The Synthesis And Characterization Of Ferrocene Essay — страница 3

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mixture of 10% ethyl acetate and 90% petroleum ether. The pencil mark should be above the solvent level. The solvent containers are covered while the plates are developing. The plates are removed when the solvent front has traveled approximately 3/4 of the distance of the plate. The plates are air dried. The TLC plates may be developed in an iodine chamber. This will result in brown spots that can be marked and identified so that the plates may be included in a laboratory report. The solutions that provide maximum separation of the two components are chosen as column chromatography solutions. For instance, ferrocene may elute with toluene while the acetylferrocene remains on the column and is then eluted with a toluene/ethyl acetate mixture. The color of the spots is helpful to

discern the individual bands that elute from the column. The crude acetylferrocene is dissolved in the solution that is selected to elute the first component. The column is assembled by placing a small piece of glass wool into the bottom of the column (50 mL buret). The glass wool is then covered with a small amount of sand and the buret is filled with the solvent that was chosen to dissolve the crude mixture. A powder funnel is used to slowly fill the column with dry silica gel to a height of approximately 30 cm. The column is never allowed to dry. Alternately, the column may be prepared by the traditional slurry method. A small amount of silica gel may be added to the crude acetylferrocene solution to make a slurry that is then added to the top of the column and covered with a

small amount of sand. The two solutions (or mixtures) are then used to purify the crude acetylferrocene. The ferrocene band is discarded and the solvent is removed from the acetylferrocene band by rotary evaporation. It may then be recrystallized from chloroform. The acetylferrocene is characterized by melting point determination, IR and UV-Vis spectroscopies, and cyclic voltammetry. ——————————————————————————– DiscussionThe experimental procedure for the synthesis of ferrocene provided above was adopted after several failed attempts to incorporate newer microscale techniques that utilize ethylene glycol (5) as the solvent rather than 1,2-dimethoxyethane. When ethylene glycol was used, an extremely viscous reaction mixture

resulted that was incapable of being stirred effectively in the micro-glassware. Our success rate with the revised preparation is 100%.Our advanced undergraduate inorganic lab is taught in the semester format with two three-hour weekly classes. The students learn to multi-task to accomplish their lab responsibilities efficiently. We have provided the following suggested format (Table 1) to accomplish the synthesis and characterization of ferrocene and acetylferrocene in two and a half weeks. This format is not provided to the students. They are innovative and are required to submit their own schedules before beginning work. The format allows instructors and teaching assistants to flexibility in the method of ensuring that the students use their time efficiently.

——————————————————————————– Table 1. Suggested Time Management Schedule Day Program1 Synthesis of Cp2Fe; teaching assistant to provide cyclopentadiene2 Sublimation of Cp2Fe; students are given Cp2Fe to perform the acetylation3 Thin layer and column chromatography of acetylferrocene followed by rotary evaporation; begin characterization of Cp2Fe (melting point, UV-Vis, IR)4 Characterization of acetylferrocene (melting point, UV-Vis, IR); CAChe modeling5 Finish characterization including cyclic voltammetry and bulk electrolysis ——————————————————————————– Crude ferrocene and acetylferrocene were synthesized in 51-79% and 27-58% yield respectively. An experimental melting

point range of 169-171 C was obtained for ferrocene. The reported melting point range is 173-174 C (3). For acetylferrocene, the experimental melting point range was 80-83 C as compared with the reported range of 81-83 C (7). Infrared spectroscopy was performed by the students on ferrocene and acetylferrocene both as a KBr pellet and as a Nujol mull on NaCl plates. The infrared spectra were comparable to those reported for ferrocene (3) and acetylferrocene (8). The main difference between the spectra of ferrocene and acetylferrocene is of course the appearance of a carbonyl stretch at 1736 cm-1 that is present in the acetylferrocene and absent in the ferrocene. Some students also observed a peak at 893 cm-1 that is attributed to the monoacetylferrocene ring. They did not observe