Post Lab Report: Synthesis of 1-bromobutane in Chem 2545, Fall 2010, Study notes of Chemistry

Download Post Lab Report: Synthesis of 1-bromobutane in Chem 2545, Fall 2010 and more Study notes Chemistry in PDF only on Docsity! Chem 2545 Fall 2010 Post Lab 7 Report (65 pts) I. Substitution Reactions: SN2 synthesis of 1-bromobutane II. Objective: The synthesis of 1-bromobutane and to be able to identify the product of the reaction by boiling point, density, and flame test. III. Summary: During the one hour reflux of 1-butanol, HBr, and sulfuric acid, two layers were formed. The clear layer was made up of the acid water mixture and the yellowish layer contained the 1-bromobutane produced during the reaction. The mass of the 1-bromobutane that was isolated was 2.1 grams. The boiling point of 1-2bromobutane was between 99°C and 100°C. When we dipped the copper wire into the vial containing the 1-bromobutane and placed in over the fire, a green flame was produced because halogens burn green according to the Beilsten Test for Halogens. The density of my product was calculated to be 1.25 g/mL. IV. Postlab Questions/Discussion of Results 1. Explain how you used your boiling point data to determine if you obtained your product. (6 pts) The known boiling point of 1-bromobutane is 101.3°C. The value of my product was somewhere between 99 and 100°C. The closer e boiling point of the product is to 101.3°C, the more sure one can be that the product is 1-bromobutane. Because my boiling point was no the exact value, I am lead to believe that there were still some impurities in my product. I am lead to believe this because impurities cause boiling point depression, meaning that the impure substance causes the pure boiling point to decrease slightly away from the pure one. 2. Explain how you used your density data to determine if you obtained your product. (6 pts) I measured the mass of 3mL of 1-bromobutane, which was 3.75 g. I used this information to calculate the density (density=mass/volume). The density was 1.25g/mL. I was able to use this value and compare it to the known product density of 1.269g/mL. Since the density I found was fairly close to 1.269g/mL, this supports the product is probably being 1-bromobutane. 1 Chem 2545 Fall 2010 3. (a) What was the color of the flame that you observed during the flame test? (2 pts) When I performed the flame test, my product produced a green flame. (b) Explain how you used this observation to support or disprove product formation. (6 pts) According to the Beilsten Test for Halogens, if the flame is green then there is a halogen present. Since I had a green flame, this supports a halogen like bromine being present and supports the idea that my product is 1-bromobutane. 4. Draw the Lewis dot structures of dimethylsulfoxide (DMSO) and 1- Bromobutane. Show all necessary charges. (10 Pts, no partial credit) 5. After the one hour reflux the reaction mixture was transferred to a centrifuge tube. The bottom aqueous acidic layer was removed and discarded, and then 2 mL of water was added to the tube. After mixing the two layers the top aqueous layer was discarded. Why do the layers switch places? (8 Pts) At first, the 1-bromobutane is the top layer and the acid aqueous layer is on the bottom. Then after the acid aqueous layer is the bottom. Then after the acid aqueous layer is removed, water is added and the organic layer is moved to the bottom layer. This is due to the fact that the concentration of the sulfuric acid and HBr is very high. The high concentration increased the density of the water and caused the aqueous acid layer to be denser than the organic layer and sink to the bottom. The density of pure water, on the other hand, is less than the density of the organic layer. Therefore, when the water was added it remained on top of the organic layer. 6. On page 68 of your lab manuals, it says “Good leaving groups are weak bases, …”. Explain why weak bases make good leaving groups. (5 Pts) Weak bases make good leaving groups because they are morst stable and less reactive. This means that they will not mind being left on their own in a solution as an anion for a while. 2