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Chemistry > Carboxylic Acids and Derivatives > Flashcards

Carboxylic Acids and Derivatives Flashcards

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1
Q

What are carboyxlic acids?

A

They contain the carboxyl group (-COOH)

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2
Q

What is the general formula for aliphatic carboxylic acids?

A

CnH2nO2

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3
Q

How to name carboxylic acids?

A

Replace ‘-e’ with ‘-oic acid’

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4
Q

How to name salts of carboxylic acids?

A

Replace ‘-oic acid’ with ‘-oate’

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5
Q

How does the boiling point of carboxylic acids change as the number of carbon atoms increases?

A

As the number of carbon atoms increases, the number of electrons in the molecule increases and more energy is required to overcome the stronger id-id between carboxylic acid molecules

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6
Q

What is glacial acid and why is it called that?

A

Anhydrous ethanoic acid as it freezes to an ‘ice-like’ solid at 17 degree celsius

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7
Q

How do carboxylic acids’ boiling point compared to alcohols of similar Mr and why?

A

Carboxylic acids have a higher boiling point compared to alcohols of similar Mr
- carboxylic acids have more extensive hydrogen bonds than alcohol as there are more sites for the formation of hydrogen bonds
- carboxylic acids form stronger hydrogen bonds than alcohol molecules as the O-H bond in -COOH is more polar due to the presence of electron-withdrawing carbonyl group

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8
Q

Are carboxylic acids soluble in water?

A

Lower carboxylic acid molecules are soluble in water because carboxylic acids can form hydrogen bonds with water molecules

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9
Q

What happens to the solubility of carboxylic acids as number of C increases?

A

As the length of non-polar hydrocarbon chain increases, solubility in water decreases while solubility in non-polar solvents increases

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10
Q

What happens when carboxylic acids in pure form and dissolved in non-polar solvents like benzene?

A

Carboxylic acids form dimers through the formation of hydrogen bonds between two acid molecules

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11
Q

What does the strength of acids depend on?

A

The stability of anion formed

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12
Q

What is the carboxylate anion stabilised by and what are the implications?

A

Carboxylate anion is stabilised by resonance, where the negative charge is delocalised over the -COO⁻, thus the two C-O bonds are equal in length

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13
Q

What affects the relative acidity of carboxylic acids?

A
  • Electron-donating groups intensify the negative charge on the -COO⁻ group, thereby destabilising the anion and reducing acid strength
  • Electron-withdrawing groups disperse the negative charge on the -COO⁻ group, thereby stabilising the anion and increasing acid strength
  • benzoic acids are stronger acids than aliphatic acids due to delocalisation of negative charge on the benzoate anion into the ring, making the benzoate anion more stable
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14
Q

Why is the delocalisation of negative charge into the benzene ring possible?

A

It possible because the C atom of -COO⁻ group is sp² hybridised, similar to the sp² hybridised C atom in the benzene ring, allowing overlap of the unhybridised p orbitals

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15
Q

What is the strength of carboxylic acids in relation to other compounds?

A

Mineral acids > RCOOH > phenol > water > alcohol

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16
Q

What are the ways to prepare carboxylic acids?

A
  • oxidation of primary alcohols and aldehydes
  • oxidation of alkylbenzenes
  • oxidation of alkenes with structure RCH=CHR’
  • hydrolysis of nitriles
  • hydrolysis of acyl chlorides and esters
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17
Q

What are the reagents and conditions for the oxidation of primary alcohols and aldehydes to prepare carboxylic acids?

A

acidified KMnO4 or acidified K2Cr2O7, heat under reflux

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18
Q

What are the reagents and conditions for the oxidation of alkylbenzenes to prepare carboxylic acids?

A

acidified KMnO4, heat under reflux

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19
Q

What are the reagents and conditions for the oxidation of alkenes with the structure RCH=CHR’ to prepare carboxylic acids?

A

acidified KMnO4, heat under reflux

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20
Q

How is vinegar produced?

A

Oxidation of ethanol by enzymes

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21
Q

What is the equation for vinegar production?

A

CH3CH2OH + O2 -(enzymes)-> CH3COOH + H2O

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22
Q

What are the reagents and conditions for the hydrolysis of nitriles?

A
  • acid hydrolysis: dilute HCl (aq)/ dilute H2SO4, heat under reflux
  • alkaline hydrolysis: NaOH (aq), heat under reflux, followed by acidification with dilute HCl (aq)/ H2SO4 (aq)
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23
Q

What is the equation for acid hydrolysis of nitriles?

