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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
What does Brady’s reagent do when carbonyl present
In presence of C=O Yellow/organic precipitate formed 2,4-dinitrophenylhydrazone
26
What is 2,4-DNP usually dissolved into make safer Because hazardous and can explode due to friction
Méthanol and conc.sulfuric acid
27
How to test for carbonyl groups
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
28
Disadvantages of BRADYS REAGENT
can’t distinguish between aldehyde or ketone Is hazardous dangerous
29
Using the mp, from Brady’s reagent experiment To identify carbonyl groups
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
Why can mp be used to distinguish
Each carbonyl compound produces different crystalline derivatives (orange precipitate) with different mps
31
How to distinguish between aldehydes and ketones
Using TOLLENS REAGENT
32
What is tollens reagent
Solution of silver nitrate dissolved in aqueous ammonia
33
Testing for aldehydes and ketones reagents and conditions
Reagents = tollens reagents Conditions = heated in 50c water bath for 10 mins
34
Making tollens reagent
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
Testing for aldehyde Using tollens reagent Practical
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
What is oxidised and reduced in Tollens reagent experiment
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
Adv and disadv Of tollens reagent
Ad = can identify and aldehyde from a carbonyl group Disad = can’t confirm if a ketone is present - short shelf life
38
Why can’t tollens reagent identify is a ketone is present
Ketones are not easily oxidised
39
Carboxyl functional groups
Carbonyl C=O | Hydroxyl O-H
40
Explanation or the water solubility of carboxylic acids in terms of hydrogen bonding
C=O and O-H are polar bonds Allowing carboxylic acids to form hydrogen bonds with H20 molecules
41
Hydrogen bonding between Carboxylic acids and H2O
The O in the OH group has a lone pair of electrons that can hydrogen bond with a H on H2O
42
when do carboxylic acids stop being soluble
More than 4 carbons in the carbon chain
43
Why are carboxylic acids only soluble with up to 4 carbons
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
Strength of carboxylic acids
Weak Partially dissociate HCOOH —> H+ + HCOO- carboxylate ion
45
Naming carboxylates = salts of CA
End names is - OATE
46
Réactions CAs can react with
Metals Metal oxides Alkalis Carbonates
47
Identifying CAs
Only common organic compound Sufficiently acidic to react with carbonates
48
What is a derivative of carboxylic acid
A compound that can be hydrolysed to form the parent carboxylic acid
49
Name carboxylic acids derivatives
Esters Acrylic chlorides Acid anhydrides Amuses
50
Naming esters from carboxylic acids
Remove -oic acid Replace with -oate First word = the alkyl chain attached to O from COO Propanoic acid —> ethyl propanoate
51
Name acyl chlorides From carboxylic acids
Remove -oic acid Replace with -oyl chloride Propanoic acid —> propanoyl chloride
52
Naming acid anhydrides
Removal of water from 2 carboxylic acids Remove acid And anhydride Ethanoic acid —> ethanoic anhydride
53
What is estérification
Reaction of alcohols with carboxylic acid to form an Ester
54
Reagents and conditions for estérification
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
Making ethyl propanoate Practical
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
How to identify if an Ester has formed
Smell the fruity scent See oily floating Ester drops on surface of water
57
What is hydrolysis of esters To form alcohols
Chemical breakdown of a compound of presence of water / aqueous solution
58
Acid hydrolysis of an Ester produces
Carboxylic acid and alcohol The Ester is broken down by water with acid catalyst
59
Reagents and conditions of acid hydrolysis
Reagents - dilute aqueous acid catalyst Conditions - Ester heated under reflux with catalyst
60
Alkaline hydrolysis of an Ester Produces
Carboxylate ion and alcohol
61
Reagents and conditions of alkaline hydrolysis
Reagents - OH- Conditions - heat under reflux with an alkaline
62
Preparation of acyl chlorides Carboxylic acid + SOCl2
Directly from their parent carboxylic acid Acyl chloride + SO2 + HCl Reaction with thionyl chloride - SO2 and HCl evolved as gases - leaving acyl chloride
63
Reagents and conditions of making an acyl chloride
Add SOCl2 to carboxylic acid Conditions - fume cupboard
64
Acyl chloride + alcohol
Ester + HCl
65
Acyl chloride + phenols
Esters + HCl
66
Acyl chloride + H2O
Carboxylic acid + HCl
67
Acyl chloride + ammonia
primary Amides + NH4Cl
68
Acyl chloride + primary amine Éthanoyl chloride + methyl amine
N- methylethanamide + HCl
69
Acid anhydride + alcohol Warmed together
Carboxylic acid + Ester

Chemistry ALEVEL - Ocr A (8 decks)

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