Amines and Amino Acids (Chapter 27.1, 27.2) Flashcards
What are amines?
Organic compounds, derived from NH3, in which one or more hydrogen atoms in the NH3 have been replaced by a carbon chain or ring
What is an aliphatic amine?
When the nitrogen atom is attached to at least one straight or branch carbon chain (alkyl group/R) e.g. methylamine, CH3NH2
What is an aromatic amine?
When the nitrogen atom is attached to an aromatic ring (aryl group/Ar) e.g. phenylamine, C6H5NH2
What are primary, secondary and tertiary amines?
- Primary: nitrogen attached to two hydrogens
- Secondary: nitrogen attached to one hydrogen
- Tertiary: nitrogen attached to zero hydrogens
How do you name primary amines?
- NH2 at the end of the chain: alkyl-amine
- NH2 mid-chain: 2-amino-alkane
How do you name secondary/tertiary amines containing the same alkyl group?
The prefixes di and tri are used to indicate the number of alkyl groups attached to the nitrogen atom e.g. di-methyl-amine
How do you name secondary/tertiary amines when two or more different alkyl groups are attached to a nitrogen atom?
- The compound is named as an N-substutured derivative of the larger group
- e.g.CH3NHCH2Ch2CH3 = N-methyl-propyl-amine
- e.g. CH3N(CH2CH3)CH2CH2CH3 = N-ethyl-N-methyl-propylamine
What do amines behave as in their chemical reactions?
Bases
Why do amines behave as bases in their chemical reactions?
The lone pair of electrons on the nitrogen atom can accept a proton
What happens when an amine accepts a proton?
- A dative covalent bond is formed between the lone pair of electrons on the nitrogen atom and the proton
- e.g. ethylamine => ethylammonium ion
Describe salt formation with amines
- Amines are bases and they neutralise acids to make salts - e.g. methylamine reacts with HCl to form the salt methylammonium chloride (CH3NH3+Cl-)
How are primary amines formed?
1) NH3 reacts with a haloalkane in a substitution reaction as the lone pair of electrons on the nitrogen atom allows NH3 to act as a nucleophile
2) this produces an ammonium salt
3) aqueous alkali is then added to generate the amine from the salt
What are the two possible ways (equations) to form a primary amine?
1) CH3Cl + NH3 => CH3NH3+Cl-
CH3NH3Cl- + NaOH => CH3NH2 + NaCl + H2O
2) CH3Cl + 2NH3 => CH3NH2 + NH4Cl?
What are the two conditions needed for the formation of (primary) amines?
1) ethanol is used as a solvent to prevent any substitution of the haloalkane by H2O and dissolves haloalkane better
2) excess NH3 is used to reduce further substitution of the amine group to form secondary and tertiary amines
How are secondary and tertiary amines formed?
1) methylamine reacts further with a haloalkane in a substitution reaction as the lone pair of electrons on the nitrogen atom allows methylamine to act as a nucleophile
2) this forms a secondary amine
3) tertiary amines can also be formed by further reaction of the secondary amine
How is phenylamine (C6H5NH2) made?
By the reduction of nitrobenzene (C6H5NO2)
Describe the formation of phenylamine from nitrobenzene?
- Nitrobenzene is heated under reflux with tin (Sn) and HCl to form the ammonium salt, phenylammonium chloride
- Phenylammonium chloride is then reacted with excess NaOH to produce the aromatic amine, phenylamine
- Sn + HCl act as a reducing agent
- nitrobenzene + 6[H] => phenylamine + 2H2O
What are amino acids?
Organic compounds with amine and carboxylic acid functional groups
Describe alpha amino acids
- The amino acids in the body are all alpha amino acids in which the NH2 group is attached to the alpha carbon atom (the second carbon atom next to the carboxyl group)
- General forumula: RCH(NH2)COOH
Why do amino acids have similar reactions to carboxylic acids and amines?
Because they have both an acidic COOH and basic NH2 functional group
Describe the reaction of the amine group in an amino acid with acids
- The amine group on the amino acid is basic and reacts with acids to make salts
- e.g. the amino acid alanine reacts with HCl to form an ammonium salt:
CH3CH(NH2)COOH + HCl => CH3CH(NH3+)COOHCl-
Describe the reaction of the carboxyl group in an amino acid with aqueous alkalis
- The COOH group on the amino acid reacts with NaOH to form a salt and water
- e.g. glycine reacts with NaOH to form an Na salt:
HCH(NH2)COOH + NaOH => HCH(NH2)COO-Na+ + H2O
Describe the esterification reaction of the carboxyl group in an amino acid with alcohols
- Amino acids are easily esterified by heating with an alcohol in the presence of concentration H2SO4
- e.g. glycine reacts with excess ethanol and a small amount of H2SO4 - the COOH group is esterified, producing an ester and the acidic conditions protonate the basic NH2 group of the ester:
HCH(NH2)COOH + C2H5OH + H+ => HCH(NH3+)COOC2H5 + H2O
How are zwitterions formed?
When, within the structure of an amino acid, the basic NH2 group accepts a H+ from the COOH group to form an ion containing both a positive and negative charge (zwitterion)
