Organic Synthesis, Aromantic Chemistry, Polymers, Amino Acids

Question 1

Comparing Base Strengths (Amines)

Answer 1

• The strength of a base is dependent on the availability of the lone pair and its ability to pick up protons

for amines

• The greater the electron density in the Nitrogen atom, the better it can pick up protons ∴ the better the base
• this is dependent on the groups attached to the nitrogen.

Question 2

Preparation of Aromatic Amines

Answer 2

• Aromatic amines are formed through the reduction of nitro aromatic compounds e.g nitrobenzene
• aromatic amines are very important for the manufacture of dyes

methods to reduce nitrobenzene:

tin and concentrated hydrochloric acid
- heat a mixture of nitrobenzene, tin and conc HCl under reflux
- form phenylammonium chloride which is soluble in water
- add a base e.g NaOH to produce phenylamine, which is insoluble in water

hydrogen and metal catalyst (platinum or nickel)

Question 3

Nucleophilic Substitution with Halogenalkanes

Answer 3

Reagents:
Aqueous, alcoholic ammonia
Conditions:
Reflux, aqueous alcoholic solution under pressure

• the product is dependent on whether the halogenoalkane or ammonia is in excess
• If ammonia is largely in excess then a primary amine will be formed
• If the halogenoalkane is an excess then the reaction with continue until a quaternary ammonium salt is formed as the amine replaces the rest of it’s hydrogens

USE:
- very rarely use this method to synthesise amines because it is very difficult to control

Question 4

Properties of Amines

Answer 4

Boiling Point -
- High boiling points
- due to the intermolecular forces (hydrogen bonding: N-H)

Structure -
Pyramidal
- 107°/107.5°
- due to the repulsion of the lone pairs

Solubility -
- soluble (somewhat) due to the polarity of the bonds
- solubility decreases as the molecules get heavier
- lower mass compounds are soluble in water due to polarity
- soluble in organic solvents (except aromatic amines due to the benzene ring)

• Lewis Bases
• Bronsted-Lawry Bases
• Nucleophiles
  ( amines act as both bases and nucleophiles, the more soluble the amine, the better it is at being a base)

Question 5

What is a Lewis Base

Answer 5

• A molecule that can donate a lone pair
• Amines can acts as Lewis Bases

Question 6

Order of Base Strengths and Why

Answer 6

strongest -> weakest:
secondary, primary, ammonia, aromatic

• electron releasing substituents (i.e CH3 groups) increase the basicity as the electron density is increased so the lone pair is more effective.
• this is the positive inductive effect
• electron withdrawing substituents (i.e benzene rings) decrease basicity as the electron density on N is lowered due to the electron density of e.g a benzene ring, by taking the lone pairs and delocalising them, making the lone pair less effective.

Question 7

Why does phenylamine form oily drops when in water?
What would happen if you added conc HCl?
What would happen if you then added NaOH and why?

Answer 7

• Phenylamine is not very soluble in water, this is due to the benzene ring being very stable and unreactive
• the acid will cause the phenylamine to dissolve
• the proton donated will turn it in to an ammonium ion
• adding NaOH will cause the oily drops to reform
• this is because it goes back to its amine structure rather than it’s ionic structure

Question 8

Reduction of Nitriles (provide a general example)

Answer 8

• both methods produce a primary amine
• Reduction using LiAlH4 in Dilute Acid
• Reduction using Hydrogen + Nickel (or other metals) catalyst
  -High Temp, High Pressure

Question 9

Advantages and Disadvantages of Aliphatic Amine synthesis methods

Answer 9

Question 10

Quaternary Ammonium Salts

Answer 10

• quaternary ammonium salts with long hydrocarbon chains are used as cationic surfactants in fabric conditioners/softners and hair softeners
• This is due to the positive cationic head that is attracted to the negatively charged fibres or protein sites on hair molecules/ fabric
  material molecules, which reduces static charge, making them softer

Question 11

Why is Nucleophilic substitution with amines so hard to control?

Answer 11

• this is due to the continuous further substitutions that occur during to the amines

e.g
bromoethane + ammonia

• first it forms a primary amine, ethylamine
• ethylamine can also act as a nucleophile so substitution occurs again
• a secondary amine is then formed but that can also go under substitution
• and this continuous until a quaternary ammonium salt is formed
• reaction ends here because there is no lone pairs available to use anymore

Question 12

Carboxylic Acid Formation using Nitriles

Answer 12

• carboxylic acids can be formed from the hydrolysis of nitriles
• nitrile is made to react with hydrochloric acid under reflux to form a carboxylic acid and ammonium chloride salt.