Question

Draw the structure of glyceryl trilaurate, a fat. Lauric acid (page 941 ) has the formula \(\mathrm{C}_{11} \mathrm{H}_{23} \mathrm{CO}_{2} \mathrm{H}\) (a) Write an equation for the base hydrolysis of glyceryl trilaurate. (b) Write an equation for the reaction that could be used to prepare biodiesel fuel from this fat.

Short answer

Glyceryl trilaurate hydrolyzes to glycerol and sodium laurate; it transesterifies to glycerol and methyl laurate.

Step-by-step solution

Understand Glyceryl Trilaurate Structure

Glyceryl trilaurate is an ester derived from glycerol and three molecules of lauric acid. Lauric acid is \( \text{C}_{11}\text{H}_{23}\text{COOH} \). The glycerol backbone is \( \text{C}_3\text{H}_5(\text{OH})_3 \). Glyceryl trilaurate has the structure: \( \text{C}_3\text{H}_5(\text{OOC} \text{—} \text{C}_{11} \text{H}_{23})_3 \).

Write Hydrolysis Reaction Equation

In base hydrolysis (saponification), the glyceryl trilaurate reacts with 3 NaOH (sodium hydroxide) to produce glycerol and sodium laurate. The equation is:\[\text{C}_3\text{H}_5(\text{OOC} \text{—} \text{C}_{11} \text{H}_{23})_3 + 3 \text{NaOH} \rightarrow \text{C}_3\text{H}_5(\text{OH})_3 + 3 \text{C}_{11}\text{H}_{23}\text{COONa}\]

Write Reaction for Biodiesel Preparation

The reaction to produce biodiesel from glyceryl trilaurate involves transesterification with methanol \((\text{CH}_3\text{OH})\). This produces glycerol and methyl laurate. The reaction is:\[\text{C}_3\text{H}_5(\text{OOC} \text{—} \text{C}_{11} \text{H}_{23})_3 + 3 \text{CH}_3\text{OH} \rightarrow \text{C}_3\text{H}_5(\text{OH})_3 + 3 \text{C}_{11}\text{H}_{23}\text{COOCH}_3\]

Key concepts

Chemical Structure

Chemical structures are like the building blocks of a molecule. For glyceryl trilaurate, envision a held-together design of glycerol and lauric acid molecules. Glycerol, the pillar, is composed of three carbon atoms each bonded to a hydroxyl group \((\text{OH})\). Lauric acid contributes a chain with the formula \(\text{C}_{11}\text{H}_{23}\text{COOH}\). Combining these, we get glyceryl trilaurate, formulated as \(\text{C}_3\text{H}_5(\text{OOC} \text{—} \text{C}_{11} \text{H}_{23})_3\).

• Glycerol forms the backbone of the structure.
• Each of the three lauric acid molecules attaches through ester bonds \((\text{---OOC} \text{---})\).

This structure is vital for its properties and reactions.

Base Hydrolysis

Base hydrolysis, also known as saponification, is a chemical reaction where an ester, like glyceryl trilaurate, is broken down using a base, typically sodium hydroxide \((\text{NaOH})\). This process results in the formation of alcohol and a salt of the acid. When glyceryl trilaurate undergoes saponification, it reacts with sodium hydroxide to produce glycerol and sodium laurate. The chemical equation is:\[\text{C}_3\text{H}_5(\text{OOC} \text{—} \text{C}_{11} \text{H}_{23})_3 + 3 \text{NaOH} \rightarrow \text{C}_3\text{H}_5(\text{OH})_3 + 3 \text{C}_{11}\text{H}_{23}\text{COONa}\]

• Glycerol is released as a simple alcohol.
• The sodium laurate is formed as a salt, a component commonly found in soaps.

This is a key reaction in producing many commercial soap products.

Biodiesel Preparation

Biodiesel preparation from fats like glyceryl trilaurate involves a process called transesterification. This is a vital step in transforming esters into biodiesel, an eco-friendlier fuel choice. For glyceryl trilaurate, the process involves reacting with methanol \((\text{CH}_3\text{OH})\) to convert it into methyl laurate, a component of biodiesel. Here's the reaction: \[\text{C}_3\text{H}_5(\text{OOC} \text{—} \text{C}_{11} \text{H}_{23})_3 + 3 \text{CH}_3\text{OH} \rightarrow \text{C}_3\text{H}_5(\text{OH})_3 + 3 \text{C}_{11}\text{H}_{23}\text{COOCH}_3\]

• Glycerol is again produced as a byproduct.
• Methyl laurate, a fatty acid methyl ester, is the desired biodiesel component.

This conversion is essential for creating a renewable energy source.

Transesterification

Transesterification is the chemical process used to change one ester into another. In the context of biodiesel production, this reaction swaps the glycerol in a fat with an alcohol, typically methanol. The primary goal is to transform the oil or fat into a methyl ester (biodiesel) and glycerol. Utilizing catalysts like sodium or potassium hydroxide, the reaction with methanol becomes more efficient and effective.

• This method is widely used in biodiesel industries due to its efficiency.
• The process is a straightforward method that brings significant environmental benefits by reducing reliance on fossil fuels.

In summary, transesterification is a central player in renewable fuel development.

Saponification

Saponification is a fascinating chemical reaction where fats react with an alkali to produce soaps and glycerol. As mentioned earlier, it is a specific type of base hydrolysis but tailored towards creating soap-like substances. Here's why it's important:

• Saponification converts triglycerides into glycerol and fatty acid salts - soaps.
• It's an essential process in the soap-making industry, traditionally using fats like glyceryl trilaurate.

Not only does it play a role in creating everyday products, but it also showcases the transformation capabilities of chemical reactions.