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A-Level Organic Chemistry AQA (Paper 2) > Amines > Flashcards

Amines Flashcards

1
Q

What are amines? (2)

A
  • Reactive compounds useful as intermediates in synthesis (making new molecules).
  • Where one or more of the hydrogen in ammonia have been replaced by an alkyl or aryl group.
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2
Q

What is an aryl group?

A

•Contains a benzene ring.

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3
Q

How are amines without isomers named?

A

•Alkyl amine.

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4
Q

How do you name amines when isomers exist?

A

•Amino group is numbered and the prefix ‘amino’ is used.

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5
Q

What is CH3NH2?

A

•Methylamine.

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6
Q

What is CH3CH2NH2?

A

•Ethylamine.

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7
Q

What is CH3CH2CH2NH2?

A

•1-aminopropane (isomers exist).

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8
Q

Draw a primary amine and give its general formula. (2)

A
  • Nitrogen, lone pair, two hydrogens, one R group.

* RNH2.

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9
Q

Draw a secondary amine and give its general formula. (2)

A
  • Nitrogen, lone pair, one hydrogen, two R groups.

* RR’NH.

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10
Q

Draw a tertiary amine and give its general formula. (2)

A
  • Nitrogen, lone pair, three R groups.

* RR’R”N.

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11
Q

In amines, what does 1º, 2º and 3º refer to?

A

•The number of of substituents (R-groups) on the nitrogen atom.

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12
Q

Where is the N joined in aromatic amines?

A

•Directly to the benzene ring.

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13
Q

What are quaternary ammonium salts? (2)

A
  • Contain quaternary ammonium ions, related to amines (not amines).
  • Don’t possess a lone pair of electrons on the N.
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14
Q

What is the shape of ammonia? (2)

A
  • Pyramidal model with bond angles of approximately 107º.

* The lone pair repels more than the bonding pairs of electrons in the N-H bonds.

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15
Q

Draw a diagram to show the polarity of amines.

A

•Polar, 𝛿+ on carbon and hydrogens, 𝛿- on nitrogen.

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16
Q

What are the boiling points of amines in comparison to alcohols? (2)

A
  • They can hydrogen bond to one another using their -NH2 groups, but nitrogen is less electronegative than oxygen in OH (O = 3.5, N = 3.0).
  • Hydrogen bonds are not as strong as those in alcohols, so boiling points are lower than alcohols, means the molecules are easier to separate.
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17
Q

What are shorter chain amines like methylamine and ethylamine? (3)

A
  • Gases at room temperature.
  • Slightly longer chains are volatile liquids.
  • Have fishy smells - rotting fish and rotting animal flesh smell of di- and triamines when proteins decompose.
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18
Q

Which amines are soluble? (3)

A
  • Primary amines with chain lengths up to around four carbon atoms are soluble in water and alcohol.
  • Hydrogen bonds are formed with solvents.
  • Most amines are soluble in a less polar solvent.
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19
Q

Why is phenylamine, C6H5NH2, not very soluble in water?

A

•The benzene ring cannot form hydrogen bonds.

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20
Q

What is the reactivity of amines? (3)

A
  • Have a lone pair of electrons which can form a bond with:
  • A H^+ ion when the amine is acting as a base.
  • An electron-deficient carbon atom, when the amine is acting as a nucleophile.
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21
Q

What is an acid?

A

•H^+/proton donor.

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22
Q

What is a base?

A

•H^+/proton acceptor.

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23
Q

Since amines can accept a proton (H^+ ion), they are…

A

•Brønsted-Lowery bases.

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24
Q

What does the reaction of amines as bases involve? (2)

A
  • Amines react with acids to form salts.

* Products are ionic compounds that will crystallise as the water evaporates - ammonium salt.

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25
Q

Write an equation for the reaction of ethylamine with dilute hydrochloric acid.

A

CH3CH2NH2 (lone pair on N) + H^+ + Cl^- —> [C2H5NH3]^+ Cl^-
Ethylamine + dilute hydrochloric acid —> ethylammonium chloride

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26
Q

Write an equation for the reaction of methylamine with nitric acid.

A

CH3NH2 (lone pair on N) + HNO3 —> [CH3NH3]^+ NO3^-

Methylamine + nitric acid —> methylammonium nitrate

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27
Q

Write an equation for the reaction of diethylamine and sulfuric acid.

