Herbert Charles Brown (22 May 1912 – 19 December 2004) was an American chemist and recipient of the 1979Nobel Prize in Chemistry for his work withorganoboranes.[2]
Brown was bornHerbert Brovarnik inLondon, to UkrainianJewish immigrants fromZhitomir, Pearl (née Gorinstein) and Charles Brovarnik, a hardware store manager and carpenter.[3] His family moved toChicago in June 1914, when he was two years old.[4][5] Brown attendedCrane Junior College in Chicago, where he met Sarah Baylen, whom he would later marry. The college was under threat of closing, and Brown and Baylen transferred toWright Junior College.[5] In 1935 he left Wright and that autumn entered theUniversity of Chicago, completing two years of studies in three quarters to earn aB.S. in 1936.[4] That same year, he became a naturalizedUnited States citizen,[6] and began graduate studies at Chicago. On February 6, 1937, Brown married Baylen, whom he would later credit with sparking an interest inhydrides ofboron that would eventually lead to the work for which he, together withGeorg Wittig, would be awarded the Nobel prize in Chemistry in 1979,[4] and the following year received his degree asPh.D.
Unable to find a position in industry, he decided to accept apostdoctoral position, beginning his academic career. He became an instructor at Chicago in 1939, and held the position for four years before moving toWayne University inDetroit as anassistant professor. In 1946, he was promoted toassociate professor, and the following year became aprofessor ofinorganic chemistry atPurdue University in 1947[7] and joined the Beta Nu chapter ofAlpha Chi Sigma there in 1960.[8] He held the position ofProfessor Emeritus from 1978 until his death in 2004.[4] TheHerbert C. Brown Laboratory of Chemistry was named after him on Purdue University's campus. He was an honorary member of the International Academy of Science, Munich.
DuringWorld War II, while working withHermann Irving Schlesinger, Brown discovered a method for producingsodium borohydride (NaBH4), which can be used to produceboranes, compounds ofboron andhydrogen. His work led to the discovery of the first general method for producing asymmetric pureenantiomers. The elements found as initials of his nameH,C andB were his working field.
Brown was quick to credit his wife Sarah with supporting him and allowing him to focus on creative efforts by handling finances, maintaining the house and yard, etc. According to Brown, after receiving the Nobel prize inStockholm, he carried the medal and she carried the US$100,000 award.
Borane, BH3, is a gaseous compound that is only present at high temperatures. It dimerises to form diborane, B2H6. Diborane has a pair ofthree-center two-electron bonds.
As a doctoral student at theUniversity of Chicago, Herbert Brown studied the reactions ofdiborane, B2H6.Hermann Irving Schlesinger's laboratory at the University of Chicago was one of two laboratories that prepared diborane. It was a rare compound that was only prepared in small quantities. Schlesinger was researching the reactions of diborane to understand why the simplest hydrogen-boron compound is B2H6 instead of BH3.[13]
When Brown started his own research, he observed the reactions of diborane withaldehydes,ketones,esters, andacid chlorides. He discovered that diborane reacts with aldehydes and ketones to produce dialkoxyboranes, which arehydrolyzed by water to producealcohols. Until this point, organic chemists did not have an acceptable method ofreducingcarbonyls under mild conditions. Yet Brown's Ph.D. thesis published in 1939 received little interest. Diborane was too rare to be useful as a synthetic reagent.[13]
In 1939, Brown became the research assistant in Schlesinger's laboratory. In 1940, they began to research volatile, low molecular weight uranium compounds for theNational Defense Research Committee. Brown and Schlesinger successfully synthesized volatile uranium(IV) borohydride, which had a molecular weight of 298. The laboratory was asked to provide a large amount of the product for testing, but diborane was in short supply. They discovered that it could be formed by reactinglithium hydride withboron trifluoride inethyl ether, allowing them to produce the chemical in larger quantities. This success was met with several new problems. Lithium hydride was also in short supply, so Brown and Schlesinger needed to find a procedure that would allow them to usesodium hydride instead. They discovered that sodium hydride andmethyl borate reacted to producesodium trimethoxyborohydride, which was viable as a substitute for the lithium hydride.[13]
Soon they were informed that there was no longer a need for uranium borohydride, but it appeared that sodium borohydride could be useful in generatinghydrogen. They began to look for a cheaper synthesis and discovered that adding methyl borate to sodium hydride at 250° produced sodium borohydride and sodium methoxide. Whenacetone was used in an attempt to separate the two products, it was discovered that sodium borohydride reduced the acetone.[13]
Sodium borohydride is a mildreducing agent that works well in reducing aldehydes, ketones, and acid chlorides. Lithium aluminum hydride is a much more powerful reducing agent that can reduce almost anyfunctional group. When Brown moved toPurdue University in 1947, he worked to find strongerborohydrides and milderaluminum hydrides that would provide a spectrum of reducing agents. The team of researchers at Purdue discovered that changing the metal ion of the borohydride tolithium,magnesium, oraluminum increases the reducing ability. They also found that introducingalkoxy substituents to the aluminum hydride decreases the reducing ability. They successfully developed a full spectrum of reducing agents.[13]
While researching these reducing agents, Brown's coworker, Dr. B. C. Subba Rao, discovered an unusual reaction between sodium borohydride andethyl oleate. The borohydride added hydrogen and boron to the carbon-carbondouble bond in the ethyl oleate. The organoborane product could then beoxidized to form an alcohol.[13] This two-step reaction is now calledhydroboration-oxidation and is a reaction that convertsalkenes into anti-Markovnikov alcohols.Markovnikov's rule states that, in adding hydrogen and ahalide orhydroxyl group to a carbon-carbon double bond, the hydrogen is added to the less-substituted carbon of the bond and the hydroxyl or halide group is added to the more-substituted carbon of the bond. In hydroboration-oxidation, the opposite addition occurs.[14]
