Key Historical Milestones

1835 — Liebig and Dumas: Aldehyde group identified The term "aldehyde" coined from "al-cohol de-hydrogenatus" (dehydrogenated alcohol). The carbonyl group in aldehydes first characterized.

1838 — Trommer's Test (predecessor to Fehling's) First copper-based reducing sugar / aldehyde test described.

1853 — Fehling's Solution developed by Hermann von Fehling Alkaline copper(II) tartrate solution developed as a standardized test for reducing aldehydes. Red Cu2O precipitate becomes diagnostic.

1853 — Cannizzaro Reaction discovered by Stanislao Cannizzaro Disproportionation of benzaldehyde with KOH discovered. Cannizzaro later (1858) used Avogadro's hypothesis to establish molecular weights.

1872 — Aldol Condensation discovered by Charles Adolphe Wurtz Acetaldehyde condensation with dilute NaOH described. The term "aldol" (aldehyde + alcohol) coined from the beta-hydroxy aldehyde product.

1882 — Tollens' Reagent described by Bernhard Tollens Ammoniacal silver nitrate silver mirror test for aldehydes reported.

1881 — Haloform Reaction understood (building on Liebig, 1832) The mechanism of trihalogenation and C-C cleavage in methyl ketones fully described.

1912 — Clemmensen Reduction by Erik Christian Clemmensen Zinc amalgam / HCl deoxygenation of carbonyl groups to methylene reported.

1946 — Wolff-Kishner Reduction (Kishner 1911, Wolff 1912, Huang Minlon modification 1946) Hydrazine/KOH reduction optimized with ethylene glycol solvent (Huang Minlon modification). Now standard for base-tolerant deoxygenations.