A

2(CH3CH2)2NH(lone pair on N) + H2SO4 —> [(CH3CH2)2NH2]2^+ SO4^2-
2(Diethylamine) + sulfuric acid —> 2(diethylamine sulfate)

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28
Q

Write an equation for the reaction of ethylamine and phosphoric acid.

A

3CH3CH2NH(lone pair on N) + H3PO4 —> [CH3CH2NH3]3^+ PO4^3-

3(Ethylamine) + phosphoric acid —> 3(ethylamine phosphate)

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29
Q

Write an equation to show the formation of ethylammonium sulfate from sulfuric acid.

A

2CH3CH2NH2 + H2SO4 —> [CH3CH2NH3]2^+ SO4^2-

2(Ethylamine) + sulfuric acid —> 2(ethylammonium sulfate)

30
Q

What does the strength of a base depend on? (2)

A
  • How readily it will accept a proton, H^+.

* E.g. Both ammonia and amines have a lone pair of electrons that attract a proton.

31
Q

What is the positive inductive effect? (3)

A
  • When alkyl groups release electrons away from the alkyl group towards the nitrogen atom.
  • Shown by an arrow e.g. R->-N(lone pair)H2.
  • It makes the lone pair of electrons more available on N.
32
Q

What does the positive inductive effect of the alkyl group do?

A

•Increases the electron density on the nitrogen atom and makes it a better electron pair donor (more attractive to protons).

33
Q

Primary alkylamines are stronger bases than…

A

•Ammonia.

34
Q

When medicinal drugs are amines, why are they supplied as hydrochlorides? (2)

A
  • To make them more soluble in the bloodstream - hydrochlorides make it an ionic compound (polar water molecules are attracted to positive and negative ions from the crystal).
  • Longer chain amines are relatively insoluble in water.
35
Q

Ionically bonded compounds exist as…

A

•Solids at room temperature - ionic bonds are held together by strong electrostatic forces of attraction.

36
Q

What problems would chirality have in e.g. pseudoephedrine’s use as a drug?

A

•It is possible that only one of the optical isomers is active as a drug.

37
Q

Why are secondary alkylamines stronger bases than primary alkylamines?

A

•They have two inductive effects.

38
Q

Why are tertiary alkylamines not stronger bases than secondary ones?

A

•They are less soluble in water.

39
Q

Why are arylamines weaker bases than ammonia? (3)

A
  • Aryl groups withdraw electrons from the nitrogen atom because the lone pair of electrons overlaps with the delocalised pi system on the benzene ring = negative inductive effect.
  • The lone pair of electrons on the nitrogen is partially delocalised into the benzene ring (electrons in p-orbitals join the pi system and cause it to extend).
  • This makes the nitrogen a weaker electron pair donor and less attractive to protons.
40
Q

What is the order of strength as a base of the following compounds; ammonia, phenylamine and ethylamine? (3)

A
  • Ethylamine > ammonia > phenylamine.
  • Ethylamine - alkyl groups are electron releasing compared to hydrogen, they push negative charge away from themselves and towards the N (inductive effect).
  • Phenylamine - delocalised pi electrons in benzene merge with the lone pair of electrons on the N, the lone pair becomes part of the delocalised cloud.
41
Q

How are the salts of amines sometimes named?

A

•As the hydrochloride of the parent amine e.g. ethylammonium chloride.

42
Q

Why does the smell of an amine disappear when an acid is added? (2)

A
  • Due to the formation of the ionic (involatile) salt.

* The smell returns if a strong base is added.

43
Q

What does the ability of a base being able accept a proton/H^+ ion depend on? (2)

A
  • The size of the delta negative charge on the amino nitrogen atom.
  • The availability of the lone pair.
44
Q

Which base is stronger, ammonia or phenylmethylamine (C6H5CH2NH2)?

A

•Could be either, phenylmethylamine (the pi system doesn’t extend to the nitrogen, so there isn’t an effect, or positive inductive effect could make the lone pair of electrons more available) or ammonia.

45
Q

What will the lone pair of electrons from an amine do?

A

•Attack positively charged carbon atoms, amines will act as nucleophiles.

46
Q

How are primary aliphatic amines (amine with no aromatic rings) produced? (4)

A
  • When halogenoalkanes are reacted with ammonia.
  • Nucleophilic substitution of the halide by NH3.
  • The primary amine produced is also a nucleophile which reacts with the halogenoalkane (if it’s in excess) to produce a secondary amine, which can then react to produce tertiary amine and then it reacts to produce a quaternary ammonium salt.
  • A mixture of primary, secondary and tertiary amines and a quaternary salt is produced.
47
Q

What are the conditions for nucleophilic substitution?

