250 years ago
1749 

• Andreas Sigismund Marggraf  obtains concentrated formic acid by distillation of red ants   

200 years ago
1799 

• Franz Karl Achard  founds the first sugarbeet factory
• Martin Heinrich Klaproth isolates mellitic acid from the mineral honey-stone   

150 years ago
1849 

• Adolph Wartz  discovers alkyl-amines
• Eduard Frankland  prepares alkanes in the reactions of alkyliodides with zinc. He also isolates the metal-organic compounds zinc-methyl and zinc-ethyl. He is also thought to have discovered the free radicals methyl and ethyl
• Herman Kolbe  proposes his "Kolbe-synthesis": synthesis of alkanes by electrolysis of fatty acids
• Charles Mansfield  synthesizes benzene which he prepares by treating nitrobenzene with nitric acid   

100 years ago
1899

• Adolf von Baeyer  and Victor Villiger  oxidize ketones to esters using peracids: Baeyer-Villiger-oxidation. They prepare organic per-oxides and per-acids such as benzoic peracid and phthalic monoperacid
• Johannes Thiele formulates his "Partial Valence Hypothesis" concerning double and triple carbon-carbon bonds with which he explains their particular reactivity
• John Norman Collie and Thomas Tickle  demonstrate that dimethylpyron forms addition products with acids, such as hydro halogenic acids and tartaric acids, etc, which are very stable. They explain this by assuming a 4-valency for oxygen. They consider these derivates to be derived from the hypothetical base H₃0.0H, named oxonium hydroxyl. They give the name oxonium salts to the derivatives
• Georg Wagner  and Hans Meerwein  succeed in the inversion of dicyclic monoterpenes eg. pinene to camphene: "Wagner-Meerwein inversion"
• Paul Sabatier and Jean Baptiste Sendérens  hydrogenate unsaturated compounds with nickel as catalyst
• Paul Walden demonstrates his " Walden-inversion" in which one optical isomer is converted into a derivative of the other by action of certain reagents eg. malic acid, when treated with PCl₅, gives 1- chlorosuccinic acid, which may be converted to 1-malic succinic acid by silver oxide
• Ludwig Knorr synthezies diacenlamber acid from acetyl-acetic acid and sodium
• Emil Erlemeyer Jr. synthesizes and separates (benzoyl) tyrosine
• W Marckwald  and Alex McKenzie  demonstrate several asymmetric syntheses
• E Wedekind demonstrates the asymmetry of the five-valency of the nitrogen atom, optical activation and auto racemization
• W J Pope and S J Peachy  separate -benzyl-phenyl-alkylmethyl ammonium in the optical antipodes by crystallization of camphor sulphonates
• Traugott Sandmeyer prepares hydrocarbo-diphenylimid from thiocabanilide and potassium exanide with white lead. This compound forms the basis of indigo   

50 years ago
1949 

• Hans Werner Kuhn develops the theory of colours of organic compounds
• E R Alexander  and E E Eliel  obtain optical active compounds with deuterium and hydrogen (R₁R₂HAC)
• Kenyon  and M P Balfe  succeed in optical separation of o-tolyl-p-tolyl carbinol
• Patil Niggli  edits "Grandlagen der Stereochernie" (Principles of Sterochemistry)
• A Skita  synthesizes stereo-isomers of amino-alcohols of the type ephedrine
• M C Rebstock et al  succeed in the explanation of the structure and the total-synthesis of chloro-amphenical
• Adolf Butanandt, H Hellmann  and E Renz  gave a new and improved synthesis of d, 1-tryptophan
• Wolfgang Langenbeck  researches the acceleration of formaldehyde condensation with organic catalysts
• Otto Warburg  edits "Wasserstoffübertragende Ferment" (Enzymes which transport hydrogen)
• Wilhelm Schenk Jr.  researches chemical and crystallographical addition compounds of urea
• R Winzinger-Aust  proposes a new method for preparing coloured salts of tri-arylpyrillium
• Otto Bayer  researches the chemistry of acryIonitriles
• Walter Reppe  researches the chemistry of acetylene and carbon monoxide
• Saunders  researches the aromatic diazo-compounds and their technical application
• Rudolf CriegIl  researches the constitution of peroxides and ozomides