(b. Elberfeld [noe Wuppertal], Germany, 21 April 1875; d. Bonn, Germany, 4 March 1951)
Pfeiffer was the son of Hermann Pfeiffer, a head clerk and later factory owner, and Emilie Willmund. He studied for two semesters at the University of Bonn under Kekule and Anschutz before entering the University of Zurich (1894), wher he became Werner’s best-known student, protege, and eventually, “chief of staff.” After receiving his doctorate in 1898, for a paper “Molekulverbindungen dr Halogenide des 4-wertigen Zinns und der Zinnalkyle” (published with Werner as coauthor in Zeitschrift für anorganische Chemie, 17 , 82–110), he studied for one semester each with Ostwald at Leipzig and Hantzsch at Wurzburg. On 14 August 1901 he married his cousin Julie Huttenhoff. In the same year, with the acceptance of his Habilitationsschrift, “Beitrag zur Chemie der Molekulverbindgungen,” he became Privatdozent at the University of Zurich and in 1908 associate professor of theoretical chemistry. In 1916, as a result of personal and political conflicts with Werner Pfeiffer left Zurich for the University of Rostock, even though Werner was ill at the time and Pfeffier was certain to be appointed his successor. In 1919 Pfeiffer moved to the Technische Houchschule in Karlsruche. Three years later he was appointed to the directorship of the chemical institute at the University of Bonn, Kekulé’s old chair, where he remained until his retirement in 1947.
Pfeiffer’s work encompassed both inorganic and organic chemistry as well as the borderland between these disciplines. As the intellectual—but not academic—successor to Werner, Pfeiffer’s main interest was in coordination compounds, particularly those of chromiuum. He investigated their constitution, configuration, isomerism, acid-base and hydrolysis reactions, and their relationships to double salts and salt hydrates. He was the first to apply Werner’s coordination theory of crystals. He also studied both inorganic and organic tin compounds, inner complexes, metal organic compounds, and the chemistry of dyes. He was a pioneer in the field of halochromism—the formation of colored substances from colorless organic bases by the addition of acids of solvents. His contributions to pure organic chemistry include studies of cyclic compounds, quinhydrones, stilbene compounds, unsaturated acids, and the relationship of ethylene compounds to ethane and acetylene compounds.
I. Original Works. Most of Pfeiffer’s work appeared in Berichte der Deutschen chemischen Gesellschaft and Zeitschrift für anorganische Chemie. His monograph Organische Molekulverbindugen (Stuttgart, 1922) was reprinted in 1927. A detailed bibliography is given in Poggendorff, VIIA, 552–553.
II. Secondary Literature. A summary of Pfeiffer’s early career apeared in the Festschrift compiled for the opening of the chemical institute of the University of Zurich, 75 Jahre chemischer Forschung an der Universitat Zurich (Zurich, 1909). There are biographical data and evaluations of Pfeiffer’s work by his former student R. Wizinger,“P. Pfeiffers Beitrag zur Entwicklung der Komplexchemie,” in Angewandte Chemie, 62A (1950), 201–205; and “In memoriam Paul Pfeiffer, 1875–1951,” in Helvetica chimica acta, 36 (1953), 2032–2037. An unpublished autobiography, “Mein Lebenslauf” (1947), is available at the University of Bonn. Angewandte Chemie, 62 , nos. 9–10 (20 May 1950), was devoted to Pfeiffer on the occasion of his seventy-fifth birthday. Biographical data can be found in G. B. Kauffman,“ Crystals as Molecular compunds: paul Pfeiffer’s Application of Coordination Theory to crystallography,” in Journal of Chemical Education, 47 (1970), 277–278; and R. E. Oesper, “Paul Pefeiffer,” ibid., 28 (1951), 62.
George B. Kauffman