Crystalline agent

The dihydrochloride is a white crystalline powder, m.p. about 225 C (decomp.). Used as an antiseptic and skin sterilizing agent, and as a bacteriostat in some pharmaceutical formulations. 

Crystalline solid m.p. 35-36 "C, b.p. 154--156 C, prepared by oxidizing A,A -dicycIo-hexylthiourea with HgO in carbon disulphide solution, also obtained from cyclohexylamine and phosgene at elevated temperatures. Used as a mild dehydrating agent, especially in the synthesis of p>eptides from amino-acids. Potent skin irritant. 

NH4)2Fe(S04)2,6H20. Pale green crystalline solid used as a standard reducing agent (e.g. for KMn04). More stable than FeS04. 

Hi at 500" C. Stable crystalline compound, gives LiOH and Hi with water (may ignite in moist atmosphere). Used as a source of Hi, as a reducing agent, and for the preparation of hydrides. 

CgH,oN20. Colourless crystalline solid, m.p. 121 °C. Made by reacting phenylhydrazine with ethyl acrylate to obtain the hydrazide which cyclizes to the product. Its major commercial importance is as a photographic developing agent, being used particularly in conjunction with hydroquinone. 

The first step in designing a precursor synthesis is to pick precursor molecules that, when combined in organic solvents, yield the bulk crystalline solid. For metals, a usual approach is to react metal salts with reducing agents to produce bulk metals. The main challenge is to find appropriate metal salts that are soluble in an organic phase. 

Figure C2.17.8. Powder x-ray diffraction (PXRD) from amoriDhous and nanocry stalline Ti02 nanocrystals. Powder x-ray diffraction is an important test for nanocrystal quality. In the top panel, nanoparticles of titania provide no crystalline reflections. These samples, while showing some evidence of crystallinity in TEM, have a major amoriDhous component. A similar reaction, perfonned with a crystallizing agent at high temperature, provides well defined reflections which allow the anatase phase to be clearly identified.

Urea reacts with formaldehyde compounds such as monomethylolurea, NH2CONHCH2OH, dimethylolurea, HOCH2NHCONHCH2OH, and others, depending on the mol ratio of formaldehyde, to urea and upon the pH of the solution. Hydrogen peroxide and urea give a white crystalline powder, urea peroxide, CO(NH2 (2 -H2 02, known under the trade name of Hypersol, an oxidizing agent. 

A significant advantage of adsorbents over other separative agents Hes in the fact that favorable equiHbrium-phase relations can be developed for particular separations adsorbents can be produced that are much more selective in their affinity for various substances than are any known solvents. This selectivity is particularly tme of the synthetic crystalline zeoHtes containing exchangeable cations. These zeoHtes became available in the early 1960s under the name of molecular sieves (qv) (9). 

Silver difluoride [7783-95-1], AgF2, is a black crystalline powder. It has been classified as a hard fluorinating agent (3) which Hberates iodine from KI solutions and o2one from dilute aqueous acid solutions on heating. It spontaneously oxidizes xenon gas to Xe(II) in anhydrous hydrogen fluoride solutions (20). 

Potassium iodate [7758-05-6] KIO, mol wt 214.02, 59.30% I, forms white, odorless crystals or a crystalline powder. It has a density 3.98 g/mL and mp of 560°C with partial decomposition. Potassium iodate is rapidly formed when potassium iodide is fused with potassium chlorate, bromate, or perchlorate. The solubihty in water is 9.16 g/100 g H2O at 25°C and 32.2 g/100 g H2O at 100°C. KIO is extensively used as an oxidizing agent in analytical chemistry and as amaturing agent and dough conditioner (see Bakery processes and leavening agents). 

Both propylene and isobutylene ate comonomers that are incorporated along the chain, resulting in additional short-chain branching. One important factor in controlling polymer crystallinity is the choice of chain-transfer agent. Ethane and methane, for example, are inefficient agents whose presence in the monomer feed stream must be considered in reaction control. 

Polypropylene molecules repeatedly fold upon themselves to form lamellae, the sizes of which ate a function of the crystallisa tion conditions. Higher degrees of order are obtained upon formation of crystalline aggregates, or spheruHtes. The presence of a central crystallisation nucleus from which the lamellae radiate is clearly evident in these stmctures. Observations using cross-polarized light illustrates the characteristic Maltese cross model (Fig. 2b). The optical and mechanical properties ate a function of the size and number of spheruHtes and can be modified by nucleating agents. Crystallinity can also be inferred from thermal analysis (28) and density measurements (29). 

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