Chemistry Homework: Organic Compounds - Thiols, Ethers, Sulfides, and Epoxides, Assignments of Organic Chemistry

Download Chemistry Homework: Organic Compounds - Thiols, Ethers, Sulfides, and Epoxides and more Assignments Organic Chemistry in PDF only on Docsity! Manashi Chatterjee Ph.D. Fall 2007 Chem 30B – Fall 2007 Homework: 2 Chapter 10: contd: 10.9 Thiols Home work: 10.13; 10.15 k, l, m (nomenclature) Reactions: Acid base reactions: More acidic than R-OH. Reacts with NaOH to form salts. Oxidation: R-SH to R-S-S-R (disulfide); reagent I2 (iodine); and even with molecular oxygen. Synthesis Problems: Home work: 10.45, 10.44 Chapter 11: Ethers, Sulfides and epoxides: 11.2: Nomenclature: Home work: 11.10, 11.11 Cyclic ether (3 membered with oxygen in ring: Oxirane; numbering of the ring starts at the oxygen) 11.3: Physical properties of ether: (Boiling point: ethers have lower boiling points than their isomeric alcohols as the lack the H-bonding that exist in alcohols. Solubility in water: because they lack polar -OH group they can not act as H-bond donors like alcohols and they are less soluble in water than alcohols; however ether oxygen can accept H-bonds from water so more soluble in water than corresponding hydrocarbons) Home work: 11.2; 11.4, 11.12, 11.13 11.4: Preparation of ethers: A. Williamson Ether synthesis: Nucleophilic displacement of halide ion or a good leaving group with an alkoxide; Competing elimination reaction (E-2) occurs especially if leaving group is on sec or tert carbon. Yields of halides are high only if leaving group is on a primary carbon. This is very important in planning a Williamson synthesis. Home work: 11.3; 11.15 B. Acid catalyzed dehydration of alcohols: Works best for symmetric ether formed from unbranched primary alcohol. (Mechanism) Home work: 11.4 C. Acid-Catalyzed addition of alcohols to an alkene (Mechanism) 1 Manashi Chatterjee Ph.D. Fall 2007 Home work: 11.16 -------------------------------------------(Quiz 2)---------------------------------------------------------------------------- 11.5 Reactions of ether: Generally used as solvents as they are resistant to chemical reactions like oxidation by potassium dichromate or potassium permanganate. Even stable towards very strong bases (except tert-alkyl ethers); not affected by mild acids at room temp. A: Acid catalyzed cleavage by concentrated HI (57 %) or HBr (48 %) and heat: (substitution mechanism) tertiary, allylic and benzylic alcohols very suspectible to cleavage by acids under mild condition Home work: 11.6, 11.17 B. Oxidation of ethers: Formation of hydroperoxide: Low boiling low molecular weight ethers react with molecular oxygen at the C-H next to the ether O to form hydroperoxides which are explosives. Radical mechanism: Rate of hydroperioxide formation higher if C-H next to oxygen is secondary or tertiary. Presence of peroxide is tested by adding aqueous solution of KI; peroxides oxidize iodide to iodine and solution turns yellow. 11.6 Silyl ether as protecting group: Converting alcohols to silyl ether (O-Si bond formation): (silicon reagents) TMSCl- trimethylsilylchloride TESCl TBDMSCl TIPSCl Deprotecting by Bu4N+F- driving force formation of Si-F bond one of the strongest bonds (582 kJ/mol) Vs Si-O (368 kJ/mol). 11.7 Epoxides: 4 ways of synthesis: A: Ethylene oxide made by passing ethylene over air and catalyst (Ag). Fails for other cyclic ethers. B: Alkene and peroxycarboxylic acids R-CO3H (MCPBA). (mechanism) reaction is stereospecific: Cis symmetric alkenes give Meso product; Trans gives enantiomers. C: Internal Nucleophilic substitution in halohydrins: (recollect halohydrin from 6.3E) stereoselctive and regioselective and for symmetric cis – trans alkenes also steroselective). Internal displacement occurs in presence of a base. D: Sharpless Asymmetric epoxidation for allylic alcohols. (Stereospecific based on the diethyl tartrate added; either enantiomer of an epoxide can be prepared depending on which enantiomer of diethyltartrate is used. With (-) diethyl tartrate, oxygen is delivered to the top face. With (+) diethyl tartrate oxygen is delivered to the bottom face. Home work: 11.8, 11.9, 11.28 Reactions of epoxides: Acid catalyzed ring opening: 2