Reaction of organic compounds

Formation and Reactions of Organic Compounds

  • The chemical reactions of carbon compounds are determined by the functional group (or groups) present within the compounds.

Alkanes

  • General Formula: CnH{2n+2}
  • Characteristics:
    • Saturated hydrocarbons with only single bonds between carbon atoms.
    • Physical state at room temperature:
    • 1 to 4 carbon atoms: Gas
    • 5 to 16 carbon atoms: Liquid
    • 17+ carbon atoms: Solid
    • Relatively unreactive due to strong C-C single bonds.

Reactions of Alkanes

Complete Combustion

  • Burns in air/oxygen to produce carbon dioxide and water vapor.
  • Produces clear, blue non-smoky flames due to low carbon-to-hydrogen ratio.
  • Exothermic reaction: Generates significant heat.

Incomplete Combustion

  • Occurs with limited oxygen supply, producing carbon monoxide and water vapor.

Substitution Reactions with Halogens

  • Occurs when a hydrogen atom in alkanes is replaced by a halogen atom (e.g., chlorine, bromine).
  • Requires energy in the form of ultraviolet light.
  • In dark conditions, no reaction occurs; reactions are slow in dim light.

Example: Halogenation of Methane

  • Reaction:
    1. CH4(g) + Cl2(g)
      ightarrow CH_3Cl(g) + HCl(g)
    2. Continued reaction leads to further substitution creating products like CCl_4 (tetrachloromethane).
  • The overall reaction can be summarized as:
    CH4(g) + 4Cl2(g)
    ightarrow CCl_4(l) + 4HCl(g)

Alkenes

  • General Formula: CnH{2n}
  • Unsaturated hydrocarbons featuring at least one carbon-carbon double bond (C=C), which increases reactivity compared to alkanes.

Reactions of Alkenes

Combustion

  • Burns in air/oxygen to produce carbon dioxide and water as steam.
  • Produces smoky yellow flames due to a higher carbon-to-hydrogen ratio than alkanes.

Addition Reactions

  • Alkenes react with small molecules to form one molecule, resulting in saturation (double bond broken).
  • Hydrogenation:
    • Reaction with hydrogen to form saturated hydrocarbons.
    • Example: C2H4 + H2 ightarrow C2H_6 (requires nickel catalyst, pressure, and heat).

Halogenation

  • Reactions with halogens (e.g., bromine) to form haloalkanes.
  • Example: C3H6 + Br2 ightarrow C3H4Br2 (decolorization of red-brown bromine).

Addition of Hydrogen Halides and Water

  • Reaction with hydrogen halides at room temperature to form haloalkanes.
  • Reaction with steam produces alcohols.

Distinguishing Alkanes from Alkenes

  • Test with bromine solution:
    • Alkenes undergo rapid addition, changing the solution from red-brown to colorless.
    • Alkanes do not cause any color change.
  • Test with acidified potassium manganate(VII):
    • Alkenes convert purple MnO₄⁻ to colorless Mn²⁺.
    • No reaction with alkanes.

Uses of Alkanes and Alkenes

Alkanes

  • Used as fuels due to easy combustion, high energy release, and clean burning.
  • Serve as non-polar solvents for soluble substances in chemicals
    • Examples: hexane for glue production, oil extraction.

Alkenes

  • Starting materials for various chemical production due to reactivity.
  • Used to manufacture alcohols, antifreeze, synthetic rubbers, and haloalkanes.
  • Undergo polymerization for producing plastics.

Alcohols

  • General Formula: CnH{2n+1}OH
  • Functional group: Hydroxyl group (-OH).
  • Reactions vary; strength decreases with more carbon atoms.

General Properties

  • Polar molecules, less volatile than alkanes.
  • Higher boiling points; solubility in water decreases with carbon number.

Reactions of Alcohols

  • Combines with sodium to release hydrogen and form sodium ethoxide.
  • Ethanol can be dehydrated to form alkenes or oxidized to carboxylic acids (like ethanoic acid) using potassium permanganate or dichromate.

Ethanol Production

  • Produced from the fermentation of carbohydrates under anaerobic conditions, with yeast converting glucose to ethanol and CO₂.

Alkanoic Acid

  • General Formula: CnH{2n+1}COOH
  • Functional group: Carboxyl group (-COOH), polar and soluble in water, weak acids.

Reactions of Aqueous Ethanoic Acid

  • Reacts with metals, hydroxides, and carbonates to produce salts and hydrogen.

Esters

  • Formed from alkanoic acids reacting with alcohols via esterification, which is a condensation reaction that produces water and requires sulfuric acid as a catalyst.

Naming Esters

  • Structural formula: derived from the acids and alcohol used. Naming: based on alcohol first (ending 'yl') then acid (ending 'anoate').

Reactions of Esters

  • Hydrolysis occurs either using dilute acid or alkali to regenerate acid and alcohol.

Saponification

  • Process of making soap from fats and oils by hydrolysis with a strong alkali, yielding soap and glycerol.

Polymerization

  • Addition Polymerization: Monomers linked without losing atoms. Example: polyethylene from ethylene.
  • Condensation Polymerization: Formed by eliminating small molecules in the process.

Environmental Impact of Synthetic Polymers

  • Pose challenges like pollution, non-biodegradability, and harming wildlife due to plastic waste.