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Chemistry ALEVEL - Ocr A > 26 - Carbonyls And Carboxylic Acids > Flashcards

26 - Carbonyls And Carboxylic Acids Flashcards

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1
Q

What is a carbonyl function group

A

C=O

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2
Q

Carbonyl groups:

A

Aldéhydes

Ketones

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3
Q

Aldéhyde structural formula

A

CHO

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4
Q

Ketone structural formula

A

CO

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5
Q

Oxidation of alcohol - aldehyde

A

Gently heat
Acidified potassium dichromate
Distillation apparatus

Produce aldehyde + water

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6
Q

Oxidation of aldehyde - carboxylic acid

A

Reflux

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7
Q

What influences the reactivity of ketones + aldehydes

A

C=O bond

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8
Q

What is a functional group

A

Area of an organic compound where a chemical reaction can happen

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9
Q

Similarities in structures between alkenes and carbonyl

A

Both contain a sigma bond between pi bond

Formed from sideways overlapping of p orbitals of adjacent atoms

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10
Q

Differences between alkenes and carbonyl

Chemical properties

A

Alkenes undergo electrophilic addition reactions

Carbonyl groups undergo nucleophilic addition

C=C - is non polar
C=O - is polar - O is more electronegative

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11
Q

What does the polar C=O bond attract

A

Reacts with nucleophiles
Attracted to slightly + C
In addition across C=O bond

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12
Q

Nucleophile definition

A

Electron pair donor

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13
Q

Nucleophilic addition steps

A
  • O atom is more electronegative than C atom
  • O atom is partially negative
  • C atom is partially positive
  • as a result + C attracts a nucleophile
  • nucleophile adds itself across C=O
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14
Q

Reducing an aldehyde / ketone

To alcohol

A

Reagent = sodium tetrahydridoborate NaBH4

Conditions = warmed with NaBH4

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15
Q

Mechanism for nucleophilic addition

With NaBH4

A
  • NaBH4 contains the hydride ion H- = nucleophile
  • partial + C attracts H-
  • H- donates lone pair to C in the C=O bond
  • dative covalent bond is formed between H- and C
  • the pi bond in C=O undergoes heterloytic fission
  • forming a negatively charged intermediate
  • O of intermediate donates lone pair of electrons to H atom in water

INTERMEDIATE PROTONATED

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16
Q

Why can’t HCN be used itself

A
  • uses NaCN and H2SO4

- Because HCN is colourless, poisonous, boils at RT - dangerous

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17
Q

Why is the reaction of carbonyl compounds with HCN useful

A

Provides a mean of increasing the length of the C chain

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18
Q

Cyanating carbonyl groups with HCN

will produce

A

hydroxynitriles = nitrile and hydroxyl group

Or cyanohydrins

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19
Q

Reagents and conditions of carbonyl reaction with HCN

A

Reagents
NaCN / H2SO4

In fume cupboard

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20
Q

Nucleophile in reaction with NaBH4

A

H-

Hydride ion

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21
Q

Nucleophile in HCN reaction

A

CN-

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22
Q

HCN mechanism

A
  • partial + charge on C attracts CN-
  • CN- donates lone pair to C
  • dative covalent bond formed
  • pi bond within C=O undergoes heterolytic fission
  • negatively charged intermediate uses lone pair to attract H+ from H2SO4
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23
Q

Difference between HCN and NaBH4 reactions

A
  • during reduction H2 is added across C=O
  • during cyanation HCN is added
  • H2 is not reactive enough to do this - needs NaNH4 reducing agent
  • HCN is reactive enough, but extremely poisonous
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24
Q

What do you use to detect carbonyl compounds

A

Brady’s reagent -

2,4xdinitrophenylhydrazine

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25
Q

What does Brady’s reagent do when carbonyl present

A

In presence of C=O

Yellow/organic precipitate formed

2,4-dinitrophenylhydrazone

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26
Q

What is 2,4-DNP usually dissolved into make safer

Because hazardous and can explode due to friction

A

Méthanol and conc.sulfuric acid

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27
Q

How to test for carbonyl groups

A

1) add excess 2,4DNP solution to test tube
2) add 3 drops of unknown compound - leave to stand
3) if no crystals form add H2SO4
4) IF YELLOW/ ORANGE PRECIPITATE = carbonyl present

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28
Q

Disadvantages of BRADYS REAGENT

A

can’t distinguish between aldehyde or ketone

Is hazardous dangerous

29
Q

Using the mp, from Brady’s reagent experiment

To identify carbonyl groups

A

1) filter out impure solid precipitate from solution
2) solid is recrystallised to produce pure sample of crystals
3) mp of purified 24DNP measured and recorded

COMPARED AGAINST DATABASE OF mp

30
Q

Why can mp be used to distinguish

A

Each carbonyl compound produces different crystalline derivatives (orange precipitate) with different mps

31
Q

How to distinguish between aldehydes and ketones

A

Using TOLLENS REAGENT

32
Q

What is tollens reagent

A

Solution of silver nitrate dissolved in aqueous ammonia

33
Q

Testing for aldehydes and ketones reagents and conditions

A

Reagents = tollens reagents

Conditions = heated in 50c water bath for 10 mins

34
Q

Making tollens reagent

A

1) add AgNO3 to test tube
2) add aq NaOH until brown precipitate formed (Ag2O)
3) add dilute NH3 until brown precipitate dissolves to clear solution

