8.7 — Smart Ways to Make Carboxylic Acids 🚀

Need a –COOH group? Choose the shortcut that fits your starting material and dive in! Every route below pops up often in competitive exams, so mastering them means quick marks. 🙌

1. Start with a Primary Alcohol or an Aldehyde 🍷 ➡️ 🧴

  • Add KMnO4, K2Cr2O7, or the Jones reagent (CrO3 + H2SO4). They push the –OH or –CHO right up to an acid.
    $$\mathrm{RCH_2OH} \;\xrightarrow[\text{any medium}]{\mathrm{KMnO_4}} \mathrm{RCOOH}$$ 🔑 You can also use mild oxidizers when the molecule is delicate. :contentReference[oaicite:0]{index=0}

2. Oxidize an Alkylbenzene 🛢️ ➡️ 🏎️

  • Vigorous hot KMnO4} or chromic acid burns the entire side-chain—no matter how long—down to a single –COOH on the ring.
    $$\text{Ar–CH}_3 \;\xrightarrow[\Delta]{\mathrm{KMnO_4}/\mathrm{H^+}}\; \text{Ar–COOH}$$ 🎉 Primary and secondary chains work; tertiary chains hardly budge. :contentReference[oaicite:1]{index=1}

3. Hydrolyze a Nitrile or an Amide 🌊

  • Nitrile first turns into an amide and then into the acid when you treat it with H+ or OH– plus water. Stop early (amides only) by lowering the temperature and time.
    $$\mathrm{RCN} \;\xrightarrow{H_2O,H^+}\; \mathrm{RCONH_2} \;\xrightarrow{H_2O,H^+}\; \mathrm{RCOOH}$$ :contentReference[oaicite:2]{index=2}

4. Use a Grignard Reagent 🧂 + CO2 = Acid

  • React RMgX with dry ice (solid CO2) to get a carboxylate. A quick acid wash liberates the carboxylic acid:
    $$\mathrm{RMgX} + \mathrm{CO_2} \;\xrightarrow{\text{dry ice}}\; \mathrm{RCOO^–MgX^+} \;\xrightarrow{H_3O^+}\; \mathrm{RCOOH}$$ 🌱 This trick adds one extra carbon—perfect for ascending the homologous series. :contentReference[oaicite:3]{index=3}

5. Hydrolyze Acyl Halides or Anhydrides 💧

  • Simply pour in water. Acyl chlorides give acids directly; anhydrides split into two acid molecules.
    $$\mathrm{RCOCl} + H_2O \rightarrow \mathrm{RCOOH} + \mathrm{HCl}$$ ⚡ Using aqueous base first forms the carboxylate, which you protonate later. :contentReference[oaicite:4]{index=4}

6. Crack Open an Ester 🥛

  • Acidic hydrolysis hands you the acid in one step:
    $$\mathrm{RCOOR’} + H_2O \xrightarrow{H^+} \mathrm{RCOOH} + \mathrm{R’OH}$$
  • Basic hydrolysis (saponification) yields a carboxylate first, then you add acid to finish the job.
    $$\mathrm{RCOOR’} + \mathrm{OH^-} \rightarrow \mathrm{RCOO^-} + \mathrm{R’OH}$$ $$\mathrm{RCOO^-} \xrightarrow{H^+} \mathrm{RCOOH}$$ :contentReference[oaicite:5]{index=5}

High-Yield NEET Nuggets 🎯

  1. Side-chain oxidation of any alkylbenzene with hot KMnO4 always gives benzoic acid. Memorize this—it shows up frequently! :contentReference[oaicite:6]{index=6}
  2. Grignard + CO2 adds one carbon atom, a favorite for “ascending the series” questions. :contentReference[oaicite:7]{index=7}
  3. Nitrile → Amide → Acid sequence appears in multi-step conversions. Practice stopping at the amide under mild conditions. :contentReference[oaicite:8]{index=8}
  4. Ester hydrolysis: know the contrast—acidic gives the acid directly, basic needs a final protonation. :contentReference[oaicite:9]{index=9}
  5. Acyl halides and anhydrides hydrolyze lightning-fast, so chemists use them when they need an acid fast. :contentReference[oaicite:10]{index=10}

Keep these pathways at your fingertips, sketch the arrows, and you’ll ace the synthesis questions with a smile! 😄