CHEM 2 - Alcohols

Oxidation of alcohols

Fermentation of ethanol

Ethanol via ethene cracking

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  • Created by: Franklin
  • Created on: 19-04-14 10:48

Oxidation of Alcohols - Primary Alcohols

( alcohols are easily oxsidised to aldehydes 

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Oxidation of Alcohols - Secondary Alcohols

( alcohols are oxidised to ketones and no further

Tertiary alcohols are not easily oxidised due to C-C bond instead of C-H being broken

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Ethanol ---> Ethanal or Ethanoic acid?


Use dilute acid and less potassium dicrhromate (IV) than is needed for oxidation to carboxylic acid

  • Use excess alcohol so there isn't enough oxidising agent for further oxidation
  • Ethanol vapourises and distils of as soon as it is formed to prevent further oxidation.


Ethanoic acid

Use concentrated acid and excess dichromate ions to ensure full oxidation

  • Heated under reflux


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Ethanol Production

Alcohols can be used as intermediates in the chemical industry

Ethanol via crude oil

Ethanol is made by reacting ethene (from crude oil - naphtha fraction) with steam using phosphoric acid (H3PO4) as a catalyst

Ethanol via fermentation of sugars

Glucose ---> 2C2H5OH + 2CO2

  • Compromise of 35 degrees is made
  • Air kept out of fermentation vessels to prevent ethanol --> ethanoic acid
  • Ethanol via fermentation is carbon-neutral: 6CO2 in via respiration, 2CO2 out via fermentation and 4CO2 out via combustion

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Tests for aldehydes and ketones

  • Aldehydes and ketones both have a C=O group which is called a carbonyl
  • Aldehydes: RCHO
  • Ketones: RCOR'


Tollens' (silver mirror) test

  • Tollens' reagent (silver nitrate in aqueous ammonia) oxides aldehydes but not ketones. Silver ions are reduced from colourless to metallic if aldehyde

Benedict's test

  • Benedict's reagent contains blue Cu(II) ions which will oxidise aldehydes but not ketones. Blue solution changes to red if aldehyde
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Dehydration of Alcohols

- OH group and a hydrogen from the next carbon is removed from the alcohol.

Elimination in the context of alcohols is always dehydration

  • Alcohol vapour is passed over excess hot sulfuric acid/aluminium oxide
  • Alkene is formed
  • Dehydration of longer-chained alcohols may produce a mixture of alkenes including E-Z isomers
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