A

•Excess concentrated ammonia dissolved in ethanol at a pressure in a sealed container.

48
Q

Write out the equations of the formation of an amine from a halogenoalkane (nucleophilic substitution), from primary amine to ammonium salt. (7)

A 
•1). Halogenoalkane and ammonia:
NH3 + RX ---> [RNH3]^+X^-
[RNH3]^+X^- + NH3 ---> RNH2 + [NH4]^+X^-
•2). Primary amine and halogenoalkane:
RNH2 + RX ---> [R2NH2]^+X^- 
[R2NH2] + X^- + NH3 ---> R2NH + [NH4]^+X^-
•3). Secondary amine and halogenoalkane:
R2NH + RX ---> [R3NH]^+X^-
[R3NH]^+X^- + NH3 ---> R3N + [NH4]^+X-
•4). Tertiary amine and halogenoalkane:
R3N + RX ---> [R4N]^+X^-
49
Q

What are the ways in which amines are made? (2)

A
  • From a halogenoalkane - nucleophilic substitution reaction.
  • From a nitrile ((lone pair on C) CN^-) - reduction (halogenoalkanes react with the cyanide ion).
50
Q

What are the problems with making amines from nucleophilic substitution? (2)

A
  • It is not efficient as the mix of products will have to be separated by fractional distillation - longer and impure method.
  • Further substitution is likely.
51
Q

How do you get a better yield of the primary amine from nucleophilic substitution?

A

•Use a large excess of ammonia.

52
Q

Describe and draw the nucleophilic substitution mechanism for making a primary amine from a halogenoalkane and ammonia. (3)

A

•Lone pair on nitrogen from ammonia attacks the delta positive on the carbon (arrow from lone pair to carbon - lone pair on nucleophile is donated to the partially positive carbon).
•Arrow from carbon to delta negative X (halogen), electrons moving to delta negative.
•Ammonia acts as a base - lone pair from N goes to hydrogen to the N-H bond to the positively charged N.
(See textbook page 44)

53
Q

How do you get a better yield of the quaternary ammonium salt from nucleophilic substitution?

A

•Use a large excess of the halogenoalkane.

54
Q

How are primary alkyl amines prepared from halogenoalkanes in a two step process? (Reduction of nitriles) (6)

A

•1). Halogenoalkanes react with the cyanide ion (in KCN) in aqueous ethanol (heating under reflux).
•The cyanide ion replaces the halide ion by nucleophilic substitution to form a nitrile:
RBr + CN^- —> R-C≡N + Br^-
•2). Nitriles contain the functional group -C≡N, they can be reduced to primary amines with a nickel/hydrogen catalyst or by LiAlH4:
R-C≡N + 2H2 –(nickel catalyst + heat)–> R-CH2NH2
OR
R-C≡N + 4[H] –(LiAlH4 in dry ether)–> R-CH2NH2
•Purer product produced - only primary amine can be formed.
•Carbon chain of the product is one carbon atom longer than the starting material.

55
Q

Describe the process of preparation of alkyl amines by reduction of nitriles. (4)

A

•Reduction of nitriles using a reducing agent e.g. LiAlH4 ([H]) (lithium aluminium hydride) in a non-aqueous solvent e.g. dry ether.
•Nitrile compound produced from a halogenoalkane by heating under reflux ethanol and KCN (aq):
RX + KCN —> RCN + KX
RCN + 4[H] —> RCH2NH2

56
Q

Describe the process of preparation of alkyl amines using hydrogen and a metal catalyst - reduction of nitriles. Use ethanenitrile (3)

A
  • Carbon-nitrogen triple bond in a nitriles reduced by reaction with hydrogen gas in the presence of a palladium/platinum/nickel catalyst.
  • Reaction takes place at a raised temperature and pressure:
  • E.g. CH3CN + 2H2 —> CH3CH2NH2
57
Q

What is phenyl amine? (3)

A
  • The simplest arylamine.
  • The starting point for making many other chemicals.
  • Made in industry using benzene produced from crude oil.
58
Q

Why would you not prepare phenylamine in a school laboratory?

A

•Benzene is carcinogenic.

