Reactions free essay sample

The purpose of this experiment is to synthesize 1-bromobutane from 1-butanol and sodium bromide. In order for this reaction to reach completion there are four major operations that need to be performed. The four major operations include refluxing, simple distillation, separation, and drying. To begin, in order for the compounds to react they will be dissolved in water and sulfuric acid will be added. The addition of sulfuric acid will then generate hydrobromic acid, an important product in the reaction mixture. The hydrobromic acid will react with the 1-butanol when heat is added to the flask during refluxing. Refluxing is the heating of a flask to boiling and then allowing the vapors to condense and run back into the reaction flask. Refluxing is a good way of keeping a reaction at a constant temperature. After refluxing is complete the reaction is distilled by the method of simple distillation. The simple distillation process is used to help remove and purify a particular substance, in this case the 1-bromobutane, from other components in the reaction flask. However, since the boiling point of 1-bromobutane is 101Â °C and the boiling point of water is 100Â °C it would be expected that there would be a large amount of water that will distill out of the flask along with 1-bromobutane. Other remaining reactants such as a small amount of alcohol and/or acid may be distilled out along with the water of 1-bromobutane. Since there is such a high probability of other components in the distillate, separation processes will need to be carried out. Water is first added to the 1-bromobutane layer to remove any leftover starting material and after the 1-bromobutane layer is isolated sodium hydroxide, water, and sodium chloride solutions are added to remove any remaining acid. Drying using anhydrous sodium sulfate is then used to remove any remaining water in the solution and then the simple distillation process is performed again on the dried 1-brombutane. It would be hypothesized that the amount of recovered 1-bromobutane will be relatively low since there are many techniques involved which allow for many places for error and product loss. Also, the theoretical yield for the experiment is 38. 06%, which is relatively low. After the recovered 1-bromobutane is weighted, infrared spectroscopy will be performed. It would be hypothesized that the 1-bromobutane spectrum would produce peaks at the characteristic alkane and halogen peaks. SN2: An SN2 reaction mechanism occurs when a nucleophile directly attacks the substrate at an angle of 180 degrees to the C-L bond. The C-L bond is then broken with the formation of the C-Nu bond. The substrate, R-L, and C-Nu are all involved in the transition state which is the rate determining step. With two reactants being involved in the transition state it is bimolecular making is an SN2. The larger the substrate and how the more condensed the skeletal structure of the more difficult it is for the nucleophile to attack the carbon, making the reaction take longer. Nucleophilicty parameters are components in a second order rate law reaction that is a constant for a given nucleophile. In order for the desired reaction to occur the leaving groups in nucleophilic substitution must be weakly basic, if a strong acid isn’t present the reverse reaction will occur. SN1: An SN1 reaction mechanism occurs in two successive steps. The first is the ionization of the C-L bond. The second step is bond formation of the C-Nu bond; this is very quick making the first step the rate determining step. Since the reaction rate depends only on the concentration of the substrate it is uni-molecular making it SN1. The substrates that tend toward SN1 reactions are ones that have their carbon mostly blocked off by bulky R groups rather than just hydrogen’s. Materials and Methods The following experiments were conducted as part of the SN2 and SN1 labs that may be found in the following citation: Gilbert, John, C. , Martin, Stephen, F. Experimental Organic Chemistry: A Miniscale and Microscale Approach. 5th ed. Brooks/Cole. 2011. Print. Experiment #15 – Preparation of 1-bromobutane, an SN2 reaction: See copy blue pages attached. Experiment #16 – Preparation of 2-chloro-2-methylbutane, an SN1 reaction: See copy blue pages attached. Data and Observations Experiment #15 – Preparation of 1-bromobutane, an SN2 reaction: See copy blue pages attached. Experiment #16 – Preparation of 2-chloro-2-methylbutane, an SN1 reaction: See copy blue pages attached. Results and Discussion Experiment #15 – Preparation of 1-bromobutane, an SN2 reaction: See copy blue pages attached. Top of Form Bottom of Form To begin, in this experiment it is important to understand why each reagent and technique was used in the synthesis of 1-bromobutane. Sodium bromide and 1-butanol are dissolved in water since the bromide ion from the sodium bromide and the four carbon chain from the 1-butanol are the desired components of 1-bromobutane. In order to get the sodium bromide and the 1-butanol to react sulfuric acid is added to react with the sodium bromide and combine with the sodium ion producing hydrobromic acid. Later, when the flask is heated the bromide ion will be able to combine with the four carbon chain of the 1-butanol. During the process of this reaction the reagents were kept cool in an ice bath to avoid the possible evaporation of any of the solution. After all four reagents were added a white residue developed in the bottom of the reaction flask. At this point the flask was