David Vofsi

The Mechanism of a Selective Permeation of Ions through “Solvent Polymeric Membranes”

Abstract The mechanism of diffusion of uranyl nitrate in “solvent polymeric membranes” was investigated. It is suggested that a “carrier” transport mechanism is responsible for the selective permeation of ions or ion pairs through such membranes. The fluidity of the membranes was investigated by proton magnetic resonance and by the “fluorescent probe” technique. Radioactive labeling was used in order to determine the self-diffusion coefficient of dicresylbutylphosphate (DCBP) which serves both as plasticizer and as complexing agent in such membranes. Comparison of its value (∼10−7 cm2/sec) with the limiting value of the diffusion coefficient of uranyl nitrate in such membranes (3.3 × 10−8 cm2/sec) indicates that the latter diffuses as a (DCBP)2UO2(NO3)2 complex. It is also suggested that the study of the “solvent polymeric membranes” may help to understand certain properties of biological membranes.

Gas chromatographic analysis of aliphatic nitriles in aqueous acidic solution.

A mixture of acrylo-, propio-, butyro-, succino- and adiponitriles in aqueous solution in the presence of HCl and KCl was analysed by gas chromatography. The method involved extraction with o-dichlorobenzene and drying over anhydrous Na2SO4 prior to injection into the chromatographic column. No adverse effect of the drying agent was detected. The same method of drying aqueous solutions for chromatographic analysis could be extended to other systems.

Heterogeneous sulphochlorination of polyethylene. The effect of polymer morphology on the reaction rates and properties of reaction products

Abstract Polyethylenes of low, middle and high density have been submitted to heterogeneous sulphochlorination in the presence of hydroperoxides as initiators. Approximately equal amounts of SO 2 Cl and chlorine could be attached to the polyethylenic precursors. Although the reaction kinetics are strongly affected by the initial morphology of the substrates, it has been found that maximum amounts of the SO 2 Cl groups which can be introduced under such conditions are determined by the fraction of the amorphous material. The reaction kinetics are also strongly affected by the presence of antioxidants. X-ray diffraction analysis, birefringence and polarized i.r. measurements indicated that the morphology of the sulphochlorinated materials and of the products of their hydrolysis is strongly affected by the initial morphology of the polyethylenic precursors. Fluorescence probe measurements revealed that in highly oriented materials, the orientation of the amorphous regions is retained even upon water swelling of the final ion exchange membranes. It has been found that the initial morphology of the polyethylenic substrates together with the degree of the chemical modification (concentration of the introduced chlorine and SO 2 Cl groups) determine the properties of the products.

Heterogeneous fluorination of chlorine containing polymers with 18-crown-6 as phase transfer agent

Abstract Effectiveness of alkali metal fluorides, complexed with crown ethers, as fluorinating agents, was investigated in nitrobenzene as mediating solvent. Partial fluorination of the surface of the crosslinked film of chlorinated polyethylene occurs within the first 2 h at 80°C. Further reaction leads to dehydrochlorination only. Up to 50% of chlorine in polyepichlorhydrin (Herchlor-H) may be replaced by fluorine. Further reaction is strongly inhibited by the presence of fluorine substituents in the neighbourhood of unsubstituted chlorines. ‘Plateau’ is reached after about 10 h at 140°C. In all investigated systems elimination, E, competes with substitution, S. It was suggested that the same transition state complex may be responsible for the two reactions. The energy of activation of the two processes is ∼5 kcal mol−1. The S E ratio decreases in the following order: primary > Secondary >>> vicinal.

Polarized infra-red studies of sulphochlorinated polyethylene and products of its hydrolysis

Abstract Band assignments in the polarized i.r. absorption spectra of sulphochlorinated polyethylene are discussed. The absorption band at 720 cm −1 and computer-resolved absorption spectra in the 1000–1600 cm −1 region have been used for conformational analysis of the reaction products. It has been concluded that gauche methylene sequences are preferentially attacked during the heterogeneous sulphochlorination of polyethylene. However, gauche and trans methylene sequences seem to be equally susceptible to chlorination. Analysis of the dichroic character of the i.r. absorption bands of products obtained from preoriented polyethylene films enabled us to elucidate the conformation of SO 2 Cl groups attached to the polymeric chains. The orientation of the parent polyethylene is preserved to a large extent in the sulphochlorinated materials and in the products of their hydrolysis.

