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Synthesis Plan Analysis
Published in John Andraos, Synthesis Green Metrics, 2018
A racemic acid (+)A is required to be separated into its constituent enantiomers using a chiral amine (+)-B. Compare the PMI for the production of the enantiomer that originates from the diastereomeric salt that precipitates out first with the PMI for the production of the enantiomer that originates from the diastereomeric salt that remains dissolved in the mother liquor. Which one is likely to be higher? Explain your answer.
Morphine Dreams: Auguste Laurent and the Active Principles of Organised Matter
Published in Ambix, 2021
By the time Pasteur began his work, there was a new, puzzling wrinkle to the story, provided by the Prussian chemist Eilhard Mitscherlich (1794-1863). Although Mitscherlich had never met Laurent, their careers had a certain parallel. For both, their first scientific publication had been in the field of mineralogy.67 Both had mastered the goniometer, which mineralogists used to measure the angles between crystal faces. It was this skill that had led Berzelius to ask Mitscherlich to help him study the compounds tartaric acid and racemic acid in 1831.68 Joseph Luis Gay-Lussac had named racemic acid in 1828, under the impression that it was an entirely new compound, the byproduct of the industrial production of tartrates.69 Berzelius, exploring whether it was an isomer of tartaric acid, asked Mitscherlich to prepare salts of the compounds and to look for differences in their crystals. Not finding any, he put the work aside until several years later, when he heard of Biot’s demonstration that tartaric acid was optically active and racemic acid was not. He redid his experiments, making crystals of the two substances by reacting them with soda and ammonium, then examining their crystalline structure. The identity was astonishing: they had the same crystalline form, with the same angles, the same specific weight, the same double refraction, the same angles between their optic axes. Dissolved in water, their refraction was the same. Mitscherlich, wrote to Biot in 1844, informing him the “nature, number, arrangement and distance of atoms are the same in the two salts that he had compared.”70 One difference alone distinguished them: the natural substance was optically active and the artificial substance was not. In 1844, Biot proclaimed the experiments “beautiful” and the results “curious.”71 Mitscherlich had provided him with samples of his material. He investigated them relentlessly, but was still puzzled about the nature of their differences in organisation.