C15 alcohols

• alcohols have the functional group -OH attached to a hydrocarbon chain
• the general formula for alcohols is C(n)H(2n+1)OH
• to name alcohols, use the root representing the number of carbons in the longest chain, a number to show which carbon the -OH group is on, and the suffix -ol

  if there is more than one -OH group, use the prefixes di-, tri-, tetra- etc
• alcohols are classified as primary, secondary or tertiary depending on how many other groups are attached to the carbon atom which has the -OH group
• primary alcohols have one other group attached to the carbon with the -OH group
• secondary alcohols have two other groups attached to the carbon with the -OH group
• tertiary alcohols have three other groups attached to the carbon with the -OH group
• the -OH group in alcohols means that they can form hydrogen bonds with each other
• alcohols have higher melting points than alkanes because they can form hydrogen bonds
• alcohols with short chains are soluble in water because the polar hydrogen bonds dominate, but alcohols with long chains are not soluble in water because the non-polar hydrocarbon chain dominates
• ethanol can be produced from hydration of alkenes, which are sourced by cracking the fractions of crude oil produced in fractional distillation
• hydration of alkenes means that water is added across the double bond
• hydration requires an acid catalyst, usually phosphoric acid, aqueous conditions, high pressure and high temperature
• ethanol can be produced from fermentation of carbohydrates
• for fermentation, enzymes break down starch into sugars which can then be fermented
• the key step in fermentation is C6H12O6 → 2C2H5OH + 2CO2, this is anaerobic respiration
• fermentation requires anaerobic conditions, a warm temperature, aqueous sugars, and yeast
• advantages and disadvantages of fermentation:

  • hydration has a very high percentage yield as the only product is ethanol, fermentation has a lower percentage yield as an aqueous solution is produced
  • hydration is much faster than fermentation
  • hydration is more expensive than fermentation as it requires a higher temperature
• alcohols can be completely combusted to produce carbon dioxide and water, or incompletely combusted to produce carbon monoxide and water
• alcohols can be dehydrated to form alkenes, using hot concentrated sulfuric acid and an aluminium oxide catalyst
• in dehydration, a water molecule is removed from the alcohol, leaving an alkene, the water molecule is made up of the -OH group and a H from a carbon next to the carbon with the -OH group
• the mechanism of dehydration:

  • in the -OH group, oxygen is delta-negative and has a lone pair, and hydrogen is delta-positive
  • the lone pair on the oxygen is attracted to the H+ ions in the solution, forming another -OH bond with one
  • the oxygen becomes positive so the electrons from the C-O bond are attracted to the oxygen and leave with it
  • a carbon does not have enough bonds, so one of the C-H bonds breaks and the electrons move to the C-C bond, forming a C=C bond
• a suitable dehydrating agent is phosphoric (V) acid
• combustion of alcohols is complete oxidation, but alcohols can also be gently oxidised in stages
• primary alcohols are oxidised to aldehydes then carboxlyic acids
• aldehydes are oxidised to carboxylic acids
• secondary alcohols are oxidised to ketones
• ketones cannot be oxidised further
• tertiary alcohols cannot be oxidised further
• the oxidation of primary alcohols to aldehydes requires distillation apparatus, dilute sulfuric acid, acidified potassium dichromate, and heat
• distillation apparatus is used because you do not want the reaction to go to completion, it prevents the condensed substances from returning to the reaction flask so that they can be collected separately
• the oxidation of primary alcohols to carboxylic acids requires reflux apparatus, concentrated sulfuric acid, acidified potassium dichromate, and heat
• reflux apparatus is used because you want the reaction to go to completion, any partially reacted substances will condense and drip back into the flask until it has all reacted
• to write equations for oxidation, represent the oxygen using the notation [O]​
• the oxidation of secondary alcohols to ketones requires acidified potassium dichromate and heat