Organic Name Reaction:
Organic Name Reaction
Clemmensen Reduction
The Clemmensen reduction is a method used to convert carbonyl groups (specifically ketones) in aromatic compounds to methylene groups (-CH₂-). It is particularly useful for reducing aryl ketones that are resistant to other reduction methods like Wolff-Kishner. The reaction employs zinc amalgam (Zn/Hg) and concentrated hydrochloric acid (HCl) as the reducing agent, typically heated under reflux. This reduction does not affect other functional groups like esters or nitro groups.
Mechanism (simplified): The zinc amalgam generates nascent hydrogen, which reduces the carbonyl to a carbinol intermediate, followed by dehydration and further reduction to the alkane. The exact mechanism involves acid-catalyzed enol formation and reduction.
Example:
Reduction of acetophenone (C₆H₅COCH₃) to ethylbenzene (C₆H₅CH₂CH₃).
Reactant: C₆H₅COCH₃ + Zn(Hg)/HCl (conc.)
Product: C₆H₅CH₂CH₃ + H₂O
This is commonly used in synthesizing alkylbenzenes from aroyl compounds.
Claisen Condensation
The Claisen condensation is a carbon-carbon bond-forming reaction between two esters or an ester and a carbonyl compound, catalyzed by a strong base (e.g., sodium ethoxide, NaOEt). It produces a β-keto ester, which can be hydrolyzed and decarboxylated to form ketones. It requires at least one ester with α-hydrogens for enolate formation.
Mechanism: Base deprotonates the α-carbon of one ester to form an enolate, which attacks the carbonyl carbon of another ester molecule, leading to a tetrahedral intermediate. Elimination of alkoxide gives the β-keto ester.
Example:
Ethyl acetate (CH₃COOCH₂CH₃) self-condenses to ethyl acetoacetate (CH₃COCH₂COOCH₂CH₃).
Reactants: 2 CH₃COOCH₂CH₃ + NaOEt → CH₃COCH₂COOCH₂CH₃ + CH₃CH₂OH + Na⁺
This is a key step in the synthesis of acetoacetic ester, used in organic synthesis for β-keto acids.Organic Name Reaction
Etard’s Reaction
Etard’s reaction is a method for oxidizing toluene or alkylbenzenes with a methyl group directly attached to the benzene ring to form benzaldehyde or aromatic aldehydes. It uses chromyl chloride (CrO₂Cl₂) in carbon disulfide (CS₂) as the solvent, followed by hydrolysis.
Mechanism: Chromyl chloride forms a chromate ester with the benzylic position, which upon hydrolysis yields the aldehyde without over-oxidation to carboxylic acid.
Example:
Toluene (C₆H₅CH₃) to benzaldehyde (C₆H₅CHO).
Reactant: C₆H₅CH₃ + CrO₂Cl₂ (in CS₂) → [C₆H₅CH=O·CrO₂Cl₂] → hydrolysis → C₆H₅CHO
This reaction is specific for side-chain oxidation at the benzylic position and is industrially important for vanillin production analogs.Organic Name Reaction
Friedel-Crafts Alkylation
Friedel-Crafts alkylation introduces an alkyl group onto an aromatic ring using an alkyl halide and a Lewis acid catalyst (e.g., AlCl₃). It works best on activated aromatic rings and can lead to polyalkylation due to the activating nature of the alkyl group.
Mechanism: The Lewis acid coordinates with the alkyl halide to form a carbocation, which electrophilically attacks the aromatic ring, followed by deprotonation to restore aromaticity.
Example:
Benzene (C₆H₆) with chloromethane (CH₃Cl) to toluene (C₆H₅CH₃).
Reactants: C₆H₆ + CH₃Cl + AlCl₃ → C₆H₅CH₃ + HCl + AlCl₃
Note: Rearrangement can occur (e.g., n-propyl chloride gives isopropylbenzene).
Friedel-Crafts Acylation
Friedel-Crafts acylation acylates an aromatic ring with an acid chloride or anhydride and a Lewis acid (AlCl₃), producing a ketone. Unlike alkylation, it stops at mono-substitution due to the deactivating acyl group.
