organic a2

• Arenes are aromatic hydrocarbons
• Aromatic hydrocarbons, like benzene, can undergo electrophilic substitution due to benzene's delocalised electron system making it a stable molecule
• Benzene is attractive to electrophiles due to the high electron density in the benzene ring
• In substitution reactions with benzene, one of the hydrogen atoms swaps places with the electrophile
• Substitution with Chlorine:

  • Requires an aluminium chloride catalyst
  • Reaction: C​6​H​6​ + Cl​2​ → C​6​H​5​Cl + HCl
  • Mechanism involves the generation of the electrophile from chlorine by the aluminium chloride catalyst
• Substitution - Nitration:

  • Requires a mixture of concentrated nitric acid and concentrated sulfuric acid to generate the electrophile
  • Reaction: H​2​SO​4​+ HNO​3​ → H​2​O + NO​2​

  +​ + HSO​4​

  • 
    
  • Mechanism involves the generation of the electrophile from the acids
• Acylation of benzene involves the substitution of an acyl group and requires ethanoyl chloride and an aluminium chloride catalyst
• Complete Oxidation of Side Chains:

  • Alkyl groups attached to benzene can be oxidised to form benzoic acid using potassium manganate(VII)
• Hydrogenation:

  • Adds hydrogen atoms around the benzene ring, forming a cycloalkane product
  • Requires a nickel catalyst and a temperature around 150​o​C
• Halogenation:

  • Halogen can bond to the benzene ring or the methyl group of methylbenzene
  • Substitution in the benzene ring requires aluminium chloride and absence of UV light
  • Substitution in the methyl group happens in the presence of UV light without a catalyst
  • Reaction can continue to replace all hydrogen atoms in the methyl group with chlorine atoms
• In the reaction of benzene with chlorine, an aluminium chloride catalyst is required
• The reaction equation: C​6​H​6​ + Cl​2​ → C​6​H​5​Cl + HCl
• Mechanism for the electrophilic substitution reaction:

  • Stage 1: The aluminium chloride catalyst generates the electrophile from chlorine: Cl​2​ + AlCl​3​ → AlCl​4​
  • ​ + Cl​+
• Stage 2: The electrophile reacts with the benzene molecule
• Stage 3: The hydrogen ion reacts with the AlCl​4​

  • ​, reforming the AlCl​3​ catalyst: AlCl​4​
  • ​ + H​+​ → AlCl​3​ + HCl
• Chlorobenzene is much less reactive than chloroalkane because the C-Cl bond in chlorobenzene is much stronger than in a halogenoalkane
• The aromatic C-Cl bond in chlorobenzene is stronger due to one of the lone pairs on the chlorine atom interacting with the delocalised electron system, strengthening the bond
• For reactions like nucleophilic substitution, the C-Cl bond in chlorobenzene requires more energy to break, making chlorobenzene less reactive
• Alcohols can form esters by acylation with acyl chlorides, where alcohol reacts vigorously with acyl chlorides, releasing steamy fumes of hydrochloric acid
• Phenol is an aromatic hydrocarbon with one alcohol group bonded to the benzene ring
• To produce the ester phenyl benzoate, phenol is first converted into an ionic compound by dissolving it in sodium hydroxide, producing the phenoxide ion which is more reactive than phenol
• Phenol is a weak acid that can donate a hydrogen ion because the phenoxide ion is relatively stable due to the delocalization of the lone pair on the oxygen atom into the pi system above and below the benzene ring
• When phenol reacts with sodium hydroxide, colourless sodium phenoxide is formed; however, phenol isn't acidic enough to react with sodium carbonate
• Phenol reacts with metals to produce hydrogen gas and a salt, but the reaction is slower than comparable acid-metal reactions due to phenol being a weak acid
• Diazonium salts, containing the diazonium ion, can react with phenol after it is dissolved in sodium hydroxide to form an azo compound, identified by a yellow solution or precipitate
• Phenol is more reactive than benzene due to the -OH functional group, making it more likely to be attacked by electrophiles; it exhibits a 2,4-directing effect where incoming groups bond to the second and fourth carbons from the hydroxyl group
• Phenol's relative acidity compared to water and ethanol is phenol > water > ethanol, with phenol being the most acidic due to the stability of the phenoxide ion formed when it donates a proton
• Formation of acyl chlorides:

  • Acyl chlorides can be formed from carboxylic acids using sulfur dichloride oxide (SOCl2)
  • Reaction: CH3COOH + SOCl2 → CH3COCl + SO2 + HCl
  • Acyl chloride can also be produced from carboxylic acids by using phosphorus(V) chloride or phosphorus(III) chloride
• Oxidation of methanoic acid:

  • Methanoic acid can be further oxidised to produce carbon dioxide and water
  • Reaction can be carried out using Fehling’s or Tollen’s reagent
  • Using Fehling’s reagent: red precipitate is observed
  • Using Tollen’s reagent: silver mirror is observed on test tube
  • Overall equation: HCOOH + [O] → H2O + CO2
• Oxidation of ethanedioic acid:

  • Ethanedioic acid can be further oxidised to produce carbon dioxide and water
  • Reaction can be carried out using warm acidified potassium manganate(VII)
  • This is a redox reaction and can be used to standardise potassium manganate(VII) solution
  • Overall equation: 5(COOH)2 + 2MnO4- + 6H+ → 10CO2 + 2Mn2+ + 8H2O
• Relative acidities:

  • Carboxylic acids > phenols > alcohols
  • Carboxylic acids are the most acidic due to the structure of the carboxylate ion
  • Phenols are more acidic than alcohols because the phenoxide ion is relatively stable
  • Alcohols are the least acidic due to the positive inductive effect
• Acidities of Chlorine-Substituted Ethanoic Acids:

  • Chlorine-substituted ethanoic acid is a stronger acid than pure ethanoic acid
  • The more chlorines substituted on to ethanoic acid, the stronger the acid will be
• Acid and Base Hydrolysis of Esters:

  • Acid hydrolysis: esters react with water with an acid catalyst, reaction is reversible
  • Alkali hydrolysis: esters can be hydrolysed by heating under reflux with a dilute alkali, reaction is not reversible
• Ester hydrolysis can be done by heating it under reflux with a dilute alkali like sodium hydroxide, producing carboxylate salt and alcohol
• To convert the carboxylate salt product into a carboxylic acid, excess strong dilute acid can be added after removing the alcohol by distillation
• Esters are commonly used commercially as solvents, perfumes, and flavorings, often found in foods to create artificial fruit smells and tastes
• Acyl chlorides, also known as acid chlorides, have a similar structure to carboxylic acids but with the -OH group replaced by a chlorine atom
• Hydrolysis of acyl chlorides occurs when they react with water, producing hydrochloric acid and a carboxylic acid
• Esters are produced when alcohols and acyl chlorides react, resulting in the production of esters and hydrochloric acid fumes
• When acyl chlorides react with ammonia, an amide and hydrogen chloride gas are produced