(yellow ) Amines and Amides

Question 1

info card read and recite

Answer 1

Amines can be considered as compounds related to ammonia, NH3, with one, two or three of the hydrogen atoms substituted by an alkyl or an aryl group, R. If the amine is not the principal group, the prefix -amino (-NH2) is used.

Question 2

Physical properties

Draw out the structure of methylamine to show the polarity of the NH2 group and the lone pair on the N atom. Identify the intermolecular bonds.

Answer 2

should have two methylamine one hydrogen is bonded to the lone pair of the other methylamine through a hydrogen bond

Question 3

describe the strength of amines hydrogen bonding

Answer 3

Shorter chain amines are gases at room temperature as this bonding is not as strong as it is in alcohols.

Question 4

Would you expect short chain primary amines to be soluble in water?

Explain your answer

Answer 4

yes

H-bonds are possible between the amine d+H attached to the electronegative N atom and lone pair on H2O also between RNH2 and d+H2O

Question 5

what is the definition of a ligand

Answer 5

A Ligand is a molecule or ion with a lone pair of electrons which can make a dative covalent bond with a metal cation forming a complex ion. (see transition metals)

Question 6

Would you expect an amine to behave as a base?
a nucleophile?
a ligand?

Explain your answer.

Answer 6

yes
yes
yes

Lone pair of e- can bond with H+ or attack a d+C or enter a metal cation orbital

Question 7

info card read and recite

Answer 7

Amines are found in nature in putrefying and decaying flesh when proteins decompose. They are associated with ammoniacal, fishy smells.

Question 8

Are the amines more soluble in hydrochloric acid than in water?

Answer 8

Yes much more soluble

Question 9

Carefully place 0.2 cm3 of ethanoyl chloride (take care) and 0.2 cm3 of the amine in separate test tubes, in a fume cupboard, and then mix. A solid compound should be obtained, whose melting temperature is characteristic of the original amine.

Describe the reaction

Which electrophilic centre is attacked?

Which bond breaks?

Answer 9

V vigorous, exothermic , HCl produced à white smoke with NH3

–d+C=O

–C-Cl

Question 10

what is the definition of a base

Answer 10

We define a base as a proton acceptor. It has a lone pair which it can use to form a dative covalent bond with a proton, which in chemistry is a H+ ion.

Question 11

how do you determin the basisity of an amine

Answer 11

Basic properties of the amine

All amines, like ammonia are basic. However their ability to act as bases is determined by

the availability of the lone pair on the nitrogen to accept a proton.

Question 12

Why is Butylamine a stronger base than ammonia

Answer 12

The Alkyl group is weakly electron donating, so can donate electrons to the lone pair on the Nitrogen, increasing it’s electron density. Making the lone pair more readily available to H+ ions

Question 13

Why is phenylamine a weaker base than ammonia

Answer 13

The lone pair on the Nitrogen overlaps with the π delocalised ring of the benzene group. This increases the electron density of the ring, but reduces the electron density of the nitrogens lone pair making it less able to accept a H+ ions

Question 14

What type of reactions do halogenoalkanes frequently undergo?

Answer 14

Nucleophilic substitution

Question 15

Why can ammonia act as a nucleophile?

Answer 15

Lone pair of electrons on NH3

Question 16

Reaction of a halogenoalkane with ammonia

Reagents:
Conditions:

give the equation and mechanisum

Mechanism for the reaction of 1-chlorobutane with limited ammonia:

the mechanism to show how the amine is released by treatment with dil. NaOH

Answer 16

Reagents: halogenoalkane

excess conc. ammonia dissolved in ethanol

Conditions: heat in a sealed tube

Mechanism for the reaction of 1-chlorobutane with limited ammonia: -
ammonia substatutes with chlorine in an nucleophilic substatution

the mechanism to show how the amine is released by treatment with dil. NaOH

OH- pulls ahydrogen off the amine this gives an electron to the amine

C4H9NH3 +NaOH —-> C4H9NH2 + H2O + NaCl

Question 17

Reaction of excess chloromethane with ammonia results in successive substitution reactions:-

Complete the equations:-
this has three steps

why is it hard to seperate these products

Answer 17

1) · CH3Cl + NH3 —> H3CNH2 + HCl (methylamine)

2) CH3Cl + CH3NH2 —> (H3C)2NH + HCl (dimethylamine)

3) CH3Cl + (H3C)2NH —> (H3C)3N + HCl (trimethylamine)

It is difficult to separate these products even by fractional distillation as their boiling points are similar.

Question 18

The Preparation of amines From Halogenoalkanes

Aliphatic amines are produced by heating the corresponding halogenoalkane in a sealed tube with excess ammonia in ethanol

During the first step of the reaction the ammonia acts as a nucleophile and then in the second step it acts as a base releasing the free amine

Draw out the mechanism using 1-bromobutane and ammonia.

Answer 18

ammonia attacks the carbon delta positive this then kicks off the bromine with heat and conc NH3 in ethanol

then addmore ammonia then then pushes the electron off one of the hydrogens from the ammonia on the amine

this makes C4H9NH2 + NH4Br

Question 19

The Preparation of amines From From Nitrile

Reduction of nitriles can also produce amines. Unlike the above reaction there is no chance of further substitutions, however if using LiAlH4 care needs to be taken as the LiAlH4 is highly flammable

Reduction can be achieved via two methods

1) Reduction using hydrogen gas and a nickel catalyst

2) Reduction using LiAlH4 in epoxyethane (dry ether), followed by dilute acid.

Answer 19

1) CH3CH2CH2CN + 2H2 —-> CH3CH2CH2CH2NH2

2)CH3CH2CH2CN + 4[H] —> CH3CH2CH2CH2NH2

Question 20

The reduction of nitrobenzene to phenylamine

give the two steps

Answer 20

Step 1

· Reducing agent: Tin and concentrated hydrochloric acid.

· Add tin to nitrobenzene, then add concentrated hydrochloric acid with cooling.

· Heat on a boiling water bath to complete the reduction. Phenylammonium chloride is formed (write the name in the equation)

Step 2

· Sodium hydroxide solution is added to liberate the phenylamine.

· Collect the phenylamine by steam distillation. (see apparatus below) Distil until no more oily drops of phenylamine distil over. Separate the oily organic layer.

· Shake with NaCl(s) to reduce the solubility of phenylamine in water.

· Separate the organic layer and dry with K2CO3(s)

· Redistil using an air condenser.

Question 21

draw out these structurs and then check them online

ethanamide

propanamide

N - methylethanamide

Benzamide

Answer 21

online

Question 22

Acid amides are organic compounds which have relatively high melting points and boiling points. Methanamide is a liquid but all other acid amides are white crystalline solids.

Identify the intermolecular bonding present

Answer 22

hydrogen bonding

it should be between the C=O and the H-N of the two same compounds

Question 23

Comment on the solubility of amides in water

Answer 23

Soluble in water due to ability to make and receive hydrogen bonds with water.

Question 24

What is the N-C-C bond angle in ethanamide? Justify your answer.

Answer 24

Approx 120o as there are 3 groups of bonding electrons around the C atom, these repel and move to a position of minimum repulsion.

Question 25

info card read and recite

Answer 25

The lone pair of electrons on the nitrogen atom is delocalised through the p bond system.This reduces the electron density on the nitrogen atom making it less basic than expected.

Question 26

does ammonia act as a nucliophile or electro phile