Alkenes and alcohols in industry, and addition polymerisation Flashcards
What are the two ways that ethanol is produced?
-direct hydration
-fermentation
What is a continuous industrial process?
one in which more reactants are added as the products are removed
Why would we do a direct hydration?
alkenes undergo a direct hydration (an addition reaction) with water in the presence of an acid catalyst to form an alcohol
What are the reactions conditions for a direct hydration?
-steam
-300C
-65 atmospheres
-concentrated phosphoric acid catalyst (H3PO4)
What are the advantages of direct hydration?
-fast reaction
-high yield of ethanol
-pure ethanol
-continuous process cheap on manpower
What are the disadvantages of direct hydration?
-uses ethene which is a finite resource
-continuous process requires expensive equipment
Why is the pressure carefully controlled in direct hydration reactions?
very high pressures could result in a polymerisation reaction
What is fermentation and it’s reaction conditions?
-when an aqueous solution of plant sugar is converted into ethanol and CO2 by living yeast cells
-anaerobic conditions and 35C, as oxygen would oxidise the ethanol to a carboxylic acid
What are the advantages and disadvantages of fermentation?
-can’t be carried out at high temperatures as yeast can’t survive
-can’t be carried out at low temperatures as enzymes aren’t activated
-batch process producing a mixture of compounds
What are the reaction conditions for the dehydration of alcohols?
300C/65 atmospheres/concentrated phosphoric acid
Draw the mechanism of the direct hydration of ethene, and write the name and conditions
-by electrophilic addition
-300C
-concentrated H3PO4 acid catalyst
-steam
-6500kPa
When used on larger alkenes, how do you know which product will be the major product?
it will be whatever one is formed from the more stable carbocation (which one is connected to the highest number of other carbons directly)
What are polymers?
long chain molecules formed when a large number of monomers join together
Give an example, and uses of natural polymers
-DNA
-natural polymers have been used for many years to make things like fabrics
Give 2 examples of artificial polymers
-artificial silk
-hard rubber
What is addition polymerisation?
the reaction in which many monomers with at least 1 C=C bond form long chains of polymers as the only product
What are addition polymers also sometimes called?
chain-growth polymers
How do you name an addition polymer?
poly(alkene name)
Why are addition polymers chemically unreactive and why is this a useful trait?
it has strong covalent bonds and no bond polarity, useful because it can’t be attacked by acids/alkalis/oxidising agents
Draw the addition polymerisation general reaction
n CH3=CH3 —-> -(- CH2CH2-)- n [FULL STRUCTURAL FORMULA DRAWN]
What mechanism are addition polymers usually formed by, and what are the common reaction conditions?
via a free radical mechanism, high pressure and a free radical initiator like an organic peroxide
What happens when you make an addition polymer from an alkene that is bigger than an alkene?
there can only be the saturated c-c bonds on the horizontal skeleton, so the extra ones are added like methyl groups to the vertical lines
CH3 H
│ │
-c—–c-
│ │
H H
Why do the properties change in polyalkene molecules?
-polyalkene molecules are usually non-polar so there are only weak van der Waals forces between the neighbouring molecules
-larger molecules have more electrons so have stronger van der Waals forces which increases the melting/boiling point
-if a molecule is not branched then the molecules can pack together more closely, (making the material stronger and more rigid) so have stronger van der Waals forces.
-if a molecule is branched then the molecules can’t pack as closely (making the material more flexible) so have weaker van der Waals forces
When can a polyalkene molecule be polar?
when it contains electronegative atoms, like in poly(chloroethene)
What is poly(ethene) used for?
making plastic bags and clingfilm
What is poly(propene) used for?
making crates/pipes/chairs/car bumpers/made into fibres used in the backing for carpets/thermal clothing/crisp packets
Why is poly(ethene) more difficult to recycle than poly(propene)?
it cannot as easily be collected, cleaned, and recycled so ends up in landfill, but poly(propene) is able to be collected-cleaned-cut up into small pieces-melted-remoulded
What is poly(chloroethene) also known as?
PVC (polyvinylchloride)
What type of intermolecular forces are present in PVC?
permanent dipole-dipole forces between the polymer chains due to the polar C-Cl bonds
What are the properties of PVC and what is it used in?
hard but brittle, used to make drain pipes and window frames
How can we make polymers more flexible?
by adding a plasticiser
How do plasticisers make polymers more flexible?
-plasticiser molecules get between the polymer chains and push them apart
-this reduces the strength of the van der Waals forces between the chains so the chains can slide around more, making the molecule more flexible
Why are polymers strong?
very large molecules so have lots of electrons so have stronger van der Waals forces that require a lot of energy to break
What is the difference between the uses for PVC and plasticised PVC and why?
plasticised PVC is much more flexible than rigid PVC, it is used to make electrical cable insulation, flooring tiles, and clothing
Why are polymers non-biodegradable?
as they are chemically inert (strong covalent bonds with no bond polarity)
What is one proposed way of disposing of polymers?
polymers are highly flammable so you can incinerate them
benefits- the heat from incineration can be used to make steam to drive turbines which would generate electricity
negatives- incineration produces greenhouse gases and other toxic gases
What are the cons of recycling polymers?
-expensive
-different types of plastics have to be separated from each other before being recycled
What are the cons of recycling polymers?
-expensive
-different types of plastics have to be separated from each other before being recycled