Mechanism: Similar to alkylation, but forms an acylium ion (R-C≡O⁺) as the electrophile, which attacks the aromatic ring.
Example:
Benzene with acetyl chloride (CH₃COCl) to acetophenone (C₆H₅COCH₃).
Reactants: C₆H₆ + CH₃COCl + AlCl₃ → C₆H₅COCH₃ + HCl
This is widely used for synthesizing aryl ketones.
Fries Rearrangement
The Fries rearrangement converts phenolic esters to ortho- or para-hydroxyaryl ketones using a Lewis acid (AlCl₃) or sometimes acid catalysts. It’s an intramolecular Friedel-Crafts acylation variant.
Mechanism: The ester is cleaved by the Lewis acid to form an acylium ion, which rearranges and attacks the phenolic ring intra- or intermolecularly.
Example:
Phenyl acetate (C₆H₅OCOCH₃) to o- and p-hydroxyacetophenone (HO-C₆H₄-COCH₃).
Reactant: C₆H₅OCOCH₃ + AlCl₃ → (major) 4-HO-C₆H₄COCH₃
The para isomer is often favored under controlled conditions.Organic Name Reaction
Gattermann-Koch Reaction
The Gattermann-Koch reaction formylates aromatic compounds (e.g., benzene) to benzaldehyde using carbon monoxide (CO), HCl, and a Lewis acid catalyst (AlCl₃/CuCl). It’s a formylation method for deactivated rings.
Mechanism: CO and HCl form a formyl cation equivalent (HCO⁺) catalyzed by CuCl, which electrophilically attacks the aromatic ring.
Example:
Benzene to benzaldehyde (C₆H₅CHO).
Reactants: C₆H₆ + CO + HCl + AlCl₃/CuCl → C₆H₅CHO + HCl
This is less common now due to the Vilsmeier-Haack alternative but useful for phenols.
Grignard Reagent
Grignard reagents are organomagnesium halides (RMgX) formed from alkyl/aryl halides and Mg in ether. They act as strong nucleophiles and bases, adding to carbonyls to form alcohols after hydrolysis.
Preparation: RX + Mg → RMgX (e.g., in dry ether).
Mechanism (addition): The carbanion-like R⁻ attacks the carbonyl carbon, forming an alkoxide, hydrolyzed to alcohol.
Example:
Methylmagnesium bromide (CH₃MgBr) with formaldehyde (HCHO) gives ethanol (CH₃CH₂OH).
Reactants: CH₃MgBr + HCHO → CH₃CH₂OMgBr → hydrolysis → CH₃CH₂OH
Versatile for C-C bond formation.
Hell-Volhard-Zelinsky Reaction
The HVZ reaction α-halogenates carboxylic acids using phosphorus or PBr₃ and halogen (Br₂ or Cl₂), introducing a bromine at the α-position for further synthesis.
Mechanism: P forms acid bromide, enolizes, and halogenates the enol form.Organic Name Reaction
Example:
Propanoic acid (CH₃CH₂COOH) to 2-bromopropanoic acid (CH₃CHBrCOOH).
Reactants: CH₃CH₂COOH + Br₂ + P → CH₃CHBrCOOH + HBr + POBr₃
Used in amino acid synthesis.
Hunsdieker Reaction
The Hunsdieker reaction decarboxylatively halogenates silver salts of carboxylic acids with bromine to form alkyl bromides.
Mechanism: Silver carboxylate reacts with Br₂ to form R-Br, CO₂, and AgBr via radical pathway.
Example:
Silver acetate (CH₃COOAg) to methyl bromide (CH₃Br).
Reactants: CH₃COOAg + Br₂ → CH₃Br + CO₂ + AgBr
Effective for primary alkyl halides.
Hoffmann Bromamide Degradation
Hoffmann bromamide degradation shortens a carboxylic acid chain by one carbon, converting amides to primary amines using Br₂ and base (NaOH).
