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A Level Chemistry > Topic 17B+C Carbonyl Compounds and Carboxylic Acids > Flashcards

Topic 17B+C Carbonyl Compounds and Carboxylic Acids Flashcards

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1
Q

What is the carbonyl functional group?

A
  • C=O
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2
Q

Draw an aldehyde and a ketone

A
  • Draw pls
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3
Q

Can aldehydes and ketones form hydrogen bonds and how does this affect their properties?

A
  • no
  • they don’t have a polar O-H bond
  • solutions of aldehydes and ketones have lower boiling points than their equivalent alcohols (which have H bonding)
  • however, they still bond through London forces and permanent dipole-permanent dipole bonds
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4
Q

Why can aldehydes and ketones hydrogen bond with water?

A
  • they have a lone pair of electrons on the O atom of C=O group
  • oxygen uses lone pairs to for H-bonds with H atoms
  • small aldehydes and ketones will dissolve in water
  • larger ones have longer carbon chains with aren’t able to form H bonds with water
  • these disrupt that H bonding between water molecules, but don’t form H bonding themselves
  • if aldehyde or ketone is large enough, the London forces between aldehyde or ketones molecules and the H bonding between water molecules will be stronger than H bonds between aldehyde/ketone and water
  • so compound won’t dissolve
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5
Q

Why are there different ways to test for aldehydes?

A
  • an aldehyde can be easily oxidised to a carboxylic acid, but ketone can’t
  • when aldehyde is oxidised, another compound is reduced, so a reagent is used that changes colour as it’s reduced
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6
Q

Describe the three ways of testing for aldehydes

A

Tollens’ Reagent:

  • a colourless solution of silver nitrate dissolved in aqueous ammonia
  • if heated with aldehyde, a silver mirror forms
  • Ag(NH3)2(+) (aq) + e- = Ag(s) + 2NH3(aq)
  • 2Ag(NH3)2(+) (aq) + RCHO(aq) + 3OH-(aq) = 2Ag(s) + RCOO-(aq) + 4NH3(aq) + 2H2O

Fehling’s or Benedict’s solution:

  • fehling’s is a blue solution of complexed copper(II) ions dissolved in sodium hydroxide (or sodium carbonate for benedicts)
  • if heated with aldehyde, copper(II) ions are reduced to a brick-red precipitate of copper(I) oxide
  • Cu2+(aq) + e- = Cu+(s)
  • RCHO(aq) + 2Cu2+ + 5OH- = RCOO-(aq) + Cu2O(s) + 3H2O(l)

Acidified dichromate(VI) ions:

  • if you heat aldehyde with acidified dichromate(VI) ions, you get a carboxylic acid
  • dichromate(VI) ions are oxidising agent [O]
  • often used is potassium dichromate(VI) with dill sulfuric acid
  • solution turns orange to green as dichromate is reduced
  • ketone won’t be oxidised
  • Cr2O7(2-) + 14H+ + 6e- = 2Cr3+ + 7H2O
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7
Q

What type of alcohol does reducing an aldehyde make?

A
  • a primary alcohol
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8
Q

What type of alcohol does reducing a ketone make?

A
  • a secondary alcohol
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9
Q

What reducing agent can be used to reduce aldehydes and ketones back to alcohols?

A
  • LiAlH4 in dry ether

- very powerful and reacts violently with water

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10
Q

Describe and draw the nucleophilic addition reaction when hydrogen cyanide reacts with carbonyls to produce hydroxynitriles

A
  • hydrogen cyanide is a weak acid: partially dissociates to form H+ + CN- ions
  • the CN- ion attacks the slightly positive carbon atom and donates a pair if electrons to it
  • both electrons from the double bond transfer to oxygen
  • H+ (from either HCN or H2O) bonds to the oxygen to form the hydroxyl group (OH)
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11
Q

Why is the hydroxynitrile product of hydrogen cyanide and carbonyls optically inactive?

A
  • groups surrounding the carbonyl carbon are planar so nucleophile can attack from either side
  • a racemic mixture is made
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12
Q

How to test for a carbonyl group and how can you identify the carbonyl compound?

A
  • 2,4-dinitrophenylhydrazine is dissolved in methanol and conc. sulphuric acid
  • it reacts to form a bright orange precipitate if a carbonyl
    group is present (only aldehydes and ketones)
  • the orange precipitate is a derivative of the carbonyl compound which can be purified by recrystallisation
  • each carbonyl compounds gives a crystalline derivative with a different melting point
  • melt and compare against known melting points to identify
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13
Q

How do some carbonyls react with iodine?

