WM - Reactions of alcohols Flashcards
What are the 3 types of alcohols?
Primary, secondary and tertiary.
How many types of alcohols are there?
3
What is a primary alcohol?
An alcohol where the OH is on a carbon with 1 alkyl attached so has 2 hydrogen atoms attached.
What is a secondary alcohol?
An alcohol where the OH is on a carbon with 2 alkyl groups attached so only has 1 carbon atom attached.
What is a tertiary alcohol?
An alcohol where the OH is on a carbon atom with 3 alkyl groups attached so that there are no hydrogens attached to the same carbon as the OH.
What are the reaction conditions for oxidising an alcohol into a carbonyl compound (aldehydes and ketones) and carboxylic acids?
Acidified potassium dichromate(VI) and heat under reflux.
Cr2O7 2- / H+ and h+r.
What are primary alcohols oxidised to?
Aldehydes and then to carboxylic acids.
What are secondary alcohols oxidised to?
Ketones only.
What are tertiary alcohols oxidised to?
They aren’t oxidised.
What types of alcohols are oxidised?
Primary and secondary but not tertiary.
When alcohols are oxidised using dichromate(VI) what is the colour change and why?
The orange dichromate(VI) ion is reduced to the green chromium(III) ion, Cr3+.
How can the reaction conditions be altered to control how far a primary alcohol is oxidised?
Gently heat the alcohol with the dichromate(VI) solution and acid in a flask to produce an aldehyde. To just get the aldehyde, the oxidising solution needs to be removed as soon as the aldehyde is formed. This can be done by using distilling apparatus where the aldehyde (which boils at a lower temp than the alcohol) evaporates and is distilled off immediately.
To produce a carboxylic acid, the alcohol has to be oxidised vigorously - mix with excess oxidising agent and h+r (meaning you increase the temp of the organic reaction to boiling point without losing anything as things that try to escape condense back down in a condenser).
How can secondary alcohols be oxidised into ketones?
By refluxing a secondary alcohol with acidified dichromate(VI).
What does [O] mean in the oxidation of alcohols?
[O] = Oxidising agent.
What can alcohols be dehydrated to form?
Alkenes.
What is the functional group in the alcohol homologous series?
The hydroxyl group, -OH.
What does whether an alcohol is primary, secondary or tertiary depend on?
Which carbon atom the -OH group is bonded to.
What is the simple way to oxidise alcohols?
Burn them.
Alcohols can be dehydrated to form what?
Alkenes.
Alkenes can be formed from the dehydration of what?
Alcohols.
How can you make ethene from ethanol?
By eliminating water from ethanol in a dehydration reaction.
What is the equation for making ethene from ethanol using a dehydration reaction?
C2H5OH –> CH2=CH2 + H2O
What happens in an elimination reaction?
A small group of atoms break away from a larger molecule. This small group is not replaced by anything else.
What are the 2 methods of dehydrating ethanol to form ethene? (Dehydrating alcohols to form alkenes.)
1) Ethanol vapour is passed over a hot catalyst of pumice stone or aluminium oxide, Al2O3 - the catalyst provides a large surface area for the reaction.
2) You can reflux ethanol with excess concentrated sulfuric acid at 170oC. The ethene produced is then collected over water.
