Reactive Forms

Amorphous carbon, having a far greater effective surface area than either diamond or graphite, is the most reactive form of carbon. It reacts with both hot concentrated sulphuric and hot concentrated nitric acids in the absence of additional oxidising agents but is not attacked by hydrochloric acid. 

A shippable but somewhat less reactive form of diketene is its acetone adduct, 2,2,6-trimethyl-4JT-l,3-dioxin-4-one (15) (103,104). Thermolysis of this safer to handle compound provides acetylketene, a reactive intermediate that can be used for acetoacetylation and cycloaddition reactions. The diketene—acetone adduct as weH as / fZ-butylaceto acetate [1694-31 -1] (also used for aceto acetylations by the trans aceto acetylation reaction) (130), are offered commercially. 

High Surface Sodium. Liquid sodium readily wets many soHd surfaces. This property may be used to provide a highly reactive form of sodium without contamination by hydrocarbons. Powdered soHds having a high surface area per unit volume, eg, completely dehydrated activated alumina powder, provide a suitable base for high surface sodium. Other powders, eg, sodium chloride, hydride, monoxide, or carbonate, can also be used. 

Silica. The siUca content of natural waters is usually 10 to (5 x lO " ) M. Its presence is considered undesirable for some industrial purposes because of the formation of siUca and siUcate scales. The heteropoly-blue method is used for the measurement of siUca. The sample reacts with ammonium molybdate at pH 1.2, and oxaUc acid is added to reduce any molybdophosphoric acid produced. The yellow molybdosiUcic acid is then reduced with l-amino-2-naphthol-4-sulfoiiic acid and sodium sulfite to heteropoly blue. Color, turbidity, sulfide, and large amounts of iron are possible interferences. A digestion step involving NaHCO can be used to convert any molybdate-unreactive siUca to the reactive form. SiUca can also be deterrnined by atomic... 

These constraints cause different reactive groups to be developed for dyeing wool. They fall into two groups novel reactive groups with more than one type of group in each molecule in order to increase the amount of dye fixed and minimise the wash-off problem, eg, Lanasol Dyes by CIBA-GEIGY, and those based on ceUulosic reactive dyes, but where the dye is appHed to the wool in a nonreactive form. On boiling, this form slowly converts to the reactive form that fixes rapidly in situ eg, the Hostalan Dyes by Hoechst, introduced in 1971 were precursors of vinyl sulfone dyes. 

For Reactive Blue 19 [2580-78-1] (Cl 61200 its reactive form, the vinyl sulfone (5), was found in the effluents of a textile mill and a wastewater treatment plant. The hydrolysis product of the vinyl sulfone was detected only in the effluent of the textile mill (257). 

The localization energies for electrophilic substitution in benzimidazole predict that all three reactive forms should undergo substitution in the 4-position. This does not explain the formation of the 5-nitro compound or that of the 2-deutero compound. It is doubtful whether any electrophilic substitution occurs preferentially in the 4-position. 

The protonated imine is the dominant reactive form. Although the protonated aldehyde is more reactive, its concentration is very low because it is much less basic than the imine or the reactant hydroxylamine. On the other hand, even though the aldehyde may be present in a greater concentration than the protonated imine, its reactivity is sufficiently less that the iminium ion is the major reactant. ... 

OZONE A reactive form of oxygen the molecule of which contains 3 atoms of oxygen. In the ozone layer it protects the earth by filtering out ultra-violet rays. At ground level, as a constituent of photochemical smog, it is an imtant and can cause breathing difficulties. 

A particularly reactive form of nitrogen can be obtained by passing an electric discharge through N2(g) at a pressure of 0.1-2 mmHg. Atomic... 

For a mobile equilibrium, proi ided sufficient time is available for the mutual transformation between the two isomers, both forms can produce derivatives that could only be derived from one of them. This holds even if the reactive form is present in very small concentration because of the constant reattainment of equilibrium the whole mass will finally react. However, if a reaction that could be given only by one particular form does not occur, the absence of this isomer at least is demonstrated. 

Dimethylquinoxaline (303) has been reported to undergo a Diels-Alder reaction with maleic anhydride to give 304, 305 having been postulated to be the reactive form. However, attempted confirmation of this unexpected result has shown that 304 is not the correct structure of the reaction product. " In 1931, other chemical evidence was advanced in support of structure 305,but it would no longer be considered valid. 

Ozone. 03, mw 48.00, triatomic oxygen, the most reactive form of oxygen a bluish, expl gas or blue liq. It is found in the atm in varying proportions (about 0.05 ppm at sea level), since it is produced continuously in the outer layers of the atm by the action of solar UV radiation on the oxygen of the air. In the laboratory ozone is prepd by passing... 

The equations describing the possible nonreactive and/or reactive forms of energy transfer at the gas-solid interface ... 

