Piria, Raffaele

Another active principle soon extracted from plants was salicylic acid. Salicin, extracted from the willow tree, has been launched in 1876 by a Scottish physician, Thomas John McLogan It was in extensive competition with Cinchona bark and quinine and never became a very popular treatment for fever or rheumatic symptoms. The Italian chemist Raffaele Piria, after having isolated salicylalde-hyde (1839) in Spireae species, prepared salicylic acid from salicin in Dumas laboratory in the Sorbonne, Paris. This acid was easier to use and was an ideal step before future syntheses. Its structure was closely related to benzoic acid, an effective preservative useful as an intestinal antiseptic for instance in typhoid fever. Acetylsalicylic acid has been first synthesized by Charles Frederic Gerhardt in 1853 and then, in a purer form, by Johann Kraut (1869). Acetylsalicylic acid synthesis with carbolic acid and carbon dioxide was improved by Hermann Kolbe in1874, but in fact nobody noticed its pharmacological interest. 

In the period from 1828 to 1829, the active ingredient in willow bark was first isolated by three individuals, the German pharmacist Johann Buchner (dates not available), the French chemist Henri Leroux (dates not available), and the the Italian chemist, Raffaele Piria (1815-1865). Buchner gave the name salicin to the bitter-tasting yellow crystals extracted from willow bark after the Latin name for the willow tree, Salix. In 1853, the French chemist Charles Frederick Gerhardt (1816-1857) developed a method for reacting salicylic acid (the active ingredient in salicin) with acetic acid to make the first primitive form of aspirin. 

The first syntheses [172] of macrocyclic scented compound were based on the Piria cyclisation (Raffaele Michele Rocco Piria (1814-1865), Italian chemist) of terminally functionalised aliphatic precursors. Thus, pyrolysis of the thorium salt of thapsic acid (Fig. 3.42) and purification via the semicarbazone gave exaltone in a yield of 5.5 % (Ruzicka cyclisation). The mechanism ofthis reactionhas not been finally established, although it is accepted that free radicals are involved in the cyclisation. [173] Oxidation using Caro s acid then gives exaltolide in 47 % yield. 

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