A

RCN + 2H₂O + H⁺ → RCOOH + NH₄⁺

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24
Q

What is the equation for alkaline hydrolysis of nitriles?

A

RCN + H₂O + OH⁻ → RCOO⁻ + NH₃
(Upon addition of dilute HCl, RCOO⁻ becomes RCOOH)

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25
Q

Do carboxylic acids behave like carbonyl compounds or alcohols?

A

Carboxylic acids behave like neither because the close proximity of C=O and O-H groups in -COOH functional group causes them to modify each other’s properties

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26
Q

Is carboxyl carbon more or less susceptible to nucleophilic attack and why?

A

It is less susceptible to attack by nucleophiles than the carbonyl carbon in aldehydes and ketones because a lone pair in the p orbital of the O atom of the -OH group will be delocalised into the pi bond of the -C=O group, causing a drift of electron density from O atom of the -OH group towards the electron deficient carbon, thus reducing the positive charge on the carboxyl carbon via the resonance effect

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27
Q

What are the reactions of carboxylic acids?

A
  • Acid property
    • reaction with reactive metals
    • reaction with bases
    • reaction with carbonates or
      hydrogencarbonates
  • Condensation to form esters
  • Nucleophilic substitution to form acyl chlorides
  • Reduction
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28
Q

What is the type of reaction of carboxylic acids with reactive metals?

A

Acid-metal reaction or redox

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29
Q

What is the equation of carboxylic acids and reactive metal?

A

RCOOH + Na → RCOONa + 1/2H₂

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30
Q

What is the equation for the reaction of carboxylic acids with bases?

A

RCOOH + NaOH → RCOO⁻Na⁺ + H₂O

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31
Q

What medium must reaction of bases be carried out and why?

A

Aqueous medium because carboxylic acids exhibit their acidic property, undergo dissociation to give H⁺ in aqueous medium

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32
Q

What is the type of reaction of carboxylic acids with carbonates or hydrogencarbonates?

A

Acid-carbonate reaction

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33
Q

What is the equation of carboxylic acids with carbonates?

A

2RCOOH + Na₂CO₃ → 2RCOO⁻Na⁺ + CO₂ + H₂O

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34
Q

What is the equation of carboxylic acids with hydrogencarbonates?

A

RCOOH + NaHCO₃ → COO⁻Na⁺ + CO₂ + H₂O

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35
Q

How to distinguish carboxylic acids from phenols and alcohols?

A

Add carbonates or hydrogencarbonates
- carboxylic acids: CO₂ evolved will form white ppt. with limewater
- phenols and alcohols: do not react with carbonates or hydrogencarbonates

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36
Q

What happens when you add mineral acids to salt of carboxylic acids?

A

RCOO⁻Na⁺ + H⁺ → RCOOH + Na⁺
Mineral acids are stronger than carboxylic acids, thus it will convert the salt back to original acid

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37
Q

What bonds does the acid property of RCOOH cleave?

A

O-H bond

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38
Q

What bonds does condensation to form esters and nucleophilic substitution to form acyl chlorides?

A

Cleavage of C-O bond

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39
Q

What are the reagents and conditions for carboxylic acids to undergo condensation to form esters?

A

alcohol (R’OH), a few drops of conc. H2SO4, heat under reflux

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40
Q

What is the type of reaction that carboxylic acids undergo to form esters?

A

Condensation

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40
Q

What is the equation of carboxylic acids undergoing condensation to form esters?

A

RCOOH + R’-OH ⇌ RCOOR’ + H₂O

41
Q

What does H2SO4 act as in the condensation of carboxylic acids to form esters?

A

The reaction of carboxylic acids to form esters is slow and reversible
- conc. H2SO4 act as catalyst
- conc. H2SO4 act as dehydrating agent to remove water formed and favour forward reaction

42
Q

Do carboxylic acids react with phenols to form esters and why?

A
  • Carboxylic acids do not react with phenols to form esters as phenol is a weaker nucleophile than alcohols
  • to form phenyl esters, phenol must be first converted to phenoxide and reacted with acyl chlorides
43
Q

What is the mechanism for carboxylic acids undergoing condensation reaction to form esters?

A

addition-elimination reaction

44
Q

Apart from forming esters, what other condensation reactions can carboxylic acids undergo?

