Benzoate Ion

Definition

The benzoate ion is the conjugate base of benzoic acid, formed when a hydrogen atom is removed from the carboxyl group. It is a common anion found in various food preservatives and pharmaceutical compounds.

5 Must Know Facts For Your Next Test

1. The benzoate ion has a delocalized negative charge, making it more stable and less reactive than the parent carboxylic acid.
2. Benzoate ions are commonly used as preservatives in food, beverages, and personal care products due to their antimicrobial properties.
3. In the presence of ascorbic acid (vitamin C), benzoate ions can form benzene, which is a known carcinogen.
4. Benzoate ions can be metabolized in the body, with the carboxyl group being oxidized to form hippuric acid.
5. The pKa of benzoic acid is 4.2, meaning the benzoate ion is the predominant species at physiological pH (around 7.4).

Review Questions

• Explain the relationship between the benzoate ion and benzoic acid, and how this relates to the structure and properties of carboxylic acids.
  • The benzoate ion is the conjugate base of benzoic acid, formed when a hydrogen atom is removed from the carboxyl group (-COOH) of benzoic acid. This transformation results in a negatively charged ion with a delocalized charge, making the benzoate ion more stable and less reactive than the parent carboxylic acid. The ability of carboxylic acids to form conjugate bases is an important structural feature that contributes to their unique chemical properties, such as their acidic nature and ability to participate in various reactions.
• Describe the role of the benzoate ion in food preservation and the potential risks associated with its use.
  • Benzoate ions are commonly used as food preservatives due to their antimicrobial properties, which help inhibit the growth of bacteria, yeasts, and molds. However, in the presence of ascorbic acid (vitamin C), benzoate ions can undergo a reaction to form benzene, a known carcinogen. This potential risk has led to increased scrutiny and regulation of benzoate ion usage in food and beverage products. Manufacturers must carefully balance the preservative benefits of benzoate ions with the need to minimize the formation of harmful byproducts like benzene.
• Analyze the significance of the benzoate ion's pKa value and its implications for the ion's behavior in the body.
  • The pKa of benzoic acid, the parent compound of the benzoate ion, is 4.2. This means that at physiological pH (around 7.4), the benzoate ion is the predominant species present. The delocalized negative charge of the benzoate ion makes it more stable and less reactive than the protonated carboxylic acid form. This has important implications for the ion's behavior in the body, as it can be more readily absorbed, transported, and metabolized. The benzoate ion can be oxidized in the body to form hippuric acid, which is then excreted. Understanding the pKa and the resulting speciation of the benzoate ion is crucial for predicting its pharmacokinetic and toxicological properties within the human body.

Related terms

Carboxylic Acid: Organic compounds containing a carboxyl group (-COOH), which consists of a carbonyl group (C=O) and a hydroxyl group (-OH).

Conjugate Base: The species formed when an acid loses a proton (H+), resulting in a negatively charged ion.

Benzoic Acid: A weak, aromatic carboxylic acid with the chemical formula C6H5COOH, commonly used as a food preservative.