Amine concentration, increase

Although individual runs for the first set of experiments follow the second-order rate law, the observed second-order rate coefficients, k, are strongly dependent on the initial amine concentrations, with the rate increasing regularly as the amine concentration increases. Nevertheless, for all of the measurements, a plot of k versus the initial amine concentration is linear, and the data can be fitted withegn.(4), with k equal to 1.87 x 10-4 l.mole-1. sec-1 and k" equal to 5.63 x 10-412. mole-2. sec-1. 

In a C02 removal system that uses wet scrubbing, the existing towers are the major limit to more capacity because they are expensive to replace. In an amine system, absorption increases as amine concentration increases. But a higher amine concentration requires (1) more filtration to clean the solution and (2) the addition of corrosion inhibitors. Another option is to change from monoethanolamine (MEA) to methyl diethanolamine (MDEA).86... 

Study of MMA polymerization initiated by the system polybutadiene (PB)— TMT showed (Table 1) that the initial rates as well as the values of M and M are changed, when the amine concentration increased, in different ways depending on the polymerization temperature. If it is 50°C, they do not practically depend on the additive concentrations. If the polymerization temperature is 60°C, the dependence of the initial velocity versus the TMT concentration has a maximum, but that for M and M values has a minimum. If the temperature is 75°C, the reducing of initial rate and growth of molecular mass of polymer ate determined. 

Free tertiary amine associates with the secondary hydrojQrl groups and leads to an amino alcohol, M (Rxn. 29). The amino alcohol forms an activated complex, C2, with the epoxy dipole (Rxn. 30). C2 dissociates to form the branched product (Rxn. 31). This mechanism accounts for the observation that branching takes place only after a certain extent of epoxy conversion, i.e., when the fi ee amine concentration increases as it is released fi om the phenol ion pair BPi in Rxn. 24. Free amine is a true catalyst in this branching reaction since it is r enerated. 

Pseudo-first-order rate constants (kou) have been measured for aminolysis of dibenzo-[l,2]oxathiin-6-oxide (166) (Scheme 29). The plot of fcobs vs amine concentration exhibits a downward curvature which levels off as the amine concentration increases. Such a downward curvature is proposed as definitive evidence for a stepwise mechanism, which is supported by the microscopic rate constants determined. ... 

Methyl dietb an olamine (MDEA) and solutions of MDEA have increased in use for gas treating (150,151). Additional gas treating capacity can often be obtained with the same working equipment, because of the higher amine concentrations that can be used. 

The rate of reaction slows down as the conversion to tertiary amine increases and primary amine concentrations drop below 1%. Conversion to 100% tertiary amine is difficult. 

The differenee in reaction rates of the amino alcohols to isobutyraldehyde and the secondary amine in strong acidic solutions is determined by the reactivity as well as the concentration of the intermediate zwitterions [Fig. 2, Eq. (10)]. Since several of the equilibrium constants of the foregoing reactions are unknown, an estimate of the relative concentrations of these dipolar species is difficult. As far as the reactivity is concerned, the rate of decomposition is expected to be higher, according as the basicity of the secondary amines is lower, since the necessary driving force to expel the amine will increase with increasing basicity of the secondary amine. The kinetics and mechanism of the hydrolysis of enamines demonstrate that not only resonance in the starting material is an important factor [e.g., if... 

From a practical perspective, amine basicity is clearly an important functional property because (as has been noted) when temperatures rise and Kb decreases, amine concentration must increase simply to maintain pH level. Often a sharp increase in concentration is needed to actually raise the pH. 

If one limits the consideration to only that limited number of reactions which clearly belong to the category of nucleophilic aromatic substitutions presently under discussion, only a few experimental observations are pertinent. Bunnett and Bernasconi30 and Hart and Bourns40 have studied the deuterium solvent isotope effect and its dependence on hydroxide ion concentration for the reaction of 2,4-dinitrophenyl phenyl ether with piperidine in dioxan-water. In both studies it was found that the solvent isotope effect decreased with increasing concentration of hydroxide ion, and Hart and Bourns were able to estimate that fc 1/ for conversion of intermediate to product was approximately 1.8. Also, Pietra and Vitali41 have reported that in the reaction of piperidine with cyclohexyl 2,4-dinitrophenyl ether in benzene, the reaction becomes 1.5 times slower on substitution of the N-deuteriated amine at the highest amine concentration studied. 

The addition of the neutral salt (the second set of experiments) accelerates the reaction rate far more than does an equivalent concentration of excess amine. In the absence of the salt, a fifteen-fold increase in the initial amine concentration (from 0.1 M to 1.5 M) raises the measured rate coefficient by a factor of four, but at a salt concentration of 0.34 M the measured second-order rate coefficient is nine times larger than with the salt absent. 

