Draw a reaction mechanism for the reaction between 1-bromobutane and sodium t-bu

Question

Draw a reaction mechanism for the reaction between 1-bromobutane and sodium t-butoxide( 2-methyl-2-propoxide). also identify the rate determining stepand use curved arrows

Explanation / Answer

CH3CH2CH2CH2—Br + NaOH -----> CH3CH2CH2CH2—OH + NaBr . It can be understood by considering the preparation of 1-bromobutane : Preparation of 1-Bromobutane: An SN2 Reaction A common technique for converting a primary alcohol to an alkyl halide involves treating the alcohol with a hydrogen halide H-X (H-X = H-Cl, H-Br, or H-I).. This reaction is reversible, and displacing the equilibrium to the right normally involves using a large excess of the acid, a strategy in accord with the LeChatlier principle. H—X + R—OH-----> R—X + H2O D where X = Cl, Br, I 1-Bromobutane may be prepared by heating 1-butanol with hydrobromic acid, H-Br, in the presence of sulfuric acid . The mechanism for this reaction has been shown to occur in two steps . The alcohol is protonated in the first H2SO4 CH3CH2CH2CH2—OH + HBr----> CH3CH2CH2CH2—Br + H2O 1- Butanol 1- bromobutane step via a Lewis acid-base reaction to give the oxonium ion 1. This oxonium ion then undergoes displacement by the bromide ion to form 1-bromobutane and water. This process is an SN2 reaction in which water is the leaving group and bromide ion is the nucleophile. The sulfuric acid serves two important purposes: (1) It is a dehydrating agent that reduces the activity of water and shifts the position of equilibrium to the right, and (2) it provides an added source of hydrogen ions to increase the concentration of oxonium ion 1. The use of concentrated hydrobromic acid also helps to establish a favorable equilibrium. No reaction occurs between 1-butanol and NaBr in the absence of strong acid, because leaving groups in nucleophilic substitution reactions must be weakly basic, as is water in Equation . If the reaction of 1-butanol and NaBr were to occur ), the leaving group would necessarily be the strongly basic hydroxide ion; thus the forward reaction ..does not occur. On the other hand, the reverse reaction between 1-bromobutane and hydroxide proceeds readily, since the leaving group in this reaction is the weakly basic bromide ion. CH3CH2CH2CH2—OH + NaBr -----> CH3CH2CH2CH2—Br + NaOH

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