amines Flashcards
what are aliphatic amines?
amines containing aliphatic - R groups, such as alkyl chains
what are aromatic amines?
- same general formula as aliphatic amines but aromatic amines must have an aromatic -R group.
describe the nature of amines
- organic compounds that contain nitrogen
- can be aliphatic or aromatic
what are amides?
organic compounds with functional group:
- RCONH2
- a derivative of carboxylic acid
what are primary amines?
- contain 1 -R group and 2 -H groups
- NRH2
what are secondary amines?
- contain 2 -R groups and 1 -H group
- NR2H
what are tertiary amines?
- conatin Three -R groups and no -H groups
- NR3
describe the nature of ammonium ions?
- possibility for fourth group (H+) to be added to ammonia through dative covalent bonding
- because of the lone pair on N
- found as ammonium salts because ion much more stable in this form
how can ammonium ions be stabilised?
-by using counter-ion to form salt
what is an amine?
- compound based on ammonia where hydrogen atoms have been replaced by alkyl or aryl groups
what behaviours do amines show?
- nucleophile
- base
what type of base are amines?
weak bases
why are amines bases?
- amines contain a lone pair of electrons
- makes amine attracted to positive charge
- gives them basic property of being able to ‘accept protons’
what determines amines strength of basicity?
- availability of electrons
- if molecule’s electron pair is more available, it’ll be a stronger base
what determines the availability of electrons on amines?
- whether -R groups push or pull electron density
lone pair of electrons more available if electron density is higher
describe why primary aliphatic amines are stronger bases than ammonia, which is a stronger base than aromatic amines
aromatic amines:
- benzene ring draws electrons towards itself and the nitrogen lone pair gets partially delocalised onto the ring
- so electron density on nitrogen decreases, making the lone pair much less available
1y aliphatic amine:
- alkyl groups push electrons onto attached groups. So the electron density on the N atom increases. Makes lone pair more available
what does the lone pair of electrons on the amines mean for the amines?
- they’re nucleophiles
- react with halogenoalkanes in a nucleophilic substitution
- or with acyl chlorides and acid anhydrides in nucleophilic addition-elimination reactions
uses of quaternary ammonium salts?
- quarternary ammonium salts with at least 1 long hydrocarbon chain used as cationic surfactants
- hydrocarbon tail will bind to non-polar substances (like grease, oils + fats)
- whilst cationic head (hydrophillic) will dissolve in water, so useful for fabric cleaners and hair products
- in addition, (ammonium ion) will bind to negatively charged surfaces such as hair and fibre. this gets rid of static, so theyre often used in fabric conditioners
state two ways aliphatic amines can be made
- heating halogenoalkane with excess ammonia
- reducing a nitrile
describe what addition of an alkyl group does to an amine and so what is the order of strength of basicity of amines?
- alkylated amines more basic than ammonia
- and alkyl -R group will increase basicity
- alkyl -R groups push electron density towards the N
- increases electron density on nitrogen, making lone pair more available so:
3y>2y>1y>NH3>aromatic amine
describe the ‘positive inductive effect’ on methylamine as an example
- H atom is slightly more electropositive than C atom
- means C atom has a slight surplus of electrons which N atom can attract towards itself
- effect known as a “positive inductive effect” and it means N atom has an excess of electron density
conditions for halogenoalkane with excess ammonia and equation
- haloalkane with excess conc. ammonia dissolved in ethanol
- pressure in a sealed container
NH3 + CH3Cl —> CH3NH2 + HCl
Order these in order of how basic they are, starting with the weakest base:
Meythl amine, phenyl amine, Ammonia
- Phenyl amine, Ammonia, Methyl amine
Why are alkyl amines the most basic?
- positive induction effect from the carbon chain makes the lone pair on the nitrogen more available for protons
mechanism name for reaction of halogenoalkanes with ammonia
nucleophilic substitution
outline mechanism with halogenoalkane and ammonia
- ammonia attacks carbon in halogenoalkane
- halogen released
- a second ammonia molecule donates its lone pair of electrons to a hydrogen (which stabilised positive charge on N), which breaks off from the alkylammonium salt
- so primary amine and ammonium salt formed
what is an issue with the production of primary amines by haloalkanes and ammonia? and how can it be solved?
- primary amine produced is a nucleophile (it has a LP of electrons)
- so it can react with remaining haloalkane in further nucleophilic substitution reactions, making secondary and tertiary amines and quarternary amines
solution: use large excess of ammonia so primary amine is main product - more ammonia so haloalkane more likely to react with that than a primary amine
describe the type of bonding present in amines
H bonding between molecules
- liquid at room temp
- weaker than in alcohols
(No H bonding between tertiary amine molceules - as no H attached to N)
conditions of forming an amine by reduction of nitrile
- KCN, warm ethanol and then LiAlH4 in ethoxyethane
- (catalytic hydrogenation) Nickel or platinum catalyst, high temp and pressure
describe the reduction of a nitrile to produce a primary amine
- use LiAlH4 (strong reducing agent) in a non-aqueous solvent (e.g. dry ether) followed by some dilute acid
- LiAlH4 too expensive for industrial use so:
nitrile reduced using H gas with metal catalyst like platinum or nickel at high temp and pressure (catalytic hydrogenation)
R-CH2-C-N + 2H2 —>
R-CH2-CH2NH2
What are the advantages and disadvantages of forming an amine through the reduction of a nitrile?
- More efficient than reacting a haloalkane with ammonia as there are no side products
- However there are 2 steps so there will be percentage yield loss between reactions
- KCN is very toxic
write out reduction of nitrile general equations in the forming of primary amines
R-X + KCN –> (warm ethanol) R-C(x3 bond)N + KX
in
R-C(x3 bond) + 4[H] —> (LiAlH4) in ethoxyethane —> R-CH2-NH2
in short: R-CN + 4[H] -> R-CH2-NH2
suggest one reason why phenylamine cannot be prepared from bromobenzene in a similar way (nucleophilic substitution)
- lone pair of electrons on ammonia will be repelled by electron density of bromobenzene
How do you make aromatic amines? Outline the process
(1) heat mixture of a nitro compound, tin metal and conc. HCl under reflux - makes a salt
(2) turn salt into aromatic amine, add an alkali such as NaOH solution
What are the uses of aromatic amines?
Dyes
What are the products and mechanism for when an amine reacts with an acyl chloride?
Nucleophillic addition/elimination
alkyl ammonium salt and amide
products of the reaction of halogenoalkane with ammonia
- primary amine and an ammonium salt
products of the reaction of halogenoalkane with a primary or secondary amine
alkyl-substituted amine and halogen acid
how is a secondary amine made from a primary amine?
- nucleophilic substitution (same mechanism as NH3 with halogenoalkane)
- electrons on nitrogen of 1y amine attack delta positive carbon
- carbon-halogen bond breaks, halogen leaves as ion and primary amine joins on, nitrogen now has a positive charge
- ammonia molecule attacks hydrogen and neighboring hydrogen stabilizes positive nitogen and hydrogen breaks off, forming ammonium ion with ammonia molcule
which is a stronger base, ammonia or cyclohexylamine?
- cyclohexylamine is a primary amine compared to ammonia
- cyclohexylamine has a greater electron density on Nitrogen lone pair
- cyclohexylamine has a greater ability to accept H+
