Nitrogen water versus

Fig. 9—Contact angle (to water) versus nitrogen content, from Refs. [81-83,85].

As an example of this nonlinear character we may consider two pairs of compounds, naphthalene versus quinoline and indole versus benzimidazole (Fig. 11.5). In both pairs of compounds the second differs from the first by a mutahon of an aromahc -CH group to an aromahc nitrogen, which introduces a strong H-bond acceptor into the molecule. In quinoline, which has no H-bond donor, the acceptor has no favorable interaction partner in the supercooled liquid or crystalline state, while it can make strong H-bonds with the solvent in water. Therefore, log Sw of quinoline is about 2 log units higher [35, 36] than that of naphthalene, i.e. the introduction of the H-bond acceptor strongly increases solubility in this... 

El-Brashy [51] reported the determination of primaquine and other antimalarials via charge-transfer complexes. Powdered sample of primaquine phosphate was dissolved in water and the solution was adjusted to an alkaline pH with 6 M ammonia and extracted with chloroform. The extract was dried with anhydrous sodium sulfate, filtered, and evaporated to dryness under nitrogen and the residue was dissolved in acetonitrile. Portions of the solution were mixed with 0.2% 7,7,8,8-tetracyanoquinodimethane, diluted with acetonitrile, and set aside for 10 min before the absorbance was measured at 845 nm versus a reagent blank. The calibration graphs were linear from 0.4 to 3 pg/mL and recovery was 98%. 

Fig. 34. A graph of versus time for a droplet of SDS in water evaporating in dry nitrogen...

An attempt to combine electrochemical and micellar-catalytic methods is interesting from the point of view of the mechanism of anode nitration of 1,4-dimethoxybenzene with sodinm nitrite (Laurent et al. 1984). The reaction was performed in a mixture of water in the presence of 2% surface-active compounds of cationic, anionic, or neutral nature. It was established that 1,4-dimethoxy-2-nitrobenzene (the product) was formed only in the region of potentials corresponding to simultaneous electrooxidation of the substrate to the cation-radical and the nitrite ion to the nitrogen dioxide radical (1.5 V versus saturated calomel electrode). At potentials of oxidation of the sole nitrite ion (0.8 V), no nitration was observed. Consequently, radical substitution in the neutral substrate does not take place. Two feasible mechanisms remain for addition to the cation-radical form, as follows ... 

Therefore, key advantages of the QCM method are that much smaller samples (one drop of water) and hence shorter times (15 min/temperature step versus several hours for conventional methods) are required for these hydrate phase equilibria measurements. The authors applied this system to measure dissociation temperatures of gas hydrates, such as methane, nitrogen, and oxygen hydrates. 

First, the effects of gas and liquid flows, co-current versus countercurrent operation, pressure and temperature were checked. As expected, based on the influence of these parameters on the vapor pressure or the vapor-liquid equilibrium (VLE), the fraction of water stripped by the nitrogen increases with increasing gas flows, decreasing liquid flows, lower pressures and higher temperatures. Countercurrent operation is more efficient than co-current operation, because the liquid phase at the inlet was already enriched with the compound which was to be separated. 

Fig. 8.28. Conversion of octanol and outlet water contents in countercurrent (A, dotted line) versus co-current (A, solid line) operation with liquid recycle (1 m of DX packings, 5 cm diameter, 160 °C, 5 barabs, liquid flow 25 kg h-, nitrogen flow 500 NmJ h 1).

By contrast, in the case of water solutions of a poly(4-vinylpyridine) partly quatemi-zed with benzylchloride, it was found that by plotting risp/c versus the [Cu]/[N] ratio (where N refers to unquatemized nitrogens), a constant value is reached at a ratio = 0.5, above which no viscosity changes are observed by further additions of Cu2+ 84>. These data apparently suggest that the Cu2+ ions coordinate only two pyridine groups. 

An early normalizing procedure, proposed by Kiselev (1957) to compare adsorption isotherms of hydrocarbons, water vapour, etc. on a series of different adsorbents, was simply to plot the surface excess concentration F (=n/A), obtained from a knowledge of the BET-nitrogen surface area, A (BET), versus p/p°. It is also possible to plot, instead of f, the reduced adsorption , n/nm, which still relies on the BET method to determine the monolayer capacity nm but does not require knowledge of the molecular cross-sectional area a. 

Instead of water or HF, one may pair HCOOH with a nitrogen base. The data on the right side of Table 2.37 indicate that the greater basicity of methylamine versus water leads to a stronger H-bond at either SCF or MP2 level of theory. Note, however, that the internuclear distances are comparable. 

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