Alcohols L.O: To understand the structure of alcohols and describe some reactions involving alcohols...
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Transcript of Alcohols L.O: To understand the structure of alcohols and describe some reactions involving alcohols...
AlcoholsL.O: To understand the structure of alcohols and describe some reactions involving alcohols
Friday, April 21, 2023
Do you remember making wine in year 8? Alcoholic drinks contain the alcohol
ethanol. The drink is produced by fermenting plant sugars
What is the combustion equation for ethanol?
Why does beer / wine smell and taste of vinegar when it is left out? Ethanol is oxidised into ethanoic acid
by microbes which live in the air
Ethanol can also be oxidised by some oxidising agents like potassium dichromate
Alcohols Alcohols (which are organic compounds as they contain carbon) have an –OH
functional group, with the general formula
CnH2n+1OH
Methanol – CH3OH
Ethanol – C2H5OH
Propanol – C3H7OH
Different alcohols are part of the same homologous series as they have the same general formula
What do you observe when sodium is reacted with waterhttp://www.youtube.com/watch?v=aGaWwnMyKVE
Alcohol As Solvents
Alcohols such as methanol and ethanol can dissolve most compounds that water dissolves but they can also dissolve substances that water cannot, such as oils, fats and hydrocarbons
Ethanol is the solvent for perfumes and aftershaves (it can mix with the oils (giving the smell) and the water)
Methylated spirits (meths) is ethanol with other chemicals added to it – meths are used as paint cleaners and fuels (though they are poisonous to drink so are dyed)
Ethanol
Ethanol is also useful as a fuel – for use in cars and other vehicles, it is usually mixed with petrol
Producing Ethanol – Hydration of Ethene
Ethanol can be produced in 3 major ways. You need to know the advantages and disadvantages of each method
Ethene, which is obtained from crude oil, can be reacted with steam under high temperature and pressure to form pure ethanol.
Ethene + Steam Ethanol
C2H4 + H2O C2H5OHConditions = 300oc, 60-70atmospheres
Advantages•100% atom economy (See 7.1)•95% yield•Produces 96% pure ethanol
Disadvantages•Feedstock is non-renewable.•Ethene must be produced by cracking which requires energy.•Process requires a lot of energy.
Producing Ethanol – Fermentation of Sugar
For thousands of years humans have been producing ethanol by fermentation of sugar. Common feed stocks are maize, corn and sugar cane.
Glucose Ethanol + Carbon Dioxide
C6H12O6 2C2H5OH + 2CO2
Conditions = 25-37oc, 1atmosphere
Advantages•Uses renewable feedstock•Operates at low temperatures and pressures•Carbon neutral fuel source
Disadvantages•Produces impure ethanol•Atom economy is 51%•Still requires fossil fuels for purification•Feed stock needs to be grown which takes land which could be used to grow food instead.
However the product is impure as concentrations higher than 15% denature the enzymes killing the yeast. To purify it distillation is used, which uses energy.
Exam Questions
Method 1 is the least sustainable as it
uses ethene which comes from crude oil
and is not renewable. Methods 2 and 3
use renewable resources which can be
regrown.
Atom economy. A process which
produces less waste is more sustainable.
If waste products can be used elsewhere
the process is more sustainable.
Exam Questions
Sodium fizzes slowly
Sodium fizzes violently on surface of water
No reaction
Ethanol and water both contain O-H groups
so react similarly. However hexane only
contains C-H and C-C bonds so is unreactive.
Exam QuestionsHigh concentrations of ethanol denature the
enzymes in yeast killing it.
Fractional Distillation
The mixture of ethanol and water is
heated. Ethanol has a lower boiling
point than water so evaporates and is
collected first.
Exam Questions
High concentrations of ethanol denature the
enzymes in yeast killing it and the reaction
does not complete. Also other reactions take
place using the glucose.
Exam Questions
At high temperatures the enzymes in the
yeast denature killing it. However at low
temperatures there is little energy for the
reaction to take place and the reaction is too
slow.
Exam Questions
Kerboodle alcohol ‘on your marks’
Ethanol
Ethanol can be manufactured by reacting ethene (from cracking crude oil) with steam –phosphoric acid is used as a catalyst: -
Ethene + Steam Ethanol
C2H4+ H2O C2H5OH
In the reaction ethanol is the only product – the process is continuous as long as ethene and steam are fed into one end of the reaction vessel, ethanol will be produced
These features make it an efficient process, but as ethene is made from crude oil, which is a non-renewable resource, it cannot be replaced once it is used up and it will run out one day
Ethanol & Fermentation
Ethanol can also be made via fermentation – sugar from plant material is converted into ethanol and carbon dioxide…
Enzymes found in single-celled fungi (yeast) are the natural catalysts that can make this process happen (this is a renewable resource): -
C6H12O6 2C2H5OH + 2CO2
More than 90% of the world’s ethanol is made by fermentation