Iodide formation reaction

An important characteristic feature, common to all these reactions, is the formation of a single product (barrier) phase. In addition, the lattice structures of both reactants and products are relatively simple and information on appropriate physical and chemical properties of these substances is available. Complex iodide formation is of particular interest because of the exceptionally large cation mobilities in these phases. Experimental methods have been described in Sect. 1 and Chap. 2. 

The two catalyst components are rhodium and iodide, which can be added in many forms. A large excess of iodide may be present. Rhodium is present as the anionic species RhI2(CO)2. Typically the rhodium concentration is 10 mM and the iodide concentration is 1.5 M, of which 20% occurs in the form of salts. The temperature is about 180 °C and the pressure is 50 bar. The methyl iodide formation from methanol is almost complete, which makes the reaction rate also practically independent of the methanol concentration. In other words, at any conversion level (except for very low methanol levels) the production rate is the same. For a continuous reactor this has the advantage that it can be operated at a high conversion level. As a result the required separation of methanol, methyl acetate, methyl iodide, and rhodium iodide from the product acetic acid is much easier. 

She and co-workers took advantage of the acyl anion equivalent formed from the addition of an NHC to an aldehyde to catalyze the formation of benzopyranones via an intramolecular S 2 displacement (Scheme 50) [167], Various aromatic aldehydes provide alkylation products in moderate yields when the leaving group is either tosylate or iodide. No reaction was observed when phenyl or methyl was placed alpha to the leaving group. 

Chlorexolone as diuretic, 1, 174 Chlorides synthesis, 1, 448 Chlorin, 4, 370 metal chelates, 4, 391 Chlorin, dihydroxy-, 4, 393 Chlorin e6, 4, 404 trimethyl ester, 4, 398 synthesis, 4, 416 Chlorination pyridazines, 3, 20, 21 Chlorine trifluoride bonding, 1, 564 Chlorin-phlorin, 4, 398 Chlorins, 4, 378 absorption spectra, 4, 389 formation, 4, 394 molecular structure, 4, 385 oxidation, 4, 395 Chlorisondamine chloride as hypertensive agent, 1, 176 Chlormethiazoles metabolism, 1, 235 Chlormethiuron against ectoparasites veterinary use, 1, 217 Chlormezanone as antidepressant, 1, 169 Chlorocruoroheme, 4, 380 Chlorofucin conformation, 7, 703 Chloronium iodide, biphenylene-reactions, 1, 566... 

Photostimulated, S r k 1 reactions of carbanion nucleophiles in DMSO have been used to advantage in C—C bond formation (Scheme 1).25-27 Thus, good yields of substitution products have been obtained from neopentyl iodide on reaction with enolates of acetophenone and anthrone, but not with the conjugate base of acetone or nitromethane (unless used in conjunction, whereby the former acts as an entrainment agent).25 1,3-Diiodoadamantane forms an intermediate 1-iodo mono substitution product on reaction with potassium enolates of acetophenone and pinacolone and with the anion of nitromethane subsequent fragmentation of the intermediate gives derivatives of 7-methylidenebicyclo[3.3.1]nonene. Reactions of 1,3-dibromo- and 1-bromo-3-chloro-adamantane are less effective.26... 

The products were isolated as esters by reaction of the acylcobalt carbonyls with an alcohol and iodine. In the case of the alkyl halides, carbon monoxide was normally absorbed, but under nitrogen, acylcobalt tricarbonyls must be formed. The reaction with alkyl halides was slow and some isomerization was noted using M-propyl iodide (formation of n-butyrates and isobutyrates). Absence of carbon monoxide promoted the isomerization. Isopropyl iodide gave no reaction. When ethyl a-bromopropionate was used, no isomerization was found at — 25 °C under carbon monoxide, but the isomerized product, diethyl succinate, was the major product at 25° C under carbon monoxide or nitrogen. Under the conditions of the experiments no isomerization of the alkyl halide itself was found. 

Because some amount of S2- may escape out as H2S during standard preparation and a small proportion may be oxidized to sulfate over a few hours, and also because methylene blue formation reaction may not thermodynamically go to completion, it is, therefore, always recommended that sulfide concentration should be determined by titrimetric iodide procedure and an average percent error of the methylene blue procedure be compared against this titrimetric procedure. 

The thermochemical aspects of these reactions have been discussed in terms of heats of formation of the halides of elements of the iron group, and of the acceptor metal (75). The yield of carbonyls was especially favored with the iodides and also with sulfides or sulfur-containing materials (76). With iron and cobalt iodides the reaction is facilitated by formation of the carbonyl iodide as an intermediate. 

