Hemihydrate Analysis

In this experiment students synthesize basic copper(ll) carbonate and determine the %w/w Gu by reducing the copper to Gu. A statistical analysis of the results shows that the synthesis does not produce GUGO3, the compound that many predict to be the product (although it does not exist). Results are shown to be consistent with a hemihydrate of malachite, Gu2(0H)2(G03) I/2H2O, or azurite, GU3(0H)2(G03)2. 

Two main categories of the wet process exist, depending on whether the calcium sulfate is precipitated as the dihydrate or the hemihydrate. Operation at 70—80°C and 30% P20 in the Hquid phase results in the precipitation of CaSO 2 filterable form 80—90°C and 40% P20 provide a filterable CaSO O.5H2O. Operation outside these conditions generally results in poor filtration rates. A typical analysis of wet-process acid is given in Table 4. For more detailed discussion of the wet-process acid, see Fertilizers. 

As far as the gypsum crystals are concerned, the analysis is identical to that for a seeded MSMPR (34). The information required is the growth rate and the mean residence time. For the hemihydrate, the analysis is that for a continuous seeded MSMPR dissolver (35), which parallels that for the crystallizer. The information needed is the dissolution rate and the mean residence time. 

Hemihydrate. Crystal structure has been determined by X-ray analysis.1 m... 

Two types of coal ash samples have been prepared routinely for analysis at the Illinois Geological Survey. Low-temperature ash samples (12), in which the bulk of the mineral matter remains unchanged, are prepared by reaction of the coal with activated oxygen in a radiofrequency field. The effective temperature produced by this device is approximately 150 °C. Such samples were unsatisfactory for emission spectroscopic analysis. It is postulated that the presence of largely unaltered mineral matter, such as carbonates, sulfides, and hemihydrated sulfates (12), caused the observed nonreproducibility of results. High-temperature ash samples, prepared in a muffle furnace, consisted mainly... 

Aspartame has been reported in a variety of solvatomorphic forms, namely one anhydrous form, two hemihydrate forms (Forms I and II) and a di-hemihydrate [8]. The structural details of the crystal properties have been discussed earlier, and will also be addressed in the discussion on thermal analysis. The room temperature transition between the hemihydrate and di-hemihydrate forms occurs between relative humidities of 40% and 60%. 

Leung et al [8] reported that the thermogravimetric analysis (TGA) of aspartame hemihydrate (Forms I and II) and aspartame dihemihydrate displayed mass losses for water (first mass loss) and methanol (second mass loss). This information is summarized in the following table ... 

At room temperature and atmospheric pressure, the relative thermal stability of the four modifications has been determined by solvent-mediated transformations and thermal analysis to be > y > Q -hemihydrate > p (Foltz et al. 99Aa,b Foltz 1994). Of the anhydrate materials is indeed the most dense as expected from this ordering (see Section 2.3), but in contradiction to the expected correlation between density and relative stability p is more dense than y (Nielsen et al. 1998). 

Method T.P41] Jq H-Cys-OH (1.21 g, lOmmol) in 90% formic acid (lOmL) was added Npys-Q (2.10g, 11 mmol). After 1 h at rt, insoluble material was filtered off, and the crude product was precipitated with EtjO and reprecipitated from MeOH with EtjO yield 2.23 g (81%) of H-Cys(Npys)-OH as the hydrochloride hemihydrate (determined by CHN analysis) mp 188-190°C (dec) -1-140.5 (c 1, MeOH). 

THAB has been prepared by neutralizing tetrahexylammonium hydroxide, obtained from the iodide by treatment with Ag20, with benzoic acid and evaporation of the water. The analysis of the dried product corresponds to a hemihydrate. The material is somewhat hygroscopic but can be dried by brief heating to 90°C. 

The solid product from each of these sets of reactions is primarily calcium sulfite hemihydrate (CaSOs-5 H2O), which has been confirmed by x-ray diffraction analysis of scrubber sludgesJ l A similar set of reactions collects sulfur trioxide (SO3) from the flue gases, forming gypsum (CaS04 2H2O) as the solid product, but under normal boiler conditions sulfur trioxide makes up only about 0.5% of the total sulfur oxides, and so its removal is less important than the removal of sulfur dioxide.l " ... 

