SNS - Organic Chemistry - Amines and Nitrogen Compounds

Question 1

Amines

Nomenclature

Answer 1

General formula NR3

Classified by the number of ayrl groups to which they are atteched - primary = 1, secondary = 2, tertiary =3, quaternary = 4 (nitrogen carries a +ve charge, so these exist as salts)

• Generally named as alylamines. Groups designated individually or by using the prefixes -di or tri if they are the same.
• The suffix -amine as added at the end.
• N- is used to label substituents attached to the nitrogen in secondary or tertiary amines
• The prefix -smino is used ot name compounds containing on OH or CO2H group
• Aromatic amines are named as derivatives of aniline (C6H5NH2)

For example, ethanamine, N,N-dimethylamine

Question 2

Amide

Answer 2

Condensation products of carboxylic acids and amines

Question 3

Carbamates

Answer 3

Or urethanes

Compounds with general formula RNHC(O)OR’

Derived from isocyanates (RNCO) by addition of an alcohol

Question 4

Enamines

Answer 4

Nitrogen analogs of enols with an amine group attached to one carbon of a double bond

Question 5

Imines

Answer 5

Nitrogen compounds containing N=C bonds

Question 6

Nitriles

Answer 6

Or cyanides

Nitrogen compounds containing N≡C bonds

Named with either the prefix -cyano or the suffix -nitrile

Question 7

Nitro Compounds

Answer 7

Contain the nitro group -NO2

Question 8

Diazo Compounds

Answer 8

Contai an N2 functionality

Tend to lose N2 to form carbenes

Question 9

Azides

Answer 9

Compounds with an N3 functionality

When lose nitrogen (N2), form nitrenes

Question 10

Properties

1. Boiling Points
2. Orbitals
3. Chirality

Answer 10

1. Boiling points between those of alkanes and alcohols. As molecular weight increases, BPs increase. Primary and secondary amines can form hydrogen bonds and thus have higher BPs than tertiary amines. Since nitrogen is not as electronegative as oxygen, hydrogen bonds of amines are weaker than those of alcohols
2. N in an amine is sp3 hybridised. Nitrogen must bond to three substituents in order to complete its octet. A lone pair occupies the last sp3
3. N with three different substituents are chiral, however enantiomers can’t be isolated, as interconnect rapidly in process of nitrogen inversion - inversion of sp3 orbital occupied by the lone pait which has low activation energy and slow only at very low temp

Question 11

Properties

Basicity

Answer 11

• Are bases and readily accept protons to form ammonium ions.
• pKb values of alkyl amines are ~4, making them slightly more basic than ammonia (pKb = 4.76) but less then OH (-1.7).
• Aromatic amines are far less basic due to the electron withdrawing efect of the ring, which reduces the basicity of the amino group. The presence of other substituents on the ring alters the basicity - electron donating groups (eg -OH, CH3, -NH2_ increase, electron withdrawing groups (eg NO2) reduce

Question 12

Properties

Acidity

Answer 12

• Also function as weak acids
• pKa values of amines are ~35 and a very strong base os required for deprotonation

Question 13

Synthesis

Answer 13

1. Alkylation of ammonia - (a) Direct, (b) Gabriel Synthesis
2. Reduction - (a) From nitro compounds, (b) From nitriles, (c) From imines (c) From amides

Question 14

Synthesis

Alkylation of Ammonia

Direct

Answer 14

Alkkyl halides react directly with ammonia to produce alkylammonium halide salts in an SN2 reaction

Ammonia functions as a nucleophile and displaces the halide atom

When the salt is treated with a base, the alkylamine product is formed

The reaction often leads to side products as the alkylamine formed is nucleophilic and can react with the alkyl halide

Question 15

Synthesis

Alkylation of Ammonia

Gabriel Synthesis

Answer 15

Converts a primary alkyl halide to a primary amine in an SN2 reaction
. The use of a disgiused form of ammonia prevents side product formation

Phthalimide (condensation product of phthalic acid and ammonia) act as a good nucleophile when deprotonated. Displaces halide ions to form N-alkylphthalimides which don’t react with alkylhalides

When the reaction is complete, the N-alkylphthalimide can be hydrolysed with an aqueous base to produce the alkylamine

Question 16

Synthesis

Reduction

Answer 16

Amines can be obtained from other nitrogen0containing compounds via reduction:

1. From Nitro compounds
2. From Nitriles
3. From Imines
4. From Amides

Question 17

Synthesis

Reduction

Nitro Compounds

Answer 17

Easily reduced to primary amines

Most common reducing agent is iron or zinc and dilute H2SO4

Especially useful for aromatic compounds as nitration of aromatic rings is facile

Question 18

Synthesis

Reduction

Nitriles

Answer 18

Can be reduced with hydrogen and a catalyst or with LAH to produce primary amines

Question 19

Synthesis

Reduction

Imines

Answer 19

Reductive amination - aldehyde or ketone is reacted with ammonia (or a secondary amine) to form a primary (aldehydes) or a secondary or tertiary (ketones) amine

When the aldehyde or ketone reacts with the amine, an imine is produced. Undergoes hydride reduction as a carbonyl does. When the imine is reduced with hydrogen in the presence of a catalyst, an amine is produced

Question 20

Synthesis

Reduction

Amides

Answer 20

Reduced with LAH to from amines

Question 21

Amines

Reactions

Answer 21

Exhaustive methylation

Question 22

Reactions

Exhaustive Methylation

Answer 22

or Hofman elimination

Amine is converted to a quaternary ammonium iodide by treatment with excess methyl iodide

Treatment with silver iodide and water converts this to the ammonium hydroxideWhen heated this undergoes elimination to form an alkene and an amine

The predominant alkene formed is the least susstituted, in contrast with normal elimination reations where the predominant alkene product is the most substituted