Grignard Reaction Preparation of Benzoic Acid Pre Lab Lillian M Dawes PDF

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THE GRIGNARD REACTION: PREPARATION OF BENZOIC ACID LAB REPORT LILLIAN M. DAWES PANTHER ID: 5469090 CHM 2010L-U25 11/4/21

Dawes, The Grignard Reaction: Preparation of Benzoic Acid Lab Purpose The purpose of this lab is to prepare benzoic acid for the generated Grignard reagentphenyl magnesium bromide. Introduction For this lab is the method being used is the Grignard reagent. The general structure of a Grignard reagent is RMgX. The R is the reagent can be any alkyl, vinyl or aryl group and the X can be any halogen. A Grignard reaction is when the coupling reaction of an alkyl gets added to a carbonyl group known as an aldehyde or ketone. For Grignard reactions to occur successfully the materials must be completely dry, this is due to the fact that the Grignard carbon is a nucleophile. This means that any water or alcohol would protonate it to form a hydrocarbon and the reaction would not work. The apparatus protects the reagent by being dry and a calcium chloride drying tube is used. The apparatus should be flamed before beginning he experiment. The suction filtration is a technique that will be conducted during this lab. A filter is a contraption that separates compounds by their size. When filtrating by gravity, this allows smaller molecules to pass through a paper and keeping the larger molecules out not permitting them to go through. The suction filtration uses a pressure gradient to filter the materials which is more efficient than filtration by gravity. When performing an effective extraction two solvents must be immiscible; the compound getting extracted should have a much higher solubility than the solvent relative to the other. Keep in mind, that polar compounds are more likely to be soluble in polar solvents versus the non-polar compounds in non-polar solvents.

In this experiment reaction bromobenzene will produce benzoic acid in a Grignard reaction. This is depicted in the following reaction mechanism:

Like is previous experiments, this experiment will utilize the thin layer chromatography (TLC) technique. The TLC is the process in which compounds are separated on a thin layer of adsorbent material in a closed atmosphere. In order to determine how accurate the experiment went, the amount of solid precipitate obtained will be calculated for the percent yield.

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Dawes, The Grignard Reaction: Preparation of Benzoic Acid Lab Reactions

Procedures Procedures Part A: Phenylmagnesium Bromide 1. Set up apparatus • Ensure all glassware is completely dry 2. Weigh 1g of Mg turning and add to round bottomed flask 3. Measure 5 mL of bromobenzene • Mix with 25 mL of dry ether 4. Pour mixture into separatory funnel 5. Obtain metal pan • Fill with hot water 6. Add bromobenzene/ether mixture to round bottom flask to cover Mg 7. Place pan of water under round bottom flask 8. Add rest of bromobenzene ether solution at a rate of 1-2 drops per second 9. Reflux mixture for about 10-15 minutes Part B: Preparation of Benzoic Acid 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

Crush 25 g of dry ice in a paper towel Weigh out 20g in a dry 250 beaker Pour Grignard’s reagent over dry ice while stirring Add 25-30 mL of hot water in small increments Add 6M HCl to mixture slowly until acidic Chill mixture in ice bath Collect product via vacuum filtration Let dry Weigh product Find melting point Mix product with 15 mL of 10% MaHCO3 Extract successively with diethyl ether

Observations

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Dawes, The Grignard Reaction: Preparation of Benzoic Acid Lab

13. 14. 15. 16. 17. 18.

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Observations

Procedures Combine ether extracts and dry over anhydrous sodium sulfate Acidify aqueous solution of sodium benzoate by adding HCl Separate via vacuum filtration Weigh product Find melting points Calculate percent yield

Table of Physical Constants Name

Formula

Molecular Weight (g/mol)

Density (m/v)

Melting Point °𝑪

Boiling Point °𝑪

Solubility

Water

𝑯𝟐 𝑶

18.022

0.997 (g/𝒄𝒎𝟑)

