Deactivating Section

After the drying section, the catalyst components stiU show chemical reactivity. Under air, the physical properties of SPS deteriorate and the color changes from white to yellow. This section describes how the residual catalysts are deactivated [13,14]. 

The dried SPS powder is fed to the deactivation vessel (V-520) and is mixed with a methanolic solution of sodium hydroxide. After the deactivation, the 

SPS cake is separated from the methanolic solution slurry by a first centrifuge (Q-520). Subsequently, this SPS cake is fed to the washing vessel (V-530) and is mixed with methanol. After the washing process, the SPS cake is separated from the methanolic slurry by a second centrifuge (Q-530) and is fed to the dryer (Q-540). The SPS powder is discharged from the bottom of the dryer. The separated liquids are purified in the methanol column (V-560) and are recycled to the methanol tank (V-500) for reuse. 

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Methoxylation of 2,5- and 2,3-dibromopyrazines provides the basis for a comparison of ortho and para direct deactivation (Section II, E, 2, e) in the mono-methoxy derivatives such as 198 and 199. Pyrazine derivatives are discussed in Sections II, C and II, D. 

For example. Figure 7.10 illustrates a reaction catalysed by [Pd(Me)(NCMe)(meso-dppbjjPFs in anhydrous CD2CI2 during which no p-OH complex was formed, whereas the bis-chelates were equally produced through a mechanism involving partial catalyst deactivation (Section 7.2.6). 

The chemical and physical structure of the adsorbent surface controls the energy of adsorption of an individual compound and hence determines its A value i.e., adsorbent selectivity is determined by adsorbent surface structure. Unfortunately, the structure of an adsorbent surface can seldom be determined by direct methods. In most cases we are forced to infer the nature of the surface from the gross physical properties and composition of the adsorbent and from its performance in chromatographic separation. Section 6-1 summarizes and discusses those adsorbent properties which we of major interest in this connection. Section 6-2 provides a general treatment of sample A values as a function of adsorbent surface area, surface activity, and extent of water deactivation. Section 6-3 discusses the standardization of the adsorbent with respect to sample A values. 

The SPS process is divided into eight sections. They are monomer purification section, catalyst section, polymerization section, styrene removal from SPS, deactivation section, pelletizing section, blending section, and shipping section. Each section will be explained from the patent information. 

Figures 12.7-12.9 show the flow diagrams of the deactivating section.

Figure 12.7 Flow diagram of the deactivating section (1). V-500 methanol tank V-510 NaOH-methanol tank V-511 NaOH feed hopper V-520 deactivation vessel V-521 SPS feed hopper Q-520 1. Centrifnge V-530 purification vessel Q-530 2. Centrifuge Q-540 methanol dryer V-550 methanol surge tank.

Figure 12.8 Flow diagram of the deactivating section (2). Q-540 methanol dryer.

Figure 12.9 Flow diagram of the deactivating section (3). V-550 methanol surge tank V-560 methanol column V-561 methanol receiver E-560 V-560 reboiler E-561 V-560 cooler.

An important example for the application of general first-order kinetics in gas-phase reactions is the master equation treatment of the fall-off range of themial unimolecular reactions to describe non-equilibrium effects in the weak collision limit when activation and deactivation cross sections (equation (A3.4.125)) are to be retained in detail [ ]. 

Even when deactivated by nitro substitution on C-5, the 2-aminothiazoles still undergo diazotization (35, 338-340). As with carbonyl derivatives (Section III.2.B), competition may occur between N nucleophilic reactivity and nitrosation of the 5-position when it is unsubstituted (341-344). 

Electrophilic aromatic substitution (Section 12 14) Halo gen substituents are slightly deactivating and ortho para directing Br... 

Deactivating substituent (Sections 12 11 and 12 13) A group that when present in place of hydrogen causes a particular reaction to occur more slowly The term is most often ap plied to the effect of substituents on the rate of electrophilic aromatic substitution... 

Molecular fluorescence and, to a lesser extent, phosphorescence have been used for the direct or indirect quantitative analysis of analytes in a variety of matrices. A direct quantitative analysis is feasible when the analyte s quantum yield for fluorescence or phosphorescence is favorable. When the analyte is not fluorescent or phosphorescent or when the quantum yield for fluorescence or phosphorescence is unfavorable, an indirect analysis may be feasible. One approach to an indirect analysis is to react the analyte with a reagent, forming a product with fluorescent properties. Another approach is to measure a decrease in fluorescence when the analyte is added to a solution containing a fluorescent molecule. A decrease in fluorescence is observed when the reaction between the analyte and the fluorescent species enhances radiationless deactivation, or produces a nonfluorescent product. The application of fluorescence and phosphorescence to inorganic and organic analytes is considered in this section. 

