The Synthesis And Characterization Of Ferrocene Essay — страница 2

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adapter. While the mixture is slowly stirred and the flask is being purged with a stream of nitrogen, the cyclopentadiene (2.75 mL) is added. The resulting solution is rose colored. The main neck is then fitted with a pressure equalizing dropping funnel (25 mL) with its stopcock open. In a second one neck round bottom flask that is fitted with a septum, FeCl2.4H30 (3.25 g) and DMSO (12.5 mL) are stirred under a nitrogen atmosphere to dissolve the FeCl2.4H30. After about five minutes, the stopcock is closed and the FeCl2 solution is added to the pressure equalizing dropping funnel. The reaction mixture in the three-neck flask is stirred vigorously and the purging with nitrogen is continued. After about ten minutes, the stopper is placed on the dropping funnel, the nitrogen flow is

reduced and drop-by-drop addition of the FeCl2 solution is begun. The rate of addition is adjusted so that the entire solution is added in 30 minutes. Then the dropping funnel stopcock is closed and vigorous stirring of the dark green solution is continued for an additional 30 minutes. Finally, the nitrogen flow is stopped and the mixture is added to a mixture of 6M HCl (45 mL) and crushed ice (50 g). Some of the resulting slurry may be used to rinse the reaction flask to maximize the product yield. The slurry is stirred for about 15 minutes and the orange precipitate is collected on a Buchner or Hirsch funnel and washed with four 5-mL portions of water. The moist solid is spread out on a large watch glass and dried in the air. The compound is then purified through sublimation in

a large glass petri dish that is placed on a warm hot plate (100 C). Care is used to avoid charring the ferrocene. The purified ferrocene is then characterized by melting point determination, UV-Vis and IR spectroscopies, and cyclic voltammetry. We are incorporating a bulk electrolysis to generate the ferrocenium cation. Preparation of AcetylferroceneAcetylferrocene is synthesized under mild conditions with a modification of the procedure reported by Bozak (4). The students are supplied with ferrocene during the second laboratory period so that the acetylation of ferrocene may take place concurrently with the purification of ferrocene. This encourages students to develop multi-tasking skills.A mixture of ferrocene (1.5 g) and acetic anhydride (5 mL) is prepared in a small

Erlenmeyer flask. To this mixture, 85% H4PO4 (1 mL) is added dropwise with constant stirring. This addition is exothermic and is accompanied by a change in color. Following the addition of the phosphoric acid, the Erlenmeyer flask is fitted with a CaCl2 drying tube. The dark green solution is then heated in a beaker of water on a hot plate for ten minutes (50 C). During this time, the solution becomes rose colored. The mixture is then poured over ice (20 g) into a large beaker that will accommodate the gas (CO2) formed during the NaHCO3 neutralization. Water is used to rinse the reaction flask and maximize the product yield. When the ice has melted, small quantities of sodium bicarbonate are added until gas evolution stops. The pH may be tested with pH paper to insure that

neutrality is achieved. This is followed by cooling the resulting orange solution in an ice bath for 30 minutes during which time a brown precipitate forms. This precipitate is collected by suction filtration using a coarse fritted funnel. The dark brown solid is then washed with distilled water to remove impurities until it is pale orange in color. It is then dried in air for 15 minutes. Thin layer chromatography is used to optimize the conditions for column chromatography of acetylferrocene. TLC plates (silica gel) are provided for student use. Alternatively, microscope slides may be used as TLC plates by applying a slurry that consists of silica gel (40 g) and chloroform (100 mL). A small amount of the crude acetylferrocene, which is a mono- and diacetylferrocene/ferrocene

mixture, is dissolved in a vial in toluene (2-3 drops). A small amount of ferrocene is also dissolved in a separate vial in toluene. A line is penciled on each slide approximately 1 cm from the bottom of the TLC plate. The plates are spotted using a fine capillary applicator approximately on the pencil line. Each plate will contain two spots, one is ferrocene and one is crude acetylferrocene. The spots are allowed to air dry and then a second spot is applied at the same location to obtain a concentrated area of compound. The identity of the spot is indicated with a pencil mark. The plates are individually placed with the spotted end in the solvent in five developing chambers. The chambers contain the following solutions: petroleum ether, toluene, ethyl ether, ethyl acetate and a