A

Condensation reaction between two carboxylic acids to form an acid anhydride

45
Q

What is the reagents and conditions for the reaction of carboxylic acids to form acyl chlorides?

A
  • PCl₅, room temperature
  • PCl₃, room temperature
  • SOCl₂, room temperature
46
Q

What is the type of reaction of carboxylic acids reacting to form acyl chlorides

A

nucleophilic substitution

47
Q

What is the equation of carboxylic acids and PCl₅?

A

RCOOH + PCl₅ → RCOCl + POCl₃ + HCl

48
Q

What is the equation of carboxylic acids and PCl₃?

A

3RCOOH + PCl₃ → 3RCOCl + H₃PO₃

49
Q

What is the equation of carboxylic acids and SOCl₂?

A

RCOOH + SOCl₂ → RCOCl + SO₂ + HCl

50
Q

What are the reagents and conditions for the reduction of carboxylic acids?

A

LiAlH₄ in dry ether

51
Q

What is the equation for the reduction of carboxylic acids?

A

RCOOH + 4[H] → RCH₂OH + H₂O

52
Q

Can carboxylic acids be reduced by other reducing agents?

A

No because carboxylic acids are more difficult to reduce than aldehydes and ketones and cannot be reduced by milder reducing agents like H2,Ni, heat or NaBH4

53
Q

What reactions can methanoic acid and ethanoic acid undergo?

A

Oxidation by acidified KMnO4

54
Q

What is the equation for methanoic acid undergoing oxidation?

A

HCOOH + [O] → CO₂ + H₂O

55
Q

What is the equation for ethanoic acid undergoing oxidation?

A

(COOH)₂ + [O] → 2CO₂ + H₂O

56
Q

What reactions do HCOOH undergo and why?

A
  • Oxidation by Fehling’s reagent and Tollens’ reagent (false positive)
  • HCOOH has an aldehyde group (-CHO) and is easily oxidised
57
Q

What do HCOOH not form?

A

It does not form RCOCl because it is high unstable and decomposes to give CO and HCl

58
Q

How are carboxylic acid derivatives formed?

A

Carboxylic acid derivatives are formed when the -OH portion of the carboxyl group is replaced by another substituent. They all contain the RCO- group (acyl group)

59
Q

What are some classes of carboxylic acid derivatives?

A
  • acyl chloride (RCOCl)
  • primary amide (RCONH₂)
  • ester (RCOOR’)
  • acid anhydride R(CO)O(CO)R’
60
Q

How to name acyl chlorides?

A

Change ‘oic acid’ to ‘oyl chloride’

61
Q

How to name ester?

A

Alkyl group attached to oxygen (alcohol portion) + change ‘oic acid’ to ‘oate’ (carboxylic acid portion)

62
Q

How to name amide?

A

Change ‘oic acid’ to ‘amide’

63
Q

How to name acid anhydride?

A

Names of acid + ‘anhydride’

64
Q

How do the boiling points of acyl chlorides and esters compared to carboxylic acids and alcohols of similar Mr?

A

Boiling points of acyl chlorides and esters are lower than carboxylic acids and alcohols because lesser energy is required to overcome the weaker pd-pd between acyl chlorides or ester molecules compared to stronger hydrogen bonds between carboxylic acids or alcohols molecules

65
Q

How do the boiling point of amides compared to carboxylic acids derivatives of comparable Mr?

A

-NH2 group allows hydrogen bonds to be formed between amide molecules, thus amides have higher boiling point

66
Q

What does the solubility of acid derivatives in water depend on?

A

Size of non-polar hydrocarbon group: the larger the size of hydrocarbon group, the less soluble the acid derivatives

67
Q

Are acyl chlorides soluble in water?

A

Soluble, they dissolve in water to form carboxylic acids and HCl (aq)

68
Q

What is the equation of acyl chlorides in water?

A

RCOCl + 2H₂O → RCOOH + HCl

69
Q

Are esters soluble in water?

A

slightly soluble (up to 3-5 C)

70
Q

Are amides soluble in water?

A

Fairly soluble due to hydrogen bonds between molecules of amides and water molecules

71
Q

What type of reaction does acyl chlorides undergo?

A
  • Hydrolysis (or nucleophilic substitution)
  • Condensation to form esters
  • Condensation to form amides
72
Q

What are the reagents and conditions for the hydrolysis of acyl chlorides?

A

Water, room temperature

73
Q

What is the equation for the hydrolysis of acyl chlorides?

