F322: Alkenes And Alcohols Flashcards
Pi bond
Formed by the sideways overlap of adjacent p-orbitals above and below the plane of the molecule (sigma bond)
Alkenes
Unsaturated hydrocarbons; CnH2n; contain at least one C=C. Trigonal planar shape around each carbon in the C=C.
Electrophilew
Electron pair acceptor
Addition
When two molecules join together to make one (100% atom economy)
Hydrogenation (general formula + conditions)
Alkene + hydrogen -> alkane
Nickel catalyst, 150 degrees
Halogenation (general formula + conditions)
Alkene + halogen -> dihalogenoalkane
Room temp in the dark
(Can be used as test for alkenes, add bromine water, orange -> colourless)
Addition of hydrogen halides (general formula + conditions)
Alkene + hydrogen halide -> halogenoalkane
Room temp in the dark
Hydration (addition at steam) (general formula + conditions)
Alkene + steam -> alcohol
200 degrees, 200 atm, phosphoric acid catalyst
Addition polymerisation (general formula + conditions)
Alkene -> poly(alkene)
TiCl3 catalyst, 60 degrees
Industrial importance of alkenes
1) manufacture of margarine by catalytic hydrogenation of unsaturated vegetable oils using hydrogen and nickel catalyst.
2) formation of polymers eg. For plastics
3) manufacture of ethanol by hydration of ethene
Disposal of polymers
1) sort and recycle
2) combust for energy production
3) feedstock for cracking in the production of plastics and other chemicals
Role of chemists
To minimise the environmental damage from:
1) the removal of toxic waste products (eg. HCl (g) from combustion of halogenated plastics)
2) the development of biodegradable and compostable polymers
Alcohols
CnH2n+1OH; functional group ROH. Short chained alcohols are soluble in water. Higher melting points than corresponding alkanes due to their ability to form hydrogen bonds.
Classification of alcohols
Primary: OH attached to carbon which is attached to 1 other C
Secondary: OH attached to carbon that has 2 C attached to it
Tertiary: OH attached to a carbon that has 3 other C attached to it
Industrial production of ethanol (fermentation of sugars)
fermentation of sugars (glucose)
C6H12O6 -> 2C2H5OH + 2CO2
Conditions: yeast, 37 degrees, absence of air
Advantages: sugar cane is renewable, low temperature required
Disadvantages: slow batch process, mixture of products (low atom economy)
Industrial production of ethanol (hydration of ethene)
Hydration of ethene:
C2H4 + H2O (g) -> CH3CH2OH
Conditions: H3PO4 catalyst, 200 degrees, 200atm
Advantages: pure ethanol (100% atom economy), fast process
Disadvantages: non-renewable ethene from crude oil, hight temp
Biofuel
Fuel made from animal or plant waste material
Use of alcohols
1) ethanol in alcoholic drinks
2) methanol as a petrol additive to improve combustion as a feedstock
Combustion of alcohols
Alcohol + oxygen -> CO2 + H2O
Oxidation of alcohols -> oxidising agent/conditions/observations
[O] -> acidified dichromate ions (H+/Cr2O7 2-)
Conditions: K2Cr2O7 and H2SO4
Observation: Orange to green
Oxidation of primary alcohols (partial)
Partial oxidation: => aldehyde
Conditions: Distill product immediately, acidified potassium dichromate.
CH3CH2OH + [O] -> CH3CHO + H2O (Ethanol -> Ethanal)
Oxidation of primary alcohols (full)
Full oxidation: => carboxylic acid
Conditions: Reflux, acidified potassium dichromate
CH3CH2OH + [O] -> CH3COOH + H2O (Ethanol-> Ethanoic acid)
Oxidation do secondary alcohols
=> Ketones
Conditions: acidified potassium dichromate
CH3CH(OH)CH3 + [O] -> CH3CH(O)CH3 (Propan-2-ol -> Propanone)
Oxidation of tertiary alcohols
Tertiary alcohols are NOT oxidised (thus reaction mixture stays orange)
Esterification of alcohols
Aka: Condensation (loss of water)
Alcohol + carboxylic acid -> ester + H2O
Eg. Methanol + propanoic acid -> methylpropanoate + H2O
Conditions: conc H2SO4 catalyst, REFLUX
Dehydration of alcohols
Aka: elimination (dehydration- loss of water)
Conditions: conc H2SO4 catalyst, heat
Alcohol -> alkene + H2O
Reflux
Continuous evaporation and condensation to prevent the loss of volatile components (those with low boiling points)
Elimination
The loss/removal of a small molecule from a larger molecule (eg. Dehydration-> water)
