Helferich

A general method for preparing acetals by treating aldehydes or ketones with the appropriate tetra-alkyl silicate, using dry hydrogen chloride as the catalyst. Helferich and Hausen, Ber. 57, 795 (1924). 

Perhaps the earliest report of the replacement of a sulfonate ester attached to a secondary carbon atom in a sugar derivative was that of Helferich (53). Under quite drastic conditions (sodium iodide in acetone, 105°C., 72 hours, sealed system) the 4-mesylate derivative 9 was converted into a crystalline 4-deoxy-4-iodo sugar derivative 10 in 46% yield. Although the position of the iodine atom was established, the configuration at C-4 was not known. 

In the Koenigs-Knorr method and in the Helferich or Zemplen modifications thereof, a glycosyl halide (bromide or chloride iodides can be produced in situ by the addition of tetraalkylammonium iodide) is allowed to react with a hydrox-ylic compound in the presence of a heavy-metal promoter such as silver oxide, carbonate, perchlorate, or mercuric bromide and/or oxide,19-21 or by silver triflu-oromethanesulfonate22 (AgOTf). Related to this is the use of glycosyl fluoride donors,23 which normally are prepared from thioglycosides.24... 

On July 5, 1982, Burckhardt Helferich died in Bonn shortly after his 95th birthday. With his death, we have lost one of the last protagonists of the classical era of carbohydrate chemistry. 

In the autumn of 1907, he started to study chemistry at the Institute chaired by Adolf von Baeyer at the University of Munich, where he passed the first Verband s examination after three semesters. In 1909, he continued his studies at the University of Berlin, gaining his doctorate in 1911 under Emil Fischer. The subject of his doctoral dissertation was Syntheses of Certain New Glucosides. The tremendous personality of Emil Fischer left its mark on Helferich for the rest of his life. In conversation with Helferich, one was often aware of the great veneration he always felt for his tutor and mentor. 

After his doctoral graduation, Helferich became Emil Fischer s personal assistant for two years, and, from 1913 onwards, a teaching assistant. Together with Fischer, he published a series of papers on glycoside synthesis during this period. His scientific career was then interrupted by the First World War, in which he served as an officer throughout. 

In 1919, he resumed his position as assistant in the Berlin Institute and, in 1920, obtained his Habilitation with a thesis on the ring-chain tautomer-ism of y- and 5-hydroxyaldehydes. In 1922, Helferich was called to the position of Departmental Head at the Kaiser Wilhelm Institute for Fibre Chemistry in Berlin-Dahlem. However, he never actually occupied this position, for, in the autumn of that year, he accepted a personal chair in organic chemistry at the University of Frankfurt in the Institute headed by Julius von Braun. 

In 1922, Helferich married Hildegard Kohlrautz. Five children were bom of this very happy and harmonious marriage. In the spring of 1925, Helferich accepted the offer of the Chair in Chemistry and the Directorship of the Chemical Institute at the University of Greifswald, becoming the successor to Pummerer. In the summer semester of 1930, he accepted the offer of the Chairmanship of the Chemical Institute at Leipzig as the successor to Hantzsch. 

The outbreak of the Second World War in 1939 made work at Leipzig extremely difficult. Many students and postgraduates were called up for military service. In the further course of the war, the Institute suffered much damage from bombing. In spite of all these difficulties, Helferich attempted to maintain the functions of the Institute until, finally, in 1945, after 15 very successful years, he was evacuated to the Western Zone by the American forces of occupation. 

During the course of his academic career, Helferich occupied many important offices. In the academic year 1951-1952, he was Dean of the Faculty of Mathematics and Natural Sciences, and, in the academic year 1954-1955, Vice-Chancellor of the Rhenish Friedrich Wilhelm University of Bonn. From 1953-1955, he was a member of the council of the Gesell-schaft Deutscher Chemiker, and was president of this society from 1956 to 1957. He made a major contribution to the rapid restoration of the scientific and personal links with foreign chemists that had been broken by the war. 

In his first independent work, Helferich prepared y-hydroxyvaleral-dehyde (4-hydroxypentanal) by reduction and ozonolysis of methylhep-tenone, readily available from citral by a retro-aldol reaction. He was able to show that, similarly to the saccharides, this hydroxyaldehyde exists in... 

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