Nitriles
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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