Edexcel A-level Chemistry Organic Reactions

Alkane → Halogenoalkane

Free radical substitution

Presence of UV light

INITATION

PROPIGATION

TERMINATION

Can be further substutions

mechanisms required

Alkene → Alkane

H₂(g)

Nickel catalyst

150°C

(addition/reduction)

Alkene → Dihalogenoalkane

Halogen - Cl₂, Br₂

RT, no UV light

(electrophilic addition)

Mechanism Required

Alkene → Diol

Acidified potassium manganate, H⁺/MnO₄⁻

Purple solution decolourises

Purple → colourless

MnO₄⁻ → Mn²⁺

(addition reaction)

Alkene → Alcohol

Steam, 300°C, 60-70atm

Phosphoric (V) acid catalyst (conc. H₃PO₄)

(hydration)

Alkene → Halogenoalkane

Hydrogen halide - HCl, HBr

RT

(electrophilic addition)

Mechanism required - minor/major products

Bromine water, BrOH

Bromine water decolourises

Brown → colourless

(addition reaction)

Alcohol → Alkene

Acid catalyst, e.g H₃PO₄

(elimination/dehydration)

Halogenoalkane → Alkene

Ethanolic potassium hydroxide, KOH(ethanol)

Ethanol used as a solvent

Heat under reflux

OH⁻ ion acts as a base

CH₃-CHBr-CH₃ + OH⁻ → CH₃=CH-CH₃ + H₂O + KBr

(elimination reaction)

Chlorination of 1°/2° alcohols

Phosphorous(V)chloride

CH₃CH₂OH ₊ PCl₅ → CH₃CH₂Cl + POCl₃ + HCl

Produces steamy/misty fumes HCl

Vigorous at RT

(substitution reaction)

Other halogenating compounds can be used e.g SOCl₂

Chlorination of 3° Alcohols

Shake with conc. HCl at RT

(CH₃)₃COH + HCl → (CH₃)₃CCl + H₂O

CP6 - chlorination of

2-methylpropan-2-ol

Bromination of Alcohols

50/50 conc. H₂SO₄/KBr

Warmed with alcohol

Reaction to form reagent:

KBr + H₂SO₄ → KHSO₄ + HBr

Reaction with HBr:

CH₃CH₂OH + HBr → CH₃CH₂Br + H₂O

Iodination of Alcohols

Red Phosphorus and I₂

Heat under reflux

Reaction to form reagent:

2P + 3I₂ → 2PI₃

Reaction with phosphorous(III)iodide

3CH₂CH₃OH + PI₃ → 3CH₂CH₃I + H₃PO₃

Halogenoalkane → Alcohol

Aqueous potassium hydroxide, KOH(aq)

Heat under reflux

Nucleophile (OH⁻, stronger than H₂O)

(Nucleophilic substitution)

Mechanism required (SN1 and SN2)

Halogenoalkane → Nitrile

KCN is aqueous ethanol

Heat under reflux

CN⁻ (nucleophile)

*example of increasing length of the carbon chain

Halogenoalkane → 1° amine

NH₃ dissolved in ethanol

Heat in a sealed tube (prevents NH₃(g) escaping)

Two step process:

NH₃ acting as a nucleophile producing a salt

(nucleophilic substitution)

Then NH₃ acts as a base → nitrile + NH₄⁺

(acid-base reaction)

Overall: CH₃CH₂Cl + 2NH₃ → CH₃CH₂NH₂ + NH₄⁺Cl⁻

Mechanism required

1° Alcohol → Aldehyde

Acidified potassium dichromate, H⁺/KCr₂O₇ (limited)

Distillation with addition

(oxidation)

2° Alcohol → Ketone

Acidified potassium dichromate, H⁺/KCr₂O₇

Heat under reflux

(oxidation)

3° Alcohol → ?

