Crystals, hydrated, obtaining

In a 500-cc. round-bottom flask fitted with a reflux condenser are placed 68 g. of phenylurea (0.5 mole) (Note i) and 120 cc. (i mole) of 42 per cent hydrazine hydrate solution (Note 2). The flask is heated on a steam bath for about twelve hours. The hot mixture is treated with a small amount of decolorizing charcoal (Norite) and filtered. The charcoal is washed with two 15-CC. portions of warm water and the filtrate and washings are then concentrated on a steam bath to about 100 cc. On coolipg in an ice bath a crop of crystals separates and is collected on a filter and washed with two 15-cc. portions of cold water. The filtrate and washings are concentrated to about 25 cc. and another crop of crystals is obtained as before. The total yield of crude compound is 47-52 g. It is white at first but sometimes turns brown on drying. It usually melts below 115° because of some unchanged phenylurea. 

Terpine hydrate, CioHig(OH)3 + HjO, is a crystalline alcohol resulting from the action of dilute mineral acids on either pinene or limonene. It can be prepared by several different methods, of W hich the following is typical A mixture of 8 parts of oil or turpentine, 2 parts of alcohol, and 2 parts of nitric acid of specific gravity 1 255 IS allowed to stand for several days in a flat basin. After standing for a few days the mother liquor is poured off from the crystals of terpine hydrate, and neutralised with an alkali, after which a second crop of crystals is obtained. 

Balke [55] obtained crystal hydrate of lithium hexafluorotantalate, LiTaF6 H20, by evaporating a solution prepared by the dissolution of Ta205 and Li2C03 in HF. Crystal hydrate of sodium heptafluorotantalate, Na2TaF7-H20, was prepared in the same way [56], while re-crystallization of Na2TaF7-H20 from water yielded sodium octafluorotantalate, Na3TaF8 [29]. 

Ferric ammonium sulfate is prepared by mixing an equimolar solution of ferric sulfate, Fe2(S04)3, and ammonium sulfate, (NH4)2S04. Hydrated crystals are obtained following evaporation and cooling of the solution. 

On cooling, colorless crystals are obtained which are dissolved in hot water. Dilute ammonia solution is added to the resulting aqueous solution to render it weakly alkaline. The base of l-p-chloro-benzyl-2-methylbenzimidazole precipitates, first in liquid form, and gradually solidifies to a white mass of its hydrate. After recyrstallization from aqueous ethanol, the product has a melting point of 67-68°C. The base of l-p-chlorobenzyl-2-methylbenzimidazole distills in the form of a colorless oil at 240-242°C/12 mm. Its hydrate of the melting point 67-68°C is obtained by trituration with water. 

Five grams of nickel(II) chloride 6-hydrate and 12.1 g. of tris(ethylenediamine)nickel(II) chloride 2-hydrate J are gently refluxed for 5 minutes with a mixture of 47.5 ml. of methanol and 2.5 ml. of water, shaking at first until all the salts are dissolved. A beautiful deep blue solution results. This is filtered by gravity while still warm into a 400-ml. beaker, and the flask and paper are washed once with 5 ml. of hot methanol. Seed crystals are obtained by adding 3 to 4 ml. of acetone slowly to 2 to 3 ml. of the blue solution and scratching or shaking until crystals form the separation of two liquid phases indicates the addition of too much acetone and makes the formation of crystals difficult. 

The calcium silicate hydrate formed in both cases appears to be a very poorly crystallized version of the natural mineral tobermorite. The use of the name tobermorite for the calcium silicate hydrate obtained in the hydration of Ca8Si05 and Ca2Si04 is not fully justified nevertheless, because in all publications from this laboratory that name was used, the usage is retained in this paper. 

Payakoff carried out the synthesis of various oxalate complexes by mechanical activation of the solid oxalic acid with hydroxides and basic salts [35], He demonstrated that the synthesis proceeded with the formation of honey-like mass from which solid complex crystal hydrates are crystallized relatively easily under aging of activating mixtures at room temperature. Ultrafine and highly reactive catalysts, pigments and other compounds of practical importance were obtained by thermal decomposition of the mentioned complexes. 

