alcohols (3.3.5)
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how are alcohols classified?
as primary, secondary or tertiary
what is the key feature of primary alcohols?
they have 2 or 3 H atoms bonded to the C atom with the OH group attached
what is the key feature of secondary alcohols?
they have 1 H atom bonded to the C atom with the OH group attached
what is the key feature of tertiary alcohols?
they have 0 H atoms bonded to the C atom with the OH group attached
what are the rules to remember when naming alcohols?
• the OH group takes priority • if there are two or more OH groups, you add an e to the name for the number of C atoms eg. butane-2,3-diol
how can an alkene be formed from an alcohol?
by an acid-catalysed elimination reaction
what reagent and conditions are needed to produce an alkene from an alcohol?
• concentrated H2SO4 • high temperature
what can alkenes produced during the elimination of alcohols be used for?
producing addition polymers without using monomers derived from crude oil
what happens to the alcohol during elimination?
• it reacts with the H^+ from the acid catalyst • the OH is removed from the carbon atom along with a hydrogen atom from the adjacent carbon (produced a water molecule) • a double bond forms between the two carbon atoms
how are alcohols produced industrially?
by hydration of alkenes in the prescence of an acid catalyst
what condition are typically used to produce alcohols industrially?
phosphoric acid catalyst, temperature of 300 degrees, pressure of 600 atm
how is ethanol produced industrially?
by the fermentation of glucose, and then the ethanol is separated by fractional distillation
what conditions are used in the fermentation of glucose?
anaerobic conditions (sealed container), temperature of 40 degrees, in solution
why are these conditions used in the fermentation of glucose?
anaerobic conditions - yeast respire anaerobically/prevents oxidation of ethanol 40 degrees - optimum for yeast in solution - allows glucose and enzymes to react
how can ethanol produced industrially by fermentation be used?
as a biofuel
what is a biofuel?
a fuel composed of grown organic matter/from living organisms
why is ethanol produced by fermentation a carbon neutral fuel?
the 6 moles of carbon dioxide given out in the fermentation of glucose and combustion of ethanol is cancelled out by the 6 moles of carbon dioxide absorbed by the plants when they grow CO2 taken in (photosynthesis): 6CO2 + 6H2O -> C6H12O6 + 6O2 CO2 given out (fermentation and combustion): C6H12O6 -> 2 C2H5OH + 2CO2 2C2H5OH + 6O2 -> 4CO2 + 6H2O
why might the suggestion that ethanol produced by fermentation is carbon neutral not be valid?
• the production of the crops which the ethanol is produced from requires processes which release CO2 - fossil fuels are needed to make fertilisers, harvested crops and transport the biofuel • CO2 is also released during combustion to provide a high temperature for the distillation of ethanol
what issues are linked to decision making about biofuel use?
• biofuels are renewable so won’t run out (can grow more crops) • biofuels are more sustainable • switching to biofuels may be problematic as car engines aren’t made to run on ethanol • land which is growing biofuels can’t be used to produce food which may lead to food shortages
what can primary alcohols be oxidised to?
aldehydes, which are further oxidised to carboxylic acids
what can secondary alcohols be oxidised to?
ketones
why aren’t tertiary alcohols easily oxidised?
• with primary and secondary alcohols there is at least 1 H atom bonded to the C atom with the -OH attached • with tertiary alcohols there is no H atom bonded to the C atom with the -OH attached
what is an example of a suitable oxidising agent?
acidified potassium dichromate (VI)
how can an oxidising agent be represented in equations?
[O]