Exp 10 Bromination of Stilbene PDF

Preview

Summary

Download Exp 10 Bromination of Stilbene PDF

Description

A Green Bromination of Stilbene and Qualitative Determination of Alkene Compounds Dennis Rossi and Roger Mendez CHM 2210L TA: Suzeeta Bhandari April 3, 2019

Intro This experiment goes through a process called a bromination reaction of alkenes, an SN2 reaction. It adds bromines across the double bond of a molecule to add vicinal bromides or neighboring bromides with the adjacent carbon where the double bond used to be. This reaction does anti addition which means the bromines add to opposite sides of where the double bond use to be (Solomon, 2016). Bromination of alkenes usually occur through an electrophilic reaction where the solvent is usually CCl¬4¬¬; the solvent has no effect on the actual reaction. For example, bromine can be used for synthesizing an alkene to alkyl halide (Markovnikov), an alkene to alkyl halide in the presence of HO-OH, and an alkene to a vicinal dibromide in the presence of CCl4. The reagents in bromination can be very hazardous and toxic. Bromination usually occurs through a chlorinated solvent and the most common solvents are carbon tetrachloride (tetrachloromethane ) and methylene chloride (dichloromethane). These solvents are known for carcinogenic. Bromine itself is very corrosive. It can be harmful to the skin which can cause severe burns and it is harmful if inhaled. However, there is a safer reagent can be used. This reagent is pyridinium tribromide, it is generated in the reaction rather than be added (Weldegirma, 2018). This reagent arises though situ. This reagent uses because it replaces more toxic reagents such as tetrachloromethane and dichloromethane. Replacing the reagents with less hazardous reagents it is not a green reaction. The Environmental Protection Agency defines green chemistry is the development of processes and products that reduce the generation of hazardous substances (EPA, 2018). The

EPA provided a big role in green chemistry by asking chemists and engineers to design chemicals or process that do not create hazardous or toxic waste (ACS, 2019). For example, the use of pyridinium tribromide is a safer route to perform this process however it still uses elemental bromine which is corrosive. Therefore, it is not completely green (Weldegirma, 2018). Atom economy is the percentage of the amount of the starting molecular atoms that are present in the products. Therefore, the higher the chemical yield the less green and safer the reaction is. On the other hand, if the reaction has low yields than it is considered more green and safer (Weldgirma, 2018).

Atom Economy %=

Molecular Mass of Product x 100 Molecular Mass ofAll Reactants

The formula above is used to calculate the percentage of atom economy. The higher the percentage the safer and green the reaction is (Greenchemuoft, 2014). For example, the generation of bromine pyridinium tribromide is a safer reaction but not an atom-economical reaction. This is because even though the desired reaction is collected, all lot of it is produced as waste (Weldgirma, 2018). Reaction

Side reaction

A)

Test Tube #1

Test Tube #1

Test Tube #1













3 drops of unknown 1 was added 1 mL ethyl acetate was added 5 drops of solution A was added Shook and stirred







3 drops of unknown 2 was added 1 mL ethyl acetate was added 5 drops of solution A was added Shook and stirred







3 drops of unknown 3 was added 1 mL ethyl acetate was added 5 drops of solution A was added Shook and stirred

Solution A 



1 mL 30 % H2O2 was added 0.2 mL HBr was added

For all test tubes:  

Any changes and color changes were observed The unknown with the alkenes was determined

B)

0.2 g of (E) – stilbene was put into a collecting with 4 mL Ethanol

A reflux was began

While the mixture was refluxing, 0.3 mL of 48% HBr was added

When reaction was complete, it was cooled then 3 mL of NaHCO3 was added

It was put into an ice bath to cool

It was refluxed for 20 minutes

Solid was collected through a vacuum filtration

1.6 mL of 30% H2O2 was added slowly

It was dried as much as possible



 

The solid was weighed and the % yield was calculated The melting point was determined He atom economy was calculated

Table of Chemicals Molecular

Molecular

Melting

Boiling

Density

formula

weight

Point

point

(g/cm3)

Ethyl Acetate

C4H8O2

(g/mol) 88.11

(oC) -83.6

(oC) 77.1

0.902

Hydrogen

H 2O 2

34.0147

-0.43

150.2

1.45

Hydrobromic Acid

HBr

80.9119

-11

122

1.49

Ethanol

C2H5OH

44.07

-114.1

78.37

0.780

(E) - Stilbene

C14H12

180.25

122-

305-

0.971

125

307

Peroxide

Structure

Sodium

NaHCO3

84.007

50

851

2.20

bicarbonate

Ethyl Acetate

Hydrogen Peroxide



Highly flammable



Strong oxidizer



Causes severe eye irritation



Causes severe eye damage and skin



May cause drowsiness or dizziness



Keep container tightly closed in well-



May cause respiratory irritation

ventilated area



Harmful if inhaled



Harmful if swallowed



Keep container tightly closed in well-

Sodium bicarbonate 

No hazards



Keep container tightly closed in wellventilated area

Hydrobromic Acid 

Causes severe eye damage and skin

burns

ventilated area Ethanol 

Highly flammable



Keep container tightly closed in wellventilated area

burns 

May cause respiratory irritations



Keep container tightly closed in well-



Harmful if swallowed

ventilated area



Causes serious eye damage



Toxic to aquatic life



Keep container tightly closed in well-

(E) – Stilbene

ventilated are

Results Observations of

Test tube #1 Test Tube #2 Test Tube #3 trans-1,2-dibromo-1,2-

Percent yield (%)

