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A-Level OCR Chemistry > Module 6: Chapter 26 (Carbonyls & Carboxylic Acids) > Flashcards

Module 6: Chapter 26 (Carbonyls & Carboxylic Acids) Flashcards

1
Q

Describe the oxidation reaction of a primary alcohol?

A

Distillation
H+/Cr2O7^2- (acidified dichromate)
primary alcohol + [O] -> aldehyde + water
orange to green

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2
Q

Describe the oxidation reaction of a secondary alcohol?

A

Reflux
H+/Cr2O7^2- (acidified dichromate)
secondary alcohol + [O] -> ketone + water
orange to green

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3
Q

Describe the oxidation reaction of a tertiary alcohol?

A

Reflux
H+/Cr2O7^2- (acidified dichromate)
NO REACTION TAKES PLACE
solution remains orange

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4
Q

Describe the colour change of acidified dichromate?

A

H+/Cr2O7^2- ORANGE -> [Cr(H2O)5SO4]+ “Cr3+” GREEN

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5
Q

What functional group do aldehydes and ketones both contain and where is it found on the carbon chain?

A

Both contain the carbonyl functional group C=O

  • Aldehydes: C=O found at the end of the carbon chain
  • Ketones: C=O is joined to 2 different carbon atoms in the chain
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6
Q

How do you name aldehydes?

A

Adding “-al” as a suffix

PentanAL, ethanAL etc

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7
Q

How do you name ketones?

A

Adding “-one” as a suffix

Propanone, pentan-2-one, hexan-2-one etc

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8
Q

What happens when aldehydes are further oxidised?

A
  • Aldehydes can be further oxidised to carboxylic acid

Aldehyde + [O] -(reflux H+/Cr2O7^2-)-> carboxylic acid

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9
Q

How can scientists distinguish between ketones and aldehydes?

A

Further oxidation as ketones can’t be further oxidised, meanwhile aldehydes will become carboxylic acids

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10
Q

What are aldehydes reduced into?

A

Primary alcohols
- warmed with aqueous tetrahydridoborate (III) NaBH4 (the reducing agent)
aldehydes + 2[H] -NaBH4-> primary alcohols

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11
Q

What are ketones reduced into?

A

ketones + 2[H] -NaBH4-> secondary alcohols

- warmed with aqueous tetrahydridoborate (III) NaBH4 (the reducing agent)

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12
Q

Describe the C=O bond

A

C=O bond is composed of a σ-bond and a π-bond

  • the σ-bond is caused by direct overlap of orbitals between the C and O
  • the π-bond is formed by sideway overlap of p-orbitals above and below the place of C and O atoms
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13
Q

Why is the C=O polar?

A
  • Oxygen is more electronegative than carbon
  • Electron density in the double bond lies closer to the oxygen atom than to the carbon atom
  • This makes the carbon end partially positive and the oxygen end partially negative
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14
Q

What happens because of the polar C=O bond?

A

Due to partially positive bond on carbon, carbonyl compounds will react with nucleophiles in a nucleophilic addition reactions

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15
Q

What is a nucleophile?

A

An electron pair donor

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16
Q

Draw the mechanism of carbonyl compounds with HCN

A

Check in book

:CN- reacts first with carbon
H+ from HCN reacts with O

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17
Q

Describe the reaction of carbonyl compounds with HCN

A
  • HCN adds across C=O bond
  • HCN is extremely poisonous so NaCN/H2SO4 is used to provide HCN
  • reaction increases carbon chain length
  • organic product is a hydroxynitrile
  • nucleophilic addition reaction
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18
Q

Draw the mechanism of an aldehyde being reduced

A

check in book

H- ion has 2 electrons that are from different atoms and comes from NaBH4
H from H2O makes hydroxyl group with oxygen

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19
Q

Draw the mechanism of a ketone being reduced

A

check in book

H- ion has 2 electrons that are from different atoms and comes from NaBH4
H from H2O makes hydroxyl group with oxygen

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20
Q

What type of reaction is ketone/aldehyde and HCN (H+/NaCN)?

A

Nucleophilic addition

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21
Q

What reagent can be used to detect presence of a carbonyl group in a ketone or aldehyde?

A

Brady’s reagent (yellow/orange precipitate)

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22
Q

What is Brady’s reagent?

A
  • Solution of 2,4-DNP dissolved in methanol and sulfuric acid
  • Detects presence of a carbonyl functional group in ketones or aldehydes only
  • Positive test results in a yellow/orange precipitate forming
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23
Q

How can the identity of ketones and aldehydes be determined?