attached to a refluxing apparatus. This process of refluxing helps to purify the mixture and keep the reaction at a constant temperature. Also, before the reaction mixture began to boil the separation of a clear top layer and a cloudy bottom layer helped to indicate that the reaction was working properly. The top layer was the alkyl bromide since the other components of the aqueous layer have the greater density. After the 45 minute refluxing process was complete, the apparatus was set up for simple distillation apparatus distillation commenced. Distillation took place until no more drops of product were dripping from the distillation head. The first drop of distillate occurred when the thermometer read 75Â °C, the actual temperature was probably a bit higher since the vapors might not have fully reached the bulb of the thermometer. The final drop of distillate was collected at about 115Â °C. Once the distillate was collected, it was placed in a seperatory funnel and the reaction flask was rinsed with 10 mL of water and added to the seperatory funnel. Rinsing the funnel ensured that all of the distillate from the distillation process was removed from the reaction flask and no product was left on the walls of the flask. After the water was added, two layers formed in the funnel. The top layer was the water and the bottom layer was the 1-bromobutane since the density of 1-bromobutane is higher than that of water. The two layers were then separated and it was placed in a separate Erlenmeyer flask. The 1-bromobutane layer was then mixed with sodium hydroxide solution. The sodium hydroxide helped to remove any remaining acid that was still present. The mixing of the two solutions in the seperatory funnel was observed as an exothermic reaction since the funnel became warm. At this point, the 1 bromobutane layer became cloudy and settled to the bottom of the funnel. The cloudy 1-bromobutane layer was transferred to a separate Erlenmeyer flask and anhydrous sodium sulfate were added to both layers and allowed to dry. The liquid was then decanted back into the initial reaction flask used earlier in the experiment. Before the reaction tube or any of the other equipment used in the previous distillation could be reused it had to be washed thoroughly with acetone to remove any traces of the prior reagents that could possibly contaminate the solution. After the decanted 1-bromobutane was added to the distilling flask shortpath distillation was performed. The first drop of distillate was collected at 85Â °C. The boiling point of 1-bromobutane is 101Â °C, so the distillation was stopped at around 102AÂ °C. Even though the first drop was collected at a low boiling point the temperature could have been higher since the vapors once again may not have fully reached the bulb of the thermometer. Also, it could have been a result of impurities in the solution such as water, which has a boiling point of 100AÂ °C and would boil and evaporate out before the 1-bromobutane. When the distillation was complete, the mass of the collected distillate was found to be 5. 737g. After comparing the experimental value of 1-bromobutane, dividing it by the calculated theoretical yield of 15. 7 g and multiplying by 100, the percent yield for this experiment was found to be 38. 06%. To calculate the theoretical yield the number of moles of each of the initial reagents in the experiment were found. The reagent with the lowest number of moles was the limiting reagent in the experiment and therefore the mass of the recovered product could not exceed that amount. Once 1-butanol was found to be the limiting reagent with 0. 110 moles, it was multiplied by the molecular weight of the product, 1-bromobutane, which was 137. 03g/mol. This resulted in the theoretical yield of 15. 07 grams. This actual value was a little more than one-third than that of the expected theoretical value. After weighing was complete, infrared spectroscopy was performed on the 1-bromobutane product. For this lab experiment the graphs acquired through IR spectra was lost and product was not saved to re-do IR spectroscopy. | | Experiment #16 – Preparation of 2-chloro-2-methylbutane, an SN1 reaction: See copy blue pages attached. SN1: First separate with sodium hydroxide and then with water in order to get the aqueous layer away from the 2-chloro-2-methylbutane. Then eliminate water using sodium sulfate. Finally distill into a cooled receiver to get rid of final impurities. Calculate the yield of the reaction. = 77. 42%. Conclusions In conclusion, the theory that 1-bromobutane could be synthesized from the starting products of 1-butanol and sodium bromide was supported after analyzing the boiling point or the distilled product during simple distillation and examining peaks at the C-H bond and carbon halogen bond points on the infrared spectrum. The process of adding sulfuric acid to the two starting reagents and applying heat was the process that carried out the reaction. During the first simple distillation the first drop of distillate occurred at 75Â °C and the first drop of distillate in the second simple distillation occurred at 85Â °C. The total amount of product obtained was 5. 737 g. When compared with the theoretical yield of 15. 07 g, the percent yield for the experiment was calculated to be 38. 06%. This supported the hypothesis that a small amount of product would be obtained as a result of all of the protocols that needed to be carried out on the obtained 1-bromobutane product such as separation, extraction, drying, and distillation.