Ethers mixed

Ethers are, in general, inert compounds and their identification presents difficulties. Further complications also arise with mixed ethers. 

Mixed ethers may be prepared by the interaction of an. alkyl halide and a sodium alkoxide (Williamson s synthesis), for example ... 

Higher alcohols (> C3) react comparatively slowly with sodium because of the slight solubility of the sodium alkoxide in the alcohol a large excess (say, 8 mols) is therefore employed. The mixed ether is distilled off, and the process (formation of alkoxide and its reaction with the alkyl halide) may be repeated several times. The excess of alcohol can be recovered. cj/cloAliphatic alcohols form sodio compounds with difficulty if small pieces... 

With mixed ethers of the type ROR the question of which carbon-oxygen bond... 

The derivatives are hydroxyethyl and hydroxypropyl cellulose. AH four derivatives find numerous appHcations and there are other reactants that can be added to ceUulose, including the mixed addition of reactants lea ding to adducts of commercial significance. In the commercial production of mixed ethers there are economic factors to consider that include the efficiency of adduct additions (ca 40%), waste product disposal, and the method of product recovery and drying on a commercial scale. The products produced by equation 2 require heat and produce NaCl, a corrosive by-product, with each mole of adduct added. These products are produced by a paste process and require corrosion-resistant production units. The oxirane additions (eq. 3) are exothermic, and with the explosive nature of the oxiranes, require a dispersion diluent in their synthesis (see Cellulose ethers). 

Difluoroethanol is prepared by the mercuric oxide cataly2ed hydrolysis of 2-bromo-l,l-difluoroethane with carboxyHc acid esters and alkaH metal hydroxides ia water (27). Its chemical reactions are similar to those of most alcohols. It can be oxidi2ed to difluoroacetic acid [381-73-7] (28) it forms alkoxides with alkaH and alkaline-earth metals (29) with alkoxides of other alcohols it forms mixed ethers such as 2,2-difluoroethyl methyl ether [461-57-4], bp 47°C, or 2,2-difluoroethyl ethyl ether [82907-09-3], bp 66°C (29). 2,2-Difluoroethyl difluoromethyl ether [32778-16-8], made from the alcohol and chlorodifluoromethane ia aqueous base, has been iavestigated as an inhalation anesthetic (30,31) as have several ethers made by addition of the alcohol to various fluoroalkenes (32,33). Methacrylate esters of the alcohol are useful as a sheathing material for polymers ia optical appHcations (34). The alcohol has also been reported to be useful as a working fluid ia heat pumps (35). The alcohol is available ia research quantities for ca 6/g (1992). 

Mixed Ether Derivatives of HEC. Several chemical modifications of HEC are commercially available. The secondary substituent is generally of low DS (or MS), and its function is to impart a desirable property lacking in HEC. 

Table 7. Typical Properties of Mixed Ether Derivatives of HEC ...

MethylceUulose and its mixed ethers are surface-active ceUulose ethers having surface tension values as low as 44 mN/m(= dyn/cm) and interfacial tension values as low as 17 mN/m(= dyn/cm) against paraffin oU. 

Chloroalkyl ethersf (chloromethyl, chloroethyl, and mixed ethers)... 

Mention may also be made of fixed diethers, some of which are unsaturated. These materials may be cured by a variety of mechanisms. An example is the allyl glycilyl mixed ether of bis-phenol A (Figure 26.15)... 

With mixed ethers of the type ROR, the question of which caibon-oxygen bond is broken first is not one that we need exanine at our level of study. 

The formation of ethers such as 1806 by EtsSiH 84b can also be catalyzed by trityl perchlorate to convert, e.g., benzaldehyde in 84% yield into dibenzyl ether 1817 [48]. The combination of methyl phenethyl ketone 1813 with O-silylated 3-phenyl-n-pro-panol 1818, in the presence of trityl perchlorate, leads to the mixed ether 1819 in 68% yield [48] (Scheme 12.15). Instead of trityl perchlorate, the combination of trityl chloride with MesSiH 84a or EtsSiH 84b and sodium tetrakis[3,5-bis-(trifluoro-methyl)phenyl]borane as catalyst reduces carbonyl groups to ethers or olefins [49]. Employing TMSOTf 20 as catalyst gives very high yields of ethers. Thus benzaldehyde reacts with O-silylated allyl alcohol or O-silylated cyclohexanol to give the... 

