alcohols Flashcards
what is the general formula for the alcohol homologous group?
CnH2n + 1OH
explain the difference between primary, tertiary and secondary alcohols
depends on which carbon atom the OH group is bonded to
explain the naming with more than one OH group
2 - diol
3 - triol etc
does a carboxylic acid take precedence over alcohols in naming
yes use the prefix hydroxy
what is the equation for fermentation
C6H12O6 → 2C2H5OH + CO2
what are the conditions for fermentation
yeast (biological catalyst)
anaerobic (without oxygen)
30-40 degrees
aqueous
when the solution reaches about 15% ethanol the yeast dies, fractional distillation to increase the concentration
what is the equation for the steam hydration of ethene
CH2=CH2 (g) + H2O (g) ⇔ C2H5OH
what are the conditions for steam hydration of ethene?
solid phosphoric acid catalyst (H3PO4)
300 degrees and 60 atm
at the moment most industrial ethanol is produced by steam hydration of ethene
yield is low - 5%, however as it is a reversible reaction so can reuse unreacted ethene gas making the yield 95%
compare the two methods of producing alcohols
fermentation
rate: slow
quality: impure + low yield
raw material: sugars (renewable)
process: batch process, expensive on manpower but cheap equipment
hydration of ethene:
rate: fast
quality: pure + high yield
raw material: ethene, crude oil and is finite
process: continuous process, not much manpower but expensive equipment
show the mechanism for making ethanol from ethene
explain how ethanol can be used as a biofuel
ethanol burns to give carbon dioxide and water and can be used as a fuel in its own right or in mixtures with petrol (gasoline) to produce ‘gasohol’ containing 10-20% ethanol
the equation for the combustion of ethanol is
C2H5OH + 3O2 → 2CO2 + 3H2O
why is using ethanol as a biofuel a good idea?
as it can be produced by fermentation it can be useful for countries without an oil industry
eg. `brazil, sugars from sugar canes are fermented to produce alcohol which is added to petrol to produce biofuel (fuel produced from a renewable biological resource)
how is ethanol thought to be a carbon-neutral fuel
carbo neutral = an activity that has no net annual carbon emissions to the atmosphere
photosynthesis : 6CO2 + 6H2O → 6O2 + C6H12O6
fermentation: C6H12O6 → 2C2H5OH + 2CO2
combustion: C2H5OH + 6O2 → 6H2O + 4CO2
there is no net gain of carbon dioxide
however may not be carbon neutral due to:
transport, harvesting crops and fertilisers
explain what primary, secondary and tertiary alcohols can be oxidised into
primary → aldehyde → carboxylic acid
secondary → ketone
tertiary → X
what is a carbonyl compound
anything containing a C=O
the general formula of CnH2nO
includes aldehydes and ketones
what is an aldehyde
have the suffix ‘-al’ and the function group is always on C1
what is a ketone
the suffix -one and function group position must be stated for ketones with 4 or more carbons
what is a carboxylic acid
have a function group COOh at the end of their carbon chain
the suffix - oic acid
explain the oxidation of primary alcohols to aldehydes
first oxidised to an aldehyde then further to a carboxylic acid
oxidising agent : [O] = H+/K2Cr2O7 ( acidified potassium dichromate VI)
conditions: distillation, aldehyde boils off as BP is lower than that of alcohols to prevent further oxidation
C2H5OH + [O] (orange) → CH3CHO + H2O (ethanal green)
explain the oxidation of primary alcohols to carboxylic acids
to produce carboxylic they must be vigorously oxidised
C2H5OH + 2[O] (XS) →CH3COOH + H2O
conditions: reflux, reflux allows the temp to be increased without losing volatile solvents + reactants or products, air can escape at the top or would be a closed system and would explode
explain the oxidation of secondary alcohols
refluxing secondary alcohol with acidified dichromate(VI) will produce a ketone
ketones can’t be oxidised easily so even prolonged refluxing won’t produce anything more
explain the oxidation of tertiary alcohols
don’t react with acidified potassium dichromate (IV) at all and the solution stays orange
the only way to oxidise is burning
explain the testing for aldehydes and ketones
they can be distinguished using oxidising agents as aldehydes are oxidised easily but ketones aren’t
can be distinguished using Tollen’s reagent or Fehling’s solution - two mild oxidising agents
a positive test indicates the presence of an aldehyde
Tollen’s reagent: [Ag(NH3)2]4 ammoniacal silver nitrate
-with an aldehyde, you get the silver mirror effect, the aldehyde is oxidised to a carbox and the colourless silver ions are reduced to silver and coats the test tube
Fehling’s solution
Blue solution containing Cu2+
aldehyde = brick red precip and decolourise the solution, Cu2+ reduced as aldehyde is oxidised
explain dehydration of ethanol
ethene can be made by eliminating water from ethanol by a dehydration reaction
CH3CH2OH → C2H4 + H2O
conditions: reflux + conc. sulfuric acid catalyst or 600 k and Al2O3 catalyst
the reaction happens in two stages:
1) CH3CH2OH + H2SO4 → CH3CH2OSO2OH + H2O
2) CH3CH2OSO2OH → CH2=CH2 + H2SO4
The sulfuric acid is regenerated and chemically unchanged at the end of the reaction so is a catalyst
explain the processes of producing alkenes from renewable resources
plants → glucose → ethanol → ethene
(extract) (fermentate) (eliminate)
show the mechanism of dehydration of ethanol
what must be remembered with dehydration of longer chain or branched alcohols
may produce a mixture of alkenes including ones with Z and E isomers
