1 Chapter 15: Alcohols, Diols, and Thiols 15.1, Lecture notes of Chemical Processes

Download 1 Chapter 15: Alcohols, Diols, and Thiols 15.1 and more Lecture notes Chemical Processes in PDF only on Docsity! 1 320 Chapter 15: Alcohols, Diols, and Thiols 15.1: Sources of Alcohols (please read) Hydration of alkenes (Chapter 6) 1. Acid catalyzed hydration 2. Oxymercuration 3. Hydroboration Hydrolysis of alkyl halides (Chapter 8) nucleophilic substitution Reaction of Grignard or organolithium reagents with ketones, aldehydes, and esters. (Chapter 14) Reduction of alehydes, ketones, esters, and carboxylic acids (Chapter 15.2 - 15.3) Reaction of epoxides with Grignard Reagents (Chapter 15.4) Diols from the dihydroxylation of alkenes (Chapter 15.5) 321 15.2: Preparation of Alcohols by Reduction of Aldehydes and Ketones - add the equivalent of H2 across the π-bond of the carbonyl to yield an alcohol R R' C O [H] R' H C O R H aldehyde (R or R´= H) → 1° alcohol ketone (R and R´≠ H) → 2° alcohol Catalytic hydrogenation is not typically used for the reduction of ketones or aldehydes to alcohols. Metal hydride reagents: equivalent to H:– (hydride) sodium borohydride lithium aluminium hydride (NaBH4) (LiAlH4) H B H HHNa+ H Al H HHLi + Al H 1.5 2.1 B H 2.0 2.1electronegativity 2 322 R1 CR2 OH H C OH R1 R2 + H: C O R1 R2 + NaBH4 synthons precursors = NaBH4 reduces aldehydes to primary alcohols NaBH4 reduces ketones to secondary alcohols NaBH4 does not react with esters or carboxylic acids H3CH2CO O O NaBH4 HOCH2CH3 H3CH2CO O HHO NaBH4 HOCH2CH3 H O OH HH O2N O2N O OHH ketones 2° alcohols NaBH4 HOCH2CH3 323 Lithium Aluminium Hydride (LiAlH4, LAH) - much more reactive than NaBH4. Incompatible with protic solvents (alcohols, H2O). LiAlH4 (in ether) reduces aldehydes, carboxylic acids, and esters to 1° alcohols and ketones to 2° alcohols. O 1) LiAlH4, ether 2) H3O + OHH H O OH HH 1) LiAlH4, ether 2) H3O + ketones 2° alcohols aldehydes 1° alcohols 5 328 15.8: Esterification - Fischer esterification: acid-catalyzed reaction between a carboxylic acid and alcohol to afford an ester. The reverse reaction is the hydrolysis of an ester Mechanism (Chapters 19 and 20) Dean-Stark Trap R1 OH C O HO-R2 + H+ R1 OR2 C O + HOH 329 Ester formation via the reaction of an acid chloride or acid anhydride with an alcohol (nucleophilic acyl substitution) Mechanism (Chapters 20) R1 Cl C O HO-R2 + R1 OR2 C O + HCl acid chloride R1 O C O C R1 O + HO-R2 R1 OR2 C O + R1 OH C O acid anhydride 6 330 15.9: Esters of Inorganic Acids (please read) R1 OH C O HO-R2+ R1 OR2 C O + HOH carboxylic acid alcohol esters N OH O O HO-R+ nitric acid N OR O O + HOH O S O OHHO HO-R+ O S O ORHO + HOH sulfate ester sulfuric acid O P OH OHHO phosphoric acid HO-R+ O P OH ORHO + HOH phosphate ester nitrate ester ONO2 ONO2O2NO nitroglycerin O S O OCH3H3CO dimethylsulfate C OC H2N H H HO2C H P O O O phosphoserine C OC H2N H H HO2C H P O O O phosphotyrosine O O O N N N O H H O O O N N N NO N H H H O O O N N O O O O O N N N NN H H H P P O O O O Phosphodiester of DNA 331 15.10: Oxidation of Alcohols 2° alcohols ketone R1 R2 C OHH R1 R2 C O[O] R1 OH C HH R1 H C O[O] [O] R1 OH C O 1° alcohols aldehyde carboxylic acids KMnO4 and chromic acid (Na2Cr2O7, H3O+) oxidize secondary alcohols to ketones, and primary alcohols to carboxylic acids. OH H O oxidation [O] reduction [H] 7 332 Oxidation of primary alcohols to aldehydes Pyridinium Dichromate (PDC) Na2Cr2O7 + HCl + pyridine Pyridinium Chlorochromate (PCC) CrO3 + 6M HCl + pyridine N H ClCrO3 - N H 2 Cr2O5 2- PCC and PDC are soluble in anhydrous organic solvent such as CH2Cl2. The oxidation of primary alcohols with PCC or PDC in anhydrous CH2Cl2 stops at the aldehyde. CH2Cl2 PCC OH CHOCO2H 1° alcohol H3O +, acetone H2Cr2O7 Carboxylic Acid Aldehyde 333 15.11: Biological Oxidation of Alcohols (please read) Ethanol metabolism: Vitamin B3, nicotinic acid, niacin N CO2H Nicotinamide Adenine Dinucleotide (NAD) OH O N HO P O OH OP O OH O OH O O O R NH2 O H H N N N N H2N R= H NADH, NAD+ R= PO3 2- NADPH, NADP+ OH O N HO P O OH OP O OH O OH O O O R NH2 O N N N N H2N reduced form oxidized form CH3CH2OH alcohol dehydrogenase H3C H C O aldehyde dehydrogenase H3C OH C O ethanol acetaldehyde acetic acid