Doctoral Work
For his Doktorarbeit , Wöhler assigned Kolbe the task of studying the action of chlorine on carbon disulfide. This proved to be a crucial choice because it led Kolbe inexorably toward an examination of the link between organic and inorganic chemistry, a topic that was at the heart of many of the theoretical debates then raging in Europe. Carbon disulfide (modern CS2 ) was a familiar substance at that time, but it was commercially unavailable, so Kolbe had to prepare it in Wöhler's lab directly from the elements. As Wöhler reported to Berzelius in a letter of 26 July 1842, it initially appeared that the products of high-temperature chlorination in a porcelain-filled tube were sulfur dichloride and a new substance that Wöhler formulated as CS+>C l. Berzelius considered this a "very interesting compound" in his preferred "four-volume" (i.e., doubled) formulation of it, CS2 +CC l2 , precisely because of its position on the organic-inorganic interface.[40] (The barred symbols represent Berzelian "double atoms," so that C l = C l2 .)
Within two weeks after writing to Berzelius, Wöhler and Kolbe had determined that no novel compound was formed after all, the second product being merely a mixture of sulfur dichloride and the previously known Kohlensuperchlorid (literally, carbon superchloride, known today as carbon tetrachloride). Still, the reaction was significant as a smooth route to preparing large quantities of the latter material, much superior to Regnault's inefficient chlorination of chloroform. Moreover, Wöhler and Kolbe found that a new compound of carbon, chlorine, and sulfur was in fact formed when the same reaction was carried out at room temperature, though at the time of writing (September 1842) they had not yet determined its formula.[41]
Berzelius wrote that both results were "extremely important" because they represented the formation of organic products from purely inorganic reactants, and he offered advice on how it might still be possible to obtain the product that Wöhler and Kolbe had thought they had isolated in July. He concluded by once again stressing the theoretical importance of these kinds of compounds and exhorting Wöhler to look at a few additional related compounds, including one he and Alexandre Marcet had discovered three decades earlier, the substance now known as trichloromethylsulfonyl chloride (formulated in Berzelian terms as CC l2 +SO2 ).[42]
Wöhler and Kolbe followed Berzelius' prescriptions and found that the compound formed by room-temperature chlorination was indeed the half-chlorinated carbon disulfide. In the paper as it appeared in Liebig's Annalen[ 43] —curiously, published under the single name "Heinrich Kolbe"—the new substance was formulated first as CSCl2 (Wöhler's preference). Kolbe then noted that the formula "probably" should be doubled to CCl4 +CS2 (Berzelius preference).