Melting point (oC)

colors Yellow/orange Yellow/orange Clear; no visible Rxn 58.2914

241-243

diphenylethane

Percent yield ( % )=

experimental x 100 theoretical

Percent yield ( % )=

0.116 x 100 0.199

0.116 x 100 =58.2914 0.199 Percent yield=58.2914

Atom Economy %=

Molecular Mass of Product x 100 Molecular Mass ofAll Reactants

All the reagents that were in liters were converted into moles and then mass. Then the numbers were input into the formula.

Atom Economy %=

Molecular Mass of Product x 100 Molecular Mass ofAll Reactants

180.25+ ( 2 ( 80.9119 ) ) +34.0147 ¿ ¿ 340.058 Theoretical Atom Economy %= ¿ 340.058 x 100=90.4196 % (180.25+ ( 2 (80.9119 ) ) + 34.0147) Ultimate Efficiency=chemical yield x atom economy Ultimate Efficiency=58.2914 x 0.904196 58.2914 x 0.904196=52.706 %

Experimental Atom Economy %=

0.116 x 100 0.0010836415+ ( ( 2 )( 0.002429622 ) ) + 0.2

0.116 x 100=56.3262 0.0010836415+ ( 2( 0.002429622 ) ) + 0.2 Ultimate Efficiency=58.2914 x 0.563262 58.2914 x 0.563262=32.8333 % Discussion In this part of this experiment, 3 test tubes were tested to observe which unknown contained the alkene. As informed by the TA, one of them was alcohol, a ketone and the other was an alkene. All of the test tubes had 5 drops of H2¬O2¬/HBr solution added to them. The first and second test tubes had a yellow solution while the third was clear. Through this observation, it shows that test tubes 1 and 2 both did not react with the solution while test tube 3 did. Therefore, test tube #3 was the unknown that contained the alkene and the other two contained alcohol and

ketone. Possible errors that could have occurred during this experiment is that there could be possible contaminations of the test tubes used and reacted differently than ideal. From experiment B, 58.2914% was our calculated percent yield. The yield gathered was lower than expected because the typical yield ranges between 80-90%. The low percent yield can be due to many errors that may have occurred during the experiment. First of all, a lot of mass was lost during multiple transfers instead of performing the reaction the same vial that the solution was to be put in. Another reason may be that upon measuring the weight of the solid, some solid was lost due to slipping off the filter paper it was to be weighed on. Some of the solutions could have been that some of the product evaporated during reflux. The melting point that was measured had a range between 239 and to 242oC. This coincided with the literature value given which was 241oC. The fact that the measured melting point was aligned with the literature shows that the experiment accomplished what it was set out to do. However, since it was a range and not exactly 241oC, this means that there must have been a small number of impurities in the solid. The experimental atom economy was calculated as 56.3262% while the theoretical was 90.4196%. Since the experimental is way below the theoretical. That means that roughly only 56.3262 of 1,2-dibromo-1,2-diphenylmethane was produced as the desired product and 43.6738% of the product was wasted. This means that it was not very efficient. But this alone is not enough, therefore the atom economy is multiplied with the chemical yield. Conclusion The theoretical background and the results gathered correlate with each other. The first part was to choose which unknown contained the alkene, and the observations allowed us to

correctly see the difference between the test tubes and correctly choose the test tube with the alkene. For the second part, the objective was to synthesize 1,2-dibromo-1,2-diphenylethane. The experiment was a success in creating the product. However, throughout the experiment, there was a loss of product. The experiment data revealed that the experiment accomplished what it was set out to do however, tiny losses can affect your atom efficiency. There are abundant reasons for how bromination reactions play a role in real life. Alkenes can be turned into a product that contains bromine and that is used for water treatment, medicines, and or for energy storage (BSEF, 2019). References Bromine Applications. http://www.bsef.com/bromine-applications/ (accessed Apr 2, 2019). Green Chemistry. https://www.epa.gov/greenchemistry (accessed Apr 2, 2019). GreenChemUofT. Green Chemistry Principle #2: Atom Economy. https://greenchemuoft.wordpress.com/2014/04/04/greenchemprinciple2/ (accessed Apr 4, 2019). Solomons, T. W. G.; Fryhle, C. B.; Snyder, S. A. Organic chemistry; John Wiley et Sons, Inc.: Hoboken, NJ, 2016 Weldegirma, Solomon. “Experiment 10: A Green Bromination of Stilbene and Qualitative Determination of Alkene Compounds.” Experimental Organic Chemistry. 8th Edition, Tampa, Pro-Copy Inc.2018. 55-61.’ What Is Green Chemistry? https://www.acs.org/content/acs/en/greenchemistry/what-is-greenchemistry.html (accessed Apr 2, 2019)....