Triacylglycerol Reactions: Hydrolysis: Videos & Practice Problems

Saponification is a base-catalyzed hydrolysis of triglycerides, producing glycerol and carboxylate salts of fatty acids, essential for soap production. The mechanism involves nucleophilic acyl substitution, comprising nucleophilic attack, leaving group loss, and proton transfer. Acid-catalyzed hydrolysis, using strong acids like HCl or H₂SO₄, also yields glycerol and fatty acids through a stepwise process. Both methods highlight the importance of ester bond cleavage in lipid chemistry, emphasizing the role of hydroxide ions and hydronium ions in forming the final products.

Triacylglycerol Reactions: Hydrolysis Concept 1

Saponification is a chemical process that involves the base-catalyzed hydrolysis of esters, specifically triglycerides, to produce glycerol and fatty acid salts. In this reaction, hydroxide ions (OH^-) break the ester bonds, resulting in the formation of carboxylate anions instead of carboxylic acids. This is significant because the negatively charged oxygen atoms in the carboxylate anions bond with positively charged sodium ions (Na⁺) when sodium hydroxide (NaOH) is used as the base, leading to the creation of salts of fatty acids.

The process of saponification is crucial in the production of soaps. When sodium hydroxide is employed, the outcome is solid soap, while the use of potassium hydroxide (KOH) yields liquid soap. This distinction is important for various applications in the soap-making industry. Overall, saponification not only illustrates the principles of ester hydrolysis but also highlights its practical applications in everyday products like soaps.

Triacylglycerol Reactions: Hydrolysis Example 1

In this exercise, we are tasked with determining the structure of a Triacylglycerol (triglyceride) that, upon complete basic hydrolysis, yields two laurate salts, one palmitate salt, and one glycerol molecule. To approach this, we need to understand the components involved in the formation of these products.

First, we recognize that the laurate salts originate from lauric acid, which is a saturated fatty acid with a carbon chain of 12 carbons (C₁₂H₂₄O₂). The palmitate salt comes from palmitic acid, another saturated fatty acid, consisting of 16 carbons (C₁₆H₃₂O₂). Both fatty acids lack double bonds, indicating they are fully saturated.

To construct the Triacylglycerol, we start with a glycerol backbone, which has the molecular formula C₃H₈O₃. The glycerol molecule serves as the central component to which the fatty acids are esterified. Each fatty acid forms an ester linkage with the glycerol through a reaction between the hydroxyl groups of glycerol and the carboxyl groups of the fatty acids, resulting in the release of water.

In our specific case, the Triacylglycerol will have two lauric acid chains and one palmitic acid chain. The structure can be visualized as follows:

• Two lauric acid chains (C₁₂H₂₄O₂) connected to the first and second hydroxyl groups of glycerol.
• One palmitic acid chain (C₁₆H₃₂O₂) connected to the third hydroxyl group of glycerol.

Thus, the complete structure of the Triacylglycerol can be represented as:

Glycerol + 2 Lauric Acid + 1 Palmitic Acid = Triacylglycerol

In summary, the Triacylglycerol molecule consists of a glycerol backbone esterified with two lauric acid chains and one palmitic acid chain, reflecting the specific fatty acid composition derived from the hydrolysis products. Understanding the relationships between fatty acids and their corresponding salts is crucial for accurately determining the structure of the starting Triacylglycerol.

The salt of a fatty acid has its ending of “ic acid” changed to “ate”. Based on this information provide the name of the salt created from the following saponification reaction. 

• A. Potassium Laurate
• B. Sodium Oleate
• C. Potassium Myristate
• D. Potassium Lactate

Answer: (C)

Triacylglycerol Reactions: Hydrolysis Concept 2

The base-catalyzed hydrolysis of triacyl molecules, such as triglycerides, follows a nucleophilic acyl substitution (NAS) mechanism, which consists of three primary steps: nucleophilic attack, loss of the leaving group, and proton transfer. This process is essential for understanding how triglycerides can be broken down into their constituent fatty acids and glycerol.

