organic chem - alcohols Flashcards
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
reactions of aldehydes
fehling’s test
tollens reagent
what is fehlings test?
contains a weak oxidising agent that can oxidise aldehydes, heated
result for al - blue solution to an orange precipitate
result for one - remains blue
what is the silver mirror test using tollens reagent
produces ammonia, warmed gently
result for al - colourless solution to silver/ black precipitate
result for one - stays colourless
tests for carboxylic acids
- indicator to test pH (r pH meter)
- add alcohol and acid catalyst
- add a solid carbonate/ hydrogen carbonate
the addition of alcohol and acid catalyst to test for a carboxylic acid
result = fruity smell due to ester formation
the addition of a solid carbonate/ hydrogen carbonate to test for a carboxylic acid
observation = fizzing/ gas produced/ bubbling
result for ketone = nothing
what is high resolution mass spectrometry?
is able to measure Mr to more decimal places (4 or 5).at this resolution, molecules with the ‘same Mr’ to 1dp can be distinguished, more sensitive
what is infra-red spectroscopy?
IR spectroscopy is a useful analytical technique used to identify functional groups in a molecule
how does IR spectroscopy work?
bonds vibrate and can absorb IR radiation to get ‘excited’. different functional groups absorb different wavelengths of this radiation
transmission % on 2250
single bonds
C - H
C- N
N - H
O - H
transmission % on 2000
Triple bonds
C =- N
transmission % on 1500
double bonds
C =C
C = O
transmission % on less than 1500
fingerprint region
completely unique for a molecule
shapes of alcohols on a IR spectroscopy
U -shaped curves
shapes of carboxylic acids on a IR spectroscopy
wide V -shaped curves
what is the purpose of small glass beads in the round-bottomed flask
to prevent bumping
why is it important to open the tap of the separating funnel
avoid pressure build up
Fractional distillation of ethanol
- turn on water
- heat flask, with a Bunsen burner
- causes water & ethanol vapours to be produced
- vapour pass up the fractionating column
- water & ethanol are separated in it
- water condenses back in the fractionating column
- observe the thermometer to keep the temp at or below the boiling point of ethanol
- use the condenser to cool the vapour and condense the ethanol back into a liquid
What is global warming
absorption occurs in atmosphere with molecules,e.g. ozone, heat is trapped within the earths atmosphere. when CFCs are released, this heating effect is enhanced leading to global warming
How are addition polymers produced
from fermentation without the need for crude oil. produces the primary alcohol, which is dehydrated to produce an alkene, which is using a production of addition polymers
Suggest why sodium carbonate solution was used to wash the distillate
Neutralise acid
Give a property of anhydrous calcium chloride, other than its ability to absorb water, that makes it suitable as a drying agent in this preparation
Does not dissolve with the cyclohexene
