Which oxidant selectively stops at an aldehyde when oxidizing a primary alcohol?

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Multiple Choice

Which oxidant selectively stops at an aldehyde when oxidizing a primary alcohol?

The key idea is how strong the oxidant is and how much water is present. PCC (pyridinium chlorochromate) in a dry, non-aqueous solvent is a mild oxidant, so it converts a primary alcohol to an aldehyde and stops there under controlled conditions. The low water content prevents formation of the hydrated form that would lead to further oxidation to the carboxylic acid, so you get the aldehyde selectively. Jones oxidation uses chromium trioxide in aqueous acid, a much stronger, water-rich system. The aldehyde formed from a primary alcohol is readily oxidized further under these conditions to the carboxylic acid, so it does not stop at the aldehyde. Since Jones oxidation pushes beyond the aldehyde and PCC under proper conditions stops at the aldehyde, the method that selectively yields the aldehyde is PCC in a suitable solvent.

The key idea is how strong the oxidant is and how much water is present. PCC (pyridinium chlorochromate) in a dry, non-aqueous solvent is a mild oxidant, so it converts a primary alcohol to an aldehyde and stops there under controlled conditions. The low water content prevents formation of the hydrated form that would lead to further oxidation to the carboxylic acid, so you get the aldehyde selectively.

Jones oxidation uses chromium trioxide in aqueous acid, a much stronger, water-rich system. The aldehyde formed from a primary alcohol is readily oxidized further under these conditions to the carboxylic acid, so it does not stop at the aldehyde.

Since Jones oxidation pushes beyond the aldehyde and PCC under proper conditions stops at the aldehyde, the method that selectively yields the aldehyde is PCC in a suitable solvent.

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