A multiply bonded nitrogen atom deactivates carbon atoms a or y to it toward electrophilic attack thus initial substitution in 1,2- and 1,3-dihetero compounds should be as shown in structures (110) and (111). Pyrazoles (110 Z = NH), isoxazoles (110 Z = 0), isothiazoles (110 Z = S), imidazoles (111 Z = NH, tautomerism can make the 4- and 5-positions equivalent) and thiazoles (111 Z = S) do indeed undergo electrophilic substitution as expected. Little is known of the electrophilic substitution reactions of oxazoles (111 Z = O) and compounds containing three or more heteroatoms in one ring. Deactivation of the 4-position in 1,3-dihetero compounds (111) is less effective because of considerable double bond fixation (cf. Sections 4.01.3.2.1 and 4.02.3.1.7), and if the 5-position of imidazoles or thiazoles is blocked, substitution can occur in the 4-position (112). 

The general discussion (Section 4.02.1.4.1) on reactivity and orientation in azoles should be consulted as some of the conclusions reported therein are germane to this discussion. Pyrazole is less reactive towards electrophiles than pyrrole. As a neutral molecule it reacts as readily as benzene and, as an anion, as readily as phenol (diazo coupling, nitrosation, etc.). Pyrazole cations, formed in strong acidic media, show a pronounced deactivation (nitration, sulfonation, Friedel-Crafts reactions, etc.). For the same reasons quaternary pyrazolium salts normally do not react with electrophiles. 

As discussed in the theoretical section (4.04.1.2.1), electrophilic attack on pyrazoles takes place at C-4 in accordance with localization energies and tt-electron densities. Attack in other positions is extremely rare. This fact, added to the deactivating effect of the substituent introduced in the 4-position, explains why further electrophilic substitution is generally never observed. Indazole reacts at C-3, and reactions taking place on the fused ring will be discussed in Section 4.04.2.3.2(i). Reaction on the phenyl ring of C- and A-phenyl-pyrazoles will be discussed in Sections 4.04.2.3.3(ii) and 4.04.2.3.10(i), respectively. The behaviour of pyrazolones is quite different owing to the existence of a non-aromatic tautomer. 

In the section dealing with electrophilic attack at carbon some results on indazole homocyclic reactivity were presented nitration at position 5 (Section 4.04.2.1.4(ii)), sulfon-ation at position 7 (Section 4.04.2.1.4(iii)) and bromination at positions 5 and 7 (Section 4.04.2.1.4(v)). The orientation depends on the nature (cationic, neutral or anionic) of the indazole. Protonation, for instance, deactivates the heterocycle and directs the attack towards the fused benzene ring. A careful study of the nitration of indazoles at positions 2, 3, 5 or 7 has been published by Habraken (7UOC3084) who described the synthesis of several dinitroindazoles (5,7 5,6 3,5 3,6 3,4 3,7). The kinetics of the nitration of indazole to form the 5-nitro derivative have been determined (72JCS(P2)632). The rate profile at acidities below 90% sulfuric acid shows that the reaction involves the conjugate acid of indazole. 

Both 1,2- and 2,1-benzisothiazoles react with electrophiles to give 5- and 7-substituted products (see Section 4.02.3.2). The isothiazole ring has little effect on the normal characteristics of the benzene ring. C-Linked substituents react almost wholly normally, the isothiazole ring having little effect except that phenyl substituents are deactivated (see Section 4.17.2.1). There are, however, considerable differences in the ease of decarboxylation of the carboxylic acids, the 4-isomer being the most stable (see Section 4.02.3.3). 

The cleaning cycles are usually controlled by a timing device which deactivates the section being cleaned. The dusts removed during cleaning are collected in a hopper at the bottom of the baghouse and then removed, through an air lock or star valve, to a bin for ultimate disposal. 

Epoxides are normally hydrogenated in preference to saturated ketones but double bonds are usually reduced under these conditions. It is possible in some cases to selectively cleave an epoxide without saturating double bonds by the use of the deactivated catalysts recommended for the partial reduction of acetylenes (see section IV) or by the addition of silver nitrate to the palladium-catalyzed reaction mixture. " ... 

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