Alkanoic acids, also known as carboxylic acids, have the functional group called the carboxyl group (–COOH).

Nomenclature of Alkanoic Acids

To name an alkanoic acid, the –e ending from the parent alkane is replaced by –oic acid. The following are the names of the first ten alkanoic acids:

1. Methanoic acid
2. Ethanoic acid
3. Propanoic acid
4. Butanoic acid
5. Pentanoic acid
6. Hexanoic acid
7. Heptanoic acid
8. Octanoic acid
9. Nonaoic acid
10. Decanoic acid

General Formula of Alkanoic Acids

The general formula for alkanoic acids is:
CnH2n+1COOH.

Example:
For n=6n = 6n=6:
C6H(2×6)+1COOH=C6H13COOHC_6H(2 times 6) + 1COOH = C_6H_{13}COOHC6​H(2×6)+1COOH=C6​H13​COOH.

Molecular and Condensed Formulae of Alkanoic Acids

Here are the molecular and condensed formulae for the first ten alkanoic acids:

• Methanoic acid:
  • Molecular: HCOOH
  • Condensed: HCOOH
• Ethanoic acid:
  • Molecular: CH₃COOH
  • Condensed: CH₃COOH
• Propanoic acid:
  • Molecular: C₂H₅COOH
  • Condensed: CH₃CH₂COOH
• Butanoic acid:
  • Molecular: C₃H₇COOH
  • Condensed: CH₃(CH₂)₂COOH
• Pentanoic acid:
  • Molecular: C₄H₉COOH
  • Condensed: CH₃(CH₂)₃COOH
• Hexanoic acid:
  • Molecular: C₅H₁₁COOH
  • Condensed: CH₃(CH₂)₄COOH
• Heptanoic acid:
  • Molecular: C₆H₁₃COOH
  • Condensed: CH₃(CH₂)₅COOH
• Octanoic acid:
  • Molecular: C₇H₁₅COOH
  • Condensed: CH₃(CH₂)₆COOH
• Nonaoic acid:
  • Molecular: C₈H₁₇COOH
  • Condensed: CH₃(CH₂)₇COOH
• Decanoic acid:
  • Molecular: C₉H₁₉COOH
  • Condensed: CH₃(CH₂)₈COOH

Structural Formulae of Alkanoic Acids

The structural formulae for the first ten alkanoic acids include:

• Methanoic acid: HCOOH
• Ethanoic acid: CH₃COOH
• Propanoic acid: C₂H₅COOH
• Butanoic acid: C₃H₇COOH
• Pentanoic acid: C₄H₉COOH
• Hexanoic acid: C₅H₁₁COOH
• Heptanoic acid: C₆H₁₃COOH
• Octanoic acid: C₇H₁₅COOH
• Nonaoic acid: C₈H₁₇COOH
• Decanoic acid: C₉H₁₉COOH

Skeletal Formulae of Alkanoic Acids

The skeletal formulae for the first ten alkanoic acids include:

• Methanoic acid: HCOOH
• Ethanoic acid: (Skeletal structure)
• Propanoic acid: (Skeletal structure)
• Butanoic acid: (Skeletal structure)
• Pentanoic acid: (Skeletal structure)
• Hexanoic acid: (Skeletal structure)
• Heptanoic acid: (Skeletal structure)
• Octanoic acid: (Skeletal structure)
• Nonaoic acid: (Skeletal structure)
• Decanoic acid: (Skeletal structure)

Natural Sources of Alkanoic Acids

• Citrus Fruits: Oranges, lemons (e.g., citric acid).
• Sour Milk: Contains lactic acid.
• Vinegar: Primarily acetic acid (ethanoic acid).
• Insect Stings: Methanoic acid from ant, bee, and nettle stings.
• Human Sweat: Contains butanoic acid.

Preparation of Alkanoic Acids

Alkanoic acids can be prepared through the oxidation of corresponding alkanols using oxidizing agents such as acidified potassium permanganate (VII) or acidified potassium dichromate (VI). The process occurs in two steps:

1. Oxidation to Alkanal: The alkanol is oxidized to an alkanal.
   RCH2OH→H+Oxidizing Agent……..RCHO+H2O
   (where R is the hydrocarbon chain)
   Example: Ethanol (C₂H₅OH) oxidizes to ethanal (acetaldehyde, C₂H₄O):
   C2H5OH→H+KMnO4………C2H4O+H2O
2. Further Oxidation to Alkanoic Acid: The alkanal is then further oxidized to form an alkanoic acid.
   RCHO→H+Oxidizing AgentRCOOH
   Example: Ethanal (C₂H₄O) oxidizes to ethanoic acid (acetic acid, C₂H₄O₂):
   C2H4O→H+KMnO4……C2H4O2

Overall Reaction

The overall reaction for the oxidation of ethanol to ethanoic acid can be summarized as:

C2H5OH→H+KMnO4……….C2H4O2

This process highlights the conversion of alkanols to alkanals and subsequently to alkanoic acids through oxidation.

