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Flashcards in Nitriles Deck (47):
1

In a coupling reaction to produce azo dyes: why do colours arise?

They arise from the overlap of Pi electrons from the -N=N- bond and the delocalised Pi electrons of the 2 benzene rings - this extended Pi system is called a conjugated system

Such systems absorb EM radiation from the visible part of the EM spectrum- they are known as chromophores

Chromophores are groups that cause a colour in a molecule

2

What is the temperature for the formation of azo dyes? Why?

Below 10 degrees because at higher temps the benzenediazonium chloride decomposes to form phenol and nitrogen gas

3

How are azo dyes produced?

From the coupling linking 2 benzene rings to form a single larger molecule under alkaline conditions using sodium hydroxide solution

4

What are the conditions for formation of azo dyes

Alkaline - NaOH solution
Below 10 degrees

5

What happens to the azo dyes once they're formed?

Filtered and purified

6

What dye does phenol produce with benzenediazonium chlorid?

Orange dye (PPT)
4-(phenylazo)phenol

7

What dye does phenylamine produce with benzenediazonium chlorid?

Yellow dye (PPT)
4-(phenylazo)phenylamine

8

What dye does naphthalen-2-ol produce with benzenediazonium chlorid?

Red dye PPT
1-(phenylazo)naphthalen-2-ol

9

What type of amines produce diazonium compounds such as benzenediazonium chloride?

Aromatic amines eg phenylamine

10

Give 2 ways to distinguish between aliphatic and aromatic amines

1- add nitrous acid to both in cold conditions, bubbles of nitrogen gas are seen with aliphatic but no bubbles seen with aromatic

2- add nitrous acid to both in cold alkaline conditions, add an aromatic compound eg phenol, a colour (ppt) is produced with the aromatic amine
No colour with aliphatic

11

What is formed when benzenediazonium chloride is warmed with potassium iodide?

Iodobenzene formed and nitrogen gas bubbles seen

12

What happens when aliphatic amines react with nitrous acid?

they react at any temperature to give a complex mixture including a corresponding alcohol and nitrogen gas (bubbles)

NUCLEOPHILIC substitution reaction

Also aromatic amines that don't have the amine group directly attached to the ring ready in this way

13

How do you form nitrous acid?

From sodium nitrate and hydrochloric acid

NaNO2 + HCl --> HNO2 + NaCl

14


Aromatic amines can produce 2 different types of products when reacted with nitrous acid: what is this dependant on?

Temperature
Room temp or below 10 degrees

15

Reaction between aromatic amines and nitrous acid at room temperature

Produce phenol and nitrogen gas (N2) (+h2O)

16

Reaction between aromatic amines and nitrous acid below 10 degrees

Benzenediazonium chloride produced

Excess nitrous acid HNO2 used to make sure all the phenylamine is converted as benzenediazonium chloride will couple with the unused phenylamine otherwise

17

What if the Reaction between aromatic amines and nitrous acid at in cold conditions was now allowed to warm to room temp with water present?

The benzenediazonium chloride would decompose to form phenol and nitrogen gas

18

Give formula of benzenediazonium chloride

C6H5N2Cl

19

What happens in the formation of nitriles from halogenoalkanes?

The carbon atoms increase by 1 in the product

20

Reagents and conditions for formation of nitriles from halogenoalkane

type of reaction.

General equation

Reflux with potassium cyanide in a solution of ethanol

NUCLEOPHILIC sub


RX+ KCN --> RCN + KX

21

Reduction of nitriles
Reagent
Conditions
Formation

Lithium aluminium hydride dry solvent

Room temp

Form primary amine via [4H]

No of C atoms stays same !!!!

22

Producing an amine from a Haloalkanes e.g butyl amine from 1-chloropropane - in this the no of c's has changed so we know we use the method in nitriles

1- form the nitrile from the halogenoalkane - KCN via ethanol and reflux : NUCLEOPHILIC sub

2- reduce the nitrile to an Amine using LiAlH4 dry solvent room temp [4H]: reduction

23

Acid hydrolysis of nitriles

Reflux with aqeous hydrochloric acid

Forms a carboxylic acid and an ammonium salt

No of c doesn't change

24

How to make a carboxylic acid from a halogenoalkane

1- form a nitrile from Halogenoalkane (KCN, ethanol, reflux)

