Electrophilic Aromatic Substitution. 13.¹ Kinetics and Spectroscopy of the Chloromethylation of Benzene and Toluene with Methoxyacetyl Chloride or Chloromethyl Methyl Ether and Aluminum Chloride in Nitromethane or Tin Tetrachloride in Dichloromethane. The Methoxymethyl Cation as a Remarkably Selective Common Electrophile

Abstract

Vacuum line kinetics studies have been made of the reaction in nitromethane between benzene and/or toluene, methoxyacetyl chloride (MAC), and AlCl(3) to produce benzyl or xylyl chlorides, CO, and a CH(3)OH(-)AlCl(3) complex. For both arenes, the rate law appears to be R = (k(3)/[AlCl(3)](0)) [AlCl(3)](2)[MAC]. When chloromethyl methyl ether (CMME) is substituted for MAC, a similar rate law is obtained. Both chloromethylation reactions yielded similar, large k(T)()/k(B)() ratios (500-600) and similar product isomer distributions with low meta percentages ( approximately 0.4) which suggest CH(3)OCH(2)(+) or the CH(3)OCH(2)(+)Al(2)Cl(7)(-) ion pair as a common, remarkably selective, electrophile. The kinetics of MAC decomposition to CMME and CO in the presence of AlCl(3) yielded the rate law R = k(2)[AlCl(3)](0)[MAC]. Here AlCl(3) is a catalyst (no CH(3)OH is formed), and thus the rate law is equivalent to the chloromethylation rate law. All three reactions have comparable reactivities, which is consistent with rate-determining production of the electrophile. Kinetics studies of benzene or toluene with SnCl(4) and MAC or CMME in dichloromethane were also completed. With MAC and benzene the rate law is R = k(3)[SnCl(4)](0)[MAC][benzene] and with toluene R = k(2)[SnCl(4)](0)[MAC]. MAC decomposition, again followed by CO production, was unaffected by the presence of either aromatic and obeyed the rate law R = k(2)' [SnCl(4)](0)[MAC] where k(2) approximately k(2)'. Chloromethylation with CMME followed the rate law R = k(3)[SnCl(4)](0)[CMME][arene] for benzene and toluene and produced a k(T)()/k(B)() ratio and product isomer distributions very similar to those determined with AlCl(3) in nitromethane, further supporting a common electrophile. Low-temperature (13)C and (119)Sn FT-NMR and Raman spectroscopic studies suggest the existence of a weak 1:1 adduct between MAC and SnCl(4) of the type RCXO --> SnCl(4), with electron donation to the metal through carboxy oxygen. Finally, an explanation is provided for the range of chloromethylation k(T)()/k(B)() values and product isomer percentages published in the literature.

Chloromethylation of Aromatic Compounds Catalyzed by Surfactant Micelles in Oil–Water Biphasic System

“…[1][2][3][4][5]. The most commonly employed procedures for chloromethylating aromatic compounds have been the use of chloromethyl methyl ether and/or bis-chloromethyl ether (or reagent combinations which can result in the formation of these ethers) and Lewis acid as the catalysts [6][7][8]. Selectivity and yield of the mono-chloromethyl derivatives are determined by the consecutive formation of the polychloromethylation byproducts and the formation of diarylmethane derivatives and other byproducts, because of the Friedel-Crafts alkylation catalyzed by the same Lewis acid, and are often not so high [9].…”

Reaction Routes of Specific Decarbonylative α,α-Diarylation of 2-Methoxypropanoic Acid Analogues in P2O5−MsOH and the Related Reagents

“…There have been some papers describing the decarbonylations of carboxylic esters and free acids , without sufficient mechanistic clarification . As far as we know, only two cases have been reported concerning the decarbonylative arylation of carboxylic acids or their derivatives. , The reaction of acids 1 described above is the first example of decarbonylative α-arylation of free carboxylic acids . However, the mechanism, scope, and limitation of this reaction have not been fully understood yet.…”