Heterogeneous reactions of polymers: 3. Conformational analysis of heterogeneously chlorinated polyethylenes

Abstract Conformational features of chlorinated polyethylenes prepared by chlorination under heterogeneous conditions are deduced from their i.r. spectra in the 600–700 cm−1 region. The concentration of vicinal chlorides in materials obtained this way is estimated by 1H-n.m.r. The effect of the reaction kinetics on the concentration of vicinal chlorides is discussed. It is shown that while conformational transitions do take place during heterogeneous chlorinations at room temperature of the low density polyethylenes, they do not occur during chlorinations of the highly crystalline high density polyethylene films. In such materials the distribution of conformers is determined by the initial conformation of the polymeric precursors and it deviates strongly from the thermodynamic equilibrium. Freezing of the thermodynamically unfavourable conformations in such materials is attributed to the low mobility of the chlorinated chains restricted by the adjacent crystalline regions. Thermal treatment of the products, above the melting temperature of the crystallites, leads to a thermodynamic distribution of the conformers. However, when such treatment is conducted under isometric conditions in a press, the conformational transitions remain severely restricted.

Formation of dialkoxyphosphinylalkylidene derivatives of galactitol by transacetalation reactions

Abstract Transacetalation reactions of galactitol with 2,2-dialkoxyethylphosphonates gave the expected 1,3:4,6-diacetal as the minor product, but the major product was 1,3:4,5 derivative. With a 3,3-diethoxypropylphosphonate, the 1,3:4,6-diacetal became the major product. The influence of the dialkoxyphosphinyl substituent on the acetal linkage is shown to be stereoelectronic.

Heterogeneous reactions of polymers: 4. Melting behaviour of heterogeneously chlorinated and sulphonated polyethylenes

Abstract The melting behaviour of heterogeneously chlorinated and sulphonated high-density polyethylene was studied by differential scanning calorimetry. It was found that an increase in Tm takes place at high degrees of substitution in the amorphous phase. For sulphonated polyethylenes the increase in Tm was also dependent on the type of the counterion. The effect is interpreted as a decrease in configurational entropy upon fusion due to the restraints that the highly chlorinated and sulphonated amorphous regions impose on the adjacent crystallites.

Reaction of phosphonated acetals. Acid-catalysed hydrolysis of dialkyl 2,2-dialkoxyethylphosphonates

The kinetics of the acid-catalysed hydrolysis of diethyl 2,2-diethoxyethylphosphonate(I) of diethyl 2,2-dimethoxyethylphosphonate(II), and of dimethyl 2,2-dimethoxyethylphosphonate(III) haye been studied in aqueous dioxan solution containing different acid catalysts. Plots of log k1 against H0 had slopes of 0.98; Plots of (log k1+H0) against log aH2O had slopes W=–0.1. The deuterium solvent isotope effect kD/kH for compound(II) in 1M-sulphuric acid at 30° was 2.8. According to the hypotheses of Zucker–Hammett and of Bunnett, the results obtained are in agreement with an A-1 mechanism. The measured second-order rate constants at 25° were: k2 3.7 × 10–4 l mols–1 for compound(I) and 1.7 × 10–4 l mol s–1 for compounds(II) and (III). Low values of the energy (15–17 kcal mol–1) and entropy (–25 to –27 cal mol–1 K–1) of activation were observed. The substituents at the central carbon atom show the expected polar effects, without any measurable steric effects. The observed values of the energy and entropy activation are correlated with the polarity of the phosphoryl group. An effect of intramolecular catalytic influence is introduced. The products of hydrolysis were identified as the corresponding aldehydes; that of compounds(II) and (III) is the novel dimethyl formylmethyl phosphonate.

Reaction of phosphonated acetals. Part 3. Acid-catalysed hydrolysis of diethyl 3,3-diethoxypropylphosphonate

The kinetics of the acid-catalysed hydrolysis of diethyl 3,3-diethoxypropylphosphonate (I) have been studied in aqueous dioxan solutions, at different acid concentrations and temperatures. The reactions follow an A1 type mechanism with the inductive effect of the phosphonated substituent having only a minor influence. The measured second-order rate constant at 30° is 0.032 l mol–1 s–1. Plots of log kobs. against log CH3O+ are not linear. The deuterium solvent isotope effect kD2O/kH2O is 2.32. The energy of activation is 92 kJ mol–1 and the entropy of activation of 21 J mol–1 K–1. General acid catalysis was not observed. An extremely rapid decrease in the rates of acid-catalysed hydrolysis was observed in going from compound (I) to diethyl 2,2-diethoxyethylphosphonate, (II), and to diethyl diethoxymethylphosphonate, (V). Compound (V) does not undergo regular acetal acid-catalysed hydrolysis.