Chapter 19.5, Problem 8PTS

Interpretation Introduction

Interpretation: The mechanism should be drawn for the following transformation.

Concept Introduction:

Acetal formation: Acetal derivative of aldehyde and ketone are prepared by an acid catalyzed dehydration reaction with alcohols and diols.

Acetals are germinal-diether derivatives of aldehydes or ketones.

Ketone derivatives of acetal once called ketal, but in modern usages has dropped this name.

Acid catalyzed formation reaction mechanism:

Step-1: An acid or base reaction, there is only a weak nucleophile we need to active the carbonyl group by protonating on O.

Step2: The nucleophilic O in the alcohol attacks the electrophilic C in the C=O, braking the pi-bond and giving the electrons to the positive O.

Step-3: An acid or base reaction, deprotonation of alcoholic oxonium ion neutralizes the charging giving the hemi acetal.

Step-4: In order for the –OH to leave we need to make it a better leaving group by protonation.

Step 5: Using the electrons form the other O leaving group departure is facilitated.

Step-6: The Nucleophilic O of the alcohol attacks the electrophilic C and the electrons of the pi- bonds to move to neutralize the charge on the positive O.

Step-7: Deprotonation of the alcoholic oxonium neutralizes the charge the charge on the positive O.