Exchange reactions of benzene

IrH5(PPr3)2 can activate the C—H bonds of benzene and catalyze the H—D exchange reaction of benzene and hydrogen (eq (71)) [81]. 

A detailed analysis of the products suggests that the adsorbed phenyl radical plays an important part in the mechanism of the exchange reaction of benzene and that this reaction is closely analogous to the exchange of the saturated hydrocarbon, cyclohexane. 

Hartung T, Baltruschat H (1990) Differential electrochemical mass spectrometry using smooth electrodes adsorption and H/D-exchange reactions of benzene on PL Langmuir 6(5) 953-957... 

The exchange reaction of benzene in deuterated acid serves as a prototype for a host of similar reactions in which an electrophile, E, is substituted for a hydrogen on the ring ... 

For the exchanges carried out in liquid ammonia, kinetic isotope effects kD kT of 2.3-2.5 have been obtained for reaction of benzene, toluene, and naphthalene and for the reactions of the 2 positions of furan and thiophene with -butoxide in dimethyl sulphoxide somewhat lower values, 1.5 and 1.3, respectively, were obtained591, but whether this was a solvent or a substituent effect is not apparent from the data. 

This discovery was quite unexpected, since iron oxide has been never reported as an active catalyst in either partial or full oxidation. The studies of two simplest reactions, i.e. O2 isotopic exchange and N2O decomposition, revealed a dramatic change of Fe properties in the ZSM-5 matrix compared to Fe203 [4]. Fe atoms lose their ability to activate O2 but gain remarkably in their ability to activate N2O. It gives rise to a great effect of the oxidant nature in the reaction of benzene oxidation over the FeZSM-5 zeolite (Table 1). Thus, in the presence of N2O benzene conversion is 27% at 623 K, while in the presence of O2 it is only 0.3% at 773 K. And what is more, there is a perfect change of the reaction route. Instead of selective phenol formation with... 

Exchange Reactions with Benzene Derivatives. Preparation of 1 3 5-Tri-, 1 2 4 5-Tetra- and Pentadeuterobenzene. J. chem. Soc. [London] 1946, 239-... 

The reaction of benzene with Cu(II) and Fe(III)-exchanged hectorites at elevated temperatures produced a variety of organic radical products, depending on the concentration of water in the reaction medium and the reaction time (90). The formation of free radicals was accompanied by a reduction in oxidation state of the metals, a process that had a zero-order dependence on the metal ion concentration. Under anhydrous conditions the free radicals appeared to populate sites in the interlayer region, the activation energies under these conditions being lower than in the hydrated samples. 

Similarly, pentafluorophenylmagnesium halides can be prepared either by direct reaction of magnesium with pentafluorophenyl halides or by an exchange reaction of alkylmagnesium halides with hydro-, bromo- and chloropentafluoro-benzenes [195,213-217] (Scheme 73). 

Cinneide and Clarke (770) have studied the activity of Pd-Au films for the deuteration and exchange of benzene and the hydrogenation of p-xylene. The authors report that the activity for the exchange reaction between benzene and deuterium persists to the palladium-lean compositions, which is in agreement with results obtained by Honex et al. (Ill) in a study of the exchange of toluene over alloys of the same kind. The rates are much reduced (by 102 to 103) compared to those found with palladium-rich films. 

The exchange reactions of organyltrialkoxysilanes with THEA mostly require heating of the components in an appropriate inert solvent (benzene, toluene, xylene, anisole, chloroform, methanol, ethanol etc.) for a long time. However, in some cases the reactions can be carried out at room temperature or, if necessary, with cooling. The transetherification rates and silatrane yields increase in the presence of an alkali metal hydroxide or alkoxide as a basic catalyst. 

This synthesis has been extended to the heavier heterobenzenes. The exchange reaction of 15 with antimony trichloride gave l-chloro-l,4-dihydrostibabenzene 18 as a crystalline solid 10>. On treatment with base, 18 afforded stibabenzene 4. While stibabenzene can be isolated and characterized, it rapidly polymerizes even from dilute solutions at ambient temperature. The reaction of bismuth trichloride and 15 afforded a good yield of crystalline 1 -chloro-1,4-dihydrobi smabenzene 19, which on reaction with base at 0 °C gave only intractable material11). However, bisma-benzene 5 has been detected both spectroscopically 241 and via chemical trapping n). 

Exchange reactions of DIB with practically any acid is the most convenient method for the preparation of [bis(acyloxy)iodo]benzenes. 

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