Water Suspension

Michael addition of thiophenol (74) to /7-methoxychalcone (70f) also proceeded efficiently in a water suspension medium. When a mixture of 70f, 74, K2CO3, 72 and water was stirred for 24 h at room temperature and the reaction product was filtered and air dried, the addition product 75 was obtained in 92% yield. Although similar Michael addition reactions can be carried out in solution [35], the procedure of the solid state reaction is rather simple, economical and free from pollution problems involving organic solvents [34]. 

The Michael addition reaction in water suspension medium is also applicable to carbon-carbon bond formation. A mixture of 70a, methyl acetylacetate (76), 72 and water was stirred for 5 h at room temperature, then the reaction product was filtered and dried to give the addition product 77 in 98% yield [34]. Although a similar solvent-free Michael addition reaction of 70a with diethyl malonate at 60 °C has been reported, organic solvent was still necessary to isolate the product from the reaction mixture [36]. 

14 Epoxidation of Chalcones with NaOCl or Ca(C10)2 in a Water Suspension 

The water suspension method described in Section 15.2.13 can also be applied to epoxidation reactions of chalcones 70 with NaOCl or Ca(C10)2. A mixture of 70a, 72 and commercially available 11 % aqueous NaOCl was stirred at room temperature for 24 h. The reaction product was filtered and dried to give 76a in quantitative yield [34]. This procedure was applied to various kinds of chalcone derivatives, and 70b-j were oxidized efficiently giving the corresponding epoxides 76b-j respectively, in good yields (Table 15-20) [34]. In the case of 70h and 70i, the oxidation reaction proceeds very fast. This organic solvent-free reaction procedure is much more simple and convenient in comparison with the usual solvent procedure [37]. Ca(OCl)2 can also be used for this epoxidation reaction in water suspension (Table 15-20) [34]. In the case of 70g and 70h, the reaction proceeds extremely quickly. However, the reaction product must be isolated from water-insoluble Ca(OCl)2 by extraction with organic solvent. Furthermore, in the case of 70d-f and 70j, the reaction products were not extracted with ether from the reaction mixture (Table 15-20). 

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The use of acids and bases to control interiDarticle forces in oxide (ceramic)-water suspensions is an example of... 

Copper-wheel engraving is used for decoration and in artware production. Abrasive compounds are appHed in water suspension to the spinning copper wheel held in a chuck. The glass is brought into contact with the wheel to produce the design (see Abrasives). 

Wet screening is being replaced in many laboratories by instmments that use a photosensor to record the diameter of each particle in a water suspension as that suspension flows past the sensor. 

Paper consists of sheet materials that are comprised of bonded small discrete fibers. The fibers usually are ceUulosic in nature and are held together by hydrogen bonds (see Cellulose). The fibers are formed into a sheet on a fine screen from a dilute water suspension. The word paper is derived from papyms, a sheet made in ancient times by pressing together very thin strips of an Egyptian reed Cjperuspapyrus) (1). 

Enameling meets decorative as weU as protective requirements. Ceramic enamels are mainly based on alkaH borosiHcate glasses. The part to be enameled is dipped into or sprayed with a sHp, ie, a water suspension of glass fragments called frit. The sHp coating is dried and fused in an enameling furnace under careful heat control (see Enamels, porcelain or vitreous). 

Emulsion Polymerization. Emulsion and suspension reactions are doubly heterogeneous the polymer is insoluble in the monomer and both are insoluble in water. Suspension reactions are similar in behavior to slurry reactors. Oil-soluble initiators are used, so the monomer—polymer droplet is like a small mass reaction. Emulsion polymerizations are more complex. Because the monomer is insoluble in the polymer particle, the simple Smith-Ewart theory does not apply (34). 

Monovalent cations are good deflocculants for clay—water sHps and produce deflocculation by a cation exchange process, eg, Na" for Ca ". Low molecular weight polymer electrolytes and polyelectrolytes such as ammonium salts (see Ammonium compounds) are also good deflocculants for polar Hquids. Acids and bases can be used to control pH, surface charge, and the interparticle forces in most oxide ceramic—water suspensions. 

Liquid Compositions. Urea—formaldehyde reaction products also are available commercially as Hquids that can be categorized into two classes, ie, water suspensions and water solutions. 

Paper may be colored by dyeing the fibers in a water suspension by batch or continuous methods. The classic process is by batch dyeing in the beater, pulper, or stock chest. Continuous dyeing of the fibers in a water suspension is adaptive to modem paper machine processes with high production speeds in modem mills. Solutions of dyestuffs can be metered into the high density or low density pulp suspensions in continuous operation. 

