Chemical Reactions: Alcohols, Aldehydes, Ketones, Esters, and Acids

Posted on Mar 19, 2025 in Chemistry

Alcohols: Substitution, Combustion, and Elimination Reactions

Substitution reaction: CH₃CH₂OH + HCl → CH₃CH₂Cl + H₂O

Combustion reaction: Produces CO₂ + H₂O

Obtaining Alcohols:

• Hydrolysis of alkyl halides.
• Hydration of alkenes catalyzed by acids.

Elimination reactions (Dehydration):

• Elimination of H₂O from alcohols.
• Reaction with strong dehydrating agents yields alkenes.
• Removal of water from two alcohol molecules forms an ether. This depends on the temperature and the alcohol ratio.

Examples:

• CH₃CH₂OH → (H₂SO₄, T > 150°C) CH₂=CH₂ + H₂O
• CH₃CH₂OH + HOCH₂CH₃ → (H₂SO₄, 130°C – 140°C) CH₃CH₂OCH₂CH₃ + H₂O

Oxidation reactions:

• CH₃CH₂OH → (Cr₂O₇^2- + H⁺) CH₃CHO → (Cr₂O₇^2- + H⁺) CH₃COOH

Aldehydes and Ketones: Reactions and Properties

Reduction reaction: CH₃CHO + H₂ (Pt) → CH₃CH₂OH

Oxidation reactions:

• Aldehydes are oxidized by mild oxidants, yielding carboxylic acids.
• Ketones are oxidized by strong oxidants, resulting in two specific carboxylic acids.

Reactions of Aldehydes:

• Tollens’ reagent: Aldehydes heated with silver nitrate in ammonia solution precipitate metallic silver, forming a mirror on the test tube: CH₃CHO + 2Ag(NH₃)₂OH → CH₃COONH₄ + 2Ag + H₂O + 3NH₃
• Fehling’s reagent: Aldehydes heated in an alkaline solution of copper(II) hydroxide in the presence of copper tartrate oxide precipitate red copper(I) oxide. The acid is neutralized to its sodium salt: CH₃CHO + 2Cu(OH)₂ + NaOH → CH₃COONa + 3H₂O + Cu₂O

Obtaining Aldehydes and Ketones:

• Aldehydes: By oxidation of primary alcohols.
• Ketones: By oxidation of secondary alcohols.

Esters: Reactions and Synthesis

Hydrolysis reactions: Ester + H₂O → (acid catalyst) Carboxylic acid + Alcohol

Saponification reaction: Ester + Alkali → Salt + Alcohol (R-COOR’ + NaOH → R-COONa + R’OH)

Ammonolysis: Ester + Ammonia → Amide + Alcohol

Production:

• Chemical synthesis (Acid + Alcohol = Ester + Water).
• From natural raw materials.

Carboxylic Acids: Reactions

Neutralization reaction: Acid + Base = Salt + Water

Long chain acid + Base = Soap

Reduction reaction: Acid → Aldehyde → Primary Alcohol

Esterification reaction: Acid + Alcohol = Ester + Water

Le Chatelier’s Principle

Le Chatelier’s principle states that a system in chemical equilibrium, when subjected to an external perturbation, responds in a way that tends to partially counteract the disturbance.

• Adding or removing a reactant or product: For a reaction aA + bB ∼ cC, if aA, bB, or cC is added, or if cC is decreased: Q_c < K_c. The equilibrium needs readjustment of the concentrations so that Q_c = K_c. If a reactant (aA or bB) is increased, the equilibrium shifts to the right.
• Effect of a catalyst: The equilibrium is reached sooner, but it does not affect the concentrations or K_c.
• Compression or expansion:
  • Compression (decreased volume, increased pressure): The reaction shifts towards the direction that decreases the total number of moles of gaseous species.
  • Expansion: The opposite effect of compression.
• Changes in temperature:
  • Increased temperature: Favors endothermic reactions (ΔH = +), shifting the equilibrium to the right.
  • Decreased temperature: Favors exothermic reactions (ΔH = -), shifting the equilibrium to the left.

Spontaneity of Reactions

ΔG = ΔH – TΔS

• Exothermic: ΔH = –
• Endothermic: ΔH = +
• X + X → X: ΔS = +
• X → X + X: ΔS = –

Conditions for Spontaneity:

• ΔH (-) and ΔS (+): Always spontaneous.
• ΔH (+) and ΔS (+): Spontaneous at high temperatures.
• ΔH (-) and ΔS (-): Spontaneous at low temperatures.
• ΔH (+) and ΔS (-): Never spontaneous.

Enthalpy: ΔH_f = ∑ ΔH_f (products) – ∑ ΔH_f (reactants)

Sequence of equations: ΔH_reaction = ΔH₁ + ΔH₂

Reaction Order: v = k[A]^m[B]ⁿ (m and n are the exponents), total order = m + n