Time of reaction

This procedure has been performed in a variety of ways [28 p714, 38-42] with variations in solvent, base and time of reaction. For piperonal conversion, the consensus is toward the use of acetic acid as the solvent, ammonium acetate as the base and 4 hours of reflux time. Dr. Alexander Shulgin, a giant in this field, prefers the use of cyclohexylamine as the base. Strike would not tend to doubt this man s choice, especially since Strike is also getting the... 

Mercuric Sulfide. Mercuric s A ide[1344 8-5] HgS, exists ia two stable forms. The black cubic tetrahedral form is obtaiaed when soluble mercuric salts and sulfides are mixed the red hexagonal form is found ia nature as cinnabar (vermilion pigment). Both forms are very insoluble in water (see Pigments, inorganic). Red mercuric sulfide is made by heating the black sulfide in a concentrated solution of alkah polysulfide. The exact shade of the pigment varies with concentration, temperature, and time of reaction. 

In industrial production of acid-modified starches, a 40% slurry of normal com starch or waxy maize starch is acidified with hydrochloric or sulfuric acid at 25—55°C. Reaction time is controlled by measuring loss of viscosity and may vary from 6 to 24 hs. For product reproducibiUty, it is necessary to strictly control the type of starch, its concentration, the type of acid and its concentration, the temperature, and time of reaction. Viscosity is plotted versus time, and when the desired amount of thinning is attained the mixture is neutralized with soda ash or dilute sodium hydroxide. The acid-modified starch is then filtered and dried. If the starch is washed with a nonaqueous solvent (89), gelling time is reduced, but such drying is seldom used. Acid treatment may be used in conjunction with preparation of starch ethers (90), cationic starches, or cross-linked starches. Acid treatment of 34 different rice starches has been reported (91), as well as acidic hydrolysis of wheat and com starches followed by hydroxypropylation for the purpose of preparing thin-hoiling and nongelling adhesives (92). 

The reaction may also be carried out in aqueous medium with an increase in the time of reaction to 4 hours. By this method the submitters obtained a 78% yield on a large-scale run. When only a single run is to be made, this procedure may be preferred as a matter of economy. 

Ordinarily the zinc-acetic acid system will not react with a 21-acetoxy-20-ketone however, if a A -double bond is also present, the 21-acetoxyl group is removed in high yield at room temperature in 3 min. Increasing the time of reaction causes subsequent reduction of the 20-ketone to hydroxyl. 

The momentum of I relative to XI + at the time of reaction can be found by following a similar path of reasoning and is ... 

In the case of products prepared from hydrolysis/condensation reactions, the time of reaction varies from a few hours to more than 3 months. Generally, the crude products precipitate from the reaction mixture and pure compound can be obtained by simple filtration followed by washing or recrystallization. However, the yields are often low and rarely exceed 50%. 

Figure 1 shows the effect of initiator concentration on optimum temperature and optimum time. It is noticed that increasing the initiator concentration hardly affects the optimum temperatures. However, optimum time decreases considerably from 297 minutes (lo = 0.03 mol/L) to 99 minutes (Iq = 0.15mol/L). As is well known, and shown in Figure 2, equilibrium monomer concentration (M, ) increases with temperature. If temperature is increased further, the monomer concentration can not be reduced to the desired final level because of high values. The initiator concentration should be chosoi taking into account the cost of the initiator and the savings due to reduced time of reaction. An initiator concentration Io=0.10 mol/L that resulted in t,=128 minutes was chosen for further simulation studies. 

Taken pH 0.1 N KSCN (ml) Time of reaction (sec) Total oxidizing capacity ... 

Amidation is particularly well adapted to use as a polymer-forming condensation reaction. The reaction is rapid above 180° to 200°C, it is remarkably free from side reactions, no catalysts are required (indeed, none are known), and the process is of the second order so that the molecular weight increases directly as the time of reaction. Molecular weights of 20,000 to 30,000 are attainable with no great difficulty under favorable conditions. This is not true of particular polyamide reactants susceptible to side reactions, as, for example, in the reaction of a diamine with glutaric acid wherein the inherent instability of the glutaric amide unit leads to decomposition. 

Simultaneous measurements of both the amount of butane evolved and the quantity of grafted organometallic fragments at increasing time of reaction allows the stoichiometry of the surface complexes Pts[SnBux] / to be determined (Fig. 7). Furthermore, extrapolation to a low amount of Sn grafted shows that a [BusSnJ Pts species is formed, which then rapidly evolved towards more dealkylated species and finally to Pts[SnBu]jy. 

