Spermaceti (a wax from the head of the sperm whale) resembles high-molecular weight hydrocarbons in physical properties and inertness toward \(\mathrm{Br}_{2} / \mathrm{CCl}_{4}\) and \(\mathrm{KMnO}_{4} ;\) on qualitative analysis it gives positive tests only for carbon and hydrogen. However, its infrared spectrum shows the presence of an ester group, and quantitative analysis gives the empirical formula \(\mathrm{C}_{16} \mathrm{H}_{32} \mathrm{O}\) A solution of the wax and \(\mathrm{KOH}\) in ethanol is refluxed for a long time. Titration of an aliquot shows that one equivalent of base has been consumed for every \(475 \pm 10\) grams of wax. Water and ether are added to the cooled reaction mixture, and the aqueous and ethereal layers are separated. Acidification of the aqueous layer yields a solid \(\mathrm{A}\), m.p. \(62-3^{\circ}\), neutralization equivalent \(260 \pm 5\). Evaporation of the ether layer yields a solid B, m.p. \(48-9^{\circ}\). Reduction by LiAlHi \(_{4}\) of either spermaceti or A gives \(B\) as the only product. B is normal alcohol. What is the structure of spermaceti?

Step by step solution

01

Determination of the Molecule's Molecular Weight

The question states that the amount of wax reacts with one equivalent of \(\mathrm{KOH}\), i.e. 1 mole of \(\mathrm{KOH}\). As we know, \(\mathrm{KOH}\) reacting with an ester will give an acid and an alcohol, hence one equivalent of KOH reacting with one ester assures that one mole of \(\mathrm{KOH}\) is reacting with one mole of spermaceti wax. Considering this, it could be concluded that the 475g of wax represented one mole of spermaceti wax. That is the molecular weight of spermaceti wax.

02

Determination of the Compound 'A'

Compound 'A', appearing after acidification, should be the carboxylic acid resulting from hydrolysis of the wax ester. The molecular weight can be found by multiplying the neutralization equivalent by the valency (which for carboxylic acids is 1). So the molecular weight of 'A' is approximately 260 g/mol.

03

Determination of Compound 'B'

In the question, reduction by \(\mathrm{LiAlH}_{4}\) of either spermaceti or 'A' gives 'B' as the only product. \(\mathrm{LiAlH}_{4}\) is a strong reducing agent and it can reduce esters as well as carboxylic acids to alcohols. So, 'B' must be an alcohol, and given it's the only product, its molecular weight must be equal to that of 'A', about 260 g/mol.

04

Structure of Spermaceti Wax

As per the empirical formula (\(\mathrm{C}_{16} \mathrm{H}_{32}\mathrm{O}\)), and the molecular weight (around 475 g/mol), the simplest structure of spermaceti wax will have a single ester group (\(\mathrm{R-COO-R'}\)). Compound 'A' and 'B' coming out of its hydrolysis should be both 16-carbon straight-chain compounds with molecular weights near 260 g/mol. So, the structures of compounds 'A' and 'B' should be palmitic acid (hexadecanoic acid) (\(\mathrm{C_{15}H_{31}COOH}\)) and hexadecanol (\(\mathrm{C_{16}H_{33}OH}\)) respectively. Thus, the structure of spermaceti would be hexadecyl hexadecanoate, a wax ester composed of 1 hexadecanol and 1 hexadecanoic acid with an ester linkage.

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