Prep of triphenylmethanol PDF

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Preparation of Triphenylmethanol

Abstract

The aim of this lab was to prepare a Grignard reagent and use it to generate carbon – carbon bonds as in the preparation of the tertiary alcohol triphenylmethanol. This particular experiment did not follow the standards of green chemistry for several reasons, including the use of volatile solvents such as diethyl ether, petroleum ether, and isopropanol. Additionally, there was chemical waste in this experiment that had to be disposed of. Regardless, the experiment was successful, and the resulting product was examined through percent yield and IR spectra analyzation. The following conclusions were determined: the mass of the product was 0.586 grams, a percent yield of 69.3% was achieved, and there was a melting point of 161.3-163.2 ℃. These results demonstrate the success of the lab. A couple errors that may have arisen in the experiment are involved in the extensive list of techniques and their proper implementation, such as extraction and the use of a separatory funnel, setting up the vacuum filtration to beget recrystallization, and not waiting the full 15 minutes to reflux.

Introduction

This lab was focused on preparing a Grignard reagent and use it to generate carbon – carbon bonds as in the preparation of the tertiary alcohol triphenylmethanol. The green nature of this experiment is basically nonexistent due the chemical waste formed in the side product of biphenyl through the coupling reaction that took place. In addition to this, volatile substances were used such as diethyl ether, isopropanol, and petroleum ether.

The mechanism of the reaction is the synthesis of phenylmagnesium bromide, a prepared reagent. During this, the coupling reaction between the Grignard reagent and unreacted aryl halide produces the side product of biphenyl. The phenylmagnesium bromide, the prepared reagent, is used with benzophenone to prepare a Grignard adduct that is hydrolyzed into

triphenylmethanol. A Grignard reagent is prepared by “reacting an organic halide with magnesium metal in an anhydrous ethereal solvent” (Kenneth et al., 2016). This ether solvent is important as it forms a soluble complex with the Grignard reagent. These reagents can be seen in primary, secondary and tertiary alkyl halides, all to form carbon-carbon bonds. There is a polar nature in the carbon-magnesium covalent bond, with the carbon holding the partial negative charge (metal is less electronegative). This particular carbon is nucleophilic and acts as a carbanion (Kenneth et al., 2016). In this particular experiment, the phenylmagnesium bromide is the Grignard reagent and it reacts with the ketone benzophenone to give a Grignard adduct, which is then hydrolyzed to a tertiary alcohol, triphenylmethanol (Catsoulis).

The techniques of recrystallization, reflux, extraction, and vacuum filtration are involved in this experiment. These techniques saw the product being collected by filtration. Vacuum filtration is observed by taking a crude product and washing it with cold water (Chem LibreTexts).

Table of Physical Constants

182.22 154.21 157.02 74.12

Melting Point (°C) 48.5 69.2 -30.72 -116.3

Boiling Point (°C) 305.4 255 156 34.6

Density (g/ml) 1.11 1.04 1.5 0.7134

36.46

-114.2

-85.05

1.2

60.1

-89.2

82.5

0.78

260.33

162

360

1.2

86.18 142.04

-73 884

62 1,429

0.64 2.66

181.31

24.85

78.8

1.14

Compound

Molar Weight (g/mol)

Benzophenone Biphenyl Bromobenzene Diethyl ether Hydrochloric Acid Isopropanol Triphenylmethano l Petroleum ether Sodium sulfate Phenylmagnesium bromide

