organic chem - alcohols Flashcards
(46 cards)
alcohols
functional group
name
general formula
-O-H
-ol
Cn H2n+1 OH
What are the two main methods of forming alcohols?
- hydration of ethene
- fermentation
hydration of ethene
produces alcohols from alkenes in the presence of an acid catalyst. usually conc. sulphuric acid, H2SO4/ phosphoric acid H3PO4 under aq conditions. high temp and pressure
why is the hydration of ethene a favourable industrial process
very high percentage yield as ethanol is the only product
disadvantages of the hydration of ethene?
- expensive due to high temp and pressure
- source of ethene is crude oil
what happens in the fermentation process?
enzymes break down starch form crops into sugars which are fermented to form alcohol. its a cheaper method as it down in low temp (30 degrees), in anaerobic conditions with yeast
why is fermentation not favoured as a process
its made in batches so its slower and has a lower % yield, and produces CO2
why is ethanol (common biofuel) said to be carbon neutral?
carbon given out when its burned is equal to the carbon taken in by the crops during this process
What molecules are alcohols
Polar molecules due to polar O-H bond
The effect of the chain on the polarity of an alcohol
The longer the carbon chain the less polar it becomes
The boiling point for alcohols
The O-H allows for hydrogen bonding. The boiling point for alcohols are significantly higher than the respective alkane and alkene
does the place where O-H group is affect the alcohols properties?
yes, the physical properties and reactions can be affected
what are the classifications of alcohols?
primary alcohol
secondary alcohol
tertiary alcohol
reaction of alcohols
dehydration
its a type of reaction not a mechanism, that form’s alkenes through the loss of H20
what is the mechanism for dehydration of alcohols and their conditions?
elimination
- high temp and pressure
- excess concentrated acid catalyst (H2SO4)
- aluminium oxide added
oxidation of alcohols
in the presence of an oxidising agent, we can form new functional groups from alcohols
what happens when you distil a primary alcohol in an oxidation reaction?
forms an aldehyde
- al
CO=H
what happens when you distil and reflux a primary alcohol in an oxidation reaction?
forms a carboxylic acid
- oic acid
CO=OH
what happens when you reflux a secondary alcohol in an oxidation reaction?
forms a ketone
- one
CO=
what happens when with a tertiary alcohol in an oxidation reaction?
no reaction
resistant to oxidation
most common oxidising agent
acidified potassium dichromate K2Cr2O7
starting and ending colour of K2Cr2O7
start (Cr2O72-) - orange
end (Cr3+) - green
gains 3 electrons so its being reduced
order of boiling points:
- propanal
- propanone
- propanoic acid
propanoic acid is the highest as hydrogen bonding is possible
propanone
propanal
which can be oxidised aldehydes or ketones?
aldehydes
