organic chemistry- alcohols Flashcards
how do alcohols differ from alkanes?
alcohols are less volatile, have a higher melting point and have greater water solubility. However the differences become smaller as the length of the carbon chain increases.
what is methanol used for?
high-performance fuel because of its efficient combustion. It is also an important chemical feedstock.
what is ethanol used for?
alcoholic drinks, fuel and feedstock.
Why do alcohols differ to alkanes when discussing bond strength and polarity?
Alkanes have non-polar bonds because the electronegativity of carbon and hydrogen are very similar which causes weak London forces in alkanes. However alcohols have a polar O-H bond because of the difference in the electronegativity of the oxygen and hydrogen atoms. The London forces are weak but there are strong hydrogen bonds between the O-H groups.
why are alcohols soluble in water?
hydrogen bonds can form between the polar O-H group and the water molecule
as the carbon chain of an alcohol increases, why does the solubility decrease?
influence of the -OH group becomes smaller.
what are primary alcohols?
methanol and ethanol as the -OH group is attached to a carbon atom that is attached to two hydrogens and one alkyl group (methanol is an exception but still classified as a primary alcohol)
what is a secondary alcohol?
the -OH group is attached to a carbon atom that is attached to one hydrogen atom and two alkyl groups.
what is a tertiary alcohol?
the -OH group is attached to a carbon atom that is attached to no hydrogen atoms and three alkyl groups
Describe the combustion of alcohols
carbon dioxide and water is released in an exothermic reaction. Large quantity of energy is released in the form of heat.
how do you oxidise primary and secondary alcohols?
primary and secondary alcohols are oxidised using an oxidising agent which is a mixture of potassium dichromate acidified with dilute sulphuric acid. If the alcohol is oxidised the orange solution containing dichromate ions (VI) reduces to a green solution contains chromium ion (III).
Describe the oxidation of primary alcohols?
they oxidise into aldehydes or carboxylic acids. The product depends on reaction conditions as aldehydes oxidise into carboxylic acids.
How do you prepare for only aldehydes from primary alcohols?
Gently heat the primary alcohol with the oxidising agent, acidified potassium dichromate (VI), and to ensure the aldehyde is formed and not the carboxylic acid, distill the mixture to prevent further reaction with the oxidising agent. Use excess alcohol.
what symbol is used to indicate the oxidising agent?
[O]
How do you prepare for a carboxylic acid from primary alcohols?
heat primary alcohol strongly under reflux with excess acidified potassium dichromate (VI). Heating under reflux ensures that aldehydes oxidise.