Cannot be oxidised

Carbonyl Compound → Hydroxynitrile

HCN is the presence of KCN(aq)

(Nucleophilic addition)

Forms pair of enantiomers

Mechanism required

Ketone → alcohol

LiAlH₄ in dry ether

(reduction)

Aldehyde → Carboxylic acid

Excess H⁺/KCr₂O₇

Heat under reflux

(oxidation)

n.b orange → green

Cr₂O₇²⁻ → 2Cr³⁺

Carboxylic acid → Alcohol

LiAlH₄ in dry ether

RT and pressure

(reduction)

Carboxylic acid → Carboxylate Salt

acid + metal → salt + hydrogen

acid + metal hydroxide → salt + water

acid + metal carbonate → salt + water + CO₂

Carboxylate salt → Carboxylic acid

add dilute acid

Carboxylic acid → Ester

Alcohol

strong acid catalyst, H₂SO₄

Heat under reflux

CH₃COOH + CH₃CH₂OH ⇌ CH₃CO₂CH₂CH₃ + H2O

reversible reaction, yield is low

Ester → Carboxylate salt

Alkaline hydrolysis

NaOH(aq)

Heat under reflux

Reaction goes to completion

→ Carboxylic acid, add dilute acid

Ester → Carboxylic acid

Acid Hydrolysis

Heat under reflux with a dilute acid

strong acid catalyst, H₂SO₄

Reaction is reversible

Carboxylic Acid → Acyl Chloride

Phosphorous(V)chloride,

CH₃COOH ₊ PCl₅ → CH₃COOCl + POCl₃ + HCl

Produces steamy/misty fumes HCl

Vigorous at RT, conditions must be anhydrous

POCl₃ and acyl chloride can be separated by fractional distillation

(substitution reaction)

Carboxylic acid → Acyl Chloride (2)

Thionyl chloride, SOCl₂

RT

CH₃COOH + SOCl₂ → CH₃COOCl + SO₂ + HCl

Both gases given off ∴ no need for fractional distillation

Acyl Chloride → Carboxylic acid

Vigorous at RT with cold water

Steamy/misty fumes HCl produced

Acyl Chloride → Ester

React with alcohol

RT

Produces steamy/misty fumes of HCl

CH₃COOH + CH₃CH₂OH → CH₃COOCH₂CH₃ + HCl

Better than reacting with a carboxylic acid because reaction is not reversible

Acyl Chloride → 1° amide

Conc. NH₃(aq)

RT

CH₃COOH + NH₃ → CH₃CONH₂ + HCl

NH₃ then acts as a base

HCl + NH₃ → NH₄Cl

White smoke of NH₄Cl is produced

Acyl Chloride → N-substituted amide

React with a 1° amine

RT

Forms an N-substituted amide and HCl

(addition-elimination reaction)

1° amine → 2° amine

Further substitution reactions with ammonia

To get mainly the quaternary ammonium salt use excess halogenoalkane

To get mainly 1° amine use excess NH₃

Mixture of products is likely

Nitrile → 1° amine

LiAlH₄ in dry ether

CH₃CN + 4[H] → CH₃CH₂NH₂

(reduction)

or...

H₂(g)

Nickel catalyst

High temp, high pressure

Nitrile → Carboxylic acid

Preparation by hydrolysis

acidic/alkaline

To purify fractionally distillate

Acid hydrolysis

Reflux with dilute acid (HCl, H₂SO₄)

Alkaline hydrolysis

Reflux with dilute NaOH

→ add dilute acid

...

...

