Alcohols

• What functional group do alcohols contain?

  Hydroxyl group (OH)
• What defines a primary alcohol?

  One alkyl group attached to carbon with OH
• How many alkyl groups are attached to a secondary alcohol?

  Two alkyl groups
• What characterises a tertiary alcohol?

  Three alkyl groups attached to carbon with OH
• Why is it important to distinguish between primary, secondary, and tertiary alcohols?

  They react differently when oxidised
• What is the general formula for alcohols?

  CnH2n+1OH
• How are alcohols named when there are multiple -OH groups?

  Use di, tri and add 'e' to stem
• Why can the -OH group of alcohols hydrogen bond with water?

  Because it is polar and has delta charges
• What is the carbon neutrality of biofuels like ethanol?

  Any CO2 given off when biofuel is burnt is absorbed during plant growth so no net addition to atmospheric CO2 levels
• What happens to the solubility of alcohols in water as the hydrocarbon chain length increases?

  Solubility decreases as the non-polar hydrocarbon chain length increases
• What type of forces do C-H bonds in alcohols exhibit?

  Van der Waals forces
• What happens during the oxidation of alcohols?

  They can form aldehydes, ketones, or carboxylic acids
• Why do alcohols have higher boiling points than alkanes of similar mass?

  Due to hydrogen bonding between alcohol molecules
• How can you distinguish between aldehydes and ketones?

  Using Fehling's or Tollens' reagent
• What color change occurs with Fehling's solution when an aldehyde is present?

  Blue Cu2+ to brick red precipitate Cu2O
• What visual change occurs with Tollens' reagent when an aldehyde is present?

  A silver mirror forms inside the flask as Ag+ ions reduced to Ag atoms
• Why do ketones not produce a color change with Fehling's or Tollens' reagent?

  They cannot be oxidised by these reagents
• What are the key points to remember about the oxidation of alcohols?


  • Primary alcohols can form aldehydes and carboxylic acids
  • Secondary alcohols form ketones
  • Tertiary alcohols cannot be oxidised by potassium dichromate
• What is the effect of temperature on yeast enzymes during fermentation?

  Too high or low temperatures denature enzymes
• Why is bioethanol not truly carbon neutral?

  Fossil fuels burned to power production processes and farm crops e.g irrigate plants + transportation
• How can aldehydes and ketones be distinguished?

  • Aldehydes can be oxidized to carboxylic acids
  • Ketones cannot be oxidized further
  • Tests: Tollens’ reagent and Fehling’s solution
• Why can't tertiary alcohols be oxidised?

  No hydrogen atom bonded to carbon with -OH group
• What are the observations during the oxidation of alcohols with potassium dichromate?


  Orange Cr2O7^2- ion reduces to green Cr^3+ ion
• What is the condition when Tollen's reagent or Fehling's solution is added?

  Heat
• What 2 ways are alcohols produced?

  Fermentation of glucose

  Hydration of ethene
• What is the overall equation for fermentation?


  Produces ethanol

  A) Fermentation
• What conditions are required for fermentation?

  • Yeast
  • Anaerobic
  • Temperature 30-40$^{\circ}C$
• What are the advantages and disadvantages of producing ethanol from fermentation?

  Advantages

  • Uses renewable resources (glucose)
  • Uses low level technology + cheap equipment so low costs

  Disadvantages

  • Batch process is slow and high production costs
  • Produces impure ethanol which requires fractional distillation
• Define biofuel

  Fuel produced from plants
• Equations to show no net contribution to CO2 with biofuel

  6CO2 molecules removed from atm during photosynthesis

  2CO2 molecules produced when 1 glucose fermented

  4CO2 molecules produced when 2 ethanol combusted

  A) Photosynthesis

  B) Fermentation

  C) Combustion

  
• What is the overall equation for the hydration of ethene?

  Produces ethanol

  A) Hydration

  
• What are the conditions for the hydration of ethene?

  • High temperature 300$^{\circ}$C
  • High pressure 70 atm
  • Strong acidic catalyst of conc H3PO4
• What are the advantages and disadvantages of producing ethanol from hydration?

  Advantages

  • Continuous process
  • Faster rate of reaction
  • Purer ethanol product

  Disadvantages

  • Uses non-renewable resources (crude oil)
  • High tech equipment
  • High energy costs for pumping high pressures required
• Mechanism for hydration of ethene

  Elimination

  A) Arrow 1

  B) Catalyst

  C) Nucleophile

  D) Arrow 2

  E) Arrow 3

  F) Catalyst

  G) Carbocation 2

  H) Carbocation 1

  
• Mechanism for dehydration of alcohols

  Elimination

  A) Catalyst

  B) Arrow 1

  C) Arrow 2

  D) Arrow 3

  
• What are the reagents and conditions for oxidising primary alcohols?

  Reagents:

  • Potassium dichromate K2Cr2O7 and dilute sulfuric acid H2SO4

  Conditions:

  • Partial oxidation: warm gently, distill aldehyde (lower bp)
  • Full oxidation: excess dichromate, heat under reflux
• What are the reagents and conditions for dehydrating alcohols?

  Reagents: Concentrated sulfuric or phosphoric acid (H2SO4 or H3PO4)

  Conditions: Heat under reflux, need H on adjacent carbon