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2012-01-17 11:55:35
Chemistry Alcohols halogenoalkanes analysis

alcohols, halogenoalkanes and analysis
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  1. Making alcohol: Fermentation
    • catalysed by an enzyme in yeast (zymase)
    • 37C
    • anaerobic
    • concentration of 14% alcohol by volume
  2. Making alcohol: Hydration of ethene
    • catalyst: phosphoric acid
    • high temperature: 300C
    • 60 atm
    • uses steam
    • 95% conversion
    • unreacted gases are recycled and passed through the reactor again
  3. Uses of alcohols
    • Methanol: clean burning fuel, feedstock, can be converted into methanal and ethanoic acid
    • Ethanol: drink, perfumes, cleaning fluids, fuel
  4. Properties of alcohols
    • Water solubility: hydrogen bonds form between the polar -OH groups of alcohol and water molecules
    • Volatility and boiling points: high melting and boiling points, low volatility because of hydrogen bonds
  5. Primary alcohol
    • -OH group attached to C bonded to no or one alkyl group
  6. Secondary alcohol
    • -OH group attached to a C bonded to two alkyl groups
  7. Tertiary alcohol
    • -OH group is attached to a C bonded to three alkyl groups
  8. Combustion of alcohols
    • Alcohols burn completely to form carbon dioxide and water
  9. Oxidation of primary alcohols
    • Distil: form an aldehyde, catalyst is acidified potassium dichromate solution (K2Cr2O7/H2SO4)
    • Reflux: form a carboxylic acid, same catalyst
    • Solution turns from orange to green
  10. Oxidation of secondary alcohols
    • Heat: form a ketone, catalyst is acidified potassium dichromate (K2Cr2O7/H2SO4)
  11. Oxidation of tertiary alcohols
    • resistant to oxidation
    • oxdidating agents remains orange
  12. Esterifaction of alcohols
    • alcohol is warmed with a carboxylic acid
    • acid catalyst: usually concentrated sulfuric acid
    • an ester and water is produced
  13. Dehydration of an alcohol
    • form an alkene
    • heating under reflux
    • phosphoric acid catalyst present
  14. Halogenoalkanes
    • general formula: CnH2n+1X (X is the halogen)
    • fluoro- F
    • chloro- Cl
    • bromo- Br
    • iodo- I
  15. Uses of halogenoalkanes
    • refridgerants
    • aerosol propellants
    • dry-cleaning solvents
  16. Halogenoalkanes- carbon-halogen bond
    • Polar: halogen atoms are more electronegative than carbon atoms, bonded electron pair is attracted more towards the halogen atom
    • polarity decreases down the halogen group- electronegativity decreases
    • electron-deficient carbon atom attracts nucleophiles
  17. Nucleophile
    electron pair donor
  18. Hydrolysis of halogenoalkanes
    a nucleophilic substitution reaction: a nucleophile is attracted to an electron-deficient centre or atom where it donates a pair of electrons to form a new covalent bond
  19. Hydrolysis of a primary halogenoalkane
    • reaction with hot aqueous acid
    • the halogen atom is replaced by a hydroxide ion
  20. Rates of primary halogenoalkane hydrolysis
    • Polarity: C-F bond is the most polar amongst the halogenoalkanes, so the carbon atom should attract the nucleophile most readily and give the fastest reaction...
    • But...
    • Bond enthalpy is more important the polarity
    • Bond enthalpy: C-I bond is the weakest so is broken more easily, so has a faster reaction . As the rate of raction increases, the bond enthalpy weakens
  21. Experiment to show rate of hydrolysis
    heating halogenoalkane with aqueous silver nitrate with ethanol added
  22. Chloroethene in the production of PVC
    • Uses: drainpipes, plastic window frames, sports equipment, toys, packaging
    • polymerisation of chloroethene
  23. Tetrafluoroethene in the production of PTFE
    • Uses: coating pans, nail polish
    • polymerisation of tetrafluoroethene
  24. CFC's
    • They were first developed, because refrigeration gases at the time were toxic. CFC replaced these gases as it was non-toxic and unreactive.
    • CFC's remain stable until they reach the stratosphere, where hey break down in the presence of UV radiation to form chlorine radicals. These radicals catalyse the breakdown of the ozone layer
  25. Percentage yield
    • Yield can be moles or mass
  26. Atom economy
    • Benefits of high atom economy: reduced amount of waste products
    • Addition reactions: 100% atom economy, no waste products
    • Substitution reactions: waste products, less efficient
    • Some reactions have a high percentage yield but low atom economy
  27. Infrared spectroscopy
    • absorption of infrared radiation causes covalent bond to vibrate (stretching or bending motion)
    • breathalysers: measure ethnol levels by using infrared spectroscopy
  28. Mass spectrometry
    • Early developments: used to determine the mass-to-charge ratios of ions
    • Uses: to identify unknown compounds, to determine the abundance of each isotope in an element, to gain further information abou the structure and chemical properties of molecules
  29. Reaction mechanism: radical substitution
    • UV radiation provides the energy to break the covalent bond
    • Bonds break by homolytic fission
  30. Reaction mechanism: electrophilic addition
  31. Reaction mechanism: nucleophilic substitution