Haloacidity

SelenazoIidin-2-4-ciiones-2-alkylidene (or arylidene) hydrazones (III) are simply prepared by base-catalysed condensation of a-haloacids on selenosemicarbazones of acetone or benzaldehvdc (Table X-21) (71). 

The action of thioamides (1) on a-haloacids or esters gives the same products (230) in moderate yields (20 to 30%) through intermediates analogous to 229. In 230, Ri is phenyl, benzyl, or -pyridyl, Rj is methyl or hydrogen (287, 324). 

This is an emerging field that has not reached its final position yet. Members of the novel class of FCP, SCP, and HAD phosphatases require Mg2+ for catalysis. An aspartate residue within the active site signature motif (DxDx(T/V)) is essential to form an acyl-phosphate intermediate. Many members of the the HAD (haloacid dehalogenase) superfamily have phosphoesterase activity [3]. Some of those protein phosphatases act on... 

The recommended method of trichloroethylene disposal is incineration after mixing with a combustible fuel (Sittig 1985). Care should be taken to carry out combustion to completion in order to prevent the formation of phosgene (Sjoberg 1952). Other toxic byproducts of incomplete combustion include polycyclic aromatic hydrocarbons and perchloroaromatics (Blankenship et al. 1994 Mulholland et al. 1992). An acid scrubber also must be used to remove the haloacids produced. 

Li Y-F, Y Hata, T Fujii, T Hisano, M Nishihara, T Kurihara, N Esaki (1998) Crystal structures of reaction intermediates of L-2-haloacid dehalogenase and implications for the reaction mechanism. J Biol Chem 273 15035-15044. 

Nardi-Del V T, C Kutihara, C Park, N Esaki, K Soda (1997) Bacterial DL-2-haloacid dehalogenase from Pseudomonas sp. strain 113 gene cloning and structural comparison with D- and L-2-haloacid dehalogenases. J Bacterial 179 4232-4238. 

The latest review about the free haloacids and their formation has been given by Grume (i) in 1963 and an extensive treatment of the fluoro derivatives is found in the work of Schmutzler (2). The only halophosphoric acids prepared up to now are HPO2F2, HjPOjF, HPO2CI2 and the mixed fluoro haloacids F1P02FX(X = Cl, Br), the most important properties of which are listed in Table 1. 

Ketene acetal synthesis by /1-elimination of haloacids from halogenated acetals under well controlled conditions using thermal activation (A), ultrasound (US) or micro-wave irradiation [92] (MW) has been described. From a mechanistic point of view, as the TS is more charge delocalized than the GS and the polarity is enhanced during the course of the reaction, a favorable microwave effect can therefore be observed (Eqs. (37) and (38) and Scheme 3.13). 

Haloacid dehalogenase-type hydrolase domain in P-type ATPase (Aravind et at, 1998a)... 

Aravind, L., Galperin, M. Y., and Koonin, E. V. (1998a). The catalytic domain of the P-type ATPase has the haloacid dehalogenase fold. Trends Biochem. Sd. 23, 127—129. 

Hisano, T., Hata, Y., Fujii, T., Liu, J. Q., Kurihara, T., Esaki, N., and Soda, K. (1996). Crystal structure of L-2-haloacid dehalogenase from Pseudomonas sp. YL. An alpha/ beta hydrolase structure that is different from the alpha/beta hydrolase fold./ Biol. Chem. 271, 20322-20330. 

Amino acid sequence relationships have suggested a number of HYL families based on percent identity, enzymes with >40% identity belonging to the same family [48]. Families so identified include the mammalian microsomal EH (HYL1), the mammalian cytosolic EH (HYL2), the plant cytosolic EH (HYL3), and bacterial C-X bond hydrolases (haloacid dehydrogenases, HAD, and haloalkane dehalogenases, HLD). 

Fischer polypeptide synthesis org chem A synthesis of peptides in which a-amino acids or those peptides with a free amino group react with acid halides of a-haloacids, followed by amination with ammonia. fish-ar pal-e pep,tTd. sin tha sas ) Fischer projection orgchem) A method for representing the spatial arrangement of groups around chiral carbon atoms the four bonds to the chiral carbon are represented by a cross, with the assumption that the horizontal bonds project toward the viewer and the vertical bonds away from the viewer fish-ar pra.jek-shon) Fischer s salt See cobalt potassium nitrite. fish-3rz solt)... 

Other haloacids with longer carbon chains can also be formed in drinking water, mostly with chlorine and chloramine. One of these, 3,3-dichloropropenoic acid, was included as a priority DBF measured in the U.S. Nationwide Occurrence Smdy [11, 12]. It was found at a maximum of 4.7 pg/L and was present in nearly all of the water-treatment plants studied. The corresponding brominated acid, 3,3-dibromopropenoic acid, has also been identified as a DBF in drinking water, as well as several other three-, four-, and five-carbcai acids and diacids [10]. 

Thienyl tellurolates also remove several different substituents such as acetoxy, mesyloxy, phenylthio and 2-thienyltelluro groups, as well as effect the reductive dehalo-genation of bromoacetanilide, and of a-haloacids (such as a-bromophenylacetic acid, a-bromo-l-naphthylacetic acid and a-chlorodiphenylacetic acid). ... 

Disinfection by-products (DBPs) form an undesired species in the chlorine disinfection processes of waters (performed with chlorine, chlorine dioxide, and chloramines). The high priority DBPs include brominated, chlorinated, and iodinated species of halomethanes, brominated, and chlorinated forms of haloacetonitriles, haloketones, haloacids, and halonitromethanes, as well as analogues of 3-chloro-(4-dichloromethyl)-5-hydroxy-2(5//)-furanone. All the high priority DBPs included in the Nation-wide DBP occurrence study are listed in Table 18.1 together with other contaminants. 

With the exception of the a-acid, haloacids behave like hydroxyacids. Heating an a-halogenated acid with alcoholic KOH leads to a,)3-unsaturated acids when there is a /3 H in the molecule. 

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