FC21: Alcohols Flashcards
What is the functional group of an alcohol
hydroxyl functional group (-OH)
What is the relative boiling/melting point of alcohols and why
relatively high for their size due to hydrogen bonding between alcohol molecules
What is the relative solubility of alcohols and why
Alcohols are highly soluble in water as they can form strong interactions (H-bonding) between the molecules. They are miscible
What is the oxidising agent used when oxidising alcohols
hot, aqueous, acidified potassium dichromate
K2Cr2O7 (aq) / H+(aq)
What is the active part of potassium dichromate when oxidising alcohols
Cr2O7 2-
What do primary alcohols form when oxidised, and what do they form if they are left with the oxidising agent for longer
primary alcohols oxidise to form aldehydes, which further oxidise to form carboxylic acids
What is the colour change of the oxidising agent when oxidising alcohols
potassium dichromate changes colour from orange to green
What do we use to acidify potassium dichromate for the oxidation of alcohols and why
sulfuric acid, not hydrochloric acid because chloride ion in HCl would oxidise to toxic chlorine gas
At what position of the chain in an aldehyde is the doubly bonded oxygen?
at start or end of chain as it is only formed by primary alcohols therefore no position number
At what position of the chain in a carboxylic acid is the COOH functional group?
at start or end of chain as it is only formed by primary alcohols therefore no position number
What do secondary alcohols form when oxidised, and what do they form if they are left with the oxidising agent for longer
secondary alcohols oxidise to form ketones, and do not further oxidise when left with the oxidising agent
What do tertiary alcohols form when oxidised, and what do they form if they are left with the oxidising agent for longer
tertiary alcohols are not oxidised by hot, aqueous, acidified potassium dichromate
At what position of the chain in a ketone is the doubly bonded oxygen?
anywhere but not the start or end of the chain as it is only formed by secondary alcohols
How can you set up an apparatus to produce a higher yield of aldehyde
use distillation
set up a stand, boss and a clamp. clamp a pear shaped flask containing the primary alcohol, oxidising agent, and anti-bumping granules
put a thermometer connector with side arm into the pear shaped flask.
put a thermometer into the thermometer connector making sure the thermometer bulb is at the exit of the side arm
put a condenser around the side arm, cold water in one end and out the other end.
attach a delivery tube and a collecting vessel at the end of the tube.
heat the pear shaped flask
How does using distillation produce a higher yield of aldehyde
any aldehyde formed will boil at a lower temperature than the original primary alcohol and other components in the mixture, as it does not form hydrogen bonding or ion dipole bonds, but weaker permanent dipole-dipole forces. Therefore the aldehyde would boil and condense into the collecting vessel
How can you set up an apparatus to produce a higher yield of carboxylic acid
use refluxing
set up a stand, boss and clamp. clamp a pear shaped flask containing primary alcohol, oxidising agent and anti-bumping granules
Put a condenser just into the opening of the pear shaped flask, cold water going in one end and out the other end
Heat the pear shaped flask
How does heating under reflux produce a higher yield of carboxylic acid
heating under reflux is continuous boiling and condensing of a reaction mixture using a condenser, so any unwanted aldehyde formed is condensed back into the oxidising agent to further oxidise into carboxylic acid
What do anti-bumping granules do and why are they used
prevents super-heating of the reaction mixture by providing nucleation sites for bubbles to form
This encourages calmer boiling and prevents the mixture boiling over into the condenser
why are alcohols polar molecules
there is a permanent dipole along the O-H bond due to the large difference in electronegativity values of O and H. The molecule is not completely symmetrical, so there is an overall dipole along the molecule and so alcohols are polar
How can you make alcohols from alkenes?
hydration
alkene + water with concentrated phosphoric acid-> alcohol
How can you make alcohols from haloalkanes? what is the mechanism for this reaction
alkane + sodium hydroxide with heat and sodium hydroxide (aq) -> alcohol + sodium halide
nucleophilic substitution
describe how you could prepare an alcohol from an alkane in two steps
- alkane + halogen under UV light -> haloalkane + hydrogen halide
- haloalkane + sodium hydroxide with heat and sodium hydroxide (aq) -> alcohol + sodium halide
What is formed when alcohols are heated with concentrated sulfuric acid and what type of reaction is this
alkene and water
dehydration / elimination
How can you convert an alcohol into a haloalkane and what type of reaction is this
add sodium halide in the presence of concentrated sulfuric acid
substitution reaction
