Crystalline dehydrates

Owerreine (266). The crystalline alkaloid, C43H48O5N4, isolated in trace amounts from Callichilia barteri shows spectral properties which are very similar to those of anhydrovobtusine (258), the non-crystalline dehydration product of vobtusine (255). The two bases, however, run quite differently on t.l.c. and there is no doubt that the two substances are not identical. It is certain that owerreine (266) is a stereoisomer of anhydrovobtusine (258) the virtually superimposable u.v. spectra suggest that the aromatic methoxy-function is again at C(17 ). The lack of material has prevented a chemical examination of owerreine. 

According to the encapsulation processes used, the matrices of encapsulation can show diverse shapes (films, spheres, irregular particles), structures (porous or compact), physical structures (amorphous or crystalline dehydrated solid, rubbery or glassy matrix). This diversity is responsible for the different diffusion of flavors (Madene et al., 2006). 

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. 

To prepare pure acetic acid (glacial acetic acid), the crude aqueous product is converted into the sodium salt, the latter dehydrated by fusionf and then heated with concentrated sulphuric acid anhydrous acetic acid, b.p. 118°, distils over. Only the preparation of aqueous acetic acid and of crystalline copper acetate is described below. 

In aqueous solutions of sulphuric (< 50%) and perchloric acid (< 45 %) nitrous acid is present predominantly in the molecular form, although some dehydration to dinitrogen trioxide does occur.In solutions contairdng more than 60 % and 65 % of perchloric and sulphuric acid respectively, the stoichiometric concentration of nitrous acid is present entirely as the nitrosonium ion (see the discussion of dinitrogen trioxide 4.1). Evidence for the formation of this ion comes from the occurrence of an absorption band in the Raman spectrum almost identical with the relevant absorption observed in crystalline nitrosonium perchlorate. Under conditions in which molecular nitrous... 

Bisa.codyl, 4,4 -(2-PyridyLmethylene)bisphenol diacetate [603-50-9] (Dulcolax) (9) is a white to off-white crystalline powder ia which particles of 50 p.m dia predominate. It is very soluble ia water, freely soluble ia chloroform and alcohol, soluble ia methanol and ben2ene, and slightly soluble ia diethyl ether. Bisacodyl may be prepared from 2-pyridine-carboxaldehyde by condensation with phenol and the aid of a dehydrant such as sulfuric acid. The resulting 4,4 -(pyridyLmethylene)diphenol is esterified by treatment with acetic anhydride and anhydrous sodium acetate. Crystallisation is from ethanol. 

Potassium Oxalate. The monohydrate [6487-48-5] K2C204-H20, mol wt 184.24, is produced as a colodess crystalline material or a white powder. The anhydrous salt [583-52-8] mol wt 166.22, is obtained when the monohydrate is dehydrated at 160°C. The monohydrate is preferred as a reagent in analytical chemistry and in miscellaneous uses principally because of its high solubihty as compared with other simple neutral oxalates the saturated solution, at 0°C, contains about 20 wt %, and at 20°C, about 25 wt %... 

Crystalline CaHPO 2H20 loses both water molecules in a single step at moderately elevated temperature or upon storage to yield the anhydrous salt. The presence of free moisture accelerates this dehydration, which results in anhydrous dicalcium phosphate, often as a hard mass. Addition of a few percent of tetrasodium pyrophosphate or trimagnesium phosphate, Mg2(P0 2> stabilizes the dihydrate. The mechanism, however, is not well understood. Nonetheless, these materials are used widely to stabilize CaHPO 2H20, particulady for toothpaste appHcations. 

Condensed phosphates are derived by dehydration of acid orthophosphates. The resulting polymeric stmctures are based on a backbone of P—O—P linkages where PO tetrahedra are joined by shared oxygen atoms. The range of materials within this classification is extremely broad, extending from the simple diphosphate, also known as pyrophosphate, to indefinitely long-chain polyphosphates and ultraphosphates (see Table 1). Both weU-defined crystalline and amorphous materials occur among the condensed phosphates. 

Sodium Pyrophosphates. Known pyrophosphate compounds in the Na20—H2O—P20 system are given in Table 10. Commercially important sodium pyrophosphates include tetrasodium pyrophosphate (TSPP), Na4P20y, and disodium pyrophosphate, Na2H2P20y, commonly referred to as sodium acid pyrophosphate (SAPP). These are prepared industrially by thermal dehydration of disodium and monosodium orthophosphate, respectively. Tetrasodium pyrophosphate exists in five crystalline modifications, only one of which is stable at room temperature. 