Mechanism: Bromination forms N-bromoamide, rearrangement to isocyanate, hydrolysis to amine.
Example:
Acetamide (CH₃CONH₂) to methylamine (CH₃NH₂).
Reactants: CH₃CONH₂ + Br₂ + 4 NaOH → CH₃NH₂ + Na₂CO₃ + 2 NaBr + 2 H₂O
Yields amines with one less carbon.
Jones Reagent
Jones reagent is a solution of chromic acid (CrO₃ in aq. H₂SO₄/acetone) used for oxidizing primary alcohols to carboxylic acids and secondary alcohols to ketones. It’s a mild, selective oxidant.
Mechanism: Chromate ester formation, followed by elimination to carbonyl.
Example:
1-Propanol (CH₃CH₂CH₂OH) to propanoic acid (CH₃CH₂COOH).
Reactant: CH₃CH₂CH₂OH + CrO₃/H₂SO₄ → CH₃CH₂COOH
Secondary: Cyclohexanol to cyclohexanone.Organic Name Reaction
Kolbe’s Reaction
Kolbe’s electrolysis decarboxylates sodium carboxylates at a mercury cathode to form alkanes (R-R) from RCOO⁻ Na⁺.
Mechanism: Anodic oxidation forms R• radicals, which couple.
Example:
Sodium acetate (CH₃COONa) to ethane (CH₃-CH₃).
Reactants: 2 CH₃COONa → CH₃CH₃ + 2 CO₂ + H₂ + 2 NaOH
Used for symmetric alkanes.
Knoevenagel Reaction
The Knoevenagel condensation is a base-catalyzed reaction between an aldehyde and an active methylene compound (e.g., malonic ester) to form α,β-unsaturated carbonyls.
Mechanism: Enolate from active methylene attacks aldehyde, dehydration.Organic Name Reaction
Example:
Benzaldehyde (C₆H₅CHO) + ethyl acetoacetate (CH₃COCH₂COOCH₂CH₃) → C₆H₅CH=CHCOCH₂COOCH₂CH₃.
Catalyst: Piperidine or base.
Meerwein-Ponndorf-Verley Reduction
MPV reduction uses aluminum isopropoxide in isopropanol to reduce ketones or aldehydes to alcohols, with transfer hydrogenation (isopropanol oxidized to acetone).
Mechanism: Aluminum coordinates to carbonyl and alkoxide, hydride transfer.
Example:
Acetophenone (C₆H₅COCH₃) to 1-phenylethanol (C₆H₅CH(OH)CH₃).
Reactants: C₆H₅COCH₃ + (CH₃)₂CHOH + Al(OiPr)₃ → C₆H₅CH(OH)CH₃ + (CH₃)₂CO
Reversible, selective for ketones.
Perkin Condensation
The Perkin reaction condenses aromatic aldehydes with acetic anhydride in the presence of acetate to form α,β-unsaturated acids.
Mechanism: Enolate from anhydride attacks aldehyde, cyclization, and hydrolysis.
Example:
Benzaldehyde + (CH₃CO)₂O + CH₃COONa → Cinnamic acid (C₆H₅CH=CHCOOH).
Used for styryl compounds.
Pinacol-Pinacolone Rearrangement
Pinacol-pinacolone rearrangement converts vicinal diols (pinacols) to carbonyl compounds (pinacolones) under acid catalysis, involving carbocation migration.
Mechanism: Protonation, water loss to carbocation, 1,2-shift of group, deprotonation.
Example:
Pinacol ((CH₃)₂C(OH)C(OH)(CH₃)₂) to pinacolone ((CH₃)₃CCOCH₃).
Reactant: (CH₃)₂C(OH)C(OH)(CH₃)₂ + H₂SO₄ → (CH₃)₃CCOCH₃ + H₂O
Group with better migratory aptitude migrates.
Reformatsky Reaction
The Reformatsky reaction forms β-hydroxy esters from α-halo esters and carbonyls using zinc.
