Question

13 SN1: Synthesis of tert-Butyl Chloride Alkyl halides can be prepared from their corresponding alcohols via an acid catalyzed substitution reaction. The mechanism of these acid catalyzed substitution reactions are labeled as Syl (substitution, nucleophilic, unimolecular) and S2 (substitution, nucleophilic, bimolecular). Tertiary alcohols follow the Snl route, primary alcohols follow the S2 route, and secondary alcohols can follow either path. Under acidic conditions, the mechanism (Figure 1) of the Sul reaction involves rapid protonation of the alcohol, followed by the loss of water as the rate-determining step. This generates a relatively stable carbocation which is then attacked by the halide ion to form the alkyl halide. Syl reactions are favored by tertiary alcohols because they tend to form more stable carbocations. CH₂ H HC OH- - HO CH₂ a Cho CH HC OH нус 2 HC HC Figure / Conversion of t-butanol into t-butyl chloride by an Syl mechanism The product will be verified by gas chromatography by comparing the chromatograms of the starting material, tert-butyl chloride standard, and your product. Confirmation of your product, Tert-butyl chloride, can also be performed by reacting the product with a solution of silver nitrate in ethanol. The tertiary alkyl halide will react by means of an Snl mechanism with the silver nitrate to form an insoluble silver halide. The appearance of a precipitate indicates a positive result indicating the presence of a tertiary alkyl halide. OBJECTIVES In this experiment, you will • Synthesize tert-butyl chloride via an Sxl reaction. • Confirm the presence of a tertiary alkyl halide using the silver nitrate test • Verify the product by gas chromatography. MATERIALS Part Synthesis of tert-Butyl Chloride 25 ml graduated cylinder 10 mL graduated cylinder 50 mL beaker 250 mL beaker 125 mL Erlenmeyer flask separatory funnel apparatus glass funnel disposable Pasteur pipets and bulb two 10 mL glass vials and caps hydrochloric acid, concentrated tert-butanol, reagent grade saturated sodium bicarbonate solution saturated sodium chloride solution sodium sulfate, anhydrous DI water ice

Answer 1

(CH3)3Cô+--- +OH (CH3)3C +___6-CI (CH3)2COHO+---5+H (CH3)3C++CH (CH3)3COH+H* (CH3)2COH, (CH3)3CCI

As you can see in the potential energy diagram above, the Activation energy required for the loss of water from the protonated alcohol is very large, this indicates that this step is the slowest step in this reaction, also this step is exothermic because the product, carbocation, is situated higher than the reactant, protonated alcohol for this step. Therefore, change in energy or enthalpy is positive for this step.

On the other hand, the last step in which the carbocation combines with the chloride ion, is an exothermic step, as the product, alkyl chloride, is situated lower than the reactants, carbocation and chloride ionm in the potential energy diagram. Also the activation energy is smaller for this step which indicates that it is a faster reaction.

The molecularity of the protonation of alcohol is 2, as the alcohol molecule is accepting a proton in this step.

The molecularity of loss of water from protonated alcohol is 1, it is a unimolecular step.

The attack of chloride ion on the carbocation takes place in a bimolecular step.