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Alcohols – nomenclature and reactions L.O. To be able to name alcohols and assign primary, secondary and tertiary status. To know some specific reactions of alcohols OH OH C C H H C C H C OH C C C C TYPES OF ALCOHOL PRIMARY ALCOHOLS SECONDARY ALCOHOLS TERTIARY ALCOHOLS OH OH OH C C H H OH at end of a chain C C C H C C C C OH at middle of a chain OH at junction of 2 chains CH3CH2CH2CH2OH CH3CH2CH(OH)CH3 CH3C(CH3)(OH)CH3 Butan-1-ol Butan-2-ol Methyl propan-2-ol ISOMERS OF PENTANOL SELECT PRIMARY (P), SECONDARY (S) OR TERTIARY (T) Make sure you can draw full displayed, structural and skeletal representations of each. CH3CH2CH2CH2CH2OH Pentan-1-ol P S T CH3CH2CH2CH(OH)CH3 Pentan-2-ol P S T CH3CH2C(CH3)(OH)CH3 2-Methylbutan-2-ol P S T CH3CH2CH(OH)CH2CH3 Pentan-3-ol P S T CH3C(CH3)2CH2OH 2,2-Dimethylpropan-1-ol P S T CH3CH(OH)CH(CH3)CH3 3-Methylbutan-2-ol P S T CH3CH(CH3)CH2CH2OH 3-Methylbutan-1-ol P S T CH3CH2CH(CH3)CH2OH 2-Methylbutan-1-ol P S T Dehydration (removal of water) of alcohols H OH C C ALKENES Removal (elimination) of water by : 1.Heating with concentrated sulphuric acid at 170C or 2. Passing vapour over Al2O3 at 350C C C + HOH NB Used to make ETHENE in countries where carbohydrate plentiful for fermentation but petroleum oil not avialable for cracking H may be removed from more than one C adjacent to C-OH mixture of alkenes Deduce the dehydration products of : 1. Ethanol? 2. Methyl-propan-2-ol? 3. Butan-2-ol ? 1. H H OH C C H H H 2. H H H C H OH C C H CH3 CH3 H CH3 C H + HOH H H C 3. OH H H C C C C H H H H H C H CH2CH3 C CH3 H H C + HOH H H CH3 + HOH and H E & Z! C H C CH3 Reaction of an alcohol (R-OH) with sodium metal an alkoxide (R-O- Na+) + hydrogen gas (H2) C-OH + Na C-O- Na+ + ½ H2 Notes : 1. The bonding is ionic between O and Na 2. The reaction is parallel (but slower) to the reaction of sodium with the OH group in water HOH + Na Na+OH- + ½ H2 Note : These are all redox reactions because the Na is oxidised (electron loss) and the H of OH is reduced (electron gain) PRIMARY ALCOHOLS SECONDARY ALCOHOLS OH C C H H TERTIARY ALCOHOLS OH C C C H OH C C C Rate decrease For isomeric alcohols: the rate of reaction with sodium decreases from primary to secondary to tertiary C Products of sodium with : 2. Methyl-propan-2-ol? 3. Butan-2-ol ? 1. H H OH C C H H 2. H H H O- Na+ C C H H H Sodium ethoxide + ½H2 H OH C C H CH3 3. CH3 H H OH H H C C C C H H H H + Na + Na H 1. Ethanol? H + Na H O- Na+ C C H CH3 CH3 Sodium (methylprop-2oxide) + ½H2 H H H O-Na+ H H C C C C H H H H Sodium but-2-oxide + ½H2 H Try some more examples for yourself! Write an equation, giving the full structure and name of the main organic product, for the reactions between : 1. Methanol + Na 2. Propan-1-ol + Na 3. Propan-2-ol + Na 4. Butan-1-ol + Na 5. Methyl-propan-1-ol + Na Substitution of an alcohol by HBr a bromoalkane δ+ δ- C-OH + HBr C-Br + H2O HBr produced by reacting KBr with conc. H2SO4. KBr + H2SO4 KHSO4 + HBr In practice, the alcohol is mixed with KBr in a reflux apparatus. The acid is then added to the mixture, drop wise. Note : This is a nucleophilic substitution because the δ+C is attacked by the δ-Br HBr substitution products of :1. Ethanol? 