Icilio Guareschi and his amazing “1897 reaction”

Organic chemistry honors Icilio Guareschi (1847–1918) with three eponymic reactions, the best known ones being the Guareschi synthesis of pyridones and the Guareschi–Lustgarten reaction. A third Guareschi reaction, the so-called “Guareschi 1897 reaction”, is one of the most unusual reactions in organic chemistry, involving the radical-mediated paradoxical aerobic generation of hydrocarbons in near-neutral water solution. A discussion of the mechanism of this amazing reaction, the only metal-free process that generates hydrocarbons, and the implications of the approach in biology and geosciences mirrors the multifaceted scientific personality of the discoverer. Thus, Guareschi’s eclectic range of activities spans a surprising variety of topics, overcoming the boundaries of the traditional partition of chemistry into organic, inorganic, and analytical branches and systematically crosses the divide between pure and applied science as well as between the history of chemistry and the personal contributions to its development.


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1. Schiff's parsimony was legendary. Paternò recalls that Schiff used to travel from Florence to Rome with a suitcase containing only a shirt and a pair of shoes that he proudly carried without a porter, claiming that there was no need to pay another person to do something he could do by himself (de Condé Paternò di Sessa, M. E. Paternò di Sessa. Emanuele Paternò di Sessa. Dall'esilio alla fama scientifica: Scienza e Politica fra il XIX ed il XX secolo vissute da un protagonista. Gangemi, Palermo, 2018, p165). Schiff was rumored to eat mostly dried chestnuts, but enjoyed excellent health until he was run over by a cart in 1899 (Guareschi, I. Atti R. Acc. Sci Torino, 1917, 53, 333-352). He never fully recovered from this accident, reminiscent of the fatal one of Pierre Curie in Paris seven years later. It was such a common belief that Schiff lived in dire poverty that, to celebrate his 70th birthday, a subscription to support him raised the equivalent of 20,000 € in the Italian and European chemical community. Schiff did not like the initiative and destined the sum to an annual prize for the best thesis in chemistry. When Schiff passed away, it was discovered that, thanks to his parsimonious life, he had accumulated a small fortune, 70% of which, amounting to over 1.5 million €, he destined in his will to the establishment of a Schiff Foundation to support disabled workers. The Foundation was extinguished only in 1983 (Costa, L.; Guarna, A.

Rendiconti della Accademia Nazionale delle Scienze detta dei XL Memorie di Scienze
Fisiche e Naturali, serie V 2011, 35, 153-164). Regarding the temperamental behavior of Schiff, suffice to mention the case of the physicist Antonio Roiti . Faced with the problem of the precise determination of some electrical constants, Roiti was working at night to avoid the interference of trams. He could do nothing, however, with the interferences created ad hoc by Schiff, who was moving heavy metallic containers in a nearby corridor to disturb the measurements. In his final report, Roiti wrote that his results were precise  2. Emanuele Paternò was remarkable not only for the discovery of the eponymous carbonylolefin photocycloaddition, but also for his clear elaboration of the tetrahedral nature of carbon, a concept that he developed while studying the isomerism of trichloroethane six years before the publication of the works by van't Hoff and Le Bel. 22-year-old Paternò published his finding in a local journal (Intorno all'azione del percloruro di fosforo sul clorale, Giornale di Scienze Naturali ed Economiche, 1869, vol. V) and then sent it to Adolf Lieben in Turin for a possible publication in Berichte. Lieben's answer was trenchant: "Your theory of tetrahedral carbon crosses the Rubicon that separates the licit speculations on how atoms combine from the illicit speculations on how atoms position in space. By rising up in space looking for atoms, you lose ground under your feet." Frustrated, Paternò abandoned the study of stereochemistry, something he regretted all his life, however without ever claiming priority for the discovery of the tetrahedral nature of carbon, whose first formulation he ascribed to Kekulé. Curiously, Kolbe commented van't Hoff 's theory of tetrahedral carbon in a way reminiscent to Lieben's comments to Paternò: According to Kolbe, van't Hoff, rather than experimental investigations, has considered more comfortable to mount Pegasus and to proclaim in his "La chimie dans l'espace" how the atoms appear to him to be arranged in space when he is on the chemical mount Parnassus which he has reached by bold flight (Kolbe, H. J. Prakt. Chem. 1877, 15, 474). Writing in the late 30s, Willstätter explained in a similar way the aversion of Haber to organic chemistry, whose PhD thesis was on the chemistry of safrole: Structural chemistry is important and beautiful as long as we do not expect the formulas to express too much. A chemist who tries to explore the concepts of affinity and valence more searchingly with the tools of organic chemistry, however, runs the  9. The case of the Eugenio Elia Levi (1883Levi ( -1917, one of the major Italian mathematicians of those times, is emblematic. In 1915, his application to join the army at the age of 32 was turned down since he was shorter than 154 cm, the minimum height to become a soldier. Unhappy, Levi appealed, and on account of a modification of the rules of enrolment, he could later enter the army and go to the front. However, when a law preventing public officers to volunteer for the army was implemented, he was sent back to the University of Genoa, which had classified his participation to teaching activities as indispensable. Claiming that the law could not be applied retroactively, Levi appealed again, and eventually managed to reach the front. He died on October 28, 1917 hit by a bullet in the head (Guerraggio, A. La Scienza in Trincea, Raffaello Cortina Editore, 2015, p 52). Levi's enthusiasm to participate in the war is reminiscent of the one of Otto Warburg, who fought on both the Western and the Eastern fronts. It took Albert Einstein, a family friend, to convince him that he was more useful to Germany in the laboratory than at the front. Eventually, he applied to be released from active service and was discharged in the summer of 1918, in the last months of the war    Gangemi, Palermo, 2018, p154).
11. Ponzio was storing all the dioximes prepared in his laboratories in a library of flasks (still preserved) that a technician had to label and update. For unclear reasons, a wall was built between the Pharmacy and the Chemistry Departments at the time of the Ponzio-Mascarelli diarchy.
12. Mascarelli succeeded Guareschi as the chair or pharmaceutical chemistry and toxicology. Of Piedmontese origin (Bra), he came from the Ciamician school in Bologna.
Mascarelli was held in high esteem by Ciamician and was given the task to order his lessons into a textbook. He is remembered for his remarkable eponimic reaction of transformation of biphenyls into fluorenes and is considered one of the founders of the chemistry of these compounds as well of the application of chlorinated diphenyls as electrical insulators. While working in Bologna, he reported in 1907 the discovery of aryliodonium salts (Mascarelli, L. Atti della R. Acc. dei Lincei. Rendiconti, cl. di Scienze Fisiche, Mat. e Naturali 1907, 16, 562-567), a reaction rediscovered three decades later. The ultimate attribution to Mascarelli of the discovery of these compounds led to the recall of a string of patents filed on aryliodonium salts.