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A2 Chemistry > amines > Flashcards

amines Flashcards

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1
Q

what are aliphatic amines?

A

amines containing aliphatic - R groups, such as alkyl chains

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2
Q

what are aromatic amines?

A
  • same general formula as aliphatic amines but aromatic amines must have an aromatic -R group.
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3
Q

describe the nature of amines

A
  • organic compounds that contain nitrogen

- can be aliphatic or aromatic

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4
Q

what are amides?

A

organic compounds with functional group:

  • RCONH2
  • a derivative of carboxylic acid
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5
Q

what are primary amines?

A
  • contain 1 -R group and 2 -H groups

- NRH2

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6
Q

what are secondary amines?

A
  • contain 2 -R groups and 1 -H group

- NR2H

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7
Q

what are tertiary amines?

A
  • conatin Three -R groups and no -H groups

- NR3

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8
Q

describe the nature of ammonium ions?

A
  • 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
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9
Q

how can ammonium ions be stabilised?

A

-by using counter-ion to form salt

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10
Q

what is an amine?

A
  • compound based on ammonia where hydrogen atoms have been replaced by alkyl or aryl groups
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11
Q

what behaviours do amines show?

A
  • nucleophile

- base

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12
Q

what type of base are amines?

A

weak bases

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13
Q

why are amines bases?

A
  • amines contain a lone pair of electrons
  • makes amine attracted to positive charge
  • gives them basic property of being able to ‘accept protons’
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14
Q

what determines amines strength of basicity?

A
  • availability of electrons

- if molecule’s electron pair is more available, it’ll be a stronger base

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15
Q

what determines the availability of electrons on amines?

A
  • whether -R groups push or pull electron density

lone pair of electrons more available if electron density is higher

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16
Q

describe why primary aliphatic amines are stronger bases than ammonia, which is a stronger base than aromatic amines

A

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

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17
Q

what does the lone pair of electrons on the amines mean for the amines?

A
  • they’re nucleophiles
  • react with halogenoalkanes in a nucleophilic substitution
  • or with acyl chlorides and acid anhydrides in nucleophilic addition-elimination reactions
18
Q

uses of quaternary ammonium salts?

A
  • 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
19
Q

state two ways aliphatic amines can be made

A
  • heating halogenoalkane with excess ammonia

- reducing a nitrile

20
Q

describe what addition of an alkyl group does to an amine and so what is the order of strength of basicity of amines?

A
  • 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
21
Q

describe the ‘positive inductive effect’ on methylamine as an example

A
  • 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
22
Q

conditions for halogenoalkane with excess ammonia and equation

A
  • haloalkane with excess conc. ammonia dissolved in ethanol
  • pressure in a sealed container
    NH3 + CH3Cl —> CH3NH2 + HCl
23
Q

Order these in order of how basic they are, starting with the weakest base:
Meythl amine, phenyl amine, Ammonia

A
  • Phenyl amine, Ammonia, Methyl amine
24
Q

Why are alkyl amines the most basic?

A
  • positive induction effect from the carbon chain makes the lone pair on the nitrogen more available for protons
25
Q

mechanism name for reaction of halogenoalkanes with ammonia

A

nucleophilic substitution

26
Q

outline mechanism with halogenoalkane and ammonia

A
  • 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
27
Q

what is an issue with the production of primary amines by haloalkanes and ammonia? and how can it be solved?

A
  • 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

28
Q

describe the type of bonding present in amines

A

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)

29
Q

conditions of forming an amine by reduction of nitrile

A
  • KCN, warm ethanol and then LiAlH4 in ethoxyethane

- (catalytic hydrogenation) Nickel or platinum catalyst, high temp and pressure

30
Q

describe the reduction of a nitrile to produce a primary amine

A
  • 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
31
Q

What are the advantages and disadvantages of forming an amine through the reduction of a nitrile?

A
  • 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
32
Q

write out reduction of nitrile general equations in the forming of primary amines

A

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

33
Q

suggest one reason why phenylamine cannot be prepared from bromobenzene in a similar way (nucleophilic substitution)

A
  • lone pair of electrons on ammonia will be repelled by electron density of bromobenzene
34
Q

How do you make aromatic amines? Outline the process

A

(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

35
Q

What are the uses of aromatic amines?

A

Dyes

36
Q

What are the products and mechanism for when an amine reacts with an acyl chloride?

A

Nucleophillic addition/elimination

alkyl ammonium salt and amide

37
Q

products of the reaction of halogenoalkane with ammonia

A
  • primary amine and an ammonium salt
38
Q

products of the reaction of halogenoalkane with a primary or secondary amine

A

alkyl-substituted amine and halogen acid

39
Q

how is a secondary amine made from a primary amine?

A
  • 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
40
Q

which is a stronger base, ammonia or cyclohexylamine?

A
  • 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+

A2 Chemistry (9 decks)

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