Organic synthesis Williamson ether

In early work, vinyl chloride had been heated with stoichiometric amounts of alkaU alkoxides in excess alcohol as solvent, giving vinyl ethers as products (210). Supposedly this involved a Williamson ether synthesis, where alkaU alkoxide and organic haUde gave an ether and alkaU haUde. However, it was observed that small amounts of acetylene were formed by dehydrohalogenation of vinyl chloride, and that this acetylene was consumed as the reaction proceeded. Hence acetylene was substituted for vinyl chloride and only catalytic amounts of alkaU were used. Vinylation proceeded readily with high yields (211). 

In addition to its uses in photography and medicine, iodine and its compounds have been much exploited in volumetric analysis (iodometry and iodimetry, p. 864). Organoiodine compounds have also played a notable part in the development of synthetic organic chemistry, being the first compounds used in A. W. von Hofmann s alkylation of amines (1850), A. W. Williamson s synthesis of ethers (1851), A. Wurtz s coupling reactions (1855) and V. Grignard s reagents (1900). 

Alternatively, the Sn2 nucleophilic substitution reaction between alcohols (phenols) and organic halides under basic conditions is the classical Williamson ether synthesis. Recently, it was found that water-soluble calix[n]arenes (n = 4, 6, 8) containing trimethylammonium groups on the upper rim (e.g., calix[4]arene 5.2) were inverse phase-transfer catalysts for alkylation of alcohols and phenols with alkyl halides in aqueous NaOH solution to give the corresponding alkylated products in good-to-high yields.56... 

A few examples will show the importance of these reactions in synthetic organic chemistry. If X is an alkoxide ion, equation (1) describes the Williamson ether synthesis (2). If X is a cyanide ion, (1) describes a standard nitrile preparation (3). If X is an aromatic nucleus, and the departure of the leaving group is facilitated by A1C13, then (1) describes the Friedel-Crafts alkylation (4). With X as the cyanate ion, (1) describes the preparation of isocyanates (5) and if it is ammonia, (1) describes a common method of preparation of amines (6). In addition, nucleophilic transmethylation is a very... 

Show how you would use the Williamson ether synthesis to prepare the following ethers. You may use any alcohols or phenols as your organic starting materials. 

Ethers are compounds that have two organic groups bonded to the same oxygen atom, ROR. The organic groups can be alkyl, vinylic, or aryl, and the oxygen atom can be in a ring or in an open chain. Ethers are prepared by either the Williamson ether synthesis, which involves Sf t2 reaction of an alkoxide ion with a primary alkyl halide, or the alkoxymercuration reaction, which involves Markovnikov addition of an alcohol to an alkene. 

Even carbowax (a chemically and thermally stable poly(ethylene glycol), when adsorbed on an inorganic salt with no other solid support, may act as a very efficient gas-solid phase-transfer catalyst. This system has been employed, for example, in the Williamson synthesis of ethers and thioethers, starting from alkyl halides and phenols or thiols in the presence of potassium carbonate as a base Gas-solid PTC shows the advantage that pure products are obtained directly, due to the absence of aqueous and organic solvents. 

In this book, we will be overwhelmingly concerned with polar or ionic mechanisms. These involve the movement of eleetron pairs, unlike radical reactions which involve unpaired electrons. The components of a polar mechanism can generally be classified as nucleophiles or electrophiles. A nucleophile ( nucleus-lover ) is typically an anion or a neutral molecule that uses an electron pair to attack another atom, ion, or molecule. The species being attacked is called an electrophile ( electron-lover ). The terms nucleophile and electrophile often refer to the classic 8 2 reaction of organic chemistry. In the example below (which happens to be a Williamson ether synthesis), the methoxide anion is the nucleophile, methyl iodide is the electrophile, and iodide is the leaving group. 

Almost all LC-polyethers mentioned in this section were prepared via the Williamson ether synthesis from a mesogenic diphenol and (di)bromoalkanes. For instance a linear LC-polyether was obtained from the cesium salt of a diazine-diphenol and 1,10-dibromodecane in NMP (210) [323]. In two cases, (211) [324] and (209) [325] interfacial polycondensation were performed using sodium hydroxide in combination with a phase-transfer catalyst and an organic solvent. Almost all LC-polyethers prepared in this... 

In Section 9.2, you saw that nucleophilic substitution reactions of alkyl halides can lead to a wide variety of organic compounds. For example, ethers are synthesized by the reaction of an alkyl halide with an alkoxide ion. This reaction, called the Williamson ether synthesis (after Alexander Williamson, who discovered it in 1850) is still considered one of the best ways to synthesize an ether. 

A small amount of another organic product is formed in a Williamson ether synthesis. What is this product when the alkyl halide used in the synthesis of butyl propyl ether is... 

In the two phase Williamson ether synthesis, the base used is concentrated aqueous sodium hydroxide. Ordinarily, 50% aqueous sodium hydroxide is used, but even more concentrated solutions seem to be more effective. The alcohol in solution is deprotonated by hydroxide either in the aqueous phase or at the interface and then solubilized in the organic phase by ion pairing with the quaternary ammonium ion. 

Anhydrous sodium or potassium carbonates have been shown to act as efficient strong bases in solid-organic liquid two-phase systems in the presence of crown ethers this by-passes the requirement for concentrated aqueous hydroxide solutions in the equivalent liquid-liquid techniques. Among the reactions possible with this new method are the alkylation of active methylene compounds, the Williamson ether synthesis, and the Darzens reaction. 

WILLIAMSON SYNTHESIS. An organic method for preparing ethers by the interaction of an alkylhalide with a sodium alcoholate (or phenolate). 

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