Chemistry - Carboxylic Acids, Esters, Nitrogen Compounds & Optical Isomerism

Carbonyl Group

-COOH

Act as weak acids

Carboxylic Acids with fewer than 6 carbons are water soluble as OH group can hydrogen bond with water

React like normal acids with metals, alkalis and carbonates

Ester Group

-COO-

Characterised by their sweet and fruit smell

Formed by Condensation Reactions with H2SO4 catalyst

Named by alcohol then carboxylic acid

Methods of making esters (5)

1. Alcohol + Carboxylic Acid (H2SO4 Cat.) → Ester + Water - Low yield + Reversible

2. Alcohol + Acid Anhydride (H2SO4 Cat.) → Ester - Irreversible, Acid Anhydrides are more reactive than Carboxylic acids (H on OH replaced with R-C=O)

3. Acyl Chloride + Alcohol → Ester + HCl

4. Acyl Chloride + Phenol (NaOH + Heat) → Ester + NaCl + H2O

5. Amino Acid + Alcohol (conc. H2SO4) → Ester(Esterified Carboxylic Acid Group & Protonated NH2 Group) + Water

Ester Hydrolysis

Forms Carboxylic Acid + Alcohol

Reflux with Dilute Acid is reversible

Reflux with dilute alkali is irreversible, forms a carboxylate salt which needs further acidification to form a carboxylic acid

Acyl Chlorides

-COCl

More reactive than carboxylic acids so often used as a starting compound in organic reactions

Prepared by reacting carboxylic acid with SOCl(l) to form Acyl chloride + SO2 + HCl

React with ammonia and primary amines to produce amides

• The lone pair on N attacks the electron deficient carbonyl carbon on Acyl chloride, producing an amide and acidic HCl

• Second Mole of Ammonia neutralises HCl

• R-COCl + 2NH3 → R-CONH2 +NH4Cl

• R-COCl + 2CH3NH2 → R-CONHCH3 + CH3NH3Cl

Basic Properties of Amines

The nitrogen can accept a proton and can therefore undergo acid-base reactions

Amine and Ammonium salts are ionic and soluble (As chain length increases, solubility decreases)

Preparing AliPHATIC amines (3)

1. Haloalkane + Ammonia → Primary Amine + Ammonium Salt (Nucleophilic Substitution requiring Heat Pressure and Ethanol)

2. Reduction of Nitriles using 4[H] & Ni Catalyst to form amine only

3. Reaction of Haloalkane with primary amines produces secondary amines (Heat & Ethanol). Tertiary amine can be formed from further reaction of the secondary amine

Preparing Aromcatic Amines

Phenylamine is an organic compound with a benzene ring & amine

Nitrobenzene can be reduced t phenylamine using a 2 stage reaction

Stage 1: Nitrobenzene is reduced to the phenyl ammonium ion using Sn & Conc HCl under reflux

Stage 2: Excess NaOH(aq) is added to the phenyammonium ion to form phenylamine

Amino Acids

Contain -NH2 (basic) and -COOH (acidic)

2-aminocarboxylic acids are naturally occurring, the R group can be acidic, basic or neutral

Amine Group can react with acids to make salts

Carboxylic Acid Group can react with bases to form salt + water & esterified with alcohol in presence of conc H2SO4 (-COOH esterified and -NH2 protonated)

Amides

R-CO-NRR

Formed by the condensation reaction of:

• Carboxylic Acid + Ammonia/Amine

• Acyl chloride + Ammonia/Amine

Can be split into primary (2 Hs), secondary (1 H and 1 R group), and tertiary amides (2 R Groups)

Stereoisomers

Molecules that have the same structural formula but different arrangement of atoms in space

Chiral Carbon

Carbon that has 4 different groups bonded to it. Compounds with a chiral centre exist as two optical isomers (non-superimposable images of each other)