Nonaqueous displacement

Methane sulfonic acid, trifluoroacetic acid, hydrogen iodide, and other Brmnsted acids can faciUtate 3 -acetoxy displacement (87,173). Displacement yields can also be enhanced by the addition of inorganic salts such as potassium thiocyanate and potassium iodide (174). Because initial displacement of the acetoxy by the added salt does not appear to occur, the role of these added salts is not clear. Under nonaqueous conditions, boron trifluoride complexes of ethers, alcohols, and acids also faciUtate displacement (87,175). 

The majority of trichloroethylene present on soil surfaces will volatilize to the atmosphere or leach into the subsurface. Once trichloroethylene leaches into the soil, it appears not to become chemically transformed or undergo covalent bonding with soil components. When trichloroethylene was absorbed onto kaolinite and bentonite, the nuclear magnetic resonance (NMR) spectra showed no evidence of chemical reactions (Jurkiewicz and Maciel 1995). Because trichloroethylene is a dense nonaqueous phase liquid, it can move through the imsaturated zone into the saturated zone where it can displace soil pore water (Wershaw et al. 1994). 

Methyl-4-phenyl-l,2,5-thiadiazole 1,1-dioxide 21 suffers proton abstraction in basic nonaqueous media to give a resonance stabilized anion 43, neutralization of which using anhydrous TFA gives the orange tautomer 4-methylene-3-phenyl-l,2,5-thiadiazoline 1,1-dioxide 44 (Scheme 3) <2001JP0217>. The tautomeric equilibrium is practically displaced toward 21 in acetonitrile and toward 44 in DMF. 

An oxoiron(V) species such as 6 derived from 1 and peroxides is accessible in nonaqueous media (51). The reaction of the tetraphenylphosphonium salt of la with 2 to 5 equivalents of m-chloroperbenzoic acid (mCPBA) at — 60°C in n-butyronitrile produces within about 10 s a bis-iron(IV)- i-oxo dimer followed by an as - yet uncharacterized EPR - silent iron(IV) intermediate. After 15 min, the deep green oxoiron(V) species 6 forms with distinct absorption maxima at 445 nm (e — 5400 Mr1 cm-1) and 630 nm (s — 4200 M-1 cm-1). At —60°C, 6 decays by 10% in 90 min, but it is stable for at least one month at 77 K. Selected spectral data for the oxoiron(V) species are shown in Fig. 13. DFT calculations favor the low-spin (S = 1/2) configuration of the ground state. The calculated Fe-0 bond length of 1.60 A is in excellent agreement with the EXAFS results. The Fe atom is displaced out of the 4-N plane by 0.5 A. 

HI = H2 + I2, the reactions of atoms with molecules and the displacement reactions between ions (such as I") and alkyl halides in nonaqueous solution. 

The ammines of cobalt(II) are much less stable than those of cobalt(III) thermal decomposition of [Co(NH3)6]Cl2 is characterized by reversible loss of ammonia, whereas that of [Co(NH3)6]Cl3 is not. In his classic dichotomy of complexes, Biltz regarded [Co (NH 3)3] Cl 2 as the prototype of the normal complex and [Co(NH3)6]Cl3 as that of the Werner or penetration complex. Hexaamminecobalt-(II) chloride has been prepared by the action of gaseous ammonia on anhydrous cobalt (II) chloride or by displacing water from cobalt(II) chloride 6-hydrate with gaseous ammonia. It may also be synthesized in nonaqueous solvents by passing dry ammonia through solutions of cobalt(II) chloride in ethanol, acetone, or methyl acetate. Syntheses in the presence of water include heating cobalt(II) chloride 6-hydrate in a sealed tube with aqueous ammonia and alcohol and the treatment of aqueous cobalt(II) chloride with aqueous ammonia followed by precipitation of the product with ethanol. The latter method is used in this synthesis. Inasmuch as the compound is readily oxidized by air, especially when wet, the synthesis should be performed in an inert atmosphere. 

A new area of research is the control of pH for nonaqueous enzyme reactions using organic pH buffers. - These buffer materials, which are soluble in nonaqueous media, strongly control the effect of pH on the reaction, and are able to override the pH memory of the enzyme before lyophilization or immobilization from an aqueous solution. - Typically, buffer salts employed are oppositely charged (e.g., / -COOH and / -COONa+, where R is hydrophobic in nature). It is the ratio of these two forms that controls the enzymatic rate. The buffers are believed to function by displacing hydrogen atoms of carboxylic acid groups on the surface of the enzyme, . - ... 

Electrolytic processes. Because of the positive oxidation potential for plutonium metal to displace hydrogen from aqueous solution, as shown in Table 9.7, nonaqueous solutions such as fused salts must be used for the electrodeposition of plutonium metal. One process involves the electrolysis of a molten equimolar mixture of LiCl-KCl containing 30 w/o FuQs. The melt is contained in a MgO-TiOi crucible heated to 950 C, with an anode through which chlorine gas can be introduced... 

Swain. C tj Brown. JFJr. Concerted displacement reactions. VII, The mechanism of acid-base catalysis in nonaqueous solvents. Journal of the American Chemical Society. 1952 74.2534-2537. 

---