Water mixture, acetic acid

Acetic acid containing less than 1% water is called glacial. It is hygroscopic and the freezing point is a convenient way to determine purity (7). Water is nearly always present in far greater quantities than any other impurity. Table 1 shows the freezing points for acetic acid-water mixtures. 

Acetic acid forms a monohydrate containing about 23% water thus the density of acetic acid-water mixtures goes through a maximum between ... 

Jensen was the first to report in 1983 that the color of the solution oscillated between pink and dark brown in the presence of cobalt(II) and bromide ions when the reaction was carried out in a 90/10 (w/w) acetic acid/water mixture (162). This color change was accompanied by a change in the redox potential and the oscillations were observed for over 16 h and 800 cycles. Presumably, the pink color corresponds to a low Co(III)/Co(II) ratio, the dark brownish black to a high Co(III)/Co(II) ratio or to a Co(III)Br complex in this reaction. 

Another recent work presents the possibility to use a membrane made by PVA-g-acrylonitrile (AN) to separate acetic acid/water mixtures by pervaporation [70], The best separation factor (14.6) has been obtained by using PVA-g-AN (52 %) membrane, at 30°C, 90 % acetic acid in the feed. The permeation rate was 0.09 kg m"2h 1. 

Two-dimensional techniques are usually employed if both phospho-glycerides and glycolipids are present, but it is possible to resolve members of both classes using a diisobutylketone-acetic acid-water mixture (40 25 5). A solvent composed of acetone, acetic acid and water (100 2 1) will separate the mono- and di-galactosyldiglycerides, which are particularly abundant in plant extracts, from phosphoglycerides, which remain at the origin. 

Acetic Acid-Water Mixture. CRUZ (4) chose this example to illustrate his method of representation of vapor-liquid equilibria of volatile weak electrolyte and to show how to obtain simply from experimental vapor-liquid equilibrium data the significant parameters. ... 

The overall effective pathlength of a CIR cell is relatively short (ca. 10 pm) which has both advantages and disadvantages. The short pathlength means that spectra can be measured even on highly absorbing samples, such as aqueous solutions, or (as in the case of methanol carbonylation reactions) acetic acid-water mixtures. 

Octaethylporphinato complexes of the type [M(OEP)(02CMe)2] (M = Zr or Hf) have been prepared by reaction of H2OEP and [M(acac)4] in molten phenol at 210-240 °C followed by crystallization from pyridine-acetic acid-water mixtures. The complexes have been characterized by IR and mass spectra703,704 and by electronic absorption and emission spectra.703 They have an eight-coordinate square antiprismatic structure (48) in which the four porphinato nitrogen atoms occupy the coordination sites on one square face and the two bidentate acetate... 

D KIE of 6.35 has been observed in the oxidation of a-deuteriomandelic acid by pyri-dinium bromochromate to the corresponding oxo acid. The analysis of the D KIE indicated that the reaction involves a symmetric transition state443. The oxidations of phosphinic and phosphorous acids by pyridinium bromochromate exhibits a substantial primary deuterium KIE444. The hydroxyacids, glycolic, lactic, mandelic and malic acids are oxidized by pyridinium hydrobromide perbromide in acetic acid-water mixtures to oxo acids445. The primary KIE in the oxidation of a-deuteriomandelic acid is kn/kn = 5.07, and it does not exhibit a solvent isotope effect. A mechanism involving hydride ion transfer to the oxidant has been proposed445. 

The use of /V-chloramines, in principle, allows the facile generation of aminyl radicals upon UV photolysis in neutral media. A radical chain can be envisioned for the formation of 2-chIoromethylpyrrolidines (Scheme 7). In practice, however, there is a slow step in this sequence, step A and/or B, such that other reaction pathways, disproportionation or H-abstraction from the solvent, compete. Surzur has studied the reaction in Scheme 7 in the alcoholic solvents MeOH and /-PrOH, which serve as hydrogen atom sources, and achieved acceptable ratios of cyclic products 25 and 26 to acyclic amine 27 (70TL3107). Other /V-chloroalkenylamines gave similar results (71TL903 80TL287). /8-chloro-substituted amine products such as 25 were the sole products when the reactions were carried out in acetic acid-water mixtures these reactions involve aminium cation radicals and are discussed further in Section III,B. 

Separation of acetic acid-water mixtures through acrylonitrile grafted poly(vinyl alcohol) membranes by pervaporation... 

Keywords Membranes Selectivity Separations Transport processes Pervaporation Acetic acid-water mixtures Poly(vinyl alcohol) membranes Graft copolymerization... 

