Interhalogen addition

The two interhalogens, ICl and IBr, have been used extensively to measure unsaturation, but the kinetics of their reaction with olefins has received very little attention. White and Robertson have established the third-order kinetics of addition, where the simple form is 

They also found the order of reactivity h IBr Bra ICl BrCl 

The high instability of bromine monochloride (the heat of formation of which has been estimated as 0.3 kcal.mole ) provides some difficulty in studying its reactions. Nonetheless, the rate of addition of mixtures of chlorine and bromine (with the total concentration of halogen constant) to c/s-cinnamic acid in carbon tetrachloride-acetic acid mixtures was greatest when [Br2]/[Cl-i] was unity . The kinetic form of the reaction was the same as that for the other interhalogens and for bromine, but not for chlorine. The possible intervention of bromine monochloride in the reaction of allyl trimethylammonium perchlorate with hypobromous acid in aqueous acid has also been reported here, the kinetics were . 

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Warning Depending on the ratio of hydrogen to halogen in a given molecule, addition of an interhalogen to that substance in the absence of solvent can result in spontaneous ignition or worse. 

This method of addition of interhalogens to double bonds has been applied to the synthesis of nucleocidin (1) from adenosine 9,10 (75) (see Scheme 1). 

There is strong evidence that the interhalogen bonds are essentially pure p bonds. By assuming for I2 that hp = 1, the isomer shift and this value for hp continue the trends of Figure 3 and thus support the picture of pure p bonding for molecular iodine. In addition, Pasternak and Sonnino (27) have also studied IBr, ICl, laCle, and ICN. 

Addition of halogens or interhalogens to perfluorohalogenothio-ketones, as already described, represents an important method for the preparation of complex sulfenyl halides. 

The reactivity of iodine has been investigated at liquid-liquid-electrode triple-phase boundary systems. Scholz et al. [162] demonstrated that the reduction of iodine dissolved in a nitrobenzene microdroplet triggered the transfer of cations from the aqueous into the organic solution phase (Scheme 6). In addition, the formation of IzCl" interhalogen anions in the organic phase was discovered and shown to be the key to the overall process. 

The interhalogen compounds obey the expectations based on the VSEPR theory, and typical structures are giver in Chapter 6. Ore compound not included there is the dimeric iodine trichloride, in which the iodine atom of the monomeric species appears to act as a Lewis acid and accept an additional pair of electrons from a chlorine atom (Fig. 17.5). 

In addition to the polyhalide ions discussed previously, which were all anionic, there are comparable cationic species known, although they have been studied considerably less. Many pure interhalogen compounds arc thought to undergo autoionization (see Chapter 10) with the formation of appropriate cationic species ... 

In general, addition of more polar interhalogen compounds (ICI, IF, BrF, ClF) to fluoroolefins proceeds as an ionic process, starting with attack of halogen bearing positive charge on the C=C bond and formation of a cyclic halonium cation (Eq. 2) [10,18]. 

As a final example of this section, we cite Benson and Haugen s (1965) electrostatic model for the prediction of activation energies for four-center gas phase reactions. Of interest here are the additions of hydrogen, halogens, interhalogens and hydrogen halides to alkenes. To obtain the calculated value of the activation energy for the addition reaction (196),... 

In order to evaluate the interhalogens, ammonium perchlorate and oxygen on a comparative basis and particularly in regard to metal additives, figure IV. A. 4, is given. This figure gives a heat of combustion plot based upon chlorine as the oxidizer. 

ClFg is an important interhalogen compound and has been studied by Breeze et a/.,368 with a small basis set. It can be regarded as derived from C1F by the addition of two fluorine atoms by way of a three-centre bond. 

Addition of interhalogen compounds to olefins affords adducts which are useful bifunctional synthons. The addition is normally according to Markovnikov, namely the more electropositive halogen adds to the less substituted carbon. With a,/ -unsaturated carbonyl... 

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