Reactions as Acids

What are Acidic Reactions?

In organic chemistry, certain functional groups display acidic properties, meaning they can donate protons ($H^+$) to form conjugate bases.

Alcohols and carboxylic acids are two important classes of organic compounds that can react as acids, but their strength and reactivity differ significantly.

• Carboxylic acids are much stronger acids than alcohols due to the presence of the carboxyl group ($-COOH$).

Reactions of Alcohols with Sodium

$$\text{Alcohol} + \text{Sodium} → \text{Alkoxide} + \text{Hydrogen gas}$$

Alcohols can react with reactive metals like sodium ($Na$), behaving like weak acids. When alcohols react with sodium, hydrogen gas ($H₂$) is produced along with an alkoxide salt.

This reaction is similar to water and sodium, but alcohols are less acidic than water.

Acidic Nature of Carboxylic Acids

Carboxylic acids, characterized by the carboxyl group ($-COOH$), are much stronger than alcohol.

• This is because the group can lose a proton ($H^+$) and form a stable carboxylate anion ($RCOO⁻$).
• The stability of the carboxylate anion is due to resonance, where the negative charge is delocalized between the two oxygen atoms. Carboxylic acids can react with metals, bases, and carbonates, releasing hydrogen gas or forming salts and water.

Reactions of Carboxylic Acids

Reaction with Magnesium (Metal)

$$\text{Carboxylic acid} + \text{Magnesium} → \text{Magnesium carboxylate} + \text{Hydrogen gas}$$

Carboxylic acids react with reactive metals like magnesium ($Mg$), producing salt and hydrogen gas.

This reaction is similar to the reaction of acids with metals such as hydrochloric acid with magnesium.

Reaction with Sodium Hydroxide (Base)

$$\text{Carboxylic acid} + \text{Sodium hydroxide} → \text{Sodium carboxylate} + \text{Water}$$

Carboxylic acids undergo neutralization reactions with bases like sodium hydroxide ($NaOH$), forming salt and water.

This reaction is common in titrations to determine the concentration of an unknown carboxylic acid solution.

This is a typical acid-base neutralization reaction.

Reaction with Sodium Carbonate (Carbonate)

$$\text{Carboxylic acid} + \text{Sodium carbonate} → \text{Sodium carboxylate} + \text{Water} + \text{Carbon dioxide}$$

Carboxylic acids react with carbonates, such as sodium carbonate ($Na₂CO₃$), to produce salt, carbon dioxide ($CO₂$), and water.

This reaction is used to test for the presence of carboxylic acids, as the release of $CO₂$ gas is visible as effervescence.