AS CHEM2 - Alcohols

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  • Created on: 20-06-11 21:15
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Alcohols
1. General
Functional group is OH
General formula is CnH2n+1OH
2. Industrial Production of Ethanol
Feedstock = starting material in an industrial process i.e. glucose or ethene here
a) Fermentation of Glucose
Slow reaction, batch process, uses renewable resources.
Requires enzyme from yeast (zymase), temperature 3540 C, no air (anaerobic).
C6H12O6 2C2H5OH + 2CO2
b) Hydration of Ethene
Fast reaction, continuous process, uses nonrenewable resources.
Requires phosphoric acid catalyst (H3PO4), temperature 300 C, pressure 6.5 Mpa
CH2=CH2 + H2O C2H5OH
c) Comparison
Glucose is produced from plants, which are a renewable resource as they only take a few months to grow
Ethene is produced from crude oil, which is a nonrenewable resource that takes millions of years to form
d) Carbon neutrality
Ethanol produced by fermentation is a biofuel i.e. it is produced from biological sources (sugar in this case)
Carbon neutral refers to activities that have no net annual carbon emissions to the atmosphere
Biofuels are not carbon neutral because it requires energy to grow the crops and convert them into fuel
3. Classifying Alcohols
Classified according to the number of carbons attached to COH
Primary alcohols have 1 carbon attached e.g. ethanol
Secondary alcohols have 2 carbons attached e.g. propan2ol
Tertiary alcohols have 3 carbons attached e.g. 2methylpropan2ol
Primary 1 Secondary 2 Tertiary 3
4. Reactions of Alcohols

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Combustion
Example C2H5OH + 3O2 2CO2 + 3H2O
Balance C's then H's then O's
Don't forget the O in the OH when balancing
b) Elimination of water to form an alkene
Example C2H5OH CH2=CH2 + H2O
Done either with hot, concentrated sulphuric acid or hot pumice (Al2O3)
This method of making ethene provides a possible route to polymers without using monomers derived from oil
(cracking of petroleum fractions).…read more

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Distinguishing between aldehydes and ketones
Aldehydes react with mild oxidising agents such as Tollens' reagent and Fehling's solution
Ketones do not react with Tollens' and Fehling's because they are not easily oxidised
Tollen's reagent is ammoniacal silver nitrate. The compound to be tested is warmed with Tollen's reagent
With Tollens' aldehydes produce a silver mirror
Fehling's contains a blue copper (II) complex.…read more

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