In the first step, a hydroxide ion acts as a nucleophile, attacking the carbonyl carbon of the ester bond in the triglyceride. The carbonyl carbon is partially positive due to the electronegativity of the adjacent oxygen, which carries a partial negative charge. This nucleophilic attack results in the formation of a tetrahedral intermediate, where the hydroxyl group is now attached to the carbon that was previously part of the carbonyl group, and the pi bond is broken, leaving the oxygen with a negative charge.

Step two involves the reformation of the carbonyl pi bond. The tetrahedral intermediate collapses, allowing the oxygen to reform the double bond while simultaneously ejecting the carboxylate group as a leaving group. This step results in the formation of a carboxylic acid and a negatively charged oxygen, which corresponds to the carboxylate anion.

In the final step, the newly formed carboxylic acid donates a proton to the alkoxide ion created in the first step. This proton transfer results in the formation of a hydroxyl group and a carboxylate anion. It is important to note that in base-catalyzed hydrolysis, the end product is a carboxylate anion rather than a carboxylic acid.

To summarize, the base-catalyzed hydrolysis of triglycerides involves a systematic breakdown of the ester bonds through nucleophilic attack, leaving group departure, and proton transfer, ultimately yielding fatty acids and glycerol. This mechanism can be repeated for each ester bond in the triglyceride, allowing for the complete hydrolysis of the molecule.

Triacylglycerol Reactions: Hydrolysis Concept 3

Triacylglycerol hydrolysis is a crucial biochemical reaction that can occur through two primary methods: acid-catalyzed hydrolysis and enzymatic hydrolysis. In acid-catalyzed hydrolysis, strong acids such as hydrochloric acid (HCl) or sulfuric acid (H₂SO₄) facilitate the breakdown of ester bonds in triacylglycerols. This process occurs stepwise, meaning that the three fatty acids are released one at a time rather than all at once. Initially, the first ester linkage is hydrolyzed, releasing the first fatty acid, followed by the second and third in subsequent steps.

During this reaction, water (H₂O) plays a vital role in cleaving the ester bonds. The addition of water results in the formation of hydroxyl (OH) groups on the glycerol molecule, which is represented as having an oxygen atom that gains a hydrogen atom. This transformation yields glycerol and three fatty acids, each characterized by a hydrocarbon tail and a carboxylic acid head. The carboxylic acid functionality is established by adding an OH group to the carbonyl carbon of the fatty acid.

In contrast, enzymatic hydrolysis employs the digestive enzyme lipase under milder conditions to achieve the same end products: one glycerol molecule and three fatty acids. Although the mechanisms differ—acid-catalyzed hydrolysis relying on strong acids and enzymatic hydrolysis utilizing lipase—the final products remain consistent. Understanding these pathways is essential for grasping lipid metabolism and the biochemical processes involved in fat digestion.

Triacylglycerol Reactions: Hydrolysis Example 2

In the reaction involving a triacylglycerol (triglyceride) and hydrogen gas (H₂) in the presence of hydrochloric acid (HCl), the process of hydrolysis occurs. This reaction leads to the cleavage of ester linkages within the triglyceride, resulting in the formation of glycerol and three distinct fatty acids.

During hydrolysis, the ester bonds between the glycerol backbone and the fatty acid chains are broken. The oxygen atoms from the glycerol molecule gain hydrogen atoms (H₂), while the carbonyl groups of the fatty acids are converted into hydroxyl groups (OH). This transformation results in the production of three fatty acids, each characterized by unique structures.

To visualize the products, one can represent the three fatty acids as follows:

• Fatty Acid 1: A straight-chain fatty acid with a specific number of carbon atoms and a carboxylic acid group (–COOH) at one end.
• Fatty Acid 2: Another straight-chain fatty acid, differing in the length of the carbon chain or the presence of double bonds.
• Fatty Acid 3: A third distinct fatty acid, which may also vary in chain length or saturation compared to the others.

Ultimately, the reaction yields glycerol and three unique fatty acids, each contributing to the diversity of lipids in biological systems. This process highlights the significance of hydrolysis in lipid metabolism and the formation of essential fatty acids.

Provide the common name of the fatty acids produced from the acid-catalyzed hydrolysis of the following triacylglycerol.

