Chapter 17: Problem 31
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.
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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.
The reaction of an \(\alpha\)-diketone with concentrated sodium or potassium
hydroxide to give the salt of an \(\alpha\)-hydroxyacid is given the general
name benzil-benzilic acid rearrangement. It is illustrated by the conversion
of benzil to sodium benzilate and then to benzilic acid. Propose a mechanism
for this rearrangement.
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)
Select the stronger acid in each set. (a) Phenol \(\left(\mathrm{p} K_{\mathrm{a}} 9.95\right)\) and benzoic acid \(\left(\mathrm{p} K_{\mathrm{a}} 4.19\right)\) (b) Lactic acid \(\left(K_{\mathrm{a}} 8.4 \times 10^{-4}\right)\) and ascorbic acid \(\left(K_{\mathrm{a}} 7.9 \times 10^{-5}\right)\)
Acetic acid has a boiling point of \(118^{\circ} \mathrm{C}\), whereas its methyl ester has a boiling point of \(57^{\circ} \mathrm{C}\). Account for the fact that the boiling point of acetic acid is higher than that of its methyl ester even though acetic acid has a lower molecular weight.
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