Date of Award
Bachelor of Science
Chromium hexacarbonyl, Cr(CO)6, has been shown to be a very effective photochemical catalyst for many reactions, such as the 1,4- hydrogenation and 1 ,4-hydrosilation of conjugated 1 ,3-dienes resulting in the formation of a cis alkene product in greater than 99% yield. Although much research has been done on the reactions which Cr(CO)6 catalyzes, not much data exists on the reactions of photochemically created fragments of Cr(CO)6 , such as Cr(CO)6. This study focuses on the reactivity of organotransition metal intermediates with the goal of contributing to the growing database of the reactions involving the photochemistry of Cr(CO)6. Particular emphasis will be given to the kinetics and mechanism of these reactions. Experiments with Cr(CO)6 require the use of an extremely pure solvents. Since it has been found that metal carbonyls are very sensitive to such impurities as water and oxygen, solvents must be dried and degassed. This is done by refluxing the solvent over CaH2 for 12 hours under flowing purified argon, followed by a second distillation in a fractionating column. Argon is purified by passing through one 13x molecular sieves column and one Oz scavenging column to remove water, oxygen and organic impurities. The chromium hexacarbonyl solution was degassed by six freeze-pump-thaw cycles. Chromium hexacarbonyl solutions have been flashed and the subsequent thermal reaction was found to follow second order kinetics. The solution was then saturated with CO and the reaction kinetics changed to pseudo-first order. Plots of kobs vs. [CO] are linear with the slope equal to the second-order rate constant. The value of this constant was found to be 1.7 x 106 M-1 s-1, which is two times sma11er than the literature value of 3.6 x106 M-1 s-1.
Zaydman, Marina, "Kinetics and mechanism of chromium hexacarbonyl photochemistry using flash by photolysis" (1997). Honors Theses. 2065.