Chapter 11: Ethers, Epoxides, and Sulfides
Table of contents of main topics:
Nomenclature of ethers
IUPAC Name
Select the longest continuous carbon chain that has OR as a substituent and number from the carbon closest to the OR group (OH has priority over OR).
Name the ether substituent (OR) with a number identifying carbon it is attached to followed by ...oxy ether
Common Name:
Identify the two R groups attached to the oxygen
Arrange R groups in alphabetical order and end the name with "ether"
If two of the same R groups are attached, then use prefix di
Preparation of Ethers
Williamson Ether Synthesis
Williamson ether synthesis is a reaction that converts alcohols into ethers (C-O-C). In the first step, alcohol is deprotonated using a strong base such as NaH. The alkoxide ion that is created is a strong nucleophile and can attack primary alkyl halides and tosylates in an SN2 reaction. The O- attacks the carbon the leaving group is attached to and the leaving group leaves.
Note: If the alkyl halide or tosylate is not primary, E2 will happen instead of SN2.
Acid Catalyzed Dehydration of Alcohols
2 alcohols can come together to form an ether with H2SO4 and heat.
Acid Catalyzed Addition of Alcohols To Alkenes
Reagent: ROH with an acid catalyst
Product: Turn double bond into single bond and add OR to the most substituted carbon from the double bond. Rearrangements are possible
Reactions of Ethers
Acid Catalyzed Cleavage By Concentration HX
Reagent: HX (X=Br or I)
Product: Break the bonds between oxygen and the two carbons it is attached to. Attach X to each carbon broken off.
In the mechanism for this reaction, first oxygen gets protonated to become a better leaving group. X- can then attack carbon that has OHR+ group and the bond between oxygen and carbon breaks giving us the first product. This process repeats again with OH getting protonated to become a better leaving group and then X attacking the carbon that the OH2+ is attached to, and OH2+ leaving.
Silyl Ethers as Protecting Groups
Alcohol groups are transformed into silyl ethers in synthesis problems where alcohols need to be protected.
Synthesis of Epoxides
Internal Nucleophilic Substitution in Halohydrins
Reagent: alkene with 1.Cl2 (or Br2), H2O 2.NaOH, H2O
Product: Turn double bond into single and attach two carbons from the double bond to an oxygen, making a triangle (epoxide)
Oxidation of Alkenes with Peroxycarboxylic Acids
Reagent: RCO3H (peroxyacid)
Product: Turn double bond into single and attach two carbons from the double bond to an oxygen, making a triangle (epoxide)
Sharpless Asymmetric Epoxidation
Reactions of Epoxides
Epoxides with Acids
Examples of Acids: HCl, HCN, H3O+, ROH2+....
Epoxides with Bases
Mayya's Trick story : Imagine epoxide has a birthday and base comes with no present since it has no hydrogens to give. Epoxide is so upset, it makes base attack the least substituted carbon.
Reaction of Epoxide with Lithium Aluminum Hydride
Reagent: 1. LiAlH4 2.H2O
Product: Get rid of the epoxide and add OH to the MOST substituted carbon from the epoxide carbons.
Sulfides
Comments