Chapter 14 Flashcards
1
Q
What are the properties of alcohols ?
A
- OH functional groups and= hydroxyl group
- the OH dictates the physical and chemical properties of the alcohol
2
Q
What are the physical properties of alcohol ?
A
- alcohols are less volatile compared to alkanes
- Higher melting points
- greater water solubility
- as the carbon chain length increases, alkanes and alcohols become more similar
- these differences are due to the polarity of the OH bond
3
Q
What is a primary alcohol ?
A
- e.g methanol, ethanol
- OH is attached to 2 hydrogens, 1 alkyl group although methanol is also a primary alcohol
4
Q
What is a secondary alcohol ?
A
- OH, is attached to 1 hydrogen, 2 alkyl groups
5
Q
What is a tertiary alcohols ?
A
- OH, is attached to 0 hydrogens, or 3 alkyl groups
6
Q
How are primary alcohols oxidised ?
A
- they can be oxidised by an oxidising agent
- this is usually potassium dichromate acidified with dilute sulphuric acid
- if alcohol is oxidised, orange dichromate ions are reduced to green solution containing chromium ions
7
Q
What are the products of the oxidation of a primary alcohol ?
A
- can be oxidised to either aldehydes or carboxylic acids
- the product depends on the reaction conditions used
- aldehydes can themselves by oxidised to form carboxylic acids
8
Q
How to make aldehydes ?
A
- gentle heating of primary alcohol with acidified potassium dichromate an aldehyde is formed
- aldehyde is distilled out of the reaction mixture as it forms, this is to stop oxidising further to carboxylic acid
- colour change from orange to green
- oxidising agents can just be written as [O]
9
Q
How to make carboxylic acids ?
A
- primary alcohol is heated strongly under reflux (even distribution of heat energy)
- this ensures that any aldehydes formed initially in reaction also undergoes oxidation to the carboxylic acid
- excess of acidified potassium dichromate
10
Q
What happens in the oxidation of secondary alcohols ?
A
- oxidised to ketones
- No further oxidation is possible when using acidified dichromate ions
- alcohol is heated under reflux
- the dichromate ions change from orange -> green
11
Q
What happens in the oxidation of tertiary alcohols ?
A
- they do not undergo oxidation reactions
- acidified dichromate ions remain orange when added to tertiary alcohols
- this is because the carbon atom attached to the OH, is bonded to 3 others carbon atoms
12
Q
What is the dehydration of alcohols ?
A
- a water molecule is removed ?
- An alcohol is heated under reflux, in the presence of an acid catalyst (sulphuric acid)
- an alkene is formed
13
Q
What happens in the substitution of alcohols ?
A
- reaction with hydrogen halide -> haloalkane
- Alcohol is heated under reflux with sulphuric acid and sodium halide
- hydrogen halide is formed
- hydrogen halide reacts with alcohol to produce Haloalkane
- overall haloalkane, water is formed
