Amine Concentration

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. 

Union Carbide has developed Amine Guard, which essentially eliminates corrosion in amine systems (32—35). It permits the use of substantially higher amine concentrations and greater carbon dioxide pick-up rates without corrosive attack. This results in an energy requirement comparable to that of the carbonate process and allows the use of smaller equipment for a specific C02-removal appHcation thereby reducing the capital cost. 

The initial anhydride concentration was about 3 x 10 M, and the amine concentration was much larger than this. The reaction was followed spectrophoto-metrically, and good first-order kinetics were observed hence, the reaction is first-order with respect to cinnamic anhydride. It was not convenient analytically to use the isolation technique to determine the order with respect to allylamine, because it is easier to observe the cinnamoyl group spectrophotometrically than to follow the loss of amine. Therefore, the preceding experiment was repeated at several amine concentrations, and from the first-order plots the pseudo-first-order rate constants were determined. These data are shown in Table 2-1. Letting A represent... 

The isolation technique showed that the reaction is first-order with respect to cin-namoylimidazole, but treatment of the pseudo-first-order rate constants revealed that the reaction is not first-order in amine, because the ratio k Jc is not constant, as shown in Table 2-2. The last column in Table 2-2 indicates that a reasonable constant is obtained by dividing by the square of the amine concentration hence the reaction is second-order in amine. For the system described in Table 2-2, we therefore find that the reaction is overall third-order, with the rate equation... 

Figure 3-14. Absorbance-time plots for the reaction of carbon suboxide and triethylamine in ether solution in the presence of acetic anhydride. The initial C3O2 concentration was 2.03 X I0 - M the amine concentrations were 3 X lO " M, 5 x 10 M, and 7 X lO " M.

Some authors use O] instead of cr as the substituent constant in such correlations.) An example is provided by the aminolysis of phenyl esters in dioxane the substrates RCOOPh were reacted with -butylamine, and the observed first-order rate constants were related to amine concentration by = k2 [amine] kj [amine]. The rate constants kz and k could be correlated by means of Eq. (7-54), the reaction constants being p = +2.14, b = + 1.03 (for A 2) and p = -1-3.03,8 = -1-1.08 (for ks). Thus, the two reactions are about equally sensitive to steric effects, whereas the amine-catalyzed reaction is more susceptible to electronic effects than is the uncatalyzed reaction. 

The amine concentration (mol/L) used in the polymerization at which the absorbance of the system was 0.40. 

These processes are characterized by a high capability of absorbing large amounts of acid gases. They use a solution of a relatively weak base, such as monoethanolamine. The acid gas forms a weak bond with the base which can be regenerated easily. Mono- and diethanolamines are frequently used for this purpose. The amine concentration normally ranges between 15 and 30%. Natural gas is passed through the amine solution where sulfides, carbonates, and bicarbonates are formed. 

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. 

To determine relative amine basicity cost-effectiveness for a specific amine concentration, compare amine Kb (at the desired operating temperature and pH) to amine cost for each of various neutralizers under consideration. 

Relative volatility This term expresses the tendency of an amine to vaporize, relative to water under the same conditions. It is, again, pH-dependent and a function of total amine concentration. 

Depending on the desired level of humidification and the type of amine used, amine concentrations in air subjected to steam humidification averaged between 0.6 and 8 ppb. 

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. 

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. 

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. 

Linking the ketone and carboxylic acid components together in an Ugi reaction facilitates the synthesis of pyrrolidinones amenable to library design. The three-component condensation of levulinic acid 30, an amine and isocyanide proceeds under microwave irradiation to give lactams 31 [65]. The optimum conditions were established by a design of experiments approach, varying the equivalents of amine, concentration, imine pre-formation time, microwave reaction time and reaction temperature, yielding lactams 31 at 100 °C in poor to excellent yield, after only 30 min compared to 48 h under ambient conditions (Scheme 11). 

Recorded kinetic curves were fitted to the five-parameter Equation (1). The parameters pj with their errors and the standard deviation of regressions are summarized in Tables 1-6. Comparison of the data confirm the previously reported (refs. 8,12) similarity in the behavior of the two isomers in the presence of strong bases in spite of the different shape of the kinetic curves. The relatively good agreement of exponents p2, P4 computed for the diastereomers at the same temperature and amine concentration demonstrates the validity of the model used. From comparison of Equations (4) and (7) it follows that both reaction must give the same exponent. 

Data given in Tables 1-6 clearly show a significant dependence of P2 and p4 on amine concentration, that is, at least one of the apparent rate constants kj contains a concentration factor. Thus, according to the mathematical considerations outlined in the Analysis of Data Paragraph, both p2, P4 exponents and the derived variables -(P2 + p)4> P2 P4 ind Z (see Eqns. 8-12) are the combinations of the apparent rate constants (kj). To characterize these dependences, derived variables -(p2+p)4, P2 P4 and Z (Eqns. 8,11 and 12) were correlated with the amine concentration using a non-linear regression program to find the best fit. Computation resulted in a linear dependence for -(p2 + p)4 and Z, that is... 

Neglecting 4 10 mol.dm 3 amine concentration Neglecting 5 10 mol.dm amine concentration... 

Exps. 3 and 4 represented positive controls, in which morpholine and sodium nitrite (NaN02) were administered in the diet. This system is known to induce tumors attributed to iji vivo NMOR production (3,. The rats were fasted overnight, presented with 2 g diet containing freshly added morpholine and NaNO , and killed 2 h later. At the higher doses, the large NMOR yield was clearly produced for the most part Jji vivo. The DMNM yield in this group indicated that some NMOR was also produced during the workup. The NMOR yield in exp. 4 was 1/1,270 of that in exp. 3, approximately in accord with the 1/1,000 ratio derived from the third-order nitrosation kinetics (3). (Both the morpholine and the NaNO doses in exp. 4 were 1/10 for those in exp. 3. Reaction rate is proportional to amine concentration and to nitrite concentration squared, and hence should be reduced 1/10 because of the drop in morpholine concentration and a further 1/100 because of the drop in nitrite concentration.)... 

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. 

We find that the rates of reaction for the various amines examined in (28) are governed by an extremely complex set of equilibria. For example, when R = n-Pr, n-Bu or s-Bu, the rate of reaction exhibit first order dependence on [EtjSiH] at constant amine concentration. However, the rate of reaction exhibits inverse non-linear dependence on [n-PrNH2] and [n-BuNH2], but positive non-linear dependence on [s-BuNH2] at constant [Et-jSiH]. Furthermore, if R t-Bu, then the rate of reaction is almost independent of both [t-BuNH2] and [EtjSiH]. Studies of the rate dependence on catalyst concentration for reaction (28) where R NH2 is n-BuNH2 reveal relative catalyst activities that are inversely dependent on [Ruo(C0) 2]. Similar studies with R NH2 = t-BuNH2 reveal that the rate or reaction is linearly dependent on [Ru3(CO) 2]. Piperidine is unreactive under the reaction conditions studied. 

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... 

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