Chapter 28 - Amines

Question 1

what makes amines useful as intermediates

Answer 1

they are very reactive

Question 2

how do you decide whether an amine is primary, secondary or tertiaryu

Answer 2

count the n umber of alkyl groups on it. 1 is primary, 2 is secondary, 3 is tertiary

Question 3

what shape are amines

Answer 3

pyramidal with bond angles 107

Question 4

why are the boiling points of amines lower than those of comparative alcohols

Answer 4

because the hydrogen bonds between amine molecules are lower than those between alcohol molecules because nitrogen is less electronegative than oxygen

Question 5

describe the solubility of different types of amines in water

Answer 5

smaller amines are more soluble, primary and secondary amines are much more soluble than tertiary amines
phenylamine isnt very soluble

Question 6

what kinds of behaviours does the lone pair on amines allow

Answer 6

lets the amine act as a base by accepting a proton
can bond with an electron deficient carbon when acting as a nucleophile

Question 7

what do amines form with acids

Answer 7

ionic salts, in an acid base reaction

Question 8

why will phenylamine (which is almost insoluble) dissolve in excess HCl

Answer 8

because it will form a phenylammonium chloride salt, which is water soluble

Question 9

what does the base stength of amine depend on

Answer 9

the availablility of the lone electron pair

Question 10

how do aliphatic and aromatic amines and ammonia compare in strength

Answer 10

aliphatic are stronger than ammonia and ammonia is stronger than aromatic

Question 11

what kind of aliphatic amines are the strongest and why

Answer 11

tertiary amines because the electron releasing (inductive) effect of the alkyl groups increases the electron density around the nitrogen which increases the availability of the lone pair

Question 12

why are aromatic amines the weakest bases

Answer 12

because the lone pair becomes delocalised ijnto benzenes ring which decreases its availability

Question 13

how do amines react with halogenoalkanes

Answer 13

in a nucleophilic substitution reaction

Question 14

what is produced when amines react with halogenoalkanes and why

Answer 14

a mixture of primary secondary tertiary amines and a quaternary ammonium salt because further substitution occurs

Question 15

what 2 routes are there to produce amines

Answer 15

reduction of nitriles and nucleophilic substitution of haloalkanes

Question 16

why is reduction of amines preferred to nucleophilic substitution of haloalkanes in amine synthesis

Answer 16

because only the desired amine is produced

Question 17

what are the 2 steps (with equations) in the reduction of nitriles to form amines

Answer 17

1: RBr + CN- —–> RCN + Br-
2: RCN + 4[H] —-> RCH2NH2

Question 18

what are the conditions of the 2 steps in the reduction of nitriles to form amines

Answer 18

1: aqueous ethanol
2: Ni (catalyst)/ H2 (reducing agent)

Question 19

what are the 2 steps to make phenylamine

Answer 19

1: make nitrobenzene from benzene via electrophilic substitution
2: reduction to phenylamine using tin and HCl

Question 20

what is the economic importance of amines

Answer 20

used in the manufacture of synthetic materials such as nylon and polyurethane, dyes and drugs

Question 21

how are N-substituted amides made

Answer 21

through acylation (addition-elimination) using an amine and an acyl chloride

Question 22

how are quaternary ammonium salts used in industry

Answer 22

in the manufacture of hair and fabric conditioners

Question 23

how do quaternary ammonium salts in conditioners work

Answer 23

wet fabric/hair picks up negative charge, so the positive cations form a coating which prevents the build up of static electricity