A
  • carbonyls that contain a methyl carbonyl group react when heated with iodine in presence of an alkali
  • yellow precipitate of triiodomethane (CHI3)
  • an antiseptic smell
  • RCOCH3 + 3I2 + 4OH- = RCOO- + CHI3 + 3I- + 3H2O
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14
Q

Draw a carboxylic acid forming hydrogen bonds with water

A
  • go go
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15
Q

Why do carboxylic bonds have relatively high boiling points?

A
  • they can form H bonds with each other
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16
Q

How soluble are carboxylic acids in water?

A
  • very soluble due to H bonding
17
Q

How and why do solubility of carboxylic acids changes as carbon chain length increases?

A
  • as length of carbon chain increases, solubility decreases
  • the hydrocarbon chains can’t form H bonds but disrupt H bonds between water molecules
  • long carboxylic acids don’t dissolve in water
18
Q

Describe the ways carboxylic acids can be formed

A

oxidation of primary alcohol and aldehydes:

  • often potassium dichromate (K2Cr2O7/H2SO4) is used
  • draw

hydrolysis of nitriles:

  • reflux the nitrile with dilute HCl and then distil off the carboxylic acid
  • draw
  • nitrile + 2H2O + HCl = carboxylic acid + NH4Cl
19
Q

What do carboxylic acids react with alkalis to form?

A
  • salt and water

- neutralisation

20
Q

What do carboxylic acids react with carbonates or hydrogencarbonates to form?

A
  • salt
  • CO2
  • water
21
Q

What do you make when reducing a carboxylic acid and how do you?

A
  • hard to reduce it
  • uses LiAlH4 in dry ether
  • reduces to a primary alcohol
22
Q

How do you make an acyl chloride from carboxylic acid?

A
  • mix with phosphorus(V) chloride

- Carboxylic acid + PCl5 = acyl chloride + POCl3 + HCl

23
Q

How do you name an ester?

A
  • alkyl group that came from alcohol is the first part

- second part is from carboxylic acid

24
Q

How do you make esters?

A
  • heat a carboxylic acid under reflux with an alcohol in the presence of a strong acid catalyst e.g. H2SO4 or HCl
  • called esterification
    e. g. ethanoic acid + ethanol = ethyl ethanoate + water
25
Q

How can you collect the ester?

A
  • reaction is reversible, so you need to separate out the product as it’s formed
  • do by distillation
  • then react with sodium carbonate to react with any carboxylic acid
  • separate with separating funnel
26
Q

Describe acid hydrolysis of ester

A
  • splits the ester into an acid and an alcohol
  • reverse of condensation reaction
  • add ester into dilute acid, such as HCl or H2SO4
  • heat under reflux
  • reversible reaction, so needs lots of water to push eqm to right
27
Q

Describe base hydrolysis of ester

A
  • reflux the ester with dilute alkali e..g NaOH
  • get a carboxylate ion and an alcohol
  • irreversible

e. g.
- ethyl ethanoate + OH- = ethanoate§ + ethanol

28
Q

What are diols?

A
  • contain two OH functional groups
29
Q

What are dicarboxylic acids?

A
  • contain 2 COOH functional groups
30
Q

What is the reaction to form polyesters (long ester chains) called?

A
  • condensation polymerisation
31
Q

Draw a polyester chain

A
  • drawwwwwwwww
32
Q

Draw Terylene and describe

A
  • formed of benzene-1,4-dicarboxylic acid and ethane-1,2-diol
33
Q

What are the properties of Terylene, PET

A
  • fibres are strong, flexible and abrasion resistant
  • terylene used in clothes to keep crease free and long lasting
  • used in carpets
  • treated terylene is used to make drink bottles and containers
34
Q

What is the functional group and general formula of acyl chlorides

A
  • COCl

- CnH(2n-1)OCl

35
Q

What do acyl chlorides react with?

A

Water:

  • a vigorous reactions with cold water, producing carboxylic acid
  • ethanoyl chloride + H2O = ethanoic acid + HCl
  • white steamy fumes of HCl

Alcohols:

  • a vigorous reaction at room temp, producing ester
  • ethanoyl chloride + methanol = methyl ethanoate + HCl
  • white steamy fumes of HCl

Conc ammonia:

  • a violent reaction at room temperature, producing an amide
  • ethanoyl chloride + NH3 = ethanamide + HCl
  • white steamy fumes of HCl

Amines:
- a violent reaction at room temp, producing an N-substituted amide
- ethanoyl chloride + CH3NH2 = H3CCO(NHCH3)
N-methylethanamide + HCl

A Level Chemistry (19 decks)

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