chapter 14 alcohols Flashcards
what is the alcohol functional group and what are some uses of alcohols?
-OH and paints, solvents, fuel, alcoholic drinks and a feedstock
what is the difference in physical properties between alcohols and corresponding alkanes?
alcohols are less volatile, have higher melting points, have greater water solubility. however the difference becomes smaller as the carbon chain increases
The differences between alcohols and alkanes can be explained by the polarity of bonds. explain this.
•alkanes have non polar bonds because the electronegativity of C and H is very similar
•alkanes therefore have LDFs between molecules
•alcohols have a polar OH bond because of the difference in electronegativity of O and H atoms
•therefore alcohols also have LDFs but also have strong hydrogen bonds.
explain the difference in bp & volatility between alkanes and alcohols.
alcohols have H bonds holding molecules together in the liquid state which much be broken for it to turn into a gas. this requires more energy than overcoming LDFs in alkanes
explain the difference in solubility in water between alcohols and alkanes.
a compound that can form H bonds with water is much more soluble than a compound which cannot. alkanes are non polar so cannot form H bonds with water. as chain length increases influence of OH decreases so solubility decreases
how are alcohols classified?
primary, secondary and tertiary.
what is a primary alcohol?
an alcohol where the OH group is attached to a carbon atom that is attached to 2 H and one alkyl group.
methanol is attached to 3 Hs but it is still classified as primary
what is a secondary alcohol?
OH group is attached to a carbon that is attached to one H and two alkyl groups
what is a tertiary alcohol?
OH group is attached to three alkyl groups
describe the combustion of alcohols.
alcohol + O2 = CO2 + H2O
•exothermic and releases lots of energy as heat
which type of alcohols can be oxidised?
primary and secondary only
what is the oxidising mixture for oxidation of alcohols?
potassium dichromate(VI) K2Cr2O7 acidified with dilute H2SO4
what is the colour change of the oxidising agent when oxidising alcohols?
orange dichromate ions (Cr2O7)2- are reduced to green chromium ions Cr3+
what two products can primary alcohols be oxidised into?
aldehydes and carboxylic acids depending on reaction conditions because aldehydes are also oxidised into carboxylic acids
how do prepare aldehydes from alcohols?
•Gentle heating of primary alcohols with acidified K2Cr2O7
•To prevent further oxidation the aldehyde is distilled out of the mixture as it forms
e.g. C4H9OH(butan-1-ol) + [O] ~~>(distil) C3H7COH(butanal) +H2O
how do you prepare carboxylic acids from alcohols?
•strongly heat primary alcohol under reflux with an excess of acidified K2Cr2O7.
•this ensures all of the alcohol is oxidised and any aldehyde formed further reacts into carboxylic acid.
what is the product of oxidising secondary alcohols?
ketones
how is a ketone formed from a secondary alcohol?
•heat under reflux with oxidising mixture.
describe the dehydration of alcohols.
an alcohol is heated under reflux in the presence of H3PO4 to remove a water molecule forming an alkene.
what type of reaction is dehydration?
elimination
describe substitution of alcohols.
alcohols react with hydrogen halides to form haloalkanes.
•alcohol is heated under reflux with sulfuric acid and sodium halide (the hydrogen halide is formed in place alongside NaHSO4)
how is the hydrogen halide made in substitution of alcohols?
NaBr(s) + H2SO4(aq) ~> NaHSO4(aq) +HBr(aq)
write the overall equation for the reaction of propanol and HBr.
propanol + NaBr + H2SO4 ~> bromopropane + NaHSO4 + H2O
