Important reagents and conditions (I)

Halogens

Displacement reactions
A halogen displacing a less reactive halogen
Hydrolysis of halogenoalkanes
Aqueous sodium hydroxide, reflux
forms alcohol & halide
Reactions with alkali at room temperature
Cl, Br & I all react with cold aqueous solution sodium hydroxide using disproportionation
Produces a mixture of halide & halite ($I$) salts
Reactions of hot alkali
This is a disproportionation reaction, however the halogen is oxidised to the 5+ state rather than the 1+ state to form $ClO_3^-$

Nucleophilic substitution

Primary halogenoalkanes ($SN_2$)
Primary halogenoalkane heated under reflux with sodium/potassium hydroxide, forms alcohol
Requires halogenoalkanes in ethanol solvent

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Tertiary halogenoalkanes ($SN_1$)
Tertiary halogenoalkane heated under reflux with sodium/potassium hydroxide, forms alcohol
Requires halogenoalkanes in ethanol solvent
First stage forms carbocation, which is rapidly attacked by hydroxide ions.

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Secondary halagenoalkanes

Secondary halagenoalkanes react using a mix of both $SN_1$ and $SN_2$

Reactions of chlorine

Chlorine with water
Disproportionation reaction, forms $HCl$ & $HOCl$ (chlorine water)
Reactions with $NaOH$
Cold, dilute, aqueous
Disproportionation reaction, forms $ClO^-$
Hot $NaOH$
Forms $ClO_3^-$

Free radical substitution

Chain initiation

  • UV light breaks down a chlorine molecule into free radicals

$Cl_2\rightarrow 2Cl\cdot$

Chain propagation

  • Reactions that have radicals on both sides

$CH_4+Cl\cdot \rightarrow CH_3\cdot+HCl$

$CH_3\cdot +Cl_2\rightarrow CH_3Cl+Cl\cdot$

Chain termination reactions

  • Radicals on the left, not on the right

$2Cl\cdot\rightarrow Cl_2$

$CH_3\cdot+Cl\cdot\rightarrow CH_3Cl$

$CH_3\cdot+CH_3\cdot\rightarrow CH_3CH_3$

Alcohols

Test for $-OH$ group
add $PCl_5$, forms misty fumes

Oxidisation

Primary alcohol to Aldehydes
Acidified $Cr_2O_7^{2-}$, heat & distil
Primary alcohol to Carboxylic acid
Acidified $Cr_2O_7^{2-}$, heat under reflux
Secondary alcohols to ketones
Acidified $Cr_2O_7^{2-}$, heat under reflux

Alkenes

Bromine water test
Goes from orange to colourless.
Ethene forms 1,2-dibromoethane
Potassium Manganate ($VII$) test
Goes from purple to colourless
Oxidising agent
Oxidation of alkenes
hot, conc. $KMnO_4$
depends on arrangement of initial alkene
forms carbonyl intermediates
if hydrocarbon group on both sides, forms two carbonyl compounds
if one hydrocarbon, one hydrogen, forms a carboxylic acid, & carbonyl
if hydrogens all round, forms $CO_2$, $H_2O$ & a carbonyl group
$KMnO_4$ oxidises Methanoic acid all the way to $CO_2$ & $H_2O$
Hydrogenation of an alkene
150-300$^{\circ}C$, 1-10atm
Hydration of alkene (industrial preparation)
$H_3PO_4$ catalyst, 300$^{\circ}C$, 65 atm, steam
Addition of hydrogen halide
Conc. Aqueous acid, room temperature

Alkanes

Cracking
450$^{\circ}C$, aluminium oxide catalyst
Forms a alkane & alkene
Reforming an alkane
Iridium catalyst, 500$^{\circ}C$

General equations for reactions

  • Acid + Base -> Salt + Water
  • Acid + Metal Oxide -> Salt + Water
  • Acid + Metal -> Salt + Hydrogen
  • Acid + Metal Hydroxide -> Salt + Water
  • Acid + Carbonate -> Salt + Water + Carbon Dioxide
  • Acid + Ammonia – Ammonium Salt
  • Reactant + Oxygen -> Oxides + Heat