Main points about alcohols
Alcohols can be primary, secondary or tertiary. It is decided on which group the OH is bonded to, and how many methyl groups there are. If there is 3 methyl groups and the OH is bonded to one of them, it is tertiary
Ethanol can be produced via fermentation, this is how -
- Fermentation is exothermic reaction, carried out by yeast anaerobically (no oxygen required)
- Yeast produces an enzyme which converts sugars (glucose). This enzymes optimum work rate is at 30-40 degrees celsius
- If it is too hot or cold, the enzyme will denature and stop working
- When the solution reaches about 15% ethanol, the yeast dies
Advantages - Cheap, uses renewable sources
Disadvantages - High labour costs, very impure, very slow
Ethanol and Alkene Production
Ethanol is almost a carbon neutral fuel. This means that the CO2 released when the fuel was burned was removed by the crop as it grew. But its not 100% carbon neutral, take into account the whole process, the machines used and the fertilisers.
You can make ethene by eliminating water from ethanol in a dehydration reaction.
This reaction allows you to produce alkenes from a renewable source
Oxidising Primary Alcohols
Primary Alcohols oxidise into Aldehyde's and Carboxcylic acid's
Aldehyde's have a hydrogen and a oxygen (double bonded) to a carbon, must be the first carbon. This is the functional group of an aldehyde.
An aldehyde can then be vigorously oxidised into a carboxcylic acid. The functional group of a carboxcylic acid is COOH.
How to oxidise a primary alcohol -
- Gently heat the ethanol with acidified potassium dichromate (IV)
- To just get an aldehyde, you need to remove the solution as soon as its formed. You can do this via distillation
- To produce a carboxcylic acid, you need to oxidise the solution vigorously.
- The solution has oxidising agents added to it under reflux. Once the vaporised solutions are cooled, they are carboxcylic acids.
A secondary alcohol oxidises into a Ketone. A functional group of a ketone is =O
When refluxing a secondary alcohol, it forms a ketone. You must mention that you oxidise it with acidified potassium dichromate (IV)
Tertiary alcohols do not oxidise unless burnt.
How to distinguish between secondary/primary -
- Fehlings solution and Benedicts solution are both deep blue copper complexes, which reduce to brick red when warmed with an aldehyde, but stay blue with a ketone
- Tollens reagent is reduced to a silver mirror when warmed with an aldehyde but does not change with a ketone. The silver will coat the inside of apparatus.
- Limewater fizzes and goes cloudy when a carboxcylic acid is present.