Dimethyl ethers, substituted

SuIfona.tlon, Sulfonation is a common reaction with dialkyl sulfates, either by slow decomposition on heating with the release of SO or by attack at the sulfur end of the O—S bond (63). Reaction products are usually the dimethyl ether, methanol, sulfonic acid, and methyl sulfonates, corresponding to both routes. Reactive aromatics are commonly those with higher reactivity to electrophilic substitution at temperatures > 100° C. Tn phenylamine, diphenylmethylamine, anisole, and diphenyl ether exhibit ring sulfonation at 150—160°C, 140°C, 155—160°C, and 180—190°C, respectively, but diphenyl ketone and benzyl methyl ether do not react up to 190°C. Diphenyl amine methylates and then sulfonates. Catalysis of sulfonation of anthraquinone by dimethyl sulfate occurs with thaHium(III) oxide or mercury(II) oxide at 170°C. Alkyl interchange also gives sulfation. 

Entries 11 and 13 in Table 3.4 present data relating the efiect of methyl substitution on methanol and methylamine. The data show an increased response to methyl substitution. While the propane barrier is 3.4 kcal/mol (compared to 2.88 in ethane), the dimethylamine barrier is 3.6kcal/mol (compared to 1.98 in methylamine) and in dimethyl ether it is 2.7 kcal/mol (compared to 1.07 in methanol). Thus, while methyl-hydrogen eclipsing raised the propane barrier by 0.5 kcal/mol, the increase for both dimethylamine and dimethyl ether is 1.6 kcal/mol. This increase in the barrier is attributed to greater van der Waals repulsions resulting from the shorter C—N and C—O bonds, relative to the C—C bond. 

Bordwell compares the alkoxy effect with the C—H BDE for dimethyl ether as reported by McMillen and Golden (1982). The latter is lower by 12 kcal mol" than that of methane, and from the comparable magnitude of the effect in the a-alkoxy acetophenonyl radical it is concluded that an additive substituent effect exists. Similar arguments hold for the dimethylamino-substituted radical. It is stated that additivity is more than expected for bis-... 

Product 117 is a convenient starting compound for the subsequent modification of photochromes. Publication (09TL1614) gives an efficient synthetic route to both symmetrical 118 and unsymmetrical 119 phenyl-substituted dihetarylethenes bearing amino, hydroxy, or carboxy groups based on a Suzuki reaction of dichloride 117 with commercially available substituted boronic acids (or their pinacol esters) in a dimethyl ether (DME)-H20 mixture (4 1). For the symmetrical products, the yields are 85-95% for the unsymmetrical products, they are 60%. 

The synthesis of acetic acid (AcOH) from methanol (MeOH) and carbon monoxide has been performed industrially in the liquid phase using a rhodium complex catalyst and an iodide promoter ( 4). The selectivity to acetic acid is more than 99% under mild conditions (175 C, 28 atm). The homogeneous rhodium catalyst is also effective for the synthesis of acetic anhydride (Ac O) by the carbonylation of dimethyl ether (DME) or methyl acetate (AcOMe) (5-13). However, rhodium is one of the most expensive metals, and its proved reserves are quite limited. It is highly desirable, therefore, to develop a new catalyst as a substitute for rhodium. 

Rhodium(II) acetate catalyzes C—H insertion, olefin addition, heteroatom-H insertion, and ylide formation of a-diazocarbonyls via a rhodium carbenoid species (144—147). Intramolecular cyclopentane formation via C—H insertion occurs with retention of stereochemistry (143). Chiral rhodium (TT) carboxamides catalyze enantioselective cyclopropanation and intramolecular C—N insertions of CC-diazoketones (148). Other reactions catalyzed by rhodium complexes include double-bond migration (140), hydrogenation of aromatic aldehydes and ketones to hydrocarbons (150), homologation of esters (151), carbonylation of formaldehyde (152) and amines (140), reductive carbonylation of dimethyl ether or methyl acetate to 1,1-diacetoxy ethane (153), decarbonylation of aldehydes (140), water gas shift reaction (69,154), C—C skeletal rearrangements (132,140), oxidation of olefins to ketones (155) and aldehydes (156), and oxidation of substituted anthracenes to anthraquinones (157). Rhodium-catalyzed hydrosilation of olefins, alkynes, carbonyls, alcohols, and imines is facile and may also be accomplished enantioselectively (140). Rhodium complexes are moderately active alkene and alkyne polymerization catalysts (140). In some cases polymer-supported versions of homogeneous rhodium catalysts have improved activity, compared to their homogenous counterparts. This is the case for the conversion of alkenes direcdy to alcohols under oxo conditions by rhodium—amine polymer catalysts... 

