alcohol

• alcohols have the functional group -OH
• alkenes can be made sustainably from alochols if the alcohol has been made via fermentation of glucose from plants

  normally alkenes are sourced from crude oil which is non renewable
• dehydration is eliminating water from alcohol to produce alkene
• dehydration requires an acid catalyst

  this can be sulfuric or phosphoric acid
• dehydration is shown using an elimination mechanism

  1. lone pair on oxygen attaches to H+ ion which has come from the acid catalyst
  2. intermediate has a o+
  3. oxygen pulls electrons in c-o bond strongly to break the bond leaving an unstable carbocation intermediate
  4. carbocation loses a H+
  5. electrons in C-H move to form C=C bond
  6. ethene made and H+ reformed
• dehydration of alcohol conducted via distillation
• when we dehydrate an alkene we get an impure product that contains alkene, alcohol, water and acid
• distillation allows us to separate impurities by boiling point
• if further separation is required after distillation, a separation funnel and addition of drying agent afterwards can be used
• making cyclohexene step 1 distillation

  add concentrated acid (Sulfuric or phosphoric) and cyclohexanol into round bottomed flask

  add anti-bumping granules for smooth boiling process

  heating mantle used to warm reactants till 83 degrees

  collect product in a conical flask but it will still have impurities (unreacted cylohexanol and water)
• we use a heating mantle not bunsen burner as cyclohexanol is flammable

  we warm till 83 degrees as it is the boiling point of cyclohexanol

  chemicals with lower boiling points will evaporate, enter the condenser, cool down and condense back into a liquid
• making cyclohexene step 2 separation

  add products from distillation to a separating funnel

  add water to dissolve soluble impurities and create an aqueous solution

  two layers will form after the solution settles

  top layer is impure cyclohexene, bottom layer is aqueous containing water soluble impurities that can be drained off
• making cyclohexene step 3 purification

  take impure cyclohexane from separation and add to round bottomed flask

  add anhydrous calcium chloride as dehydrating agent to remove aqueous substances still remaining

  invert flask and leave for 20-30 minutes
• alcohols produced by hydration of alkenes

  we use steam and an acid catalyst
• we can make ethanol by reacting steam and ethene with a phosphoric acid catalyst

  we need 300 degrees temperature and 60atm pressure
• hydration of alkene steps

  1. electrons in double bond used to form bond with H+ ion
  2. lone pair on water bonds to carbocation
  3. hydrogen lost from water
• fermentation is alternative to ethene and steam to make ethanol

  the reaction is exothermic
• using ethene to make ethanol requires crude oil which is non renewable
• making ethanol via fermentation uses renewable source of glucpse from plants and yeast
• fermentation uses yeast in anaerobic conditions

  yeast is an enzyme that converts glucose into carbon dioxide and ethanol

  the optimum temperature is 30-40 degrees
• fermentation requires little equipment and uses renewable resources so is a cheap process

  biggest cost is fractional distillation at end to produce pure ethanol, it requires energy and time
• biofuels are made from dead biological matter
• ethanol is a biofuel used as fuel in countries with good sugar cane supply

  sugar is fermented to produce alcohol

  brazil uses bioethanol in petrol
• advantages of crude oil

  • renewable and more sustainable than crude oil
  • carbon neutral as CO2 produced when biofuels are burnt is absorbed by sugar cane when it grows
• disadvantages of biofuel

  • expensive to convert existing petrol engines to take fuels with higher concentration of ethanol
  • land to grow crops is used for fuel production, may lead to shortages in sugar cane crop in brazil for example
• biofuels may not be carbon neutral as fossil fuels are burnt to transport them across the country, fossil fuels make fertilisers put on the cops and machinery to harvest the crop
• alcohols can be oxidised using acidified potassium dichromate (K2Cr2O7)

  it is a mild oxidising agent so is reduced itself

  turns from orange (Cr2O7 2- dichromate ion) to green (Cr 3+ chromium ion)
• primary alcohols can be oxidised to aldehydes then carboxylic acids
• secondary alcohols can be oxidised to ketones
• tertiary alcohols cannot be oxidised using dichromate, only burning them
• aldehyde has a C=O and C-H on the end carbon
• carboxylic acid has a C=O C-OH on the end carbon
• ketones have a c=o on an inner carbon
• distillation and reflux is used in the oxidation of alcohols
• oxidation of primary alcohols makes an aldehyde and then carboxylic acid

  difficult to extract aldehyde when heating in a boiling tube so remove it from the oxidising agent when it forms using distillation
• to turn an aldehyde into a carboxylic acid use reflux and excess oxidising agent

  the aldehyde evaporates, condenses and falls back into the flask
• reflux allows strong heating without losing volatile reactants and products
• use reflux and oxidising agent to turn secondary alcohol to ketone

  e.g propan-2-ol to propanone when potassium dichromate is added
• Fehling and Tollens are oxidising agents

  will oxidise aldehyde but not ketone

  can distinguish between the two
• Fehlings

  blue solution as it has Cu2+ ions, add when warm

  in aldehyde will form brick red precipitate

  in ketone will stay blue