Paul Walden began his early life as a poor, orphaned peasant in Latvia and died in 1957 at age 93 nearly destitute in post-World War II Germany. Yet, in between, the scientist found fame for his pioneering work in organic stereochemistry and in physical chemistry, research he performed in Latvia, Germany, and Russia.
This year marks the 150th anniversary of Walden’s birth, in July 1863. A contemporary of periodic table developer Dmitri Mendeleev and physical chemists Svante Arrhenius and Jacobus H. van’t Hoff, Walden is probably best known for his discovery of the Walden inversion, a transformation that switches the configuration of a chiral molecule with a single stereocenter into its mirror image.
In 1896, Walden reported the conversion of (+)-chlorosuccinic acid into its enantiomer, (–)-chlorosuccinic acid, in two steps and then back again in two further steps, results he published in the German journal Berichte der deutschen chemischen Gesellschaft (DOI: 10.1002/cber.18960290127).
Walden’s work on the conversion came on the heels of van’t Hoff’s proposal that a carbon atom’s single bonds could be modeled by a tetrahedron, explains Erick M. Carreira, an organic chemist at the Swiss Federal Institute of Technology (ETH), Zurich. “Van’t Hoff’s work was purely theoretical,” he says. “Walden’s key experiment provided experimental verification” for van’t Hoff’s stereochemical theory, Carreira adds.
Walden’s work helped “set a stage for how to use stereochemistry to gain insight into molecular structure and reactions,” Carreira says.
Walden made contributions to organic chemistry during a five-year diversion into the field. Most of Walden’s life’s work was in physical chemistry, says Peteris Trapencieris, head of organic chemistry at the Latvian Institute of Organic Synthesis, in Riga.
Trapencieris notes that when he first started the Paul Walden Symposium on Organic Chemistry in the late 1980s, “a friend said to me, ‘Why are you doing that? He wasn’t really an organic chemist; he was an electrochemist.’ I guess Walden was successful in almost everything he tried.”
Latvian chemists are commemorating the 150th anniversary of Walden’s birth by naming two streets for Walden, one next to Riga Technical University’s department of materials science and the other in Valmiera, the hometown of his wife. In addition, the Latvian postal service has issued a stamp in Walden’s honor. A long-standing Walden medal is awarded to Latvian chemists for outstanding work in chemistry, and an organic chemistry symposium in his honor is held every several years.
Although widely celebrated in Latvia, Walden is less celebrated in Germany, where he ended his career. This may in part be because Walden wrote often about the history of chemistry in pro-German, nationalistic prose before and during the Hitler era, which could suggest he was a Nazi sympathizer, although Walden claimed he was not an anti-Semite.
Walden was the youngest of 13 children born to poor Latvian farmers, says Erkki Hollo, Walden’s grandson. Hollo, age 73, is the only living relative of Walden’s who met the chemist in person. They met just once, around 1952, when Hollo was a boy and Walden was in his late 80s and nearly deaf.
Walden was orphaned young. His father died when he was four, and his mother passed away soon after, Hollo says. Only five of the 13 kids made it to adulthood.
Two older brothers paid for Walden to be sent to a German boarding school, where he learned both German and Russian.
After high school, Walden began studying chemistry in 1882 at Riga Polytechnic Institute, where classes were in German, the scientific lingua franca at the time. In this era, Latvia was under Russian control, but many so-called Baltic Germans living in the region had positions of power and wealth. Around the turn of the 20th century, Russian began to replace German as the academic language in the region; Walden was fluent in both.
By the time he finished his undergraduate studies in 1888, Walden had a couple of research papers to his name, one of which was based on work under chemistry professor Wilhelm Ostwald, a Baltic German who later won the 1909 Nobel Prize in Chemistry for his work on catalysis, chemical equilibria, and reaction rates.
A year before Walden’s undergraduate studies were completed at Riga, Ostwald was recruited to the University of Leipzig, in Germany. After finishing his undergraduate work, Walden began graduate work at Riga, but then followed Ostwald to Leipzig to pursue doctoral work there as well. Walden also spent time doing research at a university in Odessa, Ukraine, which, like Riga, was then under Russian control.
In 1892, at age 29, Walden started a faculty career back at Riga Polytechnic University. By 1894 he was promoted to professor of physical and analytical chemistry, says Gisela Boeck, a chemist and historian at the University of Rostock, in Germany.
When he started the faculty post, Carl Bischoff, a professor in the department who had also mentored Walden as a student, suggested that Walden try his hand at organic chemistry, Trapencieris says. This helped inspire Walden’s sojourn from physical to organic chemistry, leading to the publication of the Walden chiral inversion in 1896.