Silyl enol ethers are an elegant means to protect the reactive and hence labile enolate moiety [15]. At the time of reaction, the enolate group is generated as an intermediate and reacts with the carbonyl-carrying compound. 

TEM analyses of the colloids do not evidence any significant change in the size and shape of the particles after seven days catalytic reactions (Figure 4). No NPs were observed at long times of reaction (up to one week) starting with molecular catalysts. 

When the half-life time of reaction and the half-life time of micromixing in the absence of chemical reaction are of the same order or the former is less than the latter, the role of micromixing may become crucial. For instance, nitration or bromination of resorcinol, even when the ratio of moles of resorcinol to moles of bromine is high, can lead to predominantly disubstituted product contrary to the general belief. In such cases, in many respects, the theory of coupling between reaction and micromixing has parallels with the formalism of theory of mass transfer with chemical reaction (Bourne, 1983). 

Guideline 1. The most fundamental basis for mechanistic speculation is a complete analysis of the reaction products. It is important to obtain a complete quantitative and qualitative analysis for all products of the reaction. Inasmuch as many chemical reactions give a complex array of products, the relative proportions of which change as the time of reaction increases, it is very useful to carry out a complete analysis for the shortest possible reaction time and for successively longer periods. In this manner one can differentiate between primary products formed directly from the reactants and secondary products formed by subsequent reaction of the primary products. Such analyses can give valuable clues as to the identity of reaction intermediates. 

We have already commented that the master equation method is not suitable, at present, to handle reactive products because, inter alia, the dimensionality of the problem increases with reactions of products. There is no difficulty, in principle, to including reactive products in Monte Carlo simulation, since the time of reaction and the positions of the products can be recorded. In practice, however, this requires a greatly expanded computational effort, which is discouraging. 

React at room temperature for up to 3 days (or at 4°C, if the protein is not stable at ambient temperature). The optimal time of reaction is dependent on the protein being coupled and the number of alkyne reactive groups available. An alkynyl-protein added to the nanoparticles at a high molar ratio probably would reach maximal coupling yield in a matter of hours. 

The desorption of arsenate previously sorbed onto Fe- or Al-oxides or onto an Andisol containing 42% of allophanic materials (Vacca et al. 2002) by phosphate has been demonstrated to be affected by time of reaction, residence time of arsenate onto the surfaces and the pH of the system (Pigna et al. 2006 Pigna et al. 2007, unpublished data). Figure 9 shows the desorption of arsenate at pH 6.0 (phosphate/arsenate molar ratio of 4) when phosphate was added onto the soil (Andisol) sample 1, 5 or 15 days after arsenate (surface coverage of arsenate about 60%). After 60 days of reaction, 55% of arsenate was desorbed by phosphate when the residence time of arsenate onto the surfaces of the Andisol was 1 day, but 35 and 20% of arsenate was desorbed by phosphate with increase in the residence time up to 5 and 15 days. Further, it was also observed that by keeping the... 

I.2.3.I. Isothermal spherical particle. The shrinking core model (SCM) for an isothermal spherical particle is illustrated in Figure 9.1(a) for a particular instant of time. It is also shown in Figure 9.2 at two different times to illustrate the effects of increasing time of reaction on the core size and on the concentration profiles. 

Suppose reaction 12.3-1 is carried out in a batch reactor of volume V on a continual basis. To determine the rate of production, we must take into account the time of reaction (t in equation 12.3-2) and the down-time (td) between batches. The total time per batch, or cycle time, is... 

Determine the time of reaction, t, if fA, the fractional conversion of A, is 0.80. State any assumptions) made. 

Find the ratio of reactor volumes or residence times of reactions under dispersion conditions or plug flow over a range of Peclet numbers. Use the result of problem P5.08.08. 

The simplest case of this parameter estimation problem results if all state variables jfj(t) and their derivatives xs(t) are measured directly. Then the estimation problem involves only r algebraic equations. On the other hand, if the derivatives are not available by direct measurement, we need to use the integrated forms, which again yield a system of algebraic equations. In a study of a chemical reaction, for example, y might be the conversion and the independent variables might be the time of reaction, temperature, and pressure. In addition to quantitative variables we could also include qualitative variables as the type of catalyst. 

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