Haloacetate complexes

A mechanistic picture which reconciles the experimental results is given in Scheme 24. It is assumed that both the heteroatom and the double bond of the allyl halide compete for an electrophilic metal carbene. Heteroatom attack yields a metalated ylide 129, which may go on to ylide 131 by demetalation and/or to allylmetal complex 130. Symmetry-allowed [2,3] rearrangement of 131 accounts for product 132, and metal elimination from 130 gives rise to products 132 and 133, corresponding to [2,3] and [1,2] rearrangement, respectively, as well as haloacetate (if R3 = CHc ). 

The electroreductive dehalogenation of a-haloacetic acids has been achieved with cobalamin [387]. The hydrophobic vitamin B12 Co complex immobilized on a glassy carbon electrode (252) may catalyze the electrochemical carbon-skeleton rearrangements of... 

Absorption spectra of lanthanides in the 4f-4f region were used in the studies on complexation by haloacetates in DMF, DMSO, methanol and in mixtures of the solvents. Octacoordination in the solvents was inferred. The band intensities in pure solvents were higher than in solvent mixtures. Haloacetate appears to form an inner sphere complex in organic solvents and an outer sphere complex in aqueous media [227-231],... 

More intense bands in the 4f-4f region were observed with lanthanide complexes of mandelic, salicylic, thiosalicylic, furoic, and thiophenic acids than the acetate and haloacetate analogues [235]. Both increase in intensity and nephelauxetic effect have been observed. It seems plausible that the aromatic groups in the hydroxy acids such as benzene, thiophene or furan contribute significantly to the intensity of the hypersensitive bands of the complexes. It appears that pH has an important role in determining the stoichiometry of the complex formed. Only ML species is formed up to pH 4 and both ML2+ and ML2 are formed at a pH of 6.0. 

The binuclear Ru" carboxylates [Ru2(OCOR)2( -OCOR)2(/i-OH2)(cod)2] (R = CF3, CC13, CH2C1) have been synthesized via protonation of [Ru( j3-C3H4R)2(cod)] with haloacetic acids. Some reactions of these complexes (R = CF3) are shown in Scheme 63.2101... 

The activity of these complexes is influenced markedly by the inductive effect of the acid. In 7r-allyl nickel haloacetates and complexes of 2,6,10-dodecatriene-l,12-diyl nickel with haloacetic acids the rate of polymerization increases with the increase in acid strength [233] (Fig. 19). 

M.L. Magnuson, C.A. Kelty, Microextraction of nine haloacetic acids in drinking water at microgram per liter levels with ESI-MS of stable association complexes. Anal. Chem., 72 (2000) 2308. 

As seen from the data, water disinfected with chlorine can have a complex mixture of lipophiles and hydrophiles. The lipophilic THMs can facilitate the absorption of the hydrophilic haloacetic acids, haloace-tonitriles and haloketones. An analogy between the reproductive toxicity and carcinogenicity of DBPs can be drawn. Though no single chlorinated byproduct studied appears to be carcinogenic, there is evidence from animal studies that DBP mixtures are carcinogenicJ4°l... 

Recent improvements in the standard synthetic procedure using haloacetates have featured the use of trialkyi phosphites and activated acetates in the presence of trimethylsilyl trifluoromethanesulfonate (TMSOTf) as activating reagent. " This reaction has proved to be of great value in constructing complex sugar phosphonates. For example, in the presence of TMSOTf, the Michaelis-Arbuzov reaction between protected ketose acetates and triethyl phosphite takes place in ( 1 FC F at room temperature to produce, after deprotection, the expected diethyl l-(methoxycarbonyl)alkyl-phosphonates in high yields. -" ... 

The thermodynamic data for complexation of trivalent lanthanide and actinide cations with halate and haloacetate anions are reported. These data are analyzed for estimates of the relative amounts of inner (contact) and outer (solvent separated) sphere complexation. The halate data reflected increasing inner sphere character as the halic acid pKa increased. Use of a Born-type equation with the haloacetic acid pKa values allowed estimation of the effective charge of the carboxylate group. These values were, in turn, used to calculate the inner sphere stability constants with the M(III) ions. This analysis indicates increasing the inner sphere complexation with increasing pKa but relatively constant outer sphere complexation. 

R. Suedee, T. Srichana, C. Sangpagai, C. Tunthana, and P. Vanichapichat. Development of trichloroacetic acid sensor based on molecularly imprinted polymer membrane for the screening of complex mixture of haloacetic acids in drinking water. Anal. Chim. Acta, 504 89-100,2004. S. Chellam and S.W. Krasner. Disinfection b) roducts relationships and speciation in chlorinated nanofiltered waters. Environ. Sci. Technol., 35 3988-3999, 2001. 

Derivatization processes The derivatization carried out before or during the extraction can increase the technique sensibility and selectivity. Different derivatization techniques are discussed in Refs. [46,164]. However, it should be used only when necessary, since SPME becomes more complex. Formaldehyde exposed to a previously doped fiber with the derivatizing agent o-(2,3,4,5,6-pentafluorobenzyljhydroxylamine is converted to the oxime derivative [176]. Haloacetic acids, which are disinfection by-products, have been successfully derivatized to ethyl/methyl esters [177,178]. 

Misra and Mehta (1991) described the pseudo-hypersensitivity in complexes of Nd " " with fluorinated nucleic bases and with fluorinated nucleosides. Pr complexes with haloacetate, fluorocarboxylate, / -diketonates, diols and orthophenanthroline derivatives have been considered by Misra and Mehta (1992). The fluorocarboxylates of Pr " tend to have lower intensities for the f-f transitions with the increased number of fluorine ligands. This is understandable in terms of the electron withdrawing capacity of different fluoroalkyl groups (lower covalency). The increase in intensity in the order butane-1,4-diol electron density of the multiple bond with some sort of linear combination of Pr 5d, 6s, 6p and 4f orbitals. Misra et al. (1994a) studied 27 Nd complexes with the identical chromophore NdOeN2 (CN 8) in methanol, DMF, acetonitrile, and isopropanol. 

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