Active quartz

Mechanically activated quartz featuring active centres of various origin on its surface is a very interesting object to conduct the studies of this kind [60]. Some of these centres irreversibly annihilate during heating. 

Another hypothesis on homochirality involves interaction of biomolecules with minerals, either at rock surfaces or at the sea bottom thus, adsorption processes of biomolecules at chiral mineral surfaces have been studied. Klabunovskii and Thiemann (2000) used a large selection of analytical data, provided by other authors, to study whether natural, optically active quartz could have played a role in the emergence of optical activity on the primeval Earth. Some researchers consider it possible that enantioselective adsorption by one of the quartz species (L or D) could have led to the homochirality of biomolecules. Asymmetric adsorption at enantiomor-phic quartz crystals has been detected L-quartz preferentially adsorbs L-alanine. Asymmetrical hydrogenation using d- or L-quartz as active catalysts is also possible. However, if the information in a large number of publications is averaged out, as Klabunovskii and Thiemann could show, there is no clear preference in nature for one of the two enantiomorphic quartz structures. It is possible that rhomobohedral... 

Busch and Bailar1 obtained optically active solutions of one of the enantiomers of the ethylenediaminetetraacetato-cobaltate(III) ion by selective adsorption on optically active quartz and by fractional crystallization of the strychnine salt. More recently Dwyer, Gyarfas, and Mellor2 reported the complete resolution using d and Z-tris(ethylenediamine) cobalt(III) chloride. Precipitation of the diastereoisomers was effected by addition of ethanol to the aqueous solution. The volume of ethanol used was critical and often merely the potassium salt separated. 

Knowledge of the concentration of defects and molar disturbance enthalpies would permit calculation of the actual free energy of the solid, and also the chemical potential. These can be measured by using either solution calorimetry or differential scanning calorimetry. An example of the excess energy was given as 20-30 kj mol-i in mechanically activated quartz. Different types of reactions demand different defect types. For example, Boldyrev et al. [25] state a classification and provide examples for solid reactions with different mechanisms and necessary solid alterations. Often, reaction rates in solids depend strongly on the mass transport of matter. Lidi-ard [26] and Schmalzried [27] each provide reviews on transport properties in mechanically treated solids. The increased amount of defects allows a faster transport of ions and atoms in the solid structure. 

Schwab et al. (46, 47) showed that nickel, copper and platinum supported on optically-active quartz behave as enantioselective catalysts for the dehydrogenation and oxidation of racemic sec-butyl alcohol. At low conversion, a measurable optical rotation of the reaction solution is observed, showing that one enantiomer has reacted... 

The first resolution of trioxalatocobaltates was accomplished in 1916 with strychnine. The method of spontaneous crystallization of antipodes from a racemic mixture of a complex was first demonstrated with K3[Co(C204)s] above 13.2°, the optical antipodes may be crystallized and mechanically separated. In practice, however, the standard technique of fractional crystallization of the strychnine diastereoisomers has been used. Partial resolution on optically active quartz has also been reported. Selective decomposition of the antipodes by circularly polarized light... 

Iwasaki, I., Cooke, S.R.B. and Choi, H.S., Flotation, characteristics of hematite, goethite, and activated quartz with 18-carbon aliphatic acids and related compounds, Trans. AIME, 217, 237, 1960. 

In 1953, chemists in Russia reported the asymmetric induction in the Michael addition of cyclohexanone and 2-methylcyclohexanone to acrylonitrile in the presence of optically active quartz coated with EtOLi,EtOK,or EtONa [37]. Maximum rotations of 0.07 and 0.157 were obtained, respectively. 

Fig. 5.16. (a) Depression of various reagents on wolframate flotation 1—citric acid, 2— tartaric acid, 3—oxalic acid, 4—EDTA, 5—succinic acid, 6—lactic acid, (b) Depression of various reagents on flotation of Fe " " activated quartz 1—tartaric acid, 2—citric acid, 3— EDTA, 4—oxalic acid, 5—succinic acid, 6— butyl dicarboxylic acid, 7—lactic acid, 8—acetic acid. 

Tannins are mainly used as depressants for dolomite, calcite and silicate minerals in the flotation of scheelite, apatite, fluorite and copper sulfide. Like starch, tannins after modification by oxidation, sulfidization and aminization (tannin O, S and A, respectively) have been used as a depressant for hematite in the reverse flotation of quartz with oleic acid or dodecylamine as collectors [22]. Flotation results show quartz to be depressed by tannins in the order of tannin A > S at low concentrations of dodecylamine. When an anionic collector is used for the reverse flotation of Ca +-activated quartz with tannins as depressant for hematite, the order of depression is tannin A > O > S. 

Coupling of antibody to T2 toxin to amino-activated quartz fibers using cyanogen bromide T2 toxin from Fusarium tricinctum [5]... 

Activated Quartz with C-18 Aliphatic Acids and Related Compounds, Trans. AIME, 220, 394... 

Other examples of the applications of optical activity to heterogeneous catalysis involve hydrogenolysis, racemization reactions, and optically active catalysts prepared from optically active quartz. At room temperatures, catalytic reactions, even those which involve the optical center, usually take place with little or no racemization. At higher temperatures, considerable racemization often ensues. Applications of optical activity to heterogeneous catalysis, although of much promise, have so far been relatively little studied. 

