Interface water-phenol

Early in the 20th century the first electrochemical study at an ITIES (interface of two immiscible electrolyte solutions) on ion transfer across a water-phenol interface was reported by pioneers Nernst and Riesenfeld [1], However, it was about 70 years before the start of the many interesting electrochemical studies of ITIESs, which successfully continue today. 

SSHG may also be used as a tool to study adsorption processes. From Eq. (5), we note that the susceptibihty tensor is proportional to the number of molecules per unit surface. A simple analysis of the SH intensity as a function of the bulk solution concentration thus leads to adsorption isotherms. This has been performed at the air/water interface for phenol or SO2, for example [31,32], but the SH intensity may be monitored as a function of the applied potential across the interface. These measurements have been performed for both ONS and DBA, yielding the surface coverage as a function of potential. In the case of ONS, the increase in the surface coverage has also been correlated with the drop in the surface tension [28]. An expression for the surface coverage may be found using the Frumkin isotherm. It yields ... 

The first major observation of ionic current across the interface between two immiscible solutions was reported by Nernst and Riesenfeld," who in 1902, studied the transport of colored electrolytes across water-phenol-water concentration cells. However, it was only in 1974 that Gavach et al applied what we could call... 

It has been proposed that the a-tocopheroxyl radical can be recycled back to tocopherol by ascorbate producing the ascorbyl radical (Packer etal., 1979 Scarpa et al., 1984). The location of a-tocopherol, with its phytyl tail in the membrane parallel to the fatty acyl chains of the phospholipids and its phenolic hydroxyl group at the memisrane-water interface near the polar headgroups of the phospholipid bilayer, enables ascorbate to donate hydrogen atoms to the tocopheroxyl radical. The suitability for ascorbate and tocopherol as chain-breaking antioxidants is exemplified (Buettner,... 

Phenols are weak acids and hence can be present in the forms of neutral molecule (AH) and univalent anion (A ). We consider the transfer of acid across the interface between an organic solvent (O) and water (W) in the forms of a neutral molecule and a univalent ion, respectively. 

Pohorille, A. Benjamin, I., Molecular dynamics of phenol at the liquid-vapor interface of water, J. Chem. Phys. 1991, 94, 5599-5605. 

Puig et al. [450] determined ng/1 levels of priority methyl-, nitro-, and chloro-phenols in river water samples by an automated on-line SPE technique, followed by liquid chromatography-mass spectrometry (LC-MS) using atmospheric pressure chemical ionization (APCI) and ion spray interfaces. 

Several studies have shown that sorption of various organic compounds on solid phases could be depicted as an accumulation at hydrophobic sites at the OM/water interface in a way similar to surface active agents. In addition Hansch s constants [19,199-201], derived from the partition distribution between 1-octanol and water, expressed this behavior better than other parameters. Excellent linear correlations between Koc and Kow were found for a variety of nonpolar organic compounds, including various pesticides, phenols, PCBs, PAHs, and halogenated alkenes and benzenes, and various soils and sediments that were investigated for sorption [19,76,80,199-201]. 

General. Toluene, chlorobenzene, and o-dichlorobenzene were distilled from calcium hydride prior to use. 4-Dimethylaminopyridine (Aldrich Chemical Co) was recrystalled (EtOAc), and the other 4-dialkylaminopyridines were distilled prior to use. PEG S, PEGM s, PVP s, and crown ethers were obtained from Aldrich Chemical Co., and were used without purification. BuJ r and BU. PBr were recrystallized (toluene). A Varian 3700 VrC interfaced with a Spectraphysics SP-4000 data system was used for VPC analyses. A Dupont Instruments Model 850 HPLC (also interfaced with the SP-4000) was used for LC analyses. All products of nucleophilic aromatic substitution were identified by comparison to authentic material prepared from reaction in DMF or DMAc. Alkali phenolates or thiol ates were pre-formed via reaction of aqueous NaOH or KOH and the requisite phenol or thiophenol in water under nitrogen, followed by azeotropic removal of water with toluene. The salts were transferred to jars under nitrogen, and were dried at 120 under vacuum for 20 hr, and were stored and handled in a nitrogen dry box. 

The occurrence of an optimum frequency at 200 kHz was explained through a two step reaction pathway. In the first step water sonolysis produces radicals within the bubble. In step two the radicals must migrate to the bubble interface or into the bulk aqueous medium to form peroxide or react with the phenolic substrate. The authors suggest that the lower frequencies are the most efficient for the decomposition of molecules inside the bubble but a proportion of the radicals recombine inside the bubble at high temperature to form water thereby reducing the overall yield of H2O2 (Eqs.4.1 and 4.2). 

Fig. 9.1 Spray column for Hquid-liquid extraction. The water phase flows from top to bottom, the toluene as the lighter phase from bottom to top. If the column is always filled with water at the marked height, the toluene breaks into drops at the feeding point. When the drops have reached the water interface, they coalesce and form a continuous toluene phase. The phenol transfers from the water phase to the toluene phase.

Silica gel is a polar material. The presence of silanol groups is responsible for the acidic catalytic effect of this material (the pK of Si OH is comparable to that of phenol). The mode of action of silica gel is based on adsorption (Fig. 3.9), a phenomenon that leads to the accumulation of a compound at the interface between the stationary and mobile phases. In the simplest case, a monolayer is formed (known as a Langmuir isotherm) but there is also some attraction and interaction between molecules that are already adsorbed and those still in solution. This contributes to the asymmetry of the elution profile. Although it demonstrates good resolution and a high adsorption capacity, bare silica gel is seldom used for analytical purposes. For most applications, it must be deactivated by partial rehydration (in 3-8% water). 

Figure 13. Comparison of UV and MS chromatograms using a 1.0-mm i.d. column packed with a 5-pm diameter Supelcosil C-18. LC-MS interface used aerosol spray deposition on a moving belt. Peaks correspond from left to right to 0.2 pg each of resorcinol, 1,5-dihydroxynaphthol, and 2-methyl-phenol. Conditions 41% acetonitrile and 59% water (v/v) with 0.1% trifluoro-acetic acid at a flow rate of 40 pL/min. A, UV trace at 280 nm, 0.015 AUFS B, MS trace, selected ion chromatogram. (Reproduced from reference 54.

M. D. Alexander, "Reactions of the Alkali Metals with Water A Novel Demonstration/ J. Chem. Educ., Vol. 69,1992,418. The reaction of sodium metal with water to produce an aqueous solution of sodium hydroxide and hydrogen gas is performed at the interface between paint thinner and the more dense water. Periodically, bubbles of hydrogen gas carry the sodium metal into the organic layer, temporarily stopping the reaction. The presence of the aqueous layer is shown by a phenol-phthalein indicator color change. 

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