Determination of the optimal heat treatment temperature in the reactor is done by differential thermal analysis (DTA) and thermogravimetric analysis (TG) it appears (Fig. 2) that in our experimental procedure, for all the studied granulometries (<25 to 250 gm), a specimen fired at 398 K for 3 h contains no mote gypsum, and a specimen fired at 423 K still contains almost only hemihydrate. Above this temperature anhydrite III appears. The very small amount of anhydrite 111 contained in a specimen fired at 423 K is different from a gypsum variety, but quite stable and characteristic for a variety of gypsum (Fig. 6) fZ]. 

The X-ray diffraction analyses of water-soluble material from phosphogypsum showed only the presence of gypsum and a trace of hemihydrate. The sensitivity of this analysis was not sufficient to identify compounds of the trace elements. 

The batch precipitation tests show dramatic effects of adipic acid slurry concentration and solid phase oxidation fraction on coprecipitation of adipic acid in scrubber solids. Real world scrubbers would probably never operate at adipic acid concentrations as high as those tested and would also not likely ever produce pure phase calcium sulfite hemihydrate. Therefore, the magnitude of the results observed is somewhat a product of the laboratory test conditions. The results do, however, establish the potential importance of adipic acid coprecipitation and, hence, the need for analysis of scrubber solids for adipic acid when determining adipic acid chemical degradation rates by a mass balance calculation approach. 

The amino acid 3 has low solubility in water, although the compoimd itself binds water tightly. Elemental analysis of the amino acid fits the composition of the monohydrate, C5H4N4O2 H2O. If the acid hydrolysis reaction is neutralized with sodium bicarbonate, the sodium salt of the amino acid precipitates as a white solid. The analysis for this product fits that calculated for the hemihydrate. 

Fig. 5. A drawing showing the dimensions of the molecule of adenine as determined by x-ray analysis of crystals of adenine hydrochloride hemihydrate.

The absolute stereochemistry of stemonine (16) was revealed by X-ray analysis of its hydrobromide hemihydrate by considering anomalous dispersion effects (28). The C-NMR data for stemonine (16) has been reported without assignments (33). 

Sadly, also in the so-called high-impact journals, we often find analytical data for amorphous compounds as hydrates, hemihydrates, etc., just because the analytical figures happen to fit that particular formula adjusted for solvation. This is scientifically unsound. In a crystal, discrete numbers of solvent molecules may partake in the lattice formation. In an amorphous substance, however, this is not so. Therefore, it is likely that it is possible to find an analysis that tits any compound using solvation. Therefore, an analysis of an amorphous compound is irrelevant if it needs solvation adjustment. 

The XRD analysis indicated the final product to be y-CaS04 although diffraction peaks of calcium sulfate hemihydrate were observed, likely the result of spontaneous rehydration of 7-CaS04 into calcium sulfate hemihydrate. 

The production of commercial building materials, e.g., portland cement and stucco, utilizes calcium sulfate in the form of the dihydrate or hemihydrate.f Gypsum is added in the production of portland cement to control set. Properties of cement can be adversely affected by the formation of hemihydrate during the grinding process. In the production of stucco, the hemihydrate is the preferred form. Consequently, investigators have adapted thermal analysis methods for estimating the quantities of each phase in these products. 

Reaction kinetics from DSC, DTA or TGA, have been used to examine the stability of a limited number of pharmaceutical materials. Various models have been used including the Power Law, Avarami-Erofeev and Prout-Tomkins models [72]. These methods are also based on the Kissinger [73], ASTME 698 [74] or Ozawa [75] methods [8]. Most frequently, they have been applied to the dehydration of various materials such as theophylline monohydrate [76], phenobarbitone monohydrate or hemihydrate [77], phenylbutazone [78], oxazepam [23] and trazodone tetrahydrate [79]. The uses are limited for pharmaceutical systems, not least because dehydration is particle size dependent. Thermal analysis, especially DSC, DTA and TG, has been used outside the pharmaceutical area in the prediction of reaction kinetics as described elsewhere in this handbook. Methods used include those by Borchart and Daniels [80], Kissinger [73], Freeman and Carroll [81] and Flynn and Wall [82]. Although these techniques are well established and, if used properly, can give pertinent information, their use in pharmaceutical arenas is restricted to dehydration and decomposition. 

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