Triphenylmethanol

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Feb 20, 2024

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Preparation of Triphenylmethanol Abstract: The purpose of the Preparation of Triphenylmethanol was to synthesize phenylmagnesium bromide (the Grignard reagent) to generate carbon bonds in order to hydrolyze it into Triphenylmethanol. The process relied on the reflux reaction between the magnesium, bromobenzene and benzophenone in which through the reflux and heating the reaction can boil and interact forming layers in the solution. Those layers produced then contained the desired product of Triphenylmethanol that could then be filtered and recrystallized to achieve the purest version of this product. Once the product was dried it was weighed for its mass at 0.586 g and used to determine the melting point which resulted in at 161.3-163.2 ℃. The product was also checked through the IR spectrum that indicated the products achievement

due to correct functional groups observed in IR spectrum. With all this in data, the percent yield was calculated at 100% and atom economy calculated to 71%. The low atom economy was expected because of the use of certain chemical solutions like petroleum and diethyl ether. Any sources of error in this experiment could have been the addition of water to the solution either through air water molecules or the experiment leaving the hood. Since the melting point, IR spectrum and percent yield gave expected results for a successful experiment it can be said that minimal error can be found if any. Overall the preparation of Triphenylmethanol was successful because there were many indications such as the IR and melting point that indicate the products achievement. Introduction: This experiment deals with an addition of a organomagnesium halide in which the process is known as Grignard Reaction. The Grignard reaction was discovered by Victor Grignard, a French chemist, who reacted a halide with a magnesium metal in an ether solvent creating that carbon-metal bond. “A Grignard reagent can be prepared via the reaction of magnesium metal with organic halides in anhydrous aprotic solvents.” (Schwarz, 169). It is important to know that Grignard reagents are extremely sensitive to water and acid which is why anhydrous solvents, anhydrous meaning without water, are used with Grignard reagents. To perform this experiment in a careful and anhydrous way, the solutions added in this reaction are completely dried as well as conduct the experiment inside the hood because there are small amounts of water molecules in the air that can affect the experiment. The Grignard reagent can be formed with a primary, secondary or tertiary alkyl halide in which the alkyl portion acts as a carbanion because of it being a strong base and possess nucleophilic characteristics. This means, “The Grignard Synthesis is useful for adding carbons to molecules that have a carbonyl carbon” (Robertson). Allowing the creating of a C-C bond through the use of this organometallic reaction. The formation of the Grignard Reagent starts an R group covalently bounded to magnesium which is covalently bounded to a halide (X). the most common halogen is it bounded to is Br. For the purpose of this lab, bromobenzene is used as the bromohalide in this reaction which reacts with magnesium. This magnesium is then oxidized and the halide will be reduced. In order to conduct the Grignard reaction, magnesium is added to a round flask over heat. Then, part of a mixture of bromobenzene and anhydrous ether is added with a syringe that will begin the reaction of the solution. This will cause boiling of the solution until it reaches a reflux. Then you remove from the hot plate and once again do the same step of adding the rest of the benzophenone ether mixture to the solution over the hot. This will reflux again for a period of 15 min in which a mixture of benzophenone and ether is made and added with a syringe after the reflux is complete; this will result in the Grignard reagent. To produce the hydrolysis of the Grignard reagent, 6ml of hydrochloric acid is added that will remove the magnesium and bromide from the molecules creating a top layer of Triphenylmethanol and a lower layer of wasted items and hydrochloric excess. This solution can then be evaporated until the layers of Triphenylmethanol and biphenyl are left. To separate the biphenyl, petroleum was added and the separatory funnel allowed for separation which would dissolve biphenyl leaving a solid Triphenylmethanol that could be separated through vacuum filtration. This solid was then passed in the process of recrystallization with ether in order to extract the purest form of Triphenylmethanol product. The product was then used to determine the melting and IR spectroscopy. This solution was not done through green chemistry because of the use of

petroleum and diethyl ether. This means that there was unwanted side product of biphenyl produced and starting material chemical waste. Therefore, it is expected to receive a low atom economy but a percent yield should be successful. Chemical Reactions: Physical Properties: Compounds Melting Point Boiling Point Density Compound Structure Molecular Weight Magnesium turnings 650 o C 1090 o C 1.74 g/mL at 25 o C 24.31g/mol

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Bromobenzene -30.8 o C 156 o C 1.5g/cm 3 157.01g/mol benzophenone 47-51 o C 305 o C 1.11g/cm 3 182.22g/mol Diethyl Ether -116.3 o C 34.6 o C 713 kg/m 3 74.12 g/mol Triphenylmethanol 160-163 o C 360 o C 1.2 g/cm 3 260.3 g/mol Procedure: (ref. manual, Part III) To start the experiment, it is important to make sure every glassware is fully dried as well as the solutions going to be used. This experiment is also going to be conducted inside the hood because there are small amounts of water molecules in the air that can affect the experiment. The first material used is 0.15 of magnesium turnings which is placed in a round-bottom flask with a claisen head attached. Then, 20ml of anhydrous ethyl ether was transferred with the use of a pipet into a solution of 0.70ml of Bromobenzene in a reweighed vial and swirled until dissolved. Part of this bromobenzene solution is then added, with the use of a syringe, to the magnesium being heated at around 60 ℃. Once the solution shows a cloudiness, this indicates the reaction mechanism is beginning to take place and when the solution gathers enough heat from the hot plate a reflux takes place. When the solution begins boiling, separate from the hot plate, the solution should continue boiling either way and start to change color into a muddy brown- yellow. Then, add once again the rest of the bromobenzene and ether solution slowly over a twelve-minute period by refilling the syringe. Continue to heat the solution, starting a reflux once again that will continue for 15minutes. After reflux period is complete, add 1.09g of benzophenone in 2ml of the anhydrous ether and using the syringe again, add the solution into what is now your Grignard reagent. Continue stirring the reaction, at this point it should be a pinkish color which will then turn white as mixing keep occurring. In the next step, gather 6ml of 6M hydrochloric acid and add it to the solution. This will produce the hydrolysis of the Grignard reaction. Continue to add until two layers are observed, the top layer is the Triphenylmethanol and the lower layer is excess amount of hydrochloric acid and inorganic salts. Evaporate 5ml of ether inside the hood which should leave the layers Triphenylmethanol and biphenyl. To this,

