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Organic chemistry and synthesis A2 > Nitriles > Flashcards

Nitriles Flashcards

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1
Q

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

A

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

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2
Q

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

A

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

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3
Q

How are azo dyes produced?

A

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

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4
Q

What are the conditions for formation of azo dyes

A

Alkaline - NaOH solution

Below 10 degrees

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5
Q

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

A

Filtered and purified

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6
Q

What dye does phenol produce with benzenediazonium chlorid?

A 
Orange dye (PPT) 
4-(phenylazo)phenol
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7
Q

What dye does phenylamine produce with benzenediazonium chlorid?

A 
Yellow dye (PPT) 
4-(phenylazo)phenylamine
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8
Q

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

A

Red dye PPT

1-(phenylazo)naphthalen-2-ol

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9
Q

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

A

Aromatic amines eg phenylamine

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10
Q

Give 2 ways to distinguish between aliphatic and aromatic amines

A

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

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11
Q

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

A

Iodobenzene formed and nitrogen gas bubbles seen

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12
Q

What happens when aliphatic amines react with nitrous acid?

A

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

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13
Q

How do you form nitrous acid?

A

From sodium nitrate and hydrochloric acid

NaNO2 + HCl –> HNO2 + NaCl

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14
Q

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

A

Temperature

Room temp or below 10 degrees

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15
Q

Reaction between aromatic amines and nitrous acid at room temperature

A

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

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16
Q

Reaction between aromatic amines and nitrous acid below 10 degrees

A

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

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17
Q

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?

A

The benzenediazonium chloride would decompose to form phenol and nitrogen gas

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18
Q

Give formula of benzenediazonium chloride

A

C6H5N2Cl

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19
Q

What happens in the formation of nitriles from halogenoalkanes?

A

The carbon atoms increase by 1 in the product

20
Q

Reagents and conditions for formation of nitriles from halogenoalkane

type of reaction.

General equation

A

Reflux with potassium cyanide in a solution of ethanol

NUCLEOPHILIC sub

RX+ KCN –> RCN + KX

21
Q

Reduction of nitriles
Reagent
Conditions
Formation

A

Lithium aluminium hydride dry solvent

Room temp

Form primary amine via [4H]

No of C atoms stays same !!!!

22
Q

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

A

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
Q

Acid hydrolysis of nitriles

A

Reflux with aqeous hydrochloric acid

Forms a carboxylic acid and an ammonium salt

No of c doesn’t change

24
Q

How to make a carboxylic acid from a halogenoalkane

A

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

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

25
Q

Alkaline hydrolysis of nitriles

A

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
Q

Converting carboxylic acids to nitriles method :

A

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
Q

What do nitriles contain?

A

A nitrile group which is polar

-CN

28
Q

Naming nitriles:

A

Ethanenitrile- CH3CN

Propanenitrile- CH3CH2CN

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

29
Q

What is the reagent used to make nitriles?

A

Potassium cyanide

30
Q

General equation for formation of nitriles

A

RX + KCN —> RCN + KX

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

31
Q

General equation for the reduction f nitriles

A

RCN —-> ([4H]) RCH2NH2

Forms an amine which is RCH2NH2

No of c atoms doesn’t change

32
Q

General equation for acid hydrolysis of nitriles

A

RCN + 2H2O + HCl —> RCOOH + NH4Cl

Ammonium chloride is a co product

33
Q

Reaction equations for alkaline hydrolysis of nitriles

A

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

2- RCOO-Na+ + HCl —> RCOOH + NaCl

34
Q

Reaction step equations converting carboxylic acids to nitriles

A

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
Q

General equation for formation of nitriles

A

RX + KCN —> RCN + KX

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

36
Q

General equation for the reduction f nitriles

A

RCN —-> ([4H]) RCH2NH2

Forms an amine which is RCH2NH2

No of c atoms doesn’t change

37
Q

General equation for acid hydrolysis of nitriles

A

RCN + 2H2O + HCl —> RCOOH + NH4Cl

Ammonium chloride is a co product

38
Q

Reaction equations for alkaline hydrolysis of nitriles

A

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

2- RCOO-Na+ + HCl —> RCOOH + NaCl

39
Q

Reaction step equations converting carboxylic acids to nitriles

A

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
Q

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

A

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

41
Q

Equation to form red azo dye

A

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

42
Q

Equation for formation of yellow azo dye

A

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

43
Q

equation for formation of orange azo dye

A

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

44
Q

Reagents to form nitrous acid

A

Sodium nitrate and hydrochloric acid

45
Q

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

A

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

46
Q

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

A

C6H5NH2 + HNO2 –> C6H5OH + N2 + H2O

47
Q

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

A

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

Organic chemistry and synthesis A2 (16 decks)

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