Q14P - Organic Chemistry (Mcmurry)

Question

Show all the steps in the acid-catalyzed formation of a cyclic acetal from ethylene glycol and an aldehyde or ketone.

Step-by-Step Solution

Answer

                                     Protonation on the carbonyl group

                           Attack of one hydroxyl group from ethylene glycol

                   Formation of a protonated hydroxyl group

                                          Formation of new carbonyl

                                       Attack by the other hydroxyl group

                                               Formation of acetal

Step1: Cyclic acetals

Cyclic acetals are five or higher monomers that contain at least one unit in which two oxygen atoms are flanked by a substituted or unsubstituted methylene group. 

Step 2: Acid-catalyzed formation of a cyclic acetal

The initial step begins with the catalytic acid is protonated on the carbonyl group.

                                        Protonation on the carbonyl group

To the protonated carbonyl group, one hydroxyl from ethylene glycol is attacked.

                      Attack of one hydroxyl group from ethylene glycol

In this a proton shift takes place and it produces a protonated hydroxyl group.

                                  Formation of a protonated hydroxyl group

Removal of a water molecule by the ether oxygen and formation of a new carbonyl.

                                        Formation of new carbonyl

            Attack by the other hydroxyl group of ethylene glycol to the new carbonyl

Finally, the protonated oxygen will lose a proton and form the protected carbonyl product.

                                                   Formation of acetal