exp8w08 - Experiment 8: Williamson Ether Synthesis of...

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Experiment 8: Williamson Ether Synthesis of Phenacetin. (IR, NMR, MS) Mohrig, Chapter 19-20 The process of displacement of a halide (RX where X = Cl, Br, I) by an alkoxide anion (RO-) to form an ether is called a Williamson ether synthesis. The principal starting material of this reaction is N-(4-hydroxyphenyl)- acetamide, a compound also known as acetaminophen. It is an analgesic (a medication that reduces or eliminates pain) and antipyretic (a medication that reduces fever) and is found in many over-the-counter drugs. For exam- ple, it is the active ingredient of many Tylenol® products. The principal product phena- cetin was once the active ingredient of several analgesic and antipyretic Excedrin® medi- cations. Interestingly, phenacetin is converted in the human body to acetaminophen, which is the active agent. The phenol of acetaminophen is a relatively poor nucleophile. However, the presence of the base (potassium carbonate) causes the generation of the conjugate base of aceta- minophen. This new species is called a phenoxide anion, and it serves as a more potent nucleophile than the starting alcohol. The phenoxide anion then displaces iodide via back- side attack in a one-step process involving a negatively charged pentavalent intermediate. The rate of the reaction depends on the concentration of both the phenoxide anion and the iodoethane; so the reaction is described as S N 2 (substitution nucleophilic bimolecular). H N OH O H N O O EtI K 2 CO 3 please regenerate this completed table in part 1 of your notebook reagents Phenol potassium carbonate MEK ethyl iodide ethylated phenol phenacetin formula equiv 1 1.16 1.5 eq 1 MW 151.16 mg/mmol 138.21 mg/mmol 155.97 mg/mmol 179.22 mg/mmol den 1950 mg/mL vol 1.0 mL 0.08 mL (4 drops) mass 100 mg 180 mg 156 mg 118.56 mg mmol. 0.66 mmol 1.30 mmol 1.0 mmol 0.66 mmol mp 20 Lecture Ideas Again, discuss but don’t quiz on the mechanisms. Many 109a students have still not covered S N 2 reactions at this point in the lecture series. At this point, your students will have
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This note was uploaded on 04/07/2008 for the course CHEM 6a taught by Professor Pettus during the Winter '07 term at UCSB.

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exp8w08 - Experiment 8: Williamson Ether Synthesis of...

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