alcohols Flashcards
what is the general formula for alcohols?
Cn H2n+2 O
what is the functional group of alcohols?
R-OH
what can we classify alcohols as?
primary secondary or tertiary
what are functional group isomers of alcohols?
ethers (hydrogen from R-OH replaced with another R group)
what is hydrolysis?
breaking a bond using water
what are the three mechanisms of making alcohols?
-hydrolysis of organic hydrogensulfates
-nucleophilic substitution
-electrophilic addition (steam hydration of ethene)
what is hydrolysis?
breaking of a bond using water
how do we get alcohols from organic hydrogensulfates?
they are easily hydrolysed so hydrolyse using warm water to form alcohols
what is regenerated at the end of hydrolysis of organic hydrogensulfates and what does this act as?
sulfuric acid (H2SO4) so it acts as a catalyst
what are the 3 uses of alcohols?
-alcoholic drinks
-solvents
-chemical feedstock (used to make other chemicals)
what do we do to alkenes to make them alkanes?
hydrogenation (adding hydrogen)
what is hydrogenation?
when hydrogen is added across a C=C bond, an alkane is produced
what catalyst is used in hydrogenation of alkenes?
nickel
give an example of why hydrogenation of alkenes is an important industrial process?
margarine is produced by the hydrogenation of fats or oils which contain C=C bonds
what kind of boiling points do alcohols usually have and why?
high because they form hydrogen bonds with each other
why are only some alcohols soluble?
ones with a lower Mr are soluble in water because they can form hydrogen bonds with water
what are the conditions for making an alcohol via nucleophilic substitution?
aqueous sodium hydroxide, warm
what reaction is used in industry to produce ethanol and what mechanism does it use?
steam hydration of ethene
electrophilic addition
what are the conditions for steam hydration of ethene?
steam (300 degrees), pressure of 60atm and phosphoric acid catalyst (H3PO4)
what type of reaction is steam hydration of ethene and what does this mean for the yield?
it is reversible and the yield is very low
how is yield improved by steam hydration of ethene?
any unreacted ethene gas can be recycled and increases the overall yield
what are some advantages of using steam hydration of ethene?
-product is pure (No waste product including CO2)
-we can manipulate the reversible reaction to increase yield
-higher temperature, therefore, fast rate of reaction
-can recycle unused reactants such as ethene gas.
what are some disadvantages of steam hydration of ethene?
-reversible reaction so not 100% yield
-ethene is from crude oil contributing to environmental pollution. Thermal cracking of crude oil requires energy.
-higher temps required so higher energy consumption
what is the alternative industrial method for making alcohols that doesn’t use a mechanism?
fermentation
what are the reagents of fermentation?
yeast and glucose (C6H1206)
what are the conditions for fermentation?
30-40 degrees, aqueous, anaerobic
what is the role of yeast in fermentation?
catalyst
why is it important that fermentation occurs in anaerobic conditions?
yeast won’t ferment in oxygen
why do we use 30-40 degree temperatures for fermentation?
compromise because too high temp causes yeast to denature and not ferment
what is the equation for fermentation?
C6H1206 (aq) ——–> 2 C2H5OH (aq) + 2 CO2 (g)
when does fermentation stop and what do we do once it has stopped?
when the reaction mixture contains 15% ethanol
we use simple distillation
during simple distillation, where does water go in and out of the condenser?
in at bottom out at top
what is the type of alcohol we make during fermentation and what does this term mean?
biofuel
biofuel is fuel that is derived from biomass- that is, plant, algae material or animal waste
what do some people argue about fermentation and the production of bioethanol that is not true?
that it is carbon-neutral
what does carbon-neutral mean?
uses the same amount of CO2 from the atmosphere in its production as is released into the atmosphere when used
what can we give in support of why fermentation is supposedly carbon neutral?
3 equations
photosynthesis of glucose
6 CO2 + 6 H2O ——-> 6O2 + C6H12O6
fermentation of glucose
C6H12O6 ——–> 2 C2H5OH +2 CO2
combustion of ethanol
2 C2H5OH + 2 O2 ——–> 4 CO2 + 6 H2O
total = 0 CO2 released
why is fermentation not carbon neutral? (3)
-we produce NH3 (ammonia to use for plant fertiliser) which uses a lot of energy and releases CO2
-transport of plants and processing plants requires combustion of fuel which releases CO2
-processing of plants requires energy.
what can we eliminate alcohols to?
alkenes
what are the reagents and conditions for elimination of alcohols?
concentrated sulfuric acid, heat
what is removed and formed during elimination of alcohols?
OH removed
H atom on an adjacent carbon removed
double bond formed between two C atoms
why is elimination of alcohols useful?
can get alkenes without needing to obtain alkenes from fractional distillation followed by thermal cracking.
these alkenes can be used to make polymers
in future it may become more economical to produce ethene from ethanol made by fermentation
what is oxidation and reduction in terms of alcohols?
oxidation : gain of oxygen and loss of H atoms (electrons)
reduction: loss of oxygen and gain of H atoms (electrons)
what can alcohols be oxidised by doing?
oxidising agents such as acidified potassium dichromate (VI)
what do oxidising agents do?
cause something (alcohol) to gain an oxygen but loses one itself
in other words; oxidises something but itself is reduced
what colour change do we observe when acidified potassium dichromate (VI) acts as an oxidising agent?
orange to green
what does the type of organic product obtained via oxidation of an alcohol depend on?
the structure of the alcohol used
what are possible oxidation products of primary, secondary and tertiary alcohols?
primary: aldehyde or carboxylic acid
secondary: ketone
tertiary: NOT OXIDISED as no hydrogen atoms on C with OH
