Chapter 14 Alcohols Flashcards
Naming alcohol
The suffix -ol is added to the stem name of the longest carbon chain. The position of the alcohol functional group in the chain is indicated using a number
The alcohol homologous series
Contain the -OH functional group.
Methanol used as a fuel but can be converted into paints, solvents, insulation.
Ethanol used in alcoholic drinks and as a fuel.
Physical properties of alcohols
When comparing alcohols with alkanes with the same number of carbons:
alcohols are less volatile, have higher melting points, and greate water solubility than corresponding alkanes.
How can we explain the difference in chemical properties between the alcohols and alkanes of similar number of carbons
the alkanes have non-polar bonds because of the electronegativity of hydrogen and carbon are similar. This means they have the weak london forces for intermolecular forces.
Alcohols have a polar O-H bond becuase of electronegativity so they are polar. They will have weak london forces but also hydrogen bonds.
Volatility and boiling points of alcohols
Alcohols have a higher boiling point for the equivalent carbon alkane because they have hydrogen bonds aswell which require more energy to break
Solubility in water
Alcohols like methanol and ethanol are soluble in water because they have hydrogen bonds which means the alcohols can hydrogen bond with water molecules. However as the chain of carbons in the alcohol gets larger then the influence of the -OH group becomes relatively smaller, and the solubility of longer- chain alcohols become more like that of hydrocarbons so it decreases
Classifying alcohols
Primary alcohol - the carbon the -OH group is attached is attached to 2/3 hydrogens
Secondary alcohol - the carbon is attached to 1 hydrogen atom
Tertiary alcohol - the carbon is attached to 0 hydrogens
Combustion of alcohols
Alcohols burn completely in a plentiful supply of oxygen to produce carbon dioxide and water.
The reaction is exothermic releasing a large quantity of energy in the form of heat.
As the number of carbon atoms in the chain increases the heat released per mole also increases.
Oxidation of primary alcohols
they can be oxidised to aldehydes or carboxylic acids.
The aldehydes will be oxidised to carboxylic acids
Preparation of aldehydes
gentle heating of primary alchols with acidified potassium dichromate, an aldehyde is formed.
To ensure an aldehyde is formed rather than a carboxylic acid it is distilled out of the reaction mixture as it forms, preventing any further reactions with the oxidising agent.
The dichromate ions change colour from orange to green.
Preparations of carboxylic acids
if under reflux with a excess of acidified potassium dichromate, carboxylic acid is formed. Excess ensures it is oxidised.
Heating a reflux ensures that any aldehyde formed originally goes into a carboxylic acid.
Oxidation of secondary alcohols
they are oxidised to ketones. It is not possible to go further when oxidising ketones using acidified dichromate ions.
To ensure the reaction goes to completion, it is done under reflux with the oxidising mixture.
Dichromate changes colour from orange to green.
Oxidisation of tertiary alcohols
They don’t undergo oxidation reactions.
The dichromate remains orange when added to tertiary alchols.
Dehydration of alcohols
An alcohol is heated under reflux under the presense of an acid catalyst such as concentrated sulfuric acid or phosphoric acid. Creates an alkene product.
Example of an elimination reaction
Substitution reactions of alcohols
Alcohols react with hydrogen halides to form haloalkanes. When preparing a haloalkane, the alcohol is heated under reflux with sulphuric acid and a sodium halide the hydrogen bromide is formed in situ.
