DMF-water systems

AGR Agrawal, A.K., Jassal, M., Sahoo, A., and Garapati, S.K., Phase behavior and mechanism of formation of protofiber morphology of solution spun poly(aciylonitrile) copolymers in DMF-water system, J. Appl Polym. ScL, 119, 837, 2011. 

The chemical structure and molecular weight of the polymer both influence the rate of coagulation and the structure produced. A high molecular weight polymer coagulates more rapidly than one of lower molecular weight. It is found that in a DMF/water system, a polyether-based polymer coagulates more rapidly than a polyester-based polymer of the same urethane content. 

To separate the addition and the protonation step the CsF addition to electron-poor triple bonds was run in a biphasic DMF/water system and indeed provided the vinyl fluoride with excellent regio- and stereoselectivity [250]. 

FIGURE 8.6 The surface layer of water-precipitated membranes precipitates faster than the underlying layer. The precipitation pathway is best represented by the movement of a line through the three-component phase diagram. SEM images were taken from a membrane prepared in PVDF/DMF/water system (own data). (Data from Baker, R.W., Membrane Technology and Applications, 3rd Edition, Wiley, Chichester, 2012. http //eu.wiley.com/ WileyCDA/WileyTitle/productCd-0470743727.html.)... 

As an example of weak nonsolvent, the membrane structure prepared using 1-octanol as the nonsolvent in PVDF/DMF system is compared with PVDF/DMF/ water system in Figure 8.16. An asymmetric structure consisting of dense thin top layer was formed using water as the nonsolvent. In contrast, a symmetric structure... 

In a dual coagulation bath system, a 15% PVDF concentration in the cast solution was found to be optimum for achieving favorable characteristics such as smaller pores, high porosity, and more hydrophobicity (Ahmad and Ramli 2013). In another study, with regard to MD performance, 15% PVDF concentration was found to be optimum for both PVDF/DMA/water and PVDF/DMF/water systems (de Zdrate et al. 1995). de Z ate et al. (1995) reported that above that concentration, the PVDF membranes become too dense, whereas below that value the membrane matrix seemed to be rather inconsistent with big holes that appeared sporadically on the membrane surface. 

In addition to the reactions discussed above, there are still other alkyne reactions carried out in aqueous media. Examples include the Pseudomonas cepacia lipase-catalyzed hydrolysis of propargylic acetate in an acetone-water solvent system,137 the ruthenium-catalyzed cycloisomerization-oxidation of propargyl alcohols in DMF-water,138 an intramolecular allylindination of terminal alkyne in THF-water,139 and alkyne polymerization catalyzed by late-transition metals.140... 

One possible strategy in the development of low-overpotential methods for the electroreduction of C02 is to employ a catalyst in solution in the electrochemical cell, A few systems are known that employ homogeneous catalysts and these are based primarily on transition metal complexes. A particularly efficient catalyst is (Bipy)Re[CO]3Cl, where Bipy is 2,2 bipyridine, which was first reported as such by Hawecker et al. in 1983. In fact, this first report concerned the photochemical reduction of C02 to CO. However, they reasoned correctly that the complex should also be capable of catalysing the electrochemical reduction reaction. In 1984, the same authors reported that (Bipy)Re[C013CI catalysed the reduction of C02 to CO in DMF/water/ tetraalkylammonium chloride or perchlorate with an average current efficiency of >90% at —1.25 V vs. NHE (c. —1.5V vs. SCE). The product analysis was performed by gas chromatography and 13C nmr and showed no other products. 

Because of acid-catalyzed hydrolysis of N-vinylpyrrolidone in water, polymerization was carried out in organic solvent - DMF. Three types of samples of poly(methacrylic acid) were used syndiotactic - obtained by radiation polymerization, atactic - obtained by radical polymerization, and isotactic - obtained by hydrolysis of isotactic poly(methyl methacrylate). It was found that in all cases the rate enhancement appeared in comparison with the blank polymerization (without template). The rate enhancement became more pronounced with increasing chain length and syndiotacticity of the template. According to the authors, the rate enhancement is connected with the stronger complex formation between poly(vinyl pyrrolidone) and syndiotactic poly(methacrylic acid) then with isotactic template. This conclusion was supported by turbimetric titration in DMF/DMSO system and by model considerations. It is worth noting, however, that... 

