ALCOHOLS ETHERS & EPOXIDES

FUNCTIONAL GROUP  Alcohols contain a hydroxyl group (OH) bonded to an sp 3 hybridized carbon. The oxygen atom in alcohols, ethers and epoxides is sp 3 hybridized.  Alcohols and ethers have a bent shape like that in H 2 O.

Compounds having a hydroxyl group on a sp 2 hybridized carbon (-enols and phenols)—undergo different reactions than alcohols. Ethers have two alkyl groups bonded to an oxygen atom. FUNCTIONAL GROUP ……..CONTD.

Epoxides are ethers having the oxygen atom in a three- membered ring. Epoxides are also called oxiranes. The C—O—C bond angle for an epoxide must be 60°, a considerable deviation from the tetrahedral bond angle of 109.5°. Thus, epoxides have angle strain, making them more reactive than other ethers. FUNCTIONAL GROUP ……..CONTD.

Alcohols, ethers and epoxides exhibit dipole-dipole interactions because they have a bent structure with two polar bonds. Alcohols are capable of intermolecular hydrogen bonding. Thus, alcohols are more polar than ethers and epoxides. Physical Properties Steric factors affect hydrogen bonding.

Q. Why boiling point (b.p.) of alcohols are much higher than the corresponding alkanes? Physical Properties ……contd. Q. Why alcohols are soluble in water? Q. Why lower alcohols are more soluble in water than higher ones?

METHODS OF PREPARATION 1. From Alkyl Halides: Substrate: Alkyl Halides Reactant: Dil. NaOH/KOH Condition: Boiling condition 2. Reduction of Aldehydes and Ketones Aldehyde → 1° alcohol Ketone → 2° alcohol

METHODS OF PREPARATION 3. Addition of Grignard reagents to Aldehydes and Ketones Formaldehyde → 1° alcohol Any other Aldehyde → 2° alcohol Ketone → 3° alcohol 4. Fermentation of Carbohydratyes: Substrate: Sugars Reactant: Yeast/Mould Condition: Fermentation Product: Ethanol

METHODS OF PREPARATION 5. From Alkenes: Substrate: Alkene Reactant: H 2 SO 4 followed by hydrolysis (reaction with H 2 O) Product: Alcohol (1°, 2° or, 3°) Markonikov Rule is followed here. Only Ethene → 1° alcohol Any n-Alkene → 2° alcohol Only those alkenes which contain an alkyl group in the (=) bonded carbon → 3° alcohol

METHODS OF PREPARATION 6. From Alkenes (Hydroboration-Oxidation): Substrate: Alkene (mainly seen in case of propene) Reactant: Borane (BH 3 ) followed by reaction with basic solution of H 2 O 2 Product: Alcohol (1°) Anti-Markonikov Rule is followed here.

1.Reaction with active metals: Substrate: Alcohols Reactant: Na metal Product: Na-alkoxide & H 2 gas Indication of Acidity of alcohols Chemical Properties Q. Prove that alcohols are acidic in nature. Q. Discuss on the acidity of alcohols. Q. Why primary alcohols are more acidic than tertiary one?.

2. Formation of alkyl halides from alcohols: Substrate: Alcohols (R-OH) Reactant: Phosphorus halides- HX/PX 5 /PX 3 /SOCl 2 Product: Alkyl Halide1 Chemical Properties ……contd. 3. Reaction with sulphuric acid / Dehydration of alcohols: Substrate: Alcohols (R-OH) Reactant: H 2 SO 4 Condition: 140°C or 170°C Product: Ether (in presence of excess alcohol) or Alkene

Chemical Properties ……contd. 4. Dehydration of alcohols using catalyst: Substrate: Alcohols (R-OH) Catalyst: Al 2 O 3 (Alumina) Condition: 200°C or 350°C Product: Ether or Alkene 5. Reaction with carboxylic acids: Substrate: Alcohols (R-OH) Reactant: R-COOH Condition: Presence of conc. H 2 SO 4 (as catalyst) Product: Ester Esterification Reaction Reversible in nature

Chemical Properties ……contd. 6. Formation of esters (not esterification): Substrate: Alcohols (R-OH) Reactant: Acid halide (R-COX) or Acid anhydride (R-CO) 2 O Product: Ester 7. Reaction with Grignard reagents: Substrate: Alcohols (R-OH) Reactant: R ʹ MgX Product: Alkane

Chemical Properties ……contd. 8. Reaction with hot copper: Substrate: Alcohols (1°, 2°or 3°) Product: Aldehyde, Ketone or Alkene

How to identify Alcohols (-OH group) 1.Sodium test 2.PCl 5 test How to differentiate between 1°, 2° & 3° Alcohols 1.Lucas test (reaction with HX) 2.Dichromate test (Oxidation) 3.By Catalytic Dehydrogenation

1.Lucas test (reaction with HX) 1°, Alcohols → → → No ppt. 2° Alcohols → → → Slower ppt 3° Alcohols → → → Quick ppt 2. Dichromate test (Oxidation) 1°, Alcohols (orange color → → → Green color) = Aldehydes → Acids 2° Alcohols (orange color → → → Green color) = Ketones 3° Alcohols (solution remains orange color) 3. Catalytic Dehydrogenation 1°, Alcohols → → → Aldehydes 2° Alcohols → → → Ketones 3° Alcohols → → → Alkenes

Conversion of Alcohols 1° → → 2°: n-Propanol → → iso propanol 2° → → 3°: iso Propanol → → tert. propanol