Reactive crystallizers

Most recently, Gavezzotti (4) has analyzed theoretically certain solid state processes in terms of the volume of the constituent molecules and the size and location of the empty and filled spaces in the crystal lattice. With a statement that will be seen to be directly pertinent to the results of our investigation, he concludes that "a prerequisite for crystal reactivity is the availability of free space around the reaction site". 

In addition, a reactor may perform a function other than reaction alone. Multifunctional reactors may provide both reaction and mass transfer (e.g., reactive distillation, reactive crystallization, reactive membranes, etc.), or reaction and heat transfer. This coupling of functions within the reactor inevitably leads to additional operating constraints on one or the other function. Multifunctional reactors are often discussed in the context of process intensification. The primary driver for multifunctional reactors is functional synergy and equipment cost savings. 

The dependence of crystal reactivity is rather complicated. At small admixtures (xpcs < 0.05) the induction period is decreased but at higher concentrations substantially increased. 

The problem of crystal reactivity and diffusion limitations has been considered in detail by Makinen and Fink [170]. They provide a simple treatment for crystals approximated as a plane sheet of material which leads to the definition of a limiting crystal thickness below which kinetic measurements of second-order rate constants are not affected by rate-limiting diffusion processes. For papain [172], ribonuclease A [173] and deoxyhaemoglobin [174], where the crystal thicknesses are comparable to the critical crystal thickness, reactivities are the same in the crystal and solution. In the case of glycogen phosphorylase b Kasvinsky and Madsen [175] demonstrated that the values for both substrates, glucose 1-phosphate (37 + 8mM) and malto-heptaose (176 + 20 mM), were the same in the crystal and solution. The 10-100-fold reduction in rate, despite the fact that crystal thickness was only twice the critical thickness, may be attributable partly to the allosteric nature of this enzyme and partly to the fact that the large substrate maltoheptaose (molecular weight, 1152) may not obey the simple diffusion rules in the crystal. 

Bhattacharya S, Stojakovic J, Saha BK, MacGillivray LR (2013) A product of a templated solid-state photodimerization acts as a template single-crystal reactivity in a single polymorph of a cocrystal. Org Lett 15 744... 

How are fiindamental aspects of surface reactions studied The surface science approach uses a simplified system to model the more complicated real-world systems. At the heart of this simplified system is the use of well defined surfaces, typically in the fonn of oriented single crystals. A thorough description of these surfaces should include composition, electronic structure and geometric structure measurements, as well as an evaluation of reactivity towards different adsorbates. Furthemiore, the system should be constructed such that it can be made increasingly more complex to more closely mimic macroscopic systems. However, relating surface science results to the corresponding real-world problems often proves to be a stumbling block because of the sheer complexity of these real-world systems. 

Black phosphorus is formed when white phosphorus is heated under very high pressure (12 000 atmospheres). Black phosphorus has a well-established corrugated sheet structure with each phos phorus atom bonded to three neighbours. The bonding lorces between layers are weak and give rise to flaky crystals which conduct electricity, properties similar to those ol graphite, it is less reactive than either white or red phosphorus. 

The hydrochloride of the nitroanilin may separate out at this stage, but this does not interfere with the reaction as the hydrochloride separates in fine, feathery crystals which readily redissolve and hence are very reactive. 

Raw ] Ia.teria.ls. Most of the raw materials are oxides (PbO, Ti02, Zr02) or carbonates (BaCO, SrCO, CaCO ). The levels of certain impurities and particle size are specified by the chemical suppHer. However, particle size and degree of aggregation are more difficult to specify. Because reactivity depends on particle size and the perfection of the crystals comprising the particles, the more detailed the specification, the more expensive the material. Thus raw materials are usually selected to meet appHcation-dependent requirements. 

The requirements of thin-film ferroelectrics are stoichiometry, phase formation, crystallization, and microstmctural development for the various device appHcations. As of this writing multimagnetron sputtering (MMS) (56), multiion beam-reactive sputter (MIBERS) deposition (57), uv-excimer laser ablation (58), and electron cyclotron resonance (ECR) plasma-assisted growth (59) are the latest ferroelectric thin-film growth processes to satisfy the requirements. 

Methyllithium. MethyUithium [917-54 ] CH Li, crystallizes from benzene or hexane solution giving cubic crystals that have a salt-hke constitution (128). Crystalline methyllithium molecules exist as tetrahedral tetramers (129). Solutions of methyllithium are less reactive than those of its higher homologues. Methyllithium is stable for at least six months in diethyl ether at room temperature. A one-molar solution of methyllithium in tetrahydrofuran (14 wt %) and cumene (83 wt %) containing 0.08 M dimethyknagnesium as stabilizer loses only 0.008% of its activity per day at 15°C and is nonpyrophoric (117). 

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