Organic Chemistry Lab I (CHEM 237) Experiment 11: Kinetic Study of SN1 Solvolysis
List the procedural steps, from start to finish, that are required to convert 1-chloro-1-phenylethane into 1-phenylethanol via SN1 solvolysis in water.
The reaction is performed in ethanol/water, and will be monitored by bromothymol blue. A measured aliquot of hydroxide base is added from a burette. The alkyl halide is added and the timer is started. The time taken for the solution to turn from blue to green is recorded. The process of adding measured aliquots of base, and timing the color change is repeated several times. The reaction flask is then heated on a steam bath for twenty minutes before being titrated against base to find the amount of acid remaining in solution.
1-chloro-1-phenylethane undergoes solvolysis in water by an SN1 mechanism to make 1-phenylethanol. The reaction is followed with bromothymol blue indicator and an aliquot of sodium hydroxide base. Which of the following statements about the reaction are true?
The color of the bromothymol blue indicator changes from blue to yellow as the solution becomes acidic. Rate of gain of acid is equal to the rate of loss of alkyl halide. The reaction can be followed because acid is produced as a product. The reaction follows first order kinetics because there is one reactant in the rate determining step.
Rank the SN1 reaction rates for the following compounds:
The slow step of an SN1 reaction is the breakage of the carbon-halogen bond and formation of a carbocation. The more stable the carbocation, the faster the reaction. Therefore, the fastest SN1 substitution occurs in tertiary alkyl halides, and the slowest in primary alkyl halides. The reaction rate is decreasing in the following order: 2-iodo-2-methylhexane > 3-iodo-2-methylhexane > 1-iodo-2-methylhexane > iodomethane. Since primary carbocations are too unstable, the rate of SN1 reaction in primary alkyl halides is negligible. Primary alkyl halides undergo only SN2 substitution.
