Titration ethylene hydrogenation, 254

Thioetherification of PECH is feasibly performed in DA-solvents as already described in the patent (20J. For example, the highest substitution was obtained by the reaction of P(ECH-EO)(1 1 copolymer of epichloro-hydrin and ethylene oxide) and equimolar thiophenoxide in HMPA at 100°C for 10 h as DS 83% for sodium and 93% for potassium salts. The DS in our nucleophilic substitution was estimated by the elemental analysis as well as the titration of liberated chloride ion with mercuric nitrate (21). In the latter method, reacted medium was pretreated with hydrogen peroxide when the reductive nucleophiles which can react with mercuric ion were used. As described before for PVC, thiolation was also achieved conveniently with iso-thiuronium salt followed by alkaline hydrolysis without the direct use of ill-smelling thiolate. The thiolated PECH obtained are rubbery solids, soluble in toluene, methylene chloride, ethyl methyl ketone and DMF and insoluble in water, acetone, dioxane and methanol. 

A commercial one molar solution of borane in tetrahydrofuran, obtained from Alfa Inorganics, Inc., was standardized by measuring the amount of hydrogen evolved on titration with 40% aqueous ethylene glycol solution. 

The experimental results may be represented both by the titration curves or property-composition dependences. The extremums or bends on the titration curves indicate the formation of complexes and their composition. Thus, investigating the-possi-bility of complex formation in polyelectrolyte - nonionic polymer systems, one can use the methods of conductometric and potentiometric titration. The formation of interpolymer complexes in these systems, as some authors suggest18,211, is caused by a co-operative formation of hydrogen bonds between carboxy groups of the polyacid and oxygen atoms of nonionic polyvinylpyrrolidone or poly(ethylene glycol) and is therefore accompanied by an increase of pH of the solution. The typical titration curves for the system polyvinylpyrrolidone - copolymer maleic anhydride and acrylic add are shown in Fig. 1. The inflection points of the titration curves indicate the ratio at which the macromolecular components react with each other, i.e. the composition of the formed complexes. 

There is a simple way to avoid these problems. One can define a pH scale in a completely arbitrary manner relative to the emf of a suitable cell. One can then relate the pH on this scale to an arbitrarily defined activity of hydrogen ions, simply be setting pH = —log an+. The dissociation constants of model compounds can then be determined in terms of this arbitrary scale. This method has been used by Donovan et ai. (1959) for protein titrations in concentrated aqueous solutions of guanidine hydrochloride and of urea, and by Sage and Singer (1962) for titrations in ethylene glycol. 

The catalytic work on the zeolites has been carried out using the pulse microreactor technique (4) on the following reactions cracking of cumene, isomerization of 1-butene to 2-butene, polymerization of ethylene, equilibration of hydrogen-deuterium gas, and the ortho-para hydrogen conversion. These reactions were studied as a function of replacement of sodium by ammonium ion and subsequent heat treatment of the material (3). Furthermore, in some cases a surface titration of the catalytic sites was used to determine not only the number of sites but also the activity per site. Measurements at different temperatures permitted the determination of the absolute rate at each temperature with subsequent calculation of the activation energy and the entropy factor. For cumene cracking, the number of active sites was found to be equal to the number of sodium ions replaced in the catalyst synthesis by ammonium ions up to about 50% replacement. This proved that the active sites were either Bronsted or Lewis acid sites or both. Physical defects such as strains in the crystals were thus eliminated and the... 

The crystal structme of 28 showed that the compound adopts a pinched-cone conformation with the ethylene glycol substituents properly disposed to fold in and bind a metal cation at the base of the cahxarene and that the two thiourea units are effectively oriented to provide an anion-binding site through hydrogen bonding. NMR titrations in CD3CN of 28 with the TBA... 

---