Amine concentration, effect

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. 

Certain internal chemical treatments employed also need strict control to avoid risks of adverse chemical reaction and resultant corrosion. In particular, nitrogen-containing chemicals such as hydrazine and amines require effective monitoring to limit the concentration of ammonia release into steam because the presence of ammonia may, under certain conditions, cause stress corrosion cracking of copper and brasses. 

Corrosion may be especially rapid under existing deposits where amine is absent and the pH level is lower than that of the bulk water, as incongruent phosphate effects and concentrating effects further contribute to the problem. 

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. 

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. 

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. 

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 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] ... 

Studies of the amine concentration rate dependence show that the reactions are strictly third-order in amine for DMSO <2%. For DMSO constants >10% the reactions show the classical behaviour usually found in base-catalysed SjvAr180. The specific solvent effects observed for small additions of the HBD co-solvent are consistent with the formation of the mixed aggregate, and a linear correlation was found between kA and [DMSO], shown by equation 36, which expresses that the third-order term is more affected by the small additions of DMSO than the fourth-order term. Equation 36 is valid for [DMSO] <2% (0.282 M). 

The effect of the structure of the coinitiator is studied using 3% PDO and 5% electron donor. The measured photospeed increases in the order N-isopropylamine < dibenzylamine < triethylamine N,N dimethylbenzyl-amide < iV-benzylethanolamine < MDEA. However, a reactivity order for the electron donors can not be inferred from these data because the molar concentration is not the same for the different coinitiators. As shown for MDEA in Table 2, the variation of the photospeed with the amine concentration is not simple. The photospeed increases with increasing amine concentration up to 5%, higher concentrations resulting in lower polymerization rates. 

Figure 2. Effect of amine concentration on heptanal hydrogenation...

IR data supported the formation of rhodium carbonyl anions on addition of amine suggesting a mechanism in which these anions are in equilibrium with the active species, a hydrido rhodium carbonyl containing coordinated amine. Such a mechanism provides an explanation for the variation in catalyst activity with amine concentration and basicity and affords a method for predicting the effect of other amine ligands. 

Only the unprotonated amine with the free electron pair on nitrogen participated in the reaction (6). The dependence of the height of the more positive wave on the logarithm of the amine concentration is shown in Fig. lb the slope corresponds to a reaction of one carbonyl molecule with one amine. From the ratio of the wave-heights of the first and second waves, it is possible to calculate values of the overall equilibrium constant Ks = K 2K3HOH-], provided that the effect of protonation of the amine and of the Schiff base expressed by equations (4 a) and (4 b) is taken into account. 

Figure 3. Effect of amine concentration on swelling. Percent increase in diameter as a function of time after exposure to a pH 2.6 phosphate/citrate buffer for 1% crosslinked polyacrylamide gels with 10, 20 and 40% DMAEM.

As scientists improved their techniques for detecting low levels of amines, they began to measure the amine concentrations in postmortem human brains. Several researchers measured levels of serotonin and norepinephrine in the brains of people who had committed suicide as a result of depression and compared the levels to individuals of the same age who had been killed in accidents. The suicides brains had lower levels of serotonin. Subsequent studies also revealed that certain depressed patients had lower levels of serotonin metabolites in their cerebrospinal fluid. These findings accelerated the effort to develop drugs that would be effective on serotonergic neurons. 

Glycidyl Adducts of Aliphatic Amines. An aliphatic amine such as diethylenetriamine can be partially reacted with an epoxy, such as a DGEBA resin, to produce a low-volatility adduct. In a typical reaction, the epoxy is added slowly to a large excess of DETA. The reaction is maintained at 75°C by cooling. The reaction products are continuously agitated effectively to provide for good contact and uniform concentration effects. At the end of the reaction, excess DETA is vacuum-distilled away from the adduct. 

A detailed investigation of these reactions led to the results which are summarized in Table 2 The kinetic isotope effect for N.N-dj-m-toluidine, the kinetic order with respect to the amine and the activation parameters AH and AS change with amine concentration as well as with temperature. 

It is interesting to note that triphenylphosphine is more effective as initiator than tertiary amines. In general it can be stated that the initial rate of formaldehyde polymerization with tri-n-butylamine is proportional to the amine concentration and the initial rate is also proportional to the monomer concentration (Figs. 1 and 2). The temperature dependence of... 

Because methanol is not very polar, the elution of strong organic acids and bases requires a mobile phase with even greater polarity. This has normally been done by adding a very low concentration of acids or bases into methanol, and then the modified methanol is mixed with CO2 for separation. Citric, acetic, and chlorinated acetic acids have been used as acidic secondary modifiers, whereas isopropylamine, triethy-lamine, and tetrabutylammonium hydroxide have been served as basic secondary modifiers. A good example with ternary systems is the separation of benzy-lamines, as shown in Fig. 1. None of the three tested amines were effectively eluted by pure CO2 (Fig. la) however, some of these amines were eluted with very poor peak shapes when methanol was added to the CO2 (Fig. lb). However, the addition of isopropylamine to the methanol-modified mobile phase effectively eluted all of the three benzylamines and dramatically improved the peak shapes, as shown in Fig. Ic. 

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