Veilchenduft, ectopic olfactory receptors and endogenous volatile compounds: Who was Paul Krüger (1859-1916)?

The pharmacist and chemist Ferdinand Tiemann (1848-1899) having succeeded in the synthesis of vanillin, is considered to be the father of Geschmackstoff-Chemie (flavor chemistry). Tiemann, together with Paul Krüger (1859-1916) and then with Friedrich-Wilhelm Semmler (1860-1931), developed a method to obtain with a good yield Veilchenduft (violet scent); they condensed citral with di-methyl-ketone (acetone) thus generating an intermediate which upon exposure to an acidic environment cyclizes to ionone. By doing so the fragrance chemistry was born. Ionone (the compound responsible for the violet scent) was produced on an industrial scale at the factory of Wilhelm Haarmann (1847-1931) in Holzminden, factory renamed 1876 Haarmann & Reimer, after Karl Reimer (1845-1881) joined the group of owners. While a number of chemists and pharmacists were involved in the synthesis of Ionone (Veilchenduft; violet scent) and irone (iris scent), with few exceptions, their biographies are pretty well documented. In contrast, very little transpired about Dr. Paul Krüger, who spent some seven years trying to iron out the difficulties of ionone synthesis. The purpose of this short contribution is to shed some light on the life and work of Paul Krüger while providing an overview on the status of ionone pharmacology and to highlight the historical significance of ionone synthesis.