into a solutoin of sulphuric acid (to acidify dichromate)
- aldehyde formed is immediately distilled off, preventing further oxidation to a carboxylic acid
how does simple distillation work
separates compounds according to their boiling points
how to ensure complete reactions/prevent from boiling dry
reflux
- vapour re-enters the reaction flask to ensure solvents don’t boil dry and keep the reaction going for longer
-prevents the loss of reactant vapour
sketch distillation apparatus
sketch reflux apparatus
when and why are anti-bumping granules used?
to prevent the formation of large bubbles during distillation and reflux
