Aldehydes and ketones Flashcards Preview

Organic chemistry and synthesis A2 > Aldehydes and ketones > Flashcards

Flashcards in Aldehydes and ketones Deck (25):
1

Aldehyde test- tollens reagent I

- add solution of silver nitrate containing Ag+ ions to solution of excess ammonia to form a complex

Complex is added to aldehyde and is warmed gently - it is oxidised to the corresponding. Carboxylic acid

Ag+ ions are reduced to Ag - REDUCATION RXN

SILVER MIRROR RESULT SEEN
Doesn't work for ketones

2

Aldehyde test- fehlings

It is a complex containing copper (II) sulfate containing Cu2+ ions, which are BLUE

Complex is added to the aldehyde which is oxidised to a carboxylic acid

Copper sulfate is reduced to copper oxide containing cu+ ions which are red

REDOX RXN- COLOIR CHANGE BLUE TO RED
doesn't work for Ketones

3

Triiodomethane / iodoform

Add unknown compound to a solution of iodine and sodium hydroxide

A yellow ppt and antiseptic smell due to. Triiodomethane forming

A positive result is only seen if CH3CO is present

Ethanal is only aldehyde to give positive result
Ketones can have positive results

4

Name tests for to distinguish between aldehydes and ketones

And why?

Fehlings reagent

Tollens reagent

As they both don't work for ketones only aldehydes

5

Give the observation of an aldehyde with tollens reagent ?

A silver mirror

6

What is the observation of an aldehyde with fehlings?

Blue to red colour change

7

What type of reaction is tollens test?

Redox

8

What type of reaction is fehlings test?

Redox reaction

9

What is 2-4-DNP also known as?

What is it a test for?

Brady's reagent

Both aldehydes and ketones

10

2-4-DNP test to identify aldehyde and ketones

Add Unknown to 2,4-DNP In methanol or dilute acid

Orange crystals formed

Filter and wash cold solvent

Dry and take the MP and compare it with literature value

11

Describe 2-4-DNP

Aldehydes and ketones react to produce orange crystals (hydrazine deravatives)

It is a NUCLEOPHILIC addition + elimination RXN
Also called condensation as a molecule of water is eliminated

MPS of crystals are high due to more IMF (VDW+H bonds)- these MPS can be used to identify the original carbonyl compound by comparing it with literature value

If product is pure then MP is sharp
If product is impure then MP is over a range

12

How can the original carbonyl compound be identified in 2,4-DNP?

The MPS of the products can be used to identify original carbonyl compound by comparing it with the literature value

13

What type of reaction is aldehyde and ketone test 2,4-DNP?

NUCLEOPHILIC addition and elimination

14

What is a test for both aldehydes and ketones

2,4-Dinitrophenylhydrazine

15

What is formed in:

Tollens test

Fehlings test

Triiodomethane / iodoform

2,4-DNP

Tollens: silver mirror

Fehlings: COLOIR change blue to red

Iodoform: yellow ppt if positive result occurs

2,4-DNP: orange crystals

16

Give a test to distinguish between aldehyde and ketone

Fehlings reagent- add both to this complex which contains copper sulfate (Cu2+ ions which are blue), when aldehyde Is gently heated is oxidises to carboxylic acid- and there's a blue to red colour change with aldehyde as the cooper sulfate reduced to Cu+ ions which are red. Ketones won't react with fehlings reagent

17

What is a positive result when aldehyde or ketone reacts with a reagent

(Name reagent also)

Reagent is sodium hydroxide (aq) and iodine

Positive result is CH3CO

18

What produces orange crystals?
What type of reaction is this?

Aldehydes and ketones do with 2,4-DNP

This is a NUCLEOPHILIC addition / elimination reaction

19

What is produced in the addition of hydrogen cyanide and aldehyde or ketones

2-hydroxynitrile

20

Step by step of hydrogen cyanide adding to an aldehyde or ketone

HCN Ionises or disassociates into a H+ ion and cyanide ion - Heterolytic fission

The C on cyanide ion acts as a NUCLEOPHILE attacking the C on the carbonyl- NUCLEOPHILIC addition

A negative charge is produced in the oxygen and electron density increases - the oxygen becomes an electron pair donor attracting the H+ from the solvent eg water or the original HCN

A molecule of HCN has added across the C=O producing a hydroxy nitrile

21

Type of reaction occurring in 2,4-DNP?

NUCLEOPHILIC addition and elimination

22

What is the only aldehydes to produce a positive result with Triiodomethane/iodoform (NaOH(aq)/I2) ?

Ethanal

23

What is the positive result group for an aldehyde or ketone with iodine and sodium hydroxide (aq)?

CH3CO

24

Why is is better to use one step processes in synthesis ?

Better yield (in each stage there is waste products)

25

Why are 2 step processes carried out despite them being not as good as 1 step?

Because it's cheaper