Aromatics And Amines Flashcards
What is an aliphatic chemical
One that contains straight or branched chain organic substances
What is an aromatic / arene
One that contains benzene
What is molecular formula of benzene
C6H6
Describe the structure of benzene
Six carbon atoms in an hexagonal ring
Each carbon atom bonded to 2 carbons and one hydrogen atoms
Six p orbital electrons delocalised in a ring structure above and below the plane of carbon atoms
Why is benzene a planar molecule
All the c-c bongs are the same and have a length and bond every between a c-c single bond and a carbon carbon double bond
Why is benzene more stable than the theoretical structure by kekule
Enthaply of hydrogenation for benzene is 208 but for structure it’s 360 due to stability from delocalised electrons
Why does benzene undergo electophilic substitution instead of addition
It would break the delocalised system which would disrupt the stability of of benzene, substitution preserved the stability also benzene has high electron density so it can attract electrophiles
Why is benzene toxic
Why does methyl benzene react more readily
It is a carcinogen
The methyl side group releases electrons into the devalued system which makes it more attractive to electrophiles
What is the mechanism for the nitration of benzene called
Electrophilic substitution
What are the reagents for the nitration of benzene and conditions
Concentrated sulfuirc acid
Concentrated nitric acid
50 degrees Celsius
What is the electrophiles in the nitration of benzene
NO2 +
Why is nitration of benzenes and important reaction
Makes useful compounds like explosives and formation of amines which came be used in pharmaceuticals and dye
What is the equation for the formation of the electrophiles in the nitration of benzene
HN03 + H2SO4 ->. NO2+ HSO4- H2O
What is formed in the nitration of benzene
Nitrobenzene
What is formed in friedel crafts acylation
A phenyl ketone
What are the reagents and conditions for friedel crafts acylation
Acyl chloride in presence of anhydrous aluminium chloride catalyst
What is the mechanism for friedel crafts acylation and what is the condition
Electrophilic substitution
Heat under reflux at 50 degrees c
Why are friedel craft acylation reactions important
They introduce a reactive functional group onto benzene rings
How are aromatic amines made by reducing nitrobenzene
Heat under reflux with concentrated hydrochloric acid and tin to form a salt ( c6h5nh3+cl-)
The salt reacts with the alkali naoh to form aromatic amine
What type of reaction forms amines by nitrobenzene
Reduction
Why do primary aliphatic amines act as bronsted Lowry bases
The lone pair of electrons in the nitrogen is readily available for forming a dative covalent bond with a H+ so it accepts a proton
Why are primary aliphatic amines weak bases
Only a low concentration of hydroxide ions is produced
Why are primary aliphatic amines stronger bases then ammonia
The alkyl groups are electron releasing and push electrons towards the nitrogen atom so the lone pair of electrons on nitrogen are more readily available
Why are secondary amines stronger bases than primary amines
They have more alkyl groups substituted into the nitrogen atom in place of H so more electron density is pushed into the N atom so lone pair more readily available
How do amines react with acids
They all react to form ammonium salts
Why do primary aromatic amines not form basic solutions
The lone pair in he nitrogen delocalise with the ring of electrons in benzene so the nitrogen is less able to accept protons
How can primary amines be formed by a halogenoalakne
What is formed with it
Reacting it with excess ammonia under reflux
Alkyl ammonium salt
Why is using halogenoalakens to from primary amines not the best method
It doesn’t form a pure product because the the amine formed still has a lone pair on the nitrogen so it can keep reacting with the halogenoaljene to form secondary, tertiary and quaternary amines
In the mechanism to form amines with halogenoalaknes why is excess ammonia used
2 ammonia molecules needed
Acts as nucleophile
Then acts as a base
What are quaternary salts used as
Cationic surfactants (cleaning products)
How do cationic surfactants work
The positive nitrogen is attracted to negatively charged surfaces like glass, hair, fibres and plastics
Non polar tail attracted to oil and grease, polar head attracted to water so mix to remove grease
Positive ammonium ion attracted to negatively charged fibres and hair so removes static so used in hair conditioner and fabric softeners
How are amines prepared from nitriles (catalytic hydrogenation)
Convert halogenoalkane to nitrile using KCN in aqueous ethanol under reflux
Reduce nitrile to amine using LiAlH4 in other
Or reducing hydrogen using a nickel catalyst
Advantage and disadvantage of producing amines by catalytic hydrogenation
Only produces primary amines
Used kcn which is toxic and it’s 2 steps so might have lower yield