Mechanism: Zn inserts into C-Br, forms organozinc enolate, adds to carbonyl.
Example:
Bromoacetic ester (BrCH₂COOCH₂CH₃) + acetaldehyde (CH₃CHO) → CH₃CH(OH)CH₂COOCH₂CH₃.
Reactants: BrCH₂COOCH₂CH₃ + Zn + CH₃CHO → product.
Reimer-Tiemann Reaction
Reimer-Tiemann reaction introduces an aldehyde group ortho to phenolic OH using CHCl₃ and base (NaOH), via dichlorocarbene.
Mechanism: :CCl₂ adds to phenoxide, rearranges to salicylaldehyde.
Example:
Phenol (C₆H₅OH) to salicylaldehyde (o-HO-C₆H₄CHO).
Reactants: C₆H₅OH + CHCl₃ + NaOH → o-HO-C₆H₄CHO.
Schmidt Reaction
The Schmidt reaction converts carboxylic acids or ketones to amines or amides using hydrazoic acid (HN₃) and acid.
Mechanism: For ketones, migration to nitrilium ion, hydrolysis to amide.
Example:
Acetophenone (C₆H₅COCH₃) + HN₃/H₂SO₄ → C₆H₅NHCOCH₃ (acetanilide).
Aryl migrates preferentially.
Schotten-Baumann Reaction
Schotten-Baumann reaction acylates amines with acid chlorides in aqueous base (NaOH) to form amides.
Mechanism: Nucleophilic acyl substitution, base neutralizes HCl.
Example:
Aniline (C₆H₅NH₂) + benzoyl chloride (C₆H₅COCl) → benzanilide (C₆H₅NHCO C₆H₅).
Reactants: In NaOH(aq).
Stephen’s Reduction
Stephen’s reduction converts nitriles to aldehydes using SnCl₂/HCl, followed by hydrolysis.
Mechanism: Imine salt formation, mild hydrolysis.
Example:
Benzonitrile (C₆H₅CN) to benzaldehyde (C₆H₅CHO).
Reactants: C₆H₅CN + SnCl₂/HCl → C₆H₅CH=NH₂⁺Cl⁻ → hydrolysis → C₆H₅CHO.
Tishchenko Reaction
Tishchenko reaction dimerizes aldehydes to esters using aluminum alkoxides.
Mechanism: Aluminum enolate transfers hydride and acyl.
Example:
Acetaldehyde (2 CH₃CHO) to ethyl acetate (CH₃COOCH₂CH₃).
Catalyst: Al(OEt)₃.
Williamson’s Synthesis
Williamson ether synthesis alkylates alkoxides with alkyl halides to form ethers (SN2).
Mechanism: Nucleophilic substitution.
Example:
Sodium ethoxide (NaOCH₂CH₃) + CH₃I → diethyl ether (CH₃CH₂OCH₂CH₃).
Best for primary halides.
Wittig Reaction
Wittig reaction converts carbonyls to alkenes using phosphonium ylides (Ph₃P=CHR).
Mechanism: Ylide attacks carbonyl, forms oxaphosphetane, eliminates to alkene + Ph₃PO.
Example:
Benzaldehyde (C₆H₅CHO) + Ph₃P=CH₂ → styrene (C₆H₅CH=CH₂).
Stereochemistry controllable.
Wolff-Kishner Reduction
Wolff-Kishner reduction converts carbonyls to methylene using hydrazine (N₂H₄) and base (KOH) at high temperature.
Mechanism: Hydrazone formation, carbanion via electron transfer, N₂ loss.
Example:
Cyclohexanone + N₂H₄/KOH → cyclohexane.
Complementary to Clemmensen.
Wurtz Reaction
Wurtz reaction couples alkyl halides with Na to form alkanes (R-R).
Mechanism: Radical or organosodium intermediate.
Example:
2 CH₃CH₂Br + 2 Na → CH₃CH₂CH₂CH₃ + 2 NaBr.
For symmetric alkanes.Organic Name Reaction
Aldol Condensation
Aldol condensation involves enolate addition to carbonyl, dehydration to α,β-unsaturated carbonyl.
