Questions dealing with lipids

1. Spermaceti, a fragrant substance from sperm whales, was much used in cosmetics until it was banned in 1976 to protect the whales from extinction. Chemically, spermaceti is cetyl palmitate, the ester of cetyl alcohol (n-C₁₆H₃₃OH) with palmitic acid. Draw its structure.



2. Stearolic acid, C₁₈H₃₂O₂, gives stearic acid on catalytic hydrogenation. Treatment with permanganate gives nonanoic acid and nonanedioic acid. Draw the structure of stearolic acid.



3. C₂₇-phthienoic acid, C₂₇H₅₂O₂, is obtained from the saponification of the fatty capsule of the tubercle bacillus. On injection into animals, it causes lesions typical of tuberculosis. On the basis of the following information, assign a structure to this acid:



C₂₇-phthienoic acid + O₃ followed by Zn/H₂O ® CH₃COCO₂H



  C₂₇-phthienoic acid + KMnO₄ ® acid "A" (C₂₄H₄₈O₂)



  methyl ester of "A" + 2C₆H₅MgBr followed by water ® "B" (C₃₆H₅₈O)



  "B" + H⁺/D ® "C" (C₃₆H₅₆)



  "C" + CrO₃ ® benzophenone + ketone "D" (C₂₃H₄₆O)



  "D" + I₂/NaOH ® CHI₃

"A" + Br₂/P ® "E"



  "E" + alc KOH ® acid "F" (C₂₄H₄₆O₂)



  "F" + KMnO₄ ® CH₃(CH₂)₁₇COCH₃

Note: KMnO₄ is a vigorous oxidizing agent. Thus not all bond cleavage occurs at double bonds. In the last step, four carbons are lost.

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