Facile Halogen Exchange Reactions:  Chloroform with Bromoform and Carbon Tetrachloride with Carbon Tetrabromide

Abstract

Both of the title systems undergo rapid halogen exchange (half-life ca. 1−2 min) in N-methylpyrolidinone with catalytic sodium hydroxide at room temperature. Yet they differ markedly in response to added p-dinitrobenzene. The rate of the haloform exchange is unaffected, whereas the rate of the carbon tetrahalide exchange is severely retarded. The known base-induced halogen exchange reaction between chloroform and bromoform is shown not to proceed through a reversible carbene intermediate as claimed in the literature. It appears to be best described in terms of the so-called RARP mechanism (radical anion−radical pair). The mechanism proposed for the rapid exchange between carbon tetrachloride and carbon tetrabromide is initial electron transfer, halide ion loss, and ensuing radical chain scrambling of halogen atoms. The acronym RARC, standing for radical anion−radical chain, is proposed.

The First Efficient Iodination of Unactivated Aliphatic Hydrocarbons

“…This also made the use of quaternary ammonium salts as phase-transfer catalysts, which are deactivated in the presence of iodide, unnecessary. [21,22] The identification of CI 4 is difficult because its 13 C NMR signal at d À 292 is strongly broadened. Scheme 1.…”

“…[12±14] To date, there is no preparative method to produce iodoalkanes directly from aliphatic compounds. [21,22] The identification of CI 4 is difficult because its 13 C NMR signal at d À 292 is strongly broadened. [17] The mechanistic evidence suggests that these reactions are initiated by reduction of CBr 4 , [18,19] subsequently leading to the tribromomethyl radical, .…”

Tetraethylene Glycol Adducts of Alkaline Earth Halides

“…No precipitated formation of AgCl was observed, but upon addition of a MI 2 , almost instantaneously, a white precipitate forms showing that the iodide substitution happens almost immediately. There exist also kinetic studies of exchanges in haloforms; For example, exchange reactions in solvents like tetrachloromethane or tetrabromomethane were studied by Orvik et al [59] He also investigated halogen exchange between chloroform and bromoform and their kinetics, nevertheless his exchange reactions were performed in a basic media. More recent studies about halogen exchange in solvents were performed by Baughman et al [60] …”

Die erste effiziente Methode zur Iodierung nichtaktivierter aliphatischer Kohlenwasserstoffe

“…Daraufhin untersuchten wir, ob CI 4 im Gleichgewicht aus in CH 2 Cl 2 gelöstem Iodoform über festem Natriumhydroxid gebildet wird; entsprechende Gleichgewichte sind für andere Polyhalogenmethane bekannt. [21,22] Die Identifizierung von CI 4 gestaltet sich schwierig, da sein 13 C-NMR-Signal bei d À 292 stark verbreitert ist. [23] Sowohl die Raman-als auch die Infrarot-Banden sind wegen der hohen Symmetrie (T d ) sehr schwach und nicht von den denen anderer Polyhalogenmethane zu unterscheiden; die UV-Spektroskopie ist gleichfalls ungeeigntet.…”