Question 12

Identify P:

• Step i: Oxymercuration-demercuration of the terminal alkyne $H-C \equiv C-(CH_2)_{15}CO_2Et$ gives a methyl ketone: $CH_3-CO-(CH_2)_{15}CO_2Et$.
• Step ii: Clemmensen reduction ($Zn-Hg/HCl$) reduces the ketone to a methylene group: $CH_3-CH_2-(CH_2)_{15}CO_2Et$, which is ethyl stearate ($CH_3(CH_2)_{16}CO_2Et$).
• Step iii: Acidic hydrolysis ($H_3O^+, \Delta$) of the ester gives the carboxylic acid $\text{P}$: $CH_3(CH_2)_{16}COOH$ (Stearic acid, $C_{18}H_{36}O_2$).

Identify Q:

• Glycerol ($C_3H_8O_3$) reacts with excess stearic acid ($\text{P}$) to form a triester (tristearin): $C_3H_5(OH)_3 + 3 C_{17}H_{35}COOH \rightarrow C_3H_5(OOC(CH_2)_{16}CH_3)_3 (\text{Q}) + 3 H_2O$.

Identify R:

• Saponification of 1 mole of $\text{Q}$ with excess $\text{NaOH}$ yields 3 moles of sodium stearate ($C_{17}H_{35}COONa$).
• Treatment with $\text{CaCl}_2$ yields Calcium stearate (Ca-soap $\text{R}$): $2 C_{17}H_{35}COONa + CaCl_2 \rightarrow (C_{17}H_{35}COO)_2Ca (\text{R}) + 2 NaCl$.
• From 3 moles of sodium stearate, $1.5$ moles of $\text{R}$ are produced.

Calculate Mass of R:

• Molecular weight of $\text{R}$ ($C_{36}H_{70}O_4Ca$): $M = (18 \times 12 + 35 \times 1 + 2 \times 16) \times 2 + 40 = 283 \times 2 + 40 = 566 + 40 = 606$ g/mol.
• Mass of $\text{R} = 1.5 \text{ moles} \times 606 \text{ g/mol} = 909 \text{ g}$.