Chapter 27- Amines, amino acids and polymers

Amines

Organic compounds derived from ammonia (NH3) where one or more of the hydrogen atoms have been replaced with an alkyl or aryl group

Naming primary amines

-amine

naming secondary or tertiary Amine

If same group is present use di or tri to show the number of groups e.g. dimethylamine

naming amines with two different groups

1. Identify longest C chain attached to nitrogen

2. Identify alkyl groups attached to the N and list them at the start of the name, with prefix N-, N-, in alphabetical order

E.g. N-ethyl-N-methylpropylamine

Naming amines with side groups

when amine group is on any other carbon but C-I, the prefix ‘amino’ is used with a number to indicate the Position along the chain

Properties of amines

• polar- amino group, NH2, is polar

• Soluble in water- the -NH2 group in a primary amine can form a H bond with water, solubility decreases with increasing carbon chain length because the polar -NH2 group contributes less to overall characteristics of molecules

Amine functional group

-NH₂

amines reacting as bases

• Lone pair of electrons on the N atom can accept a proton. It forms a quaternary ammonium ion with a tetrahedral shape and positive charge

• (Alkyl) amine + H⁺ → (alkyl)ammonium ion

Amines forming salt

amine + acid→ akylammonium + salt

• Amines react with acids to make salts via neutralisation reactions

Aliphatic

branched or unbranched

Preparation of primary aliphatic amines

step 1-

• Haloalkane + ammonia → ammonium

• Conditions: excess NH₃, ethanol solvent (to prevent Subsitution of the haloalkane with H₂O to form an alcohol)

Step 2-

• Ammonium salt + NaOH → amine + NaCl + H₂O

Alternative method:

• Nitrile + hydrogen → amine

• Ni catalyst

Preparation of secondary aliphatic amines

step 1-

• Haloalkane + amine → 2^o ammonium salt

• Lone pair on N of primary amine can be further substituted by a haloalkane

Step 2-

• 2^o ammonium salt Lone+ NaOH → 2^o amine + NaCl + H₂O

• Conditions: same as primary

Preparation of tertiary aliphatic amines

step 1-

• 2^oamine + haloalkane → 3^o ammonium salt

Step 2-

• 3^oammonium salt + NaOH → 3^o amine + NaCl + H₂O

Preparation of aromatic amines

nitrobenzene can be reduced to form phenylamine

1. Reflux Sn/HCl

2. Aq NaOH in excess

General formula for amino acid

-RCH(NH₂)COOH

Amino acid

bi-functional molecule containing both an amine and a carboxylic acid group

Alpha amino acid

Amine group and carboxylic acid attached to the same central carbon atom (alpha C)

Reactions of amine group in carboxylic acids

Acids

• Amino acid + acid → ammonium salt

Acyl chloride

• Amino acid + acyl chloride → amide + HCl

Reactions of carboxyl group in amino acids

alkalis

• Amino acid + alkali → salt + water

Alcohols

• Amino acid + alcohol → ester + water

• Conc H₂SO₄ must be present

Zwitterions

two ions- at a specific pH the number of protonated amine groups is equal to the number of deprotonated acid groups. There is no overall charge on the amino acid molecule. This pH is called the isoelectric point.

Chiral centre

a carbon atom attached to four different carbon atoms

Optical isomers/enantiomers

non-superimposable mirror images

Drawing enantiomers

draw one tetrahedral molecule, then draw a dotted line to represent a mirror

Physical properties of enantiomers

• Mpt and bpt and solubility is identical

• Rotation of plane-polarised light= opposite

Chemical properties of enantiomers

• reaction with non-optically active compounds is identical to

• Reaction with optically active compounds the rate differs

Making nitriles from nucleophilic Subsitution

halogenoalkane + cyanide ion → nitrile + halide ion

• Reagent: haloalkane with NaCN or KCN in ethanol

• Conditions: reflux

• Use ethanol- water would result in OH- ions which would react to form alcohols

• Increases C chain length by 1

Reduction of nitriles

nitrile + hydrogen → amine

• Ni catalyst

Hydrolysis of nitriles

Nitrile + water + dilute aqueous acid (HCl) → carboxylic acid

• Heat

Condensation polymerisation

The joining of monomers with the loss of a small molecule, usually water or hydrogen chloride

Two ways to make a polyester

1. Single monomer with carboxylic acid at one end and an alcohol the other

2. Two monomers, one a dicarboxylic acid and the other a diol

Dipeptides

Formed from two acids in a condensation reaction

Two methods of making a polyamide

1. Single monomer with carboxylic acid at one end and an amine at the other

2. Two monomers, one a dicarboxylic acid and the other a diamine

Zwitterions of amino acids

at a specific pH, the number of protonated amine groups is equal to the number of deprotonated acid groups. There is no overall charge on the amino acid molecule. This pH is called the isoelectric point.

Amino acids reacting in acidic conditions

amine groups is protonated to form NH₃⁺

Amino acids reacting in alkaline conditions

carboxylic group is deprotonated to form -COO

Acid hydrolysis of a peptide

conditions: reflux/het with aq HCl and there must be water

Alkaline hydrolysis of a peptide

conditions: reflux/heat with aq NaOH