Chemistry
Ether Reactions
Ether reactions involve the chemical transformations of ethers, which are organic compounds with an oxygen atom bonded to two alkyl or aryl groups. Common reactions include cleavage of ethers to form alcohols, as well as reactions with strong acids or oxidizing agents to produce various functional groups. Ethers can also undergo substitution reactions to form new compounds.
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3 Key excerpts on "Ether Reactions"
eBook - PDF- T. W. Graham Solomons, Craig B. Fryhle, Scott A. Snyder(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
Ethers are like alkanes in that they undergo halogenation reactions (Chapter 10), but these reactions are of little synthetic importance. They also undergo slow autoxidation to form explosive peroxides (see Section 11.3D). The oxygen of the ether linkage makes ethers weakly basic. Ethers can react with pro- ton donors to form oxonium salts: O + HBr + Br – H An oxonium salt + O 11.12A Cleavage of Ethers Heating dialkyl ethers with very strong acids (HI, HBr, and H 2 SO 4 ) causes them to undergo reactions in which the carbon–oxygen bond breaks. Diethyl ether, for example, reacts with hot concentrated hydrobromic acid to give two molecular equivalents of bromoethane: 2 HBr H 2 O Br 2 + + O Cleavage of an ether The mechanism for this reaction begins with formation of an oxonium cation. Then, an S N 2 reaction with a bromide ion acting as the nucleophile produces ethanol and bromo- ethane. Excess HBr reacts with the ethanol produced to form the second molar equivalent of bromoethane. Ether Cleavage by Strong Acids A MECHANISM FOR THE REACTION [ [ Step 1 H—Br + + – H + Ethanol Bromoethane Br O O Br H + O Step 2 O Br + + Br – H H H—Br H + O H H + O In step 2 the ethanol (just formed) reacts with HBr (present in excess) to form a second molar equivalent of bromoethane. PRACTICE PROBLEM 11.16 When an ether is treated with cold concentrated HI, cleavage occurs as follows: R − O − R + Hl ⟶ ROH + Rl When mixed ethers are used, the alcohol and alkyl iodide that form depend on the nature of the alkyl groups. Use mechanisms to explain the following observations: (a) OMe OH HI + MeI (b) OMe I HI + MeOH 514 CHAPTER 11 ALCOHOLS AND ETHERS: Synthesis and Reactions 11.12B Cleavage of Alkyl Aryl Ethers When alkyl aryl ethers react with strong acids such as HI and HBr, the reaction produces an alkyl halide and a phenol. The phenol does not react further to produce an aryl halide because the phenol carbon–oxygen bond is very strong and because phenyl cations do not form read- ily.
eBook - PDF- John A. Olmsted, Gregory M. Williams, Robert C. Burk(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
However, the number of distinctly different types of organic reactions is surprisingly small. In this chapter, we will study three important types of reactions; namely, substitution, elimination, and addition reactions. In a substitution reaction, as the name suggests, one functional group is substituted for another. An example is shown below, where a nitro group substitutes for a hydrogen atom on a benzene ring: HNO 3 NO 2 H 2 O H 2 SO 4 + + In an elimination reaction, atoms or groups of atoms that are bound to adjacent carbon atoms are eliminated, generally as a small molecule. This results in the formation of a double bond between the carbon atoms. For example, ethanol can undergo a reaction to form ethene with the elimination of water: H OH H H H H H H H H H 2 O + And finally, in an addition reaction, a molecule is added across a double (or triple) bond, resulting in a single (or double) bond. An example is the chlorination of ethene to make 1,2-dichloroethane: Cl Cl H H H H H H H H Cl 2 + Chemical Space—How Many Possible Drug Compounds Are There? New drug molecules have been synthesized and tested by the thou- sands over the years. However, recent estimates suggest that only a tiny fraction of the potential medicines that could be made have been synthesized so far. Some estimates suggest that there are as many as 10 60 potentially interesting small molecules that we have yet to synthesize or test. This staggering number is not too different from estimates of the number of atoms in the universe—how can we possibly decide which compounds to spend time and effort on? Combinatorial chemistry involves the automated synthesis of huge libraries of different but related compounds. Pharmaceu- tical companies in particular have used robotic approaches to syn- thesize hundreds of thousands of new and unique compounds per year.
eBook - PDF- T. W. Graham Solomons, Craig B. Fryhle, Scott A. Snyder(Authors)
- 2017(Publication Date)
- Wiley(Publisher)
Image Source Michael Patrick O’Neill/Photo Researchers, Inc. 526 CHAPTER 11 ALCOHOLS AND ETHERS: Synthesis and Reactions SUMMARY AND REVIEW TOOLS In addition to Section 11.17, which summarizes many of the reactions of alkenes, alcohols, and ethers, the study aids for this chapter also include key terms and concepts and a Synthetic Connections chart. PROBLEMS NOMENCLATURE 11.25 Give an IUPAC substitutive name for each of the following alcohols: (a) OH (c) HO OH (e) OH (b) OH (d) OH (f) OH The body’s system to eliminate these toxic chemicals begins by oxidizing their carbon frameworks using enzymes known as cytochrome P450s; these enzymes are found in the liver and intestines. For both aflatoxin B 1 and benzo[a]pyrene, at least one of their double bonds can be converted into an epoxide, as shown below. The next step is for a highly polar nucleophile, such as glutathione, to add to that reactive ring system and make the resulting molecule water soluble so it can be excreted quickly. However, these reactions are risky because other nucleophiles can attack as well. For example, nucleotide bases within DNA can also react with these epoxides. If that happens, as shown for the epoxidized form of benzo[a]pyrene, cancer can result. Thus, the epoxide in these instances is a two-edged sword—it serves as a way to remove a potentially toxic molecule while also creating a species that is sometimes even more dangerous and reactive than the original material. As a challenge question, why do you think the two nucleophile additions shown below occur only at the indicated positions? O O O OCH 3 O O Aflatoxin B 1 [can be excreted] cytochrome P450s H H O O O OCH 3 O O H H O O O O OCH 3 O O H H Gt OH O –O 2 C H N NH CO 2 NH 3 O HS Glutathione (Gt) – + Benzo[a]pyrene [carcinogenic] cytochrome P450s DNA OH HO O DNA OH HO HO DNA To learn more about these topics, see: 1.
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