WALDEN, PAUL (ALSO KNOWN AS PAVEL IVANOVICH VALDEN)

(b. Rosenbeck parish, Wenden district [now Latvian S.S.R], Russia, 26July 1863; d, Gammertingen, Germany, 22 January 1957), chemistry.

The son of Latvian farmers, Walden was orphaned as a child and was obliged to earn his living as a private tutor. In 1882 he entered the chemistry department of the Riga Polytechnical School, where he began his scientific work under F. W. Ostwald. His first scientific work led to the discovery of the Ostwald–Walden empirical rule, which makes it possible to determine the basicity of multiatomic acids and bases according to molar (gram molecular) electroconductivity (1887). After Ostwald moved to Leipzig, Walden became Carl A. Bischoff’s assistant and turned his interest to organic stereochemistry. However, he did not abandon his initial work in electrochemistry; his first doctoral dissertation (1891) was devoted to the determination of the affinities of organic acids by conductometric methods. After graduating in 1889, Walden remained at the Polytechnicum as an assistant (since 1888), becoming professor in 1894. His work with Bischoff, his visit to Adolf von Baeyer, and his frequent visits to Ostwald’s laboratory in Leipzig enabled him to combine the viewpoints of organic and physical chemistry and Walden set as his lifework the synthesis of these two disciplines. He became one of the founders of physical organic chemistry.

Walden’s stereochemical research led him to the discovery of “Walden’s inversion” (1896), so named by Emil Fischer, in which one optical isomer is converted into its optic antipode by the action of specific reagents so that a change in absolute configuration occurs. Because it did not coincide with existing representations of substitution reactions, the Walden inversion elicited an extended discussion. The mechanism of Walden inversion was clarified in 1934-1937 by E. D. Hughes and C. K. Ingold. They demonstrated that inversion is always involved in nucleophilic substitution reactions involving two steps (S_N2–mechanism).

Walden also conducted detailed studies of autoracemization, sought to relate the degree of specific rotatory power to the chemical structure of an organic molecule, and attempted to substantiate the presence of optically active compounds in crude oil (an argument for biogenesis of petroleum, first mentioned by Walden). These data formed the basis for his second doctoral dissertation, on optical isomerism. After defending it in St. Petersbrug in 1899 and becoming professor of inorganic and analytical chemistry at the Riga Polytechnical Institute, Walden embarked upon a study of the electrochemistry of nonaqueous solutions. Between 1900 and 1934 he determined the degree of ionization of about fifty polar nonaqueous solvents, including liquified SO₂, SO₂Cl₂, SOCl₂, chlorosulfonic acid, anhydrous sulfuric acid, formamide, nitromethane, esters, and acid anhydrides. He introduced the concepts of solvation and solvolysis, and pioneered in the representation of the ionic mechanism of several reactions. In 1906 he introduced a formula, relating the viscosity of the solvent η and the equivalent electroconductivity of a given electrolyte λ, λ_∞ . η_∞ =constant, where λ_∞ is the equivalent electroconductivity at infinite dilution of a certain ion (electrolyte, and where η_∞ is the viscosity of the solvent at infinite dilution of a certain ion (electrolyte). Walden’s work facilitated the rapprochement of the physical and chemical theories of solutions, and the rules that he discovered furthered the construction of the modern theory of acids and bases, the theory of electrolytes, and the study of the mechanism of organic reactions.

Walden earned international recognition for having established empirical laws relating surface tension, critical parameters, and hidden heat of fusion to the molecular weight (degree of association) of liquids, thereby contributing to the study of intermolecular forces in liquids.

Elected a member of the St. Petersburg Academy of Sciences in 1910, Walden combined his professorial duties in Riga with his directorship of the Academy’s chemistry laboratory in St. Petersburg (since 1911). He devised a project for establishing an academic institute of chemistry in St. Petersburg, and he was active in scientific education in Russia, furthering the rational use of the nation’s natural resources. He wrote the first extensive work on the history of chemistry in Russia (1914, printed in 1917). A founder of Latvia University in Riga, he became its first rector in 1919.

Following the establishment of the postwar nationalist regime in Latvia, Walden emigrated to Germany in August 1919 and became professor of chemistry at the University of Rostock. He continued his research on the electrochemistry of nonaqueous solutions, on which he wrote several monographs. After retiring in 1934 he devoted himself almost exclusively to the history of chemistry. During World War II he moved to Frankfurt-am-Main, and then to Tübingen, where until the age of ninety he lectured on the history of chemistry at the university. His later writings were dedicated to the history, psychology, and logic of chemistry; several were of an autobiographical character. He received honorary doctorates from several universities, was elected a member of scientific academies, and was an honorary member of the Chemical Society of London.

BIBLIOGRAPHY

I. Original Works. Walden published more than 300 scientific papers. His writings include “Ocherk istorii khimii v Rossii” (“Essay on the History of Chemistry in Russia”), intro. to A. Ladenburg, Lektsii po istorii razvitia khimii ot Lavuazie do nashikh dney (“Lectures on the History of the Development of Chemistry From Lavoisier to the Present” ; Odessa, 1917, pp. 361–654); Nauka i zhizn (“Science and Life”), 3 pts. (Petro-grad, 1919-1921); Optische Umkehrerscheinungen (Waldensche Umkehrung) (Brunswick, 1919); “Elektrochemie nichtwässriger Lösungen,” in Handbuch derangewandten physikalischen Chemie, XIII (Leipzig, 1924); “Leitvermögen der Lösungen” (3pts.) in F. W. Ostwald et al., Handbuch der allgemeinen Chemie, IV a, IV b (Leipzig, 1924); Chemie der freien Radikale (Leipzig, 1924); and Geschichte der organischen Chemiet seit 1880 (Berlin, 1941).

II. Secondary Literature. See W. Hückel, “Paul Walden, 1863-1957,” in Chemische Berichte, 91 (1958), xix-lxv, with complete bibliography of Walden’s writings: J. Stradinš, Cilvēki, eksperimenti, idejas (Riga, 1965), 217–258; Materialy dlya biograficheskogo slovarya deystvitelnykh chlenov imperatorskoy Akademii nauk (“Materials for a Biographical Dictionary of Members of the Imperial Academy of Sciences”), I (Petrograd, 1915); J.Stradinš, “K biografii paula Valdena” (“On the Biography of Paul Walden”), in lz istorii estestvoznania i tekhniki Pribaltiki, 1 (1968), 157–167; Y. Soloview and J. Stradinš, “Paul Valden kak istork khimii” (“Paul Walden as a Historian of Chemistry”), ibid, 5 (1976); and I. Walden-Hollo, “Vospominania obottse” (“Recollections of My Father”), in Nauka i tekhnika (Riga, 1975), no. 3, 33–35; no. 4, 33–35.

Janis Stradin̦Š