Chapter 15 Alcohols Diols and Thiols 1 Sources of Alcohols Ten billion pounds of methanol prepared annually in the USA using zinc chromium oxide catalyst CO H2 CH3OH Fermentation of vegetables yields ethanol and CO2 Hydration of ethylene and propene yields ethanol and isopropyl alcohol 2 Naturally Occurring Alcohols 3 Reaction Review 4 Reaction Review 5 Reduction of Aldehydes and Ketones Metal Catalyzed Hydrogenation General reaction Examples 6 Reduction of Aldehydes and Ketones Metal Hydride Reducing Agents Most common reagents Sodium borohydride NaBH4 Lithium aluminum hydride LiAlH4 7 Reduction of Aldehydes and Ketones Metal Hydride Reducing Agents General Reaction 8 Reduction of Aldehydes and Ketones Metal Hydride Reducing Agents Examples 9 Mechanism of Borohydride Reduction 10 Mechanism of Aluminum Hydride Reduction Reduction 11 Reduction of Carboxylic Acids 12 Alcohols from Epoxides Reaction of Grignard reagents with epoxides Mechanism 13 Preparation of Diols Catalytic hydrogenation of two aldehydes Name diols similar to alcohols replacing ol ending with diol List the location of each of the hydroxyl groups i e the product above is 3 methyl 1 5 pentanediol 14 Preparation of Diols Vicinal Diols Dihydroxylation of Alkenes using osmium tetraoxide 15 Preparation of Diols The ester is cleaved by other oxidizing agents like hydroperoxides Example 16 Reaction Review 17 Reaction Review 18 Conversion of Alcohols to Ethers Acid catalyzed reaction Example 19 Mechanism of Formation of Ethers Step 1 Protonation Step 2 Nucleophilic attack 20 Mechanism of Formation of Ethers Step 3 Deprotonation 21 Mechanism of Formation of Ethers Acid catalyzed intramolecular reaction 22 Esterification Acid catalyzed condensation of an acid and an alcohol Reversible reaction Water can be removed via distillation and or an excess of the alcohol is used to drive the reaction to the ester product 23 Alcohol Acid Chloride Reaction of alcohols with acid chlorides yield esters Weak base neutralizes the acid Example 24 Alcohol Acid Anhydride Reaction of alcohols with an acid anhydride yield esters Weak base neutralizes the acid Example 25 Ester Formation The stereochemistry of the alcohol is not affected during the reaction 26 Oxidation of Alcohols Primary alcohols yield aldehydes or carboxylic acids dependent on reagent Chromic acid oxidizes to the carboxylic acid in aqueous environment 27 Oxidation of Alcohols Secondary Alcohols yield ketones 28 Mechanism of Oxidation Utilizing Chromic Acid Step 1 Nucleophilic Attack Step 2 b Elimination 29 Mechanism of Oxidation Chlorodimethylsulfonium ion as oxidant Generation of the oxidant Example 30 Biological Oxidation of Alcohols Oxidation of Ethanol NAD Mechanism 31 Sustainability and Synthesis Chromic acid is a stoichiometric reagent and an environmental hazard Sodium perchlorate has non toxic by products Reaction is improved with a catalyst that reacts with perchlorate to forms the active oxidant Example Oxidative Cleavage of Vicinal Diols Periodic acid cleaves vicinal diols Example 33 Thiols Contain the SH group Have a foul odor 34 Thiols Acidity Thiols are more acidic than alcohols and can be deprotonated to form nucleophiles Nucleophilic substitution reactions form thiols or sulfides 35 Comparison of Polarity Electrostatic potential maps 36 Oxidation of Thiols Sulfur can be oxidized 37 Oxidation of Thiols Biochemically more important is the oxidation of thiols to disulfides 2 RSH RSSR 38 Oxidation of Thiols Oxidation can also be achieved in the lab 39 Spectroscopic Analysis of Alcohols and Thiols IR O H stretching 3200 3650 cm 1 C O stretching 1025 1200 cm 1 S H stretching 2550 2700 cm 1 weak 40 Spectroscopic Analysis of Alcohols and Thiols Proton NMR O H 1 5 5 ppm Signal disappears with the addition of D2O 41 Spectroscopic Analysis of Alcohols and Thiols NMR The deshielding effect of oxygen on the chemical shift of both C and H is greater than the effect of the less electronegative 1 13 H NMR C NMR 42 Spectroscopic Analysis of Alcohols and Thiols MS The molecular ion is usually small for alcohols and loss of water M 18 is common Primary alcohols often fragment to lose protonated formaldehyde 43