organics - amines

Question 1

what is an amine

Answer 1

-derivative of ammonia in which one or more of the hydrogens is replaced by an alkyl group
-have some hydrogen bonding but it isnt as strong as in alcohols - although not in tertiary
-room temp they are liquids

Question 2

what are the 3 types of amines

Answer 2

known as aliphatic
-primary
-secondary
-teritary

dependent on how many alkyl groups there are

Question 3

what is important about an amine compared to ammonia

Answer 3

the nitrogen has a lone pair of electrons

Question 4

what are aromatic amines

Answer 4

-have a N joined directly to the benzene ring

Question 5

what are quaternary ammonium salts

Answer 5

-contain quaternary ammonium ions and are related to amines
-but are not amines and do not pocess a lone pair of electrons on the N

Question 6

how are amines named

Answer 6

The common way to name amines is to use the alkyl (or aryl) prefix followed by -amine - use this one mainly

The IUPAC systematic name uses the numbered prefix amino- followed by the alkane (or aromatic) stem

Question 7

the prep of primary aliphatic amine with NH3 and halogenoalkanes

Answer 7

-halogenoalkanes are reacted with an excess of NH3 dissolved in ethanol at pressure in a sealed conatiner
-by nucleophlic substitution
-NH2 replaces the halogen and NH4halogen is also produced

Question 8

what is the general reaction for nucleophilic sub with NH3 and halogenoalkane

Answer 8

R-X + 2 NH3 = R-HH2 + NH4X

Question 9

why is nucleophilic sub with NH3 and halogenoalkane not as commonly used

Answer 9

-amine product can react further with more of the haloalkane to form secondary,tertiary and quaternary ammonium salts

-problem minimsed by using an excess of conc ammonia

Question 10

how does reduction of nitrile compounds work

Answer 10

-formation of a nitrile from a halogenoalkane
-reduction of the nitrile to form an amine

nitrile vapour and hydrogen gas are passed over a nickel catalyst or LiAlH4 in dry ether to form primary amine

the product has one more carbon that the starting material

Question 11

general equation for step 1 of reduction of nitrile to form a primary amine

Answer 11

R-X + KCN = R-C triple bond N + KX
with warm ethanol

Question 12

what is the general equation for step 2 of reduction of nitrile to form a primary amine

Answer 12

R-C triple bond N + 4[H] = R-CH2-NH2
with LiAlH4 in dry ether
or
R-C triple bond N + 2H2 = R-CH2-NH2
with nickel catalyst and heat

Question 13

why is reduction of a nitrile the more common way to produce an amine

Answer 13

-one product rather than a mixture is produced

Question 14

how are primary aromatic amines usually produced

Answer 14

-prepared by synthesis of ntiro compounds using tin and conc HCl
-this process alone would produce the ammonium salt so NaOH is added to give the amine

Question 15

what are the steps of the reaction of nitrobenzene to give amine

Answer 15

Step 1- Benzene undergoes nitration with concentrated nitric acid (HNO3) and concentrated sulfuric acid (H2SO4) at 25 to 60 oC to form nitrobenzene

Step 2 - Nitrobenzene is reduced with hot tin (Sn) and concentrated hydrochloric acid (HCl) under reflux to form an acidic mixture that contains the organic product C6H5N+H3

Step 3 - Sodium hydroxide (NaOH) is added to the acidic reaction mixture to form phenylamine

Step 4 - The phenylamine is separated from the reaction mixture by steam distillation

Question 16

what is the general equation for the production of an aromatic amine

Answer 16

benzene ring with NO2 on it + 6[H] = benzene ring with NH2 on it + 2H2O
with Sn + HCl followed by NaOH

Question 17

are amine B-L acids or B-L bases

Answer 17

B-L bases - proton acceptors

Question 18

why are amines weak acids

Answer 18

-are weak acids and act as bases bc they have a lone pair on the N whihc can readily accept a proton

Question 19

what effects the strength of an amine

Answer 19

-ability of the lone pair of electrons on the nitrogen to accept and H/proton and form a dative covalent bond
-the more readily a proton is attracted the stronger the base is or the higher the electron density on the lone pair of the nitrogen

