Alternate Ether Preparations

The Williamson Ether Synthesis is not the only ether preparation available, and it is not suitable for sterically crowded ethers. Ethers can also be synthesized by the addition of an alcohol to an alkene. Just as hydration of an alkene gives an alcohol product (water as a nucleophile installs an OH group), addition reactions in the presence of an alcohol gives an ether product (alcohol as a nucleophile installs an OR group). Two examples are shown below the alkene can react initially with either a strong acid or a mercury cation (alkoxymercuration-demercuration). 

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Cleavage conditions for alkyl benzyl ethers prepared from acid-labile benzyl alcohols are similar to those for the corresponding benzyl esters (Table 3.30). Aryl benzyl ethers, however, are generally cleaved more easily by acidolysis than esters or alkyl ethers. Phenols etherified with hydroxymethyl polystyrene, for instance, can even be released by treatment with TFA (Entry 1, Table 3.31). It has also been shown that Wang resin derived phenyl ethers are less stable than Wang resin derived esters towards refluxing acetic acid [29]. Alternatively, boron tribromide may be used to cleave aryl ethers from hydroxymethyl polystyrene [573],... 

Polymers containing chromophores such as acridine and azobenzene have also been prepared by palladium-catalyzed amination according to two approaches [222-224]. The first approach involved the polymerization of monomers containing the chromophore. For example, 4-aminoazobenzene was condensed with 1,3-dibromobenzene (Eq. (39)) or 4,4 -dibromobiphenyl ether to form polymeric materials with Mw values of 9.0 x 103 and 19 x 103, respectively. Alternatively, polymers prepared by polymerization of 4-bromostyrene or copolymerization of styrene and 4-bromostyrene were coupled with N-phenyl-4-amino azobenzene. Substitution of the aryl bromides by the amino azobenzene unit was essentially quantitative when using P(tBu)3 as the ligand. 

The synthetic utility of 4a-c and closely related derivatives has been explored. Compound 4c reacts with methyl iodide in diethyl ether to afford the dimeric Ln Grignard reagent [Yb[C(SiMe3)3 (p-l)(OEt2)]2 5 by o-bond metathesis [9c]. Compound 5 is remarkably stable to Schlenk equilibria in diethyl ether solutions and may alternatively be prepared by the treatment of 4c with 1,2-diiodoethane or from the... 

Some recent highlights include adaptation of Katritzky s benzo-triazole syntheses to ether preparation , generation of acyl radicals by carbonylation , and oxidative ring closures with Fe(C104)3 (as an alternative to the harsher Mn(III) route) . Bis(phosphonium) anhydrides are finding diverse applications, and a number of new vanadium reagents have materialized, e.g. a V(II) complex dimer for cross-coupling of aldehydes as an alternative to the McMurry route . ... 

Polycarbonates have attracted attention in recent years because of their potential use in biomedical applications based on their biodegradability, biocompatibility, low toxicity and good mechanical properties [67]. These polymers can be prepared by the ROP of cyclic carbonate monomers by anionic, cationic, and coordination catalysts. However, lipase-catalyzed polymerization seems to be a feasible alternative to prepare polycarbonates as chemical methods often suffer from partial elimination of carbon dioxide (resulting in ether linkages), require extremely pure monomers and anhydrous conditions. 

The preparation of diethyl ether is described here for the sake of completeness. It is an unsuitable exercise for beginners. Di-n-butyl ether (Section 111,57) offers an excellent alternative. 

Both reactants m the Williamson ether synthesis usually originate m alcohol pre cursors Sodium and potassium alkoxides are prepared by reaction of an alcohol with the appropriate metal and alkyl halides are most commonly made from alcohols by reaction with a hydrogen halide (Section 4 7) thionyl chloride (Section 4 13) or phosphorus tri bromide (Section 4 13) Alternatively alkyl p toluenesulfonates may be used m place of alkyl halides alkyl p toluenesulfonates are also prepared from alcohols as their imme diate precursors (Section 8 14)... 

Quaternary ammonium alkyl ethers are prepared similarly an alkaline starch is reacted with a quaternary ammonium salt containing a 3-chloto-2-hydtoxyptopyl or 2,3-epoxyptopyl radical. Alternatively, such derivatives can be prepared by simple quaternization of tertiary aminoalkyl ethers by reaction with methyl iodide. Sulfonium (107) and phosphonium (108) starch salts have also been prepared and investigated. Further work has explained the synthesis of diethyl aminoethyl starch (109) as well as the production of cationic starches from the reaction of alkaline starch with... 

