Organic Chemistry Fourth Edition David Klein Chapter 13 Ethers and Epoxides Thiols and Sulfides This deck contains equations authored in Math Type For the full experience please download the Math Type software plug in Copyright 2021 John Wiley Sons Inc 13 1 Introduction to Ethers Definition An ether group includes an oxygen atom that is bonded to two alkyl groups R groups can be alkyl aryl or vinyl groups not acyl groups this is an ester not an ether Copyright 2021 John Wiley Sons Inc 2 13 1 Introduction to Ethers Common Compounds Ether is a common functional group in many natural and synthetic compounds Copyright 2021 John Wiley Sons Inc 3 13 2 Naming Ethers Common Names Common names are often used for ether 1 Name each R group 2 Arrange them alphabetically 3 End with the word ether Copyright 2021 John Wiley Sons Inc 4 13 2 Naming Ethers Systematic Names IUPAC systematic names o The larger R group is the parent chain o The smaller R group is the alkoxy substituent Practice with SkillBuilder 13 1 Naming an Ether Copyright 2021 John Wiley Sons Inc 5 13 3 Structure and Properties of Ethers Bond Angle The bond angle in ethers is very similar to that found in water and in alcohols o The oxygen atom is sp3 hybridized o The larger the R group the wider the bond angle Copyright 2021 John Wiley Sons Inc 6 13 3 Structure and Properties of Ethers H Bonding Recall alcohols have relatively high boiling points as a result of H bonding Ethers can act only as H bond acceptors Copyright 2021 John Wiley Sons Inc 7 13 3 Structure and Properties of Ethers Boiling Point Ethers cannot H bond among themselves and so their B P s are much lower than alcohols of comparable size The larger the ether the higher the B P London dispersion forces Copyright 2021 John Wiley Sons Inc 8 13 3 Structure and Properties of Ethers Solvents Ethers are common solvents used for organic reactions Relatively low boiling points easily removed by evaporation They are fairly unreactive Copyright 2021 John Wiley Sons Inc 9 13 4 Crown Ethers Concept Metal atoms with a full or partial positive charge are stabilized by ether solvents Ethers are used as solvents for Grignard reactions because they stabilize the Mg atom Copyright 2021 John Wiley Sons Inc 10 13 4 Crown Ethers Overview Crown ethers have been shown to form especially strong attractions to metal atoms The multiple ether groups result in stronger metal attraction The s in their names refer to the total number of atoms and the number of oxygens Copyright 2021 John Wiley Sons Inc 11 13 4 Crown Ethers Matching Metal with Crown The size of the metal must match the size of the crown to form a strong attraction 18 crown 6 is the ideal size to trap a potassium cation Copyright 2021 John Wiley Sons Inc 12 13 4 Crown Ethers Solubilize the Metal Cation Metal ions are not soluble in low polarity solvents The crown ether complexes to the metal cation and the resulting complex is soluble Crown ethers are used to help ionic salts needed for organic reactions to dissolve in organic solvents Copyright 2021 John Wiley Sons Inc 13 13 4 Crown Ethers Solubilization Concept The F ion below is ready to react because the K ion is hosted by 18 crown 6 Without the crown ether the solubility of KF in benzene is miniscule Copyright 2021 John Wiley Sons Inc 14 13 4 Crown Ethers Choice of Crown Ether Choosing a crown ether depends on the metal cation present in a reaction Practice with CONCEPTUAL CHECKPOINT 13 4 Copyright 2021 John Wiley Sons Inc 15 13 5 Preparation of Ethers Industrial Prep Industrially diethyl ether is prepared by the acid catalyzed dehydration of ethanol Simple symmetrical ethers can be prepared this way Copyright 2021 John Wiley Sons Inc 16 13 5 Preparation of Ethers Williamson Ether Prep The Williamson ether synthesis is a viable approach for many asymmetrical ethers Copyright 2021 John Wiley Sons Inc 17 13 5 Preparation of Ethers Williamson Ether Mechanism The Williamson ether synthesis is a viable approach for many asymmetrical ethers Since this is SN2 substitution it only works well with unhindered 1 and methyl alkyl halides Copyright 2021 John Wiley Sons Inc 18 13 5 Preparation of Ethers Two Routes Consider the two possible routes to synthesize methyl t butyl ether via Williamson ether synthesis This route will work because it requires a methyl halide This route will not work as it requires a 3 halide Practice with SkillBuilder 13 2 Preparing an Ether Copyright 2021 John Wiley Sons Inc 19 13 5 Preparation of Ethers Review Recall that oxymercuration demercuration can be used to synthesize alcohols from alkenes section 8 7 Markovnikov regioselectivity Copyright 2021 John Wiley Sons Inc 20 13 5 Preparation of Ethers Application to Ethers Similarly alkoxymercuration demercuration can be used to synthesize ethers Also Markovnikov regioselectivity Practice CONCEPTUAL CHECKPOINTS 13 7 13 9 Copyright 2021 John Wiley Sons Inc 21 13 6 Reactions of Ethers Acid Promoted Cleavage Ethers can undergo acid promoted cleavage Copyright 2021 John Wiley Sons Inc 22 13 6 Reactions of Ethers Alkyl Halides Acidic cleavage of ethers to produce an alkyl halide works with HBr and HI If R group is 3 then cleavage occurs via SN1 mechanism If R group is aryl or vinyl substitution doesn t occur Practice with CONCEPTUAL CHECKPOINT 13 10 Copyright 2021 John Wiley Sons Inc 23 13 6 Reactions of Ethers Autooxidation Recall section 10 9 ethers undergo autooxidation Laboratory samples of ether must be frequently tested for the presence of hydroperoxides before they are used explosive The autooxidation occurs through a free radical mechanism Copyright 2021 John Wiley Sons Inc 24 13 6 Reactions of Ethers Initiation and Propagation Copyright 2021 John Wiley Sons Inc 25 13 6 Reactions of Ethers Termination and Summary Recall that the net reaction is the sum of the propagation steps Copyright 2021 John Wiley Sons Inc 26 13 7 Nomenclature of Epoxides Cyclic Ethers For cyclic ethers the size of the ring determines the parent name of the molecule Oxiranes are also known as epoxides Copyright 2021 John Wiley Sons Inc 27 13 7 Nomenclature of Epoxides Common Molecules An epoxide can have up to 4 R groups Although they are unstable epoxides are found commonly in nature Copyright 2021 John Wiley Sons Inc 28 13 7 Nomenclature of Epoxides Two Methods There are two methods for naming epoxides 1 The oxygen is treated as a side group and two numbers are given as its locants 2 Oxirane is used as the parent name Copyright 2021