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Participation and rearrangement in the gas‐phase elimination kinetics of 3‐( o ‐methoxyphenyl)propyl‐1‐methanesulphonate and 4‐( p ‐methoxyphenyl)butyl‐1‐methanesulphonate
Author(s) -
Martin Ignacio,
Chuchani Gabriel,
Dominguez Rosa,
Rotinov Alexandra
Publication year - 1992
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.610051103
Subject(s) - chemistry , substituent , medicinal chemistry , kinetics , gas phase , stereochemistry , reaction rate constant , oxygen atom , ion , organic chemistry , molecule , physics , quantum mechanics
The gas‐phase unimolecular elimination of the methanesulphonates in the temperature range 289.0‐331.4°C and pressure range 18–152.5 Torr follows a first‐order rate law. The rate coefficients for the homogeneous reactions are expressed by the following equations: for 3‐( o ‐methoxyphenyl)propyl‐1‐methanesulphonate log[ k 1 (s −1 )] = (12.04 ± 0.32) − [(167.8 ± 3.6) kJ mol −1 ] (2.303 RT ) −1 and for 4‐( p ‐methoxyphenyl)butyl‐1‐methanesulphonate log [ k 1 (s −1 )] = (12.82 ± 0.30) − [(175.1 ± 3.4) kJ mol −1 ] (2.303 RT ) −1 . The oxygen atom of the CH 3 O substituent in 3‐( o ‐methoxyphenyl)propyl‐1‐methanesulphonate appears to participate directly in the C–O bond polarization in order to produce some of the cyclic product dihydrobenzopyran. A parallel reaction occurs with 4‐( p ‐methoxyphenyl)butyl‐1‐methanesulphonate where the p ‐anisyl substituent participates in the elimination process through a five‐membered spiro intermediate for the formation of the cyclic product 6‐methoxy‐1,2,3,4‐tetrahydronaphthalene. The second pathway of this elimination takes place via normal formation of the corresponding unsaturated aromatic hydrocarbons. These reactions are interpreted in terms of an intimate ion‐pair type of mechanism.