Experiment 12 Post Lab Organic Chemistry 1 Lab PDF

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Jacqueline VanEyk Section #: 031 TA: Mohammad Nazmus Sakib Experiment 12 Title: Grignard Reaction: Synthesis of Triphenylmethanol Introduction The objective of this experiment was to use magnesium metal to treat bromobenzene in order to get phenyl magnesium bromide (a Grignard reagent). Phenyl magnesium bromide then reacts with benzophenone in stiu to produce triphenylmethanol. A Grignard reagent is an organomagnesium halide. Meaning that a Grignard reagent is made up of an organic halide and magnesium metal (Weldegirma, 2020). The reagent is created by a reaction between the magnesium metal and the organic halide in an ether solution. In this case the organic halide that was used to create the Grignard reagent was bromine. The halides used in Grignard reagents can either be Chlorine, Bromine, or Iodine, never Florine. The reagents are most productive when they are used as nucleophiles in organic reactions. Grignard reagents are well known to act as both strong bases and great nucleophiles. Grignard reagents are typically used to react with aldehydes and ketones in order to create either tertiary or secondary alcohols. Grignard reagents are very reactive with water and will react to form alkanes which is unwanted in a Grignard reaction. Since the reaction with water is unwanted it is important to keep the experiment dry and all sources of water far away from the reaction so as to avoid contaminating the experiment. Thus, the solvent used must not have any water present. In order to make sure that water was not involved in this experiment the glassware was placed in an oven to ensure that it was all dry and

clean and the solvent used was anhydrous diethyl ether. If the reagent were to react with water, there would be no way of separating it out of the product that is formed. For example

CH3CH2MgBr + H2O → CH3CH3 + Mg(OH)Br

The inorganic product, Mg(OH)Br, is referred to as a "basic bromide" and is a sort of half-way stage between magnesium bromide and magnesium hydroxide (Clark, 2020).

The mechanism of the preparation of Phenyl Magnesium bromide:

Mechanism for the preparation of Triphenylmethanol

Possible undesired side reactions: Phenyl magnesium bromide + phenyl bromide  biphenyl

Phenyl magnesium bromide + water  benzene

Phenyl magnesium bromide + carbon dioxide + acid  carboxylic acid

Phenyl magnesium bromide + oxygen + acid  phenol

Experimental Section Part A: Preparation of phenyl magnesium bromide Added 0.5g of magnesium metal turnings to the 10mL vial, then gently crushed for 1520min. The solution was a brownish-grey color

Preweighed a 10mL conical vial. Added 1.5mL bromobenzene, 5mL anhydrous diethyl ether and then swirled to dissolve.

Transfered the solution to a dry conical vial and caped it quickly.

Part B: Synthesis of triphenylmethanol Dryed and fit a 5mL conical vial with a claisen adapter that cotained CCl and septum. Added about 3mL of phenylmagnesiumbromide

Combined the two organic layers, dryed with anhydrous Na2 SO4 , and evaporated the solvent. The mixture should be a light brown oil.

Prepared 0.27g benzophenone in a 0.5mL anhydrous ether in a 3mL conical vial then capped it. Added benzophenone solution to the grignard solution with a syringe.

The aqueous layer was the bottom layer. Added 1-2mL of diethyl ether, shook then drew off the bottom layer using a syringe and discarded it.

Removed the septum and stired the mixture with a clean dry spatula. Rinsed the empty vial containing benzophenone with 0.2mL of diethyl ether, added to red mixture.

Capped and occasionally stired the mixture. Added 2mL of 6M HCl to neturalize. Observed the two layers that formed.

Added 1mL of petroleum ether. Heated the mixture in a steam bath then cooled to room temperature. Collected the product via vaccum filtration. Recrystalized the product from isopropanol. Collected the crystals and dryed them. Weighed the product. Then determined the melting point.

