Acylation+of+Ferrocene


 * Introduction**

In the continuation of exploring aromatic electrophilic substitution reactions, this weeks lab introduced the addition of an acetyl group to a compound. This is a highly useful addition reaction resulting in the increase of carbons on the starting material. In synthesis, the products can then be reduced to alkanes. The process was discovered in the pursuit to form synthetic diamond by Charles Friedel and James crafts in 1887.

Ferrocene is reacted with acetic anhydride and phosphoric acid to form acetylferrocene. Use of these reagents results in the reduction of aluminum and acidic waste. This reaction also eliminates the use of organic solvents traditionally used with acetyl chloride and aluminum chloride. The greener technique results in the formation of a selective product while learning an important method of forming c-c bonds.



Procedure:
Procedure can be found Here: [|The Friedel-Crafts Reaction]

Source: Doxsee, K. M.; Hutchison, J. E. //Green Organic Chemistry - Strategies, Tools, and Laboratory Experiments//, Print 2004; pp 225-230.

**Data**  ﻿Ferrocene is an opaque, rich orange powder.

 Acetic anhydride and phosphoric are both clear and colorless liquids.

 NaOH is a clear and colorless liquid.

 NaHCO3 is an opaque white powder.

 1.502g ferrocene balanced and placed in reaction container. 5.0mL acetic anhydride was added to the round bottom flask (RBF), followed by 1.0mL of 85% phosphoric acid. No reaction was evident during the addition of acetic anhydride, but when phosphoric acid was introduced to the solution it turned color to a dark red/brown.

 The RBF was gently agitated and heated intermittently for a period of time. During this time, the solution gradually changed colors to a much richer hue of rust red. Once all of the solute had dissolved, the highly odiferous solution was attached to the reflux tube and submerged in hot water with the stir rod gently aggregating the solution.

 Within five minutes, the solution was a much more vibrant red, having lost a substantial portion of the dominant brown hues present before.

 After ten minutes of gentle heating the solution had shifted to a very dark purple.

 25.275g of H2O(s) was measured and placed in a 250mL beaker and the contents of the RBF were poured over the ice. A substantial amount of dark blue/black solid remained in the RBF, so it was flushed out twice using 5mL deionized H2O(l) each time.

 The resultant solution in the new beaker was stirred for 5 minutes. The color was a ferrous green/brown.

 The beaker containing the solution was placed on a stir-plate while 37.5mL NaOH(l) was added. During this addition the solution changed color and physical character. Previously a homologous mixture, the solution separated into an aqueous layer with large flakes in suspension. The suspended solid was orange, and the liquid was clear with an orange hue. As the magnetic stir rod continued, the flakes of solid diminished in size until they were a fine powder suspension.

 3.693g NaHCO3 added in small portions until the pH of the solution was neutralized. Litmus paper tests confirmed. No bubbling was observed during this addition.

 The solution was allowed to sit for 20 minutes. Within minutes of being left alone the solution separated back into two layers: orange powdery suspension on the bottom and a thick orange colored liquid on top.

 Upon completion of the 20 minute rest period the product was vacuum filtered.

 The resultant solid was pressed between two pieces of filter paper surrounded by hand-towels until no more liquid could be extracted via this method.

 The orange solid was separated into two roughly equal portions. One of these halves, identified as portion A, was placed on a pre-weighed piece of filter paper. Portion B was put into an Erylenmeyer flask containing a magnetic stir bar and 20.0mL of toluene; this apparatus was placed on a stirring hot pad set to low heat.

<span style="display: block; font-family: Calibri; font-size: 12pt; line-height: normal; margin: 0in 0in 10pt; text-align: left;"> The solid began to dissolve immediately changing the color of the liquid from clear and colorless to a very rich translucent red/orange.

<span style="display: block; font-family: Calibri; font-size: 12pt; line-height: normal; margin: 0in 0in 10pt; text-align: left;"> Once completely dissolved, a spatula’s worth of charcoal was added and allowed to interact with the solution.

<span style="display: block; font-family: Calibri; font-size: 12pt; line-height: normal; margin: 0in 0in 10pt; text-align: left;"> Hot filtration was used to extract the charcoal and other impurities from the solution.

<span style="display: block; font-family: Calibri; font-size: 12pt; line-height: normal; margin: 0in 0in 10pt; text-align: left;"> During the filtration process no crystals were observed.

<span style="display: block; font-family: Calibri; font-size: 12pt; line-height: normal; margin: 0in 0in 10pt; text-align: left;"> Due to the length of time required to complete the hot filtration, the filtered solution in the bottom of the flask was at room temperature by the time all of the solution was filtered.

<span style="display: block; font-family: Calibri; font-size: 12pt; line-height: normal; margin: 0in 0in 10pt; text-align: left;"> Examining the contents of the flask, no crystals were evident in suspension, in the neck of the flask, or on the hot filtering apparatus. The contents of the flask were a brandy colored liquid and a significantly less viscous milky-white and grey translucent substance inferior to the brandy colored substance.

