4.6 Amines

Question 1

What is an amine?

Answer 1

Amines are derivatives of ammonia where one or more of the hydrogen atoms has been replaces with an organic group

Question 2

Describe the difference between primary, secondary and tertiary amines

Answer 2

Molecule of ammonia, NH3:
1. If one of hydrogens is replaced with an organic group it is a primary amine.
2. If two of the hydrogens are replaced with an organic group it is a secondary amine
3. If all three of the hydrogens are replaced with an organic group it is a tertiary amine.

Question 3

Structure of a quaternary ammonium ion

Answer 3

N+ w/ four diff R groups (R denoting an organic alkyl/ aryl group)

Question 4

Give two common methods of producing aliphatic amines:

Answer 4

1. Nucleophilic substitution of halogenoalkanes with ammonia.
2. Reduction of nitriles

Question 5

What conditions are required for primary amines to be formed from halogenoalkanes?

Answer 5

The halogenoalkane must be warmed with excess ethanolic ammonia inside a sealed tube.

Question 6

draw the mechanism for the rctn between bromoethane and ammonia

Answer 6

bromoethane w br on end dipole, NlonepairH3 arrow to carbon -> intermediate carbon has both Br- and N+H3 arrow from one H on NH3 to N and arrow from line between C-Br to Br which breaks off end same as start but NH2 subbed for Br

Question 7

When a halogenoalkane reacts with ammonia why do you get a mixture of products?

Answer 7

the rctn will produce a mixture of primary, secondary and tertiary amines and quaternary ammonium salts, because when a primary amine produced it acts as a nucleophile in further reactions, when it reacts in further nuclephilic substitution reaction, secondary amines produced, substitution reactions continue takign place until quaternary ammonium salt is produced

Question 8

Why can primary, secondary and teriary amines act as nucleophiles when quaternary ammonium ions can not?

Answer 8

in primary, secondary and tertiary amines the nitrogen has a lone pair of electrons allowing it to act as a nucleophile, the nitrogen atom in quaternary ammonium salt does not have a lone pair of electrons so cannot act as a nucleophile

Question 9

chemical eqn for the reaction of bromoethane with excess ammonia to form ethylamine:

Answer 9

CH3CH2Br + 2NH3 -> CH3CH2NH2 + NH4Br

Question 10

chemical eqn for the reaction of methylamine with bromoethane to form methylethylamine:

Answer 10

2CH3NH2 + CH3CH2Br -> CH3NHCH2CH3 + CH3NH3+Br-

Question 11

how can the amine be released from an amine salt?

Answer 11

treat the amine salt with an alkali eg: NaOH

Question 12

chemical eqn for the rctn of methylammonium chloride with sodium hydroxide?

Answer 12

CH3NH3+Cl- + NaOH -> CH3NH2 + H2O + NaCl

Question 13

how can a nitrile be reduced to an amine?

Answer 13

the reducing agent LiAlH4 used, which is a non aqueous solvent should be added to the nitrile followed by some dilute acid

Question 14

chemical eqn for reduction of ethanenitrile to ethylamine?

Answer 14

CH3CN + 4[H] -> CH3CH2NH2

Question 15

what compounds can aromatic amines be reduced from

Answer 15

aromatic amines are produced from reduction of nitro compounds like nitrobenzene

Question 16

reducing agent used for reduction of nitro compounds to aromatic amines?

Answer 16

metallic tin and conc hydrochloric acid

Question 17

chemical eqn for the reduction of nitrobenzene to phenylamine?

Answer 17

benzenering-NO2 + 6[H] -> benzenering-NH2 + 2H2O

Question 18

why do amines act as bases?

Answer 18

the nitrogen atom in amines has a lone pair of electrons, meaning amines can form a dative covalent bond with a hydrogen ion, therefore amines can act as bases as they accept protons

Question 19

how does the strength of a base depend on the availability of the lone pair of electrons?

Answer 19

the more available a lone pair of electrons is the more likely they are to accept a proton so the stronger a base it will be, the higher the electron density of a lone pair, the more available the lone pair is

Question 20

arrange following amines in order of decreasing strength of base: ammonia, primary aromatic amine, primary aliphatic amine

Answer 20

in order of decreasing strength of base: primary aliphatic amine, ammonia, primary aromatic amine

Question 21

why are primary aromatic amines weaker bases than ammonia?

