Covalent iodide derivatives

Still another possibility of isomerization is illustrated by the easy interconversions between pentaphenylpentadienoie aeid chloride and 2-chloropentaphenyl-3-eyelopenten-l-one. Interestingly, 2,4,6-trimethylpjrrylium iodide maj be sublimed without decomposition in a vacuum, possibly as a covalent 6-iodo-4-methyl-3,5-heptadien-2-one or 2-iodo-2,4,6-trimethyl-2H-pyran valenee isomer. In a related case, chlorocyclopropenes are covalent and are converted into cyclo-propenium derivatives only by the action of Friedel-Crafts catalysts (electron-deficient metallic chlorides) (ef. also Section II,C, 2,c.)... 

Aryl iodides are exceptional among the aromatic halogen compounds in that they form a series of derivatives in which the iodine exhibits a covalency greater than one. Some typical interconversions for which experimental conditions are given (Expts 6.31 to 6.36) are summarised below. 

Recent concerns over the residual concentration of free thioxanthone photoinitiators and amine coinitiators in coatings and inks on food packaging have resulted in the evolution of macroinitiators <2002PLM4591, 2003JPH(159)103> or polymeric photoinitiators <1996MI379> wherein the thioxanthone unit and, in some instances, the amine coinitiator are covalently bound to a copolymer which is formulated with the ink or coating and then photocured in the normal way. Several copolymers, for example, 636, based upon the polymerization of acrylate esters derived from 4-hydroxythioxanthones with either acrylamide or 2-acryloxyethyltrimethylammonium iodide co-monomer have been explored as water-soluble photoinitiators <2005JPH(169)95>. 

A new, more accurate electron diffraction study of gaseous mercuric chloride has been reported.159 The interatomic distances (Hg—Cl = 2.25 A, Cl—Cl = 4.48 A) are shorter than previously reported values by 0.02 to 0.09 A. A complete normal-co-ordinate analysis of bis(methylthio)mercury has also been reported.160 The Raman spectra of gaseous mercuric chloride, bromide, and iodide have been reported.161 The bond polarizability derivatives calculated from the data increase in the order Cl < Br < I, suggesting an increased degree of covalence in the mercury-halogen bond with increasing size of the halogen atom. 

Inhibition of the type I deiodinase by PTU is uncompetitive with substrate and competitive with cofactor. This is the case for the ORD of T4 and rT3 as well as for the IRD of T3 and T3S [7,8]. Persistent inactivation of enzyme by PTU and covalent labelling with radioactive inhibitor requires the presence of substrate and is only reversed with high DTT [42,47], All available evidence indicates that PTU reacts with a substrate-induced enzyme intermediate. As thiourea derivatives are particularly reactive towards sulfenyl iodide (SI) groups, generation of an enzyme-SI intermediate is thought to precede thiouracil inhibition through mixed disulfide formation [7,8]. 

Tributylstannyl ethers are covalent derivatives with the nucleophilic properties of soft metal alkoxides they react with benzyl bromide on heating in non-polar solvents in the presence of tetraalkylammonium bromides or iodides to give the O-benzyl ether [Scheme 4.166]. 309 310 The moisture sensitive tributylstannyl ethers are formed by reaction of an alcohol with bis(tributyltin) oxide (bp... 

Factors analogous to those which limit the stability of perfluoroalkylboron compounds are even more dominant in the case of aluminium. Indeed, no perfluoroalkyl derivatives of tri-covalent aluminium have been obtained, although salts of the type Li[( -C3F7)2All2] are produced [83] in reactions of perfluoroalkyl iodides with LiAlH4. 

Thallium(I) halides, TlX, are stable compounds which in some ways resemble Ag(I) halides. Thallium(I) fluoride is very soluble in water, but TlCl, TlBr and Til are sparingly soluble the trend in solubilities can be traced to increased covalent contributions in the ionic lattices for the larger halides, a situation that parallels the trend for the Ag(I) halides (see Section 5.15). In the solid state, TIF has a distorted NaCl lattice, while TlCl and TlBr adopt CsCl structures. Thallium(I) iodide is dimorphic below 443 K, the yellow form adopts a lattice derived from an NaCl structure in which neighbouring layers are slipped with respect to each other and, above 443 K, the red form crystallizes with a CsCl lattice. Under high pressures, TlCl, TlBr and TU become metallic in character. 

This structure can also be derived from the hep structure by replacing the metal atoms in the unit cell by I atoms and by adding Cd atoms at the corners of the unit cell. Thus, the 1 ions sit in an hep arrangement with the Cd ions between them. The more covalent AB2 phases tend to form the Cdl2 structure. Thus, the larger polarizable iodides and bromides form this structure with highly polarizing cations, while the fluorides favor the rutile structure. 

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