A

RCOCl + H₂O → RCOOH + HCl

74
Q

What is the distinguishing test for acyl chlorides?

A
  • Add water: reaction is vigorous and resultant acidic solution turns moist blue litmus paper red
  • Then add AgNO3: white ppt. of AgCl formed
75
Q

How does benzoyl chloride’s reactivity compare with alkyl acyl chloride?

A

Benzoyl chloride is much less reactive than alkyl acyl chloride (reacts slowly with water) because declocalisation of electron density between p orbital of Cl atom and the pi bond of the C=O group and the pi electron cloud of benzene ring reduces partial charge on the carbonyl carbon

76
Q

What is the relative ease of hydrolysis of acyl chloride (RCOCl), alkyl chloride (RCl) and aryl chlorides (Ar-Cl)?

A

acyl chlorides (RCOCl) > alkyl chlorides (RCl) > aryl chlorides (Ar-Cl)
- Carbonyl carbon atom in -COCl is highly electron negative as it is bonded to 2 electronegative atoms O and Cl and hence is easily attacked by nucleophiles
- Carbon atom of C-Cl bond is less electron deficient than that in RCOCl
- aryl chlorides have stronger C-Cl bond due to delocalisation of lone pair of electrons on Cl atom into the benzene ring, resulting in partial double bond character

77
Q

What are the reagents and conditions of the hydrolysis of alkyl chlorides?

A

NaOH (aq), heat

78
Q

What are the reagents and conditions of the hydrolysis of aryl chlorides?

A

No reaction

79
Q

What type of reaction is the formation of esters from acyl chlorides?

A

Condensation

80
Q

What are the reagents and conditions for the formation of ester from acyl chlorides?

A
  • alcohol, room temperature
  • phenol, NaOH, room temperature
81
Q

Why is NaOH(aq) needed to react with acyl chlorides to form esters?

A

Phenol is a weak nucleophile and must be first converted to phenoxide ion, which is a stronger nucleophile

82
Q

What type of reaction is the formation of amides from acyl chlorides?

A

Condensation

83
Q

What is the equation to form primary amide from acyl chlorides?

A

RCOCl + NH3 → RCONH2 + HCl

84
Q

What is the equation to form secondary amides form acyl chlorides?

A

RCOCl + R’NH2 → RCONHR’ + HCl

85
Q

What is the equation to form tertiary amides from acyl chlorides?

A

RCOCl + R’NHR’’ → RCONR’R’’ + HCl

86
Q

What reactions do esters undergo?

A
  • Acid hydrolysis
  • Alkaline hydrolysis
87
Q

What happens when you hydrolyse esters?

A

Esters form back their corresponding carboxylic acids and alcohols

88
Q

Why can’t you just hydrolyse esters with water?

A

Hydrolysis of esters by heating with water occurs very slowly, this hydrolysis can be catalysed by heating with acid or induced by heating with alkali

89
Q

What are the reagents and conditions for acid hydrolysis?

A

dilute HCl (aq)/ H2SO4 (aq), heat under reflux

90
Q

What is the equation for acid hydrolysis of esters?

A

RCOOR’ + H2O ⇌ RCOOH + R’OH

91
Q

What are the reagents and conditions for alkaline hydrolysis of esters?

A

NaOH (aq), heat under reflux

92
Q

What is the other name for alkaline hydrolysis?

A

Saponification because traditionally soap is made by alkaline hydrolysis of fats and oils

93
Q

How does alkali induce hydrolysis of esters?

A

Alkalis induce hydrolysis by providing a stronger nucleophile, OH⁻

94
Q

What is the difference between acidic hydrolysis of esters and alkaline hydrolysis of esters apart from the medium?

A

alkaline hydrolysis reaction is irreversible while acidic hydrolysis of ester is reversible

95
Q

Why is alkaline hydrolysis of esters reaction irreversible?

A

Under alkaline conditions, carboxylate salt is obtained and the resonance stabilised carboxylate anion shows little tendency to react with an alcohol

96
Q

What are the uses of esters?

A
  • perfume and flavouring material
  • solvents for paints and vanishes
  • analgesic (painkiller)
97
Q

What are the uses of amides?

A
  • analgesic (painkiller)
  • caffeine
98
Q

What are the uses of ester?

A
  • aspirin
  • anaesthetic
99
Q

What is the type of reaction of carboxylic acids with bases?

A

Acid-base reaction

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