Final Brominating Alkenes Lab Report PDF

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NAME: Mostafa Saber EXPERIMENT: Brominating Alkenes

TA: Symone Carty DATE: 06/16/2020

COURSE & SECTION NO.: CHEM 3221-11029

! Pre-Laboratory Assignment: 1a. It is corrosive and a lachrymator so the chemical must be used in a fume hood at all times. Avoid contact with skin and fumes with eyes and mouth by wearing goggles and gloves. b. It is corrosive and one must avoid skin contact. 2- Cinnamic acid – 150 mg Cis- stilbene – 100 uL Trans – stilbene – 100 mg Pyridinium tribromide – 200-385 mg Moles of cinnamic acid = 0.150 g / 148.16 g/mol = 0.001 moles Theoretical mass of dibromo product formed = 0.001 mol x 307.97 g/mol = 0.312 g cis-stilbene (100 uL = 0.1 ml) moles of cis-stilbene = 0.1 ml x 1.01 g/mol/180.25 g/mol = 0.00056 mols Theoretical mass of dibromo product formed = 0.00056 mol x 340.05 g/mol = 0.19 g trans-stilbene moles of tran-stilbene = 0.1 g/180.25 g/mol = 0.00055 mols Theoretical mass of dibromo product formed = 0.00055 mol x 340.05 g/mol = 0.19 g

3-

4a.

b.

Purpose: The purpose of this experiment is to synthesize vicinal dihalides by brominating alkenes. Characterize vicinal dihalides by using the silver nitrate test and by using melting point measurement to determine the relative stereochemistry. Background: The halogenation of alkenes is an important reaction in the chemical industry. For example, over 8,000,000 tons of 1,2-dichloroethane per year are produced by the addition of chlorine to ethylene. This product is used both of as a solvent and in the preparation of polyvinyl chloride, a common organic polymer used in household plumbing. The products obtained from alkene halogenation or called vicinal dihalides because the two halogen substituents attached to adjacent carbon atoms. When the halogen used is either bromine or chlorine, halogenation of alkenes occurs

rapidly at room temperature resulting vicinal dihalides are stable. Fluorination is a violent reaction that is difficult to control and is accompanied by several side reactions. Iodination is an endothermic process, resulting in vicinal diiodides that tend to revert to alkenes. Consequently the most applications of alkene bromination are chlorination and bromination. Typically, alkenes undergo reactions through electrophilic addition, a process in which the alkene pi bond is replaced with two sigma bonds. Reactions:

Table of Physical Constants: Substance Structural Formula

Molecular Weight (g/mol)

Melting Point (oC)

Boiling Point (oC)

Density (g/ml)

