Ethere protonated

The benzene rings A and B derived from the H NMR spectrum can be completed using Table 41.1. The way in which the enol ether is bonded is indicated by the correlation signal of the proton at Sh = 8.48. The structural fragment C results. Incorporating the C atom resonating at 5c = 123.3, which has not been accommodated in ring A or B and which is two bonds Jch) removed from the enol ether proton. 

Figure 18.4 The 1H NMR spectrum of dipropyl ether. Protons on carbon next to oxygen are shifted downfield to 3.4 S.

Enol ether protons are interesting in that their chemical shifts are unusually high field in comparison with other alkenes on account of lone pair donation into the double bond from oxygen (Structure 5.5). No special precautions are necessary when dealing with them as this is reflected in the values obtained using Table 5.6. 

Substitution of methanol by another alcohol such as propanol would not be expected to radically change selectivity because in both cases a proton donor solvent is present. However, a greater change in selectivity can be expected by using ethyl ether (proton acceptor) or methylene chloride (large dipole moment). 

Whereas the C2—C4 alcohols are not carboxylated under the usual Koch-Haaf conditions, carboxylation can be achieved in the HF-SbF5 superacid system under extremely mild conditions.400 Moreover, Olah and co-workers401 have shown that even methyl alcohol and dimethyl ether can be carboxylated with the superacidic HF-BF3 system to form methyl acetate and acetic acid. In the carboxylation of methyl alcohol the quantity of acetic acid increased at the expense of methyl acetate with increase in reaction time and temperature. The quantity of the byproduct dimethyl ether, in turn, decreased. Dimethyl ether gave the desired products in about 90% yield at 250°C (90% conversion, catalyst/substrate ratio =1 1, 6h). On the basis of experimental observations, first methyl alcohol is dehydrated to dimethyl ether. Protonated dimethyl ether then reacts with CO to yield methyl acetate [Eq. (5.154)]. The most probable pathway suggested to explain the formation of acetic acid involves the intermediate formation of acetic anhydride through acid-catalyzed ester cleavage without the intervention of CO followed by cleavage with HF [Eq. (5.155)]. 

In the case where the silyl ketal is made up of the 2-phenylethanol and (+)-ethyl lactate (3a), the more basic oxygen would be the one on the 2-phenylethanol moiety. However protonation and eventually dissociation of this alcohol leads back to the starting silyl ether. Protonation could also occur on the oxygen of the (+)-ethyl lactate moiety. Once the (+)-ethyl lactate is protonated it could dissociate resulting in newly formed silyl ether. This newly formed silyl ether can react with the dissociated (+)-ethyl lactate, or it can go on to react with another 2-phenethyl ethanol which is present in a higher concentration than the dissociated (+)-ethyl... 

Ternary Blend of Deuterated Polystyrene/Poly(vinyl methyl ether)/protonated... 

Poly (vinyl methyl ether)/Protonated Polystyrene The High Concentration Method... 

When three isomers of hydroxyacetophenone were treated separately with 4-fluoronitrobenzene [156] 369 (Scheme 122) and potassium carbonate (DMF, 120 °C) the para- and meta-isomers gave the respective diaryl ethers (0-arylation products). The ortho-isomer 370 behaves in a different way the C-arylation product 373 was formed exclusively (isolated in 73% yield). 0-Arylation of 370 occurred first to give diaryl ether (protonated 371) and this is followed by the rearrangement through the intermediate 372. At lower temperature (60 °C) 371 (protonated) could be isolated in 21% yield along with unchanged 370. 

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