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Williamson ether synthesis
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==Scope== The Williamson reaction is of broad scope, is widely used in both laboratory and industrial synthesis, and remains the simplest and most popular method of preparing ethers. Both symmetrical and asymmetrical ethers are easily prepared. The intramolecular reaction of [[halohydrin]]s in particular, gives [[epoxide]]s. In the case of asymmetrical ethers there are two possibilities for the choice of reactants, and one is usually preferable either on the basis of availability or reactivity. The Williamson reaction is also frequently used to prepare an ether indirectly from two alcohols. One of the alcohols is first converted to a leaving group (usually [[tosylate]]), then the two are reacted together. The alkoxide (or [[aryloxide]]) may be primary and secondary. Tertiary alkoxides tend to give elimination reaction because of steric hindrance. The alkylating agent, on the other hand is most preferably primary. Secondary alkylating agents also react, but tertiary ones are usually too prone to side reactions to be of practical use. The leaving group is most often a halide or a sulfonate ester synthesized for the purpose of the reaction. Since the conditions of the reaction are rather forcing, [[protecting group]]s are often used to pacify other parts of the reacting molecules (e.g. other [[alcohols]], [[amine]]s, etc.) The Williamson ether synthesis is a common organic reaction in industrial synthesis and in undergraduate teaching laboratories. Yields for these ether syntheses are traditionally low when reaction times are shortened, which can be the case with undergraduate laboratory class periods. Without allowing the reactions to reflux for the correct amount of time (anywhere from 1–8 hours from 50 to 100 °C) the reaction may not proceed to completion generating a poor overall product yield. To help mitigate this issue microwave-enhanced technology is now being utilized to speed up the reaction times for reactions such as the Williamson ether synthesis. This technology has transformed reaction times that required reflux of at least 1.5 hours to a quick 10-minute microwave run at 130 °C and this has increased the yield of ether synthesized from a range of 6-29% to 20-55% (data was compiled from several different lab sections incorporating the technology in their syntheses).<ref>{{Cite journal|last=Baar|first=Marsha R.|last2=Falcone|first2=Danielle|last3=Gordon|first3=Christopher|date=2010|title=Microwave-Enhanced Organic Syntheses for the Undergraduate Laboratory: Diels−Alder Cycloaddition, Wittig Reaction, and Williamson Ether Synthesis|journal=Journal of Chemical Education|volume=87|issue=1|pages=84–86|doi=10.1021/ed800001x|bibcode=2010JChEd..87...84B}}</ref> There have also been significant strides in the synthesis of ethers when using temperatures of 300 °C and up and using weaker alkylating agents to facilitate more efficient synthesis. This methodology helps streamline the synthesis process and makes synthesis on an industrial scale more feasible. The much higher temperature makes the weak alkylating agent more reactive and less likely to produce salts as a byproduct. This method has proved to be highly selective and especially helpful in production of aromatic ethers such as anisole which has increasing industrial applications.<ref>{{Cite journal|last=Fuhrmann|first=Edgar|last2=Talbiersky|first2=Jörg|date=2005|title=Synthesis of Alkyl Aryl Ethers by Catalytic Williamson Ether Synthesis with Weak Alkylation Agents|journal=Organic Process Research & Development|volume=9|issue=2|pages=206–211|doi=10.1021/op050001h}}</ref>
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