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Organic compounds, derived from NH3, in which one or more hydrogen atoms in the NH3 have been replaced by a carbon chain or ring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)
Why do zwitterions have no overall charge?
Bc the positive and negative charges cancel out
What is the isoelectric point and why is it significant>
- The pH at which the zwitterion is formed
- Each amino acid has its own unique isoelectric point
- If an amino acid is added to a solution with a pH more than or less than its isoelectric point, the amino acid behaves as an acid/base and the NH3+/COO- lose/gains a proton
What are amides?
- The products of reactions of acyl chlorides with NH3/amines
- They are common in nature e.g. in proteins, the bonds are amine groups
What is the amide functional group?
CON - a carbonyl group bonded to oxygen
What are primary, secondary and tertiary amides?
- Primary: nitrogen is bonded to two hydrogens e.g. propanamide
- Secondary: nitrogen is bonded to one hydrogen e.g. N-methylethanamide
- Tertiary: nitrogen is bonded to zero hydrogens e.g. N,N-dimethylmethanamide
What are stereoisomers?
Compounds with the same structural formula but a different arrangement of atoms in space
What is optical isomerism?
A type of stereoisomerism
Where is optical isomerism found?
In molecules that contain a chiral centre
What is a chiral centre?
A carbon atom attached to 4 different atoms/groups of atoms
What does the presence of a chiral centre in a molecule lead to?
The existence of two non-superimposable mirror image structures
What are enantiomers (optical isomers)?
Two molecules that are non-superimposable mirror image structures of each other (one isomer cannot be superimposed upon the other)
What is there for each chiral carbon atom?
One pair of optical isomers
What is the chiral carbon atom labelled with?
An asterisk (*)
What do all alpha amino acids (except glycine) contain?
A chiral carbon atom, with the alpha carbon atom bonded to 4 different atoms/groups of atoms
What does chirality apply to?
Any centre that holds attachments that can be arranged as two non-superimposable mirror image forms
What atoms can chiral centres be?
Not just carbon atoms
What are the bond angles in amines/ammonia?
107 degrees
What is the equation for the reaction of methylamine with water?
CH3NH2 + H2O => CH3NH3OH
Why is it difficult to produce primary amines using the nucleophilic substitution of haloalkanes?
It is difficult to control further substitution as the ethyl groups are activating ∴ the lone pair becomes increasingly electron dense
What is the role of Sn in the reduction of nitrobenzene?
The electron donor
What is the role of HCl in the reduction of nitrobenzene?
The proton donor
What is the role of NaOH in the reduction of nitrobenzene?
To generate the free amine back again
What is more basic, phenylamine or ethylamine?
Ethylamine as it has a very high electron density on the nitrogen and in phenylamine, the lone pair on the nitrogen is delocalised into the pi system
What does the basicity of an amine depend on?
The electron density on nitrogen
What two types of isomerism does stereoisomerism include?
Geometric and optical
What three types of isomerism does structural isomerism include?
Chain, position and functional
Why is ethylamine a stronger base than ethanamide?
- The amide bond is very stable and the C=O group is deactivating due to resonance
- The alkyl groups on ethylamine are activating
What is the equation for the formation of ethanamide?
CH3COCl + 2NH3 => CH3CONH2 + NH4Cl
Why is further substitution not a problem in the synthesis of amides?
Bc of the resonance in primary amides which stabilises the amide and prevents further substitution
Why can amino acids be combined to give a variety of polypeptides?
There are 20 different types of alpha amino acids, each with different R groups, which can be combined in any order
