First order rate constant, sodium

Influence of OH concentration on the reaction rate constant. From the dependence of the observed first order rate constant on the sodium hydroxide concentration, shown in Table 3, it can be established that equation (2) holds, where ko represents the contribution due to the unimolecular decomposition process and koH is the contribution due to the base-catalysed process in alkaline medium. 

The experimentally observed pseudo-first order rate constant k is increased in the presence of DNA (18,19). This enhanced reactivity is a result of the formation of physical BaPDE-DNA complexes the dependence of k on DNA concentration coincides with the binding isotherm for the formation of site I physical intercalative complexes (20). Typically, over 90% of the BaPDE molecules are converted to tetraols, while only a minor fraction bind covalently to the DNA bases (18,21-23). The dependence of k on temperature (21,24), pH (21,23-25), salt concentration (16,20,21,25), and concentration of different buffers (23) has been investigated. In 5 mM sodium cacodylate buffer solutions the formation of tetraols and covalent adducts appear to be parallel pseudo-first order reactions characterized by the same rate constant k, but different ratios of products (21,24). Similar results are obtained with other buffers (23). The formation of carbonium ions by specific and general acid catalysis has been assumed to be the rate-determining step for both tetraol and covalent adduct formation (21,24). 

Figure 2 illustrates the variation of the first-order rate constants, kv, with [CTABr] for reactions of benzoic anhydride with 0.01 M NaOH and with 0.02 M sodium formate. The lines are calculated using the ion-exchange treatment with the following parameters Ks = 650 M (3 = 0.75, Kgr = 10 for X = OH- and HCO 2 and kM = 200 and 0.06 s 1 for OH" and HCO 2 respectively. Similar values of the rate constants were used in fitting the data... 

A similar dependence of the first-order rate constants with respect to the quantity of added water has been reported for the reaction of sodium formate with 1,4-dichlorobutane and related displacement reactions, In these studies tetra- n-butylammonium hydrogen sulphate and tetra- n-butylammonium bromide were used as catalysts and chlorobenzene as the solvent. 

The effects of micelles of cetyltrimethylammonium bromide (CTABr), tetradecyl-trimethylammonium bromide (TTABr) and sodium dodecyl sulfate (SDS) on the rates of alkaline hydrolysis of securinine (223) were studied at a constant [HO ] (0.05 m). An increase in the total concentrations of CTABr, TTABr and SDS from 0.0 to 0.2 M causes a decrease in the observed pseudo-first-order rate constants (kobs) by factors of ca 2.5, 3, and 7, respectively. The observed data are explained in terms of pseudophase and pseudophase ion-exchange (PIE) models of micelles. Cationic micelles of CTABr speed attack of hydroxide ion upon coumarin (224) twofold owing to a concentration effect. ... 

Figure 2. Kinetic plot of pseudo-first-order rate constant for reaction of paraoxon (kohc) versus concentration of added sodium perborate at 27.5 oc avvarious pH in 0.1 mol dm borate buffer.

Duynstee and Grunwald present some experimental data for Reaction (F) in the presence of hexadecyl trimethyl ammonium bromide (CTABr, C = cetyl) and sodium dodecyl sulfate (NaLS, L = lauryl). Sodium hydroxide was the source of OH" in all cases. A pseudo-first-order rate constant of 2.40 x 10-2 s-1 is observed for A CTABr. Use the following absorbance data to evaluate NaLS for this reaction ... 

The results obtained with sodium and water differ somewhat from those described above. Three runs were made, and except for three traces of the last run only a single rate was observed. Figure 3 shows a plot of log k (where k is the pseudo-first-order rate constant) vs. log [water concentration]. The order in water found from this plot is 1.6 compared to a value of 1.1 for the slowest rate of cesium with water also shown in Figure 3. 

In the reactions discussed and exemplified above, reactants, transient species and products are related by linear sequences of elementary reactions. The transient species can be regarded as a kinetic product and, if isolable, subject to the usual tests for stability to the reaction conditions. Multiple products, however, may also occur by a mechanism involving branching. Indeed, the case shown earlier in Fig. 9.5b, where the transient is a cul de sac species, is the one in which the branching to the thermodynamic product P and kinetic product T occurs directly from the reactant. In the absence of reversibility, the scheme becomes as that shown in Scheme 9.8a, where the stable products P and Q are formed as, for example, in the stereoselective reduction of a ketone to give diastereoisomeric alcohols. The reduction of 2-norbornanone to a mixture of exo- and cndo-2-norbornanols by sodium borohydride is a classic case. The product ratio is constant over the course of the reaction and reflects directly the ratio of rate constants for the competing reactions. The pseudo-first-order rate constant for disappearance of R is the sum of the component rate constants. 

The influence of sodium dodec3d sulfate, hexadecyltrimethyl-ammonium bromide and a polyoxyethylene(18) dodecylphenol on the hydrolysis of the Schiff bases p-chlorobenzylidene-l,l-dimethylethyl-amine, p-methoxybenzylidene-l,l-dimethylethylamme, and benz-hydrilidenedimethylammonium iodide (iV,iV-dimethylbenzophenone-imonium iodide) have been investigated (Behme and Cordes, 1965). The observed pseudo-first order rate constant for the hydrolysis ofp-chloro-... 