A
  1. Separate precipitate by filtration from solution
  2. Recrystallise to obtain a pure sample
  3. Measure the melting point
  4. Measured melting point can be compared to known values
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24
Q

What reagent can be used to distinguish between aldehydes and ketones?

A

Tollen’s reagent

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25
What is Tollen's reagent?
Solution of silver nitrate in aqueous solution
26
What is the positive test result of using Tollen's reagent?
In the presence of an aldehyde only a silver mirror is formed in an oxidation reaction
27
What reactions happen with Tollen's reagent with a positive test result?
Ag+ ions act as the oxidising agent, Ag+ ions are reduced to silver and aldehyde is oxidised to a carboxylic acid
28
What is the functional group of carboxylic acids?
-COOH (or -CO2H)
29
What are the partial charges on the carboxyl functional group?
partially positive = C and H | partially negative = O
30
How are carboxylic acids synthesised?
Oxidation of primary alcohols (heating with H+/K2Cr2O7 under reflux)
31
What is the suffix (naming) or carboxylic acids?
-oic acid (Methanoic Acid)
32
What is a dicarboxylic acid?
- Contains 2 carboxyl functional groups | - suffix "-dioic acid" final e is kept of the alkane (e.g. Ethanedioic acid)
33
How are benzene rings named with carboxylic acids?
Benzoic acid
34
What type of acids are carboxylic acids?
Weak acids, they only partially dissociate in aqueous solution CH3COOH(aq) ⇌ H+(aq) + CH3COO-(aq)
35
Describe the solubility of carboxylic acids?
The presence of polar C=O and O-H bonds means that carboxylic acids can form hydrogen bonds to themselves and also with water molecules - hydrogen bonds can form at 3 places on the carboxyl function group with water
36
Describe the trend in solubility within carboxylic acids?
As the number of carbon atoms increases, the non-polar carbon chain has a greater effect on the overall polarity of the molecule, and the solubility decreases.
37
Describe the trend in boiling points with carboxylic acids?
as the length of the carbon chain increases melting points increase as more hydrogen bonds have to break between molecules
38
Describe the reaction between carboxylic acids and alkalis?
Alkali + Carboxylic Acid -> Carboxylate + Water - Neutralisation reaction - e.g. KOH (aq) + CH3COOH (aq) → CH3COOK (aq) + H2O(l) - can omit charges on carboxylate ion CH3COO-K+(aq) - potassium ethanoATE produced (sodium salt of ethanoic acid)
39
What is the ionic equation for the reaction between carboxylic acid and an alkali?
H+(aq) + OH- (aq) → H2O (l)
40
What is the reaction between carboxylic acid and a carbonate?
Carboxylic acid + Carbonate → Carboxylate + CO2 + H2O - e.g. Na2CO3(aq) + 2CH3COOH (aq) → 2 CH3COONa(aq) + CO2(g) + H2O(l) - sodium ethanoate produced - neutralisation (?)
41
What is the reaction between carboxylic acid and a metal?
Carboxylic Acid + Metal → Carboxylate + Hydrogen Gas - E.g. Mg(s) + 2CH3COOH(aq) → (CH3COO)2Mg(aq) + H2(g) - Magnesium Ethanoate produced (CH3COO-)2Mg^2+ - redox reaction (?)
42
How do you draw a salt produced from a carboxylic acid?
drawing the molecules in full, you draw the negative charge on the O molecule and the metal molecule next to it with the positive charge, e.g. O-Na+ - if the metal has a charge greater than +1 then the organic molecule doubles and write brackets around it
43
What are the 7 reactions involving carboxylic acids?
carboxylic acid + metal -> salt + hydrogen carboxylic acid + metal oxide -> salt + water carboxylic acid + alkali -> salt + water carboxylic acid + carbonate -> salt + water + CO2 carboxylic acid + alcohol -> ester + water carboxylic acid + SOCl2 -> acyl chloride + SO2 + HCl carboxylic acid + carboxylic acid -> acid anhydride + H2O
44
What is a derivative of a carboxylic acid?
compound that can be hydrolysed to form the parent carboxylic acid
45
What are the 4 derivatives of carboxylic acids?
ester acyl chloride amide acid anhydride all have the acyl RCO group
46
How do you name an ester?
- first part of the name is the alkyl group from the alcohol ( e.g. propanol becomes propyl) - second part of the name is from the carboxylic acid, "oic acid" replaced by "oate" (e.g. ethanoic acid becomes ethanoate Propyl Ethanoate
47
What is the general reaction for an ester?
carboxylic acid + alcohol ⇌ ester + water
48
What conditions does esterification happen under?
