Organic Lab 7
Amanda Jornd Experiment 7- Synthesis and Reactivity of tert-Butyl Chloride Via an SN1 Reaction
Introduction/Background: Alkyl halides are compounds in which a halogen atom replaces a hydrogen atom of an alkane. Alkyl halides are classified as primary, secondary, or tertiary depending on the number of alkyl substituents directly attached to the carbon attached to the halogen atom. The purpose of this lab was to properly prepare t-butyl chloride from t-butyl-alcohol in concentrated hydrochloric acid. The reaction occurs through a nucleophilic substitution, which is when a nucleophile replaces the leaving group in the substrate. In this lab, the hydroxyl group of t-butyl alcohol is replaced by a chlorine atom. The reaction proceeds through an SN1 mechanism (Weldegirma 38-41). “A nucleophile is any neutral or uncharged molecule with an unshared pair of electrons. In the substitution reaction, the nucleophile donates an electron pair to the substrate, leading to the formation of a new bond to the nucleophile, while breaking the existing bond to the leaving group”.
The two types of nucleophilic substitution reactions, SN1 and SN2, are identified based on whether the different steps occur simultaneously (SN1) or in two separate steps (SN2). To synthesize the t-butyl chloride, the t-butyl alcohol goes through an SN1 reaction. Also, the nature of the solvent can affect which substitution reaction will occur. Polar protic solvents typically favor SN1 reactions. This is because the SN1 mechanism is carried out in two steps and the polar protic solvent produces both a cation and an anion that are capable of stabilizing the charges on the ions formed during the reaction. Because an SN2 reaction occurs in one step, this is unfavorable; however, the SN2 reactions tend to favor polar aprotic solvents. Another factor affecting the type of substitution reaction is the nature of the leaving group. Since the SN1 reactions occur in one step, they generally require an excellent leaving group and won’t typically run with a poor leaving group. The SN2 reaction also favors excellent leaving groups but can run with any type of leaving the group because it is run in two different steps. To synthesize the t-butyl chloride, the t-butyl alcohol goes through an SN1 reaction. If an alkyl halide is a primary one, it can then react with iodide ions in the sodium iodide solvent by an SN2 mechanism showing a precipitate of insoluble sodium chloride. Heat can also be used in this process to speed up the reaction. The first test we ran was t-butyl chloride and sodium iodine. After mixing the two compounds, there was only a slight tint to the liquid but remained clear and precipitate free for 6 minutes of being room temperature. We then placed it in warm water in which there was no precipitate that formed while being heated.
This test yielded a negative result. The second test that we ran was t-butyl chloride and silver nitrate. Directly after mixing the compounds, there was an immediate white precipitate that had formed. This test yielded a positive result. A negative result with sodium iodide and a positive result of silver nitrate concluded that our solution of t-butyl chloride was a pure tertiary alkyl halide. Our third test was run with t-chloro butane and sodium iodide. This test initially did not form a precipitate while it was kept at room temperature. We then used a warm water bath in which after 5 minutes the solution formed a white precipitate and a yellow liquid. This shows that this test was a positive test. The fourth test was with t-chloro butane and silver nitrate. This test did not form a precipitate at room temperature or during the steam bath. This shows a negative result. With the t-chloro butane, the negative result with silver nitrate and the positive result of sodium iodide prove that this is indeed a primary alkyl halide.
Conclusion
In this lab, we properly carried out an SN1 reaction from t-butyl alcohol to t-butyl chloride and found that we did in fact create at-butyl chloride by getting a positive result from our silver nitrate test in the end. Although we weren’t able to visibly see with our eye the nucleophilic attack, the steps that we carried out in the lab showed the separated layers and that there were reactions going on during each step. The organic layer that was continuously washed was undergoing the slow reaction process during each separating stage. In the end, after the distillation of the solution, the SN1 reaction was completely carried out. The information from this data has revealed that it is possible to carry out an SN1 reaction in a lab; however, in the process of washing the product, there will be a lot of material lost giving a low percent yield in the end. It would be smart to use chemicals that are inexpensive and in large quantities to carry out these types of reactions. The information and techniques performed in this lab could be applied to other situations in an industrial setting. One example of this could be creating chlorofluorocarbons which used to be produced for aerosol cans and other products. Although these are no longer widely used in the world due to the ozone effect, the SN1 reaction could be done with these chemicals. Overall, the lab accomplished what it was set out to do.
Reference
- “Chemical Book. ” 2008.
- http://www.chemicalbook.com/ProductIndex_EN. asp&xgt; Solomons, T. W. Graham, and Craig Fryhle. Organic Chemistry. 10th. 1. New Jersey: John Wiley & Sons, Inc., 2011. 99-102.