Hazards

Acetic acid

60.05

16.6

118

1.049

Corrosive

1,2-dibromo-1,2diphenylethane

340.07

235 to 241

324

1.613

Irritant

2,3-dibromo-3phenylpropanoic acid

307.97

200

213.5 +/- 42

1.9

Irritant

Ethanol

46.07

-114.1

78.37

0.789

Flammable Irritant

Pyridinium tribromide

319.84

-8

240 to 242

1.03

Corrosive

Silver nitrate

169.87

212

440

4.35

Toxic Oxidizer

Cis-stilbene

180.25

5 to 6

135

1.011

Irritant

Trans-stilbene

180.25

122 to 125

307

0.971

Irritant

Procedure: Cis-stilbene 1- Remove the 5.0-mL RBF from the apparatus. 2- Place 100 uL of cis-stilbene, 2.0 mL of acetic acid, and 200 mg of pyridinium tribromide in the RBF. 3- Add a magnetic stir bar. Trans-stilbene 1- Remove the 5.0-mL RBF from the apparatus. 2- Place 100 mg of trans-stilbene, 2.0 mL of acetic acid, and 200 mg of pyridinium tribromide in the RBF. 3- Add a magnetic stir bar. Part 2: 1- Reattach the RBF to the reflux apparatus. 2- Start the flow of water through the condenser. 3- Heat the reaction mixture to reflux while stirring. 4- Reflux for 15 minutes. 5- Afterwards, remove the RBF from the heat and allow to cool for 5 minutes. 6- Remove the condenser and use forceps or a magnetic wand to remove the stir bar. 7- Add 2.5 mL of DI water to the RBF. 8- Prepare an ice-water bath by half-filling a 250-mL beaker with equal volumes of ice and water. 9- Place the RBF in the ice-water bath b\for 15 minutes. 10- While the reaction mixture is cooling in the ice bath, assemble a vacuum filtration apparatus. 11- Turn on the water to the aspirator and moisten the filter paper with a few drops of water. 12- Filter the crystalline solid and wash with 3 mL of DI water. 13- Allow the crystals to dry in the Hirsch funnel by pulling air through the funnel for 15 minutes. 14- Weigh the dried product and record its mass. 15- Using 2 small test tubes, dissolve approximately 10 mg of the products in 0.5 mL of 95% ethanol. 16- To these test tubes, add 0.5 mL of 2% ethanolic silver nitrate. 17- To another small test tube, add 0.5 mL of 95% ethanol only. 18- Allow the test tubes to stand for 5 minutes and then record the presence or absence of a precipitate. Observations/ Data: Trans-stilbene weight = 0.101 g Trans-stilbene is not solid at room temperature Pyridinium tribromide weight. = 0.210 g Filter paper weight = 0.180 g Weighing dish weight = 1.698 g Weighing dish + filter paper + crystals = 1.981 g

A: cis-stilbene – liquid turned cloudy white with precipitate at bottom B: trans-stilbene - liquid turned cloudy white with precipitate at bottom C: blank – liquid is clear Cis-stilbene melting-point range: 98 -108 oC Trans-stilbene melting-point range: 216 – 218 oC Calculations: Theoretical yield: 0.1 g C14H12 x (1 mol C14H12 / 180.25 g C14H12) (1 mol C14H12Br / 1 mol C14H12) (340.07 g C14H12Br / 1 mol C14H12Br) = 0.189 g C14H12Br Actual yield: Final weight of plate, paper, and product – weight of plate – weight of paper = 1.98 g – 1.697 g – 0.180 g = 0.103 g % yield = (0.103 g / 0.189) x 100 = 54.50% Results: The %yield was 54.50% which is not high and this could have been due to several reasons including spills and other experimental errors, as well as losses due to an incomplete reaction or undesirable side reactions. In looking at the results of the test tube reactions, test tubes A and B contained a cloudy white solution, while test tube C contained a clear solution. It is evident that test tube A and B contained the alkene due to the color change that occurred. Because a visible color change took place, it is feasible to say that they were the only compounds that reacted with ethanolic silver nitrate. The melting point range for cis-stilbene was 98 – 108 oC which is much higher than the literature value of 5 - 6 oC, while the melting point range for the trans-stilbene product was 216 – 218 oC which is also higher than the literature value of 122 – 125 oC. These drastic changes in the melting point range could have due to the presence of impurities. Conclusion: The objective of this experiment was to qualitatively analyze unknowns using bromine in order to determine which unknown contained an alkene. Moreover, a secondary objective was to generate trans-1,2-dibromo-1,2diphenylethane through the bromination of stilbene. The experiment was successful in demonstrating how qualitative analysis can be used to determine if unknown solutions contain alkenes. Moreover, it was also successful in demonstrating how recrystallization can be used to further purify a product. Post-Laboratory Questions: 1a. Cis-stilbene melting-point range: 98 -108 oC which is similar to that of 1,2-dibromo-1,2diphenylethane. Trans-stilbene melting-point range: 216 – 218 oC which is close to that of erythro. b.

2a. b.

The products turned cloudy white. When silver nitrate was added, both products turned white and precipitate formed at the bottom....