2. Methyl-propan-2-ol? 3. Butan-2-ol ? 1. H H OH C C H H 2. H H H Br C C H H Bromoethane + H2O OH C C H CH3 CH3 H H OH H H C C C C H H H H + HBr + HBr H H 3. H H H Br C C H CH3 + HBr CH3 Methyl-2-bromopropane + H2O H H H Br H H C C C C H H H H 2-Bromobutane + H2O H Reaction of alcohols with phosphorus pentachloride (PCl5) R-OH (l) + PCl5 (s) C-Cl (l) +HCl (g) + POCl3 (l) Fumes of HCl being given off makes this a useful reaction to identify the presence of an alcohol functional group. Try some more examples for yourself! Give the full structure and name of the main organic product produced by : 1. Methanol + HBr 2. Propan-1-ol + HBr 3. Propan-2-ol + HCl 4. Butan-1-ol + HBr 5. Methyl-propan-1-ol + HCl AS Chemistry OXIDATION OF ALCOHOLS OXIDATION OF ALCOHOLS Oxidised to aldehydes and acids or ketones NOT for PRIMARY SIGNIFICAN for SECONDARY alcohols T for alcohols TERTIARY -CH2OH -C-CH(OH)-Calcohols! NB Oxidant = hot acidified Cr2O72- [dichromate(VI)] ion] Provided by mixture of potassium dichromate(VI), K2Cr2O7, and excess dilute sulphuric acid, H2SO4. Oxidant is represented by : [O] OBSERVATION: Orange Cr2O72- reduced to green Cr3+ SECONDARY PRIMARY C H C C C C H OH + [O] H C + H2O Aldehyde O + [O] OH C Acid C H C OH + [O] C TERTIARY C O C C C C C OH + [O] NO SIGNIFICANT OXIDATION + H2O Ketone O + [O] NO FURTHER OXIDATION - no C – H bond - no C–H bond Any oxidation that does occur involves breaking C-C bonds loss of original structure. What are the oxidation products of : 1. Ethanol? 2. Methyl-propan-2-ol? 3.Butan-2-ol? CH3CH2OH CH3C(CH3)(OH)CH3 Primary Tertiary CH3CH2CH(OH)CH3 Secondary Controlling Oxidation Products To Maximise the Production of an ALDEHYDE To Maximise the Production of an ACID or a KETONE This is PARTIAL oxidation This is FURTHER oxidation Use only molar proportions of dichromate and acid Use excess of dichromate and acid Use minimum contact time between alcohol and oxidant by use of immediate distillation Use maximum contact time between alcohol and oxidant by use of reflux Add acidified dichromate to the alcohol to avoid the presence of excess oxidant Pre-mix acidified dichromate and alcohol to ensure excess oxidant at all times 1. Reflux with conc. NaOH in ethanol Alkene(s) C=C 2. + HBr 1 Eliminations Halogenoalkane C-Br 3. Reflux with aq. NaOH 3. Heat with excess conc. NH3 in ethanol Primary amine C-NH2 3. Heat with NaBr + conc. H2SO4 Electrophilic 2 addition Nucleophilic 3 substitutions Alcohol C-OH 5. Heat with carboxylic acid (-COOH) + conc. H2SO4 cat. Ester CO.OC 4 Oxidations 5 Condensations Ketone C-CO-C (if alcohol SECONDARY) 4. Heat with molar propns. of K2Cr2O7 + dil. H2SO4 ; distil Aldehyde CHO (if alcohol PRIMARY) 5. Heat with alcohol (C-OH) + conc. H2SO4 catalyst 4. Reflux with excess K2Cr2O7 + dil. H2SO4 Acid COOH