As described more fully in Sections 3.1-3.3, with increasing pH the reactive forms of the diazotizing agent are converted into ineffective ones, namely free nitrous acid, HN02, and the nitrite ion, N02. From the discussion of the mechanism of diazotization it will also become apparent why the reaction proceeds better, that is faster, in dilute hydrochloric than in dilute sulfuric acid. With very slow diazotizations for instance, because of high dilution as in nitrite titrations, the use... 

We now know that Hammett s explanation is correct in all its aspects. This result is especially noteworthy because Hammett arrived at his conclusions not through extensive experimentation in his laboratory, but by the consistent application of the newer theories of organic chemistry to kinetic results already published by others. This is not the only example of such anticipation of views (now generally accepted) to be found in Hammett s book, and it is worth remembering that Hammett expressly postulates the diazonium ion as the reactive form of the diazo compound in coupling, in contrast to the then current opinion that the diazohydroxide was the effective species. 

A minor component, if truly minute, can be discounted as the reactive form. To continue with this example, were KCrQ very, very small, then the bimolecular rate constant would need to be impossibly large to compensate. The maximum rate constant of a bimolecular reaction is limited by the encounter frequency of the solutes. In water at 298 K, the limit is 1010 L mol-1 s"1, the diffusion-controlled limit. This value is derived in Section 9.2. For our immediate purposes, we note that one can discount any proposed bimolecular step with a rate constant that would exceed the diffusion-controlled limit. 

Thus, we have in Eqs. (6-128)—(6-130) a situation where a prior equilibrium converts a significant fraction of the reactant to a new form. Here it is more reactive than the original, but in another case it could be a dead end. [The reader should reconsider reaction (3-23) in light of this treatment.] On the other hand, the same kinetic form represents the scheme in Eqs. (6-126)—(6-127), where only a minute fraction of the starting complex is present in a highly reactive form. 

Aluminum oxide, A1203, is known almost universally as alumina. It exists with a variety of crystal structures, many of which form important ceramic materials (see Section 14.22). As a-alumina, it is the very hard, stable, crystalline substance corundum impure microcrystalline corundum is the purple-black abrasive known as emery. Some impure forms of alumina are beautiful, rare, and highly prized (Fig. 14.25). A less dense and more reactive form of the oxide is y-alumina. This form absorbs water and is used as the stationary phase in chromatography. 

In order to give useful information about an enzyme, a conformationally restricted active-site-directed analog inhibitor need not bind to the enzyme irreversibly. In a study of the enzyme fructose 1,6-diphosphatase from rabbit liver, Benkovic et al, have investigated the question of the reactive form of the fructose 1,6-diphosphate in the enzymatic process (104,105). Three likely forms are shown in structures 50, 51 and 52. 

It transpires that Cr207 plays a minor part in oxidation mechanisms and that H2Cr04 is the reactive form of Cr(VI) and accordingly most reactions are acid-catalysed. 

The second term dominates and is characterised by p = +1.30 (using a-meta constants), E = 10.8 kcal.mole , dS = —22.8 eu and k jko > 1-8. experiments show the major source of oxygen in the acid produced is the solvent, which suggests the hydrate anion is the reactive form, viz. 

While the action of various accelerators is not altogether clear, many of them (tetramethylthiuram disulfide, for example) may decompose with the release of radicals which accelerate step (i). Others (e.g., the diphenylguanidine type) appear to promote the normal reactions of sulfur, perhaps by catalyzing the conversion of cyclic sulfur (Ss) to a more soluble and reactive form.2 >27 efficiency of sulfur utiliza-... 

The low permittivity of these liquids compared with water inhibits dissociation of the acids so that cement formation demands much more reactive basic oxides. Oxides and hydroxides that are capable of cement formation are ZnO, CuO, MgO, CaO, Ca(OH)2, BaO, CdO, HgO, PbO and BiaOj (Brauer, White Moshonas, 1958 Nielsen, 1963). In practice these are confined to two calcium hydroxide and special reactive forms of zinc oxide. 

Another particularly reactive form of titanium is generated by including 0.25 equivalent of I2. This reagent permits low-temperature reductive deoxygenation to alkenes.241... 

Other reactive forms of nickel including nickel boride283 and nickel alkoxide complexes284 can also be used for desulfurization. Tri-n-butyltin hydride is an alternative reagent for desulfurization.285... 

Carbon tetrafluoride and all polyfluorinated hydrocarbons are very stable and inert molecules. This inertness can be attributed to the strength of the CF bonds and the close packing of the inert fluoride-like ligands around the carbon atom, which effectively prevent attack by a nucleophile on the carbon atom. In contrast, even though BF3 has stronger bonds than CF4, it is more reactive, forming adducts such as BF3-NH3 because the boron atom is only three-coordinated and there is space around it for an additional ligand. 

---