Which of the following reagents can be used to convert a primary alcohol into a carboxylic acid?

• A. $\mathrm{LiAlH}4$ (lithium aluminum hydride)
• B. $\mathrm{NaBH}4$ (sodium borohydride)
• C. $K_2{\mathrm{Cr}}_2{O}_7$ with $H_2\mathrm{SO}4$ (potassium dichromate in sulfuric acid)
• D. $\mathrm{PCC}$ (pyridinium chlorochromate)

Answer: (C)

Verified step by step guidance

1. Identify the goal: converting a primary alcohol into a carboxylic acid requires a strong oxidation reaction that fully oxidizes the alcohol beyond the aldehyde stage.
2. Understand the reagents: LiAlH4 (lithium aluminum hydride) and NaBH4 (sodium borohydride) are reducing agents, so they will not oxidize the alcohol but rather reduce compounds, thus they are not suitable for this transformation.
3. PCC (pyridinium chlorochromate) is a mild oxidizing agent that typically oxidizes primary alcohols only to aldehydes, not further to carboxylic acids.
4. Potassium dichromate (K2Cr2O7) in sulfuric acid (H2SO4) is a strong oxidizing agent capable of fully oxidizing primary alcohols to carboxylic acids by first forming an aldehyde intermediate and then further oxidizing it to the acid.
5. Therefore, the reagent that can convert a primary alcohol into a carboxylic acid is potassium dichromate in sulfuric acid, as it provides the necessary oxidative strength to complete the transformation.