2- acid hydrolysis of the nitrile aqeous HCl to produce carboxylic acid

25

Alkaline hydrolysis of nitriles

Reflux with aqueous NaOH a

Produces sodium salt and ammonia gas

No of c doesn't change

Then add aqueous HCl to salt to form carboxylic acid + Sodiumchloride

26

Converting carboxylic acids to nitriles method :

1- add ammonium carbonate to acid to produce ammonium salt

2- concert salt to amide by Heating (it dries on heating)


3- HEAT amide with PHOSPHORUS (V) OXIDE P4O10 - THE AMIDE DEHYDRATES TO FORM A NITRLE (No of C doesn't change)

27

What do nitriles contain?

A nitrile group which is polar
-CN

28

Naming nitriles:

Ethanenitrile- CH3CN

Propanenitrile- CH3CH2CN

(The C in the CN counts as a carbon atom!!!)

29

What is the reagent used to make nitriles?

Potassium cyanide

30

General equation for formation of nitriles

RX + KCN ---> RCN + KX


C on the CN act as a carbon atom so c's increase by 1

31

General equation for the reduction f nitriles

RCN ----> ([4H]) RCH2NH2

Forms an amine which is RCH2NH2

No of c atoms doesn't change

32

General equation for acid hydrolysis of nitriles

RCN + 2H2O + HCl ---> RCOOH + NH4Cl

(Ammonium chloride is a co product)

33

Reaction equations for alkaline hydrolysis of nitriles

1- RCN + H2O + NaOH ---> RCOO-Na+ + NH3 (g)

2- RCOO-Na+ + HCl ---> RCOOH + NaCl

34

Reaction step equations converting carboxylic acids to nitriles

1- RCOOH + (NH4)2CO3 --> RCOO-NH4+ + CO2 + H2O

2- RCOO-NH4+ ----> (heat) RCONH2 + H2O
(amide)

3- RCONH2 -----> RCN + H2O
(Using phosphorus (v) oxide and heat)

35

General equation for formation of nitriles

RX + KCN ---> RCN + KX


C on the CN act as a carbon atom so c's increase by 1

36

General equation for the reduction f nitriles

RCN ----> ([4H]) RCH2NH2

Forms an amine which is RCH2NH2

No of c atoms doesn't change

37

General equation for acid hydrolysis of nitriles

RCN + 2H2O + HCl ---> RCOOH + NH4Cl

(Ammonium chloride is a co product)

38

Reaction equations for alkaline hydrolysis of nitriles

1- RCN + H2O + NaOH ---> RCOO-Na+ + NH3 (g)

2- RCOO-Na+ + HCl ---> RCOOH + NaCl

39

Reaction step equations converting carboxylic acids to nitriles

1- RCOOH + (NH4)2CO3 --> RCOO-NH4+ + CO2 + H2O

2- RCOO-NH4+ ----> (heat) RCONH2 + H2O
(amide)

3- RCONH2 -----> RCN + H2O
(Using phosphorus (v) oxide and heat)

40

Reaction equation for formation of a Diazonium compound (benzenediazonium chloride)

C6H5NH2 + NaNO2 + 2HCl ---> C6H5N2Cl + NaCl + 2H2O

41

Equation to form red azo dye

C6H5N2Cl + C10H7OH + NaOH --> C6H5N2C10H6OH + NaCl + H2O

42

Equation for formation of yellow azo dye

C6H5N2Cl + C6H5NH2 + NaOH ---> C6H5N2C6H4NH2 + NaCl + h2O

43

equation for formation of orange azo dye

C6H5N2Cl + C6H5OH + NaOH ---> C6H5N2C6H4OH + NaCl + h2O

44

Reagents to form nitrous acid

Sodium nitrate and hydrochloric acid

45

Excess nitrous acid is used in the reaction of aromatic amines below 10 degrees, why?

Excess hno2 used to make sure all the phenylamine is converted otherwise the benzenediazonium chloride will couple with the unused phenylamine

46

Equation for the reaction of aromatic amines with nitrous acid at room temp

C6H5NH2 + HNO2 --> C6H5OH + N2 + H2O

47

What is the origin of a colour of an azo dye eg Methyl red ? (2)

N=N double bond is a chromophore

Compound absorbs all colours but the colour it is, (in this case red).
the remaining frequencies are transmitted which gives the colour