Alcohols

• Alcohol basics:

  General formula: C(n)H(2n+1)OH

  Functional group: -OH

  IUPAC naming: prefix-position-ol

  bond angle: ~105°
• Alcohol Classification

  • primary = -OH attached to 1 R group
  • secondary = -OH attached to 2 R groups
  • teritary = -OH attached to 3 R groups
• Alcohol boiling & melting points

  High due to hydrogen bonding
• Solubility of alcohols

  -OH can form H bonds with water

  H bonds with -OH predominate in short chain alcohols

  longer C chain predominates -OH group in longer alcohols & are insoluble in water
• Making ethanol from crude oil: Hydration of ethene

  • alkene + steam -> alcohol
  • 100% atom economy
  • mechanism: electrophilic addition
  • reagent: H2O(g)
  • Conditions: H3PO4 catalyst, 300°C, 60 atm
• Making ethanol by fermentation

  • enzymes in yeast respire anaerobically
  • conditions: anaerobic, yeast enzyme (zymase), 37°C
  • C6H12O6(aq) -> 2C2H5OH(aq) + 2CO2(g)

  Advantages of fermentation

  • uses renewable resources (ethene can come from dehydrating ethanol made from sugar)
  • carbon-neutral

  Disadvantages of fermentation

  • slow batch process
  • uses up land
  • not very pure - fractional distillation needed as ethanol is dissolved in water
• Carbon-neutrality formulae:

  input: photosynthesis -> 6H2O + 6CO2 -> C6H12O6 + 6O2

  output: fermentation -> C6H12O6 -> 2C2H5OH + 2CO2

  combustion -> 2C2H5OH + 6O2 -> 6H2O + 4CO2
• Elimination/Dehydration

  • alcohol -> alkene
  • water molecule eliminated
  • reagent: dehydrating agent/catalyst
  • 1st conditions: excess, hot, concentrated H2SO4 at 170°C(acid-catalyst)
  • 2nd conditions: heated alcohol vapour passed over Al2O3 at 600°C
• Mechanism:

  A) lone pair leaves O & goes to H+

  B) water leaves taking shared bond pair from C-O with it

  C) Carbocation forms & takes electron pair

  
• Halogenoalkane elimination v alcohol elimination

  Halogenoalkanes:

  • alkali reagent
  • no carbocation intermediate
  • 1 step
  • not catalysed

  alcohols:

  • acid reagent
  • carbocation intermediate
  • 2 step
  • catalysed
• Oxidation

  [O] = oxidising reagent

  1° alcohol + [O] -> aldehyde + [O] -> carboxylic acid

  2° alcohol + [O] -> ketone

  3° alcohol -> no reaction (no H bonded to carbon with -OH)

  conditions: heated under reflux

  reflux = process of boiling a liquid so that any vapour is liquified and returned to the stock

  oxidising agent: H+/Cr2O7^2- (dilute sulfuric acid & potassium dichromate)

  • orange -> green once reduced
• Testing for alcohols

  alcohol + carboxylic acid -> ester

  • if alcohol is present -> ester made -> sweet smell made

  differentiating 1° & 2° alcohols from 3° alcohols

  • can use H+/Cr2O7 (reflux)
  • 1° & 2° alcohols - orange -> green
  • 3° alcohol - stays orange (no reaction)
• Testing for aldehydes v ketones

  Tollen's reagent

  • if aldehyde present -> silver mirror made
  • if ketone present -> no reaction
  • reagent gently oxidises the aldehyde

  Fehling's test

  • if aldehyde is present -> blue to brick red precipitate
  • if ketone present -> no observable reaction
• Oxidation formulae

  A) primary

  B) alcohol

  C) aldehyde

  D) carboxylic acid

  E) secondary

  F) alcohol

  G) ketone

  H) teriary

  I) alcohol

  J) no reaction

  
• aldehyde -> carboxylic acid || 2° alcohol -> ketone

  A) condenser

  B) cold water in

  C) water out

  D) acidified potassium dichromate (in excess)

  E) heat

  F) anti-bumping granuales

  G) NO GAPS & OPEN TOP

  
• 1° alcohol -> aldehyde

  under reflux & distillation

  A) condenser

  B) cold water in

  C) water out

  D) thermometer

  E) heat

  F) acidified potassium dichromate (NOT in excess)

  G) beaker

  H) anti-bumping granuales

  
• Required Practical 5 - Dehydration of cyclohexanol (elimination) pt1


  1. Measure volume of cyclohexanol & add to weighed pear-shaped flask & reweigh

  2. Add around 8.0cm of concentrated H3PO4 or H2SO4 (specific vol) & add anti-bumping granuales

  3. Heat gently & distill any liquid which boils below 100°C

  4. Pour distillate into separating funnel & add saturated sodium chloride or sodium carbonate to neutralise remaining H3PO4. Shake to separate mixture into 2 layers.
• Required practical 5 - Dehydration of cyclohexanol pt 2

  5. Run off the lower layer & transfer top layer to conical flask

  6. Add anhydrous calcium chloride to remove water from the cyclohexene. Shake & leave to rest until it becomes clear.

  - anhydrous calcium chloride doesn't react with cyclohexene

  7. Decant liquid into clean, dry sample container. Reweigh & calculate mass of cyclohexene.

  8. Test distillate using bromine water