Sodium Chlorate Crystals Research Articles

Nongrowing Faces of Sodium Chlorate Crystals in Supersaturated Solution

The results of investigations of {100}, the nongrowing faces of sodium chlorate crystals in supersaturated solutions, are presented. It occurred that some of the faces did not grow, whereas the neighbor faces of the same crystals grew. The dissolution and refaceting of the crystals did not affect the probability of the nongrowing face appearance and the reduction of the range of face growth rates. Nongrowing faces are very stable; they start to grow at a relatively high supersaturation, face by face or several faces simultaneously. The order of the start of the growth is random, subsequently grown neighbor or opposite faces. Possible reasons for coexistence of growing and nongrowing faces, Ostwald ripening, microscopic conditions in the crystallization cell, microstructure of crystal face, and the impurity effects are discussed.

An investigation into the effect of mixing on the secondary nucleation of sodium chlorate in a stirred tank and an oscillatory baffled crystallizer

This paper reports the outcome of the examination of the effect of mixing intensity on the secondary nucleation mechanism of seeded crystallization of sodium chlorate in various configurations of stirred tank crystallizer (STC) and oscillatory baffled crystallizer (OBC). The results show that for the STC, an un-scraped system always yielded crystals of the same enantiomorphism as the seed crystal. The introduction of scraping to the STC resulted in product crystals of the opposite enantiomorphism to the seed being formed, however changing the rate of stirring (RPM) had no influence over the percentage similarity to the seed crystal. For the OBC, scraping always gave a product crystal crop with less than 100% similarity to the seed. Similarly, this was unaffected by altering the frequency of oscillation. Removing the scraping effect brought an increase of the similarity to the seed but the product crystals never reached 100% similarity to the seed enantiomorphism. For both scraped and un-scraped OBCs, reduction of the oscillation amplitude did increase the similarity of the products to the seed and 100% similarity to the seed was repeatedly achieved at the lowest operating amplitude for the un-scraped OBC. These findings provide further insight into the nucleation mechanism in the OBC and suggest that an alternative mechanism to that in the STC is observed.

Achiral Metastable Crystals of Sodium Chlorate Forming Prior to Chiral Crystals in Solution Growth

Chiral symmetry breaking in NaClO3 crystallization from an aqueous solution with perturbations has been of great interest. To understand the mechanism, several models focusing on the early stage of the crystallization have been proposed. However, they are ambiguous because the early stage has been barely explored directly. Here, we investigate the early stages of the crystallization process driven by droplet evaporation using a combination of direct in situ microscopic observations and cryogenic single-crystal XRD experiments. We demonstrate that an achiral crystal having P21/a symmetry, which is newly discovered for a solution growth, first appears in the droplet and then transforms into the chiral crystals. Additionally, determination of the lattice constants by XRD experiments (a = 8.42 A, b = 5.26 A, c = 6.70 A, β = 109.71°) revealed that the achiral phase should be identical to Phase III (a = 8.78 A, b = 5.17 A, c = 6.83 A, β = 110°), which is a high-temperature phase from a melt growth of NaClO3. We...

Dissolution of sodium chlorate crystals in supersaturated solutions

The results of the investigations regarding the growth and the dissolution behavior of small sodium chlorate crystals at temperatures near saturation temperature of (31.00±0.02)°C are presented. Above this temperature all the observed crystals dissolved, as was expected. At temperatures between 30.5°C and 31.0°C coexistence of growing, non-growing and dissolving crystals was occurred. At temperatures below 30.5°C dissolution of the crystals did not occur. A significant growth/dissolution rate dispersion existed at all temperatures. Possible reasons for simultaneous growth and dissolution are discussed.

Colloquium: Homochirality: Symmetry breaking in systems driven far from equilibrium

Subsequent to the discovery of chirality of organic molecules by Pasteur, living organisms have been found to utilize biomolecules of only one handedness. The origin of this homochirality in life still remains unknown. It is believed that homochirality is attained in two stages: the initial creation of a chirality bias and its subsequent amplification to pure chirality. In the last two decades, two novel experiments have established the second stage in different fields: Soai and co-workers achieved the amplification of enantiomeric excess in the production of chiral organic molecules, and Viedma obtained homochirality in the solution growth of sodium chlorate crystals. These experiments are explained by a theory with a nonlinear evolution equation for the chiral order parameter; nonlinear processes in reactions or in crystal growth induce enantiomeric excess amplification, and the recycling of achiral elements ensures homochirality. Recycling drives the system to a state far from equilibrium with a free energy higher than that of the equilibrium state.

