amines, benzene, acylation Flashcards
What is the formula of benzene ?
C6H6
What is the length of the C-C bond in benzene ?
- between length of a single and double bond
- 134 pm –> length of a double bond
- 154 pm –> length of a single bond
what reactions do arenes undergo ?
electrophilic substitution
What is Friedel -Crafts acylation ?
acyl group (RCO) is added onto a benzene ring
Why is FC acylation used ?
makes benzene more reactive ( by weakening the structure)
How is the strongly positive electrophile generated in FC acylation ?
acyl chloride reacts with a halogen carrier ( AlCl3)
this forms RCO + ( + is on the C) and ALCl4 -
What is the catalyst in FC acylation ?
AlCl3 ( as it is regenerated)
What are the conditions for FC acylation ?
under reflux + in dry ether solvent
what is nitration of benzene used for ?
dyes for clothing & explosives like TNT
How is the powerful electrophile in nitration of benzene made ?
Give the half equations for formation of electrophile
by reacting concentrated HNO3 and H2SO4
HNO3 + H2SO4 –> H2NO3+ (+) HSO4-
H2NO3 + —> NO2 + (+) H2O
NO2 + is the electrophile
What temperature should the reaction be carried out ? Why ?
below 55 degrees C
This prevents multiple NO2 substitutions happening
What is the catalyst for nitration of benzene ?
H2SO4
H+ made when C–H bond breaks reacts with HSO4 - to regenerate H2SO4
what is an arene
any molecule that contains a benzene ring
why is benzene so stable ?
- delocalised ring of electrons spreads out electron density
- equal C–C bond lengths
- flat, cyclic molecule which allows for max overlap of p-orbitals for optimum delocalisation
- high symmetry
what are amines derived from ?
ammonia molecules
What do amines all contain ?
N atom, where the H atoms are replaced with an alkyl/aryl group
Structure of a quaternary amine ?
R4N +
( N surrounded by 4 alkyl/aryl grps)
What are quaternary ammonium salts used for ?
shampoo, laundry detergents & washing up liquids
What are cationic sufactants ?
quaternary ammonium salts with a long hydrocarbon tail
What are quaternary ammonium salts ?
made up of a quaternary ammonium ion ( R4N+) & a counterion ( negatively charged) ie Br- , Cl- or OH-
counterion balances out the positive charge from R4N+
How does washing liquid work ( cationic surfactant)
- non polar HC tail attracts the oil
- polar head ( R4N+) attracts the water
- allows oil and water to mix, so grease can be removed
How does hair conditioner/ fabric softener work ?
R4N+ is attracted to “-“ charged fibres ( in clothes) & hair, to remove static
Why do quaternary ammonium salts not act as bases ?
N has a “+” charge, so repels the H+
N also doesn’t have a lp of electrons
the strength of the base is dependent on what ?
the availibility of the lp of electrons on the N
this depends on the electron density at N
how can aliphatic amines be made ?
- reacting a haloalkane with excess ammonia
- reducing a nitrile
in reacting a haloalkane with excess ammonia, the ammonia acts as what ?
- initially acts as a nucleophile
- in second stage, acts as a base
what is the downside of the method of making an amine by reacting a haloalkane with exc ammonia ?
produces secondary, tertiary and quaternary salts ( inst of just pure ammonium salts)
so product is impure
What are the reagents, and relevant conditions needed for reducing nitriles ?
nickel catalyst + H2 gas
high temp & pressure
Or
strong reducing agent ( LIAlH4) & dilute acid
in dry ether & at room temp
pros of using reducing nitriles method to make aliphatic amines ?
- pure product made
- cheapest way in industry
How can aromatic amines be made ?
reducing nitro-compounds like nitrobenzene
What are the steps for reducing nitro-compounds ?
- nitrobenzene heated under reflux with conc HCl and tin catalyst
- salt formed reacts with alkali ie NaOH tp produce aroma amine
condition for reducing nitro-compounds
under reflux
what are amides ?
derive from - COOH acids and amines
have the funct group -CONH2
what is an n-subs amide ?
one of the H atoms in the amide is replaced with an alkyl grp
What is the funct grp of acid chloride
RCOCl ie ethanoyl chloride (CH3COCL)
What is an acyl functional grp
RCO ( C is bonded to O with db)
What is the functional group for an acid anhydride ?
RCOOCOR ie ethanoic anhydride ( CH3COOCOCH3)
What three factors affect the rate of nucleophilic addition- elimination ?
- magnitude of delta positive charge on carbonyl carbon
- How easily Z ( the leaving grp) is lost
- how good the nucleophile is
What is the mech for acylation reactions called ?
nucleophilic addition -elimination
What are the conditions for reactions of acid derivatives with nucleophiles ?
room temp
When an acid chloride/anhydride reacts with ammonia what is formed
amide
When an acid chloride/anhydride reacts with amine what is formed
N-substituted amide
When an acid chloride/anhydride reacts with alcohol what is formed
ester
When an acid chloride/anhydride reacts with water what is formed
carboxylic acid
what are advantages of ethanoic anhydride over ethanoyl chloride ?
- cheaper
- less corrosive
- doesn’t react with water as readily
- safer, as byproduct of the reaction is ethanoic acid inst of HCl
what is aspirin made from
reaction with salicylic acid and ethanoyl anhyride
