Organic compounds crystallization

Through luck, in 1848, Louis Pasteur was able to separate or resolve racemic tartaric acid into its (+) and (—) forms by crystallization. Two enantiomers of the sodium ammonium salt of tartaric acid give rise to two distinctly different types of chiral crystal that can then be separated easily. However, only a very few organic compounds crystallize into separate crystals (of two enantiomeric forms) that are visibly chiral as are the crystals of the sodium ammonium salt of tartaric acid. Therefore, Pasteur s method of separation of enantiomers is not generally applicable to the separation of enantiomers. 

Most organic compounds crystallize in the monoclinic or orthorhombic crysta systems, which contain substantial macroscopic anisotropies, and thus the single crystal CD technique cannot be applied, although our method of measuremei may be useful if the macroscopic anisotropies are not very large. An alternative... 

Most organic compounds crystallize in the monoclinic or orthorhombic crystal systems, which contain substantial macroscopic anisotropies, and thus the singlecrystal CD technique cannot be applied, although our method of measurement may be useful if the macroscopic anisotropies are not very large. An alternative way to obtain crystalline-specific information is to examine the microcrystalline state. Measurements can be usually made either in nujol mull or KBr disc form, where microcrystals are dispersed randomly either in nujol or in a KBr microcrystalline matrix. The method was developed and applied to inorganic complexes by Mason [34], Bosnich [35], and Kuroda [9,10], and since then its application to metal complexes has been carried out sporadically [36,37]. Recently, the technique has become popular in the field of organic chemistry as well, probably stimulated by our work [38]. An alternative technique recently developed by us is diffuse reflectance CD (DRCD) which will be briefly described in V.B.2. 

Acetic acid, merouridi- Acetic acid, mercury(2+) salt A13-04458 Anthracene, 1,4-dihydro-, compd. with mercury diacetate (1 1) Bis(acetyloxy)mercury Caswell No, 543A CCRIS 7488 Diacetoxymercury EINECS 216-491-1 ERA Pesticide Chemical Code 052104 HSDB 1244 Mercuriacetate Mercuric acetate Mercuric diacetate Mercury acetate Mercury di(acetate) Mercury diacetate Mercury(2-f) acetate Mercury(ll) acetate Mercuryl acetate NSC 215199 UN1629, Catalyst for organic synthesis, pharmaceuticals. Used for mercuration of organic compounds. Crystals mp = 178-180 soluble in H2O (40 g/100 ml), EtOH LDso (rat orl) = 4 mg/kg, Atomargtc Chemetals Cerac Noah Chem. Thor. 

The goal of early stage solid-state analysis is the determination of the tendency of a compound to crystallize into different forms. It may have many forms like sulfathiazole with at least four polymorphs [6] or methylestradiol with one anhydrous form, two hydrated forms and at least two solvated forms [4]. This information guides the course of the future studies. If only one pharmaceutically significant form exists, then the subsequent studies should be straightforward and relatively rapid. If many forms exist, choosing the optimal form for development may require extensive time and study. It is useful to operate on the principle that all organic compounds crystallize in different forms and that the only questions are How many and How important McCrone [7] put the matter this way ... 

Unfortunately, less than 10% of organic compounds crystallize as a conglomerate (the remainder form racemic crystals) largely denying the possibility of separating enantiomers by simple crystallization techniques - such as by seeding a supersaturated solution of the racemate with crystals of one pure enantiomer. 

Experimental studies concerning crystallization from W/O microemulsions use thermal analysis methods to characterize the microemulsions themselves, to determine thermodynamic parameters of crystallization, and to characterize the final products. A large number of studies are concerned with the state of water in ionic [109] and nonionic [110] W/O microemulsions. It has been shown that because of the close proximity of the interface, the properties of the water molecules are quite different from those of water in the bulk, and this difference in itself may have a profound effect on the solubilization and crystallization of solutes. The problem is discussed in detail in two other chapters (by Schulz et al. and by Garti et al.) in this book and will not be reiterated here. In this presentation we describe (1) calorimetric studies of the formation of nanosized inorganic crystallites and (2) the use of TG and DSC in the characterization of a water-soluble organic compound crystallized in a W/O microemulsion. 

