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.
Describe the oxidation of secondary alcohols?
Secondary alcohols oxidise to ketones and it is not possible to oxidise ketone further using acidified dichromate (VI) ions. It is heated under reflux with the oxidising agent
Describe the oxidation of tertiary alcohols?
Tertiary alcohols don’t undergo oxidation reactions. The acidified potassium dichromate (VI) solution stays orange.
Describe the dehydration reaction of alcohols
water molecule is removed from alcohol forming an alkene. Alcohol is heated under reflux in the presence of an acid catalyst such as concentrated sulphuric acid or concentrated phosphoric acid. It is an elimination reaction.
Describe the substitution reaction of alcohols to form haloalkanes
Alcohols react with hydrogen halides to form haloalkanes. The alcohol is heated under reflux with sulphuric acid and a sodium halide causing a hydrogen halide to form and NaHSO4. The hydrogen halide formed reacts with the alcohol to form a haloalkane.
what is the difference between aldehydes and ketones?
aldehydes must have the presence of a hydrogen atom attached to the carbon-oxygen double bond unlike ketones
what smell is produced in the full oxidation of primary alcohols and partial oxidation?
full oxidation: vinegar smell
partial oxidation: fruity smell
complete combustion(sufficient oxygen) of alcohols forms?
carbon dioxide and water
incomplete combustion (insufficient oxygen) of alcohols forms?
carbon monoxide and water
further insufficient oxygen produces: carbon(soot) and water
what are the reagents and conditions needed for hydration of alkenes to form alcohols?
steam and acid catalyst
how is alcohol produced from yeast?
yeast produces alcohol and carbon dioxide in anaerobic and warm (35degrees) conditions
what is the formula for yeast?
C6H12O6