Answer 21

primary aromatic amines have a benzene ring which has a delocalised ring of electrons which draws electrons towards itself, this means the lone pair on nitrogen gets partially delocalised into the ring which decreases the electron density of nitrogen, the lone pair is hence much less available

Question 22

why are primary aliphatic amines stronger bases than ammonia?

Answer 22

primary aliphatic amines have an alkyl group which ‘pushes’ electrons towards the nitrogen atom, increasing the electron density of nitrogen, making the lone pair more available

Question 23

name the mechanism for the reaction between amines and ethanoyl chloride:

Answer 23

nucleophilic addition-elimination

Question 24

draw mechanism for rctn between ethanoyl chloride and methylamine??

Answer 24

CH3-CdoublbondO-Cl dipole between C&O lone pair on N of NH2CH3 attacks C+ intermediate: NH2CH3 attaches on end Cl moved below attacked C C-O(has -ve charge and two lone pairs arrowfrom one lp to line between) arrow from line between C-Cl to Cl and arrow from line inbetween N+vecharge-H to N then end prod CH3-CdoublebondO-N-CH3-H + HCl

Question 25

IUPAC name of the organic product formed when ethanoyl chloride reacts with methylamine?

Answer 25

N-methylethanamide

Question 26

what can be used to test for primary amines?

Answer 26

cold nitric(III) acid

Question 27

what do primary aliphatic and aromatic amines produce when they react with nitric(III) acid at room temp??

Answer 27

aliphatic amines produce alcohols
aromatic amines produce phenols

Question 28

observations when a primary aliphatic amine reacts with cold nitric(III) acid??

Answer 28

burst of nitrogen whihc is a colourless and odourless gas

Question 29

what is produced when primary aromatic compounds react with nitric(III) acid at temps below 10C??

Answer 29

benzenediazonium compounds

Question 30

what are diazonium ions?

Answer 30

diazonium ions are ions which contain an N2+ grp

Question 31

displayed structure of a benzenediazonium ion:

Answer 31

benzene ring w N+triplebondN attatched

Question 32

what are coupling rctns??

Answer 32

coupling rctns are organic rctns involving joining of two chemical species, an alkaline solution is required for coupling to occur

Question 33

describe the coupling rctn of benzenediazonium chloride with phenol:

Answer 33

first a solution of sodium hydroxide is produced by dissolving phenol in sodium hydroxide, next the solution is cooled and added to benzenediazonium chloride, a yellow-orange ppt formed the product is known as an azo compound

Question 34

what are azo compounds??

Answer 34

compounds in which two benzene rings are joined by a nitrogen bridge

Question 35

displayed chemical eqn for rctn of a phenoxide ion w/ a benzenediazonium ion:

Answer 35

benzenering-Ominus + benzenering-NplustriplebondN -> benzenering-NtriplebondN-benzenering-OH

Question 36

Describe the coupling reaction of benzenediazonium chloride with naphthalen-2-ol:

Answer 36

first naphthalen-2-ol is dissolved in sodium hydroxide solution os cooled and added to benzenediazonium chloride, bright red ppt forms, azo compound

Question 37

displayed formula of the azo compound formed when naphthalen-2-ol reacts with benzenediazonium chloride:

Answer 37

benzenering-NtriplebondN-twostacked benzenerings top one w/ Oh in 1st postion

Question 38

describe coupling rctn of benzenediazonium chloride with phenylamine:

Answer 38

phenylamine is added to a cold solution of benzenediazonium chloride a yellow solid azo compound produced

Question 39

what is a chromophore?

Answer 39

a chromophore is a group or atom responsible for the colour of a compound

Question 40

why can azo compounds be used as dyes?

Answer 40

the nitrogen grp in azo dyes has indicator properties, depending on conditions it interacts differently with light due to different wavelengths of light being absorbed or reflected, meaning azo compounds form brightly coloured compounds and so are good for use as dyes

Question 41

how do coloured compounds arise?

Answer 41

coloured compounds arose due to the absorbance and reflection of light by the compound, when white light shines on substance some wavelegths are absorbed but remaining wavelengths are reflected and transmitted, these reflected wavelengths correspond to a specific colour which is then obsereved

Question 43

how can methyl orange be used to distinguish between acids and bases?

Answer 43

methyl orange is an azo compound whihc is red in acids and yellow in bases, acidic conditions nitrogen grp gains a hydrogen causing it to interact differently with light appearing red, in basic conditions hydrogen ion is lost so nitrogen grp reflects yellow wavelengths appearing yellow