Mason and Tranter performed calculations and alleged that a 1.4% excess of /- over r/-quartz on the surface of Earth is the inevitable consequence of a parity-violating energy difference (PVED). They calculated that the /-quartz is stabilized by lO kT per Si02 unit This allegation is based on a report that there is 50.17% /-quartz and 49.3% r/-quartz in 16,807 samples collected worldwide that is an excess of 1.4% of /-quartz. But a more recent survey of 27,053 samples yields 50.17 % r/-quartz and 49.83 % /-quartz, which is a. 0.39 % excess of r/-quartz. Therefore it is necessary to accept the fact that the terrestrial distribution of optically active quartz crystals is quite random and, consequently, no basis exists for calcula-... 

As5mimetric adsorption on quartz powder was also shown by measurements of the adsorption capacity of d- and /-quartz in relation to (S)-(-)-2-methylbutan-l-ol ( at is, the commercial (-)-amyl alcohol, AmOH, consisting of 75% (-)-alcohol in a mixture with 3-me ylbutan-l-ol) adsorbed on samples of d- and /-quartz with equal surface areas, and the decrease in optical rotation was measured after adsorption It was found that c/-quartz adsorbed more (-)-AmOH by 2.3% than /-quartz. Taking into account the 1 m surface areas of the quartz samples, this 2.3% amounts to 0.06% (-)-AmOH more than /-quartz. In contrast, it is also necessary to note that Ohara et al. tried in vain to resolve 2-butanol on optically active quartz. 

Thus, optically active quartz crystals remain the only relatively effective stereoselective inorganic adsorbent and this fact must be used in discussions of the role of as5mimetric adsorption on quartz crystals in the origin (or amplification) of optical activity on the surface of the Earth (see Bernal and... 

This chapter summarizes data about the application of chiral metal catalysts supported on optically active quartz crystals in hydrogenation and other reactions. Despite the low enantioselective efficiency of these catalysts, recent result show that almost 100% enantioselectivity results when they are involved in autocatalytic processes. 

Schwab and Rudolph " prepared chiral catalysts by supporting the metals on the surfaces of ferreted fine powdered optically active quartz crystals, which proved to be active during as3nnmetric dehydrogenation and dehydration of racemic butan-2-ol. The dehydration-dehydrogenation reactions of butan-2-ol (Scheme 2.1.) were carried out in the vapor phase at... 

Catalysts based on /-quartz predomonantly decomposed the (+)-enantiomer of butan-2-ol, so the product mixture had a (-)-optical rotation. Considering the mechanism of action of that chiral catalyst the authors concluded that a maximal effect may be attained at small coverings of metal (close to a monoatomic layer) on the chiral surface of the optically active quartz. Increasing the content of metal increased the rate of reaction but decreased the asymmetric effect and as well as the resulting optical rotation of the product (Figure 2.2.). 

Samples of quartz crystals were crushed into micron size particles using vibro-set with W-carbid. They did not indicate the condition of the pounding of the crystals although it is well known that crushing of the optically active quartz particularly with vibro-mil can cause twinnings formation, amorphisation of quartz, and its hydrophilisation... 

Results received in the studies of quartz-catalysis allow one to suggest that the mechanism of action of quartz catalysts is a result of as5mimetrie adsorption on the surfaee of optically active quartz. The effeetiveness of asymmetric catalysis is determined by the ability of the catal54ic system to form the labile diastereomeric complex intermediate, whieh will be determined by the extent of spatial correspondenee of the configuration of the reacting molecule to the structure of the surface of the... 

Recently it has been shown that optically active quartz crystals as asymmetric inductors become very effective in autocatalytic enantioselective reactions. Soai et al. have shown that in asymmetric autocatalysis, the action of small amounts of chiral reaction products (involved in the reaction cycle) may enhance the enantioselective excess by a factor of 94 after introduction of an intermediate into the reaction. Optically active synthetic quartz crystals were used in this reaction with ratios of 1 1.9 quartz to aldehyde and 1 2.2 quartz to diisopropyl-zinc. 

Klabunovskii E.I. (1951) Asymmetric synthesis by means of catalysts based on optically active quartz. Thesis, M.V. Lomonosov Moscow State Univ, Moscow, USSR. 

Amariglio A., Amariglio H. and Duval X. (1969) Resolution of various racemates by gas chromatography on optically active quartz column,... 

In the retrospective account from the year 1860 in which this anecdote is found, Pasteur carefully and correctly distinguished between superposable mirror images, which constitute symmetrical (molecu-larly identical) objects, and nonsuperposable mirror images, which are asymmetric (and molecularly distinct, hence isomeric). The first material discovered to be optically active, quartz, was found to lose its... 

Dreizler and Schafer (1990) also stated that the concentration of less active quartz in the coarse fraction of the raw material decreases sinterability, increases energy requirements or free lime, and increases development of belite nests. A chemical method of evaluating the burnability of various particle-size fractions of the feed, involving the calculation of the "weighted mean of the lime saturation standard," along with microscopy of the feeds, was said to be a very cost-effective tool in control of energy consumption and cement quality. For this study, six raw feed size fractions, from <32 to >200 pm, were investigated. 

Quartz Usually quartz is the gangue in other minerals Amines, fatty acids (for activated quartz)... 

Ferrous sulfate and ferric sulfate Granularity 45-900 10 % solution Depressing sulfide ores Depressing the floatation of dissociated Au Activating quartz, increasing the recovery of PbS depressed by chromate improving the separation of nonmetallic ores ... 

Al2(S04)3 Granularity 45-900 5 % Improving the floatation of feldspar when using cationic collector depressing calcite, fluorite, and some other nonmetallic ores activating quartz ... 

---