The Synthesis of Hexaphenylbenzene

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Feb 20, 2024

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The Synthesis of Hexaphenylbenzene Abstract: The purpose on conducting the experiment on The Synthesis of Hexaphenylbenzene is to convert Tetraphenylcyclopentadienone into Hexaphenylbenzene with the use of a dienophile. This reaction preparation is called a Diels-Adler Reaction were the initial adduct of carbon monoxide is lost to become aromatic. The way to conduct this experiment is by combining the Tetraphenylcyclopentadienone and the diphenyl acetylene with hot silicone oil to produce crystals from the reaction. Those crystals are then combined with hexane and collected through vacuum filtration with additional solution of hexane and toluene for better crystallization. The collected and dried product was weighed for a mass of 0.1177g but no melting point was collected because of its high melting properties. The percent yield was calculated with the mass

of the final product where it resulted in 51.3% yield. The atom economy was a good 95%. Any sources of error from this product can be too high of a boil during the experiment as well as inconsistent flame moving around the tube. The desired product was achieved but the percent yield was low meaning not all reactants converted into the product. Chemical Mechanism: Property Table: Compounds Meltin g Point Boilin g Point Density Compound Structure Molecular Weight Diphenyl acetylene 62.5 o C 170 o C 990kg/m 3 178.23g/mol Tetraphenylcycl opentadienone 217- 220 o C 617 o C 1.2g/cm 3 384.47g/mol Hexane -95 o C 68.73 o C 655kg/m 3 86.18g/mol

Hexaphenylbenz ene 454- 465 o C 534 o C 1.1g/cm 3 534.7g/mol Toluene -95 o C 110.6 o C 867 kg/m 3 92.14g/mol Introduction: This experiment was based on the Diels-Alder cycloaddition reaction where Tetraphenylcyclopentadienone and diphenyl acetylene was combined to produce the product of Hexaphenylbenzene. “A Diels-Alder reaction is a [4+2] cycloaddition of a conjugated diene and dienophile, which in turn constitutes a powerful synthesis of a six-membered ring.” (Osipov). In this case, the diene of the reaction is the Tetraphenylcyclopentadienone which give the 4pi electrons while the dienophile is the diphenyl acetylene giving 2pi of electrons. These make the formation of new o-bonds that are more stable. The combination of both these molecules would form a bicyclic adduct but it this adduct it not isolated because the initial adduct loses carbon monoxide in order to convert into an aromatic molecule. Once the reaction occurs and the crystals are formed in the solution it is collected through vacuum filtration which is another important process in the experiment as it collected the product. During this process, hexane and toluene is added to the crystals as it helps produce the crystals due to the polarity of toluene and the non-polar properties hexane contains. It is important to know that the melting point is not able to be determine in this experiment “Hexaphenylbenzene melts higher than 450 o C, well above the maximum temperature of the Mel-Temp thermometer.” (Schwartz) For this reason, the melting point is not determine for the product of this experiment. Procedure: Begin by combining 0.100g of Tetraphenylcyclopentadienone and 0.100g of diphenyl acetylene into a test tube with 1ml of high-boiling silicone oil. Take that mixture and produce a gentle boil for it because the solution is intense and will begin changing colors as the reaction is taking place. Let the solution react for 15 min as the product will separate as tan crystals. After the time, cool to room temperature before adding 4ml of hexane. Stir the solution with a stirring rod. Now the crystals created can be collected using the Hirsch funnel; wash the solids with an additional 2ml of hexane and 2 x 2ml of cold toluene to get a good crystallization. Let the crystals air dry until the next day before measuring the mass and determining the melting point. Data: Table 1: Number of measured compounds used and final mass results with percent yield Mass of Tetraphenylcyclopentadienone 0.1058g Mass of Diphenylacetylene 0.1080g Experimental mass of product 0.1177g

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Theoretical mass of product 0.228 Percent Yield 51.3% Atom Economy 95% Calculations: .1058 g 178.23 g / mol = 0.000593 mol 0.000593 mol x 384.47 = .228 theoretical massof product % yieldof product = Experiment mass of product Theoretical Mass x 100 0.1177 0.228 g = .516 x 100% = 51.6% yield of product massof atoms ∈ product massof reactantsused = % atomeconomy 534.70 g ( 384.47 + 178.23 ) = 95% atomeconomy Discussion: The synthesis of Hexaphenylbenzene involved the reaction between Tetraphenylcyclopentadienone and diphenyl acetylene where its combination with hot silicone oil would induce a Diels-Alder cycloaddition reaction. From this reaction, the carbon monoxide would be lost to produce the final product of Hexaphenylbenzene. The collected crystals with the use of the vacuum filtration were then washed with hexane and toluene to help with the crystallization process. The dried-out crystals were then weighed for their mass which was 0.1177g. The melting point for this experiment was not gathered because of the high melting points of Hexaphenylbenzene being so high. The theoretical melting point is above 450C which cannot be calculated in the lab because it is more than the max temperature of the thermometers. The percent yield was calculated to a 51.6% which is low because not all reagents were able to convert into the product. This was an expected percent yield from this reaction because of the multiple steps the molecules have to go through to achieve the product. The atom economy was 95% which means not much solution was wasted during the creation of the Hexaphenylbenzene. Any sources of error in this lab can be the filtering of the crystals since there could’ve been crystals lost in the process of filtering. In the end, the experiment was successful because the production of Hexaphenylbenzene was achieved. Conclusion: This experiment involved performing a Diels-Alder cycloaddition reaction between Tetraphenylcyclopentadienone and diphenyl acetylene where the resulting product would be

Hexaphenylbenzene. The total mass of product gathered was 0.1177g and the melting point was not able to be determine because it has a very high point. The percent yield was a low 51.6% and the atom economy was a 95% indicating little waste from this experiment. Any sources of error from this experiment can be the any crystals lost in the solution or producing a high boil in the mixture instead of a gentle boil. The desired product was achieved and was successful. Reference: 1. Katz/Schwartz pp. 103-107 Organic Chemistry , Laboratory Manual, Fourth Edition. 2. Osipov. (n.d.). Diels-Alder Reaction. Retrieved December 12, 2020, from https://www.organic-chemistry.org/namedreactions/diels-alder-reaction.shtm