Alcohols Routes
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Flashcards in this deck (14)

  • What are the reagents and conditions for industrial hydration (electrophilic addition) of alkenes to form alcohols?

    • Reagent: H2O (steam)
    • Conditions: 300°C, 6.5Ă—10^3 kPa, concentrated H3PO4 catalyst
    • Context: In industry
    alkene hydration industrial

  • What reagent and conditions form alkyl hydrogen sulfate from an alkene in the lab?

    • Reagent: Concentrated H2SO4
    • Conditions: Cold
    • Mechanism: Electrophilic addition
    alkene electrophilic lab

  • How is alkyl hydrogen sulfate converted to an alcohol (hydrolysis)?

    • Reagents: Alcohol, H2O
    • Condition: Warm
    • Process: Hydrolysis
    alkylhydrogensulphate hydrolysis

  • Which reducing reagent is used for nucleophilic addition to aldehydes/ketones that requires aqueous ethanolic conditions and reflux?

    • Reagent: NaBH4
    • Method: Aqueous ethanolic, reflux
    • Note: Provides H-; NaBH4 does not reduce benzene
    aldehyde ketone reduction

  • Which reducing reagent for carbonyls must be used anhydrous with alcohol and reflux and can reduce benzene?

    • Reagent: LiAlH4
    • Method: Anhydrous, alcohol, reflux
    • Note: LiAlH4 does reduce benzene
    aldehyde ketone lialh4

  • What are the reagent and conditions for catalytic hydrogenation of aldehydes/ketones?

    • Reagent: H2 with Ni catalyst
    • Condition: 150°C
    • Effect: Reduces carbonyls (does reduce benzene at these conditions)
    hydrogenation aldehyde ketone

  • What are the reagent, catalyst, condition, and product for dehydration (elimination) of alcohols?

    • Reagent: None (mechanism: elimination)
    • Catalyst: Concentrated H2SO4
    • Condition: 180°C
    • Product: Alkene
    alcohol elimination dehydration

  • How is a primary alcohol oxidized to an aldehyde using potassium dichromate?

    • Reagent: K2Cr2O7 + dilute H2SO4
    • Condition: Warm, distil
    • Product: Aldehyde
    alcohol oxidation aldehyde

  • How is a primary alcohol oxidized to a carboxylic acid using excess oxidant?

    • Reagent: Excess K2Cr2O7 + dilute H2SO4
    • Condition: Reflux
    • Product: Carboxylic acid
    alcohol oxidation carboxylicacid

  • What reagent and condition oxidize a secondary alcohol to a ketone?

    • Reagent: K2Cr2O7 + dilute H2SO4
    • Condition: Heat
    • Product: Ketone
    alcohol oxidation ketone

  • What are the reagents, catalyst, condition, and product for esterification of a carboxylic acid?

    • Reagent: Alcohol
    • Catalyst: Concentrated H2SO4
    • Condition: Reflux
    • Product: Ester
    carboxylicacid esterification ester

  • Which reagents produce esters via nucleophilic addition–elimination?

    • Reagents: Acyl chloride or acid anhydride
    • Product: Ester
    ester acyl anhydride

  • What are the reagents, conditions, and product for nucleophilic substitution of haloalkanes with hydroxide?

    • Reagent: OH- as nucleophile
    • Conditions: Warm, aqueous
    • Product: Alcohol
    haloalkane nucleophilesubstitution

  • What reagents and conditions are listed in the text for fermentation of glucose to alcohol?

    • Reagent: None
    • Catalyst: Yeast
    • Condition: 37°C, anaerobic
    • Product: Alcohol
    glucose fermentation ethanol
Study Notes

Quick overview

  • These notes summarize common reaction routes between alkenes, alcohols, aldehydes/ketones, carboxylic acids, esters, haloalkanes and glucose (fermentation). Focus is on reagents, conditions, products and mechanism types.

Alkenes — electrophilic addition (hydration)

  • Reaction: alkene + water → alcohol (hydration) via electrophilic addition.
  • Industrial conditions: steam hydration using H2O (steam), catalyst conc. H3PO4, typically \(300^\circ\mathrm{C}\) and \(6.5\times10^{3}\ \mathrm{kPa}\).
  • Mechanism outline: alkene pi bond attacks H+, forms carbocation, water attacks carbocation, deprotonation gives alcohol (Markovnikov addition).

Alkyl hydrogen sulfate (lab route) and hydrolysis

  • Formation (electrophilic addition): alkene + concentrated H2SO4 → alkyl hydrogen sulfate (cold, lab method).
  • Hydrolysis: alkyl hydrogen sulfate + H2O (or alcohol) + heat → alcohol (or ester) after acid workup.
  • Notes: this is a two-step lab route to hydration; industrial hydration (acid-catalysed steam) is often preferred for large scale.

Aldehydes and ketones — nucleophilic addition (reduction)

  • General: the carbonyl carbon is electrophilic; nucleophilic hydride donors reduce C=O to alcohol (nucleophilic addition mechanism).

NaBH4

  • Reagent: NaBH4 in aqueous ethanolic solution.
  • Conditions: usually room temp to reflux depending on substrate; method commonly described as aqueous/ethanolic.
  • Selectivity: reduces aldehydes and ketones, does not reduce aromatic rings (benzene).

