(1826-1910) Italian chemist who revived interest in the work of Avogadro that had, in 1811, revealed the difference between atoms and molecules, and so established atomic and molecular weights as the basis of chemical calculations.
Cannizzaro also worked in aromatic organic chemistry. In 1853 he discovered reactions (named for him) that make benzyl alcohol and benzoic acid from benzaldehyde.
Cannizzaro was born in Palermo, Sicily, and studied at Palermo, Naples, and Pisa. In 1848 he fought in the Sicilian Revolution, and was condemned to death, but in 1849 escaped to Marseille and went on to Paris. He was a professor at the Technical Institute of Alessandria, Piedmont, 1851–55, followed by professorships at Genoa, Palermo, and Rome. He became a senator 1871 and eventually vice president.
Cannizzaro's reaction involves the treatment of an aromatic aldehyde with an alcoholic solution of potassium hydroxide. The aldehyde undergoes simultaneous oxidation and reduction to form an alcohol and a carboxylic acid. It is an example of a disproportionation reaction, and finds many uses in synthetic organic chemistry.
Reviving Avogadro's hypothesis 1858, Cannizzaro pointed out that once the molecular weight of a volatile compound had been determined from a measurement of its vapor density, it was necessary only to estimate, within limits, the atomic weight of one of its elemental components. Then in investigating a sufficient number of compounds of that element, the chances were that at least one of them would contain only one atom of the element concerned, so that its equivalent weight (atomic weight divided by valence) would correlate with its atomic weight.