Several crystalline condensed phosphates may also be formed by the dehydration of monosodium phosphate (MSP). Maddrell s salt exists as Form 11 (high temperature MaddreU, NaPO -ll, insoluble metaphosphate-11) and Form 111 (low temperature MaddreU, NaPO -lll, insoluble metaphosphate-111). Both forms are highly polymerized and difficult (slow) to dissolve in water. Mixtures of the two forms are marketed as a dental abrasive for toothpaste formulations containing soluble fluoride. Maddrell s salt is also used with disodium phosphate as a cheese emulsifying aid. 

Crystalline TSP is a dodecahydrate with somewhat variable composition between the limits of (Na PO I2H2O) 0.25NaOH and (Na PO I2H2O) l/TNaOH. It is manufactured by crystallisation below 60°C from a solution with an Na20/P20 mole ratio slightly lower than 3.25. Crystals are isolated by centrifugation and air-dried at ca 40°C to minimise dehydration. 

Physical and Chemical Properties. Trimellitic acid and trimellitic anhydride are odorless white crystalline soHds in their pure form. The acid is reasonably stable up to the melting point, where dehydration to the anhydride occurs. The anhydride reacts with atmopsheric moisture, even at room temperature, to revert to the acid. Physical properties of the acid and its anhydride are Hsted in Tables 29—31. 

Further deprotonation, dehydration, and polymerization of monomers and dimers may yield ringlike stmctures of hydroxy—aluminum complexes (10). Coalescence of ring compounds into layers by further growth results in the formation of crystalline aluminum hydroxide at pH 6, the point of minimum aqueous solubiUty. 

Total sugar products are also produced by dehydrating hydroly2ate to a mixture of crystals and amorphous glass. This product is not produced in significant quantities in the United States or Europe but is popular in Japan and Korea where it represents 40—50% of total crystalline dextrose sold (14). 

Pure talc is thermally stable up to 930°C, and loses its crystalline bound water (4.8%) between 930 and 970°C, leaving an enstatite (dehydrated magnesium siUcate) residue. Most commercial talc products have thermal loss below 930°C on account of the presence of carbonates, which lose carbon dioxide at 600°C, and chlorite, which loses water at 800°C. Talc is an insulator for both heat and electricity. 

Oxides and Hydroxides. ThaHous oxide is most readily obtained by dehydration of TlOH ia high vacuum at 50°C. It is black, crystalline, and hygroscopic. It reacts with water to form the hydroxide and dissolves ia ethanol to yield the ethoxide (9). 

Cobalt(II) chloride hexahydrate [7791-13-1], C0CI2 6H20 is a deep red monoclinic crystalline material that deflquesces. It is prepared by reaction of hydrochloric acid with the metal, simple oxide, mixed valence oxides, carbonate, or hydroxide. A high purity cobalt chloride has also been prepared electrolyticaHy (4). The chloride is very soluble in water and alcohols. The dehydration of the hexahydrate occurs stepwise ... 

Cobalt(II) hydroxide [1307-86-4], Co(OH)2, is a pink, rhombic crystalline material containing about 61% cobalt. It is insoluble in water, but dissolves in acids and ammonium salt solutions. The material is prepared by mixing a cobalt salt solution and a sodium hydroxide solution. Because of the tendency of the cobalt(II) to oxidize, antioxidants (qv) are generally added. Dehydration occurs above 150°C. The hydroxide is a common starting material for the preparation of cobalt compounds. It is also used in paints and Hthographic printing inks and as a catalyst (see Paint). 

Gopper(II) Sulfates. Copper(II) sulfate pentahydrate [7758-99-8] CuS04-5H20, occurs in nature as the blue triclinic crystalline mineral chalcanthite [13817-21 -5]. It is the most common commercial compound of copper. The pentahydrate slowly effloresces in low humidity or above 30.6°C. Above 88°C dehydration occurs rapidly. 

Molecular sieves are an adsorbent that is produced by the dehydration of naturally occurring or synthetic zeolites (crystalline alkali-metal aluminosilicates). The dehydration leaves inter-crystalline cavities into which normal paraffin molecules are selectively retained and other molecules are excluded. This process is used to remove normal paraffins from gasoline fuels for improved combustion. Molecular sieves are used to manufacture high-purity solvents. 

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