Compounds of pharmaceutical interest can exist in different solid forms. Broadly, they can be classified as being in the amorphous or in the crystalline state. In crystalline pharmaceuticals, solvates are formed when the solvent molecule is incorporated, either stoichiometrically or non-stoichiometrically, in the crystalline lattice. Hydrates are a subclass of solvates, wherein the incorporated solvent is water. Because of regulatory considerations, non-aqueous solvates find limited use as pharmaceuticals. Our dis-cu.ssions will, therefore, be restricted to hydrates. If the solvent is non-volatile, co-crystals are obtained, and this is an emerging field in solid-state pharmaceutics. In case of weakly acidic and basic compounds, salt forms are prepared with the goal of obtaining the desired biopharmaceutical properties. Figure 3 is a schematic representation of the various types of solid forms of interest in pharmaceuticals (6). 

Many crystals grown from aqueous solution are hydrates (see Chapter 7). Dehydration often precedes loss of other ligands or decomposition of other constituent ions. If water loss is the reaction to be studied, the possibility that partial dehydration may have occurred during storage must be investigated. Information on the water content of the reactant and the importance of any intermediate steps in dehydration must be considered. The conditions during dehydration can influence the reactivity of the anhydrous salt, or the lower hydrate, obtained. The product formed during dehydration in vacuum is often amorphous or microcrystalline, while... 

The solid-liquid state diagram of the GB-water system shown in Figure 52.3 was constructed from data obtained in the present study supplemented by the existing ones (Landolt-Bornstein, 1962). As the DSC heating scans obtained with the system in the concentration above 60 wt% were complicated, there remained ambiguity in the diagram about the existence of crystal hydrates other than monohydrate. Although eutectic... 

On electron gas theory Ae = fe /4ma and on the model a = nd. We see Ae will decrease as the number of conjugated ir electrons increases. While in principle a protein may extend the conjugation path for tt electrons, in practice this can hold for only a few adjacent amino-acid residues if hemoglobin in the dry state is any guide, since the A obtained for the over-all conductivity of this molecule by Cardew is 2.7 e.v., the globin effectively insulating the haem from each other in the crystal. Hydration may in certain instances lower this value, but this is still to be investigated fully. 

The compound is obtained very easily by admixing a soluble azide to an aqueous thallium(I) salt solution. The product precipitates immediately as a straw-yellow crystal powder. Larger crystals are obtainable by cooling hot, saturated aqueous solutions [62]. Combinations such as thallium sulfate/ potassium azide [237] and thallium nitrate/ammonium azide [61] may be used for the preparation. This author prefers thallium perchlorate and sodium azide, because favorable solubility products of the ions involved and the absence of hydration lead to a material that is free of coprecipitated ions. For example, to a stirred solution of 200 g TICIO4 in 1600 ml water is admixed 45 g sodium azide dissolved in 150 ml water. The dense precipitate is washed with cold water until perchlorate free, and then with acetone. Practical yield, 152 g. The product should be stored completely dry as the damp material tends to discolor [236]. 

A solution of 5 g. (0.027 mol) of potassium oxalate 1-hydrate in 20 ml. of water is added to a slurry of 6 g. (0.014 mol) of uranium(IV) oxalate 6-hydrate in 50 ml. of water. The reaction is complete after the mixture has been heated on a steam bath for 1 hour. The dark green filtrate is treated with 200 ml. of absolute alcohol, which is added drop by drop from a separatory funnel while the mixture is stirred. J Small light green crystals are obtained, which are quickly dried by washing them several times with absolute alcohol and finally with ether. To avoid oxidation, potassium tetraoxalatouranate(IV) is stored in a desiccator over phosphorus (V) oxide. 

Figure 6 A comparison of the rendered surfaces of TEM reconstructions of the active RecA-DNA filament (left) and the inactive RecA-DNA filament (right) with the RecA crystal surface (center). The RecA crystal surface, obtained by X-ray crystallography, has been rendered at low resolution, to be comparable with the TEM reconstructions. Both the active and inactive filament reconstructions are from averages of frozen-hydrated specimens imaged with cryo-EM. (Reproduced with permission from Egelman EH and StasiakA (1993) Electron microscopy of RECA-DNA complexes Two different states, their functional significance and relation to the solved crystal structure. Micron 24 309-324.)...

The same co-crystal hydrate is also obtained by the neat grinding of theophylline hydrate with anhydrous dtric add, the neat grinding of anhydrous theophylline with dtric acid monohydrate, as well as the neat grinding of theophylline monohydrate with dtric add monohydrate. Neat grinding of anhydrous theophylline and anhydrous dtric acid, by contrast, leads to the formation of an anhydrous co-crystal of 1 1 stoichiometry (Figure 8.18(c)). The similarity of the supramolecular motifs within the co-crystal hydrate to those observed in theophylline monohydrate and citric acid monohydrate crystals (Figure 8.19) suggests that, in the presence of water, the co-crystal hydrate could... 

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