Lab 5 Williamson Ether Synthesis PDF

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Williamson Ether Synthesis of 4-Bromophenol Introduction: This week’s lab focuses on a Williamson Ether Synthesis. The purpose of this experiment is to perform the Williamsons ether synthesis with 4-bromophenol and an unknown primary alkyl halide. The primary alkyl halide will be one of three things: 1-bromopentane, 1-bromo-3-methylbutane, or 1-bromobutane. This reaction can only occur with a primary or a secondary halide. If it were to occur with a tertiary halide, it would turn into an elimination reaction rather than a substitution reaction. The peroxide ion is formed after the deprotonation of 4bromophenol and will serve as a nucleophile in the SN2 attack on the primary alkyl halide. This primary alkyl halide is unknown and will be determined through IR spectroscopy and HNMR. Tetrabutylammonium bromide (TBAB) will be used as a phase transfer catalyst (PTC), which allows the phenoxide ion and the water insoluble primary alkyl halide to interact. The goal is to obtain the ether product in a sufficient purity and yield to obtain spectra that can be analyzed. Microwave reflux, liquid/liquid extraction, mini flash chromatography, TLC, FTIR spectroscopy, and HNMR will be utilized to conduct this experiment. Balanced equations and Mechanisms:

Table of Reagents: Compound Name

Structure

4-bromophenol

Molecular Weight (g/mol) 173.01

Melting Point (°C) 66.4

Boiling Point (°C) ---

Density (g/cm^3) 1.84

Potassium hydroxide

56.11

380

---

2.04

1-bromopentane

151.05

-95

---

1.218

1-bromo-3methylbutane

151.05

-112

---

1.21

1-bromobutane

137.02

-112

---

1.269

Tetrabutylammonium bromide

322.37

102-106

Diethyl ether Sodium Sulfate

71.123 142.036

Methylene chloride

82.93

Water

18.02

1.15

---

34.6 ---

0.714 ---

---

39.6

1.33

100.0

1.00

Safety Information: General: Safety Glasses and lab gloves must always be worn. Make sure the snorkels are positioned properly, turned on, and are functioning properly before dispensing liquids. Avoid breathing fumes or allowing liquid to meet skin. Any vapor or liquid exposure should be reported to the TA immediately. Dispose of all liquid and solid waste in the appropriately labeled bottle in the lab hood. Chemical: 4-bromophenol: Target organ damage; acute toxicity. Hazardous in skin contact (irritant), eye contact (irritant), and ingestion. Do not breathe fumes. Potassium hydroxide: Mutagenic effects for mammalian somatic sells; toxic to upper respiratory tract, skin and eyes, target organ damage; local skin destruction. Hazardous in skin contact (irritant), eye contact (irritant), ingestion. Keep away from heat. Do not breathe fumes. 1-bromopentane: Target organ damage; acute toxicity. Hazardous in skin contact (irritant), eye contact (irritant), ingestion. Keep away from heat. Keep container dry, do not breathe fumes. 1-bromo-3-methylbutane: Developmental toxicity. Hazardous in skin contact (irritant), eye contact (irritant), and ingestion. Keep away from heat. Keep container dry, do not breathe fumes. 1-bromobutane: Target organ damage; toxic to lungs, mucous membranes. Hazardous in skin contact (irritant), eye contact (irritant), and ingestion. Keep away from heat. Keep container dry, do not breathe fumes. Tetrabutylammonium: Hazardous in skin contact (irritant), eye contact (irritant), and ingestion. Keep away from heat. Keep container dry, do not breathe dust. Diethyl Ether: Mutagenic effects for somatic cells; toxic to skin, CNS, and target organ damage. Hazardous in skin contact (irritant), eye contact (irritant), and ingestion. Keep away from heat, do not breathe fumes.

