Mada za sehemu hiiOrganic ChemistryMada 4
- Introduction to organic chemistry
- Hydrocarbons
- Alcohols
- Carboxylic acids
A carboxylic acid is an organic compound containing a carboxyl functional group (-COOH). The general formula is R-COOH, where R represents the alkyl group.
- Example 1: If R = CH₃, the carboxylic acid is ethanoic acid (CH₃COOH).
- Example 2: If R = C₂H₅, the carboxylic acid is propanoic acid (C₂H₅COOH).
Note: The carboxyl group is always fixed at the terminal carbon atom, unlike alcohols, where the functional group (-OH) can move.
The homologous series of carboxylic acids is represented by the general formula:
where n represents the number of carbon atoms.
| Number of Carbons (n) | Name | Molecular Formula |
|---|---|---|
| 1 | Methanoic acid | CH₂O₂ |
| 2 | Ethanoic acid | C₂H₄O₂ |
| 3 | Propanoic acid | C₃H₆O₂ |
| 4 | Butanoic acid | C₄H₈O₂ |
| 5 | Pentanoic acid | C₅H₁₀O₂ |
| 6 | Hexanoic acid | C₆H₁₂O₂ |
- Replace the suffix "-ane" from the alkane with "-oic acid".
- The longest carbon chain must include the carboxyl group.
- If substituents are present, their positions are indicated, starting the numbering from the carboxyl group.
Examples:
- CH₃CH₂COOH → Propanoic acid
- CH₃CH₂CH₂CH₂COOH → Pentanoic acid
- (CH₃)₂C(COOH)CH₃ → 3,3-Dimethylbutanoic acid
Physical properties
- State: Lower members (e.g., formic and acetic acids) are liquids; higher members are solids.
- Solubility: Soluble in water due to hydrogen bonding. Solubility decreases with chain length.
- Odor: Characteristic sharp or sour smell (e.g., vinegar).
Chemical properties
Carboxylic acids exhibit acidic behavior and undergo a variety of reactions.
Reaction with bases (neutralization)
Carboxylic acids react with bases to form salts and water.
Reaction with metals
They react with reactive metals to form salts and hydrogen gas.
Esterification
Carboxylic acids react with alcohols to form esters in the presence of concentrated sulfuric acid.
Reaction with phosphorus halides
Carboxylic acids react with phosphorus halides to form acyl halides.
Reduction
Carboxylic acids can be reduced to primary alcohols using reducing agents such as lithium aluminum hydride (LiAlH₄).
- Food Industry: Acetic acid is used in vinegar as a preservative.
- Pharmaceuticals: Used to produce drugs like aspirin.
- Soap Production (Saponification): Carboxylic acids react with bases to form soaps
Saponification is the reaction of an ester with a strong base to produce soap and glycerol.
| Alcohol (-OH) | Carboxylic Acid (-COOH) |
|---|---|
| Functional group is -OH | Functional group is -COOH |
| Can occur at any position in the chain | Functional group is always terminal |
| Weakly acidic | Stronger acidity than alcohols |
- Overexposure can cause irritation to the skin and eyes.
- Methanoic acid is toxic and can cause burns or damage to the respiratory system if inhaled.
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