Interfacial condensation system

Though modifications of dextran by condensation with organo-tin halides was effected utilizing a number of reaction systems, only the aqueous interfacial condensation system was chosen for an extensive evaluation of a number of reaction variables. 

In both cases yield was markedly dependent on the molar ratio of the reactants, reaching a maximum at a 3 2 ratio of dibutyltin dichloride to dextran-hexose units. This coincides with a 1 1 ratio of reactive Lewis acid to base groups (i.e., equal molar amounts of reactive groups present) and is consistent with results obtained from studying a number of other interfacial condensation systems. 

Another unique and specific feature of the interfacial reaction is the formation of aggregate of dye molecules, metal complexes, and other solvophobic molecules. As reported in many interfacial adsorption systems, the saturated interfacial concentration of usual molecules is of the order of 10 10mol/cm2, which can be attained even under an extremely low bulk phase concentration. This means that the liquid-liquid interface is ready to be saturated to form a two-dimensionally condensed state for the adsorbate. In solvent extraction process of metal ions, we used to find formation of some precipitate at the interface, which is called crud. The study of the interfacial aggregate is therefore important to know the real interfacial reaction as met in the industrial solvent extraction where rather concentrated solutes have to be treated. 

Interfacial polycondensations can also be carried out in vapor-liquid systems. Reaction takes place at the interface between an aqueous solution of a bifunctional active hydrogen compound and the vapor of diacid chloride. Interfacial condensation is commercially important in the synthesis of polycarbonates (1-52). Polymerizations based on diacids are always less expensive than those that use diacid chlorides. In the polycarbonate case, however, the parent reactant, carbonic acid, is not suitable and the derived acid chloride, phosgene (COCI2), must be used. 

The product was obtained in 83% yield by the reaction of acryoyl chloride and ethylenediamine by an interfacial condensation in a chloroform water system. Crystallization from acetone gave a 64% yield of colorless material (m.p. 142°-143.4 C). 

Carraher and Schroeder accomplished the synthesis of uranyl polyesters utilizing both the aqueous interfacial and aqueous solution condensation systems. The aqueous solution system is preferred because of the added effort and cost introduced when employing the interfacial system. Further the aqueous solution system is a more natural system in that a) water is often employed as a coolant in nuclear reactors, b) water is the chief agent for uranium,in the form of the water soluble uranyl ion,movement in mine dumps and uranium rich earth surfaces and, c) water is involved in many of the commercially utilized uranium recovery procedures. 

We recently reported the modification of dextran as a function of a number of reaction systems. Briefly modification was accomplished employing both aqueous and nonaqueous interfacial condensation techniques and utilizing the aqueous interfacial system except employing copper-diamine aqueous solutions. While some organic solution condensations permitted the successful condensation of organostannanes with dextran, the vast majority of attempted systems did not give the desired product. 

Modification of dextran through condensation with organo-stannane halides was studied as a function of a variety of low temperature condensation systems. Modification was general for the classical interfacial and bisethylenediamine copper-inter-... 

A similar pH profile study was made for the interfacial condensation of hydro-quinone and Cp2ZrCl2. There is an obvious difference in the pH-yield trend results in comparison to the aqueous solution systems. Medium product yields are achieved even at low pH s. In fact, better yields are achieved in the pH ranges where little or no diol is deprotonated in comparison to pH s where the hydroquinone is deproto-nated. The results are consistent with the diol being in its nondeprotonated form in interfacial systems. 

It is difficult to experimentally demonstrate that Et NHCl is acting as a PTA in these situations. Even so several observations can be made. First, the yield trends as a function diol are different for the two types of condensation systems, solution and interfacial, but are similar for each system regardless of whether the base is sodium hydroxide or triethylamine for M=Ti. This is consistent with reaction with the reactants being CP2M and RO for the aqueous solution systems but CP2MCI2 and ROH for the interfacial systems and for reaction occurring within the organic phase. For M=Zr the yield trends are similar... 

Polymerization may be carried out with monomer alone (bulk), in a solvent (solution), as an emulsion in water (emulsion), or as droplets, each one comprising an individual bulk polymerization, suspended in water (suspension). All four methods are commercially applied to radical-initiated chain polymers such as polystyrene. Most ionic and coordination complex systems are inactivated by water, so that only bulk or solution methods can be used. Also, rather few condensations are carried out in emulsion or suspension. However, ethylene dichloride and sodium polysulflde are condensed to give ethylene polysulflde rubber and sodium chloride in an aqueous emulsion. Gas-phase polymerization and interfacial condensation are special techniques, which are mentioned in Section 5.3. 

The scale of components in complex condensed matter often results in structures having a high surface-area-to-volume ratio. In these systems, interfacial effects can be very important. The interfaces between vapor and condensed phases and between two condensed phases have been well studied over the past four decades. These studies have contributed to technologies from electronic materials and devices, to corrosion passivation, to heterogeneous catalysis. In recent years, the focus has broadened to include the interfaces between vapors, liquids, or solids and self-assembled structures of organic, biological, and polymeric nature. 

It is interesting to employ the system consisting of mixed adsorbed film of 1-pctadecanol and dodecylammonium chloride because the former shows the phase transition from an expanded to a condensed state ( ). The interfacial tension was measured as a function of temperature at various bulk concentrations under atmospheric pressure and the molecular interaction between film-forming components was considered. 

For interfacial systems, potential functions should ideally be transferrable from the gas-phase to the condensed phase. Aqueous-mineral interfaces are not in the gas phase (although they may be close, see (7)), but both the water molecules and the atoms/ions in the substrate are in contact with an environment that is very different from their bulk environment. The easiest different environment to test, especially when comparing with electronic structure calculations, is a vacuum, so there is likely to be a great deal of information available on either the surface of the solid or the gas-phase polynuclear ion or the gas-phase aquo complex (i.e., Fe(H20)63+, C03(H20)62-). The gas-phase transfer-ability requirements on potential functions are challenging, but it is difficult to imagine constructing effective potential functions for such systems without using gas-phase systems in the construction process. This means that any water molecules used on these complexes must also transfer from the gas phase to the condensed phase. A fundamental aspect of this transferability is polarization. 

Interphase — A spatial region at the interface between two bulk phases in contact, which is different chemically and physically from both phases in contact (also called interfacial region). The plane that ideally marks the boundary between two phases is called the interface. Particles of a condensed phase located near a newly created (free) surface are subject to unbalanced forces and possibly to a unique surface chemistry. Modifications occurring to bring the system to equilibrium or metastability generally extend somewhat into one of the phases, or into both. 

---