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Carboxylic acids Flashcards

1
Q

Physical properties of carboxylic acids and derivatives

A

Structure: Simple molecular structure
1. Higher BP than alkenes (hydrogen bond between carboxylic acid molecules > idid)
2. BP increases down the group
3. Higher BP than alcohols with same alkyl chain
( Alcohols have electron withdrawing carbonyl group –> -OH group more polarised –> carboxylic acid forms stronger intermolecular hydrogen bonds than alcohols –> more energy needed )
4. Higher BP than acyl chlorides and esters
(Hydrogen bond vs pdpd)
5. Soluble in water
6. Insoluble in organic solvents

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2
Q

Structure and bonding of acyl chlorides and esters

A

For both:
Bonding: pdpd
Structure: simple molecular structure

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3
Q

Synthesis of carboxylic acid

A
  1. oxidative cleavage of alkenes
  2. oxidation of primary alcohols
  3. oxidation of aldehydes
  4. acidic hydrolysis of nitriles
  5. hydrolysis of acyl chlorides
  6. hydrolysis of esters
  7. hydrolysis of amides
  8. side-chain oxidation to give benzoic acid
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4
Q

oxidative cleavage of alkenes

A

Hot KMnO4, H2SO4(aq)

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5
Q

oxidation of aldehyde

A

K2Cr2O7/KMnO4, H2SO4(aq), heat under reflux

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6
Q

oxidation of primary alcohol

A

K2Cr2O7/KMnO4,H2SO4(aq), heat under reflux

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7
Q

Side-chain oxidation to give benzoic acid

A

KMnO4, H2SO4(aq), heat under reflux
–> white ppt of benzoic acid

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8
Q

Acidic hydrolysis of nitriles

A

HCl/H2SO4(aq), heat under reflux

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9
Q

Hydrolysis of amides
(Synthesis of carboxylic acids)

A

H2SO4(aq), heat under reflux

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10
Q

Hydrolysis of acyl chlorides

A

H2O(l), rtp (milder conditions because acyl chlorides are very reactive)

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11
Q

Hydrolysis of esters

A

HCl/H2SO4(aq), heat under reflux

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12
Q

Reactions of carboxylic acids

A
  1. condensation to form esters
  2. nucleophilic substitution to form acyl chlorides
  3. redox (acid-metal)
  4. Acid-base
  5. Acid-carbonate
  6. oxidation of ethanedioic acid
  7. oxidation of methanoic acid
  8. reduction to form alcohols
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13
Q

Condensation to form esters
(carboxylic acid)

A

alcohol, concentrated H2SO4, heat under reflux

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14
Q

Nucleophilic substitution to form acyl chloride
(carboxylic acid)

A

PCl5, room temperature OR
PCl3, heat under reflux OR
SOCl2, heat under reflux

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15
Q

Redox (acid-metal)
(carboxylic acid)

A

Na(s) ,produce H2 gas
OH –> O-Na+

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16
Q

Acid-base
(carboxylic acid)

A

NaOH(aq), produce H2O
OH–>O-Na+

16
Q

Acid-carbonate
(carboxylic acid)

A

Na2CO3(aq), produce CO2 and H2O
OH–>O-Na+

16
Q

Oxidation of methanoic acid
(carboxylic acid)

A

K2Cr2O7/KMnO4, H2SO4(aq), heat under reflux
–> must have H on C atom thus oxidation occurs

17
Q

Oxidation of ethanedioic acid
(carboxylic acid)

A

*special case for strong oxidation
KMnO4, H2SO4(aq), heat under reflux

18
Q

Reduction of alcohols
(carboxylic acid)

A

LiAlH4 in dry ether

19
Q

Synthesis of acyl chlorides + reagents

A

Nucleophilic substitution (carboxylic acid)
- PCl5, room temperature OR
PCl3, heat under reflux
SOCl2, heat under reflux

20
Q

Reactions of acyl chlorides

A
  1. Hydrolysis of acyl chlorides (synthesis of carboxylic acids)
    - H2O(l), rtp
  2. Condensation of acyl chlorides to form amides
  3. condensation of acyl chlorides to form esters
21
Q

Condensation of acyl chlorides to form amides

A

NH3/amine, rtp

22
Q

Condensation of acyl chlorides to form esters

A

alcohol+acyl chlorides, rtp

acyl chlorides + phenol:
1. NaOH(aq)
2. add acyl chloride, rtp

23
Q

Why does carboxylic acids not react with phenols?

A
  • Phenols are weak nucleophiles because the LP of electrons on O delocalises into benzene ring
  • electrons on O less available for donation to the carbon deficient C in carboxylic acid
24
Q

Why acyl chlorides react with phenols?

A

Carbonyl carbon in acyl chloride is highly electron deficient

25
Q

Synthesis of esters

A
  1. condensation of alcohols and carboxylic acid
  2. condensation of acyl chlorides and alcohols
  3. condensation of acyl chlorides and phenols
26
Q

Reactions of esters

A
  1. acidic hydrolysis
    HCl/H2SO4(aq), heat under reflux
  2. alkaline hydrolysis
    NaOH(aq), heat under reflux
  3. reduction to form CH2OH and alcohol
    LiAlH4 in dry ether
27
Q

Why acyl chlorides most reactive?

A
  • Cl is electron-withdrawing via the inductive effect (due to EN difference)
  • OH, -OR, and -NH2 are all electron-donating via the resonance effect (due to delocalisation of electrons)
  • C in Cl most electron-deficient, thus most susceptible to nucleophilic attack
28
Q

Why amides less reactive than esters

A
  • N is less EN than O
  • LP of electrons on N delocalises across C=O to a larger extent
  • C in amides less electron deficient than C in esters
  • attracts nucleophile less readily than esters
29
Q

Distinguishing tests for carboxylic acids

A

acid-carbonate reaction
Na2CO3(aq)
effervescence of CO2 gas which forms white ppt in Ca(OH)2.

30
Q

why are carboxylic acids acidic?

A
  • electron-withdrawing COOH group
  • disperses negative charge
  • more stable conjugate base
  • more acidic

chemistry (13 decks)

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