Ethers Nomenclature alkylalkylether dimethylether diethylether prefix alkoxy- (the base for the name is the bigger part of molecule) ethyl-4-methoxybutanoate 4-bromo-3-butoxybenzaldehyde Ethers Ethers are very volatile: compare boiling temperature with alcohol diethylether b.p. 34oC ethanol b.p. 78oC tetrahydrofuran THF b.p. 67oC diphenylether b.p. 259oC nc-O= 1060 – 1150 cm-1 Ethers ethers belong to low reactive compounds and therefore are often used as solvents expected reactivity : 1.interaction of free electron pairs with electrophiles 2.electron gap at C atom in the neigbourhood of oxygen offers possibility of nucleophilic atack 3.hydrogen atom in b-position may be attacked by a base in elimination reactions Ethers expected reactivity : 1. interaction of free electron pairs with electrophiles 2. electron gap at C atom in the neigbourhood of oxygen offers possibility of nucleophilic atack for reaction concentrated acids are needed reactivity HI > HBr > HCl temperature = 120o – 140oC (press vessels) !!Nonsymmestrical ethers splitting!! Ethers expected reactivity : 1. interaction of free electron pairs with electrophiles 2. electron gap at C atom in the neigbourhood of oxygen offers possibility of nucleophilic atack 3. hydrogen atom in b-position may be attacked by a base in elimination reactions tert. ethers rather undergo elimination reaction than substitution Ethers !!!Ethers often form peroxides – dangerous explosives compounds!!! Ethers Cyclic ethers: Oxiranes (epoxides) show other reactivity connectes with a bond angle strain in small three member ring – the ring can be easily split Preparation: oxidation of olefins oxiran (ethylenoxid, epoxide) 1,2-epoxycyklopentane Priležajev oxidation = (cis – addition) Ethers The oxirane ring may be opened either under acid or base catalysis, results at nonsymmetrical oxiranes then may differ After protonation of oxirane oxygen atom the ring is opened in direction to form a stable cation, which in following step is attacked by the present anion Opening in the presence of a base takes place from the less sterically hindered side, where the nucleophile is bound and proceeds the ring opening. The alkoxide this way formed is stabilized by proton from reaction medium. Ethers oxetan is more resistant against acid action, but finaly the ring may be open tetrahydrofuran is resistant against acids and is opened only by concentrated acids crown –ethers 18-crown-6 is able to complexate K+ cation Ethers Epoxides resines epichlorhydrine + dian (2,2-bis-(4-hydroxyfenyl)propane) two component glue: 1. the polymer above 2. component - hardener As a hardener are used: diamines, glycoles, dicarboxylic acids anhydrides, or other acids and bases They are opening the epoxide ring and binding chains of prepolymer together into hard mass with netlike structure of resin Sulfur analogs of alcohols, phenols and ethers thioles (earlier mercaptanes) sulfides ethanthiol butan-2-thiol ethylmethylsulfid dimethylsulfid Prefix -- sulfanyl event. alkylsulfanyl 2-sulfanylethanol 4-methylsulfanylbenzaldehyd Sulfur analogs of alcohols, phenols and ethers When compared with alcohols they are more volatile (the hydrogen bonds formed here are not so strong) and therefore smell also in small quantity Ethanol b.v. 78oC Ethanthiol b.v. 37oC 3-methylbutanthiol diallylsulfid propanthiol General reactivity: 1.Sulfur atom is nucleophilic and reacts very well with all electrophilic centra 2.Hydrogen atom at sulfur is acidic 3.The bond S-H is only little polar and therefore radical splitting is possible to expect Sulfur analogs of alcohols, phenols and ethers Hydrogen atom is more acidic than in alcohols and therefore can be removed even by a weak base and in water H2O H2O pKa = 10 (thiol) compare pKa = 16 (alcoholes) General reactivity: 1.Sulfur atom is nucleophilic and reacts very well with all electrophilic centra 2.Hydrogen atom at sulfur is acidic 3.The bond S-H is only little polar and therefore radical splitting is possible to expect Sulfur analogs of alcohols, phenols and ethers thiol is stronger acid than alcohol !Be carefull! Thiolate is stronger nucleophile than alkoholate It is caused by better polarizibility of sulfur Alcoholates rather enter into elimination reactions and thiolates prefer nucleophilic substitution reactions Sulfur analogs of alcohols, phenols and ethers General reactivity: 1.Sulfur atom is nucleophilic and reacts very well with all electrophilic centra 2.Hydrogen atom at sulfur is acidic 3.The bond S-H is only little polar and therefore radical splitting is possible to expect Sulfur analogs of alcohols, phenols and ethers Bond C – S is less polar than bond C – O (oxygen atom is more electronegative) the bond is difficult to split – substitution is difficult the formed radicals enter dimerization - formation of disulfides dialkyldisulfid General reactivity: 1.Sulfur atom is nucleophilic and reacts very well with all electrophilic centra 2.Hydrogen atom at sulfur is acidic 3.The bond S-H is only little polar and therefore radical splitting is possible to expect Sulfur analogs of alcohols, phenols and ethers reversible process in a brain – responsible for process of remembering cystein cystin sulfur derivatives undergo easy oxidation gentle oxidation reagents strong oxidation reagents (HNO3, KMnO4 ….) sulfenic acid sulfinic acid sulfonic acid Sulfur analogs of alcohols, phenols and ethers General reactivity : 1.basic properties 2.high nucleophility 3.sensitivity against oxidation SULFIDES in properties similar to ethers, but they have higher boiling temperatures then ethers in acids they dissolve under formation of sulfonium salts, which in water split back Sulfur analogs of alcohols, phenols and ethers the formed sulfonium salts may be used for alkylation of nucleophiles General reactivity : 1.basic properties 2.high nucleophility 3.sensitivity against oxidation