Stanislao Cannizzaro

Stanislao Cannizzaro ( born July 13, 1826 in Palermo, † May 10, 1910 in Rome ) was an Italian chemist and politician. Cannizzaro was able to explain the difference of atomic and molecular weight, he realized that hydrogen gas is present as molecular chemistry and helped to correct empirical formulas. He found a preparation process of aromatic aldehydes from the corresponding carboxylic acids and alcohols.

Life and work

Stanislao Cannizzaro, the tenth child of a family in Palermo, learned in a high school grammar, rhetoric, poetry, philosophy, mathematics, geography and was already 15 years old an award in mathematics. Cannizzaro studied 1841-1845 medicine in Palermo, at age 19, he had already published three scientific papers. In 1845 he became an assistant to Raffaele Piria in Pisa. He was closely associated with another wizard Piria, Cesare Bertagnini ( discovery of the reaction of aldehydes with alkali sulfite ), friends.

It was 1847 Cannizzaro part in the uprising movement for Italian unification. He was an artillery officer and youngest member of the movement. The uprising was crushed and Cannizzaro fled to Marseilles, he was convicted in 1849 in Messina to death in absentia. In Paris, Canizzarro employed together with Cloez with the synthesis of cyanamide. In 1851 he returned to Italy, he first got a job as a professor in Alessandria.

In 1851 he was appointed Professor of Physical Chemistry at the Collegio Nazionale in Alessandria. In the house of Bertagninis in Pisa, he found that in the reaction of benzaldehyde, benzyl alcohol and benzoic acid in an alkaline medium was born. This reaction takes its name, the Cannizzaro reaction. A part of the benzaldehyde is reduced ( benzyl alcohol ) and the other part is oxidized ( to benzoic acid ). By distillation of benzyl alcohol he could win the first aromatic primary alcohol. His work has been reprinted in Liebigs Annalen 1853.

Cannizzaro provided a unification of the then misunderstood ratios of atom and molecule, and resorted to the law of Avogadro. He was a professor at the Universities of Genoa (1855 ), Palermo ( 1861-1871 ), and finally from 1871 in Rome. In Rome Cannizzaro studied various natural substances, especially santonin.

Cannizzaro and the atomic weight

Leading Cannizzaros importance was marked by a clear elaboration of atomic weight and molecular weight. Already the Italian physicist Amedeo Avogadro had in 1811 published the hypothesis that equal volumes of any gas at identical pressure and temperature conditions contain the same number of particles (see Avogadrosches law and Avogadro's number ). Avogadro difference in particles in the gas phase between atoms ( molecules élémentaires ) and molecules ( molecules integrantes ) and assumed that atoms in the gas phase are available, not individually but as paired atoms.

These ideas have come a long time forgotten.

The influential chemist Jöns Jakob Berzelius introduced the concept of the atom. In place of the embossed Avogadro's concept of elementary molecules he put the concept of the atom. However, a source for later confusion created by the exchange of names. The atom was an elementary and unbound particles for him. For elementary gases such as hydrogen, this meant that they also present unbound in the gas space. According to the molecular theory of Berzelius molecules were separable substances, so that at that time formed a false notion of molecules and atoms in the gas space. To confuse you further contributed also the reference point for the atomic weights; Oxygen was given the arbitrary reference point and atomic weight 100

Charles Frédéric Gerhardt found in 1842 in terms of gas densities of organic compounds, that there were difficulties with the determination of the molecular size. After that would come the water equivalent molecular formula H4O2 and the carbon dioxide of the formula C2O4 or the molecular size would be halved. Gerhardt suggested to divide the molecular size, so that the oxygen received the equivalent weight of carbon 12, the value 16, the sulfur the value 32 Gerhardt had not yet distinguished by equivalent weights of atomic and molecular weights. He had assumed that one molecule of a uniform gas, a substance that was not divisible. Gerhardt said that certain molecules ( or atoms ) 1, 2, 4 can occupy parts by volume. For oxides, the situation became even more complicated because several atomic weights for the same element in different compounds were possible. Gerhardt's theses led to incorrect atomic weights of the metals, so many other chemist Gerhardt rejected theses.

Of great importance for the modern molecular theory had the presentation of the organometallic compound Zinkethyl ( diethylzinc ) by Edward Frankland. Gas density and chemical composition of Zinkethyl were carefully examined Cannizaro. After Cannizzaros considerations to the zinc had twice as high atomic weight - as previously adopted by Gerhardt - will be given. Hydrogen gas had a molecule of two atoms be, each hydrogen atom had an atomic mass of 1 possess. The ethyl group in Zinkethyl had to occur in the gaseous molecule twice.

Charles Adolphe Wurtz had read the writing of Cannizzaro in 1858 and in 1860 invited all the leading chemists of the world to a congress in Karlsruhe in order to make known Cannizzaros ideas about the atomic weight. When chemists Congress 1860 in Karlsruhe, the chemists present were informed in clear form by a brief elaboration ( Sunto ) Cannizzaro. Conference delegates voted in favor of the new shape of the atomic weight. Cannizzaro were then offered several professorships at various universities. However, he decided to Palermo, his native city.

Awards

For he had discovered method for the determination of the atomic weights of the specific heat of volatiles he received the Copley Medal of the Royal Society. In 1871 he was appointed Senator, since 1873 he was a regular member of the Accademia dei Lincei in Rome. In 1926 the Società chimica italiana by a centennial celebration.

In Palermo, Rome Vittoria and science high schools are named after him.

745650
de