Which reagent is commonly used to oxidize primary alcohols to aldehydes?

Pyridinium chlorochromate (PCC) is a well-established reagent for the selective oxidation of primary alcohols to aldehydes. The reaction proceeds without further oxidation to carboxylic acids, which is a common drawback with some other oxidizing agents. PCC is favored because it provides a milder oxidation condition, allowing for the formation of aldehydes rather than over-oxidation to carboxylic acids.

In contrast, other reagents listed do not selectively achieve this transformation. KMnO4 is a strong oxidizing agent that can oxidize primary alcohols all the way to carboxylic acids and beyond. NaBH4 is a reducing agent, primarily used for the reduction of carbonyl compounds rather than oxidation. LiAlH4 is also a strong reducing agent, effective for converting esters and carboxylic acids to alcohols, but it does not oxidize primary alcohols. Therefore, the selective oxidation capability of PCC makes it the correct reagent for converting primary alcohols to aldehydes.