0°C

𝟏𝟎𝟎°C

n/a

Water, Calcium Chloride

CaCl2

110.98

2.15

772

1,935

Magnesium

Mg

24.31

1.738

650

1,091

Bromobenzene

C6H5Br

157

1.540

-31

156

Diethyl Ether

(C2H5)2O

74.12

0.713

-116

34.6

C6H5MgBr CO2

181.31 44.01

1.14 1.98

N/A -56.3

N/A -78.46

HCl

34.46

1.18

-62

108

Ether

C7H6O2

122.12

1.27

122

250

Benzene

NaHCO3

84.01

2.2

300

851

Water

Acetic Acid Water Diethyl Ether Nonpolar

Bromide Phenylmagnesium

Carbon Dioxide Hydrochloric Acid Benzoic Acid Sodium Bicarbonate

DiethylEther Water

Water, Anhydrous Sodium Sulfate

Na2SO4

110.98

1.086

783

1600

Acetic Acid

Dawes, The Grignard Reaction: Preparation of Benzoic Acid Lab

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Data Reaction Fastest Reaction

Section A Test tube #3 n-Butyl bromide

↨

Test tube #5 n-Butyl chloride Test tube #4 Sec-Butyl chloride

Section B Test tube #5 n-Butyl chloride Test tube #4 Sec-Butyl chloride Test tube #3 n-Butyl bromide

Test tube #2 Allyl chloride

Test tube #1 t-Butyl Chloride

Test tube #3 n-Butyl bromide Test tube #5 n-Butyl chloride Test tube #2 Allyl chloride Test tube #1 t-Butyl Chloride *This data chart is comprised of data collected after the halide observations were organized*

Slowest Reaction

Calculations Actual Yield • Pre-weighed flask = 120.34g • Flask with product = 126.97g

6𝑚𝑙 𝐶5 𝐻12 𝑂

126.97g-120.34=6.63g

Theoretical Yield

Percent Yield 𝑎𝑐𝑡𝑢𝑎𝑙 𝑦𝑒𝑖𝑙𝑑 𝑥100 𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙

0.815𝑔 𝐶5 𝐻12 𝑂 1𝑚𝑜𝑙 𝐶5 𝐻11 𝐶𝑙 106.59𝑔 𝐶5 𝐻11 𝐶𝑙 1𝑚𝑜𝑙 𝐶5 𝐻12 𝑂 𝑥 𝑥 𝑥 88.15𝑔 𝐶5 𝐻12 𝑂 1 𝑚𝑜𝑙 𝐶5 𝐻12 𝑂 1 𝑚𝑜𝑙 𝐶5 𝐻11 𝐶𝐿 1𝑚𝑙 𝐶5 𝐻12 𝑂

= 5.912g

6.63𝑔 𝑥100 5.912𝑔 =112% yield

Conclusions In this lab we were able to exhibit the methods and understanding of nucleophilic substitutions using Sn1 and Sn2 Reaction mechanisms. This experiment was based around finding the total actual yield and the theoretical yield of the product. T-amyl alcohol, t-amyl chloride, hydrochloric acid, sodium chloride amongst some other compounds were used in this experiment to create the substitution reaction. After conducting the experiment, the total actual yield was found to be greater than that of the expected theoretical yield therefore demonstrating that an error must have occurred during the experiment because the yield being 100% is not accurate. The error was known after already conducting the experiment and was human error as using 12mL of t-amyl was used by mistake due to following the manual versus the 6mL that was instructed via the TA on the PowerPoint. Utilizing double the amount of compound significantly distorted the results rendering the results inaccurate for the timeframe used. The experiment may have been effective if done for a longer period of time or utilize the proper amount of solution as instructed as the product was over saturated and could not perform correctly.

Dawes, The Grignard Reaction: Preparation of Benzoic Acid Lab

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Overall, the experiment with the nucleophilic substitution of bimolecular (SN2) and unimolecular (SN1) reactions rendered results and had various stages to observe interpreting this experiment to be semisuccessful.

Citations Keller, Leonard, Lichter, Joseph, and Miguel, Lilia San. Organic Chemistry I & II Laboratory Manual. Macmillan Learning, 2014...