Probing into Nucleation Mechanisms of Cooling Crystallization of Sodium Chlorate in a Stirred Tank Crystallizer and an Oscillatory Baffled Crystallizer

In this paper we report our recent studies into why different nucleation behaviors in cooling crystallizations were observed in a stirred tank crystallizer (STC) and an oscillatory baffled crystallizer (OBC). Using sodium chlorate as the model compound and setting up a number of hypotheses, we identified and verified different nucleation mechanisms for the above two systems: while under the same operational conditions, secondary nucleation occurred exclusively in the STC where the product crystals bore the same handedness as the seeds; a combination of primary and secondary nucleation was displayed in the OBC where a mixture of left- and right-handed crystals coexisted when a single-handedness crystal was seeded. Through further hypothesis, we established the vital link between the nucleation mechanisms and the ways mixing is generated in the two systems and discovered that the scraping action between the baffle edge and the wall of the crystallizer could be the main culprit for the unexpected primary nuc...

A novel hydrometallurgy of molybdenite concentrate and its kinetics

BACKGROUND: In recent years, there has been an increasing focus on the hydrometallurgical processing of molybdenite, with the decline of high-grade and easily handled molybdenum minerals. In this work, the technology of molybdenum extraction from molybdenite concentrate using sodium chloride electrolyte and its kinetics have been investigated. RESULTS: The results show that leaching temperature, sodium chlorate and sulfuric acid concentration significantly affected molybdenum extraction compared with other experimental parameters. With a NaClO3 concentration of 320.39 g L−1; sulfuric acid concentration of 73.3 g L−1, a liquid-solid ratio of 5:1, temperature 70 °C, agitation speed 500 rpm, the molybdenum dissolution rate achieved was 99.67% in 240 min. The activation energy of the dissolution reaction was 104.57 kJ mol−1. CONCLUSION: The synthesized sodium chlorate electrolyte, an effective leaching agent, was used directly for the treatment of molybdenite concentrate. Removal of the crystallization and purification of sodium chlorate significantly reduced production costs. The results indicated that the inner diffusion and external diffusion control models were not suitable for this leaching reaction and the dissolution process was controlled by chemical reaction. Copyright © 2012 Society of Chemical Industry

Long-Time Growth Rate Changes of Sodium Chlorate, Potassium Dihydrogen Phosphate, and Rochelle Salt Crystals Independent of Growth Conditions

Results of investigations of the changes in growth rate inherent to crystals (i.e., independent of macroscopic external conditions) during a 15-h growth period are presented. The results of the investigations regarding the time evolution of the growth rate dispersion are also presented. The majority of the investigations were carried out with sodium chlorate crystals, and several experiments were carried out with potassium dihydrogen phosphate (KDP) and Rochelle salt crystals. It was found that, for the majority of the crystals, the main changes in growth rate occurred in the initial growth stage, which extended to for up 4 h. These growth rates probably slowly decrease toward the end of the growth run. Some of the very high initial growth rates that decreased during the initial growth period were followed by relatively high intermediate growth rates for the next few hours and then subsequently decreased. The growth rates for the majority of crystals probably gradually decreased after 15 h of growth. The ...

ChemInform Abstract: Chiral Crystallization and the Origin of Chiral Life on Earth

AbstractReview: 40 refs.

Chiral crystallization and the origin of chiral life on earth

AbstractThe creation of chirality on Earth and the development of chiral life have been discussed in this highlight. Convincing evidence for the introduction of chirality on Earth is still fragmentary. We believe that by a combination of chiral crystallization and formation of helical polymers with preferred chiral conformational structure is the key to this question. This concept of macromolecular asymmetry has inspired ideas and resulted in possible rules for how chiral life as we know it, could have been introduced. These investigations needed the understanding of the requirements for chiral crystallization, for the stereochemistry of the initial formation of helical polymers, the measurements of optical activity of solids and their coordination with the fundamentals of chirality. Spacial modeling of the “oligo‐crystallization” of sodium chlorate led to the conception of “isotactic” linear crystallization, which involves helical propagation. It seems to require unequal sizes of the cations and anions, which, by branching propagation leads to three‐dimensional chiral crystal formation. Linear “isotactic” propagation of crystallization seems to be equivalent to stereo and conformational specific polymerization. One and a half turns of the helix seems to be required for stereo‐ and conformational specificity, that is, between the pentamer and hexamer in chloral polymerization (11/3 or nearly 4/1 helix) and between trimer and tetramer for the sodium chlorate crystal (2/1 helix). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Study on a novel optical filter by internal reflection and optical rotation

Based on the optical rotatory dispersion and the isotropy of the sodium chlorate crystal, a new type of optical filter by internal reflection and optical rotation is firstly developed. Due to the speciality of the zero reflectivity when the linearly polarized light is reflected at Brewster angle, the optical filter can give a good filtering effect by using only a single polarizer. The filtering characteristics were analyzed by Mueller matrix and tested by experiment. The results show that the intensity of emitted red or green light can be continuously modulated by changing the angle of the polarizer. The extinction of green or red light appears when the rotation angle of the polarizer is respectively 133.36° or 173.06° relative to the initial position. The isolation of green and red can be about 10 dB.

