Halogenated aliphatic substrates

Tables IV through IX summarize the data that are currently available on the rates of bimolecular substitution and dehydrohalogenation reactions between sulfur nucleophiles and halogenated aliphatic substrates in aqueous solution (i.e., either measured in water or extrapolated to water from a non-aqueous or partially aqueous solvent). The sulfrir nucleophiles considered in these tables are HS-, S2-, S42-, S52- (Table IV), S2032 (Tables V and VIII), SO32-, HSO3 (Table VI), thiolate anions (Tables VII, VIII, and IX), thiols, thioethers, and thioadds (Table VII).

Table Vm. Competition Between Dehydrohalogenation and Substitution Pathways for Reactions Between Halogenated Aliphatic Substrates and Sulfur Nucleophiles (Rate Constants Expressed in Units of M V1.)...

Table IX. Second-order Rate Constants (M V1) for Dehydrohalogenation and Substitution Reactions of Halogenated Aliphatic Substrates with Sulfur Nucleophiles (ks>E and kS(SN> Respectively), Compared to the Corresponding Rate Constants for H20 (kn20,E d kH20,SN> Respectively)...

The addition of halogenated aliphatics to carbon-carbon double bonds is the most useful type of carbon-carbon bond forming synthetic method for highly halogenated substrates Numerous synthetic procedures have been developed for these types of reactions, particularly for the addition of perfluoroalkyl iodides to alkenes using thermal or photolytic initiators of free radical reactions such as organic peroxides and azo compounds [/]... 

Naphthalene is toxic to the lung and these metabolic pathways are important in this toxicity (see below). There are many types of substrates for glutathione conjugation including aromatic, aliphatic, heterocyclic and alicyclic epoxides, halogenated aliphatic and aromatic... 

Bailey, W.F., Metal-Halogen Exchange (M <-> X) Involving Aliphatic Substrates Using Alkyllithiums, FMC Lithium Link, Spring 1994. 

Table 2.8 compares hydrolysis half-lives with half-lives for reaction with sulfur-based nucleophiles for several halogenated aliphatics. These data show that the environmental half-lives for substrates such as 1-bromohexane and 1,2-dibromoethane can be substantially reduced in the presence of HS and polysulfides. Enhanced degradation of 2-bromopropane and 1,1,1-trichloroethane, as well as chloroform and carbon tetrachloride (results not shown) was not observed, suggesting that steric hindrance significantly impedes reaction with the sulfur based nucleophiles (Haag and Mill, 1988a). 

The first group is represented by the alcohol dehydrogenases (ADHs) that can be used for the synthesis of chiral alcohols. There are several commercially available ADHs isolated from yeast or horse liver (NADH dependent), or T. brockii (NADPH-dependent) that can be used for different types of substrates. Lactobacillus kefir produces an (/ )-ADH that accepts a broad variety of ketone substrates (ring halogenated, aliphatic, open-chain ketones, 2- and 3-ketoesters, and cyclic ketones), producing, for example, enantiomerically pure I -l-(2-pyridyl ethanol), / -(l-trimerhylsylyl)-l-butyn-3-ol or 5-phenylbutan-2-ol (Hummel 1990). 

Halogenated aliphatic transformations can be complicated by substrate interactions and substrate toxicity. When competitive inhibition occurs, or in equations 7 or 8 can be modified, such that ... 

Transformation of halogenated aliphatics has been shown to take place at the FeS surface and to follow pseudo-first-order kinetics under conditions where reactive surface sites are present far in excess of the organic substrate 14), The prime notation ( ) on certain rate constants discussed below indicates correction to account for partitioning of reactants between the sample aqueous and vapor phases (75, 43, 54, 55). These corrected rate constants represent those that would be observed in a headspace-free system. 

The third composition in Table IV seems to be related to the aromatic sulfonate/polycarbonate technology just discussed with some modifications being necessary in order to compensate for the aliphatic nature of the polypropylene (17. 181 substrate. In this case the aromatic sulfonate is replaced with a metal salt (preferably magnesium stearate). A silicone oil and or gum has been added to enhance the intumescent character and a small amount of inert filler and decabromodiphenyl oxide is included probably to improve the molding characteristics of the total composition. Fire retardant compositions with a good surface char can be obtained at total loadings only about half that required for the halogen/antimony oxide composition. 

In addition to carbonyl substrates, imines have been used extensively with phosphorus-halogen reagents for the preparation of a variety of phosphonates and phosphinates. Combined in a reaction medium, secondary amines react with formaldehyde and phosphorus trichloride134 135 or alkyldichlorophosphines136 to produce N,N-disubstituted aminomethylphosphonates or -phosphinates. These reactions occur under mild conditions with good yield. Similarly, aliphatic carboxylic amides react with aldehydes to generate imines, which can be used in situ with diphenylchlorophosphine to produce... 

Substitution of scheme a forms a well-documented class of reactions (see Costentin et al. 1999,2000, Costentin and Saveant 2000, Corsico and Rossi 2000, 2002, 2004, Adcock et al. 2001, Vanelle and Crozet 2002, Medebielle et al. 2002, Galli and Rappoport 2003, Rossi et al. 2003, Vanelle et al. 2004, and Bnden et al. 2005 and references therein). In contrast to conventional nucleophilic substitution, the nncleophile, Nu-, reacts not with the substrate, RX, to give a product but with the radical R. The latter emerges as a result of R-X bond cleavage. Snbstitnent X is very often a halogen atom, bnt other leaving groups can also be used (see section 7.8.1). In the majority of aromatic Sr I reactions, the anion-radical RX- (R=Ar) is the observable intermediate. It is depicted in scheme a. With aliphatic snbstrates, snbstitntion takes place rather than 8 2 or S l substitutions, and the concerted mechanism depicted in scheme b is feasible. 

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