This is a reaction in which neutral molecules react to give a dipolar or ionic transition state, and some rate acceleration from the added neutral salt is to be expected53, since the added salt will increase the polarity or effective dielectric constant of the medium. Some of the rate increases due to added neutral salts are attributable to this cause, but it is doubtful that they are all thus explained. The set of data for constant initial chloride and initial salt concentrations and variable initial amine concentrations affords some insight into this aspect of the problem. 

The strategy for the asymmetric reductive acylation of ketones was extended to ketoximes (Scheme 9). The asymmetric reactions of ketoximes were performed with CALB and Pd/C in the presence of hydrogen, diisopropylethylamine, and ethyl acetate in toluene at 60° C for 5 days (Table 20) In comparison to the direct DKR of amines, the yields of chiral amides increased significantly. Diisopropylethylamine was responsible for the increase in yields. However, the major factor would be the slow generation of amines, which maintains the amine concentration low enough to suppress side reactions including the reductive aminafion. Disappointingly, this process is limited to benzylic amines. Additionally, low turnover frequencies also need to be overcome. 

Phase-transfer catalysis is a special type of catalysis. It is based on the addition of an ionic (sometimes non-ionic like PEG400) catalyst to a two-phase system consisting of a combination of aqueous and organic phases. The ionic species bind with the reactant in one phase, forcing transfer of this reactant to the second (reactive) phase in which the reactant is only sparingly soluble without the phase-transfer catalyst (PTC). Its concentration increases because of the transfer, which results in an increased reaction rate. Quaternary amines are effective PTCs. Specialists involved in process development should pay special attention to the problem of removal of phase-transfer catalysts from effluents and the recovery of the catalysts. Solid PTCs could diminish environmental problems. The problem of using solid supported PTCs seems not to have been successfully solved so far, due to relatively small activity and/or due to poor stability. 

The presence of anionic or cationic groups at a 0.4 M.S. level inhibited adsorption and interlayer entrapment of 2.0 M.S. hydroxyethyl cellulose(HEC) from fresh water solutions. The lack of adsorption of the cationic HEC is surprising it is related to hydration of the quaternary amine group. Increasing adsorption and interlayer entrapment is observed with both the cationic and anionic HECs with increasing sodium chloride concentration. 

The study of co-oxidation of both hydrocarbons and amines proved the strong retarding effect of aliphatic amines on hydrocarbon oxidation [18], The rate of hydrocarbon oxidation was found to drop with an increase in the amine concentration. The rate of oxidation v depends on the amine concentration in accordance with equation [19] ... 

As mentioned earlier, those factors which favor formation of Ru(CO) — decreases in concentration and increases in CO pressure — favor higher turnover numbers in the WGSR. Increases in amine concentration and in temperature also improve the rates of H2 production. Thus, at 155°, 0.0082 mM Ru CO)- and 1080 psi... 

When A JRNIBIois -C 1, ko (for low values of initial amine concentration when fluoro derivatives are used, or when Kc is a low value as in cases of chloro derivatives), k0bs is ko (the uncatalysed process). When A C[RNH2] becomes a high value (because [RNH2] is increased), there is a leveling-off of the rate as shown in Figure 1. 

Non-linear kinetics have been reported for aminolysis of sulfamate esters RNHSO2ONP (Np=/7-N02C6H4) in chloroform. The first-order rate constants obs for reaction with imidazoles (primarily) under pseudo-first-order conditions display saturation curvature with increasing amine concentration, according to the expression... 

Sprague-Dawley rats have shown that chronic administration of low doses of the nonselective TCP, of FTCP, and of the MAO A-selective clorgyline leads to sustained increases in brain amine concentrations in the frontal cortex, nucleus accumbens, caudate nucleus, hippocampus, and hypothalamus with minimal regional differences [56],... 

The linear relationships in Figure 9 indicate that Reaction 10 is relatively unimportant under these conditions. If it were important, one would expect (3) a decrease in the ratio of Rch4/R1/2c2ho as the concentration of amine is increased for ... 

Alteration of this epoxy structure is the result of the fact that the epoxy molecules are both reacting and diffusing at the same time. This process forms a concentration gradient with a high epoxy monomer concentration at the surface which gradually reduces to the bulk concentration away from the surface. The properties of an epoxy with an excess of resin can be quite different from the stoichiometric amount. Figure 2, for example, illustrated the alteration of cured epoxy mechanical properties with epoxy/amine ratio. Excess epoxy or less than the stoichiometric amount of amine produces a brittle material if the mixture is cured in the same manner as the stoichiometric amount (Fig. 2). The stoichiometric sample has the lowest modulus while excess amine produces increased brittleness. The potential for variation in local properties within the epoxy due to the presence of a 200 nm or less layer must be considered. 

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