Gas-phase heteroaromatic substitution. 3. Electrophilic methylation of furan and thiophene by CH/sub 3/XCH/sub 3//sup +/ (X = F or Cl) ions

Journal Article · Wed Dec 15 04:00:00 EST 1982 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00389a035· OSTI ID:6179679

Angelini, G; Lilla, G; Speranza, M

A previous radiolytic study on the gas-phase methylation of pyrrole and N-methylpyrrole by CH/sub 3/XCH/sub 3//sup +/ (X = F or Cl) ions, from the ..gamma.. radiolysis of CH/sub 3/X, is extended to furan (3) and thiophene (4). The mechanism of the substitution and of the subsequent isomerization occurring via intramolecular 1,2 methyl-group shifts is discussed and the substrate and positional selectivity of the selected electrophilic species evaluated. As for pyrroles, gas-phase CH/sub 3/FCH/sub 3//sup +/ methylation of furan and thiophene is characterized by a scarce substrate discrimination (k/sub S//k/sub B/ = 1.2 (3), 0.8 (4)), accompanied by an appreciable positional selectivity toward those substrate positions with the highest negative net charge (O:..cap alpha..:..beta.. = 36%:35%:29% for 3; S:..cap alpha..:..beta.. = 19%:43%:38% for 4). On the contrary, CH/sub 3/ClCH/sub 3//sup +/ confirms its inherent affinity toward n-type nucleophilic centers by attacking preferentially the heteroatom of 3 and 4. In light of the previous results concerning CH/sub 3/XCH/sub 3//sup +/ methylation of pyrroles, it is concluded that gas-phase attack of CH/sub 3/XCH/sub 3//sup +/ on simple five-membered heteroaromatics is essentially regulated by the electrostatic interaction established within the encounter pair. A close correspondence does exist between this rationalization of the present gas-phase results and recent theoretical predictions.

• Research Organization: Instituto di Chimica Nucleare del C.N.R., Rome, Italy
• OSTI ID: 6179679
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 104:25; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
400201 -- Chemical & Physicochemical Properties
400600* -- Radiation Chemistry
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTION KINETICS
CHEMICAL REACTION YIELD
CHEMICAL REACTIONS
CHEMISTRY
CHLORINATED ALIPHATIC HYDROCARBONS
DATA
DECOMPOSITION
ELECTROMAGNETIC RADIATION
EXPERIMENTAL DATA
FLUORINATED ALIPHATIC HYDROCARBONS
FURANS
GAMMA RADIATION
HALOGENATED ALIPHATIC HYDROCARBONS
HETEROCYCLIC COMPOUNDS
INFORMATION
IONIZING RADIATIONS
KINETICS
METHYL CHLORIDE
METHYL FLUORIDE
METHYLATION
NUMERICAL DATA
ORGANIC CHLORINE COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC FLUORINE COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
ORGANIC SULFUR COMPOUNDS
RADIATION CHEMISTRY
RADIATION EFFECTS
RADIATIONS
RADIOLYSIS
REACTION KINETICS
THIOPHENE
YIELDS