Completion of reaction

Initiators. The degree of polymerization is controlled by the addition rate of initiator(s). Initiators (qv) are chosen primarily on the basis of half-life, the time required for one-half of the initiator to decay at a specified temperature. In general, initiators of longer half-Hves are chosen as the desired reaction temperature increases they must be well dispersed in the reactor prior to the time any substantial reaction takes place. When choosing an initiator, several factors must be considered. For the autoclave reactor, these factors include the time permitted for completion of reaction in each zone, how well the reactor is stirred, the desired reaction temperature, initiator solubiUty in the carrier, and the cost of initiator in terms of active oxygen content. For the tubular reactors, an additional factor to take into account is the position of the peak temperature along the length of the tube (9). 

The reaction takes place at atmospheric pressure. For stable control of the reaction rate, the reaction is first carried out at a temperature of 50°C and then at 60°C. Overall, this batch reaction takes about 9 hours. After completion of reaction, the slurry is diluted to about 70% sulfuric acid solution, and cmde sulfamic acid crystals are separated by centrifuge. The crystals are dissolved in mother Hquor to make a saturated solution at 60°C and the solution is concentrated under vacuum at 40°C. Purified sulfamic acid is obtained by recrystallization. 

TABLE 23-6 Typical Values of Kgo for Absorption in Towers Packed with 1.5-in Intalox Saddles at 25% Completion of Reaction ... 

The time-dependence of enantioselectivity in the reaction thiophenol with 3-cro-tonoyl-2-oxazolidinone catalyzed by l ,J -DBFOX/Ph-Ni(C104)2-3H2O at room temperature in THF is shown in Scheme 7.44. After 3 h, the yield of the thiol adduct is 70% with the enantioselectivity of 91% ee, but the enantioselectivity was 80% ee at the completion of reaction after 24 h (yield 100%). Although the catalyst maintains a high catalytic activity, and hence a satisfactory enantioselectivity, at the early stage of reaction, the deterioration of catalyst cannot be neglected thereafter even under neutral conditions. 

The time required for the completion of reaction varies with the rate of stirring. When the stirring is very vigorous most of the water comes over within twelve hours. 

Fig. 1. Generalized a—time plot summarizing characteristic kinetic behaviour observed for isothermal decompositions of solids. There are wide variations in the relative significance of the various stages (distinguished by letter in the diagram). Some stages may be negligible or absent, many reactions of solids are deceleratory throughout. A, initial reaction (often deceleratory) B, induction period C, acceleratory period D, point of inflection at maximum rate (in some reactions there is an appreciable period of constant rate) E, deceleratory (or decay) period and F, completion of reaction.

Shell Chemical material (92% minimum purity) was used. It was noted by the checkers that redistilled isoprene gave slightly better yields. The excess isoprene serves both as a solvent and for mass action. Moreover, dichlorophenylphosphine tends to dissolve in the product, and excess isoprene, by extracting the solid, promotes completion of reaction. 

The development of fast reaction techniques has allowed a detailed kinetic study of the T1(III)-1-V(III) system. Daugherty followed the course of the reaction by monitoring the appearance of V(IV) at 760 m/i. 70-90 % completion of reaction corresponded to 25-30 sec. Spectrophotometric observations revealed... 

One commonly found feature is a reduction in process times, simply because flow conditions allow a faster sequence of all necessary processing steps such as mixing and completion of reaction and promote reaction by optimized transport properties. 

During the course of reaction, samples were withdrawn at suitable time intervals from the reactor and analyzed by infrared spectroscopy. After the completion of reaction, the... 

Addition of alcohol occurs on P=N bond of 11,2,3]diazaphospholo[ 1,5-a pyridine (2) and P=C bond of 11,4,2 diazaphospholo[4,5-a Ipyridinc (76) in the presence of sulfur or selenium. In the case of 2, addition is followed by 1,3-H shift and a catalytic amount of the respective alkoxide is required for completion of reaction at room temperature. The reaction of 2 with thiophenol is completed at reflux temperature in the presence of sulfur (Scheme 24) [88],... 

The decomposition of initiator can be followed by usual analytical methods and k can be determined. The efficiency factor/can be obtained by comparing the amount of initiator [I] decomposed with the number of polymer chain formed. The rate of polymerization can be determined by monitoring the change in a physical or chemical property of the system. Generally, dilatometry technique is used for determination of the rate of polymerization. Let the extent of polymerization be small and concentration of initiator be constant. Let r0, rt and r be the readings on dilatometer initially, at time t and at the completion of reaction, respectively. If reaction is first order in [M],... 

Method C (with microwave irradiation) An intimate mixture of the ester (25 mmol), Aliquat (l g, 2.5 mmol) and powdered KOH (3.25 g) is subjected to microwave irradiation. On completion of reaction, the mixture is washed with CH,Cl, and the residue is acidified with aqueous HCl. The carboxylic acid is isolated as described in 9.2.1.B [e.g. 87% from PhC02Me (30 sec) 83% from PhC02C8H17 (l min) 75% from 1,4,6-Me3QH2C02Me (2 min)]. 

Run Reagents Quantities (moles X 10 ) Time (hours) Temp. ( O Completion of reaction (%)... 

The rate laws (8.29) and (8.30), with [Cr(II)]t ,a[ in excess, lead to oxidation by Co(C204)j and Ij" showing initially pseudo zero-order kinetics. As the concentration of the oxidant decreases however, Arjfoxid] S and some deviation from linearity for the plot occurs and eventually becomes first-order, although this may be near to the completion of reaction. With Co(edta) in deficiency, the reaction is pseudo first-order. 

The material freed from the chromium salts should be checked for completeness of reaction by gas chromatographic analysis to ensure the absence of starting material. 

At every stage of the development process, the results of a reaction or process stage will be analysed in one of two ways. The reaction mixture itself will be sampled and analysed to yield information such as extent/completion of reaction, reaction yield or reaction purity. Alternatively, the reaction product will be isolated and dried before sampling and analysis. Typical analytical information in this case would include both chemical and physical characterisation, plus quantitative data to ensure conformance with some pre-defined specification or to provide batch data on which a suitable specification will ultimately be based. Note that however quickly the analytical data are provided, there is a disconnect from the reaction, which means that reaction control is impossible and that... 

Fig. 2.7 Fluorous phase catalytic hydroboration. The procedure involves stirring the catalyst (0.1 mol%) in the fluorous phase with neat reactants at 40-45 °C, the cooling on completion of reaction and extracing with THF.

The three secondary hydroxyl groups in the 12-posihon are somewhat slow to react with diisocyanates and generally require heat for the completion of reaction. This can be of advantage or disadvantage depending upon the specific application. Modifications of CO and particularly of ricinoleic acid through esterification results in products that are of considerable interest as polyols for various urethane applications [88, 89]. 

Sodium amalgam (1%) is produced by adding Na chunks to the requisite amount of mercury, which is being stirred in a 500-mL three-necked amalgam-reduction flask.6 This flask is equipped with a stopcock at the bottom to remove amalgam after completion of reaction. 

A study of the completion of reaction vs. time was also made on the direct esterification of a typical olefin with a primary alkyl acid 0-phthalate. By titration of the reaction mass with 0.5N sodium hydroxide, we determined the rate of reaction using standard conditions of catalyst level, reaction temperature and olefin excess as previously described. The acid value reached a minimum and longer time cycles did not reduce this to any great extent. 

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