An unknown secondary alcohol A is heated with concentrated H ₂ SO ₄ to yield a major alkene B. When alkene B is treated with a cold, dilute aqueous solution of KMnO ₄ (Baeyer's reagent), it yields butane-2,3-diol. The starting alcohol A is:

Step-by-step solution

The final product is butane-2,3-diol, which is a vicinal diol. Vicinal diols are formed by the syn-hydroxylation of alkenes using Baeyer's reagent (cold, dilute aqueous KMnO ₄ ). Working backwards, the alkene B that yields butane-2,3-diol upon hydroxylation must be but-2-ene. Alkene B (but-2-ene) is formed as the major product of the acid-catalyzed dehydration of alcohol A. According to Saytzeff's rule, the dehydration of butan-2-ol yields but-2-ene as the major, more substituted alkene. Therefore, the secondary al