Clarification, 65 acetate

Polymer Membranes These are used in filtration applications for fine-particle separations such as microfiltration and ultrafiltration (clarification involving the removal of l- Im and smaller particles). The membranes are made from a variety of materials, the commonest being cellulose acetates and polyamides. Membrane filtration, discussed in Sec. 22, has been well covered by Porter (in Schweitzer, op. cit., sec. 2.1). 

In a 100-ml flask is placed a mixture of 19.5 g (0.18 mole) of freshly sublimed, pulverized selenium dioxide, 15 g (0.10 mole) of df/-camphor and 15 ml of acetic anhydride. The flask is fitted with a magnetic stirrer and a condenser, and the mixture is heated to 135° on an oil bath with stirring for 16 hours. After cooling, the mixture is diluted with ether to precipitate selenium, which is then filtered off, and the volatile materials are removed under reduced pressure. The residue is dissolved in ether (200 ml), washed four times with 50-ml portions of water and then washed several times with saturated sodium bicarbonate solution (until the washes are basic). The ether solution is finally washed several times with water, then dried, and the ether is evaporated. The residue may be purified by sublimation at reduced pressure or recrystallized from aqueous ethanol (with clarification by Norit, if necessary). The product is yellow, mp 197-199°. 

Clarification by removal of casein with such agents as calcium chloride, acetic acid, cooper sulfate, or rennin has often been employed to obtain a serum more suitable for refractometric measurements. Obviously the composition, and hence the refractive index, of such sera will depend on the method of preparation. Furthermore, some of the serum proteins may be precipitated with the casein by some of the agents used, particularly if the milk has been heated. Refractive index measurements of such sera are not generally considered as satisfactory as freezing point measurements for detection of added water (David and MacDonald 1953 Munchberg and Narbutas 1937 Schuler 1938 Tell-mann 1933 Vleeschauwer and Waeyenberge 1941). Menefee and Overman (1939) reported a close relation between total solids in evaporated and condensed products and the refractive index of serum prepared therefrom by the copper sulfate method. Of course, a different proportionality constant would hold for each type of product. 

Clarification with Carrez solutions can be used to eliminate interfering compounds (14,44,45). Purification, isolation, or concentration of the extract can also be performed by solid-phase extraction with C8 (53) or Cl8 (46,47,75). Hayakawa et al. (75) used Sep-Pak Cl8 cartridges for the separation of aspartame from its degradation products. The sample was applied to the Sep-Pak, and degradation products and aspartame were eluted with 10% and 30% methanol in acetate buffer, respectively. 

In alkaline solution (0.1 M KOH) and in the presence of N 0, the formation of formaldehyde and acetic acid is observed.137,138 The mechanism of these reactions still awaits clarification. 

Broth Samples. Clarification with Zinc Acetate-Potassium Ferrocyanide. Transfer an aliquot of filtered broth expected to contain between 5 and 15 mg. of... 

Two enzymes are commonly used for amperometric biosensors, namely lactate oxidase (LOD) and lactate dehydrogenase (LDH). It should be noted that, in this instance, LOD refers to the enzyme which catalyses the reaction shown in Fig. 23.4, in which the products are pyruvate and H202. This type of enzyme was formerly assigned the E.C. number 1.1.3.2, but this was confused with lactate monooxygenase (E.C. 1.13.12.4), which is also commonly referred to as type I lactate oxidase [55] or simply lactate oxidase [56] whose products are acetate, C02 and H202. The LOD which catalyses the reaction shown in Fig. 23.4 has also been referred to as type II lactate oxidase [55] following clarification of this point in a published letter [57], current publications refer to this enzyme as E.C. 1.1.3.x. 

In the original isolation of stachyose described8 by Planta and Schulze, the minced tubers of Stachys tuberifera were pressed and extracted with water. The juice, after clarification with lead acetate and mercuric nitrate, was treated with hydrogen sulfide. After removing the metal sulfides and neutralizing the filtrate with ammonia, the... 

Naphthyl caprylate (b) p-Nitrophenol methods Thiomersal, bile salts, Ca Production of (3-naphthol-Fast Blue complex, clarification with ethanol-ethyl acetate, spectrophotometry at 540 nm Bacterial lipase Versaw et al. (1989)... 

Delfini, C., Contemo, L., Giacosa, D., Cocito, C., Ravaglia, S., Bardi, L. (1992) Influence of clarification and suspended solid contact on the oxygen demand and long-chain fatty acid contents of free run, macerated and pressed grape musts, in relation to acetic acid production. Viticultural andEnological Sciences, 47, 69-75. 

Ironically, until 1953, Nazarov incorrectly described the mechanism of the general transformation which now bears his name. In 1952, Braude and Coles were the first to suggest the intermediacy of car-bocations and demonstrated that the formation of 2-cyclopentenones actually proceeds via the a,a -divi-nyl ketones (equation 1). This fact together with further mechanistic clarification, has led to the specific definition of the Nazarov cyclization as the acid-catalyzed closure of divinyl ketones to 2-cyclopentenones. This process was already documented in 1903 by Vorliinder who isolated a ketol of unknown structure by treatment of dibenzylideneacetone with concentrated sulfuric acid and acetic acid followed by mild alkaline hydrolysis (equation 2). The correct structure of Vorliinder s ketol, finally proposed in 1955, ° arises from Nazarov cyclization followed by oxidation and isomerization. Other examples of acid-catalyzed cyclizations of divinyl ketones exist in the early literature. ... 

Amusingly enough, we have managed to devise not one but four more or less acceptable routes, arriving at two hypothetical (Va, Vb) and two real (Villa, Vlllb) structures by quite dissimilar approaches. Mechanistically speaking, this predicament is unacceptable and demands further experimental clarification. Fortunately, labeling experiments have been performed using 0 tracers specifically at the acetate carbonyl of I. After hydrolysis of II the label was found in the alcohol by-product. The only route that accounts for this observation is the sequence B, D of Scheme 48.2. As a consequence, were compound I really optically active (it was not in the actual experiment), only the optically active Vila should have been obtained. Since asymmetric syntheses are an important subject of research nowadays, the real experiment should be run. 

The extension of the reaction with sodium iodide to tosyl derivatives of other acetals of iditol, glucitol, and mannitol could provide evidence for the conformation of 2,4 3,5-diacetals of mannitol and, more important, lead to a clarification of the steric requirements of this reaction. The importance of 2,4 3,5-diacetals of talitol, at present unknown, is now clear they will have one axial and one equatorial terminal group (see LIU), and the trans ring junction imposes a rigidity of conformation greater than that of any of the diacetals with cis junctions. 

Cellulose acetate Clarification sterilization Good for biological applications. + -... 

Acylation. When sodium salicylate is refluxed with cyanogen bromide in acetic acid, carbon dioxide is evolved and acetylsalicylic acid is formed the reaction awaits clarification. ... 

The main volatiles in wines are the higher aliphatic alcohols, ethyl esters, and acetates formed from yeasts during fermentation. Acetates are very important flavors characterized by fruity notes, C4-Ci0 fatty acid ethyl esters manly confer fruity scents to the wine. Other wine aroma compounds are C6 alcohols, such as 1-hexanol and cis- and trans-3-hexen-l-ol, 2-phenylethanol, and 2-phenylethyl acetate. Contents of these compounds in wine are linked to the winemaking processes used fermentation temperature, yeast strain type, nitrogen level in must available for yeasts during fermentation, clarification of wine (Rapp and Versini, 1991). Much literature on the wine aroma compounds was reported in reviews by Schreier (1979) and Rapp (1988). 

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