Unit 4.4 Aldehydes and Ketones Flashcards
1
Q
What can oxidising primary/secondary alcohols give u?
A
Aldehydes or ketones
2
Q
What’s the oxidising agent used for the oxidisation of primary/secondary alcohols?
(Either one)
A
- Acidified potassium dichromate (VI)
- Acidified potassium manganate (VII)
3
Q
Which alcohol being oxidised creates the formation of an aldehyde?
A
Primary alcohols
4
Q
Show me the equation of the formation of an aldehyde from the oxidisation of primary alcohols
(Whiteboard needed)
A
Where’s your whiteboard?
5
Q
Which alcohol being oxidised creates the formation of a ketone?
A
Secondary alcohols
6
Q
Show me the equation of the formation of a ketone from the oxidisation of secondary alcohols
(Whiteboard needed)
A
Where’s your whiteboard?
7
Q
What are the 2 reagents used to distinguish between aldehydes and ketones
A
- Tollen’s reagent
- Fehling’s reagent
8
Q
What consists of Tollen’s reagent?
(2 things + 1 what?)
A
- Mild oxidising agents such as Ag+
- Usually an ammoniacal solution of silver nitrate
- contains diamminesilver(I) ion, [(NH302Ag]+)
9
Q
What does Tollen’s reagent oxidise?
A
The aldehyde
10
Q
What observations are there from aldehyde with Tollen’s reagent?
and how?
A
- Silver mirror forms
- Oxidised further
11
Q
What does Tollen’s reagent not oxidise?
A
The ketone
12
Q
What observations are there from ketone with Tollen’s reagent?
and how?
A
- No observable change or goes black
- Cannot be oxidised further
13
Q
Equation for aldehyde with Tollen’s reagent?
A
Get your whiteboard
Carboxylic acid formed i think
14
Q
Equation for ketone with Tollen’s reagent?
A
It don’t work
15
Q
What is step 1 of Tollen’s reagent experiment
(Method)
A
- Add 1cm (depth) of silver nitrate to a boiling tube
16
Q
What is step 2 of Tollen’s reagent experiment
(Method)
(2-way)
A
- Add sodium hydroxide dropwise
- until a brown ppt appears
17
Q
What is step 3 of Tollen’s reagent experiment
(Method)
(2-way)
A
- Add ammonia (ammonium hydroxide)
- until the brown ppt disappears
18
Q
What is step 4 of Tollen’s reagent experiment
(Method)
(2-way)
A
- Add a squirt of glucose (aldehyde substitute)
- to the mixture and warm in water bath
19
Q
What consists of Fehling’s reagent?
A
2 solutions
20
Q
What is solution A of Fehling’s reagent?
A
Aqueous copper(II) sulfate
21
Q
What is solution B of Fehling’s reagent?
A
Sodium potassium tartrate (dissolved aq sodium hydroxide don’t listen to that part it’s wrong lol)
22
Q
What does Fehling’s reagent oxidise?
A
The aldehyde
23
Q
What observations are there from aldehyde with Fehling’s reagent?
A
Blue to brick-red
24
Q
What does Fehling’s reagent not oxidise?
A
The ketone
25
What observations are there from ketone with Fehling's reagent?
No observable change
26
Equation for aldehyde with Fehling's reagent?
Get the whiteboard
27
Equation for ketone with Fehling's reagent?
It don't work
28
What is step 1 of Fehling's reagent experiment
(Method)
1. Place 1cm depth of solution A in a test tube
29
What is step 2 of Fehling's reagent experiment
(Method)
2. Add 1cm depth of solution B to solution A
30
What is step 3 of Fehling's reagent experiment
(Method)
3. Add a few drops of the aldehyde
31
What is step 4 of Fehling's reagent experiment
(Method)
4. Place in a warm water bath
32
What are 2 reagents used to reduce aldehydes and ketones?
- Sodium borohydride (NaBH3)
- Lithium aluminium hydride (LiAlH4)
33
What are the reaction conditions needed to reduce aldehydes and ketones
Dissolve in acid/water
34
Eqn of reduction of aldehydes and ketones
(Whiteboard)
(Just do aldehyde insteada ketone)
H3C-C(=O)-H + 2[H] -> H3C-CH(OH)-H
35
If u add HCN to ethanal/propanone, what's that mechanism called?
Nucleophilic addition
36
What is the rate and how do u increase it?… for the addition of HCN to ethanal/propanone?
- Slow
- Increases by addition of alkali/cyanide ions
37
How does adding alkali for the addition of HCN to ethanal/propanone greatly increase rate?
(2-way)
- Neutralises some of the HCN molecules
- giving higher conc. of cyanide ions
38
Equation of addition of HCN to ethanal/propanone?
(Whiteboard)
H3C-C(=O)-H + HCN/KCN -> H3C-CH(OH)-CN
39
Mechanism of addition of HCN to ethanal/propanone?
(Do ethanal insteada propanone)
(Whiteboard)
Refer to the booklet
40
How do u convert ethanenitrile to its corresponding carboxylic acid?
Hydrolysis
41
What happens if u do acid hydrolysis towards ethanenitrile?
(2 things)
- You gain an ethanoic acid
- almost similar to normal hydrolysis
42
How is acid hydrolysis performed towards ethanenitrile?
(2-way)
- Nitrile heated under reflux
- with dilute acid (e.g. dilute hydrochloric acid)
43
Even if u do acid hydrolysis, how would u gain just the carboxylic/ethanoic acid?
Distill off the mixture
44
Equation of acid hydrolysis towards ethanenitrile?
