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Chemistry, Module 6 OCR > 6.1.2, 3 Carbonyl compounds, Carboxylic Acids and esters > Flashcards

6.1.2, 3 Carbonyl compounds, Carboxylic Acids and esters Flashcards

1
Q

What are carbonyls and how are they identified (5)

A
  • Aldehydes and Ketones: CHO/ CO
  • Test:
    Brady’s reagent (2,4- DNP) which is an oxidising agent
    When positive for carbonyls: orange crystals are formed which are hydrozones
  • To further detect what carbonyl, the crystals are filtered and dried, with its melting point detected.
  • The melting point is compared to a database to identify the compound
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2
Q

Test to distinguish Aldehydes from Ketones? (3)

A
  • Tollen’s reagent (oxidising agent) Silver nitrate is reacted with NaOH and dissolved with ammonia

The presence of silver mirrors indicate aldehyde whereas no mirrors will indicate a ketone

Ag+ ions are reduced to silver which forms the mirrors

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3
Q

Describe the reduction of a carbonyl with NaBH4 (6)

A
  • Nucleophillic addition
  • Reactant:
    Warm and aqueous NaBH4 + carbonyl
  • Nucleophlie formed: Hydride ion H-
  • Reduction of Aldehyde forms primary alcohol
  • Reduction of Ketone forms secondary alcohol
  • Overall reaction:
    Carbonyl + NaBH4 = Primary/secondary alcohol + OH-
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4
Q

Describe the reduction of carbonyls using HCN (5)

A
  • Nucleophillic addition
  • HCN is very hazardous therefore NaCN and H2SO4 is used
  • CN group extends the alkyl chain which is useful for fuels
  • Nucleophile: CN-
  • Overall reaction:
    Carbonyl + HCN= hydroxynitriles + OH-
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5
Q

Describe the bonding in the carbonyl group (C=O) (4)

A
  • The C=O bond is polar due to O being more electronegative
  • The double bond has a sigma bond between C and O each orbital containing an electron
  • Pi bonds due to the sideways overlapping of p orbitals above and below C and O atoms
  • The shape of the C=O forms a trigonal planar with a greater angle between C and O (121) due to the repulsion of Oxygen’s lone pair of electrons
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6
Q

Describe the oxidation of carbonyls (4)

A
  • Oxidising agent:
    Acidified K2Cr2O7 and H2SO4 catalyst
    (Cr2O72-, H+)
  • Aldehyde is oxidised to a carboxylic acid
    Colour change of orange to green is observed
  • Ketone cannot be oxidised
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7
Q

How do you test for alkenes? (2)

A
  • Bromine water is added which is originally orange.

- Alkene decolourises bromine as bromine is added across the double bond of the Alkene

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8
Q

How do you test for carboxylic acids?

A
  • Add aqueous sodium carbonate or sodium hydrogencarbonate.
  • Effervescence is observed in the presence of the acid.
  • Blue litmus paper also turns red which indicates the pH is less than 7, therefore an acid.
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9
Q

Explain the solubility of alcohols and carbonyls compared to carboxylic acids.

A
  • Carboxylic acids> Alcohols> Carbonyls
  • Carboxylic acids can make the most H-bonds with water. It contains a polar O-H group AND a polar C=O group
  • Alcohols are more soluble than carbonyls due to the polar OH group can make more H-Bonds than C=O in carbonyls
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10
Q

What is formed when a carboxylic acid reacts with:

  • Metals
  • Alkali
  • Metal carbonate
A
  • Metal: forms a salt and hydrogen gas
  • Alkali: Forms a salt and water.
  • Metal carbonate: Forms a salt, carbon dioxide and water.
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11
Q

What is a carboxylic acid derivative?

A
  • Any compound that can be hydrolysed to form the parent carboxylic acid

All contain:

  • An alkyl group/ H
  • Bonded to C=O
  • Bonded to another alkyl group
Includes: 
Esters
Acyl chlorides
Acid anhydrides
Amides
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12
Q

What is an Acyl group?

A

Formed when a carboxylic acid reacts with thionyl chloride(SOCl2)

This reaction forms SO2 and HCl in gaseous form, which is dangerous, therefore the reaction has to be taken place in a fume cupboard.

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13
Q

Describe the reaction of Acyl chloride with alcohols.

A

Forms an ester and hydrogen chloride

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14
Q

Describe the reaction of Acyl chlorides and phenol.

A

Produces an a phenyl ester and hydrogen chloride

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15
Q

Describe the reaction between water and an Acyl chloride.

A

Forms a carboxylic acid and hydrogen chloride in a hydration reaction.

The reaction is very vigorous and produces very dense HCl fumes

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16
Q

Describe the reaction of an Acyl chloride and ammonia

A

Forms and amide and ammonium chloride

Ammonia acts as a Nucleophile by donating a lone pair from N to the electron deficient species.

17
Q

Describe the reaction of an Acyl chloride and a primary amine

A

Forms a secondary amide where the N atom has 2 C atoms attached to it.

+ an alkyl ammonium chloride

18
Q

Compare the reactivity of Acyl chlorides, acid anhydrides and Carboxylic acids.

A

Acyl chloride> acid anhydrides> Carboxylic acids

19
Q

What are the two different ways of hydrolysing esters?

A

Acid hydrolysis: produces a carboxylic acid and an alcohol

Alkaline hydrolysis: produces a carboxylate salt and an alcohol

20
Q

Describe acid hydrolysis. (4)

A

The ester is broken down in a reversible reaction:

  • Under reflux
  • Using dilute aqueous acid

The ester is hydrolysed by the water from the aqueous acid, the acid acts as a catalyst.

Products formed:
Parent carboxylic acid + parent alcohol.

eg Methyl butanoate will form:
Butanoic acid + methanol.

21
Q

Describe alkaline hydrolysis (saponification). (4)

A

The ester is broken down in an irreversible reaction:

  • Under reflux
  • Aqueous hydroxide ions

Products formed:
Carboxylate salt + parent alcohol

eg Methyl butanoate with NaOH will form:
Sodium butanoate + Methanol

22
Q

Describe 2 different esterification processes.

A

Condensation reaction:

  1. Carboxylic acid is warmed with an alcohol.
    Catalyst: dilute H2SO4
  2. Acyl chloride and alcohol are heated together.
23
Q

Describe the process of forming a carboxylic acid.

A

Acyl chloride + water

forms carboxylic acid + HCl in a violent, vigorous reaction.

24
Q

Describe the reaction between an acid anhydride and an alcohol.

A

This is a form of esterification:

Acid anhydride reacts with an alcohol to form:
Ester + carboxylic acid.

No other products formed- It is not condensation

25
Q

How are acid anhydride form?

A

The reaction between two carboxylic acids

Acid–> COOH
ANHYDride–> Without water.

Water is removed to form the acid anhydride.

26
Q

Describe how an acyl chloride can be used to form:
primary amide
secondary amide

A

Primary amide:
R-COCl reacts with excess ammonia.
This forms a primary amide and ammonium chloride salt:

R-COCl + 2NH3 –> R-CONH2 + NH4+ Cl-

Secondary amide:
R-COCl reacts with an excess primary amide.
This forms a secondary amide and an ammonium salt with an alkyl chain:

R-COCl+ 2R-NH2 –> R-CONH-R + R-NH3+ + Cl-

Chemistry, Module 6 OCR (4 decks)

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