Circular Dichroism Tensor of a Triarylmethyl Propeller in Sodium Chlorate Crystals

In 1919, Perucca reported anomalous optical rotatory dispersion from chiral NaClO(3) crystals that were colored by having been grown from a solution containing an equilibrium racemic mixture of a triarylmethane dye (Perucca, E. Nuovo Cimento 1919, 18, 112-154). Perucca's chiroptical observations are apparently consistent with a resolution of the propeller-shaped dye molecules by NaClO(3) crystals. This implies that Perucca achieved the first enantioselective adsorption of a racemic mixture on an inorganic crystal, providing evidence of the resolution of a triarylmethyl propeller compound lacking bulky ortho substituents. Following the earlier report, NaClO(3) crystals dyed with aniline blue are described herein. The rich linear optical properties of (001), (110), and (111) sections of these mixed crystals are described via their absorbance spectra in polarized light as well as images related to linear dichroism, linear birefringence, circular dichroism, and anomalous circular extinction. The linear dichroism fixes the transition electric dipole moments in the aromatic plane with respect to the growth faces of the NaClO(3) cubes. Likewise, circular dichroism measurements of four orientations of aniline blue in NaClO(3) fix a bisignate tensor with respect to the crystal growth faces. Electronic transition moments and circular dichroism tensors were computed ab initio for aniline blue. These calculations, in conjunction with the crystal-optical properties, establish a consistent mixed-crystal model. The nature of the circular extinction depends upon the crystallographic direction along which the crystals are examined. Along 100, the crystals evidence circular dichroism. Along 110, the crystals evidence mainly anomalous circular extinction. These two properties, while measured by the differential transmission of left and right circularly polarized light, are easily distinguished in their transformation properties with respect to reorientations of the sample plates. Circular dichroism is symmetric with respect to the wave vector, whereas anomalous circular extinction is antisymmetric. Analysis of Perucca's raw data reveals that he was observing a convolution of linear and circular optical properties. The relatively large circular dichroism should in principle establish the absolute configuration of the propeller-shaped molecules associated with d- or l-NaClO(3) crystals. However, this determination was not as straightforward as it appeared at the outset. In the solid state, unlike in solution, a strong chiroptical response is not in and of itself evidence of enantiomeric resolution. It is shown how it is possible to have a poor resolution-even an equal population of P and M propellers-within a given chiral NaClO(3) crystal and still have a large circular dichroism.

Enantiomorphic symmetry breaking in crystallization of molten sodium chlorate

Enantiomorphic symmetry breaking of stirred samples of molten sodium chlorate is demonstrated, revealing the unexpected involvement of an achiral solid phase. The results should stimulate future computational models of nucleation, including symmetry breaking, and have implications for mechanisms that invoke enantiomorphism in natural minerals to explain biohomochirality.

Growth rate changes of sodium chlorate crystals independent of growth conditions

Results of investigations of the growth rate changes inherent to the crystal are presented. It is shown that, in initial growth stage, there exist crystal growth rate changes independent of experimental conditions, with tendency to level during the time. Time evolution of sodium chlorate crystals growth rate dispersion is also presented. The results obtained show that these changes must be included in the interpretations of the growth rate changes affected by various parameters (supersaturation, temperature, fields, stress, impurities, etc.), which have not previously been taken into account. These results may improve the current crystal growth theories.

Crystallization of Sodium Chlorate withd-Glucose Co-Solute Is Not Enantioselective

New evidence is presented that crystallization of sodium chlorate in the presence of the chiral co-solute d-glucose does not bias the growth of levorotatory crystals over dextrorotatory. The weighted mean percentage of d-NaClO3 was found to be Wd = 50.4 ± 1.4, compared to previous experiments of Kipping and Pope showing Wd = 31.7 ± 0.9 [J. Chem. Soc. Trans. 1898, 73, 606]. Possible explanations for the discrepancy between the historical results and the present work are discussed. The present work casts doubt on a result that has been accepted for over a century, concerning the ability of a chiral molecule to influence asymmetric crystallization, which has been used to promote theories on the possible origins of biological homochirality.

