Download Questions on Reaction of Ethers and Epoxides - Assignment | CHEM 302 and more Assignments Organic Chemistry in PDF only on Docsity! CHEM302, Spring 2009 Dr. Ruder 1 Class Activity 2 Reactions of Ethers and Epoxides Ethers are not very reactive but ring-strained epoxides react easily. Model 1: Ether Cleavage with HBr In the presence of strong acids like HBr and HI, ethers are cleaved to form alkyl halides. R O R' H Br+ R O R' H + Br ROH + R'Br HBr RBr + H2O step 1 step 2 step 3 Questions 1. (a). What is the role of the ether in step 1 of Model 1 (nucleophile, electrophile, acid, base)? (b). Draw curved arrows to show electron movement for step 1. (c). What purpose does this first step serve and what is this process called? (d). Compare the reaction of an ether with acid (step 1) to the reaction of an alcohol with acid. Are there any differences? Explain. 2. For step 2 of the reaction shown in Model 1: (a). Draw curved arrows to show electron movement for step 2. (b). What is the leaving group in step 2? (c). Assuming that the R’ group is primary, by what mechanism does the reaction in step 2 occur (SN1, SN2, E1, E2, addition)? Explain. 3. In step 3 of the reaction shown in Model 1, the alcohol reacts with an additional equivalent of HBr to form an alkyl bromide. Draw the complete mechanism for step 3. 4. (a). The reaction of the phenyl ethyl ether with HBr is shown below. Draw the mechanism, using curved arrows to show electron movement. O CH2CH3 HBr OH CH3CH2Br + excess CHEM302, Spring 2009 Dr. Ruder 2 (b). Once your group has reached agreement on the above questions, determine whether you would expect the phenol to react further with HBr to form PhBr. (HINT: substitution reactions do not occur at sp2 hybridized centers). Explain. Model 2: Reactions of Epoxides Epoxides are more reactive than acyclic ethers because three membered rings are unstable due to ring strain. Epoxides can react under acidic or basic conditions to result in a ring opening reaction. O HHO acidicbasic HO OH HO OH H2O Questions 5. Consider the acid catalyzed opening of epoxide in Model 2: (a). Draw curved arrows to show electron movement for step 1 shown below. O H H2O O H + O H H step 1 (b). Draw the mechanism for the protonation of an alcohol (ROH + H3O+), and compare to the protonation of the epoxide shown above. What is the same and what is different? (c). What is the purpose of protonation of the epoxide? (d). In the second step of the mechanism (shown below), identify the nucleophile and the electrophile. Draw curved arrows to illustrate this step. H2O O H + step 2 HO OH2 (e). What process must occur to convert the product of step 2, to the final product diol? (f). Once your group has reached agreement on the above questions, draw the product that would form if the acid catalyzed opening of epoxides was conducted in acid and methanol.