- catalysed by concentrated sulfuric acid (acidic) - under reflux - condensation reaction - reversible reaction eventually becomes an epm
49
Methanol + butanoic acid?
Methanol + butanoic acid ⇌ methyl butanoate + water | with concentrated H2SO4 under reflux
50
What bond is broken in ester hydrolysis?
single C-O bond
51
What is hydrolysis?
The chemical breakdown of a compound in the presence of water or in aqueous solution
52
What is a condensation reaction?
2 small molecules react together to form a larger molecule, with the elimination of a small molecule such as water
53
What happens in acid hydrolysis?
ester + water ⇌ carboxylic acid + alcohol - heated under reflux - catalysed with dilute aqueous acid - excess water can be added to push epm to the right and increase yield
54
What happens in alkaline hydrolysis?
ester + water -> salt + alcohol - salt is a sodium carboxylate (write the charges in structure) - irreversible - heated under reflux with NaOH(aq) solution
55
What is the structure of an acyl chloride?
Cl attached to a C attached to = O
56
How are acyl chlorides formed?
carboxylic acid + thionyl chloride (SOCl2) -> acyl chloride + sulfur dioxide (SO2(g)) + hydrogen chloride (HCl(g)) - harmful gases produced
57
How do you name an acyl chloride?
replace -oic acid with -oyl chloride
58
Are acyl chlorides reactive?
- very reactive - very useful in organic synthesis - react with nucleophiles by losing Cl- whilst retaining C=O
59
Draw/write the structure of an acid anhydride?
ethanoic anhydride H3C-C(=O)-O-C(=O)-CH3
60
How is an acid anhydride made?
removing water from 2 carboxylic acid molecules | 2 carboxylic acid -> acid anhydride + water
61
How do you name an acid anhydride?
replace acid with anhydride
62
What are the 3 reactions for preparing esters?
1. carboxylic acid + alcohol ⇌ ester + water (with concentrated acid catalyst) 2. acyl chloride + alcohol -> ester + hydrogen chloride 3. acid anhydride + alcohol -> ester + carboxylic acid - no catalyst needed as they are more reactive than carboxylic acids
63
Ethanol + propanoyl chloride
Ethanol + propanoyl chloride -> ethyl propanoate + HCl
64
Ethanol + ethanoic anhydride
Ethanol + ethanoic anhydride -> ethyl ethanoate + ethanoic acid
65
What is a phenol?
the hydroxyl group is attached directed to a benzene ring (hexagon)
66
What are the 2 reactions for phenols?
acyl chloride + phenol -(room temp)-> ester + hydrogen chloride acid anhydride + phenol -(heat under reflux)-> ester + carboxylic acid - acylating agents - anhydrous conditions
67
What are the 4 overall reactions of acyl chlorides?
acyl chloride + alcohol -> ester + HCl acyl chloride + phenol -> ester + HCl acyl chloride + water -> carboxylic acid + HCl acyl chloride + ammonia -> amide + ammonium chloride
68
What are the 5 overall reactions of carboxylic acids?
carboxylic acid + metal -> salt + hydrogen carboxylic acid + alkali -> salt + water carboxylic acid + metal oxide -> salt + water carboxylic acid + carbonate -> salt + water + CO2 carboxylic acid + alcohol -> ester + water
69
What are the 2 reactions for acid anhydrides?
acid anhydride + alcohol -> ester + carboxylic acid | acid anhydride + phenol -> ester + carboxylic acid
70
Ethanoic acid + Ca
(H3CCOO-)2Ca^2+ (write this even in formula) + H2
71
Propanoic acid + MgO
(CH3CH2COO-)2Mg2+ + H2O
72
Ethanoic acid + KOH
CH3COO-K+ + H2O
73
Propyl butanoate + water
Propyl butanoate + water ⇌(dilute acid) propanol + butanoic acid
74
How can you distinguish between ketones and aldehydes? (ie after Brady's reagent has been added)
- recrystallise to purify - find the melting points - compare it with known values
75
Bond angles in the COOH
angle around C = 120º | angles around O = 104.5º
76
What happens if you add HCl to a compound with more than one ester groups?
C-O bond splits in all ester groups and creates more products
77
What happens if a molecule has a hydroxyl group at one end and a carboxyl group at another, then in refluxed with an acid catalyst?
functional groups react with each other on the same molecule (form a ring)
78
What are the apparatus parts of reflux?
- condenser (water out on top and water in on bottom) - pear shaped flash - anti bumping granules
79
What is the process of reflux?
A technique used for boiling volatile/flammable reactants/products over a prolonged period of time. - any vapour formed is condensed back to a liquid and returned to the pear-shaped flask

A-Level OCR Chemistry (21 decks)

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