Benzene → Cyclohexane

H₂(g)

Nickel Catalyst

200°C, 30atm

Benzene → Chlorobenzene

Cl₂ and a halogen carrier

(halogen carrier polarises the Cl₂/Br₂)

Formation of electrophile:

AlCl₃ + Cl₂ → AlCl₄⁻ + Cl⁺

C₆H₆ + Cl₂ → C₆H₅Cl + HCl

Catalyst is regenerated:

H⁺ + AlCl₄⁻ → AlCl₃ + HCl

(electrophilic substitution)

Mechanism required

Benzene → Bromobenzene

Br₂ and a halogen carrier (catalyst)

Catalyst created in situ by reacting ion fillings with dry ether

Formation of electrophile:

FeBr₃ + Br₂ → FeBr₄⁻ + Br⁺

C₆H₆ + Br₂ → C₆H₅Br + HBr

Catalyst is regenerated:

H⁺ + FeBr₄⁻ → FeBr₃ + HBr

(electrophilic substitution)

Mechanism required

Benzene → Nitrobenzene

Conc. nitric acid in the presence of a sulphuric acid catalyst

In situ forms the electrophile, NO₂⁺ (nitronium ion)

Formation of the electrophile:

HNO₃ + 2H₂SO₄ → NO₂⁺ + 2HSO₄⁻ + H₃O⁺

H₂SO₄ catalyst is reformed:

H⁺ + HSO₄⁻ → H₂SO₄

(electrophilic substitution)

Mechanism required

Phenol → 2,4,6-tribromophenol

Bromine water

RT

Product is a white solid

(-OH group is 2,4 directing)

Benzene → Alkybenzene

FRIEDAL-CRAFT REACTION

Chloroalkane (RX) in the presence of anhydrous

aluminium chloride catalyst

Heat under reflux

Dry inert solvent (ether)

Formation of the electrophile: (CH₃CH₂⁺)

AlCl₃ + CH₃CH₂Cl → CH₃CH₂⁺ + AlCl₄⁻

H⁺ produced reacts with AlCl₄⁻ → reform catalyst + HCl

(electrophilic substitution)

Mechanism required

Benzene → Phenylketone

FRIEDAL-CRAFT REACTION

Acyl chloride (RCOX) in the presence of an anhydrous

aluminium chloride catalyst

Heat under reflux 50°C

Dry inert solvent (ether)

Formation of the electrophile: CH₃CO⁺

AlCl₃ + CH₃COCl → CH₃CO⁺ + AlCl₄⁻

H⁺ produced reacts with AlCl₄⁻ → reform catalyst + HCl

(electrophilic substitution)

Mechanism required

Nitrobenzene → Phenylamine

Sn (Tin) and HCl

Heat under reflux

(reduction)

C₆H₆NO₂ + 6[H] → C₆H₆NH₂ + 2H₂O

produces phenyl ammonium ion (∴ add NaOH)

C₆H₆NH₃⁺ + OH⁻ → C₆H₆NH₂ + H₂O

Best separated by steam distillation

... Or

Can use Fe and HCl

Halogenoalkane → Grignard Reagent

R-Br + Mg→ R-Mg-Br

halogenoalkane is dissolved in dry ether then reacted with magnesium

heat under reflux

Grignard Reagent → 1° Alcohol

React with methanal

RMgX + HCHO → RCH₂OH + Mg(OH)X

added dilute acid to obtain desired product (H₂O/H⁺)

extends the carbon chain by 1 C

Grignard Reagent → 2° Alcohol

Reaction with an aldehyde (not methanal)

RMgX + CH₃CH₂CHO → CH₃CH₂C(OH)R +Mg(OH)X

added dilute acid to obtain desired product (H₂O/H⁺)

extends the carbon chain by variable amount

Grignard Reagent → 3° Alcohol

React with a ketone

RMgX + CH₃COCH₃ → (CH₃)₂RCOH + Mg(OH)X

added dilute acid to obtain desired product (H₂O/H⁺)

extends the carbon chain by variable amount

Grignard Reagent → Carboxylic acid

React with CO₂, then hydrolysis using a dilute acid

RMgX + CO₂ → RCOO⁻[MgX]⁺ → RCOOH + Mg(OH)X

added dilute acid to obtain desired product (H₂O/H⁺)

extends the carbon chain by 1 C