The effect of stirring on sodium chlorate crystallization under symmetry breaking conditions

The effect of the stirring rate on the crystallization of sodium chlorate was studied in more than 200 experiments using a set-up that allows to perform sets of 20 simultaneous experiments. The crystallization conditions were those that according to previous results lead to only one of both L and D enantiomorphic forms under stirring. The probability of D crystallization was determined using a statistical analysis based on the central limit theorem. The stirring dependence of induction times and crystal size distribution is reported. The stirring effect was correlated with differences between surface and bulk crystallization. The probability of D crystallization was detected to be slightly higher than that of the L, in contradiction with some previous reports, and that might be attributed to the chiral contamination of the bio-organic world on the starting materials and on the system. Our analysis allows to detect that the D-enantiomorph induction by chiral contamination occurs mainly in the nucleation at the interface air/water, which can be related to the expected higher concentration of the contaminants (bioorganic chiral amphiphiles e.g. DNA or proteins) on the surface of the solution.

Optical diagnostic and modeling solution growth process of sodium chlorate crystals

Both a real time optical interferometric experiment and a numerical simulation of two-dimension non-steady state model were employed to study the growth process of aqueous sodium chlorate crystals. The parameters such as solution concentration distribution, crystal dimensions, growth rate and velocity field were obtained by both experiment and numerical simulation. The influence of earth gravity during crystal growth process was analyzed. A reasonable theory model corresponding to the present experiment is advanced. The thickness of concentration boundary layer was investigated especially. The results from the experiment and numerical simulation match well.

Direct detection of chlorine-35 multiple-quantum NMR transitions in a single crystal of sodium chlorate†

35Cl (spin 3/2) in sodium chlorate has a strong quadrupole coupling, similar in size to its interaction with a magnetic field of 11.7 T (500 MHz for protons). This means that it obeys neither the standard nuclear quadrupole resonance (NQR) nor the nuclear magnetic resonance (NMR) rules. Recently, we have published a theoretical approach that allows us to calculate the transition frequencies of such a system without approximations. This exact solution is applicable to any spin, with any relative ratio of Zeeman to quadrupole coupling, so we can map out how NQR becomes NMR as the magnetic field is increased. In the general situation, the selection rules restricting direct observation to only single quantum transitions break down and nominal multiple-quantum transitions become directly observable. The transition frequencies depend on the Zeeman interaction, the quadrupole coupling and the orientation of the crystal in the magnetic field. Sodium chlorate is an ideal sample, since we can use the 23Na NMR spectrum to determine the orientation of the crystal. 23Na (spin-3/2) has a weak quadrupole coupling and there are four molecules per unit cell. The positions of the quadrupole satellites from the four molecules are sufficient to determine the orientation, so the sodium nucleus acts as an internal goniometer. Since we already know the magnetic parameters for 35Cl, we can predict where to look for its resonances, which can range from less than 10 MHz to greater than 150 MHz. A single spin-3/2 has 6 possible transitions, so the four molecules in the unit cell should show 24 transitions. We have observed 17 of them.

Highly enantioselective asymmetric autocatalysis induced by chiral ionic crystals of sodium chlorate and sodium bromate

Chiral crystals of sodium chlorate and sodium bromate induced highly enantioselective organic synthesis in combination with asymmetric autocatalysis. (S)-5-Pyrimidyl alkanols with up to 98% ee were obtained in the enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehydes in the presence of d-sodium chlorate. On the other hand, (R)-5-pyrimidyl alkanols with up to 98% ee were obtained for the corresponding reaction in the presence of l-sodium chlorate. Chiral crystals of d- and l-sodium bromate were also found to work as chiral initiators.

Selective growth and distribution of crystalline enantiomers in hydrogels.

The crystallization of sodium chlorate (NaClO3) is a classic example of spontaneous chirality, since it is achiral in solution but adopts a chiral form in the solid state. While crystal growth of NaClO3 from pure aqueous solutions yields a 50:50 statistical distribution of d- and l-crystals, large enantiomeric excesses of either d- and l-crystals can be achieved by crystal growth in agarose gel, a naturally occurring chiral polysaccharide. The influence of gel density (0.1-0.75 wt %), temperature, and the diffusion of cosolvents on crystal distribution was discerned from statistical data obtained from 752 gel-mediated crystallization experiments yielding 12,384 individual crystals. These studies demonstrate that the magnitude and direction of the bias can be selectively engineered toward either d- or l-forms by changing the gelation conditions. Aqueous agarose gels infused with 48 wt % NaClO3 at 6 degrees C, favored the growth of d-NaClO3 crystals, with ee's reaching 22% at the highest gel concentrations. Crystal growth under methanol diffusion favored deposition of the opposite enantiomorph, l-NaClO3. The bias in the crystal distribution is enhanced at higher temperatures. Aqueous gels at 24 degrees C infused with methanol cosolvent favored l-NaClO3, with ee's reaching 53%. The changing magnitude and direction of the enantiomorph bias can be ascribed to differences in the agarose conformation and intermolecular interactions between the gel and crystal surfaces that inhibit the formation of the two enantiomers to different extents.