Sir William Henry Perkin accidentally discovered “mauveine”, the first commercial synthetic dyestuff — Physical Chemistry Chemistry Question
Perkin Junior
Sir William Henry Perkin accidentally discovered “mauveine”, the first commercial synthetic dyestuff, in 1856 while working in his home laboratory. His love of chemistry was passed on to his eldest son William Henry Perkin, Jr. (1860-1929). William Henry Perkin Jr is best known for his work on the synthesis and structure elucidation of natural products including α-terpineol. Perkin’s synthesis of this monoterpene forms the basis of this question.
As Perkin stated, the synthesis of α-terpineol (F) “was undertaken with the object of synthesising…terpineol…, not only on account of the interest which always attaches to syntheses of this kind, but also in the hope that a method of synthesis might be devised of such a simple kind that there would no longer be room for doubt as to the constitution of these important substances”.
We begin Perkin’s synthesis of α-terpineol with the ketone A.
[VISUAL]
Identify the intermediates B, C, D and E.
Model Answer
B: 4-hydroxy-4-methylcyclohexanecarboxylic acid
C: 4-bromo-4-methylcyclohexanecarboxylic acid
D: 4-methylcyclohex-3-enecarboxylic acid
E: ethyl 4-methylcyclohex-3-enecarboxylate
What reagent would you use to convert E into α-terpineol F.
Model Answer
excess MeMgI (excess methylmagnesium iodide)
Suggest reagents for the preparation of A from 4-hydroxybenzoic acid. α-Terpineol F has been used to prepare other monoterpenes.
Model Answer
Step 1: H2 with a transition metal catalyst (e.g., Pt) to reduce 4-hydroxybenzoic acid to 4-hydroxycyclohexanecarboxylic acid.
Step 2: An oxidizing agent (e.g., Jones reagent, CrO3 / H2SO4) to oxidize the secondary alcohol of 4-hydroxycyclohexanecarboxylic acid to ketone A (4-oxocyclohexanecarboxylic acid).
Treatment of α-terpineol F with potassium hydrogen sulfate gave compound G which reacts with two equivalents of bromine. Identify G given that it is chiral.
Model Answer
G is limonene (1-methyl-4-(prop-1-en-2-yl)cyclohex-1-ene)
Treatment of α-terpineol F with aqueous acid gives compound H. Exposure of H to stronger acid gives I. Identify H and I.
In the 1H NMR spectrum of H addition of D2O results in the disappearance of one signal corresponding to two hydrogens, whereas the 1H NMR spectrum of compound I remains unchanged on addition of D2O.
Neither compound H nor I are chiral, and neither react with bromine.
Model Answer
H is terpin (p-menthane-1,8-diol)
I is 1,8-cineole (eucalyptol)