(Solved): A synthesis of ascorbic acid (vitamin C, 1) starting from D-(+)-galactose (2) is shown below (Hawor ...

A synthesis of ascorbic acid (vitamin C, 1) starting from D-(+)-galactose (2) is shown below (Haworth, W.N., et al., J. Chem. Soc., 1933, 1419-1423). Consider the following questions about the design and reactions used in this synthesis: 2 6 $?\begin{array}{l}6\\ (1){\mathrm{NH}}_2)\mathrm{NaOC}\\ \text{ (2) }\end{array}$ ${\mathrm{PhNHNH}}_2$ $8\%\mathrm{HCl}$ 3 ${\mathfrak{KMnO}}_4$ 5 4 8 ${\mathrm{KCNCaCl}}_2$ 9 Why did Haworth and co-workers introduce the acetal functional groups in $3$ ? Acetonide acetal protecting groups were installed in 3 to protect the from 3 to 4. groups from oxidation in the step (b) In the reaction from 5 to 6 you can assume that there was acid (e.g., $\mathrm{HCl}$ ) present with the sodium amalgam. What reaction occurred here and from what functional group did that reaction actually proceed? The hemiacetal group of 5 is in equilibrium with the from which it is derived. The reaction shown involves of the keto equilibrium form to alcohol 6.