The industrial Wacker process is carried out in aqueous hydrochloric acid using PdClj/CuCh as the catalyst under oxygen pressure. The oxidation of higher terminal alkenes under the same conditions is slow and sometimes accompanied by undesired by-products formed by the chlorination of carbonyl com-poimds by CuCh, and isomerization of double bonds. Earlier examples of oxidation of various alkenes, mainly in aqueous solutions, have been tabulated.The pseudo-first-order rate constants for oxidation of various alkenes, relative to the value for cycloheptene, with PdCb in the presence of benzoquinone in aqueous solution have been rqwrted. An accelerating effect of surfactants such as sodium lauryl sulfate on the stoichiometric oxidation of higher alkenes in an aqueous solution has been reported. 

Figure 7 Effect of pH 6.2 phosphate buffer concentration and sodium sulfite on the observed first-order rate constant for the photodegradation of daunorubicin hydrochloride. O Without PABA with PABA. Abbreviation PABA, p-Aminobenzoic acid. Source From Ref. 75.

The effect of several commonly employed macromolecules on the apparent first-order rate constant of photobinding of riboflavin solutions has been reported (28). In this report, it was reported that polyethylene glycol 4000 slightly enhanced, and sodium decylsulfate enhanced the aerobic photofading of riboflavin, whereas... 

Fig. 13 Chemical degradation in freeze dried hGH formulated with trehalose as a function of water content at 40 C and 50°C. The pseudo first-order rate constant for degradation (%/month) is given for the combination of asparagine deamidation and methionine oxidation. The formulation is hGH trehalose in a 1 6 weight ratio with sodium phosphate buffer (pH 7.4) at 15% of the hGH content. The highest moisture content samples were collapsed after storage at both 40°C (moderate collapse) and 50°C (severe collapse). The water content that reduces the glass transition temperature of the formulation to the storage temperature is denoted Wg. O = 40°C storage = 50°C storage. (From Ref. l)...

H202 or in boiling base to an RUO2 colloid which can be stabilized by sodium dodecylsulfate (SDS) or poly(vinyl alcohol). Such stabilized RUO2 colloids have radii of 90nm and shelf lives of over six months compared with 30 nm and less than one month for more conventional colloids. Typical first order rate constants for the oxidation of water by [Fe(bipy)3] are 0.4 s at pH 7 for the SDS protected colloid and —0.04 s at pH 9 for the SMA protected colloid. ... 

The same author found that under controlled humidity conditions degradation was first order at 23 to 90% relative humidity (RH) and 64 to 90°C for trihydrate and at 50 to 90% RH and 40 to 70°C for sodium salt, although at 23% RH sequential reactions occurred with the sodium salt [40], The logarithm of the first order rate constants at a fixed temperature increased linearly with RH [40] or with the logarithm of the vapour pressure [41], confirming the importance of water for the degradation of these compounds. 

The kinetics of stability of sulfacetamide solutions at pH 7.5 to 9.3 by heating at 90° to 120°C has been studied and the activation energy of the reaction has been determined (109). The optimum pH for the stability of sulfacetamide solutions at 90° to 120°C is 8-8.5 (HO). The first-order rate constants for the degradation of sulfacetamide solutions at 120°C in the presence or absence of sodium metabisulfite have been determined. Sulfanilamide, in heat degraded solutions, has been shown to be insignificant in the development of color due to heat stress (48). 

These species form a network in which the ionic aggregates provide the weak links. Stress relaxation tecnniques are utilized, and from the relaxation times the kinetic parameters are calculated. For the sodium sulfonate terminal groups, the first order rate constant is given by k = 7.11 x 109 exp (-94,000/RT) with AH in Joules/mol. 

Chojnowski and Mazurek16 have studied the reaction of phenyldimethyl silanolates with cyclosiloxanes under conditions where siloxane bond redistribution reactions involving the polymer and the catalyst are completely suppressed. For the reaction of sodium phenyldimethyl silanolate (I) with 2,2,5,5-tetramethyl-l-oxa-2,5-disilacyclopentane (II) they find that the rate of disappearance of I in an excess of II follows first-order kinetics. The observed first-order rate constant k varies with the initial... 

The observation that polar solvents increase the rate of the base catalysed polymerization of cyclosiloxanes was first reported by Hyde13. The considerable rate enhancement that can be obtained by using these dipolar aprotic solvents is well illustrated in Table 1, taken from the data of Yuzhelevskii and coworkers18 for the (DF)3/sodium siloxanolate system. k0 is the observed first-order rate constant in the absence of an activator solvent. 

Figure 3. Variation in the pseudo-first-order rate constant for the reaction of 2-hydroxyethanesulfonyl chloride (IX) with aqueous sodium chloride solution (pH 5.00 and ionic strength was 0.3 M with NaCl04, 25.0 °C).

Rate-retarding effects of ca 105 were observed in hydrolyses of sodium alkyl sulphates in basic solution60, where Z is the strongly electron-donating substituent O-. Primary substrates showed second-order kinetics, but first-order rate constants were obtained for secondary alkyl substrates e.g. for i-propyl at 100 °C, the (interpolated) rate constant is 3.0 x 10 6 s-1 for the sulphate salt, whereas for hydrolysis of i-propyl tosylate the (extrapolated) rate constant is 0.7633. 

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