The thermal cracking reaction to obtain cyclopentadiene is shown in figure 2. The thermal cracking was done using a Vigreaux column, which is a type of fractionating column used to separate vapours according to their volatility or boiling point.
The column consists of a series of downward-pointing indentations to increase the surface area available for repeated condensation and evaporation of the vapours in the column. A temperature of — oC was used to heat up the dicyclopentadiene upon which it forms the cyclopentadiene. This cyclopentadiene was collected as the distillate as it is less volatile than the dimer.
The temperature at the top of the column registers the boiling point of the cyclopentadiene which is around 39oC. The cyclopentadiene is condensed and collected as the distillate, kept cool in an ice bath.
B: Synthesis of Ferrocene Part a — Preparation of potassium cyclopentadienide solution The cyclopentadienyl solution is prepared by reacting potassium hydroxide, KOH, with cyclopentadiene in anhydrous 1,2-dimethoxyethane DME. Aprotic solvents like DME solvate the cations but do not solvate the anions. Hence, as the anion OH- is not solvated or stabilized, it can react very easily and deprotonate the cyclopentadiene to form the cyclopentadienyl anion.
KOH is hygroscopic hence it should be added quickly to the DME solvent to prevent the absorption of water vapour from the air, which would lead to the formation of KOH solution which is immiscible with the organic layer made up of cyclopentadiene. Acetylferrocene may have traveled more slowly along the film because the molecule is larger or because it binds more strongly to the silica.
I would like to see you discuss the bands lower on the TLC sheet than the acetylferrocene. I suspect you have the products there of di and triacetylation. Additionally, the TLC shows that not all of the ferrocene was acetylated. Ferrocene is the limiting reagent in this procedure so some other reason must explain why acetylation of ferrocene was incomplete. Time may have been the limiting factor.
If the acetylation step had run longer, it may have gone to completion for all the ferrocene. This could also attribute to the slightly lower than expected melting point experimental Although the m. The theoretical yield for this product is the mass of the number of moles of ferrocene completely converted to acetylferrocene.
That is: 8. The final product weight was less than the theoretical yield of 1. Wear gloves whenever handling ferrocene or when cleaning glassware. Obtain a yield of the sublimed ferrocene. Set this iron-stained glassware aside for our stockroom staff.
Therefore we will collect the filter paper from the suction filtration that contains residual ferrocene. Part C: Acetylation of Ferrocene Perform this procedure in partners, and wear gloves whenever handling ferrocene or acetylferrocene. Add purified ferrocene 0. Attach a CaCl2 drying tube to the round bottomed flask and heat the solution in a 50 oC warm water bath for 10 minutes. Pour the reaction mixture into a mL beaker containing crushed ice 1.
Cool the mixture in an ice bath, then collect the solid product by suction filtration using a Hirsch funnel. Wash the solid with a few mL of distilled water and squeeze between sheets of fresh filter paper to remove excess water. Run a TLC of your product alongside the starting material ferrocene, using an eluent composed of hexane and ethyl acetate.
As a class, together experiment with different ratios of hexane to ethyl acetate in order to determine the best solvent system for future column chromatography. The ideal column conditions are for the compound of interest acetylferrocene to have an Rf near 0. Part D: Column Chromatography Purify the acetylferrocene using column chromatography and the solvent system previously determined to be optimal by the class.
Collect the fractions into small test tubes. When ferrocene has eluted off the column, increase the solvent polarity to more rapidly elute the acetylferrocene. When all colored components have eluted, combine all fractions containing apparently pure acetylferrocene into a round bottomed flask rinse test tubes into the flask with a small amount of acetone. Remove the solvent using the rotary evaporator.
Peterson, and G. Pass nitrogen into the flask for about 1 min. Evaporate the solvents in the hood using very gentle airflow. Determine the limiting reagent for the synthesis of ferrocene. The structure of ferrocene initiated an explosion of interest in metal-carbon bonds and initiated the development of organometallic chemistry. Heat the mixture for 30 minutes.
I would like to see you discuss the bands lower on the TLC sheet than the acetylferrocene. Lifting it may lift the upper culture dish off and cause it to fall or disturb the sublimed ferrocene resulting in a loss of ferrocene. The theoretical yield for this product is the mass of the number of moles of ferrocene completely converted to acetylferrocene. KOH is hygroscopic hence it should be added quickly to the DME solvent to prevent the absorption of water vapour from the air, which would lead to the formation of KOH solution which is immiscible with the organic layer made up of cyclopentadiene. That is: 8.
Collect the resulting precipitate on a Hirsch funnel.
If any gets on you or your clothing, remove affected clothing, rinse immediately with water. Background: Ferrocene is a historically important molecule. The recognition of the "sandwich" structure of C10H10Fe in spawned transition metal based organometallic chemistry. Calculate and report your actual percent yield. The solution may turn a deep burgundy, green or black color as potassium cyclopentadienide is formed.
Hydrochloric acid HCl : Very acidic liquid.
It may be purified by sublimation. Between injections remove both needles from the septum and shake the vial vigorously. The crude product was then dried before carrying out the sublimation. Ferrocene Related documents. The total preparation of ferrocene requires about four hours. Collect the resulting precipitate on a Hirsch funnel.
However, do not use this method after the beginning stages of the sublimation, or you will breathe toxic ferrocene vapors. The cyclopentadiene is condensed and collected as the distillate, kept cool in an ice bath. Dissolving the FeCl2. It was theorized that a portion of the product was still locked into the gummy substance that was left behind, and that attributed to the lower than expected yield. After sitting for a week the yellow smears spread out and changed to a faint greenish blue color.
Dry the crystals on a watch glass in your drawer until the next laboratory.
Ferrocene is insoluble in water, and thus it forms an orange precipitate that was filtered off using suction filtration. Attach a CaCl2 drying tube to the round bottomed flask and heat the solution in a 50 oC warm water bath for 10 minutes.