Methane with iodine

From l,l,-/)i.v-(3-methyl-4-imidazoline-2-selone)methane with iodine bromide, a solid compound containing disordered molecules with T-shaped CSeI2 and Br-Se(C)-I functions in the same crystal was isolated from 1,2-fe-(3-methyl-4-imidazoline-2-selone)ethane with iodine bromide, a solid... 

Compare chlorination of methane with iodination. The relevant bond dissociation enthalpies are given in the equation. 

Hubig, S. M., Jung, W. and Kochi, J.K. (1994). J. Org. Chem. 59, 6233. Note the competition between ion-pair and radical-pair collapse in halogenation with iodine monochloride on p. 279 is exactly analogous to that in nitration with tetranitro-methane in eqns 82/83 (vide infra)... 

However, since 1970 the preferred method of acetic acid manufacture is carbonylation of methanol (Monsanto process), involving reaction of methanol and carbon monoxide (both derived from methane) with rhodium and iodine as catalysts at 175°C and 1 atm. The yield of acetic acid is 99% based on methanol and 90% based on carbon monoxide. 

The simplest iodoalkane, CH3I, has been studied repeatedly by MW and ED (Table 43). The re value for the C—I distance from a combined MW/IR investigation and the rg value which is reported in a recent ED analysis of the entire series of the iodomethanes CH I, n = 1 to 4, are in perfect agreement. The gas-phase studies for the methanes with two or more iodines were performed at 360 K for CH2I2, at 400 K for CHI3 and at 425 K for CI4. Within the combined experimental uncertainties the C—I bond distances remain constant for mono-, di- and triiodomethane and increases by ca 3 pm in carbon tetraiodide. As in the case of carbon tetrachloride and tetrabromide, this increased bond length in CI4 can be rationalized by steric repulsions between the iodine atoms. The large steric requirement of... 

The reagents for iodine fluoride addition to unsaturated centers are iodine229 or A -iodosuc-cinimide (NIS),221 258 and iodine pentafluoride, hydrogen fluoride,221,258 potassium fluoride, silver(I) fluoride229 278 or ammonium hydrogen difluoride/aluminum trifluoride220 as fluoride ion sources. In addition to the in situ iodofluorinations with iodine monofluoride,l96,22< 227 and (difluoroiodo)methane,194,19 iodofluorination with bis(pyridine)iodonium tetrafluoro-borate219 is described. 

The condensation of two molecules of primary selenoamides proceeds with bromine under extrusion of selenium to give selenadiazoles [93]. The reaction of selenocarbonates, selenothiocarbonates [94], and selenourea [95] with bromine and iodine has been widely tested. The products depend on the amount of halogen used. For example, in the reaction of N-methylthiazoline-2(3H)-selone, the use of one equivalent of bromine gives hypervalent lO-Se-3 complexes 44, whereas two equivalents of bromine cleave the carbon selenium double bond to give product 45. A similar hypervalent compound is formed from 4-imidazolin-2-selone,but the iodination of bis(imidazolin-2-selone)methane gives iodinated product 46. The availability of some of halogen adducts has been tested as a conducting material. 

The radiolysis of ethane has been studied almost exclusively in the gas phase. The products of reaction are mainly hydrogen, n-butane, ethylene, propane and methane with smaller quantities of acetylene, isobutane and isopentane - °°. When the radiolysis is conducted with NO added as a radical scavenger, the hydrogen and n-butane yields are reduced and propene and butene are observed as products > The radiolysis of ethane with iodine vapor has shown that the radicals H, C2H5, and CH3 along with smaller quantities of C3H7, C4H9 and CH2 are present . 

Analyze the first crop of triphenylmethanol and the residue from the evaporation of the mother liquors by thin-layer chromatography. Dissolve equal quantities of the two solids (a few crystals) and also biphenyl in equal quantities of dichloromethane (1 or 2 drops). Using a microcapillary, spot equal quantities of material on silica gel TLC plates (Eastman No. 13181) and develop the plates in an appropriate solvent system. Try 1 3 dichloro-methane-petroleum ether first and adjust the relative quantities of solvent as needed. The spots can be seen by examining the TLC plate under a fluorescent lamp or by treating the TLC plate with iodine vapor. From this analysis decide how pure each of the solids is and whether it would be worthwhile to attempt to isolate more triphenylmethanol from the mother liquors. 

Methane does not react with iodine at all. With fluorine it reacts so vigorously that, even in the dark and at room temperature, the reaction must be carefully controlled the reactants, diluted with an inert gas, are mixed at low pressure. We can, therefore, arrange the halogens in order of reactivity. 

Problem 2.2 Calculate for the corresponding steps in the reaction of methane with (a) bromine, (b) iodine, (c) fluorine. 

Compare the second reaction in each pair methyl radical reacting with chlorine is more exothermic than methyl radical reacting with iodine this does not explain how iodine prevents the chlorination reaction. Compare the first reaction in each pair chlorine atom reacting with iodine is very exothermic whereas chlorine atom reacting with methane is slightly endothermic. Here is the key chlorine atoms will be scavenged by iodine before they have a chance to react with methane. Without chlorine atoms, the reaction comes to a dead stop. 

The value of Gtotalgas was found to be 0.87 [385]. Methane and hydrogen are the main products [386, 387]. A new absorption at 11.25 pm, assigned to vinylidene double bonds, was observed [386]. Total unsaturation was measured by titration with iodine monochloride. It corresponds to the formation of 1.87 double bonds per main-chain scission irrespective of temperature. Main-chain scissions were determined at various temperatures (Table 28). An Arrhenius-type plot of Gscission versus temperature gives an activation energy of 2.5 kcal mole-1 above 0°C. Below 0°C, the temperature coefficient is negligible. 

At the normal dose rates used in radiolysis this abstraction reaction is not quantitative (37) owing to competing radical-radical reactions, so that the methane produced is not a true measure of the radical yield. For example, for methyl chloride solutions the methane observed in the absence of radical scavengers is only 75% of the methyl radical detected with iodine. For methyl iodide the methyl iodide is itself a radical scavenger... 

Grignardization of compormd (I) with iodine-activated magnesium shavings plus a few drops of 1, 2-dibromo-methane must be carried out very carefully to obtain the corresponding derivative (II). 

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