Question 20

what factors effect the basicity/strength of amines

Answer 20

-postive inductive effect
-delocalisation

Question 21

how does positive inducitve effect cause basicity

Answer 21

some groups such as alkyl groups donate electron density to the nitrogen atom causing the lone pair of electrons to become more avaliable and increasing the basicity

Question 22

how does delocalisation affect the basicity of the amine

Answer 22

-presence of aromatic rings such as benzene ring cause the lone pair on the N to be delocalised in the ring
-lone pair becomes less avaliable to form a dative covalent bond with ammonia and decreases the amines basicity

Question 23

general equation for amine and water to give a primary amine

Answer 23

R-NH2 + H2O = R-NH3+ + OH-

Question 24

general equation to show how secondary amines act as B-L bases

Answer 24

R1-NH-R2 + H+ = R1-NH2+-R2

Question 25

what does an amine make when it reacts with and acid and how can it do this

Answer 25

salt
base + acid = salt and ion of acid

Like ammonium salts, amine salts are soluble ionic compounds, so when the alkyl group is small they are water soluble but become less so as the carbon chain increases

Question 26

what is the general order of base strength in amines

Answer 26

teritary amine > secondary amine > primary amine > NH3 > aromatic amine

Question 27

3’ , 2’ and 1’ amine strength compared to ammonia

Answer 27

-the more alkyl groups that are sub on the N in place of H the more electron density is pushed onto the N
-this is because the inductive effect of alkyl is greater than that of H - so alkyl groups oush electron density towards the N atom better than H

Question 28

aromatic amine strength comapred to ammonia

Answer 28

-lone pair on the N is partially delocalised in the benzene ring, leading to a reduction in the electron density on the N atom so weaker base strength

Question 29

comparison statement bwt strength of amines

Answer 29

-state which is stronger
-eg primary amine vs ammonia
-then say that the stronger has a greater electron density on the N lone pair
-thus greater ability to accept H+

Question 30

what smell do amines have and why

Answer 30

Amines have a fishy smell, which disappears as soon as you add an acid, because you are making an non-volatile salt. Decomposing fish give off amines which are produced by the bacterial decomposition of proteins.

Question 31

why can the products of nucleophilic substitution react with halogenoalkanes

Answer 31

-the amine also has a lone pair on the N
-so this will react with the halogenalkane
-the product of the reaction has a higher electron density on the N lone pair and is even better at reacting with halogenoalkanes than the original molecule

Question 32

what happen if a large excess of ammonia is used in nucleophilic sub

Answer 32

primary amine is the main product

Question 33

what happens if a large excess of haloalkane is used in nucleophilic sub

Answer 33

quaternary ammonium salt is the main product - all groups surronding the N are alkyl - usually CH3 and whatever orginal group was on

Question 34

how can nucleophilic sub be affected by electron density

Answer 34

• H on the N can be successively replaced by the R group from the haloalkanes

Question 35

what is the order of nucleophilic sub reactions to produce subsequent amines

Answer 35

ammonia - primary amine - secondary amine - tertiary amine - salt
keep add RX

secondary amines are also N sub amines

Question 37

what are soap and detergent molecules called

Answer 37

-surfactants

Question 38

what do soaps and detergents consit of

Answer 38

-ionic head /hydrophilic as it can dissolve in water
-hydrophobic long alkyl chain tail - this dissovles grease - grease is not soluble in water

Question 39

how do miscelles form

Answer 39

-when the soap/detergent surround the dirt/grease molecules with the hydrophobic tails in the centre dissolving the grease and the hydrophilic heads on the outside dissolving in the water

Question 40

what are used as cationic surfactants

Answer 40

-quaternary ammonium slats with long alkyl chain
-fabric softners often contain these as most of the surface material is -ve charged

Question 41

nucleophilic addition elimination of amines

Answer 41

-amines can react with acid anhydride or acyl chloride to replace the H on the N with the acyl group
-produces an amide and a molecule of HCl or carboxylic acid depending wether an acyl chloride or acid anhydride is used
-a second molecule of amine reacts with HCl/ carboxylic acid to form a salt

Question 42

second equation for producing an salt - nucleophilic addition - elimination

Answer 42

H+ + RNH2 = RH3+