977. Acid-catalysed ether fission. Part I. A new mechanism, in sulphuric acid

Collisions of Organic Molecules with Concentrated Sulfuric Acid: Scattering, Trapping, and Desorption

“…Figure c shows that accommodated dimethyl ether molecules also dissolve for long times in the acid. Cryoscopy and NMR studies indicate that dimethyl ether mostly undergoes simple protonation but may be cleaved to generate methyl hydrogen sulfate at high temperatures or long reaction times. , The 1−2% change in thermal desorption from t exp = 0.045 to 0.303 s corresponds to a many second average residence time, reflecting the basic character of the ether. Acetaldehyde also undergoes reversible protonation and desorption, but on a much faster time scale of ≈0.1 s because of its lower basicity. ,, Although we did not record spectra of acetaldehyde as a function of t exp , the trends in Figure suggest that its TD component is larger than for dimethyl ether because of this reversible protonation and desorption.…”

“…3 Figure 5c shows that accommodated dimethyl ether molecules also dissolve for long times in the acid. Cryoscopy 46 and NMR 47 studies indicate that dimethyl ether mostly undergoes simple protonation but may be cleaved to generate methyl hydrogen sulfate at high temperatures or long reaction times. 8,46 The 1-2% change in thermal desorption from t exp ) 0.045 to 0.303 s corresponds to a many second average residence time, reflecting the basic character of the ether.…”

Heterocations in Superacid Systems

“…78 In a solution of HSO 3 F-SbF 5 , protonated n-butyl methyl ether 23 does not show any significant change, neither cleavage nor rapid exchange, as indicated by the NMR spectrum up to þ40 C. Above þ40 C, however, it cleaves and a sharp singlet appears at d 1 H 4.0. To rationalize these observations, the mechanism outlined in Scheme 4.2 has been proposed.…”

Synthesis of some new 4-aryloxmethylcoumarins and examination of their antibacterial and antifungal activities

“…The 1 H-NMR of these compounds showed the absence of one methyl group and lesser number of aromatic protons, which indicated cleavage of the ether linkage. 14 The 1 H-NMR of the ether 7a shows two CH 3 groups at 2⋅33 and 2⋅45 δ ppm whereas its corresponding nitrated product shows the absence of one CH 3 group. The two singlets observed at 6⋅65 (6⋅44) and 8⋅52 (8⋅44) correspond to C 3 -H and C 7 -H respectively, which agrees with the predicted values given in parenthesis.…”