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Chapter 17: Problem 53

So far, you have seen a number of reducing agents used in reactions. Functional groups react differently with each of these reagents. With this in mind, complete the following reaction, which is the last step in a synthesis of fexofenadine, a nonsedating antihistamine sold under the trade name Allegra.

Short Answer

Expert verified
Answer: The main functional group change during the last step of the fexofenadine synthesis is the reduction of the carboxylic acid group (COOH) to an alcohol group (OH). The reducing agent used to accomplish this change is lithium aluminum hydride (LiAlH4).

Step by step solution

01

Identify the reactant and reagent

First, let's identify the reactant, which is the molecule undergoing the synthesis of fexofenadine and the reagent which will be used in the reaction. Reactant: Fexofenadine molecule with a carbonyl group (C=O) and a carboxylic acid functionality (COOH) Reagent: Reducing agent (since synthesis requires a reducing agent)
02

Choose the appropriate reducing agent

Since fexofenadine has both a carbonyl group and a carboxylic acid functionality, it's important to choose a reducing agent that would specifically reduce the carboxylic acid group without affecting the carbonyl group. One common reducing agent for this purpose is lithium aluminum hydride (LiAlH4).
03

Write the reaction equation

Now we can write the reaction equation, showing the reactant, the reagent (LiAlH4), and the product (fexofenadine). Reactant + LiAlH4 -> Fexofenadine
04

Identify the change in functional groups

The main change that happens in this reaction is the reduction of the carboxylic acid group (COOH) to an alcohol group (OH), while the carbonyl group remains unchanged.
05

Complete the reaction

Now that we have identified the role of the reducing agent (LiAlH4) and the functional group change, we can complete the reaction. The carboxylic acid group (COOH) in the fexofenadine molecule will be reduced to an alcohol group (OH), while the carbonyl group remains unchanged: Fexofenadine (with COOH) + LiAlH4 -> Fexofenadine (with OH)

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Most popular questions from this chapter

On a cyclohexane ring, an axial carboxyl group has a conformational energy of \(5.9 \mathrm{~kJ}\) (1.4 kcal)/mol relative to an equatorial carboxyl group. Consider the equilibrium for the alternative chair conformations of trans- 1,4 -cyclohexanedicarboxylic acid. Draw the less stable chair conformation on the left of the equilibrium arrows and the more stable chair on the right. Calculate \(\Delta \mathrm{G}^{0}\) for the equilibrium as written and calculate the ratio of the more stable chair to the less stable chair at \(25^{\circ} \mathrm{C}\).

Write the products of the following sequences of reactions. Refer to your roadmaps to see how the combined reactions allow you to "navigate" between the different functional groups. Note that you will need both your old Chapters 6-11 roadmap and your new Chapters 15-17 roadmap for these. (a) 1\. NBS A haloarene (b) 2\. Mg, ether 3\. \(\mathrm{CO}_{2}\) \(\begin{array}{ll}\text { An alkene } & \text { 4. } \mathrm{HCA}, \mathrm{H}_{2} \mathrm{O} \\ & \text { 5. } \mathrm{CH}_{2} \mathrm{~N}_{2} \\\ & \text { 6. } \mathrm{CPBA}\end{array}\) (c) O=C(O)C1CCCCC1 (d)

Excess ascorbic acid is excreted in the urine, the \(\mathrm{pH}\) of which is normally in the range 4.8-8.4. What form of ascorbic acid would you expect to be present in urine of \(\mathrm{pH} 8.4\) free ascorbic acid or ascorbate anion? Explain.

We have studied Fischer esterification, in which a carboxylic acid is reacted with an alcohol in the presence of an acid catalyst to form an ester. Suppose that you start instead with a dicarboxylic acid such as terephthalic acid and a diol such as ethylene glycol. Show how Fischer esterification in this case can lead to a macromolecule with a molecular weight several thousand times that of the starting materials. O=C(O)c1ccc(C(=O)O)cc1 (PET) 1,4-Benzenedicarboxylic acid \(\quad 1,2\)-Ethanediol (Terephthalic acid) (Ethylene glycol) As we shall see in Section 29.5B, the material produced in this reaction is a highmolecular-weight polymer, which can be fabricated into Mylar films and into the textile fiber known as Dacron polyester.

Low-molecular-weight dicarboxylic acids normally exhibit two different \(\mathrm{p} K_{\mathrm{a}}\) values. Ionization of the first carboxyl group is easier than the second. This effect diminishes with molecular size, and for adipic acid and longer chain dicarboxylic acids, the two acid ionization constants differ by about one \(\mathrm{p} K\) unit. $$ \begin{array}{|llll|} \hline \text { Dicarboxylic Acid } & \text { Structural Formula } & \mathrm{p} \kappa_{\mathrm{a} 1} & \mathrm{p} K_{\mathrm{a} 2} \\ \hline \text { Oxalic } & \mathrm{HOOCCOOH} & 1.23 & 4.19 \\ \text { Malonic } & \mathrm{HOOCCH}{ }_{2} \mathrm{COOH} & 2.83 & 5.69 \\ \text { Succinic } & \mathrm{HOOC}\left(\mathrm{CH}_{2}\right)_{2} \mathrm{COOH} & 4.16 & 5.61 \\ \text { Glutaric } & \mathrm{HOOC}\left(\mathrm{CH}_{2}\right)_{3} \mathrm{COOH} & 4.31 & 5.41 \\ \text { Adipic } & \mathrm{HOOC}\left(\mathrm{CH}_{2}\right)_{4} \mathrm{COOH} & 4.43 & 5.41 \\ \hline \end{array} $$ Why do the two \(\mathrm{p} K_{\mathrm{a}}\) values differ more for the shorter chain dicarboxylic acids than for the longer chain dicarboxylic acids?
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