Sabrina(Jingyao) Liao
Simpson University / Organic Chemistry II
Purpose
The purpose of this experiment is to synthesize 1-phenylethanol from acetophenone using sodium borohydride as the reducing agent.
Reaction
Mechanism
Table of reactants and reagents
Reactant/ reagent | amount | moles | Molar mass | density | bp/mp | comment |
acetophenone | 12.086g | 0.10mol | 120.4g/mol | 1.03g/cm3 | 202.4 celcius/20.2 celcicius | reactant |
Sodium borohydride | 1.509 g | 0.040 mol | 37.83 g/mol | 1.07g/cm3 | 500 celcius/ 400celcius | reagent |
Hydrochloride | 10ml | 0.33 mol | 36.49 g/mol | 1.2 g/cm3 | -85celciu/-114.8celcius s | reactant |
ethanol | 30ml | 0.514 mol | 46.07 g/mol | 0.79g/cm3 | 78.37celciu/ 104 celcius | solvent |
Methylene chloride | 20 ml | 0.41 mol | 50.49 g/mol | 1.03g/cm3 | 39.6 °C celcius/ −96.7 °Ccelcius | Solvent for extraction |
Magnesium sulfate | 2 scoops | N/A | 120.366 g/mol | 2.66 g/cm3 | 330 celcius/ 1124 celcius | Drying agent |
Mass of empty 100ml round bottom flask: 62.624g
Calculations:
Acetophenone no. of mol: 12.086g / 120.4g/mol= 0.10 mol
Sodium borohydride no. of mol: 1.509 g / 37.83 g/mol= 0.040 mol
Hydrochloride no. of mol: (1.2 g/cm3= 1.2 g/ml) mass= 10ml x 1.2g/ml=12 g; no. of mol= 12g /36.49 g/mol=0.33 mol
Ethanol no. of mol: mass=0.79 g/ml x 30ml =23.7 g; no.mol=23.7g / 46.07 g/mol= 0.514 mol
Methylene Chloride no. of mol: mass= 1.03g/ml x 20ml= 20.6 g; no. mol=20.6g/ 50.49 g/mol=0.41 mol
Procedure
Figure. 1. Set up of distillation apparatus
Firstly, A magnetic stir bar was placed inside a 150ml beaker with 1.509 g sodium borohydride inside. Then, 30 ml of 95% ethanol was added into the beaker which was then placed on a stirring plate to get mixed thoroughly. Thirdly, 12.089 g of acetophenone was weighed and obtained inside a 125ml- Erlenmyr flask. Around 0.5 ml of acetophenone was added into the Erlenmyer flask every 2 minutes until all of the acetophenone was inside the flask. The addition process took 35 mins in total and white precipitation was observed during the process. After that, the Erlenmyer flask was cooled down by an ice bath, followed by being placed on the stir plate at room temperature for 20 minutes. Then, 10 ml of HCl was added to the mixture in a fume hood. Afterward, the flask was placed on a hot plate and heated for 15 minutes to get rid of the ethanol. The mixture was then transferred into a separatory funnel and 20ml of methylene chloride was added into the funnel. To rinse off the remained mixture on the wall of the flask into the separatory funnel, 30ml of H2O was used. The funnel was then shaken thoroughly, followed by the solution being left to stand to allow the layers to settle. After that, the mixture was purified by the bottom layer(CH3Cl2) being drained. Another 20 ml of methylene chloride was added into the funnel and the bottom layer was drained again. The mixture was filtered into a preweighed 100ml-round bottom flask (weighed 62.624g) by using a glass funnel with filter paper in it. A distillation apparatus was set up as in the picture shown above (Fig 1.). Eventually, 10.10 g of 1-phenyl ethanol was distilled. The IR spectrum of the product was then examined by an IR spectrometer.
Table of products
products | yield(g) | Yield (mol) | Theoretical yield (g) | Molar mass | Percent yield | mp/bp | density |
1-phenyl ethanol | 10.10 g | 12.1 mol | 4.89 g | 122.16 g/mol | 207% | 20 celcius / 205 celcius | 1.012 g/cm3 |
Calculations
Yields of 1-phenylethanol= 72.726g- 62.624g(mass of 100ml round bottom flask)= 10.10 g
1-phenyl ethanol no. of mol: 122.16g/mol / 10.10 g =12.1 mol
Theoretical no. of moles of 1-phenylethanol= Sodium borohydride no. of mol(since it’s limiting reactant) = 0.04 mol
Theoretical yield of 1-phenyl ethanol: theoretical mass=0.04 mol x 122. 16 g/mol= 4.89 g
Percent yield: %= 10.10 g/4.89 g= 2.07 =207%
Discussion
The IR spectrum of starting material (Fig 3.) and product (Fig 2.) is shown in the images below. In the IR spectrum of acetophenone (starting material), a distinctive peak is observed at 1700 cm^-1. This indicates the presence of a conjugated carbonyl group. However, in the IR spectrum of 1-phenylethanol (product), this peak is notably absent, suggesting the carbonyl group was gone after the synthesis process. Conversely, the IR spectrum of 1-phenylethanol illustrates a prominent peak at 3345.11 cm^-1, corresponding to the presence of an alcohol functional group, indicating the product was made. This peak is not observed in the spectrum of acetophenone.
In conclusion, based on the IR result obtained, 1-phenyl ethanol was successfully synthesized from acetophenone by reacting with sodium borohydride and hydrochloride. The percentage yield of 200 percent might be due to the impurities of the products caused by inefficient extraction or incomplete drying when using magnesium sulfate.
Figure 2. Experimental product IR spectrum
Figure 3. IR spectrum of starting material
Works Cited
PubChem. “PubChem.” Nih.gov, National Library of Medicine, 2022, pubchem.ncbi.nlm.nih.gov/.