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)
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 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 (addition of water) 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 and oxyegn would cause the ethanol to be oxidised to ethanal
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 (acid catalysed) eliminate alcohols to?
alkenes
what are the reagents and conditions for elimination of alcohols?
concentrated sulfuric acid or phosphoric acid, heat (under refluc)
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) (it is acidified with dilute sulfuric acid)
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
what is the apparatus needed to oxidise primary alcohols to aldehydes?
simple distillation to produce an aldehyde
anti-bumping granules in flask
what do anti-bumping granules do?
prevent the formation of large bubbles forming that result in violent boiling
what is the apparatus needed to oxidise primary alcohols to carboxylic acids?
reflux as the boiling point of carboxylic acids is much higher than due to hydrogen bonding
anti-bumping granules
how we do test for an aldehyde?
-tollens reagent (silver mirror test) it is a colourless solution containing Ag+ ions
-fehling’s solution, it is a blue solution of copper (II) ions
both are weak oxidising agents
describe how to use tollens reagent to test for an aldehyde?
put 2 cm3 silver nitrate in a test tube. add a few drops NaOH to form a brown precipitate. Add dilute NH3 to dissolve precipitate. warm this with the unknown
what is a positive test with tollens?
a silver mirror forms and a carboxylic acid has been made from the aldehyde
describe how to use fehling’s solution to test for an aldehyde?
add 2cm3 of fehlings to unknown and warm in water bath
what is a positive test with fehlings?
a brick red precipitate forms due to Cu2O and a carboxylic acid has been produced from an aldehyde
how do we test for carboxylic acids using tollens and fehlings?
tollens and fehlings give a negative result
how do we test for carboxylic acids?
sodium carbonate (Na2CO3) or sodium hydrogen carbonate (NaHCO3)
produces CO2 gas which we bubble through limewater and observe a milky white emulsion (fizzing/ bubbling)
what are the products of testing for a carboxylic acid?
carbon dioxide, salt and water
why is there no test for ketones?
can’t be oxidised further
how do we test for an alcohol?
react with sodium to produce a salt and hydrogen
observation; fizzing
what are the bond angles in alcohols and why?
all the H-C-H bonds and C-C-O bonds are 109.5 (tetrahedral), because there are 4 bonding pairs of electrons repelling to a position of minimum repulsion
the H-O-C bond is 104.5 because there are 2 bonding pairs of electrons and 2 lone pairs repelling to a position of minimum repulsion. Lone pairs repel more than bond pairs so bond angle reduced.
in distillation, what can be done to increase yield of distillate?
only collect the distillate at the desired b.p. of the aldehyde and not higher
collection glass can be cooled in ice
what is reflux used for?
when heating organic reaction mixtures for long periods of time. the condenser prevents organic vapours from escaping by condensing them ack to liquids.
why is the end of the condenser never sealed in reflux?
build up of gas pressure could cause apparatus to explode
what is a good thing about producing alkenes from alcohols?
provides a possible use to polymers without using monomers derived from oil
What is a general equation for the oxidation of primary alcohols?
RCH2OH + [O] ——-> RCHO + H2O
