Nitriles Flashcards
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
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
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
What are the conditions for formation of azo dyes
Alkaline - NaOH solution
Below 10 degrees
What happens to the azo dyes once they’re formed?
Filtered and purified
What dye does phenol produce with benzenediazonium chlorid?
Orange dye (PPT) 4-(phenylazo)phenol
What dye does phenylamine produce with benzenediazonium chlorid?
Yellow dye (PPT) 4-(phenylazo)phenylamine
What dye does naphthalen-2-ol produce with benzenediazonium chlorid?
Red dye PPT
1-(phenylazo)naphthalen-2-ol
What type of amines produce diazonium compounds such as benzenediazonium chloride?
Aromatic amines eg phenylamine
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
What is formed when benzenediazonium chloride is warmed with potassium iodide?
Iodobenzene formed and nitrogen gas bubbles seen
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
How do you form nitrous acid?
From sodium nitrate and hydrochloric acid
NaNO2 + HCl –> HNO2 + NaCl
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
Reaction between aromatic amines and nitrous acid at room temperature
Produce phenol and nitrogen gas (N2) (+h2O)
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
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
Give formula of benzenediazonium chloride
C6H5N2Cl
What happens in the formation of nitriles from halogenoalkanes?
The carbon atoms increase by 1 in the product
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
Reduction of nitriles
Reagent
Conditions
Formation
Lithium aluminium hydride dry solvent
Room temp
Form primary amine via [4H]
No of C atoms stays same !!!!
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
Acid hydrolysis of nitriles
Reflux with aqeous hydrochloric acid
Forms a carboxylic acid and an ammonium salt
No of c doesn’t change
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
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
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)
What do nitriles contain?
A nitrile group which is polar
-CN
Naming nitriles:
Ethanenitrile- CH3CN
Propanenitrile- CH3CH2CN
(The C in the CN counts as a carbon atom!!!)
What is the reagent used to make nitriles?
Potassium cyanide
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
General equation for the reduction f nitriles
RCN —-> ([4H]) RCH2NH2
Forms an amine which is RCH2NH2
No of c atoms doesn’t change
General equation for acid hydrolysis of nitriles
RCN + 2H2O + HCl —> RCOOH + NH4Cl
Ammonium chloride is a co product
Reaction equations for alkaline hydrolysis of nitriles
1- RCN + H2O + NaOH —> RCOO-Na+ + NH3 (g)
2- RCOO-Na+ + HCl —> RCOOH + NaCl
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)
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
General equation for the reduction f nitriles
RCN —-> ([4H]) RCH2NH2
Forms an amine which is RCH2NH2
No of c atoms doesn’t change
General equation for acid hydrolysis of nitriles
RCN + 2H2O + HCl —> RCOOH + NH4Cl
Ammonium chloride is a co product
Reaction equations for alkaline hydrolysis of nitriles
1- RCN + H2O + NaOH —> RCOO-Na+ + NH3 (g)
2- RCOO-Na+ + HCl —> RCOOH + NaCl
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)
Reaction equation for formation of a Diazonium compound (benzenediazonium chloride)
C6H5NH2 + NaNO2 + 2HCl —> C6H5N2Cl + NaCl + 2H2O
Equation to form red azo dye
C6H5N2Cl + C10H7OH + NaOH –> C6H5N2C10H6OH + NaCl + H2O
Equation for formation of yellow azo dye
C6H5N2Cl + C6H5NH2 + NaOH —> C6H5N2C6H4NH2 + NaCl + h2O
equation for formation of orange azo dye
C6H5N2Cl + C6H5OH + NaOH —> C6H5N2C6H4OH + NaCl + h2O
Reagents to form nitrous acid
Sodium nitrate and hydrochloric acid
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
Equation for the reaction of aromatic amines with nitrous acid at room temp
C6H5NH2 + HNO2 –> C6H5OH + N2 + H2O
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