Sodium Sulfate: Hazardous in skin contact (irritant), eye contact (irritant), and ingestion. Do not breathe dust. Methylene Chloride: Toxic to lungs, CNS, Liver, mucous membranes, target organ damages. Hazardous in skin contact (irritant), eye contact (irritant), inhalation, and ingestion. Do not breathe fumes. Experimental Procedure: Microwave-Promoted William Ether Synthesis Collect 8 mL of the conjugate base of 5-bromophenol solution and place it in the white Teflon microwave vessel Add 2.90 g of tetrabutylammonium bromide (TBAB) followed by a 3.02 g of the unknown alkyl halide to the vessel Add stir bar to the vessel and return to your TA Extraction Remove the stir bar from the vessel and pour the solution into a separatory funnel Add 10 mL of distilled water and 10 mL of diethyl ether into the funnel and mix well Separate the resulting layers into two beakers Return the aqueous layer back into the separatory funnel and extract with 10 mL of diethyl ether and separate the layers into two labeled beakers Combine the two organic layers and wash the ether layer three times with 15 mL of 5% KOH each time, setting aside the aqueous layer each time Dry the ether layer with sodium sulfate Column Chromatography Secure the column with a clamp and pack a steady amount of DCM through the top of the column using a pipette MAKE SURE that DCM is continuously added until you are ready When ready to purify, add the product mixture into the column using a clean pipette Add 5-10 mL of DCM to the column after all the product mixture has been added to ensure all produce has been collected Once finished, return the used column to the TA, and transfer the purified product into a pre-weighed beaker Solvent Removal and TLC Position the snorkel over the pre-weighed beaker containing the product and boil off the solvent at approximately 40 ° C While one person is watching the removal of the solvent, the other should spot 4-bromophenol dissolved in DCM and alkyl bromide onto a TLC plate, leaving a third spot of your final product After most of the solvent has been removed, spot the TLC plate with a spot of the dilute product, and run the plate in DCM Continue with the removal process until the ether and DCM have been removed Collect the final mass, an IR spectrum, and HNMR spectra Post Lab Data: Unknown Code: OJ23BR43N Starting weight of 4-bromophenol: 3.46 g Starting weight of alkyl bromide: 3.024 g Starting weight of 25% potassium hydroxide: 7.12 g Starting wight of TBAB: 2.905 g Reflux Time: 30mins

Volume of water added before wash: 10 mL Volume of diethyl ether used to rinse spin vane: used 1st 10 mL of extraction solvent Volume of diethyl ether extractions: 2 *10 mL (20 mL) Volume of 5% KOH washes: 3* 15 mL (45 mL) Total volume of methylene chloride used for column: 10 mL Weight of the recovered product: 3.159 g Miscellaneous Experimental Observations: 2-bromophenol: 6.922 and its slight pink; 25% KOH: 14.247 g (12mL); 250 mL beaker weight 112.434 g; beaker and product: 115.593 g Results:

Limiting Reagent Calculations: Percent Yield Calculations:  % yield: = (3.159 g/ 4.86 g) x 100% = 65 %  3.46 g 4-bromophenol x (1 mol 4-bromophenol / 173.01 g 4-bromophenol) x (1 mol 1-bromo(isopentyloxy)benzene / 1 mol 4-bromophenol) (243.14 g 1-bromo-(isopentyloxy)benzene/ 1-bromo(isopentyloxy)benzene) = 4.86 g 1-bromo-(isopentyloxy)benzene  3.024 g 1-bromo-3-methylbutane x (1 mol 1-bromo-3-methylbutane / 151.05 g 1-bromo-3-methylbutane x (1 mol 1bromo-(isopentyloxy)benzene / 1 mol 1-bromo-3-methylbutane) (243.14 g 1-bromo-(isopentyloxy)benzene / 1 mol 1bromo-(isopentyloxy)benzene) = 4.87 g 1-bromo-(isopentyloxy)benzene  7.12g KOH x (1 mol KOH / 56.11 g KOH) x (1 mol 1-bromo-(isopentyloxy)benzene / 1 mol KOH) (243.14 g 1bromo-(isopentyloxy)benzene / 1 mol 1-bromo-(isopentyloxy)benzene) = 30.9 g 1-bromo-(isopentyloxy)benzene Limiting reagent: 4-bromophenol Discussion: FTIR Spectrum Analysis: Initially, the first functional group to notice is the peak at around 3000 for sp3 hybridized carbon-hydrogen bonds, and as well, we see the two peaks at around 1500 and 1450, indicating a benzene ring of some sort, which could possibly lead to identifying our product as 1-bromo-(isopentyloxy)benzene. The presence of a peak at ~1200 cm^-1 shows that there could be a C-O single bond in the molecule. From the IR spectrum analysis, there are no characteristics that can narrow our decision down to one product. HNMR Spectrum Analysis: Going downfield, the integrated values are respectively two, two, two, and three. There is a single large peak at 0.0 ppm, indicating a hydrogen on the hydroxyl group, which could mean some reagent is left over. The signals around 1.0 ppm to 1.5 ppm indicate there are 7 hydrogens on the sp3 carbons, which corresponds with the butyl group on 1-bromo-4-butoxybenzene. At 3.7 ppm, the signal corresponds to a carbon being adjacent to an oxygen. The signals at occur around 6.6 ppm and 7.3 ppm further lead us to identifying the product by indicating the presence of hydrogens attached to a benzene ring. Conclusion: This information leads us to believe that the unknown product is 1-bromo-4-(isopentyloxy) benzene, which indicates that the unknown primary alkyl bromide is 1-bromo-3-methylbutane.

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