All enthalpy of solution measurements were carried out with an LKB 8700-1 precision calorimetry system. The experimental procedure and tests of the calorimeter have been reported previously (3, 4, 5). The purification of the solvent DMF (Baker Analyzed Reagent) and of all solutes used has been described in the same papers. The solvent mixtures were prepared by weighing and the mole fraction of water in the DMF-water mixtures was corrected for the original water content of the amide as measured by Karl Fischer titration. 

In view of the different behavior of n-Bu4NBr in mixtures of DMF and NMF and of DMF and water, we recently (6) derived an equation for the excess enthalpy of solution in the DMF-water mixture (AHE(M)) by use of a simple hydrophobic hydration model. Summarizing this derivation, we conceived the enthalpies of solution in the DMF-H20 system (AH°(M)) as being the result of two effects (a) When the hydrophobic hydration of tetraalkylammonium ions is absent, the corresponding enthalpy of solution in pure water AH K O) and in the mixture AHJ(M) should be correlated by ... 

Water-in-oil gel emulsions were tested in enzymatic aldolization of selected N-Cbz-amino aldehydes (Figure 19.3), N-Cbz-3-amino propanal (4), N-Cbz-glycinal, (5), (S)-N-Cbz-alaninal (6), and (R)-N-Cbz-alaninal (7) catalyzed by RAMA and L-rham-nulose-1-phosphate aldolase (RhuA) and L-fuculose-1-phosphate aldolase (FucA) from Escherichia coU [27,28]. The largest differences between conventional dimethyl formamide (DMF)/water co-solvent systems and gel emulsions were observed with RAMA and FucA catalysts (Figure 19.3). The emulsion media enhanced the catalytic efficiency of RAMA towards the N-Cbz amino aldehydes tested three, five. 

Homopropargylic alcohols as well as propargylic epoxides and pentynols readily form cyclic ruthenium alkoxycarbenes upon intramolecular nucleophilic addition of the OH group to the electrophilic a-carbon of ruthenium-vinylidene species. Their oxidation in the presence of N-hydroxysuccinimide leads to the formation of penta-lactones. The best catalytic system reported until now for this transformation of but-3-ynols is based on RuCl(C5H5)(cod), tris(2-furyl)phosphine, NaHCOs as a base, in the presence of nBu4NBr or nBu4NPp6, and N-hydroxysuccinimide as the oxidant in DMF-water at 95 °C (Scheme 8.11) [22]. 

In the experiments of Hayes et al. (1975) DMSO was marginally better than DMF or sulfolane for dissolving humic substances (Table 4). In the ESR there was evidence of a higher free radical concentration in DMSO than in either DMF or sulfolane. Because DMSO would not be expected to generate free radicals, it is reasonable to infer from the ESR data that humic components, which are insoluble in the DMF- and sulfolane-water systems, were dissolved in this solvent. Elemental contents were similar for the humic and fulvic acids of the DMSO extracts, and these data infer that the major difference between the two fractions was one of molecular size. However, some fulvic acid materials were observed to precipitate during dialysis, as was noted for the DMF and sulfolane systems. 

Method of cleavage Cleavage is generally performed by protodesilylation. The conditions depend very much on the nature of the aromatic system, as well as on the substitution. Either neat TFA, TFA vapor or TFA/CH2CI2 can be used. Electron-poor aromatic systems require treatment with CsF in DMF/ water (4 1) at 110 °C. 

These systems were tested in the enzymatic aldolization of a variety of A/-Cbz-aminoaldehydes catalyzed by D-fructose-l,6-bisphosphate aldolase from rabbit muscle (RAMA) and L-rhamnulose-1-phosphate aldolase and L-fuculose-1-phosphate aldolase from E. coli (Espelt et al. 2003 a,b, 2005). The largest differences between conventional DMF/water cosolvent systems and gel emulsions were observed with RAMA catalyst (Fig. 6.5.11). 

In simpler cases, solubility measurements in solvent mixtures may also provide information on the solvating effects of the solvent components. On the basis of such solubility measurements in solutions of Hgl2 in a dimethylformamide-dimethyl sulphoxide solvent mixture, for instance, Gaizer and Beck [Ga 67] have shown that Hgl2 forms a mixed solvate with the two solvents. In an analogous study, they drew attention to the phenomenon that in a dimethylformamide-water system mixed solvates Hgl2 DMF-H20 are formed. 

Lin, D.J., Chang, C.L., Huang, F.M. and Cheng, L.P. 2003. Effect of salt additive on the formation of microporous poly(vinyhdene fluoride) membranes by phase inversion liom LiC104/water/DMF/PVDF system, 44(2) 413-422. 

---