The unreacted ethanol and the diethylether product retained >98% of from the starting 0-ethanol, indicating that no isotope scrambling occurred. Data in Table 4 demonstrate that was retained in the mixed ether and ethanol attack of the acid-activated 2-pentanol via an axial S 2 rear-attack was the predominant synthesis pathway. Evidently, the shape selectivity induced by the 2 M-5 zeolite channel structure (Figure 2) plays an important role in achieving the remarkably higher configuration inversion... 

Using the mixed ether with Si—0—Ge bridges as reagent, the preferred formation of (CH3)3Si(P02Cl2) is found 82). 

HPC exhibited a notable increase in adsorption with increasing NaCl concentration. Entrapment in the interlayer of recovered sodium montmorillonite did not vary with salinity the extent of entrapment was greater with the 4 M.S. HE and HP celluloses than either of the 2.0 M.S. polymers. Mixed ethers of HEC (2 M.S.) containing an anionic (carboxymethyl) or cationic (3-0-2-hydroxypropyltrimethylaramonium chloride) group at 0.4 M.S. levels did not adsorb from fresh water. Adsorption of these polar mixed ethers increased with increasing electrolyte until electrostatic and solvation effects were negated in 0.54N NaCl solutions and the adsorbed amounts typical of a 2 M.S. HEC were observed. Interlayer entrapments comparable to the equivalent M.S. HEC were observed at lower (0.18N) electrolyte concentrations. 

Iodide is a good nucleophile. It attacks the least substituted carbon of the oxonlum ion formed in step 1 and displaces an alcohol molecule by S 2 mechanism. Thus, in the cleavage of mixed ethers with two different alkyl groups, the alcohol and alkyl Iodide formed, depend on the nature of alkyl groups. When primary or secondary alkyl groups are present. It Is the lower alkyl group that forms kyl Iodide (Sn2 reaction). 

In all of the above preparations the lithium exchange step was conducted in ether. The use of a mixed ether-THF solvent system would probably improve the yields (Section VI,H, 1). 

The same type of addition—as shown by X-ray analysis—occurs in the cationic polymerization of alkenyl ethers R—CH=CH—OR and of 8-chlorovinyl ethers (395). However, NMR analysis showed the presence of some configurational disorder (396). The stereochemistry of acrylate polymerization, determined by the use of deuterated monomers, was found to be strongly dependent on the reaction environment and, in particular, on the solvation of the growing-chain-catalyst system at both the a and jS carbon atoms (390, 397-399). Non-solvated contact ion pairs such as those existing in the presence of lithium catalysts in toluene at low temperature, are responsible for the formation of threo isotactic sequences from cis monomers and, therefore, involve a trans addition in contrast, solvent separated ion pairs (fluorenyllithium in THF) give rise to a predominantly syndiotactic polymer. Finally, in mixed ether-hydrocarbon solvents where there are probably peripherally solvated ion pairs, a predominantly isotactic polymer with nonconstant stereochemistry in the jS position is obtained. It seems evident fiom this complexity of situations that the micro-tacticity of anionic poly(methyl methacrylate) cannot be interpreted by a simple Bernoulli distribution, as has already been discussed in Sect. III-A. 

Ethylhydroxyethylcellulose (EHEC) is a nonionic mixed ether available in a wide variety of substitutions with corresponding variations in aqueous and organic liquid solubilities. It is compatible with many oils, resins, and plasticizers along with other polymers such as nitrocellulose. EHEC is synthesized through a two-step process beginning with the formation of the HEC-like product through reaction between the basic cellulose and ethylene oxide. The second step involves further reaction with ethyl chloride. 

It should be noted that the following positions are synonymous in D- or L-mannitol and d- or L-iditol 1 and 6, 2 and 5, and 3 and 4. Sorbitol, because of lower optical symmetry, would form even more derivatives. The number of possible acetals is much smaller and that of metallic complexes still smaller. The number of various theoretical permutations of mixed ether-esters, ether-acetals, etc., utilizing readily available reagents, runs into the hundreds of thousands. 

When the iodides are submitted to the action of sodic ethylate, a mixed ether (or a simple ether if s=2) is formed... 

The residues of different acids can unite to form mixed anhydrides analogous to the mixed ethers. Aceto>benzoic anhydride is a body of this class. 

Oxidation of the aldehyde group in mixed ether (60-2) by means of perchlorate affords the corresponding carboxylic acid. That product is then converted to its acid chloride (60-6) with thionyl chloride. Treatment of this last intermediate with the substituted pyridine (60-7) leads to the corresponding amide and thus pidamilast (60-8) [62]. 

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