Most organic and metal-organic compounds crystallize as molecular sohds where the three-dimensional structure is constmcted by the packing of molecules in the sohd state. 

Gavezzotti A 1991. Generation of Possible Crystal Structures from the Molecular Structure for Low-polarity Organic Compounds, journal of the American Chemical Society 113 4622-4629. 

Solid organic compounds when isolated from organic reactions are seldom pure they are usually contaminated with small amounts of other compounds ( impurities ) which are produced along with the desired product. Tlie purification of impure crystalline compounds is usually effected by crystallisation from a suitable solvent or mixture of solvents. Attention must, however, be drawn to the fact that direct crystallisation of a crude reaction product is not always advisable as certain impurities may retard the rate of crystallisation and, in some cases, may even prevent the formation of crystals entirely furthermore, considerable loss of... 

Add 1 drop (0 05 ml.) of concentrated nitric acid to 2 0 ml. of a 0 5 per cent, aqueous solution of paraperiodic acid (HjIO,) contained in a small test-tube and shake well. Then introduce 1 op or a small crystal of the compound. Shake the mixture for 15 seconds and add 1-2 drops of 5 per cent, aqueous silver nitrate. The immediate production of a white precipitate (silver iodate) constitutes a positive test and indicates that the organic compound has been oxidised by the periodic acid. The test is based upon the fact that silver iodate is sparingly soluble in dilute nitric acid whereas silver periodate is very soluble if too much nitric acid is present, the silver iodate will not precipitate. 

Lead oxide is used in producing fine "crystal glass" and "flint glass" of a high index of refraction for achromatic lenses. The nitrate and the acetate are soluble salts. Lead salts such as lead arsenate have been used as insecticides, but their use in recent years has been practically eliminated in favor of less harmful organic compounds. 

Urea has the remarkable property of forming crystalline complexes or adducts with straight-chain organic compounds. These crystalline complexes consist of a hoUow channel, formed by the crystallized urea molecules, in which the hydrocarbon is completely occluded. Such compounds are known as clathrates. The type of hydrocarbon occluded, on the basis of its chain length, is determined by the temperature at which the clathrate is formed. This property of urea clathrates is widely used in the petroleum-refining industry for the production of jet aviation fuels (see Aviation and other gas-TURBINE fuels) and for dewaxing of lubricant oils (see also Petroleum, refinery processes). The clathrates are broken down by simply dissolving urea in water or in alcohol. 

The primary Cr—O bonded species is cbromium (VT) oxide, CrO, which is better known as chromic acid [1115-74-5], the commercial and common name. This compound also has the aliases chromic trioxide and chromic acid anhydride and shows some similarity to SO. The crystals consist of infinite chains of vertex-shared CrO tetrahedra and are obtained as an orange-red precipitate from the addition of sulfuric acid to the potassium or sodium dichromate(VI). Completely dry CrO is very dark red to red purple, but the compound is deflquescent and even traces of water give the normal mby red color. Cbromium (VT) oxide is a very powerful oxidi2er and contact with oxidi2able organic compounds may cause fires or explosions. 

Chromium trioxide (chromic anhydride) [1333-82-0] M 100.0, m 197°, dec at 250° to Cr203, d 2.70 (pK 0.74, pK 6.49, for H2Cr04, chromic acid). Red crystals from water (0.5mL/g) between 100° and -5°, or from water/conc HNO3 (1 5). It separates when potassium or sodium dichromate are dissolved in cone H2SO4. Dried in a vacuum desiccator over NaOH pellets hygroscopic, powerful oxidant, can ignite with organic compounds. It is a skin and pulmonary IRRITANT. 

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