Pervaporation is a membrane separation process where the liquid feed mixture is in contact with the membrane in the upstream under atmospheric pressure and permeate is removed from the downstream as vapor by vacuum or a swept inert gas. Most of the research efforts of the pervaporation have concentrated on the separation of alcohol-water system [1-20] but the separation of acetic acid-water mixtures has received relatively little attention [21-34]. Acetic acid is an important basic chemical in the industry ranking among the top 20 organic intermediates. Because of the small differences in the volatility s of water and acetic acid in dilute aqueous solutions, azeotropic distillation is used instead of normal binary distillation so that the process is an energy intensive process. From this point of view, the pervaporation separation of acetic acid-water mixtures can be one of the alternate processes for saving energy. 

In the present study we have aimed to separate acetic acid-water mixtures using AN grafted PVA membranes and studied the permeation characteristics of PVA-g-AN membranes as a function of membrane thickness, temperature, feed composition and pressure. 

The permeation and separation characteristics of PVA-g-AN membranes toward acetic acid-water mixtures were expressed as permeation rate (flux) (0, separation factor (a) and pervaporation separation index (PSI). 

Aminabhavi and Naik [37] obtained similar results in the pervaporation of acetic acid-water mixtures by using PVA membranes. They reported that for 20 wt.% acetic acid solutions separation factor stayed constant at 35 and 45 °C although permeation rate increased with temperature. 

Similar results were obtained in the pervaporation separation of acetic acid-water mixtures using blended polyacrylic acid-nylon 6 membranes [22], poly(4-vinylpyridine-co-aciylonitrile) membranes [11] and in the permeation and separation of aqueous alcohol solutions through PVA-AN-HEMA latex membranes [5],... 

Comparison of the performance of the membranes based on pva for the pervaporation separation of acetic acid-water mixtures... 

For comparison purposes several results regarding the separation of acetic acid-water mixtures obtained by various authors with different type of membranes listed in Table 5. One can see that PVA-g-AN membranes have high selectivity although they have almost the same permeation rate depending on the feed composition and temperature than the membranes studied up in the table. 

R.Y.M. Huang, A. Moreira, R. Notarfonzo, X.F. Xu, Pervaporation separation of acetic acid-water mixtures using modified membranes. Part I. Blended poly(acrylic acid) (PAA)-nylon 6 membranes, J. Appl. Polym. Sci. 35 (1988) 1191-1200. 

R.Y.M. Huang, C.K. Yeom, Pervaporation separaion of aqueous mixtures using crosslinked poly(vinyl alcohol) membranes. Part III. Permeation of acetic acid-water mixtures, J. Membr. Sci. 58 (1991) 33-47. 

S.Y. Lu, C.P. Chiu, FLY. Fluang, Pervaporation of acetic acid/water mixtures through silicate filled polydimethylsiloxane membranes, J. Membr. Sci. 176 (2002) 159-167. 

G. Asman, O. anh, Characteristics of permeation and separation for acetic acid-water mixtures through poly(vinyl alcohol) membranes modified with poly(acrylic acid), Sep. Sci. Technol. 38 (2003) 1963-1980. 

Jeanes and associates23 used the ratio of the RF values of maltose and D-glucose as a criterion for choosing suitable solvent mixtures. The adaptability of ternary solvent mixtures was commended. After testing a number of mixtures made up of an alcohol (1-butanol, ethanol, or fusel oil), an acid or base, and water, as well as collidine-pyridine-water mixtures, they recommended basic mixtures, in particular, 1-butanol-pyridine-water. The composition of mixtures containing acid may change as a result of esterification. For example 1-butanol-acetic acid-water mixtures should be allowed to stand for some time before use.21 To obviate esterification of solvent, Hanes and Isherwood used ZerZ-pentyl alcohol in solvent mixtures containing acid.30... 

Partenheimer W. The aerobic oxidative cleavage of lignin to produce hydroxyaromatic benzaldehydes and carboxylic acids via metal/bromide catalysts in acetic acid/water mixtures. Adv Synth Catal. 2009 351 456-66. 

For the acid-catalysed reaction, substituent effects have been examined principally in water and acetic acid-water mixtures. The main feature is that the effects are usually small. In Table 3 are also listed the Hammett p-values obtained for acetophenones and arylmethyl phenyl ketones. The slightly negative p-values account for the cationic character of the transition state and for opposite effects on the pre-equilibrium constant and on the elementary rate constant for proton abstraction. 

Briones, J.A., J.C. Mullins, M.C. Thies, B.-U. 1987. Ternary phase equilibria for acetic acid-water mixtures with supercritical carbon dioxide. Fluid Phase Equiil. 36 235-246. 

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