<span style="display: block; font-family: Calibri; font-size: 12pt; line-height: normal; margin: 0in 0in 10pt; text-align: left;"> This solution was vacuum filtered to isolate any solid. The contents resting upon the filter paper were washed with less than 1mL of toluene. No crystals or powder were found on the filter paper.

<span style="display: block; font-family: Calibri; font-size: 12pt; line-height: normal; margin: 0in 0in 10pt; text-align: left;">Mass of Crude Product: <span style="display: block; font-family: Calibri; font-size: 12pt; line-height: normal; margin: 0in 0in 10pt; text-align: left;">3.104 grams

<span style="display: block; font-family: Calibri; font-size: 12pt; line-height: normal; margin: 0in 0in 10pt; text-align: left;">Mass of product for purification: <span style="display: block; font-family: Calibri; font-size: 12pt; line-height: normal; margin: 0in 0in 10pt; text-align: left;">1.306 grams A table of the most important quantitative data would be a welcome addition here. So.....no melting point? That's too bad. I would have liked to see data on "Portion B" of your crude product.

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In the continuation of lab experiments utilizing electrophilic aromatic substitution reactions the acylation of ferrocene was explored. This two step process involves ferrocene with a relatively benign phosphoric acid and acetic anhydride. Typically the friedel crafts reaction occurs with a strong Lewis acid resulting in large amounts of acidic waste. When observing the mechanism of the Friedel-Crafts acylation, one might wonder how the acyl group is prepared for ferrocene to attack the electrophile, or ferrocene responsible for cleaving the bond of the acetic anhydride. ======

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The argument could be made that both occur. Since the addition of any acid also results in the addition of water, the protination of acetic anhydride results in a great leaving group. The generation of the acyl electrophile results in an electropositive carbon ready for the substitution reaction to occur. Ferrocene, acting as the nucleophile, then attacks the protinated acetic anhydride with a pair of delocalized electrons resulting in a substitution reaction. Any base close to the molecule will quickly eliminate the hydrogen at the reaction site returning resonance to the aromatic molecule. The final product represented acetylferrocene with either one or two acyl groups. ======

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In the work up of the product, half of the crude product was set aside for purification. 1.306 grams of crude product was added in a small Erlenmeyer flask with 20mL of toluene was heated to the dark orange solution. As indicated in the directions, a spatula full of decolorizing carbon was added to the mixture. Care was taken prevent adding excess carbon to maximize yield. Deionized water was heated and a hot filtration funnel was prepared. ======

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Problems ensued with filtering the solution. After the first pour was filled to the brim, a small amount of water connected with the solution potentially contaminating the products. Slow filtration also occurred with the first observance of drops after two minuets. The slow filtration lasted 40 minuets. There were no crystals forming on the perimeter of the filter, however, small beads of orange solution did become more viscous on the perimeter. This was an indication that either the constant replacement of hot water in the filter was doing the job it was supposed to, or there were other problems occurring. The long filtration time allowed for the solution to cool to room temperature so the filtered solution was reheated for recrystallization. After the solution cooled to room temperature it was placed in ice. No apparent crystals were forming. Both group members noticed an oily like substance forming at the bottom of the flask. In hopes of having crystals, the solution was filtered with oily residue last to leave the flask. No product was recovered although the phenomenon known as "oiling out" occurred. ======

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This opalescent “oil” like liquid occurs in unwanted cases since the oil typically is good at dissolving impurities. Some known causes of oiling out are when the solution is super saturated with solvent forming two distinct liquid layers preventing crystallization. This possible source for error could be responsible since only a small amount of crude product was used in purification while the procedure may have been for the entire crude product. The reduction of toluene from 20mL to 10mL could possibly prevent super saturation from the solvent. Annother possible source of error could have occurred during the hot filtration. Deionized water came in contact with the solution in a few occasions over the 40 minute filtration. This contamination also could have led crystallization problems. Other sources for error could result in contaminated glassware mixing with the solution preventing crystallization. Nonetheless, even though no observable product was recovered a valuable learning experience occurred in adding c-c bonds to compounds and preventing “oiling out” ======

Good discussion of oiling out. I wish your group would have collected some data on the portion of crude product that was set aside. What happened to that sample? Your score is unfortunately impacted by the problems you faced during the lab.

This report earned the following scores for: format (2/2) style (2/2) data (2/3) quality of result (1/1) quality of reported data (1/1) conclusion (1/2) error (1/1) post-lab Q (2/2) for a total of 11/14.

** Post Lab: ** Find and write two additional examples of Friedel-Crafts acylation reactions.
**Figure 1:** 3,5-diarylcyclopentenone via friedel-crafts acylation of vinyl

**Figure 2:** Trifluoromethanesulfonic acid catalyzed Friedel-Crafts acylation of aromatics with β -lactams



Figure1 obtained from: [| http://www.organic-chemistry.org/abstracts/literature/082.shtm]

Figure 2 obtained from: [| http://www.organic-chemistry.org/abstracts/lit2/604.shtm]

Figure 1 obtained from: http://www.organic-chemistry.org/abstracts/literature/082.shtm Figure 2 obtained from: http://www.organic-chemistry.org/abstracts/lit2/604.shtm