Soru

Passage:
In the mid-nineteenth century, textile dyeing relied heavily on natural agricultural extracts, primary among which was alizarin, a red pigment derived from the roots of the madder plant (Rubia tinctorum). Because cultivating madder required extensive arable land and intense seasonal labor, the supply of natural alizarin was subject to severe price fluctuations. In 1868, organic chemists Carl Graebe and Carl Liebermann achieved a major industrial breakthrough by synthesizing alizarin from anthracene, a previously low-value byproduct of coal tar distillation. Previous attempts to produce synthetic substitutes for madder pigment had failed because researchers attempted to oxidize naphthalene derivatives directly rather than isolating the anthracene core. Graebe and Liebermann recognized that anthracene shared a structural carbon framework with natural alizarin, allowing them to dibrominate anthraquinone as an intermediate step. Although their initial synthetic protocol was commercially cost-prohibitive due to the expense of bromine, Heinrich Caro of the Badische Anilin- & Soda-Fabrik (BASF) developed an alternative sulfonation route in 1869 that bypassed bromine entirely. This processual modification dramatically reduced production costs, enabling industrial-scale production. Consequently, within a decade of Caro's refinement, European agricultural cultivation of madder collapsed almost entirely, marking one of the earliest instances where a synthetic chemical compound rendered a traditional agricultural export crop obsolete.

According to the passage, earlier efforts to synthesize a replacement for madder pigment failed primarily because researchers did which of the following?