Iodides by halogenation

A-Bromoamides and imides are simply converted to the corresponding iodides by halogen exchange with alkyl iodides701. 

Triphenylstannylmethyllidlium, (C6Hs)3SnCH2Li (1). Mol. wt. 370.98. The reagent is obtained in almost quantitative yield from (triphenylstannyl)methyl iodide by halogen-metal exchange with n-butyllithium. ... 

Tetraalkyl and tetraaryl germanium compounds possess monomeric structures with tetrahedrally sited germanium. They are thermally stable and tend to be chemically inert halogenation requires a catalyst (equations 18.49 and 18.50). Chlorides can be obtained from the corresponding bromides or iodides by halogen exchange (equation 18.51). The presence of halo-substituents increases reactivity (e.g. equation 18.52) and makes the halo-derivatives synthetically more useful than R4Ge compounds. 

Various halogenating agents have been used to replace hydroxyl with chlorine or bromine. Phosphoms trihaUdes, especially in the presence of pyridine, are particularly suitable (17,18). Propargyl iodide is easily prepared from propargyl bromide by halogen exchange (19). 

Both ( )- and (Z)-l-halo-l-alkenes can be prepared by hydroboration of 1-alkynes or 1-halo-l-alkynes followed by halogenation of the intermediate boronic esters (244,245). Differences in the addition—elimination mechanisms operating in these reactions lead to the opposite configurations of iodides as compared to bromides and chlorides. 

Metal halides can in some cases, be used to replace other atoms or groups besides fluorine with halogen Polyfluoroacyl fluorides and chlorides can be converted to fluoroalkyl iodides by simply heating the reactant in the presence of an alkali metal iodide [[Pg.382]

This reaction, parallel with 10-77, is the standard method for the preparation of sulfonyl halides. Also used are PCI3 and SOCI2, and sulfonic acid salts can also serve as substrates. Sulfonyl bromides and iodides have been prepared from sulfonyl hydrazides (ArS02NHNH2, themselves prepared by 10-126) by treatment with bromine or iodine.Sulfonyl fluorides are generally prepared from the chlorides, by halogen exchange. 

This catalytic cycle, generating acetyl iodide from methyl iodide, has been demonstrated by carbonylation of anhydrous methyl iodide at 80°C and CO partial pressure of 3 atm using [(C6H5)4As][Rh(CO)2X2] as catalysts. After several hours reaction, acetyl iodide can be identified by NMR and infrared techniques. However, under anhydrous conditions some catalyst deactivation occurs, apparently by halogen abstraction from the acetyl iodide, giving rhodium species such as frans-[Rh(CO)2I4] and [Rh(CO)I4] . Such dehalogenation reactions are common with d8 and d10 species, particularly in reactions with species containing weak... 

More often the passive layer is broken down locally and then the steel is said to be attacked by localized corrosion, the most important forms being pitting, crevice corrosion, and corrosion cracking. Most often the localized corrosion is caused by halogen ions such as chloride, bromide, and iodide. Pitting or pitting corrosion is seen as small pinholes on the surface of the steel. This section describes electrochemical instrumental methods to investigate and measure this form of corrosion attack. 

Phosphine oxides are similar excellent orf/zo-directors which have seen only limited use so far. The iodide 123, for example—a precursor of a new class of bisphosphine ligands—can be made by cooperatively-directed ortholithiation of the phosphine oxide 122, itself derived by halogen-metal exchange from 121 (Scheme 53) . 

Successful lithiation of aryl halides—carbocyclic or heterocyclic—with alkyUithiums is, however, the exception rather than the rule. The instability of ortholithiated carbocyclic aryl halides towards benzyne formation is always a limiting feature of their use, and aryl bromides and iodides undergo halogen-metal exchange in preference to deprotonation. Lithium amide bases avoid the second of these problems, but work well only with aryl halides benefitting from some additional acidifying feature. Chlorobenzene and bromobenzene can be lithiated with moderate yield and selectivity by LDA or LiTMP at -75 or -100 °C . 

Tris trifluoromethyl phosphine bums in air, but, unlike its methyl analogue, has not so far been found to form addition compounds with sulphur, carbon disulphide or silver iodide. With chlorine it forms the addition compound P(CF3)3Cl2 (b.p. 94°), and there is some indication that an addition compound of lower stability may be formed with bromine. With either of these halogens at higher temperatures, partial replacement of CF3 by halogen occurs and a similar reaction occurs with iodine, yielding some P(CF3)2l and P(CF3)l2. 

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