Charge Transfer Complex Role in the Formation of Chlorobenzene in the γ‐Irradiated Carbon Tetrachloride‐Benzene System

The formation of carbon tetrachloride‐benzene charge transfer complex was confirmed by UV and NMR spectrometric studies. A change in UV spectrum of benzene is observed upon addition of carbon tetrachloride. Whereas the appearance of new bands supports the formation of charge transfer complex. NMR study shows that, chemical shift of benzene pmr signal depends on the CCl₄‐C₆H₆ molar ratio. This observation is another criterion for the formation of benzene‐carbon tetrachloride charge transfer complex. Job's Continuous Variation method indicates that a 2:1 CCl₄‐C₆H₆ charge transfer complex (2:1 CTC) is formed. The association constants (K_2:1) of (2:1 CTC) was found to be 0.0197 M^?2. The maximum concentration of (2:1 CTC) was found to be in samples with 2:1 CCl₄‐C₆H₆ molar ratio (33% benzene mole). On the other hand the maximum yield of chlorobenzene was obtained, also, upon radiolysis of CCl₄‐C₆H₆ samples at a 2:1 molar ratio (33% benzene mole). Therefore, it could be concluded that (2:1 CTC) participates in the formation of chlorobenzene upon radiolysis of the benzene‐carbon tetrachloride system. This conclusion was supported by the dependence of the chlorobenzene yield of a γ‐irradiated carbon tetrachloride‐benzene system (2:1 molar ratio) on irradiation time according to a third order kinetic equation with a very good linearity (R² = 0.9977). Accordingly, the rate constant for the chlorobenzene formation under this condition was found to be ≈ 5.5 × 10^?7 L².mol^?2.h^?1. We propose a radiation chemical mechanism in which the 2:1 CTC plays a role in the formation of chlorobenzene.     

Signal uncertainty and psychometric functions in profile analysis

Experiment 1 was conducted to compare the effects of signal frequency uncertainty on the detection of a change in spectral shape and on the detection of a tone in wideband noise. Results indicate that for both tasks the uncertainty effect was small, being on average about 3 dB. In a second experiment, psychometric functions were measured for the detection of changes in the spectral shape of multicomponent complexes. Psychometric functions for profile tasks have a 25-dB range and are similar to those measured for the detection of an increment in the level of a single sinusoid. These psychometric functions are different from those found when detecting a signal in noise, which typically have a 10-dB range. Three equations for the shape of the psychometric functions were compared. The difference in the resulting fits was small, thus preventing an unambiguous choice of functional form.     

Mechanism for defoaming by oils and calcium soap in aqueous systems

The effect of oils, hardness, and calcium soap on foam stability of aqueous solutions of commercial surfactants was investigated. For conditions where negligible calcium soap was formed, stability of foams made with 0.1 wt% solutions of a seven-EO alcohol ethoxylate containing dispersed drops of n-hexadecane, triolein, or mixtures of these oils with small amounts of oleic acid could be understood in terms of entry, spreading, and bridging coefficients, i.e., ESB analysis. However, foams made from solutions containing 0.01 wt% of three-EO alcohol ethoxysulfate sodium salt and the same dispersed oils were frequently more stable than expected based on ESB analysis, reflecting that repulsion due to overlap of electrical double layers in the asymmetric oil-water-air film made oil entry into the air-water interface more difficult than the theory predicts. When calcium soap was formed in situ by the reaction of fatty acids in the oil with calcium, solid soap particles were observed at the surfaces of the oil drops. The combination of oil and calcium soap produced a synergistic effect facilitating the well-known bridging instability of foam films or Plateau borders and producing a substantial defoaming effect. A possible mechanism of instability involving increases in disjoining pressure at locations where small soap particles approach the air-water interface is discussed. For both surfactants with the triolein-oleic acid mixtures, calculated entry and bridging coefficients for conditions when calcium soap formed were positive shortly after foam generation but negative at equilibrium. These results are consistent with the experimental observation that most defoaming action occurred shortly after foam generation rather than at later times.