Orgolab 5 - lab 5 write up PDF

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Experiment 5: Friedel- Crafts Acylation of Ferrocene

Experiment # 5: Friedel- Crafts Acylation of Ferrocene

INTRODUCTION: The Friedel-Crafts reaction represents electrophilic aromatic substitution reactions. The acylation reaction utilizes a Lewis acid catalyst, such as BF3 and AlCl3, in order to produce an acyl cation that adds to the aromatic ring. The Friedel-Crafts acylation reaction requires the addition of the acylium cation to one of the carbon atoms on the ring, followed by loss of a proton. The acylium cation serves as a solvent for the reaction and is produced from acetic anhydride. The product will be red 1,1-diacetyferrocene is both rings react. The product will be the orange acetylferrocene if only one ring reacts. In order to reduce the formation of 1,1diacetylferrocene, the reaction time of the experiment is reduced. The objective of the experiment is to synthesize, isolate, and characterize acetylferrocene. Column chromatography is a technique used to separate the desired product from unreacted starting material and side products. Finally, melting temperature and 1H NMR analysis is used to characterize the synthesized product. Below is the reaction equation.

DATA:

Part I Synthesis of Acetylferrocene

Mass of ferrocene (g)

.2616 g

Volume of acetic anhydride (mL)

2.0 mL

Mass of filter paper (g)

0.1381 g

Mass of filter paper and crude product (g)

1.2342 g

Mass of crude product (g)

1.0961 g

Part II Column Chromatography Mass of test tube 1 (g)

7.6563 g

Mass of test tube 2 (g)

7.6984 g

Mass of test tube 1 and ferrocene dried solid (g)

7.6670 g

Mass of test tube 2 and acetylferrocene dried solid (g)

7.825 g

Mass of ferrocene solid (g)

0.0107 g

Mass of acetyl ferrocene solid (g)

0.1266 g

Part III Melting Temperature Measure melting temperature range (°C) Isolated ferrocene

172-173 °C

Isolated acetylferrocene

81-83 °C

RESULTS AND DISCUSSIONS: For part I synthesis, a 10mL round bottom flask, air-cooled condenser, and a drying tube was collected. The drying tube was then charged with Drierite using cotton pieces, then attached to the top of the air condenser. Then about 0.25 g of dry ferrocene was transferred to the round

bottom flask. 2.0 mL of acetic anhydride was then added to the ferrocene in the vial with a spin vane. After the ferrocene has dissolved, the drying tube was disconnected and 10 drops of 85% phosphoric acid was added as a catalyst. Mixture was then warmed in a hot water bath for about 10 minutes while stirring. The flask was then cooled in an ice water bath and 1.0 mL of ice cold water was added to the mixture. The reaction was then poured over ice in a 50mL beaker and neutralized by adding 10% NaOH. The resulting orange solution was cooled in an ice water bath for 30 minutes and vacuum filtration was used to collect the solids. The solid was then washed, dried, and weighed. For part II column chromatography, 0.1 g of the sample was dissolved in about 0.5 mL of diethyl ether and stoppered to prevent evaporation. Next, the chromatography column is assembled by placing a piece of cotton into the bottom of the 10 mL serological pipet followed by 0.5 cm of sand and enough silica to fill the pipet about 2/3 full. After tapping the pipet to pack the silica, another 0.5 cm of sand is added to the top of the pipet. Using the flash technique. A pipet bulb was used to push the solvent through. 5 mL of hexane was the eluted so that the column does not get dry. Once the clear portion is collected in the waste flask, the ferrocene fraction (yellow band) and acetylferrocene fraction (orange band) is collected a separate test tubes after passing the pipet column with 9:1 hexane/acetone. Finally, vacuum filtration was done to collect the solids. Dry solids were then weighed for melting temperature and NMR analysis the following week. For part III, a small amount of ferrocene and acetyl ferrocene was packed 1-2 mm deep into a capillary tube separately. Melting temperature was measured using Vernier Melting Station. For part IV, 200 uL of deuterated chloroform, CDCL3 was added to each of the test tubes containing ferrocene and acetyl ferrocene and stoppered. 1H NMR was the acquired using the picoSpin NMR spectrometer.

From part I synthesis of acetylferrocene, the mass of ferrocene was .2616 g. The volume of acetic anhydride added was 2.0 mL. After collecting the solids using vacuum filtration, the mass of filter paper was obtained to be 0.1381 g. The mass of the filter paper and crude product was 1.2342 g, therefore the mass of the crude product was 1.0961 g. For part II column chromatography, two clean test tubes were obtained and weighed. The mass of test tube 1 was 7.6563 g and the mass of test tube 2 was 7.6984 g. After collecting the ferrocene in test tube 1 and acetylferrocene in test tube 2, the mass of ferrocene solid (yellow band) was found to be 0.0107 g and the mass of acetylferrocene solid (orange band) was found to be 0.1266 g. Finally, for part III melting temperature, the isolated ferrocene had a melting temperature range of 172173°C (literature melting point is 172.5°C) and the isolated acetylferrocene had a melting temperature of 81-83°C (literature melting point is 83°C). Therefore, the limiting reagent was ferrocene because there was less product of isolated ferrocene and isolated acetylferrocene. Since 1 mole of ferrocene is equal to 1 mole of acetylferrocene, one can calculate the percent acetylferrocene in the crude product using the masses of the isolated products. Starting with the mass of ferrocene started (0.2616 g) with in part I multiplied by the molecular weight of ferrocene (186.04 g/mol) multiplied by 1:1 ratio, one will get 0.00141 moles of acetylferrocene. Taking 0.00141 moles of acetylferrocene and multiplying it by the molecular weight of acetylferrocene (228.07 g/mol), one will obtain the theoretical yield of 0.32158 g of acetylferrocene. The actual percent yield is found by using the mass of the crude product (0.1266 g) divided by the theoretical yield ( 0.32158 g), one will obtain a 39.36% actual yield. The yield and percent yield for this experiment was low due to ineffective reaction with respect to yield. The majority of the yield was likely lost due to overheating the initial solution of ferrocene, acetic anhydride, and phosphoric acid, in the presence of O2, resulting formation of the black

polymer. One way to improve the experiment would be to perform the lab in an inert environment under nitrogen gas, without the presence of O2.

CONCLUSION: The purpose of this experiment was to synthesize, isolate, and characterize acetylferrocene by using techniques like column chromatography and melting temperature analysis. Column chromatography was used to separate the desired product, acetylferrocene, from unreacted starting material and side products. Since the compounds are colored, ferrocene is the yellow band while acetylferrocene is the orange band, it made it easier to see the separation. Overall, the desired product acetylferrocene was formed. This was verified through 1

H NMR analysis and the characteristic melting point range of the final product. The limiting

reagent was ferrocene because there was less product of isolated ferrocene and isolated acetylferrocene. The yield and percent yield for this experiment was low due to ineffective reaction with respect to yield. REPORT QUESTIONS: If the reaction time were extended, I would expect the second acetylation to occur on the second ring because there is more room and also acts as a nucleophile....