Suzuki Coupling Lab Report PDF

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Suzuki Coupling Lab Report...

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Suzuki Coupling Experiment 9

Section A01 19 November 2021

Purpose The purpose of this lab is to react p-bromobenzoic acid with phenylboronic acid using Suzuki coupling. Suzuki coupling inks two aromatic compounds together, with one aromatic ring containing a halogen. The halogen act as an electrophile while the aromatic ring without the halogen acts as a nucleophile, allowing cross coupling to occur at the site of the halogen. Please see Figure 1 for the reaction.

Figure 1. The Suzuki coupling in the reaction of p-bromobenzoic acid with phenylboronic acid.

Experimental Please refer to Chapter 25 in the lab manual for the experimental procedure and Appendix D for observations made during the experiment.

Results and Discussion In the first step of the experiment a solution was prepared from 0.359 g of sodium carbonate and six mL of deionized water. In a 50 mL Erlenmeyer flask 0.195 g of 4bromobenzoic acid was mixed with 0.148 g of phenylboronic acid. The sodium carbonate solution was added to the flask and stirred using a magnetic stirbar for ten minutes. The flask was heated in a sand bath to a temperature of 70˚C and 0.4 mL of a pre-prepared Pd catalyst was added to the flask. The reaction then proceeded stirring on the hot plate for 60 minutes. An ice bath was prepared while the reaction was proceeding, and ten mL of 1M aqueous HCl was set aside for use once the reaction had cooled. When the reaction mixture had cooled to room

temperature the ten mL of HCl was added dropwise and a cream-colored precipitate was formed. The mixture was tested using pH paper to ensure it was acidic. The precipitate was separated by vacuum filtration and the Pd waste was discarded in the marked container for proper disposal. The precipitate was then heated with HCl and EtOH using the hot plate, allowed to cool to room temperature, and then set on an ice bath. After fifteen minutes on the ice bath the recrystallized product was separated with vacuum filtration and allowed to dry further on a piece of filter paper. The mass of the recrystallized product was 0.085 g, or a 35.4% yield. An IR spectrum was obtained, and the melting point was determined to be 199-205˚C. Please see Appendix B for the IR spectrum. The IR spectrum did not have any significant peaks to report due to the unsuccessful reaction. There should have been peaks reported around 3000 cm-1 from the -OH group and 1780-1710 cm-1 for the carboxylic acid carbonyl group. Similarly, the experimental melting range was much higher than the literature value of 164-168˚C (3). Conclusion This is experiment was unsuccessful in isolating biphenyl-3-carboxylic acid. The IR spectrum showed that there was not a carboxyl group present as would be expected from the product. It is likely that the product was mainly the phenylboronic acid, since the IR spectra are similar. The product was a cream colored solid, which is the expected appearance of biphenyl-3carboxylic acid, but it is also the appearance of phenylboronic acid and 4-bromobenzoic acid, which was likely what was causing the coloration of the solid (1, 3). Similarly, the experimental melting range was significantly higher than noted in literature. The experimental melting range was more like the melting range of phenylboronic acid, which is 212-216˚C (3).

It is likely that the catalyst did not react with the phenylboronic acid and the 4bromobenzoic acid. This could be because the solution did not reach an adequate temperature for the catalyst to work. It is also possible that the recrystallization of the crude product was unsuccessful in isolating a pure product.

Appendix A (calculations) Theoretical yield of biphenyl-3-carboxylic acid: 0.148 g phenylboronic acid x

1 mol phenylboronic acid 121.9 g

1 mol biphenyl−3−carboxylic acid 1 mol phenylboronic acid

x

Percent yield of biphenyl-3-carboxylic acid: 0.085 g =0.354 x 100=35.4 % 0.24 g

Appendix B (spectra)

x

198.2 g 1 mol biphenyl−3−carboxylic acid

= 0.24 g

Morgan Miller suzuki 80

1 8 8 8 .3 3

75 70

0 -5

8 1 3 .1 1

5 4 2 .6 1 4 7 8 .1 1 4 5 7 .9 9

6 4 4 .7 7

1 0 0 6 .4 4 9 3 5 .6 7

6 9 4 .4 3

1 2 8 5 .2 8

5

1 3 1 5 .8 6

1 6 7 2 .5 2

10

1 4 4 9 .3 4

15

8 6 0 .8 5

20

7 8 7 .3 5 7 4 5 .6 3 7 3 3 .9 3

25

1 1 2 9 .0 0

30

1 4 2 0 .2 2

35

1 1 9 2 .8 4 1 1 2 0 .8 0 1 1 0 7 .8 4

1 5 8 1 .4 7 1 5 6 1 .4 9

40

1 6 0 6 .3 9

% T r a n s m itta n c e

45

1 0 1 9 .7 7

50

1 1 5 8 .6 0

55

2 5 4 7 .0 4

2 8 1 0 .1 1

60

1 0 7 7 .1 1 1 0 3 8 .2 5

1 5 1 8 .0 3 1 4 8 7 .0 2

65

-10 4000

3500

3000

2500 2000 Wavenumbers (cm-1)

1500

1000

500

No significant peaks to report.

Appendix C (questions) 1. Since the Suzuki reagent is electrophilic in nature anything that decreases the nucleophilicity of the reactants is undesirable. In this case, the carboxyl group of p-bromobenzoic acid decreases the nucleophilicity of the compound, thus resulting in an unfavored reaction. With pbromobenzyl alcohol, however, the benzyl ring is nucleophilic, and the carboxyl group increases the nucleophilicity of the ring, favoring this reaction. 2. Moles of product = 0.085 g biphenyl−3−carboxylic acid x

1 mol =0.0004 mol 198.22 g

Moles of catalyst =

0.4 mL x

0.025 mol 1L =0.00001 mol x 1L 1000 mL

Moles of product per mole of catalyst =

0.0004 mol product =40 0.00001mol catalyst

Turnover number = mole ratio = 40 3. phenylboronic acid = 122 g/mol, Pd = 106 g/mol, 1:1 molar ratio, used 0.148 g of phenylboronic acid 106 g Pd x 0.148 g phenylboronic acid=0.129 g Pd 122 g phenylboronic acid

Appendix D (experimental records) See attached lab notebook sheets for experimental data.

Sources 1. Chemistry LibreTexts. https://www.chem.libretexts.org (accessed November 2021) 2. Friestad, G. K. Organic Chemistry Laboratory Manual; Department of Chemistry, University of Iowa: Fall 2020. 3. PubChem. https://pubchem.ncbi.nlm.nih.gov (accessed November 2021)...