Properties of carboxylic acids

Page 1: Properties of Carboxylic Acids

Overview

  • Carboxylate salts are utilized as preservatives and flavor enhancers in various food products such as soups and seasonings.

  • Sodium propionate is a common preservative used in cheeses and baked goods, inhibiting spoilage from microorganisms.

Page 2: Polarity of Carboxylic Acids

Key Features

  • Carboxylic acids exhibit strong polarity due to the presence of two polar groups:

    • Hydroxyl group (–OH)

    • Carbonyl group (C=O)

Page 3: Boiling Points of Carboxylic Acids

Factors Affecting Boiling Points

  • The polar carboxyl groups enable carboxylic acids to form multiple hydrogen bonds with themselves.

  • This hydrogen bonding significantly increases the boiling points when compared to alcohols, ketones, and aldehydes of similar molar mass.

Page 4: Carboxylic Acids and Dimers

Dimers Formation

  • The higher boiling points result from the formation of dimers between two carboxylic acids.

  • Each dimer is held together by two hydrogen bonds, effectively doubling the molecular mass and consequently increasing the boiling point.

Page 5: Learning Check 1

Activity

  • Match the compounds 2-butanol, pentane, and propanoic acid with the following boiling points:

    • 141 ℃, 100 ℃, 36 ℃.

Page 6: Solution to Learning Check 1

Boiling Points Factors

  • Boiling points increase due to:

    • Increased formation of hydrogen bonds.

    • Increased dipole-dipole attractions.

    • Increasing molar mass.

Page 7: Further Solution Details

Boiling Points Comparison

  • Pentane:

    • Cannot form hydrogen bonds (lowest boiling point at 36℃).

  • 2-Butanol:

    • Can form hydrogen bonds (boiling point 100℃).

  • Propanoic acid:

    • Forms dimers, leading to the highest boiling point at 141 ℃.

Page 8: Solubility in Water

General Trends

  • Carboxylic acids have the ability to form hydrogen bonds with water.

  • Solubility Assessment:

    • Highly soluble if they have 1 to 5 carbon atoms.

    • Less soluble as the carbon chain length increases.

  • Example: Acetic acid forms hydrogen bonds with water molecules.

Page 9: Acidity of Carboxylic Acids

Acid Characteristics

  • Carboxylic acids are regarded as weak acids.

  • They dissociate in water to produce carboxylate ions and hydronium ions.

  • The ability to lose a proton is stabilized by the two oxygen atoms in a carboxylate ion that can share the negative charge.

Page 10: Properties Summary of Carboxylic Acids

Key Properties Table

IUPAC Name

Structural Formula

Boiling Point (°C)

Solubility

Acid Ionization Constant (Ka at 25°C)

Methanoic acid

HCOOH

101

Soluble

1.8 x 10^(-4)

Ethanoic acid

CH3COOH

118

Soluble

1.8 x 10^(-5)

Propanoic acid

CH3CH2COOH

141

Soluble

1.3 x 10^(-5)

Butanoic acid

CH3(CH2)2COOH

164

Soluble

1.5 x 10^(-5)

Pentanoic acid

CH3(CH2)3COOH

187

Soluble

1.5 x 10^(-5)

Hexanoic acid

CH3(CH2)4COOH

205

Slightly soluble

1.4 x 10^(-5)

Benzoic acid

C6H5COOH

250

Slightly soluble

6.4 x 10^(-5)

Page 11: Learning Check 2

Activity

  • Write the balanced equation for the ionization of butanoic acid in water and identify the resulting carboxylate ion.

Page 12: Solution to Learning Check 2

Ionization Equation

  • Write the balanced equation representing the ionization of butanoic acid in water to determine the carboxylate ion formed.

Page 13: Neutralization of Carboxylic Acids

Reaction Overview

  • Carboxylate salts are produced when a carboxylic acid reacts with a strong base like NaOH or KOH.

  • The naming convention for the carboxylate ion replaces the '-ic acid' ending with '-ate'.

Page 14: Properties of Carboxylate Salts

Characteristics

  • Carboxylate salts are:

    • Ionic compounds with strong attractions between positively charged metal ions and negatively charged carboxylate ions.

    • Typically solid at room temperature.

    • Possess high melting points.

    • Usually soluble in water.

Page 15: Carboxylic Acids as Preservatives

Practical Applications

  • Sodium propionate is added to various foods such as bread and cheeses to prevent spoilage.

  • Sodium benzoate is another additive used in juices and salads to inhibit the growth of mold and bacteria.

Page 16: Additional Preservative Example

Flavor Enhancers

  • Monosodium glutamate (MSG) is added to a variety of foods including meats and vegetables to enhance flavor, although it may trigger headaches in some individuals.

Page 17: Learning Check 3

Activity

  • Write the equation for the reaction of propanoic acid with NaOH.

Page 18: Solution to Learning Check 3

Reaction Equation

  • Write the equation detailing the reaction between propanoic acid and NaOH to demonstrate the neutralization process.

Page 19: Carboxylic Acids in Metabolism

Metabolic Role

  • At cell pH levels, carboxylic acids dissociate, with carboxylate ions participating in the citric acid cycle (Krebs cycle).

  • Succinic acid is an example, existing in equilibrium with its carboxylate ion, succinate.

Page 20: Metabolic Processes Overview

Glycolysis and Lactic Acid

  • During glycolysis, glucose is converted into pyruvate, the carboxylate salt of pyruvic acid.

  • Under anaerobic conditions (low oxygen), pyruvate is reduced to form lactic acid or the lactate ion.

Page 21: Citric Acid Cycle Dynamics

Energy Production

  • In the citric acid cycle, di- and tri-carboxylates are oxidized and decarboxylated, producing energy for cellular functions.

  • Example: Citrate (six carbons) is oxidized to a five-carbon compound.

Page 22: Further Citric Acid Cycle Reaction

Cycle Continuation

  • The cycle progresses as α-ketoglutarate loses a carbon to form a four-carbon succinate.

  • Subsequent reactions ultimately convert succinate to oxaloacetate.