add 3ml of petroleum which will dissolve the biphenyl, leaving the Triphenylmethanol solid ready to be collected with vacuum filtration. Recrystallize your product with hot isopropanol and cool in ice bath to purify the solid which can then be passed through vacuum filtration once again. Both vacuum filtrations should be 10 min to dry the solution. At this point you have the whole product that can be weighed and used to gather the IR spectrum. Data: Table 1: Number of measured compounds used and final mass results with percent yield Mass magnesium turnings (reagent) 0.158 g Mass bromobenzene (reagent) 0.510 g Mass benzophenone (reagent) 1.087 g Melting point of product 161.3-163.2 ℃ Experimental mass of product 0.586 g Theoretical mass of product 0.583 g Percent Yield 100% Atom economy 71% Calculations: .510 g 157.01 g / mol = 0.0032 mol 0.0032 mol x 182.22 = .583 theoretical massof product % yieldof product = Experiment mass of product Theoretical Mass x 100 0.586 g 0.583 g = 0.226 x 100% = 100% yield of product massof atoms ∈ product massof reactantsused = % atomeconomy 260.3 g ( 182.22 + 157.01 + 24.31 ) = 71% atomeconomy IR spectrum: Figure 1: IR Spectrum of Triphenylmethanol product

When observing the IR spectrum of the experimental product Triphenylmethanol, there are present bands of O-H seen in the area of 3400cm-1 indicating alcohol in the product. This also shows the product was achieved successful because the O-H band was important in noticing if the hydrolysis was completed in the experiment and the final product was complete. Another observed functional group is the C-H group noted in the 1400cm-1 and 750cm-1 from the benzene aromatic molecules in the product. The determined melting point of this product resulted in 161.3-163.2 ℃ whereas the Triphenylmethanol pure product normally has a melting point around 160-163 o C. Because of the extreme similarities in both melting points and correlation of functional groups observed in the IR spectra, it can be inferred that the product was achieved successfully. Discussion: This experiment included the process of using Grignard reagent which means that the presence of water cannot be present due to the sensitivity to water and acid that Grignard reagent contain. The purpose of synthesizing the Grignard reagent made of phenylmagnesium bromide was achieved as the preparation of the Grignard reaction was successful enough to be hydrolyzed into the desired product of Triphenylmethanol. With the process of reflux and careful procedure in order to avoid water into the reaction, this product was achieved. The steps into this experiment included to the use of heat, a separatory funnel, vacuum filtration for the Triphenylmethanol and recrystallization in order to gather the product in its most pure form. When testing the Triphenylmethanol product for its melting point, the product seemed accurate as the normal melting point of Triphenylmethanol is 160-163 o C and the product produced in the experiment ended with a melting point of 161.3-163.2 ℃. The IR spectrum of this product also

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presented the correct expected bands since there was a O-H band in the 3400cm-1 wavelength indicating the hydrolysis in the experiment was successful for the product as it created the O-H. It also presented the C-H bands of the aromatic rings around the 1400cm-1 and 750cm-1. The functional groups seen in the IR spectrum of the product correlate to Triphenylmethanol meaning the product was successfully achieved. When calculating the percent yield the limiting reagent was determined as bromobenzene were it was used to calculate the theoretical mass of the product. The mass of the experimental product was then divided by the theoretical mass to yield a 100% yield in the experiment. On the other hand, the atom economy was calculated with the mass of the product divided by the mass of all reagents, this yielded a low atom economy of 71% which was expected because the experiment was not necessary green because of the use of diethyl ether and petroleum. This low atom economy is caused by the unwanted side product of biphenyl and chemical waste at the end. Any sources of error in this experiment could have been the addition of water to the solution either through air water molecules or the experiment leaving the hood. Conclusion: In conclusion, the experiment was performed carefully in order to avoid water molecules, which Grignard reagents are sensitive to, to incorporate into the solution being created. With the process of synthesizing the Grignard reagent and then hydrolyzing the solution, the products of Triphenylmethanol was achieved. Due to the high percent yield of 100%, the expected bands observed in the IR spectrum of the product and the similarity in melting points between both the product and pure Triphenylmethanol; the experiment for the preparation of Triphenylmethanol was a successful experiment. The sources of error could’ve come from water or acid getting into the solution because of no careful procedure but this is not expected to had happened because of the good results the final product presented. Reference: 1. Katz/Schwartz pp. 169-172 Organic Chemistry, Laboratory Manual, Fourth Edition 2. Robertson, Donald. Grignard Synthesis: Synthesis of Triphenylmethanol. (n.d.). Retrieved October 20, 2020, from http://home.miracosta.edu/dlr/211exp2.htm