Question

Triethanolamine, (HOCH, \(\left.\mathrm{CH}_{2}\right)_{3} \mathrm{~N}\), is a widely used biological buffer, with maximum buffering capacity at pH \(7.8\). Propose a synthesis of this compound from ethylene coide and ammonia.

Short answer

Question: Describe the synthesis of triethanolamine (HOCH₂CH₂)₃N from ethylene oxide and ammonia. Answer: The synthesis of triethanolamine from ethylene oxide and ammonia involves a series of reactions. Firstly, ethylene oxide reacts with ammonia to form ethanolamine. Next, ethanolamine reacts with another molecule of ethylene oxide to form diethanolamine. Finally, diethanolamine reacts with one more molecule of ethylene oxide to produce triethanolamine.

Step-by-step solution

Identify the reactants

Ethylene oxide: H₂C=CH-O + (NH₃): Ammonia

React ethylene oxide and ammonia

In the presence of a suitable catalyst, ethylene oxide will react with ammonia, leading to the formation of ethanolamine, an intermediate compound. Ethylene oxide + ammonia → ethanolamine H₂C=CH-O + NH₃ → HOCH₂CH₂NH₂

React ethanolamine with ethylene oxide

Now, we will add another molecule of ethylene oxide to the ethanolamine compound. Ethanolamine + ethylene oxide → diethanolamine HOCH₂CH₂NH₂ + H₂C=CH-O → HOCH₂CH₂NH(CH₂CH₂OH)

React diethanolamine with ethylene oxide

Finally, we will add one more molecule of ethylene oxide to the diethanolamine. Diethanolamine + ethylene oxide → triethanolamine HOCH₂CH₂NH(CH₂CH₂OH) + H₂C=CH-O → (HOCH₂CH₂)₃N

Final Synthesis

Overall, the synthesis of triethanolamine from ethylene oxide and ammonia can be summarized as follows: Ethylene oxide H₂C=CH-O + NH₃: Ammonia → HOCH₂CH₂NH₂: Ethanolamine HOCH₂CH₂NH₂: Ethanolamine + H₂C=CH-O: Ethylene oxide → HOCH₂CH₂NH(CH₂CH₂OH): Diethanolamine HOCH₂CH₂NH(CH₂CH₂OH): Diethanolamine + H₂C=CH-O: Ethylene oxide → (HOCH₂CH₂)₃N: Triethanolamine

Key concepts

Ethylene Oxide Reactions

Ethylene oxide is a highly reactive epoxide, often involved in the synthesis of various organic compounds. Due to its strained three-membered ring structure, it is quite eager to open and react with an array of nucleophiles. In industrial and laboratory settings, ethylene oxide is used to produce solvents, antifreeze, textiles, detergents, and pharmaceuticals, among other things.

When ethylene oxide is treated with a nucleophile such as ammonia, the ring opens to form an ethanolamine. This reaction is crucial in producing compounds like triethanolamine, which finds use in a multitude of applications, including as a bio-buffering agent. The synthesis from ethylene oxide is considered atom-economical and efficient, which is why it's a favored method in chemical manufacturing.

In educational materials, it is helpful to visualize the small, strained ring of ethylene oxide being attacked by the nucleophile, leading to the transformation into a more stable structure. This mechanical perspective aids in understanding why ethylene oxide is so reactive.

Nucleophilic Addition to Epoxides

The nucleophilic addition to an epoxide is a fundamental type of reaction in organic chemistry. Epoxides, such as ethylene oxide, are three-membered cyclic ethers with considerable ring strain, making them highly susceptible to nucleophilic attack. In the synthesis of triethanolamine, ammonia acts as the nucleophile that opens the epoxide ring of ethylene oxide to form an amino alcohol—a reaction that is an example of a nucleophilic addition.

During the reaction, the nucleophile donates a pair of electrons to the electrophilic carbon atom of the epoxide, opening the ring and leading to the formation of a new bond. This reaction generally proceeds under mild conditions, often only requiring a suitable catalyst or an appropriate pH environment to steer the reaction towards the desired product. Understanding the mechanism of nucleophilic addition to epoxides helps in grasping how complex amines like triethanolamine can be synthesized from simpler molecules.

Amine Buffering Agents

Amine buffering agents are compounds that help maintain the pH of a solution within a narrow range, which is essential for various biological and chemical processes. Triethanolamine, for example, is widely used as a biological buffer with maximum buffering capacity around pH 7.8, making it suitable for many biological systems that operate near neutral pH.

Buffers work by reacting with added acids or bases to dampen changes in the pH of the solution. Amines, being weak bases, can accept protons from acids, thus neutralizing the acids without causing a significant shift in pH. Conversely, the conjugate acid form of the amine can donate a proton when the solution becomes too basic. The amine's ability to go back-and-forth between these two forms is what makes it an effective buffer. In the case of triethanolamine, its three ethanol groups increase its solubility in water, further enhancing its buffering capabilities.

In educational settings, it could be beneficial to include practical examples of buffering in action, such as its use in cosmetic products to maintain skin's pH or in biochemical assays where precise pH control is paramount, thereby illustrating the real-world applications of amine buffering agents.