Impurities formation mechanism

It is well documented that the isoimide is the kinetically favoured product and that isomerization yields the thermodynamically stable imide when sodium acetate is used as the catalyst. High catalyst concentrations provide maleimides with low isoimide impurity. The mechanism by which the chemical imidization is thought to occur is shown in Fig. 3. The first step in the dehydration reaction may be formation of the acetic acid-maleamic acid mixed anhydride. This species could lose acetic acid in one of the two ways. Path A involves participation by the neighboring amide carbonyl oxygen to eject acetate ion with simultaneous or subsequent loss of proton on nitrogen to form the isoimide. Path B involves loss of acetate ion assisted by the attack of nitrogen with simultaneous or subsequent loss of the proton on nitrogen to form the imide. If the cyclodehydration is run in acetic anhydride in the absence of the base catalyst, isoimide is the main reaction product. 

This multidisciplinary team approach toward impurity identification was successfully applied to the identification of this impurity. Each and every discipline played a very important role. Without SPE enrichment to remove the drug substance from the impurities, the impurity could not be purified by preparative HPLC. The novel acidic degradation study of the impurity provided very valuable information of the structure of the impurity. Mass spectrometry and nuclear magnetic resonance spectroscopy were the ultimate tools in this structure elucidation. Furthermore, the formation mechanisms were concluded by a careful examination of the process. 

Figure 1.3 present spectra of XLV dye solution absorbtion in the mixture of formic and trifluoro-acetic acids, solutions of dyed fibres before and after spinneret, which are practically laid on each other, showing full solution of the dye and good homogeneization of polymer melt. It should be noted that the samples of fibres, being studied, fully dissolved in solvents without formation of residues (possible products of dye and PCA interaction), which tells about inertia of components regarding each other. Blinding screen was caused mainly by impurities of mechanical nature. 

The Frenkel process (Equation 5.1) is the main defect formation mechanism in a-quartz. The 7.6 eV optical absorption band of Si-Si bonds is commonly observed in a-quartz exposed to various excitation sources including y-rays (Cannas et al. 2004, Nelson and Weeks 1961) and neutrons (Guzzi et al. 1992, Mitchell and Paige 1956). Upon exposure to particle beams, however, dangling bond pairs (Equation 5.2), which are considered to be due to the mechanism specific to fl-Si02, are also formed. Such dangling bond pairs are probably formed in the amorphized region within the collision cascade formed by the displacive collision mechanism. This mechanism is needed to be excluded to examine the intrinsic defect formation in a-quartz by electronic excitation. In addition, a-quartz often contains metallic impurities, such as aluminum and alkaline ions, and the effect of these metallic impurities on the Frenkel defect process remains unclear. 

The probability of formation of the local heat source greatly increases if the distribution of pore sizes in the material of the separator is highly nonuniform and the local defect of the film at lithium falls in an anomalously narrow pore (small S). This probability also highly increases in the case of nonuniform electrolyte and the defect falls in a pore, where the concentration of the ionic compound is decreased (small k). Thus, the appearance of local heat sources, capable of initiating CPS destruction during storage, is less probable the smaller the content of impurities (including mechanical ones) in lithium, the more uniform the pore sizes in the separator material and the more uniform the distribution of concentration of ionic compound (fluoroborate, lithium preparation, etc.) in the bulk separator. 

Addressing the chemical impurity formation during extrusion is also generally achieved through process modification by altering the mechanical energy input and residence time of the process. However, it may not be possible to adjust these attributes independently of the composition while balancing requirements for amorphous material formation and minimization of impurity formation. Formulations may... 

According to Ref. [88], the activation of methanol via a trimethyl oxonium rearrangement for first carbon/carbon bond formation is relevant only during an incubation period at low temperature. They suggested that the impurity-driven mechanism may gain more importance at higher temperatures [88]. 

Acetone is a coproduct of butane LPO. Some of this is produced from isobutane, an impurity present in all commercial butane (by reactions 2, 13, 14, and 16). However, it is likely that much of it is produced through the back-biting mechanisms responsible for methyl ketone formation in the LPO of higher hydrocarbons (216). 

Water as an impurity is known to promote the breakaway corrosion of a number of metals in addition to iron in CO2 the effect has been reported for magnesium (hydrocarbons have more effect on the oxidation of this metal), beryllium, zirconium and sodium. In the latter case water is known to convert the oxide to deliquescent NaOH but acceleration of beryllium oxidation probably results from hydride formation and mechanical damage to the oxide. 

Dithiols and dienes may react spontaneously to afford dithiols or dienes depending on the monomer dithiol ratio.221 However, the precise mechanism of radical formation is not known. More commonly, pholoinilialion or conventional radical initiators are employed. The initiation process requires formation of a radical to abstract from thiol or add to the diene then propagation can occur according to the steps shown in Scheme 7.17 until termination occurs by radical-radical reaction. Termination is usually written as involving the monomer-derived radicals. The process is remarkably tolerant of oxygen and impurities. The kinetics of the tbiol-ene photopolymerizalion have been studied by Bowman and... 

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