Mechanism: Base-catalyzed enolization, addition, elimination.
Example:
2 Acetaldehyde (CH₃CHO) → crotonaldehyde (CH₃CH=CHCHO).
Self or crossed.Organic Name Reaction
Baeyer-Villiger Oxidation
Baeyer-Villiger oxidation converts ketones to esters using peracids (e.g., mCPBA), with migratory aptitude order.
Mechanism: Peracid adds, Criegee intermediate, migration of antiperiplanar group.
Example:
Acetophenone (C₆H₅COCH₃) → phenyl acetate (C₆H₅OCOCH₃).
Aryl > alkyl migration.Organic Name Reaction
Beckmann Rearrangement
Beckmann rearrangement converts oximes to amides using acid (e.g., PCl₅), anti-migrating group.
Mechanism: Protonation, migration to nitrilium, water addition.
Example:
Acetophenone oxime (C₆H₅C(CH₃)=NOH) → acetanilide (C₆H₅NHCOCH₃).
For caprolactam synthesis.Organic Name Reaction
Arndt-Eistert Synthesis
Arndt-Eistert synthesis homologates carboxylic acids to one more carbon via diazoketone and Wolff rearrangement.
Mechanism: Diazoketone + Ag₂O → ketene, adds to nucleophile.
Example:
Benzoic acid → phenylacetic acid (C₆H₅CH₂COOH).
Via C₆H₅COCHN₂.Organic Name Reaction
Benzoin Condensation
Benzoin condensation dimerizes aromatic aldehydes using cyanide catalyst to α-hydroxy ketones.
Mechanism: Cyanohydrin umpolung, enolate addition.
Example:
2 Benzaldehyde → benzoin (C₆H₅CH(OH)COC₆H₅).
CN⁻ catalyst.Organic Name Reaction
Cannizzaro Reaction
Cannizzaro reaction disproportionates aldehydes without α-H to alcohol and acid (base-catalyzed).
Mechanism: Hydride transfer between two aldehydes.
Example:
2 Formaldehyde → methanol + formate.
Or benzaldehyde to benzyl alcohol + benzoate.Organic Name Reaction
Acyloin Condensation
Acyloin condensation reduces esters to α-hydroxy ketones using Na in xylene.
Mechanism: Radical anion coupling.
Example:
Diethyl adipate → cyclopentanone precursor (HOCH₂(C=O)(CH₂)₃CH₂OH).
For cyclic ketones.Organic Name Reaction
Birch Reduction
Birch reduction reduces aromatic rings to 1,4-cyclohexadienes using Na/NH₃/EtOH.
Mechanism: Electron addition, protonation.
Example:
Benzene → 1,4-cyclohexadiene.
Anisole gives unconjugated enol ether.Organic Name Reaction
Diels-Alder Reaction
Diels-Alder is [4+2] cycloaddition of diene + dienophile to cyclohexene.
Mechanism: Concerted pericyclic.Organic Name Reaction
Example:
1,3-Butadiene + ethylene → cyclohexene.
With maleic anhydride for endo product.
Dieckmann Reaction
Dieckmann is intramolecular Claisen for diesters to cyclic β-keto esters.
Mechanism: Enolate attacks ester.
Example:
Diethyl adipate → 2-carbethoxycyclopentanone.
NaOEt catalyst.Organic Name Reaction
Curtius Reaction
Curtius rearrangement converts acid azides to isocyanates, then amines.
Mechanism: Migration to nitrene-like.
Example:
RCOOH → RCON₃ → RN=C=O → RNH₂ (via H₂O).
For amine homologation.Organic Name Reaction
Dienone-Phenol Rearrangement
Dienone-phenol rearrangement converts cyclohexadienones to phenols under acid catalysis.
Mechanism: 1,2-migration restores aromaticity.
Example:
4,4-Dimethylcyclohexa-2,5-dien-1-one → 3,4-dimethylphenol.
H₂SO₄ catalyst.
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