LiAlH4

  • Reagent: LiAlH4 (LAH) in anhydrous solvent (ether), quench with alcohol/water after reaction.
  • Conditions: anhydrous, controlled addition and reflux as needed.
  • Reactivity: much stronger than NaBH4; reduces aldehydes, ketones and some other reducible groups; handle under dry conditions.

Catalytic hydrogenation (H2 / Ni)

  • Reagent/conditions: H2 with Ni catalyst at elevated temperature (example note: \(150^\circ\mathrm{C}\) reported).
  • Reactivity: reduces C=O to alcohol and can reduce other unsaturated systems depending on conditions (may reduce aromatic rings under forcing conditions).

Alcohols — elimination and oxidation

Elimination (dehydration to alkenes)

  • Reaction: alcohol → alkene + H2O via elimination (E1/E2).
  • Reagent/catalyst: concentrated H2SO4 (acid catalyst), heat (example condition: \(180^\circ\mathrm{C}\)).
  • Mechanism: protonation of OH, loss of water to form carbocation (for tertiary/secondary) or concerted elimination for primary, then deprotonation gives alkene.

Oxidation of primary alcohols

  • Mild oxidation (stop at aldehyde): oxidant potassium dichromate (\(\mathrm{K_2Cr_2O_7}\)) + dilute H2SO4, warm and distil to remove aldehyde as formed.
  • Strong/complete oxidation (to carboxylic acid): excess oxidant (\(\mathrm{K_2Cr_2O_7}\) + H2SO4), heat under reflux.
  • Key control: distillation or limiting oxidant helps isolate aldehyde; excess oxidant and reflux push to carboxylic acid.

Oxidation of secondary alcohols

  • Reagent: \(\mathrm{K_2Cr_2O_7}\) + dilute H2SO4, heat (reflux) → ketone.
  • Tertiary alcohols generally resist oxidation under these conditions (no H on carbon bearing OH).

Carboxylic acids — esterification (Fischer esterification)

  • Reaction: carboxylic acid + alcohol ⇌ ester + water.
  • Conditions: conc. H2SO4 as acid catalyst, heat under reflux; equilibrium can be shifted by removing water or using excess reagent.
  • Product: ester (named by alcohol + acid portions).

Esters — synthesis from acyl derivatives

  • From acyl chloride: acyl chloride + alcohol → ester + HCl; fast, high yield; mechanism: nucleophilic acyl substitution (addition–elimination).
  • From acid anhydride: acid anhydride + alcohol → ester + carboxylic acid (or its derivative); also nucleophilic acyl substitution.
  • Notes: acyl chlorides are more reactive than anhydrides; both bypass equilibrium limitations of Fischer esterification.

Haloalkanes — nucleophilic substitution

  • Reaction: haloalkane + nucleophile (e.g., OH–) → substituted product via SN1 or SN2 depending on substrate.
  • Example: haloalkane + aqueous OH– (warm) → alcohol; conditions favour SN2 for primary, SN1 for tertiary.
  • Acid-catalysed reactions with alcohol (H2O + dilute H2SO4, heat/reflux) can give substitution or, with alcohol solvent and acid, can give ether/ester side-products depending on reagents.
  • Note: hydrolysis of haloalkanes normally yields alcohols; ester formation requires reaction with an acid derivative or acid-catalysed alcohol substitution.

Glucose — fermentation

  • Biological route: glucose → ethanol (alcohol) + CO2 in presence of yeast (anaerobic conditions).
  • Typical conditions: about \(37^\circ\mathrm{C}\) and absence of oxygen (anaerobic). Product commonly called ethanol.

Mechanism summary (short)

  • Electrophilic addition: alkene pi bond attacks electrophile → carbocation intermediate → nucleophile attacks.
  • Nucleophilic addition (carbonyl): nucleophile (hydride, etc.) attacks C=O → alkoxide intermediate → protonation → alcohol.
  • Nucleophilic acyl substitution: nucleophile adds to carbonyl of acyl derivative → tetrahedral intermediate → leaving group departs → new acyl compound.
  • Nucleophilic substitution (haloalkanes): SN2 = backside attack (concerted); SN1 = carbocation intermediate (two-step).

Key practical tips & comparisons

  • To reduce aldehydes/ketones selectively use NaBH4; use LiAlH4 when stronger reducing power required but must be anhydrous.
  • To isolate aldehyde from primary alcohol oxidations: use mild oxidant/short reaction time and distillation to remove aldehyde.
  • Fischer esterification is equilibrium-controlled; use excess alcohol or remove water to drive to products.
  • Industrial hydration of alkenes (steam + H3PO4) is used when high throughput and continuous conditions are needed.

Common reagents & shorthand cheat-sheet

  • Oxidant: \(\mathrm{K_2Cr_2O_7}\) + H2SO4 (oxidation of alcohols).
  • Mild hydride donor: NaBH4 (reduces C=O, not aromatic rings).
  • Strong hydride donor: LiAlH4 (reduces many functional groups; dry conditions).
  • Catalytic hydrogenation: H2 + Ni (reduces C=O and C=C under suitable conditions).
  • Acid catalysts: conc. H2SO4 or conc. H3PO4 for dehydration/esterification/hydration.