A-level Chemistry: 3.3.5 Alcohols

higher

∵ -OH group in alcohol means hydrogen bonding occurs between molecules

hydrogen bond to water molecules

Non-polar hydrocarbon chain

∵ of hydrogen bonding predominates

Non-polar hydrocarbon chain dominates

Allows you to make alkenes from renewable resources i.e. without crude oil

Product: Alkene

• Al2O3 Catalyst

• 450 K

• Concentrated, hot H2SO4

Elimination

H2SO4 - acts as a catalyst

Uses the fact that chemicals have different boiling points & separates them out to get a single purified substance

• Hydration

• Fermenation

1. Hydration of ethene using steam to produce ethanol

2. Acid catalyst

3. High temperature + high pressure

4. H2O added across double bond

• 
  300°C

• Pressure of 60 atm

• Solid phosphoric(V) acid catalyst
  

  • H3PO4

• Fermentation (exothermic reaction) is carried out by yeast in anaerobic respiration

• Yeast produces an enzyme that converts sugars into ethanol and carbon dioxide

• Ethanol formed is separated by fractional distillation

Low tech process (uses cheap equipment & renewable resources)

Fractional distillation is needed for purification = expensive & time consuming

C2H4(g) + H2O(g) ⇌ C2H5OH(g)

1. Burn them

2. Use oxidising agent acidified potassium dichromate(VI), K2Cr2O7 to mildly oxidise them

• Loss of electrons

• Gain of oxygen

• (Loss of hydrogen)

• Gain of electrons

• Loss of oxygen

• (Gain of hydrogen)

Chemical that accepts electrons and gets reduced

(supplies the oxygen or removes the hydrogen)

Chemical that donates electrons and gets oxidised

(removes the oxygen or supplies the hydrogen)

Aldehydes and then to carboxylic acids

1. Gently heating alcohol with potassium dichromate(VI) & sulfuric acid in test tube = aldehyde

2. To get just aldehyde, distill it off immediately

Alcohol has to be vigorously oxidised:

alcohol is mixed with excess oxidising agent & heated under reflux

• Any escaped vapour is condensed back into liquid

• So any unreacted aldehyde can be oxidised/react further

Ketones

Reflux a secondary alcohol with acidified potassium dichromate(VI)

Primary and secondary alcohol:
Orange → Green

Tertiary alcohol:

No colour change - remains orange

Orange dichromate(VI) ion, Cr2O72-, is reduced to green chromium(III) ion, Cr3+

NO

∵ of lack of hydrogen atoms on carbon atom which the hydroxyl group is attached to

By burning them

CBA

Alkene, ketone, alcohol

• Dipole-dipole forces between butanal molecules

• Hydrogen bonds in both other molecules

• Dipole-dipole forces are weaker than hydrogen bonds, require less energy to break

• Oxidising agent

• 2 hydrogen atoms removed

• Forming water

Functional group (OH) at the end of the chain

1. Mixture of liquids heated to boiling point for prolonged time

2. Vapour is formed which escapes from liquid mixture & is changed back into liquid + returned to liquid mixture

3. Any alcohol and aldehyde that initally evaporates can then oxidised