59
Q

Describe how you would produce phenylamine from benzene. (8)

A

•1). Benzene is reacted with a mixture of concentrated nitric and concentrated sulfuric acid, to produce nitrobenzene:
Benzene + HNO3 –(conc H2SO4)–> nitrobenzene + H2O
•2). Nitrobenzene is reduced to phenylamine, using tin and hydrochloric acid as the reducing agent [H].
•Tin and hydrochloric acid react to form hydrogen, which reduces the nitrobenzene by removing oxygen atoms of the NO2 group and replacing them with hydrogen atoms:
Nitrobenzene + 6[H] –(Sn/HCl, room temp)–> phenylamine + 2H2O
C6H5NO2 + 6[H] —> C6H5NH2 + 2H2O
•Since the reaction is carried out in HCl, the salt C6H5NH3^+Cl^- is formed and NaOH is added to liberate the free amine:
C6H5NH3^+Cl^- + NaOH —> C6H5NH2 + H2O + NaCl

60
Q

What is the equation of the formation of phenylamine from benzene? (4)

A

Benzene + HNO3 –(conc H2SO4)–> nitrobenzene + H2O
Nitrobenzene + 6[H] –(Sn/HCl, room temp)–> phenylamine + 2H2O
C6H5NO2 + 6[H] —> C6H5NH2 + 2H2O
•Since the reaction is carried out in HCl, the salt C6H5NH3^+Cl^- is formed and NaOH is added to liberate the free amine, it neutralises the HCl:
C6H5NH3^+Cl^- + NaOH —> C6H5NH2 + H2O + NaCl

61
Q

How are amides formed? (3)

A
  • In a nucleophilic addition elimination reaction - when amines react with acid chlorides and acid anhydrides, produces N-substituted amides.
  • The amine adds on to the acid chloride and then HCl is eliminated.
  • Reaction is useful in forming polymers e.g. nylon.
62
Q

What are amines used in?

A

•The manufacture of synthetic materials e.g. nylon and polyurethane, dyes and drugs (aryl amines).

63
Q

What are quaternary ammonium compounds used industrially in? (4)

A
  • The manufacture of hair and fabric conditioners.
  • They have a long hydrocarbon chain and a positively charged organic group, so they can form cations.
  • Both wet fabric and hair pick up negative charges on their surfaces.
  • Positive charges of the cations attract them to the wet surface and form a coating that prevents the build-up of static electricity - keeps the surface of the fabric smooth (in fabric conditioner) and prevents the flyaway hair in hair conditioners.
64
Q

Why are fabric and hair conditioners called cationic surfactants?

A

•In aqueous solution, the ions cluster with their charged ends in water and their hydrocarbon tails on the surface.

65
Q

What do surfactants consist of? (4)

A
  • An ionic head - dissolves in water (hydrophilic).
  • Long alkyl chain/tail - dissolves in grease (not soluble in water) (hydrophobic).
  • Micelles are formed as the soap/detergent molecules surround the dirt/grease molecules, with hydrophobic tails in the centre, dissolving the grease.
  • Hydrophilic heads around the outside dissolving the water.
66
Q

Suggest why an aryl hydride e.g. chlorobenzene (C6H5Cl) does not react with a nucleophile e.g. ammonia under the normal conditions of nucleophilic substitution? (2)

A
  • The delocalised pi system of electrons above and below the benzene ring repels the lone pair of electrons on the nucleophile.
  • The nucleophile cannot attack any of the carbon atoms.
67
Q

Which groups are electron-releasing? (4)

A

•Alkyl, esters, alcohols and amines.

68
Q

Which groups are electron-withdrawing? (4)

A

•Nitro/-NO2, acyl chlorides, acid anhydrides, carboxylic acids.

69
Q

Describe how you would prepare 2-phenylethylamine in a three-step synthesis starting from methylbenzene. (3)

A
  • 1). Free radical substitution, Cl2 and UV light to form chloromethylbenzene.
  • 2). Nucleophilic addition, KCN solution, alcoholic, followed by dilute HCl to form benzyl cyanide or phenylacetonitrile.
  • 3). Reduction, H2/Ni catalyst or LiAlH4 in dry ether to form 2-phenylethylamine.
70
Q

What are the uses of methylphenylbenzene? (6)

A 
Making:
•Dyes.
•Quaternary ammonium salts.
•Cationic surfactants.
•Hair conditioner.
•Fabric softener.
•Detergents.
71
Q

For the reduction of nitrobenzene, what is the reducing agent?

A

•Sn/HCl.

A-Level Organic Chemistry AQA (Paper 2) (17 decks)

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