Mechanism and Scheme
- (3 pts) Epoxidation of an alkene requires a peroxyacid. Briefly explain the difference between a
carboxylic acid and a peroxy acid.
a. A carboxylic acid has a carbon with a double bond to an oxygen and another bond to and
-OH group
b. A peroxy acid contains a C-O-OH so it has an extra oxygen atom. A peroxy acid is
weaker than carboxylic acid. - (4 pts) What is the name of and abbreviation for the peroxyacid being used for this experiment?
a. Meta-chloroperbenzoic acid (m-CPBA) - (8 pts) Draw the structure of this peroxy acid.
The Correct Answer and Explanation is :
The difference between a carboxylic acid and a peroxy acid lies in the presence of an additional oxygen atom in the peroxy acid. Here’s a breakdown:
- Carboxylic Acid:
- A carboxylic acid has a structure where a carbonyl group (C=O) is bonded to a hydroxyl group (-OH), making it a functional group denoted as -COOH. The key features of a carboxylic acid are:
- A double bond between carbon and oxygen (carbonyl group, C=O).
- A single bond between the carbonyl carbon and an -OH group (hydroxyl).
- Carboxylic acids are relatively weak acids due to the ability of the carbonyl oxygen to stabilize negative charges when the hydrogen ion (H⁺) dissociates.
- Peroxy Acid:
- A peroxy acid (also known as a peracid) is a type of carboxylic acid where the hydroxyl group (-OH) is replaced with a peroxy group (-O-OH). The structure of a peroxy acid can be represented as R-CO3H, where the central carbon is double-bonded to an oxygen and single-bonded to a second oxygen, which is also bonded to a hydrogen atom (-OOH).
- The presence of the extra oxygen atom (in the peroxy group) makes peroxy acids stronger oxidizers compared to carboxylic acids, which is why they are often used in reactions like epoxidation, where the added oxygen helps form an epoxide.
Peroxy Acid Used in Epoxidation:
The peroxy acid typically used in this experiment is meta-chloroperbenzoic acid (abbreviated m-CPBA). It is a widely used peroxy acid for the epoxidation of alkenes. The structure of m-CPBA is composed of a benzene ring with a chlorine atom at the meta position relative to the carboxyl group and an -O-OH (peroxy) group attached to the benzoic acid structure.
Explanation of m-CPBA:
Meta-chloroperbenzoic acid (m-CPBA) is favored in epoxidation reactions because of the strong electrophilic nature of the oxygen in the peroxy group (-O-OH). This group readily transfers oxygen to the alkene, creating a three-membered ring structure known as an epoxide.
Here is a brief summary of its structure and functionality:
- It contains a benzene ring (C₆H₅) with a chlorine atom at the meta position (relative to the carboxyl group).
- The carboxyl group (-COOH) is bonded to the ring, and the peroxy group (-O-OH) is attached to this structure.
Structure of m-CPBA:
- The oxygen from the peroxy group (-O-OH) is highly electrophilic, which makes it effective for reactions such as epoxidation, where the alkene reacts with the peroxy acid to form the epoxide.