Iodide divalency

A rather rare perfluoroalkyl iodide addition to divalent carbon atom has been performed in the case of isocyanides under thermal or copper catalyzed conditions [14I (equation 122)... 

Iodomethylzinc iodide is often refened to as a carbenoid, meaning that it resembles a carbene in its chemical reactions. Caibenes are neutral molecules in which one of the caibon atoms has six valence electrons. Such caibons aie divalent they are directly bonded to only two other atoms and have no multiple bonds. Iodomethylzinc iodide reacts as if it were a source of the caibene H—C—H. 

Moreover, the Relative Size argument also applies to those divalent iodides which are approximately close-packed arrays of iodide (cp. Wyckoff 24)). The following table shows for such compounds the gram-formula weights, the X-ray determined densities, and hence the volume Vanion (cc/gm/atom) occupied by the iodide gram/ion, which has a minimum value of about 28 cc. 

Table 9. Volume per iodine ion in divalent ionic iodides (data from Wyckoff (24))...

A reasonable mechanism for the iodine oxidation of 5-Trt cysteine peptides is given in Scheme 6. 45 Reaction of iodine with the divalent sulfur atom leads to the iodosulfonium ion 5 which is then transformed to the sulfenyl iodide 6 and the trityl cation. Sulfenyl iodides are also postulated as intermediates in the iodine oxidation of thiols to disulfides. The disulfide bond is then formed by disproportionation of two sulfenyl iodides or by reaction between the electrophilic sulfur atom of R -S-I and the nucleophilic S-atom of a second R -S-Trt molecule. The proposed mechanism suggests that any sulfur substitution (i.e., thiol protecting group) capable of forming a stabilized species on cleavage, such as the trityl cation, can be oxidatively cleaved by iodine. 

We must, however, ensure that there is no contaminant such as free Fe3+ in the solution before the potassium iodide is added otherwise, more I- will be oxidized than there is Cu2+ in the sample (reaction 15.12). The effective concentration of Fe3+ can be reduced to negligible levels by adding sodium fluoride to complex it. (The divalent copper ion is little affected.)... 

Good yields are obtained only if the oxidation of the divalent lead to the tetravalent stage is complete. To test for plumbous lead, add ten drops of the reaction mixture to five milliliters of water and boil gently for a few minutes to hydrolyze all the tetravalent lead to lead dioxide. When the latter settles, filter the hot mixture, cool under the tap, and add several drops of saturated potassium iodide. A yellow precipitate of lead iodide constitutes a positive test. 

In 1939 Klemm and Doll [276] prepared all the halides of divalent europium and studied the magnetic characteristics of these compounds. The magnetic susceptibilities (X g) and effective moments of the fluoride, chloride, bromide and iodide are tabulated in Table 15. Except for the... 

Various methods [282] have been used to prepare anhydrous chlorides of the rare earths. Taylor and Carter [283] describe a general method for the preparation of high purity anhydrous halides in good yield. This method involves heating in vacuo, a molecularly dispersed mixture of hydrated rare earth halide with proper ammonium halide until the water and ammonium halide are expelled. All the trihalides except the iodides of Sm and Eu can be obtained using this proceedure. In the case of Sm and Eu the divalent iodides, Sml2 and Eul2 are obtained. 

The reaction is catalyzed by divalent heavy metal ions, especially by Cu2+ and Co2+. It follows zeroth order, so it is independent of the concentration of the reactants Na2S03 and 02( ) but only depends on the rate of mass transfer. The remaining sulfite is oxidized to sulfate by the addition of iodine and the iodide generated is back-titrated with thiosulfate [Eqs. (8.37), (8.38)]. 

As for palladium discussed above, the majority of platinacyclopentanes are based on the divalent metal. However, the structurally characterised complex [Pt(C4H8) (Ph)I(bipy)] 91 has been obtained by treating [Pt(C4H8)(bipy)] 85 with di-phenyliodonium triflate followed by triflate-iodide metathesis [Eq. (36)]. As in the palladium example 79 described above, both cis and trans oxidative addition products are observed.103 Prior to this, the structurally characterised platinum(IV) derivative [Pt(C4H8)I2(PMe2Ph)2] 92 had been obtained via trans oxidative addition of iodine to [Pt(C4H8)(PMe2Ph)2] [Eq. (37)].113... 

In the presence of iodide ion, and in acid medium, Mn4+ is reduced back to divalent Mn2+, thus liberating I2. 

It is based on the addition of Mn2+ solution, followed by die addition of a strong alkali to die sample in a glass-stoppered bottle. Dissolved 02 rapidly oxidizes an equivalent amount of the dispersed divalent manganous hydroxide precipitate to hydroxides of higher valence states. In die presence of iodide ions in an acidic solution, the oxidized manganese reverts to die divalent state, with die liberation of a quantity of iodine equivalent to die original dissolved 02 content. The iodine is then titrated with a standard solution of thiosulfate. The titration end point can be detected visually with a starch indicator, or by potentiometric techniques. The liberated iodine can be determined colorimetrically. 

Table 2 Polymerization of isoprene with divalent lanthanide iodides Lnl2 (Ln = Nd, Sm, Dy, Tm) and Lni2(THF)x (Ln = Sm, Tm) as initiators (from [95])...

Reduction of the copper(II) halides to copper(I) halides may be carried out using sulfite or copper metal. If the reduction with copper metal is carried out in concentrated HC1 solution, the solution takes on an intermediate black color before fading to the colorless CuCl ion. The black color is probably due to dimeric or polymeric ions having copper in both the +1 and +2 states, for example, Cl—Cu—Cl—CuC12(H20) . The reduction of divalent copper by cyanide to form the cyano complex, Cu(CN)73, was mentioned in Chapter 10, and the reaction between cupric and iodide ions is similar to this, releasing iodine and forming the very insoluble copper iodide ... 

The Simmons-Smith reagent, named for the two DuPont chemists who discovered it, is made by adding methylene iodide to the zinc-copper couple (zinc dust that has been activated with an impurity of copper). The reagent probably resembles iodomethyl zinc iodide, ICH2ZnI. This kind of reagent is called a carbenoid because it reacts much like a carbene, but it does not actually contain a divalent carbon atom. 

Peroxide Value, Fats and Oils (PV) (Cd 8-53) determines all substances, in terms of milliequivalents of peroxide per 1000 g of sample, that oxidize potassium iodide (KI). These substances generally are assumed to be peroxides or products of fat oxidation. Phosphorus in Oils (Ca 13-55) estimates the phospholipid content of crude, degummed, and refined vegetable oils in terms of phosphorus. Refineries often use induction coupled plasma (ICP) spectrographs to analyze divalent cations rapidly in aspirated crude oil. The calcium and magnesium measured are mainly responsible for nonhydratable phosphatides (NHP) and are determined directly. An AOCS method for analysis by ICP is being developed. 

P. Girard, J. L. Namy, and H. B. Kagan, Divalent lanthanide derivatives in organic synthesis. 1. Mild preparation of samarium iodide and ytterbium iodide and their use as reducing or coupling agents,. /. Am. Chem. Soc., 102 (1980) 2693-2698. 

Some polymeric, formally divalent iodides, have been made by treating (SiPh2) with HI and A1C13 these are Sijg, Si5I10, and Si5I12. 

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