Preparation of aldehydes and ketonesऐल्डिहाइड और कीटोन बनाने की विधियाँPreparation of aldehydes and ketones

Class 12 Chemistry · Chapter 8 · interactive diagram

Parts and what they mean

• Primary alcohol (RCH₂OH) (प्राथमिक ऐल्कोहॉल (RCH₂OH)) — Oxidation or dehydrogenation gives an aldehyde.
• Secondary alcohol (R₂CHOH) (द्वितीयक ऐल्कोहॉल (R₂CHOH)) — Oxidation gives a ketone.
• Aldehyde formed (बना ऐल्डिहाइड) — With strong oxidants it would go on to the acid, so PCC (pyridinium chlorochromate) is used to stop here.
• Ketone formed (बना कीटोन) — Ketones resist further mild oxidation.
• Hydrogen (dehydrogenation) (हाइड्रोजन (विहाइड्रोजनन)) — Alcohol vapour over heated Cu or Ag loses H₂ — an industrial method for volatile alcohols.
• Alkene (but-2-ene) for ozonolysis (ओज़ोनोलिसिस हेतु ऐल्कीन (ब्यूट-2-ईन)) — O₃ then Zn dust + water cleaves C=C into two C=O groups (NCERT Example 8.1 vi).
• Two molecules of ethanal (एथेनैल के दो अणु) — The product depends on the substitution pattern of the alkene: aldehydes, ketones or a mixture.
• Ethyne + water (एथाइन + जल) — Hydration in the presence of H₂SO₄ and HgSO₄.
• Acetaldehyde — the ONLY aldehyde from alkyne hydration (ऐसीटैल्डिहाइड — ऐल्काइन जलयोजन से बनने वाला एकमात्र ऐल्डिहाइड) — Ethyne gives ethanal; every other alkyne gives a ketone.
• Propyne (प्रोपाइन) — Hydration follows Markovnikov’s rule (NCERT Intext 8.2 iii).
• Propanone (acetone) (प्रोपेनोन (ऐसीटोन)) — Other alkynes give ketones.
• Acyl chloride + hydrogen (ऐसिल क्लोराइड + हाइड्रोजन) — Hydrogenated over palladium on barium sulphate — Rosenmund reduction.
• Aldehyde + HCl (Rosenmund reduction) (ऐल्डिहाइड + HCl (रोज़ेनमुंड अपचयन)) — BaSO₄ poisons (partly deactivates) Pd so the aldehyde is not reduced further to an alcohol.
• Nitrile (RCN) (नाइट्राइल (RCN)) — Reduced by stannous chloride + HCl.
• Imine intermediate (RCH=NH) (इमीन मध्यवर्ती (RCH=NH)) — Hydrolysis of the imine gives the aldehyde.
• Aldehyde (Stephen reaction) (ऐल्डिहाइड (स्टीफ़न अभिक्रिया)) — RCN → RCH=NH → RCHO.
• Unsaturated nitrile (असंतृप्त नाइट्राइल) — DIBAL-H [diisobutylaluminium hydride, AlH(i-Bu)₂] reduces –CN selectively to an imine, then water gives –CHO.
• Aldehyde — the C=C is NOT reduced (ऐल्डिहाइड — C=C अपचयित नहीं होता) — Shows the selectivity of DIBAL-H.
• Ester (एस्टर) — Esters are also reduced to aldehydes by DIBAL-H.
• Aldehyde from the ester (undecanal) (एस्टर से ऐल्डिहाइड (अनडेकेनैल)) — CH₃(CH₂)₉CHO; the –OC₂H₅ part leaves as ethanol.

Original diagram drawn by Simple Learning Hub, based on the NCERT textbook. Report a mistake