Important Compounds

Chemical Formula

Benzophenone

C13H10O

Biphenyl

C12H10

Bromobenzene

C6H5Br

Diethyl ether

C4H10O

Hydrochloric acid

HCl

Structure

Isopropanol

C3H8O

Triphenylmethanol

C19H16O

Petroleum ether

C4H14

Sodium sulfate

Na2SO4

Phenylmagnesium bromide

C6H5BrMg

Methods The glassware was carefully cleaned and dried painstakingly. Then, the drying tube was charged with anhydrous calcium chloride pelts that were held in place by cotton plugs. The condenser which consisted cotton, followed by calcium chloride, was set up. Then, around 0.15 grams of magnesium turnings were obtained, and they were placed into the round-bottom flask with a stir bar. The reaction vessel was then immediately assembled to prevent interaction with atmospheric water. At this point, 20 mL of anhydrous ethyl ether was collected. Then, 0.70 mL of bromobenzene was placed into the 5-mL reaction vials and remeasured for accuracy. This was the time that the bromobenzene and diethyl ether solution was prepared, with 1 mL was syringed into the vessel. The solution began to bubble and a cloudy and brown color was observed as the magnesium dissolved. Then, once the mixture began to boil, it was removed from the heat. The rest of the bromobenzene and ether solution was gradually added and the solution was allowed to reflux for 15 minutes. While refluxing, benzophenone and diethyl ether solution was prepared by taking 1.09 grams of benzophenone and dissolving it in 2 mL anhydrous ether. This is the Grignard reagent, and it was then allowed to cool. The benzophenone solution was then slowly added to the reaction vessel using a syringe. A pinkish color was observed here until a white solid was formed. Then, the next session involved hydrolysis of the adduct, where 6 M of hydrochloric acid was collected and added to the solution. The mixture was then stirred with a stirring rod. The acid was added until two distinct layers (an organic and aqueous layer) were observed and no solids were present. The organic and aqueous fraction were then separated using a funnel. Extraction was involved through the aqueous layer with the aid of the additional ether. The organic fractions were then combined and dried over sodium sulfate for about 15 minutes. The ether was

evaporated using heat. Here, an oily texture was observed in the crude product. Petroleum ether and heat was then added to dissolve the side product of biphenyl. The solution was allowed to cool to room temperature and air dried as well. The product was then crystallized using hot isopropanol. It was then washed with the hot isopropanol until the next session. Then, the product was measured. Following the successful execution of the experiment, the percent yield, melting points and IR spectra were all analyzed and calculated.

Reaction Mechanism

Data & Results Percent Yield of Triphenylmethanol Calculation M (magnesium turnings) = 0.158 g m (benzophenone) = 1.087 g m (triphenylmethanol) = 0.586 g

Actual Value: 0.586 g Theoretical Value: 0.21 g benzil 0.51 g bromobenzene x

Percent Yield=

260.33 g triphenyl. 1 mol triphenyl . 1 mol bromobenzene x x =0.85 g triphenylm 157.02 g bromobenzene 1 mol benzophenone 1 mol triphenyl .

Actual 0.586 g x 100=69.3 % = Theoretical 0.85 g

Melting Point Dried Product – 161.3-163.2 ℃ Literature value – 162 oC

Figure 1. This figure shows the IR spectra analyzed of triphenylmethanol. There is an OH stretch at 3300, a CH stretch at around 3000, and the presence of benzene rings at around 1500. This spectra, when compared to benzophenone, does not have the C=O stretching.

Conclusion

This lab was successful in creating triphenylmethanol. The lab was not green chemistry as there was a side product of byphenyl. The process of recrystallization yielded to a product that

weighed 0.586 grams, and the percent yield was 69.3%. The melting point also shows how successful the lab was, as the literature melting point is 162 degrees Celcius, and what was observed was a melting point of 161.3-163.2. The IR spectra of triphenylmethanol when analyzed shows how similar it is to benzophenone, although benzophenone has a CH stretching at a higher value than triphenylmethanol, and a C=O stretching that triphenylmethanol does not. A couple of errors that may have contributed to the experiment include not drying the materials completely before the initiation of the experiment, as this is very important. Another possible error was that if the reaction mixture did not bubble and change color, neglecting to lightly crush the magnesium turnings with a glass stirring rod to jumpstart the reaction. Other errors include sealing the vessel improperly or not allowing the product to recrystallize completely for accurate measurement of the crude product.

Citations Kenneth F. Cerny, Marietta H. Schwartz and Christopher E. Katz, 2016, Laboratory Manual for Organic Chemistry (4th edition)

Libretexts. (2020, September 23). Recrystallization. Retrieved February 18, 2021, from https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_ Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Physical_Properti es_of_Matter/Solutions_and_Mixtures/Case_Studies/RECRYSTALLIZATION Peter Catsoulis. Blackboard, Preparation Triphenylmethanol. Department of Chemistry at the University of Massachusetts Boston....