chapter 15 - alcohols Flashcards
what’s a primary alcohol?
1 R group/ 2 hydrogen groups attached onto the carbon with the hydroxide group.
what’s a secondary alcohol
2 R groups / 1 hydrogen group attached onto the carbon with an alcohol on.
what’s a tertiary alcohol
where there are 3 R groups and no hydrogen groups attached to the carbon with the hydroxide group
what’s an aldehyde
a C=O at the end of a carbon chain
name it by (al) eg methanal, pentanal
what’s a ketone
C=O in the middle of a carbon chain
name it by stating where the C=O is. eg propanone, pentan-2-one
what’s a carboxylic acid
a COOH group at the end of a carbon chain
eg, ethanoic acid, 2-methylpropanoic acid.
what is hydration overall
a way ethanol is produced
hydration of ethene in the presence of an acid catalyst
what is fermentation overall
a way of producing ethanol
fermentation of a wide variety of plant materials
uses of ethanol
- as a solvent
- in cosmetics
- used in the manufacture of ethyl ethanoate and other esters
- in the production of ethoxyethane
- as a motor fuel blending agent
what is hydration in producing ethanol. in detail
hydration of ethene
C2H4(g) + H2O(g) = C2H5OH(g)
fractional distillation is used
catalyst (concentrated H3PO4 or concentrated H2SO4)
temperature = 300 degrees celsius
pressure = 65 atm
fast process. takes seconds
continuous process
high equipment costs and energy costs. low labour costs
fermentation to produce ethanol in detail
C6H12O6(aq) = 2CH3CH2OH(aq)+ 2CO2(aq)
catalysed by enzymes found in yeast, enzymes operate best around 37 degrees and normal atmospheric pressure.
oxygen free (anerobic process)
the maximum yield of ethanol that any one batch can achieve is around 15%. this is because at higher concs the enzymes are poisoned. to increase the concentration of ethanol solution obtained, it must be distilled.
the process is long. takes days
batch process
What are the advantages of hydration
It is a continuous process
It’s produces a purer product which requires less refinement
What are the disadvantages of hydration
ethene is non-renewable. It’s comes from crude oil
What are the advantages of fermentation
Sugar is renewable. Uses renewable resources
The equipment is cheap. Lower equipment costs as there are low temperatures
What are the disadvantages of fermentation
it is a batch process. Which is relatively slow
ethanol needs distilling As it is not pure. Costs more money to process it
What is the difference between a continuous process and a batch process
A continuous process is a flow of product between every step of the process with no breaks.
A batch process involves a sequence of steps in a specific order which have to be repeated over and over
Oxidation of alcohols overall
primary alcohols = aldehydes = carboxylic acids
secondary alcohols = ketones
tertiary alcohols cannot be oxidised
is ethanol as a biofuel (produced by fermentation) carbon neutral?
During photosynthesis six carbon dioxide molecules are taken in
6CO2+6H2O=C6H12O6+6O2
During fermentation and combustion six molecules of carbon dioxide are released
C6H12O6=2C2H5OH+2CO2
2C2H5OH+6O2=4CO2+6H2O
Therefore there is no net release of carbon dioxide in theory
However this does not take into account transport, and machinery Which produces carbon dioxide blah blah blah blah blah and then
Oxidation of primary alcohols into aldehydes
Example: ethanol
condensed equation:
CH3CH2OH+(O)= CH3CHO+H2O
Conditions: the alcohol is in excess. oxidising agent added in drops. Has to occur via distillation as this will prevent further oxidation
Oxidising agent: acidified potassium dichromate (K2Cr2O7)
Colour change: orange solution to green solution
product:ethanal.
Oxidation of primary alcohols to carboxylic acids
eg:ethanol
Condensed equation:
CH3CH2OH+2(O)= CH3COOH+H2O
oxidising agent:(O) Acidified potassium dichromate (VI)
Conditions: heat on the reflux then distill the product.
Colour change: orange solution to green solution
oxidation of secondary alcohols to ketones
Eg:propan-2-ol
Condensed equation:
CH3CH(OH)CH3+(O)=CH3C(O)CH3+H2O
Oxidising agent: acidified potassium dichromate
Conditions: heat on the reflux for completion
Colour change: Orange solution to green solution
Oxidation of Tertiary alcohols
Tertiary alcohols cannot be oxidised at all, oxidation is not possible. This difference in chemical behaviour can be used to distinguish between tertiary alcohols and primary/secondary alcohols.
What colour change would occur if a primary or secondary alcohol was heated with acidified potassium dichromate solution.
You would see a colour change from an orange solution to a green solution
What colour change would occur if a tertiary alcohol was heated with acidified potassium dichromate solution
No reaction occurs, therefore the colour of the solution will remain orange and there will be no visible change.
A test to distinguish between aldehydes and ketones is heating with fehlings solution. What would the observation with an aldehyde be versus a ketone.
Observation with an Aldehyde- from a blue solution to a brick red Precipitate
Observation with the Ketone-The solution will remain blue
Another test to distinguish between aldehydes and ketones is to heat with Tollens reagent. What would the observations be with an aldehyde versus a ketone
Observation with an aldehyde-the solution will turn from a colourless solution to a silver mirror.
Observation with a ketone-The solution will remain colourless and there will be no visible change
Describe in detail normal distillation (distillation)
This process is used to separate organic compounds and to prevent an organic reaction to going to completion.
For example to obtain a pure sample of a Ketone/oxidising a primary alcohol into an aldehyde.
The reactants are heated gently to the boiling point of the desired products. This desired product vaporises while the others remain in the pear-shaped flask.
- Anti-bumping granules (prevent rigourous bubbling/large bubbles forming)
- Water goes in at the bottom/lowest point
- One of the reactants or oxidising agent is added drop wise through the dropping funnel
- The thermometer measures the temperature of the vapours
- The distillate is collected in a conical flask that is sat in an ice bath to keep it as a liquid and stop the product from evaporating.
Describe in detail fractional distillation
It allows substances to vaporise when heated, the fractionating column is not at the bottom and it is cooler further up.
- As the vapours rise up the fractionating column the different substances drop below their boiling point I’m temporarily collected at a particular level.
- The fraction with the lowest boiling point reaches the top, here it’s condensers, and runs down the condenser.
- The fraction is removed, and a separate flask/beaker is put at the end of the condenser. The temperature is then increased allowing collection of the next fraction to occur.
- This is repeated until all fractions are collected.