Ma.nufa.cture. The preparation of sulfuryl chloride is carried out by feeding dry sulfur dioxide and chlorine into a water-cooled glass-lined steel vessel containing a catalyst, eg, activated charcoal. Alternatively, chlorine is passed into Hquefted sulfur dioxide at ca 0°C in the presence of a dissolved catalyst, eg, camphor, a terpene hydrocarbon, an ether, or an ester. The sulfuryl chloride is purified by distillation the commercial product is typically 99 wt % pure, as measured by ASTM distillation method D850. 

Alternatively, thermal cracking of acetals or metal-catalyzed transvinylation can be employed. Vinyl acetate or MVE can be employed for transvinylation and several references illustrate the preparation especially of higher vinyl ethers by such laboratory techniques. Special catalysts and conditions are required for the synthesis of the phenol vinyl ethers to avoid resinous condensation products (6,7). Direct reaction of ethylene with alcohols has also been investigated (8). 

Virtually all of the organo derivatives of CA are produced by reactions characteristic of a cycHc imide, wherein isocyanurate nitrogen (frequendy as the anion) nucleophilically attacks a positively polarized carbon of the second reactant. Cyanuric acid and ethylene oxide react neady quantitatively at 100°C to form tris(2-hydroxyethyl)isocyanurate [839-90-7] (THEIC) (48—52). Substitution of propylene oxide yields the hydroxypropyl analogue (48,49). At elevated temperatures (- 200° C). CA and alkylene oxides react in inert solvent to give A/-hydroxyalkyloxazohdones in approximately 70% yield (53). Alternatively, THEIC can be prepared by reaction of CA and 2-chloroethanol in aqueous caustic (52). THEIC can react further via its hydroxyl fiinctionahty to form esters, ethers, urethanes, phosphites, etc (54). Reaction of CA with epichlorohydrin in alkaline dioxane solution gives... 

A simple test for ether peroxides is to add lOmL of the ether to a stoppered cylinder containing ImL of freshly prepared 10% solution of potassium iodide containing a drop of starch indicator. No colour should develop during one minute if free from peroxides. Alternatively, a 1% solution of ferrous ammonium sulfate, O.IM in sulfuric acid and O.OIM in potassium thiocyanate should not increase appreciably in red colour when shaken with two volumes of the ether. 

Iron pentacarbonyl and l-methoxy-l,4-cyclohexadiene react as shown by Birch and oo-workera, but in dibutyl ether this solvent has been found superior. The tricarbonyl(methoxy-l,3-cyclohexadiene)iron isomers undergo hydride abstraction with triphenylmethyl tetrafluoro-borate to form the dienyl salt mixture of which the 1-methoxy isomer is hydrolyzed by water to the cyclohexadienone complex. The 2-methoxy isomer can be recovered by precipitation as the hexafluoro-phosphate salt. By this method the 3-methyl-substituted dienone complex has also been prepared from l-methoxy-3-methylbenzene. The use of the conjugated 1-methoxy-1,3-cyclohexadiene in Part B led to no increase in yield or rate and resulted chiefly in another product of higher molecular weight. An alternative procedure for the dienone is to react tricarbonyl(l,4-dimethoxycyclohexadiene)iron with sulfuric acid. ... 

A detailed procedure for the preparation of cholestanyl methyl ether from cholestanol has been published 11) and a survey of the usefulness of the reagent has also appeared 12). There appears to be no particular advantage to this procedure over the more convenient alternatives given above. 

A solution of sodium methoxide is prepared by adding 1.3 g (0.056 g-atom) of sodium in small pieces to 16 ml of carefully dried methanol in a small round-bottom flask. (Alternatively, 3.1 g of dry commercial sodium methoxide can be used.) To this solution is added 10 g of the previously isolated mixture of reaction products, and the flask is heated at reflux on a steam bath for 4 hours. Methanol and methyl carbonate are then distilled insofar as possible at steam-bath temperature from the clear yellow solution. The cooled cloudy solution is then washed with ether to remove neutral materials, and the desired product is precipitated from the alkaline solution by treatment with carbon dioxide gas. The material so obtained is collected by suction filtration and washed well with water. The slightly pink crystalline powder weighs 38-40 g (56-59 %). The material may be recrystallized from benzene or methanol, mp 163-164°. 

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