Question Details

In the following reaction sequence, the major product P is formed.

Glycerol reacts completely with excess P in the presence of an acid catalyst to form Q. Reaction of Q with excess NaOH followed by the treatment with CaCl2 yields Ca-soap R, quantitatively. Starting with one mole of Q, the amount of R produced in gram is ______.

[Given, atomic weight: H = 1, C = 12, N = 14, O = 16, Na = 23, Cl = 35, Ca = 40]

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Correct Answer :

909

Solution :

Let's break down the reactions step-by-step to identify P, Q, and R:

Step 1: Formation of P
The starting material is ethyl octadec-17-ynoate:
H-CC-(CH2)15-CO2Et
(i) Hydration of the alkyne using Hg2+/H3O+ yields a methyl ketone:
CH3-CO-(CH2)15-CO2Et
(ii) Clemmensen reduction (Zn-Hg/HCl) reduces the ketone group to a methylene group (-CH2-):
CH3-CH2-(CH2)15-CO2Et=CH3-(CH2)16-CO2Et
(iii) Acidic hydrolysis (H3O+,Δ) of the ester yields stearic acid:
P=CH3-(CH2)16-COOH (Stearic acid, C17H35COOH)

Step 2: Formation of Q
Reaction of glycerol with excess stearic acid (P) in the presence of an acid catalyst results in the esterification of all three hydroxyl groups of glycerol to form the triacylglycerol, tristearin (Q):
Glycerol+3 C17H35COOHQ (C17H35COO)3C3H5+3 H2O

Step 3: Formation of Ca-soap R
Saponification of 1 mole of Q with excess NaOH yields 3 moles of sodium stearate:
(C17H35COO)3C3H5+3 NaOH3 C17H35COONa+C3H5(OH)3
Treatment of these 3 moles of sodium stearate with CaCl2 forms the calcium soap (calcium stearate, R):
2 C17H35COONa+CaCl2(C17H35COO)2Ca (R)+2 NaCl
From the stoichiometry:
1 mole of Q3 moles of C17H35COONa1.5 moles of (C17H35COO)2Ca

Step 4: Calculation of Mass of R
Let us calculate the molecular weight of R, (C17H35COO)2Ca (which has the molecular formula C36H70O4Ca):
Molar mass of R=(36×12)+(70×1)+(4×16)+40
Molar mass of R=432+70+64+40=606 g/mol
Therefore, the mass of R produced starting with 1 mole of Q is:
Mass of R=1.5 moles×606 g/mol=909 grams

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