• A. Palmitoleic acid
• B. Lauric acid
• C. Palmitic acid
• D. Myristic acid

Answer: (B)

Triacylglycerol Reactions: Hydrolysis Concept 4

In the acid-catalyzed hydrolysis of triacylglycerol (triglyceride) molecules, the mechanism follows a nucleophilic acyl substitution (NAS) pathway, which is characterized by multiple steps due to the involvement of acid. This process begins with the protonation of the carbonyl oxygen by a hydronium ion, leading to a positively charged intermediate. The first step involves proton transfer, where the carbonyl oxygen gains a proton, resulting in a carbonyl group that can only form one pi bond.

Next, a water molecule acts as a nucleophile, attacking the carbonyl carbon. This nucleophilic attack results in the formation of a tetrahedral intermediate, where the carbonyl carbon is now bonded to the water molecule. The oxygen in this intermediate carries a positive charge due to the formation of three bonds. A subsequent proton transfer occurs between the attached water molecule and another water molecule present in the aqueous environment, generating a new hydronium ion and further stabilizing the intermediate.

In the following step, a double bond is formed between the hydroxyl oxygen and the carbon, leading to the expulsion of the alkoxyl leaving group. This step is crucial as it regenerates the carbonyl group and results in the formation of a carboxylic acid. The final step involves the deprotonation of the hydroxyl group by another water molecule, restoring the carbonyl and yielding the carboxylic acid product along with a regenerated hydronium ion, which acts as the acid catalyst throughout the reaction.

Overall, the acid-catalyzed hydrolysis of triglycerides results in the formation of carboxylic acids and glycerol, with the mechanism highlighting the importance of proton transfers and nucleophilic attacks in the reaction pathway. This process can be applied to each fatty acid chain within the triglyceride, demonstrating the versatility of acid-catalyzed hydrolysis in lipid chemistry.

Propose a possible mechanism for the following reaction. 

In the process of acid-catalyzed hydrolysis of a triacylglycerol (triglyceride), the reaction results in the formation of glycerol and three fatty acids. The mechanism begins with the protonation of the carbonyl oxygen in the triglyceride, which enhances its electrophilicity. This step is crucial as it prepares the carbonyl carbon for nucleophilic attack.

Next, a water molecule acts as a nucleophile, attacking the carbonyl carbon. This leads to the formation of a tetrahedral intermediate, where the bond between the carbonyl carbon and the oxygen is broken, resulting in the generation of a hydroxyl group (–OH) and a positively charged intermediate. A proton transfer occurs, facilitated by another water molecule, which stabilizes the intermediate by converting the positively charged oxygen into a neutral hydroxyl group.

As the reaction progresses, the intermediate undergoes a rearrangement where the hydroxyl group can act as a good leaving group. The oxygen reforms a double bond with the carbon, leading to the expulsion of the leaving group, which is a fatty acid chain. This step is critical as it results in the release of one fatty acid and the formation of a carboxylic acid.

Following this, the remaining structure still contains two fatty acid chains attached to the glycerol backbone. The process of acid-catalyzed hydrolysis continues, repeating the steps for the remaining fatty acid chains. Each cycle results in the release of a fatty acid and the conversion of the glycerol backbone into a fully hydrolyzed product.

Ultimately, the complete hydrolysis of the triacylglycerol yields one glycerol molecule and three carboxylic acids, along with hydronium ions that are present in the solution. This mechanism illustrates the importance of protonation and nucleophilic attack in the hydrolysis of ester bonds in triglycerides, highlighting the role of acid catalysis in facilitating the reaction.

An optically inactive triacylglycerol molecule undergoes base-catalyzed hydrolysis to produce 1 glycerol molecule, 1 mole of laurate and 2 moles of myristate. Determine the structure of the triacylglycerol molecule.

In this scenario, we are tasked with determining the structure of an optically inactive triacylglycerol molecule that undergoes base-catalyzed hydrolysis, yielding one molecule of glycerol, one mole of laurate, and two moles of myristate. To begin, we recognize that laurate and myristate are the carboxylate anions derived from lauric acid and myristic acid, respectively. Lauric acid contains 12 carbon atoms and is saturated, while myristic acid has 14 carbon atoms and is also saturated.

