Organic Chemistry Flashcards
Thermal cracking
High temperature (700°c) and high pressure (7,000 kPa) Produces a higher proportion of alkenes A free radical mechanism
Catalytic cracking
High temperature (700K) and slight pressure involving a zeolite catalyst (aluminosilicates) Produces motor fuels and aromatic compounds A carbocation mechanism
Economic reasons for cracking alkanes
Produces shorter chain fractions which are in higher demand (more useful/valuable)
Also produces alkenes which are more reactive
Pollutants caused by combustion
Carbon monoxide, nitrogen oxides, sulfur dioxide, carbon particulates, unburnt hydrocarbons, carbon dioxide, water vapour
Flue Gas desulfurisation
Calcium oxide reacts with water and SO2 to produce calcium sulfite
Calcium carbonate reacts with oxygen and SO2 to produce calcium sulfate and CO2
Catalytic converters
Removes gaseous pollutants from internal combustion engines
A honeycomb coated with platinum and rhodium metals
CO, NOx and unburnt hydrocarbons react with each other
Chlorination of alkanes
Free radical substitution
Need UV light and an excess of methane
Chain reactions produce a mixture of products
Chlorofluorocarbons
Destroy the ozone, which protects the Earth from UV rays
Chlorine free radicals catalyse the breakdown of O3
Reactivity of halogenalkanes
Increases down the group as bond enthalpy decreases
Even though bond polarity decreases
CHEET & PAWN
Primary haloalkane, Aqueous solvent, Warm, Nucleophilic
Concentrated NaOH, Hot, Ethanol solvent, Elimination, Tertiary haloalkane
Reactivity of alkenes
More reactive than alkanes due to the high electron density of the carbon-carbon double bond (attacked by electrophiles)
Alkenes in steam
React with water to produce alcohols
Positive inductive effect
Alkyl groups have a tendency to release electrons, which stabilises the positive charge of the intermediate positive carbocation
The product will tend to come from the more stable carbocation
Poly(chloroethene)
Used for drainpipes
Used for aprons when plasticiser added
Plasticisers
Small molecules get between the polymer chains, forcing them apart
This allows the, to slide over each other so they’re flexible
Addition polymers reactivity
They’re unreactive because they have no double bonds (saturated) and strong, non-polar bonds
Low density polythene
Made by polymerising ethene at high temperature and pressure
Free radical mechanism produces a chain-branching polymer
Flexible so used for packaging and electrical insulation
High density polythene
Uses a Ziegler-Natta catalyst which produces less branching
Chains pack together well so high melting point
Used as milk crates, buckets and bottles (rigid)
Recycling polymers
Mechanical- ground up pellets melted and reused
Feedstock- heated to produce monomers, then make new plastics
Melting point and solubility of alcohols
High melting point due to hydrogen bonding
-OH group can form H-bonds with water molecules
Short chain hydrocarbons soluble in water
Producing ethanol from crude oil
Ethene is hydrated with a phosphoric acid catalyst
The process is continuous, rate of reaction fast and product pure
Producing ethanol from sugar
Sugar cane is fermented, and the yeast anaerobically respires to produce ethanol from glucose
35°c used so enzymes don’t denature (and no air present)
Enzymes unable to function over 15% ethanol
Batch process, slow rate of reaction and impure product (fractional distillation)
Biofuel
A fuel derived or produced from renewable biological sources
Dehydration of alcohols
Produces sustainable alkenes if alcohol made from fermentation
Need excess hot concentrated sulfuric acid
Alkenes used to produce addition polymers