Table of Contents

Chemical

Bromobenzen e

Phenyl magnesium bromide

Triphenylmethanol

Diethyl ether

Calcium chloride

Sodium sulfate

Formula

C6H5Br

C6H5MgBr

C19H16O

C4H10O

CaCl2

Na2SO4

IUPAC Name

Phenyl bromide

Phenyl magnesium bromide

Triphenylmethanol

Diethyl ether

Calcium chloride

Sodium sulfate

Molar Mass

157.01 g/mol

181.31 g/mol

260.33 g/mol

74.12 g/mol

110.99 g/mol

142.04 g/mol

Melting Pt

-30.72oC

153-154oC

164oC

-116.3oC

722oC

888oC

Boiling Pt

156oC

78.8oC

380oC

34.6oC

1935oC

1429oC

Hazards

Flammable, irritant, environmental hazard

Flammable, corrosive

Skin, eye, and lung irritant

Flammable, irritant

Eye irritant

Health hazard

Chemical

Hydrochloric acid

Benzophenone

Isopropanol

Formula

HCl

C13H10O

C3H8O

IUPAC Name

Hydrochloric acid

Diphenylmethanone

Isopropyl alcohol

Molar Mass

36.46 g/mol

182.22 g/mol

60.096 g/mol

Melting Pt

-30oC

48.5oC

-89oC

Boiling Pt

47.8oC

305.4oC

82.6oC

Hazards

Corrosive, acute toxic

Health hazard, environmental hazard

Flammable, irritant

Results

Product

Appearance

Mass

Melting Point

Crude

Yellowish/white

0.281g

161.2oC

Pure

White crystals

0.113g

163.8oC

29.27%

Percent Yield Theoretical: 164oC

Melting Point 0.27g benzophenone x

0.0014817 moles x

% Yield =

0.113 g 0.386 g

1mol 182.22 g

260.33 g 1mol

Experimental: 163.8oC

= 0.0014817 moles

= 0.386g

X 100 = 29.27%

Discussion In this experiment the calculated percent yield was 29.27%. This is a relatively low percent yield and could be attributed to the fact that Grignard reactions are highly reactive with water. Many precautions were made in order to ensure that the reaction would not be compromised by water. However, it is possible that during the experiment the reaction was contaminated with water causing an unwanted side reaction that used some of the phenyl magnesium bromide and created benzene. The contamination could have occurred when transferring mixtures between glassware. The low percent yield could also be attributed to a misstep in the experimental procedure. A mistake was made, and petroleum ether was added to the mixture both before and after heating the oil substance. Also, some of the product both crude and pure could have been lost while collecting the solids from the vacuum filtration funnel.

The theoretical melting point of triphenylmethanol is 164oC. After collecting the crude product, the melting point was found to be 161.2oC which is very close to the actual melting point. The crude product was the recrystallized and the pure product was collected. The melting point of the pure product was found to be 163.8oC which is almost exactly 164oC. Based on how close the theoretical and experimental melting points are, it can be assumed that the experimental product only had small amounts of impurities left in it. The purity of the experimental product could have been enhanced by preforming the recrystallization process again.

Grignard reagents are known to act as both good nucleophiles and strong bases, therefore, it was important that an aprotic solvent was used during this experiment. Meaning, that Grignard reagents are highly reactive to solvents such as water or acidic protons and will perform unwanted side reactions if an improper solvent is used. Without the used of an aprotic solvent the final product would not have form.

Conclusion

The objective of this experiment was to use magnesium metal to treat bromobenzene in order to get phenyl magnesium bromide (a Grignard reagent). Phenyl magnesium bromide then reacts with benzophenone in stiu. to produce triphenylmethanol. The theoretical background and experimental results are connected. This can be seen when comparing the theoretical and experimental melting points of triphenylmethanol. The theoretical melting point was 164 oC and the experimental melting point was 163.8oC. The experimental data reveals that phenyl magnesium bromide was formed and was used to synthesize triphenylmethanol. Grignard reagents and reactions are being used in many different industries. For example, Grignard reagents are commonly used to manufacture chemo-catalyst for its application in pharmaceutical

and chemical industries. Also, due to the development of eco-friendly products with soil enriching properties, the market for Grignard reagents is making a leeway in the agrochemical industry (Clare, 2017). The experiment accomplished what it set out to do. A Grignard reagent was formed and was used to synthesize triphenylmethanol.

References

Weldegirma, Solomon. “Experiment 12: Grignard Reaction: Synthesis of Triphenylmethanol.” Experimental Organic Chemistry Laboratory Manual: CHM 2210L and CHM 2211L, 9th ed., ProCopy, 2020, pp. 65–68. Clark, Jim. “Grignard Reagents.” Chemistry LibreTexts, Libretexts, 13 Sept. 2020, chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modules_(Organic_C hemistry)/Aldehydes_and_Ketones/Synthesis_of_Aldehydes_and_Ketones/Grignard_Reag ents. Clare. Grignard Reagents Market: Pharmaceutical Industry to Remain the Dominating End User Segment Throughout the Forecast Period: NAFTA and Europe Industry Analysis and Opportunity Assessment, 2016 - 2026, Reportlinker, 11 Jan. 2017, www.prnewswire.com/news-releases/grignard-reagents-market-pharmaceutical-industryto-remain-the-dominating-end-user-segment-throughout-the-forecast-period-nafta-andeurope-industry-analysis-and-opportunity-assessment-2016---2026300389751.html#:~:text=Grignard%20reagents%20are%20commonly%20used,leeway %20in%20the%20agrochemical%20industry....