35
Q

Testing for aldehyde
Using tollens reagent

Practical

A

1) pour unknown solution into test tube
2) add equal volumes of fresh Tollens reagent (short shelf life)
3) leave for 10 mins in water bath at 50c

IF SILVER MIRROR FORMED = ALDEHYDE PRESENT

36
Q

What is oxidised and reduced in Tollens reagent experiment

A

Ag+ acts as an oxidising agent in presence of ammonia (NH3)

Ag+ is reduced to Ag = silver mirror

Aldehyde is oxidised to carboxylic acid

37
Q

Adv and disadv

Of tollens reagent

A

Ad = can identify and aldehyde from a carbonyl group

Disad = can’t confirm if a ketone is present
- short shelf life

38
Q

Why can’t tollens reagent identify is a ketone is present

A

Ketones are not easily oxidised

39
Q

Carboxyl functional groups

A

Carbonyl C=O

Hydroxyl O-H

40
Q

Explanation or the water solubility of carboxylic acids in terms of hydrogen bonding

A

C=O and O-H are polar bonds

Allowing carboxylic acids to form hydrogen bonds with H20 molecules

41
Q

Hydrogen bonding between Carboxylic acids and H2O

A

The O in the OH group has a lone pair of electrons that can hydrogen bond with a H on H2O

42
Q

when do carboxylic acids stop being soluble

A

More than 4 carbons in the carbon chain

43
Q

Why are carboxylic acids only soluble with up to 4 carbons

A

As the number of Cs in the car in chain increases
The polarity or the Carboxylic acid decreases
And the solubility of the Carboxylic acid decreases

As the non polar chain has a greater effect on the overall polarity

44
Q

Strength of carboxylic acids

A

Weak

Partially dissociate

HCOOH —> H+ + HCOO- carboxylate ion

45
Q

Naming carboxylates

= salts of CA

A

End names is

  • OATE
46
Q

Réactions CAs can react with

A

Metals
Metal oxides
Alkalis
Carbonates

47
Q

Identifying CAs

A

Only common organic compound

Sufficiently acidic to react with carbonates

48
Q

What is a derivative of carboxylic acid

A

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

49
Q

Name carboxylic acids derivatives

A

Esters
Acrylic chlorides
Acid anhydrides
Amuses

50
Q

Naming esters

from carboxylic acids

A

Remove -oic acid
Replace with -oate

First word = the alkyl chain attached to O from COO

Propanoic acid —> ethyl propanoate

51
Q

Name acyl chlorides

From carboxylic acids

A

Remove -oic acid
Replace with -oyl chloride

Propanoic acid —> propanoyl chloride

52
Q

Naming acid anhydrides

A

Removal of water from 2 carboxylic acids

Remove acid
And anhydride

Ethanoic acid —> ethanoic anhydride

53
Q

What is estérification

A

Reaction of alcohols with carboxylic acid

to form an Ester

54
Q

Reagents and conditions for estérification

A

Reagents:
Conc. H2SO4 catalyst

Conditions:
- the reaction is reversible - need to separate products as formed

Small esters - warm and distil out = because more volatile
Large Ester - reflux and use fractional distillation to separate

55
Q

Making ethyl propanoate

Practical

A

1) pour 2cm3 of ethanol and propanoic acid into polling tube
2) add a few drops H2SO4
3) place boiling tube in 80c water bath leave for 5 mins
4) pour contents into Na2CO3 beaker - removes un reacted carboxylic acids

56
Q

How to identify if an Ester has formed

A

Smell the fruity scent

See oily floating Ester drops on surface of water

57
Q

What is hydrolysis of esters

To form alcohols

A

Chemical breakdown of a compound of presence of water / aqueous solution

58
Q

Acid hydrolysis of an Ester produces

A

Carboxylic acid and alcohol

The Ester is broken down by water with acid catalyst

59
Q

Reagents and conditions of acid hydrolysis

A

Reagents
- dilute aqueous acid catalyst

Conditions
- Ester heated under reflux with catalyst

60
Q

Alkaline hydrolysis of an Ester

Produces

A

Carboxylate ion and alcohol

61
Q

Reagents and conditions of alkaline hydrolysis

A

Reagents
- OH-

Conditions
- heat under reflux with an alkaline

62
Q

Preparation of acyl chlorides

Carboxylic acid + SOCl2

A

Directly from their parent carboxylic acid

Acyl chloride + SO2 + HCl

Reaction with thionyl chloride
- SO2 and HCl evolved as gases - leaving acyl chloride

63
Q

Reagents and conditions of making an acyl chloride

A

Add SOCl2 to carboxylic acid

Conditions
- fume cupboard

64
Q

Acyl chloride + alcohol

A

Ester + HCl

65
Q

Acyl chloride + phenols

A

Esters + HCl

66
Q

Acyl chloride + H2O

A

Carboxylic acid + HCl

67
Q

Acyl chloride + ammonia

A

primary Amides + NH4Cl

68
Q

Acyl chloride + primary amine

Éthanoyl chloride + methyl amine

A

N- methylethanamide + HCl

69
Q

Acid anhydride + alcohol

Warmed together

A

Carboxylic acid + Ester

Chemistry ALEVEL - Ocr A (8 decks)

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