Mixed liberated particles can be separated from each other by flotation if there are sufficient differences in their wettability. The flotation process operates by preparing a water suspension of a mixture of relatively fine-sized particles (smaller than 150 micrometers) and by contacting the suspension with a swarm of air bubbles of air in a suitably designed process vessel. Particles that are readily wetted by water (hydrcmhiric) tend to remain in suspension, and those particles not wetted by water (hydrophobic) tend to be attached to air bubbles, levitate (float) to the top of the process vessel, and collect in a froth layer. Thus, differences in the surface chemical properties of the solids are the basis for separation by flotation. 

It was claimed that the maximum continuous operating temperature in most chemical environments was 120°C and even 140-150°C in some instances. The major chemical applications were in the form of pipe and tank linings and injection moulded valve and pump parts. Coatings could be applied to metals by means of fluidised bed, water suspension and organic dispersion techniques. 

Carbon blacks are synthetic materials which essentially contain carbon as the main element. The structure of carbon black is similar to graphite (hexagonal rings of carbon forming large sheets), but its structure is tridimensional and less ordered. The layers of carbon blacks are parallel to each other but not arranged in order, usually forming concentric inner layers (turbostratic structure). Some typical properties are density 1.7-1.9 g/cm pH of water suspension 2-8 primary particle size 14-250 nm oil absorption 50-300 g/100 g specific surface area 7-560 m /g. 

Antimony trioxide (SbaOj). It is produced from stibnite (antimony sulphide). Some typical properties are density 5.2-5.67 g/cm- pH of water suspension 2-6.5 particle size 0.2-3 p,m specific surface area 2-13 m-/g. Antimony trioxide has been the oxide universally employed as flame retardant, but recently antimony pentoxide (SbaOs) has also been used. Antimony oxides require the presence of a halogen compound to exert their fire-retardant effect. The flame-retarding action is produced in the vapour phase above the burning surface. The halogen and the antimony oxide in a vapour phase (above 315 C) react to form halides and oxyhalides which act as extinguishing moieties. Combination with zinc borate, zinc stannate and ammonium octamolybdate enhances the flame-retarding properties of antimony trioxide. 

During the filtration test of a water suspension containing 14.5 % calcium carbonate in a filter press (A = 0.1 m 50 mrn cake thickness temperature 23 C), the following data were obtained ... 

We wish to separate titanium dioxide particles from a water suspension. The method chosen is centrifugation. The unit is a continuous solid-bowl type with a bowl diamter of 400 mm, a length to width ratio of 3.0, and the unit operates at 2,000 rpm. The feed contains 18 % (weight basis) solids and is fed to the unit at 2,500 Liters/hr at a temperature of 95° F. The average particle size is 65 /tm. (a) Determine the amount of solids recovered per hour (b) Determine the solids concentration in the centrate (c) Determine the horsepower requirments for the centrifuge (d) Size a graviy settler to remove an additional 15 % of the solids. 

Thermal solid-state reactions were carried out by keeping a mixture of powdered reactant and reagent at room temperature or elevated temperature, or by mixing with pestle and mortar. In some cases, the solid-state reactions proceed much more efficiently in a water suspension medium or in the presence of a small amount of solvent. Sometimes, a mixture of solid reactant and reagent turns to liquid as the reaction proceeds. All these reactions are called solid-state reactions in this chapter. Solid-state reactions were found to be useful in the study of reaction mechanisms, since it is easy to monitor the reaction by continuous measurement of IR spectra. 

Very interestingly, bromination of the crystalline powder of 1 with 7 in a water suspension medium proceeded much more efficiently. For example, a suspension of powdered 1 and 7 in a small amount of water was stirred at room temperature for 15 h, and the reaction mixture was filtered and air-dried to... 

Complexation with a Chiral Host in a Water Suspension Medium... 

Some solid-solid reactions were shown to proceed efficiently in a water suspension medium in Sect. 2.1. When this reaction, which gives a racemic product, is combined with an enantioselective inclusion complexation with a chiral host in a water suspension medium, a unique one-pot preparative method of optically active product in a water medium can be constructed. Some such successful examples are described. 

Table 10 Result of one-pot preparation method of optically active epoxides (67a-d) by a combination of epoxidation of cyclohexenone and enantiomer resolution in a water suspension medium... 

When a mixture of methyl phenyl sulfide (69a) (1 g, 8.1 mmol), 30% H2O2 (1.84 g, 16.2 mmol), and water (10 ml) was stirred at room temperature for 24 h, rac-lOa was produced (Scheme 11). To the water suspension medium of rac-70a was added 10c (2 g, 4 mmol), and the mixture was stirred for 15 h to give a 1 1 inclusion complex of 10c with (+)-70a. Heating the filtered complex in vacuo gave (+)-70a of 57% ee (0.45 g, 82% yield). From the filtrate left after separation of the inclusion complex, (-)-70a of 54% ee (0.4 g, 73% yield) was obtained by extraction with ether. By the same procedure, optically active 70b-d were also prepared (Table 11). In the case of (+)-70b and (-)-70c,the efficiency of the enantiomeric resolution was very high. 

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