(Whiteboard)
H3C-C≡N -> H3C-C(=O)OH + +NH4
-> = (H+/H2O) or (HCl(aq))
45
What are 2 other hydrolysis' other than normal hydrolysis?
- Acid hydrolysis
- Alkali/Base hydrolysis
46
What is acid/alkali hydrolysis used for?
Produce carboxylic acids
47
What's the difference with alkali/base hydrolysis?
(2 things)
- It is a two-step reaction
- Produces a salt first
48
What happens if u do alkali/base hydrolysis towards ethanenitrile?
(2-way)
- Gain solution containing ethanoate ions
- and ammonia
49
Equation of alkali/base hydrolysis towards ethanenitrile?
H3C-C≡N -> H3C-C(=O)O-Na + NH3
-> = NaOH(aq)
50
What's the 2nd step to gaining the carboxylic acid after step 1 of alkali/base hydrolysis towards ethanenitrile?
(4 things)
- Liberate the "weak acid"
- Supply enough hydrogen ions from a strong acid
- (Hydrochloric acid)
- Enough to the mixture = acidic
51
Equation of step 2 of alkali/base hydrolysis towards ethanenitrile?
H3C-C(=O)O-Na+ -> H3C-C(=O)OH + Na+/Cl-?
-> = HCl(aq)
52
What are 2 other ways to distinguish between aldehydes and ketones?
- Reaction with 2, 4-DNP
- Reaction with Iodoform
53
Long form of 2,4-DNP?
2, 4-dinitrophenylhydrazine reagent
54
What usually happens during the reaction with 2,4-DNP and aldehyes/ketones
(2 things)
- Carbonyl group undergoes nucleophilic attack
- Adduct loses a small molecule (usually H2O)
55
What happens when the carbonyl compound reacts with the reagent "2,4-DNP"?
How’s the of carbonyl compound identified?
(2 things + 1 thing)
- Results in a yellow/orange solid (corresponding hydrazone)
- Derivatives may be isolated & purified
- Based on the mp of the 2,4-**dinitrophenylhydrazone** that is formed
56
How many steps are there to the method of the reaction with 2,4-DNP?
5 steps
57
Step 1 of the reaction with 2,4-DNP w/ aldehydes/ketones
(3-way)
- Add 10 drops of the aldehyde/ketone
- to a solution of 2,4DNPH
- in ethanol
58
Step 2 of the reaction with 2,4-DNP w/ aldehydes/ketones
Observer the formation of an orange ppt
59
Step 3 of the reaction with 2,4-DNP w/ aldehydes/ketones
Filter under reduced pressure
60
Step 4 of the reaction with 2,4-DNP w/ aldehydes/ketones
(1 thing + 2-way)
- Recrystallised from min. volume of hot ethanol
- To obtain pure sample
- filter under reduce pressure
61
Step 5 of the reaction with 2,-DNP w/ aldehydes/ketones
Measure melting point of sample
62
What observations are there with aldehyde and 2,4-DNP reagent?
Orange crystal formed
63
The deduction of an aldehyde with 2,4-DNP reagent?
Contains a carbonyl group
64
What observations are there with ketone and 2,4-DNP reagent?
Red-yellow crystal formed
65
The deduction of a ketone with 2,4-DNP reagent?
Contains a carbonyl group
(hm)
66
What is the reaction with 2,4-DNP an example of?
Nucleophilic addition then elimination mecahnism
(**You don't need to know the mechanism**)
67
Explain the theory of the reaction with 2,4-DNP?
(1 thing + 2-way)
- 2,4-DNPH forms derivative of the aldehyde-ketone that is a solid
- Once purified, can measure mp of solid
- then compare result to a literature ref.
68
What does it mean if the mp of the solid formed is sharp?
(Theory of the reaction with 2,4-DNP)
Substance is pure
69
What does it mean if the sample of the solid melts over a range?
(Theory of the reaction with 2,4-DNP)
Probably impure
70
How does the iodoform test take place?
(4 steps)
- Iodine solution added to small amount of aldehyde/ketone,
- followed by enough NaOH solution,
- to remove the colour of iodine
- If nothing happens, warm the mixture gently
71
What is the positive result with the iodoform test?
- Very pale yellow precipitate of iodoform (CHI3)
72
How else can a positive result with the iodoform test be recognised?
(2 things)
- Faintly "medical" smell
- Used as an antiseptic on sticky plasters
73
How many steps are there to the method of the iodoform test?
6 steps
74
State step 1 of the iodoform test
1. Add 1 cm3 of propanone to a conical flask
75
State step 2 of the iodoform test
(2-way)
2. To 12 cm3 of deionised water
2. add 5g of potassium iodide (KI)
76
State step 3 of the iodoform test
3. Add 5 cm3 of "M sodium hydroxide
77
State step 4 of the iodoform test
(2-way)
4. Add 20 cm3 of sodium chlorate(I) solution (sodium hypochlorite)
4. slowly from separating/dropping funnel
78
State step 5 and 6 of the iodoform test
5. Swirl to mix
6. Observe any changes
79
What's the theory with the iodoform test?
(2-way + 1 thing)
- Iodine reacts with methyl carbon
- to form CHI3 that leaves the molecule
- Iodorm gives a characteristic hospital smell
80
Another word for iodoform
(we aren't meant to like this one)
Triiodomethane
81
What other positive test can u get with the iodoform test?
(3-way)
- Ethanol (only primary alcohol),
- & secondary alcohols,
- where OH group next to methyl group
82
Little tweaks perhaps, then u can spam ppq
HOWEVER, chem tests always intertwine with other topics. Therefore, U should, definitely, clarify on 4.2 probably? Or some of them, it's knowing the tests that appears to be very important ¬.¬
