Download Ethers and Epoxides: Nomenclature, Properties, Synthesis, and Reactions and more Study notes Organic Chemistry in PDF only on Docsity! CEM 143 Summer 2009 Chapter 8 Study Sheet Ethers and Epoxides General Formula: R-O-R Nomenclature: When naming the –OR group as a subsituent use the alkyl substituent name, subtract –yl ending and add –oxy ending. For example: CH3O O O O O methoxy ethoxy propoxy isopropoxy t-butoxy Otherwise, name each substituent on either side of the oxygen and then add ‘ether’ at the end. For example: O O O O O diethyl ether or ethyl ether or ethoxy ethane diphenyl ether or phenyl ether ethyl methyl ether or methoxy ethane t-butyl methyl ether ethyl isopropyl ether *Use whichever method that makes the molecule easier to name* For example: O 2-ethoxy-3-methylbutane This is hard to name as a substituent so name RO- as a substituent and name like an alkane making sure to give the -alkoxy group the lowest number! Physical Properties…Ethers vs. Alcohols: Ethers do not have the –OH functionality therefore there is NO acid/base chemistry and ethers cannot hydrogen bond with themselves. However, they can act as hydrogen bond acceptors with water and alcohols. Grignard reagents are VERY strong nucleophiles/bases and are considered unstable. Ethers are able to solvate Grignard reagents and stabilize them: R MgX O O **Since Grignard reagents are VERY strong bases the reaction MUST BE FREE OF H2O AND ALCOHOLS!!!!!** R Mg Br H2O CH3OH HO Mg Br H3CO Mg Br R-H R-H + + Fast & irreversible!!! R can be an aromatic ring... Br Mg0 ether MgBr D2O D + DO-Mg-Br D2O is heavy water... D = deuterium which is an isotope of H HO Br Mg 0 ether No Reaction! This kills (quenches) the Grignard as its formed! Later we’ll see that Grignard reagents are very versatile in synthesis! Lithium analog of Grignard reagents: General Reaction: R X 2 Li0 ether R Li X = Cl, Br, I lithium metal Alkyl lithium reagent + Li-X H3C Br 2 Li0 ether + LiBrCH3 - Li+ Like Grignard reagent... VERY strong nucleophile/ base!!! Preparation of Ethers: Acid Catalyzed – simplest – only works for SYMMETRIC ethers: OH2 H2SO4 O diethylether OH H2SO4 How does it work? Like last chapter... O H H OH Good leaving group! O H + -HSO4 -HSO4 O Cleavage of Ethers: Use strong acid such as HCl, HBr or Hi O HI OH + CH3I O HI CH3I + CH3CH2OH and/or CH3CH2I + CH3OH This reaction is a SN2 reaction so the 1st reaction only can make phenol and methyliodide because you cannot do and SN2 reaction on sp 2 hybridized carbon. But on the ethylmethylether both carbons next to the oxygen are sp3 hybridized and therefore the reaction can proceed 2 different ways. sp2 sp3 sp3 sp3 Cleavage using BBr3: BBr3 does the same thing but by a different mechanism. The same rules as above apply… O 1) BBr3 OH + CH3I O CH3I + CH3CH2OH and/or CH3CH2I + CH3OH 2) H2O 2) H2O 1) BBr3 Cyclic Ethers: O O O O ethylene oxide (oxirane) trimethylene oxide tetrahydrofuran (THF) tetrahydropyran (THP) Important reactivity Excellent solvent 2 or more oxygen atoms in a ring makes things interesting... O O O O OO O O O OO O1,4-dioxane [12]-crown-5 [18]-crown-6 The 'crown' molecules are named as such: [total number of C's and O's]-crown-(number of O's) The crown molecules are known as specific ion binding molecules: O O OO Li+ O O O OO O K+ The pictures above are exactly like the picture of ethers solvating ions. In crowns, it is just one molecule with multiple ether sites...the only difference is that the space within the cycle is sized such that only one size of ion can fit inside. So the [15]-crown-5 is specific for Li+ and the [18]-crown-6 is perfect for K+. Epoxides: Synthesis of Epoxides: O Epoxides are 3-membered rings that contain oxygen. They are very strained and therefore very reactive!! Operacid General Reaction: R O O O H General formula of a peracid: These to oxygens make it a 'per' acid rather than just a carboxcylic acid. Like hydrogen peroxide: H O O H
