Kharasch, Morris

Kharasch, Morris S., 220 Kiliani-Fischer synthesis, 1001, 1009 Kinetic control, 380—381 O-acylation of phenols, 952 addition... 

In the early days of alkene chemistry, some researchers found that the hydrohalogenation of alkenes followed Markovnikov s rule, while others found that the same reaction did not. For example, when freshly distilled but-l-ene was exposed to hydrogen bromide, the major product was 2-bromopropane, as expected by Markovnikov s rule. However, when the same reaction was carried out with a sample of but-l-ene that had been exposed to air, the major product was 1-bromopropane formed by antl-Markovnikov addition. This caused considerable confusion, but the mystery was solved by the American chemist, Morris Kharasch, in the 1930s. He realised that the samples of alkenes that had been stored in the presence of air had formed peroxide radicals. The hydrohalogenation thus proceeded by a radical chain reaction mechanism and not via the mechanism involving carbocation intermediates as when pure alkenes were used. 

Pauson obtained his Ph.D. from the University of Sheffield in 1949 and then moved to the Duquesne University in Pittsburgh, where he was offered the post of a temporary Assistant Professor without interview. Following his interests in non-benzenoid systems, he attempted to prepare fulvalene (see Scheme 5.1) but, as mentioned above, isolated ferrocene instead. After he finished his 2-years term at Duquesne, he spend the academic year 1951-1952 at the University of Chicago as a postdoctoral fellow working on peroxide chemistry with Morris S. Kharasch, in those days the pope in this field. In 1953, he was appointed to a DuPont... 

Later, Morris Kharasch found that, if the reaction occurs in the presence of air, oxygen or a small amount of a peroxide, then the reaction goes in the reverse order H goes to the C with the smaller number of H atoms and the Br to the other, so forming 1-bromopropane. A summary of the mechanism of what is going on here is given in Section 6.2.4 as an extension topic at the end of this unit. 

Another famous appHcation of mechanistic chemistry was contributed by Morris Kharasch (1895-1957) at the University of Chicago. It was well known since the mid-19th century that addition reactions of HX (HCl, H-OH, etc) to unsymmetrical alkenes occur in a manner that places hydrogen on the olefinic carbon attached to more hydrogen atoms than the other olefinic carbon (Markovnikov s rule). However, when HX is hydrogen bromide (HBr), addition is typically anti-Markovnikov. Kharasch found that traces of peroxides (commonly present on glassware surfaces) initiate a free radical chain reaction for HBr (not for other HX). Careful removal of peroxides Ifom glassware prior to reaction removes the potential free radical mechanism and HBr adds in a normal Markovnikov mode (intermediacy of carbocation, rather than Ifee radical, intermediates). 

Second, it was the year that I arrived at the University of Chicago, and, on the recommendation of Max Tishler, looked up Morris Kharasch as a possible research sponsor and was thus trapped by this new field. There I worked on some aspects of the abnormal addition problem, showing in part that it was not restricted to terminal olefins, and, with inate caution declified an invitation to investigate the chemistry of acetyl peroxide. 

Begun in this year under editorship of Morris Kharasch (University of Chicago) acquired by the American Chemical Society in 1955. 

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