The properties of the ethers may be summarized hy (ltvvilh the exception of dimethyl ether which is a gas. die ethers arc volatile, mobile, inflammable liquids that are lighter than H O 121 they are relatively inert chemically, not being acted on by alkali metals or alkalis and not reacting with dilute acids (31 they form substitution producls when reacted wiih chlorine and bromine and (4t they decompose when healed with strong acids, yielding esters. 

Anodic substitution can also occur easily in the a-position to heteroatoms like nitrogen or oxygen. Thus, the indirect electrochemical oxidation of ethylene glycol dimethyl ether in methanol using tris(2,4-dibromophenyl)amine as redox catalyst leads to the formation of 2-methoxyacetaldehyde dimethylacetal [25] ... 

CO2-PEG system is also effective for the scandium-catalyzed aldol reactions, and poly(ethylene glycol) dimethyl ether (PEG(OMe)2, MW = 500) is more effective than PEG (Scheme 3.12) [57]. Emulsions in C02-PEG(0Me)2 medium are observed when the concentration of the additive is 1 g/L. Not only benzal-dehyde but also substituted aromatics, aliphatic, and a, /]-unsaturated aldehydes react smoothly, and various silicon enolates derived from a ketones, esters, and thioesters also react well to afford the corresponding aldol adducts in high yields. 

Other Co(II)-complexes that were applied in the photosensitized reduction of C02 to CO (and concomitant H2-evolution) include Co(II)-ethylene glycol dimethyl ether complexes [178], and different tetraaza-macrocyclic Co(II)-complexes such as 27,28. A closely related system, where Ni(II)-tetraaza macrocycle (29) substitutes the cobalt homogeneous complexes in the photosystem including Ru(bpy) + as photosensitizer and ascorbic acid as electron donor, has been reported by Tinnemans [181] and Calvin [182],... 

In principle, fused tropones behave similarly to their monocyclic analogs (73CRV293, p. 329). IR spectra could be used, for instance, to identify isomeric anhydrosepedonin dimethyl ethers 418a-c (Scheme 112 69MI3) and pyrazolotropones substituted at N-l (98b) or N-2 (91JHC717). Table XVII contains selected IR data of relevant compounds as assigned by the respective authors. 

Block et al.194 examined the effects of trimethylsilyl substitution on the first vertical ionization potentials by photoelectron and Penning ionization electron spectroscopy studies of a range of cyclic and noncyclic sulfides and ethers. It was shown that substitution of oxirane 218 with a trimethylsilyl substituent as in 219 lowered the ionization potential by 0.90 eV (20.8 kcal/mol), while similar substitution of dimethyl ether 220 in 221 lowered the ionization potential by 0.64 eV (14.8 kcal/mol). By comparison, the effects of silyl substitution on sulfur lone-pair ionization potentials was found to be smaller thus the ionization potential of dimethyl sulfide 222 is lowered by 0.37 eV upon trimethylsilyl substitution in 223, and the trimethylsilyl-substituted thiirane 225 is lowered by 0.59 eV relative to thiirane 224. The raising of the energy of the sulfur lone-pair electrons in the thiirane 225 is also apparent from its UV spectrum, where there is a bathochromic shift in the absorption maximum compared to the parent 224. 

Wheland (1960) made the point in several ways that these principles could lead to absurd errors. When ethyl chloride is treated with hydroxide ion, we obtain ethanol, not dimethyl ether but when iso-bornyl chloride is treated in the same way we obtain camphene after a deep-seated skeletal rearrangement. Although nucleophilic substitution at an ethylenic center goes with retention (Miller and Yonan, 1957), the Walden inversion undercuts any general principle of minimum configurational change. Likewise, an early PLM representation of the... 

Similar complex dependences for HE are observed in aqueous mixtures of 1,4-dioxan, 1,3-dioxan, trimethylene oxide, ethylene glycol dimethyl ether (Morcom and Smith, 1970 Nakayama and Shinoda, 1971), or 1,3-dioxolan (Blandamer et al., 1969b). However, not all TA mixtures have this S-feature, e.g. alkyl substituted amides + water (Assarson and Eirich, 1968), and t-butylamine + water at 313 K (Duttachoudhury and Mathur, 1974). The HE dependences for TA systems are very complex. Even for ethanol-water mixtures at 298 K... 

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