Two years after that paper was published, Walden married a Baltic German woman living in Latvia named Wanda Wilhelmine, whom he had met during his summer holidays in the Latvian countryside.
Subsequently, Walden refocused his career once again on physical chemistry. He was already renowned in the area, Boeck says, for teaming up with Ostwald to propose a theory on a controversial topic of that era. At the time chemists such as Arrhenius, van’t Hoff, and Mendeleev debated how ions dissolve in solution. Walden helped resolve the debate by proposing a still-correct theory about how ions associate with counterions when they dissolve, Boeck says.
Walden is also often hailed as the father of ionic liquids, salts that are liquids at room temperature, “but I don’t agree,” Boeck says. Although Walden did publish a paper in 1914 about the conductivity of an ionic liquid called ethylammonium nitrate (Bull. Russian Acad. Sci. 405), he didn’t recognize its potential applications, she says. Furthermore, in 1908, six years before Walden’s paper on ethylammonium nitrate, a chemist named Carl Schall, a pupil of Ostwald’s in Leipzig, had already published work on several salts that melted at low temperature, the defining characteristic of an ionic liquid (Zeitschrift für Elektrochemie1908,14, 397).
Boeck became interested in the Latvian chemist because in 1919, after 25 years at Riga, Walden immigrated to Germany and accepted a position at the University of Rostock, where Boeck is now employed.
Walden likely left his university post in Riga, where he had become university rector, because of upheaval and instability in the region after World War I, Trapencieris says, when Latvia declared its independence from Russia. In the University of Rostock’s archives, Boeck found the university’s offer of employment to Walden, which was addressed to a refugee camp in Germany where Walden was living.
Despite his German education, German language skills, and Baltic German wife, not all of Walden’s new colleagues in Rostock were happy he had been hired, Boeck says. According to university records, she says, “several people were against it.” They argued that his German wasn’t good enough and that he was too Russian, because he had received many Russian accolades and had been admitted to the prestigious St. Petersburg Academy of Sciences.
“The direct result of this is that Walden used every possibility to prove himself to his German colleagues,” Boeck says. At Rostock, Walden wrote many papers on the history of chemistry that left readers with the impression that “all chemistry was German chemistry,” she says. The same held true for a tome he later published called “Three Thousand Years of Chemistry,” Boeck adds.
Walden retired from the University of Rostock in 1934, the year after Hitler came to power. Because of Walden’s pro-German and nationalistic writings about the history of chemistry, written prior to and during Hitler’s ascendance, some chemists have flagged him as a Nazi sympathizer.
Boeck says Walden was a member of the National Socialist Teachers League (Nationalsozialistischer Lehrerbund) and a financial supporter of the Nazi military (Förderndes Mitglied der SS). “In this sense he was a Nazi sympathizer,” she says. “But there’s no proof he was an anti-Semite.” For example, Walden wrote that he tried to help a former Jewish student during the Nazi era.
Boeck points out that many notable chemists joined Nazi organizations to protect themselves from persecution and that many publications from Nazi times were rife with nationalistic propaganda. Walden may have taken the path of least resistance, willingly toed the Nazi party line, or been bullied or blackmailed into showing respect for German nationalism. “We don’t know much about him personally from that time,” Boeck says.
Indeed, scholars of Walden’s work have been stymied with regard to information about his life in Germany because his home in Rostock was bombed by the Allies in 1942 and burned to the ground. In the house were all of Walden’s personal papers as well as a library of more than 10,000 books he had collected over his life, Trapencieris says.
As a result, Walden and his wife became homeless. In 1942 and 1943, during the height of WWII, they moved all over Germany, living in Berlin, Frankfurt, Bühl, Tübingen, and finally Gammertingen. That’s where Walden, then in his 80s, taught chemistry again in 1946 to make ends meet, a position arranged for him by Nobel Prize winner Adolf Butenandt, Boeck says.
Walden’s financial problems were because of post-WWII Germany’s division into four parts. Tübingen and Gammertingen were in the French district, while Rostock, where his pension was, was in the Russian district and thus not accessible to him.
On the one visit Hollo made to Germany in the 1950s, when Walden was in his 80s, Hollo says his grandfather “couldn’t hear very well, so we didn’t communicate very much. But he wrote notes about chemistry constantly. I would guess even on his last day he wrote these notes.”
“I’ve read that Walden was once asked, ‘What’s your nationality?’ ” Trapencieris says, because Walden was at times called a German, a Latvian, or a Russian. “After a pause he answered, ‘I’m a chemist.’ ”