According to the MD simulations examined for cesium iodide solutions of 2.78 mol dm-3 (Csl H20 = 1 20) at 25 and 64°C and 5.56 mol dm-3 (Csl H20 = 1 10) at 64°C (34), higher ion pairs than 1 1 form in the 2.78 mol dm-3 solution, but formation is suppressed as the temperature is raised. Thus, ion-pair formation reactions between cesium and iodide, both of which are weakly hydrated, must be exothermic, although no thermodynamic data are available in the literature. The increase in concentration at a given temperature (64°C) enhances the formation of the ionic aggregates from raCsI = 1.07 to 1.80. 

It is possible to eliminate by-product lead metal formation in the PbXa-RM reaction without recourse to a low reaction temperature by simply conducting the reaction in the presence of an organic halide, preferably a bromide or iodide. This reaction was originally demonstrated by Gilman and coworkers 149,152) and is represented by the equations ... 

The -deuterium KIE for the bromide and for the iodide ion reaction are significantly different and indicate that the nucleophiles are part of transition state of the rate-determining step of these reactions and the decomposition of the halides in chloroform occurs by way of an S 2 mechanism within a triple ion and not through carbocation formation. The kinetic study alone could not distinguish between the mechanistic alternatives, since the same kinetic expression would be obtained for all of the mechanisms. 

Both Bu3SnH and (Me3Si)3SiH are able to defunctionalize alkyl iodides or bromides but not alcohols. On the other hand, in the so-called Barton-McCombie reaction they can defunctionalize certain alcohol derivatives, namely, ones that contain a C=S double bond (e.g., thiocarboxylic esters or thiocarbonic esters). Figure 1.32 shows how the OH group of cholesterol can be removed by means of a Barton-McCombie reaction. The C=S-containing alcohol derivative used there is a xanthate (for the mechanism of the formation reaction of xanthates, see Figure 7.4). 

A nucleophilic attack by 4.7 on CH3I produces 4.8 and I. Conversion of 4.8 to 4.9 is an example of a carbonyl insertion into a metal alkyl bond. Another CO group adds onto the 16-electron species 4.9 to give 4.10, which in turn reacts with I to eliminate acetyl iodide. Formation of acetic acid and recycling of water occur by reactions already discussed for the rhodium cycle. Apart from these basic reactions there are a few other reactions that lead to product and by-product formations. As shown in Fig. 4.4, both 4.9 and 4.10 react with water to give acetic acid. The hydrido cobalt carbonyl 4.11 produced in these reactions catalyzes Fischer-Tropsch-type reactions and the formation of byproducts. Reactions 4.6 and 4.7 ensure that there is equilibrium between 4.7 and 4.11. 

Hypophosphorous acid-starch solution test Iodates are reduced by hypo-phosphorous acid eventually to iodides. The reaction takes place in three stages (with the transitional formation of phosphorous acid) ... 

Vinyl halides represent yet another important class of intermediates in the conversion of ketones to alkenes. The most widely applied conditions for the conversion of ketones into vinyl halides are those developed by Barton et a/. ° for the conversion of 3p-acetoxyandrost-5-ene-17-one into 3P-hydroxyandrosta-5,16-diene (Scheme 44). These conditions of vinyl halide formation and subsequent reduction have been useful in a number of steroid systems for the introduction of a A -carbon-carbon double bond and have been shown to be compatible with such functional groups as alcohols, isolated double bonds and acetals. The scope of vinyl iodide formation from hydrazones has been studied by Pross and Stemhell, and recently the original reaction conditions were improved by using sterically hindered guanidine bases rather than triethylamine. Haloalkenes have also been prepared from the corresponding ketones by treatment with iodoform and chromium chloride or with phosphorous penta-halides. ... 

The Ce(IV)-As(III) reaction is catalyzed by iodine and thereby furnishes the basis for the determination of traces of iodine. A possible pathway involves the formation of I or I by reaction of I with Ce(IV). The rate of the overall reaction (15-23) is determined by that of (15-27), which is proportional to the steady-state concentration of iodide ion. Because each iodide ion enters the catalytic cycle many times, the method is extremely sensitive. Chloride is beneficial in the iodide-catalyzed reaction, presumably through formation of ICl as an intermediate that inhibits formation of HIO3 as an unreactive product. ... 

Up to pH 9 the iodine-iodide half-reaction is independent of pH. From pH 9 to 11 the formation of hypoiodite is appreciable but, since hypoiodite oxidizes arsenic(III) to arsenic(V) stoichiometrically,... 

---