14 Alcohols Flashcards
What are the physical properties of alcohols?
- Less volatile
- Higher melting points
- Greater water solubility
Why do alcohols have a higher boiling point?
- Alcohols have a polar O-H bond because of the difference in electronegativity of the oxygen and hydrogen atoms. Whereas, alkanes have non-polar bonds because the electronegativity of hydrogen and carbon are very similar.
- The intermolecular forces will be very weak London forces in alcohols but there will also be a much stronger hydrogen bonds between the polar O-H groups.
Why is alcohol soluble in water?
1) Alcohols are completely soluble in water, as hydrogen bonds form between the polar -OH group of the alcohol and the water molecules.
2) As the hydrocarbon chain increases in size, the influence of the -OH groups becomes relatively smaller, and the solubility of longer-chain alcohols decreases.
Examples of primary alcohols
Methanol, ethanol
What are primary alcohols?
An alcohol in which the OH group is attached to a carbon atom that is attached to two or three hydrogen atoms.
Examples of tertiary alcohols
2-methylpropan-2-ol, 2-methylbutan-2-ol
What are secondary alcohols?
An alchohol in which the -OH group is attached to a carbon atom that is attached to one hydrogen atom and two alkyl groups.
What are tertiary alcohols?
An alcohol in which the -OH group is attached to a carbon atom that is attached to no hydrogen atoms and three alkyl groups.
What is the oxidising agent for primary and secondary alcohols?
Potassium dichromate (K2Cr2O7) acidified with dilute sulfuric acid (H2SO4)
How do you know if an alcohol has been oxidised?
The orange solution containing dichromate ions is reduced to a green solution containing chromium ions.
What can primary alcohols be oxidised to?
Either aldehydes or carboxylic acids.
How can you ensure that the aldehyde is prepared rather than the carboxylic acid?
- The aldehyde is distilled out of the reaction mixture as it forms.
- This prevents any further reaction with the oxidising agent
What does aldehyde end with?
-Al
How are primary alcohols heated with acidified potassium dichromate to form an aldehyde?
Gentle heating
How are primary alcohols heated with acidified potassium dichromate to form a carboxylic acid?
Heated strongly under reflux
What are secondary alcohols oxidised to?
Ketones
Ends with -one
How are secondary alcohols heated?
Heated under reflux
Do tertiary alcohols undergo oxidation reactions?
No, they do not undergo oxidation reactions.
What is dehydration?
- Any reaction in which a water molecule is removed from the starting material.
- An alcohol is heated under reflux in the presence of an acid catalyst such as concentrated sulfuric acid or concentrated phosphoric acid.
- The product is an alkene.
What are substitution reacts of alcohols?
- Alcohols react with hydrogen halides to form haloalkanes.
- Alcohol is heated under reflux with sulfuric acid and a sodium halide
What happens during reflux?
1) Obtain round bottom flask
2) Add sodium dichromate, sulfuric acid, ethanol, anti-bumping granules.
3) Fasten the round bottom flask back with the rest of the reflux apparatus.
4) Turn the tap on and allow cold water to flow around the condensor.
5) Turn heat source on
6) Bring reaction mixture to boil for 20 minutes.
Why are anti-bumping granules used?
- Provide a surface for bubbles to form.
- Reducing the size of bubbles formed.
- Reducing vibration within glassware.
