Rate Constants Of Hydrolysis Reactions Research Articles

Weakened adhesion force between extracellular polymeric substances of waste activated sludge caused by rhamnolipid leading to more efficient carbon release.

Rhamnolipid (RL), a biosurfactant produced by bacteria, is investigated to alter the physical characteristics of extracellular polymeric substance (EPS) of waste-activated sludge (WAS), and subsequently promotes hydrolysis and acidogenesis during anaerobic digestion for short chain fatty acids (SCFAs) production. The results revealed that RL could decrease the adhesion force of EPS from 13.46 nN to 1.08 nN, resulting in EPS disintegration layer by layer, decreasing the median particle size by 31.57 μm and releasing abundant soluble organic matter. The cell number of living bacteria remained stable after RL pretreatment (2.59 × 109 vs. 2.66 × 109), indicating that RL has a minimal impact on microbial cells (only ~2% bacterial lysis was observed). The kinetic studies of ammonia nitrogen release and SCFA production suggested that, in the RL-pretreated WAS, the reaction rate constants for hydrolysis and acidogenesis were respectively 2-fold and 1.5-fold higher than those of the control group.

Hydrothermal Degradation of Rutin: Identification of Degradation Products and Kinetics Study.

The model glycoside compound quercetin-3-O-rutinoside (rutin) was subjected to subcritical water within the temperature range of 120-220 °C, and the hydrothermal degradation products were analyzed. Two kinetic models describing the degradation of this compound in two different atmospheres (N2 and CO2), used for pressure establishment in the reactor, have been developed and compared. Reaction was considered a successive one with three irreversible steps. We confirmed that rutin degradation to quercetin follows first-order kinetics. At higher temperatures quercetin is further degraded in two degradation steps. Formations of 3,4-dihydroxybenzoic acid and catechol were described with the zero-order kinetic models. Reaction rate constants for hydrolysis of glycoside to aglycone in a CO2 atmosphere are higher compared to those in a N2 atmosphere, whereas at higher temperatures reaction rate constants for further two successive reactions of aglycone degradation are slightly lower in the presence of CO2. The difference in reaction activation energies is practically negligible for both gases. Furthermore, degradation products of sugar moieties, that is, 5-hydroxymethylfurfural and 5-methylfurfural, were also detected and analyzed.

Study on ketalization reaction of poly(vinyl alcohol) by ketones. IX. Kinetic study on acetalization and ketalization reaction of 1,3-butanediol as a model compound for poly(vinyl alcohol)

A kinetic study was carried out on the acetalization reaction of 1,3-butanediol, as a model compound for poly(vinyl alcohol) (PVA), in water, under acidic conditions. Since these equilibrium constants of ketalization reaction of 1,3-butanediol and ethylene glycol are so small, the kinetic parameters were estimated from the hydrolysis reactions of the corresponding ketals. It was made clear that these reactions proceed in the reversible bimolecular reaction, and the heat of reaction and activation energy are nearly equal to that of PVA. The rate constants of hydrolysis reaction (k′s) of model compounds were calculated on the basis of value of acetone ketal, Hammett-Taft's equation log k′s/k′so – 0.54(n – 6) = ρ*σ* was established, and the value of ρ* was obtained (3.60), which coincided with the value of PVA. Therefore, it was made clear that the hydrolysis reactions of acetals and ketals are electrophilic reaction (SE II reaction) and the step of rate determination is the formation of hemiacetal and hemiketal. The rate constants of hydrolysis reaction of 1,3-butanediol acetals and ketals were approximately 10–20 larger, and those of ethylene glycol were approximetly 50–80 larger except for ketals, and those of ethanol were roughly 2000–10,000 larger compared with that of high-molecular weight compound (PVA). It can be well explained that these differences in the rate constant depend on their entropy and the mobility of molecules. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1719–1931, 1997

Synthesis and hydrolysis of chemodegradable cationic surfactants containing the 1,3‐dioxolane moiety

AbstractIn acid‐catalyzed reactions of long‐chain aliphatic aldehydes (Ia‐d wherea=n‐C7H15;b=n‐C9H19;c=n‐C11H23; d=n‐C13H27), and tridecan‐7‐on (Ie) with 3‐chloro‐1,2‐propane‐diol, 2‐alkyl‐ and 2,2‐dihexyl‐4‐chloromethyl‐1,3‐dioxolanes (IIa‐e) were obtained. They were reacted with anhydrous dimethylamine to obtain, respectively, 2‐alkyl‐and [(2,2‐dihexyl‐1,3‐dioxolan‐4‐yl)methyl] dimethylamines (IIIa‐e), which were quaternized with methyl bromide to obtain the desired ammonium bromides (IVa‐e). The structure and purity of the compounds was proved by mass spectrometry and proton nuclear magnetic resonance spectroscopy. Additionally, [(2‐methyl‐1,3‐dioxolan‐4‐yl)methyl] trimethylammonium bromide and [(2,2‐dimethyl‐1,3‐dioxolan‐4‐yl)‐methyl] trimethylammonium bromide were synthesized as nonaggregating standards. Hydrolysis reactions of the synthesized ammonium bromides were performed by 0.1 M hydrochloric acid in 1∶1 (vol/vol) 1,4‐dioxane‐water mixtures at 50, 60 and 70°C. Rate constants of hydrolysis reactions were determined by observing carbonyl group formation at 280 nm. The hydrolytic reactivity of the studied surfactants (IVa‐c,e) was determined under unaggregated conditions. Compound IVd showed decreased reactivity. The length of the 2‐alkyl group has a minor effect on rate constant values. The influence of various substituents at the C‐4 atom of the 2‐nonyl‐1,3‐dioxolan‐4‐yl derivatives on rate constants was also investigated.

High pressure 29Si NMR study of the sol-gel process

29Si-NMR spectroscopy is used to investigate the role of pressure on the hydrolysis and condensation kinetics of the tetramethoxysilane (TMOS) sol-gel process under neutral conditions. The time evolution of the concentrations of the various functional groups in a neutral solution has been monitored as a function of pressure from 40 bar to 460 bar. The concentration changes of TMOS and both the hydrolysis and condensation products are accelerated by pressure. The features of the time evolution of each species are very similar to each other between 40 to 460 bar by using t/t as the time scale. Quantitative reaction rate constants for hydrolysis and gol condensation reactions are found for the early stage of the process; the latter (0.91·10 −2/hrM) was higher than the former (1.73·10 −4/hrM) at 1 bar. The observed activation volumes of these two reactions are determined as −29 cm 3/mole for hydrolysis and −44 cm 3/mole for condensation reactions, which confirms that pressure has a larger effect on the condensation rate than on the hydrolysis rate. These ΔV ≠ values are discussed in terms of the intrinsic and solvation components of the activation volume based on the transition state theory. A comparison has been made to related data from sol-gel systems under other conditions.