The key detail provided is that the triacylglycerol is optically inactive, indicating that it lacks chirality. This suggests a symmetrical arrangement within the molecule. To analyze chirality, we focus on the second carbon of the glycerol backbone. For the triacylglycerol to be symmetrical and thus optically inactive, the two myristate groups must be attached to the same carbon atom, specifically carbon number 2 of the glycerol. This means that the structure must have two myristate chains and one laurate chain attached to the glycerol backbone.

To visualize the structure, we can denote the glycerol backbone as follows:

Glycerol: C₁ - C₂ - C₃

Where:

• C₁ is connected to a myristate (C₁₄H₂₈O₂)
• C₂ is connected to one laurate (C₁₂H₂₄O₂) and one myristate (C₁₄H₂₈O₂)
• C₃ is connected to another myristate (C₁₄H₂₈O₂)

This arrangement ensures that carbon number 2 is bonded to two identical myristate groups and one laurate group, creating a symmetrical structure. The presence of two identical groups at carbon number 2 prevents chirality, confirming the molecule's optical inactivity.

In summary, the structure of the triacylglycerol molecule can be represented as follows:

Triacylglycerol: C₁₄H₂₈O₂ (myristate) - C₁₂H₂₄O₂ (laurate) - C₁₄H₂₈O₂ (myristate)

This configuration illustrates the triacylglycerol's composition and confirms its optically inactive nature due to the symmetrical arrangement of its fatty acid chains.

Here’s what students ask on this topic:

What is saponification and how does it relate to soap production?

Saponification is the base-catalyzed hydrolysis of triglycerides, typically using sodium hydroxide (NaOH) or potassium hydroxide (KOH). This reaction breaks the ester bonds in triglycerides, producing glycerol and carboxylate salts of fatty acids. These carboxylate salts are the key components in soap. When NaOH is used, it produces solid soap, while KOH results in liquid soap. The process involves nucleophilic acyl substitution, where the hydroxide ion attacks the carbonyl carbon, leading to the formation of glycerol and fatty acid salts.

What is the mechanism of base-catalyzed hydrolysis of triacylglycerols?

The base-catalyzed hydrolysis of triacylglycerols follows a nucleophilic acyl substitution (NAS) mechanism. It involves three main steps: nucleophilic attack, loss of the leaving group, and proton transfer. First, the hydroxide ion (OH^-) attacks the carbonyl carbon of the ester bond, forming a tetrahedral intermediate. Next, the intermediate collapses, expelling the alkoxide ion as a leaving group. Finally, a proton transfer occurs, resulting in the formation of glycerol and carboxylate anions (fatty acid salts).

How does acid-catalyzed hydrolysis of triacylglycerols differ from base-catalyzed hydrolysis?

Acid-catalyzed hydrolysis of triacylglycerols uses strong acids like hydrochloric acid (HCl) or sulfuric acid (H₂SO₄) and proceeds through a stepwise mechanism. It involves proton transfer, nucleophilic attack, and loss of the leaving group, similar to base-catalyzed hydrolysis. However, the products are glycerol and free fatty acids, not carboxylate salts. The process is slower and requires more steps due to the need for protonation and deprotonation at various stages.

What are the products of enzymatic hydrolysis of triacylglycerols?

Enzymatic hydrolysis of triacylglycerols, typically catalyzed by the enzyme lipase, produces glycerol and three fatty acids. This reaction occurs under milder conditions compared to acid or base-catalyzed hydrolysis. The enzyme specifically targets the ester bonds in the triglyceride, facilitating their cleavage and resulting in the same products as acid-catalyzed hydrolysis: glycerol and free fatty acids.

What role do hydroxide ions play in the saponification process?

In the saponification process, hydroxide ions (OH^-) act as nucleophiles that attack the carbonyl carbon of the ester bonds in triglycerides. This nucleophilic attack initiates the hydrolysis reaction, leading to the formation of a tetrahedral intermediate. The intermediate then collapses, expelling the alkoxide ion and forming carboxylate anions (fatty acid salts) and glycerol. The hydroxide ions are crucial for breaking the ester bonds and driving the reaction to completion.