Draw the correct organic product for the oxidation reaction: Select Draw Rings More // C H O Na2Cr207, acetone H2SO4 OH Give the product expected when the following alcohol reacts with pyridinium chlorochromate (PCC). (Assume that PCC is present in excess.) Draw the product OH PCC CH2Cl2 HO H
The correct answer and explanation is:
Correct Answer:
The oxidation reaction of the alcohol with pyridinium chlorochromate (PCC) in CH₂Cl₂ will result in the formation of a carbonyl compound. The specific product depends on the type of alcohol being oxidized.
- If the alcohol is primary (R-CH₂OH): PCC will oxidize it to an aldehyde (R-CHO).
- If the alcohol is secondary (R₁-CH(OH)-R₂): PCC will oxidize it to a ketone (R₁-CO-R₂).
- If the alcohol is tertiary (R₁R₂R₃-C-OH): No reaction occurs because tertiary alcohols lack a hydrogen atom on the carbon bonded to the -OH group, which is necessary for oxidation.
Example:
For a secondary alcohol like cyclohexanol (C₆H₁₁OH), the oxidation by PCC will yield cyclohexanone (C₆H₁₀O).
Reaction: Cyclohexanol → Cyclohexanone
Explanation (300 words):
PCC (C₅H₅NH[CrO₃Cl]) is a mild oxidizing agent commonly used to selectively oxidize alcohols. It operates under anhydrous conditions (e.g., in CH₂Cl₂), making it ideal for synthesizing aldehydes and ketones without over-oxidation.
Mechanism:
- Primary Alcohols: PCC oxidizes primary alcohols to aldehydes by removing two hydrogens—one from the hydroxyl group and one from the carbon directly attached to it. This reaction avoids further oxidation to carboxylic acids because PCC lacks water, which is needed to hydrate aldehydes for over-oxidation.
- Secondary Alcohols: PCC oxidizes secondary alcohols to ketones by removing the same two hydrogens. Since ketones cannot be oxidized further under these conditions, the reaction stops at the ketone stage.
- Tertiary Alcohols: Tertiary alcohols do not react with PCC as they lack a hydrogen atom on the carbon attached to the hydroxyl group.
PCC is a preferred reagent because it offers excellent selectivity, works under mild conditions, and avoids unwanted over-oxidation. This makes it valuable for synthesizing sensitive aldehydes and ketones in organic chemistry. Its use in inert solvents like CH₂Cl₂ ensures minimal side reactions, preserving the integrity of the target molecules.