Reactions (and mechanisms) Flashcards
Complete combustion
alkane+O2 -> CO2 + H2O
Incomplete combustion
alkane+O2-> CO + H2O
alkane+O2-> C+ CO +H2O
Catalytic cracking
zeolite catalyst + 450oC
hydrocarbon-> shorter chain alkane+alkenes
Isomerisation
alkane->branched alkane
Reforming
Alkane->cyclic alkane+H2
Free radical substitution
Initiation reaction
(homolytic fission of halogen using UV)
Br2-> 2Br
Propagation reaction
(radical halogen and alkane)
(radical alkane and diatomic halogen)
Br + CH4 -> HBr + CH3
CH3 + Br2 -> CH3Br + Br
Termination steps
(Two radicals)
Br+Br->Br2
Br+CH3->CH3Br
CH3+CH3>C2H6
Hydrogenation
alkene+ hydrogen -> alkane
(Ni catalyst 150’C)
catalytic hydrogenation produces margarine by reacting polyunsaturated vegetable oils with hydrogen and a nickel catalyst
Halogenation
alkene+halogens-> dihalogenoalkane
alkene+hydrogen halide -> halogenoalkane
Can make isomers
Hydration
alkene+steam->alcohol
(acid catalyst e.g. H3PO4 300’C 6MPa)
hydration makes ethanol from ethene
When unsymmetrical alkenes react with a H20 you can make isomers
Elecrophilic addition
When a (halogen) approaches the alkene, a temporary induced dipole is formed, giving the halogen a slightly negative and slightly electropositive end.
Curly arrow starts at the pi-bond (C=C) and points to electropositive end of halogen.
Second curly arrow shows movement of bonded pair of electrons in the halogen bond to the slightly electronegative end resulting in heterolytic fission of this bond.
An intermediate carbocation and a negative halide ion are formed.
The third curly arrow is from the :X- lone pair of halide to the + carbocation.
Addition polymerisation
Addition polymerisation of alkenes
one alkene molecule (monomer) joins to others and a long-chain molecule (polymer) is formed.
Combustion of alcohols
C2H5OH+3O2->2CO2+3H2O
Esterification
Alcohols with carboxylic acids in the presence of an acid catalyst
Dehydration
Elimination of H2O from alcohols in presence of an acid catalyst and heat (forms alkene and water)
Can use cyclic hydrocarbons
Can form isomer (double bond in different place depending on H lost)
Fermentation
Fermentation from sugars ie from glucose
anaerobic fermentation involving yeast
C6H12O6(aq)->2CH3CH2OH(aq)+2CO2(g)
Oxidation of primary alcohols, secondary and tertiary alcohols
Cr2O72-/H+ (ie K2Cr2O7/H2SO4)
Each oxidation reaction is accompanied by a colour change from orange to green.
Use [O] to represent the oxidising agent.
the oxidation of primary alcohols form aldehydes when distilled and carboxylic acids when refluxed (and water produced)
the oxidation of secondary alcohols form ketones (and water produced)
the resistance to oxidation of tertiary alcohols
Hydrolysis
The hydrolysis of halogenoalkanes is a (nucleophilic) substitution reaction.
When a primary halogenoalkane is heated under reflux with a hot aqueous solution of an alkali (NaOH or KOH, water solvent), its oxidised to a primary alcohol.
CH3CH2Br+NaOH->CH3CH2OH+NaBr
Rate of hydrolysis
Aqueous silver nitrate in ethanol can be used to compare these rates, H2O can be assumed to be the nucleophile. Ag++X-—>AgX(s)
Alternatively, hot aqueous alkali can be used, followed by the neutralisation and addition of aqueous silver nitrate. In this reaction, OH- is the nucleophile.
The Haber process
N2+3H2->2NH3
iron catalyst
ozone maintenance
O3+(UV)->O2+O
O2+O->O3 (+heat)
O2+O ⇌?O3
Ozone break down
R+O3->RO+O2
RO + O->R + O2
Catalytic converter
4CO+2NO2->4CO2+N2
Adsorption of CO and NO to the catalyst surface (must be weak enough for adsorption and desorption but strong enough to weaken bonds and allow reaction)
Chemical reaction
Desorption of CO2 and N2 from the catalyst surface