Physical Properties of Alkanoic Acids

• State: Liquids at room temperature.
• Solubility: Smaller alkanoic acids are soluble in water, while larger ones are not. Solubility decreases with increasing molecular size due to the increasing proportion of hydrocarbon.
• Melting and Boiling Points: Increase with molecular size due to:
  • Increased van der Waals forces.
  • Hydrogen bonding between molecules from the –OH group in the carboxyl group.
• Viscosity: Increases with molecular mass due to stronger hydrogen bonds.

Chemical Properties of Alkanoic Acids

• Reactions with Metals: Produce salts and hydrogen.
  • Example: Mg (s) + 2 CH3COOH (aq) →(CH3COO)2Mg (aq) + H2
• Reactions with Alkalis: Produce salt and water (neutralization).
  • Example: NaOH (aq) + CH3COOH (aq) →CH3COONa (aq) + H2O (l)
• Reactions with Carbonates: Produce salts, carbon dioxide, and water.
  • Example: 

CaCO3 (s) + CH3COOH (aq) →(CH3COO)2Ca (aq) + CO2 (g) + H2O (l)

• Esterification: React with alkanols to produce alkanoates (esters).

Effect of Alkanoic Acids on Acid-Base Indicators

• Turn blue litmus paper red.
• Have pH values less than 7.
• Appear colorless in phenolphthalein.

Electrical Conductivity of Alkanoic Acids

Alkanoic acids conduct electricity in aqueous solutions due to ionization. For example, the ionization of ethanoic acid is represented as:

CH3COOH (l) + H2O (l) ⇌CH3COO−(aq)+H3O+(aq)

Uses of Alkanoic Acids

• Food Preservatives: e.g., ethanoic acid.
• Solvents: e.g., ethanoic acid.
• Production of Esters.
• Manufacture of Medicines: such as aspirin.

Topic 9: Alkanoates

Definition: Alkanoates, also known as esters, are organic compounds formed when alkanoic acids react with alkanols in the presence of a catalyst.

Functional Group of Alkanoates

The functional group of alkanoates is represented as –COO–.

Nomenclature of Alkanoates

The name of an alkanoate consists of two parts:

• The alkyl part from the alkanol comes first.
• The acid part follows, with the ending –oic replaced by –oate.

Examples:

1. Ethanoic Acid + Methanol
   • Alkyl part: methyl
   • Acid part: ethanoate
   • Name: Methyl Ethanoate
2. Butanoic Acid + Ethanol
   • Alkyl part: ethyl
   • Acid part: butanoate
   • Name: Ethyl Butanoate

Drawing Structures of Alkanoates

To draw structures of alkanoates formed from alkanoic acids and alkanols, follow these steps:

1. Write the structures of the alkanoic acid and the alkanol separately.
2. Remove the –H from the acid and the –OH from the alkanol.
3. Combine the remaining parts, starting with the acid part followed by the alkanol part.

Examples:

1. Methanol + Methanoic Acid
   • Structures:
     • Methanol: H3C−OH
     • Methanoic Acid: HCOOH
   • Alkanoate Structure: HCOOCH3 (Methyl Methanoate)
2. Propanol + Propanoic Acid
   • Structures:
     • Propanol: H3C−CH2−CH2OH
     • Propanoic Acid: C2H5COOH
   • Alkanoate Structure: C2H5COOCH2CH3​ (Propyl Propanoate)

Deducing Reactants from Alkanoate Structures

To determine the reactants of esterification given the structure of the alkanoate:

Example:

1. Structure Analysis
   • Alkanoate with 4 carbon atoms indicates the alkanoic acid is Butanoic Acid.
   • Alkyl part with 3 carbon atoms indicates the alkanol is Propanol.
   • Reactants: Butanoic Acid + Propanol
2. Another Example
   • Alkanoate with 2 carbon atoms indicates the acid is Ethanoic Acid.
   • Alkyl part with 4 carbon atoms indicates the alkanol is Butanol.
   • Reactants: Ethanoic Acid + Butanol

Sources of Alkanoates

1. Natural Sources:
   • Fruits and flowers
   • Fats and oils
2. Synthetic Preparation:
   • Alkanoates can be synthesized through condensation reactions of alkanoic acids.

Properties of Alkanoates

• Pleasant Fruit Smells: e.g., Ethyl Butanoate smells like pineapple.
• Volatile Liquids.
• Solubility: Small chain alkanoates are fairly soluble in water; solubility decreases with increasing chain length.
• Lower Melting and Boiling Points: Alkanoates have lower melting and boiling points than their corresponding alkanoic acids and alkanols due to the absence of free –OH groups, preventing hydrogen bond formation.
• Hydrolysis: Alkanoates react with sodium hydroxide in the presence of water to produce soap, a process called saponification.

Uses of Alkanoates

• Flavoring Agents: Used in sweets and biscuits.
• Fragrances: Commonly used in perfumes.
• Solvents: Employed in glues because of their easy evaporation.