Acid Catalyst For Hydrolysis Research Articles

Waugh Type Polyoxometalate Enneamolybdomangate(IV) as an Acid Catalyst for Hydrolysis and as an Oxidant for Aspirin: A Kinetic Study

The oxidations of aspirin and salicylic acid by enneamolybdomanganate(IV) were studied in perchloric acid medium. The aspirin undergo hydrolysis prior to the oxidation to generate salicylic acid, which was found to be catalyzed by both HClO4 as well as the oxidant. The rate of hydrolysis of aspirin catalyzed by the oxidant was found to be lesser than that of HClO4. A mechanism based on the kinetic results is proposed for oxidation of both aspirin and salicylic acid. Initially, aspirin undergo hydrolysis to give salicylic acid, which is catalyzed by both the oxidant, which also acts as an acid catalyst and the HClO4 used. The salicylic acid generated in prior hydrolysis reacts with an oxidant undergoing oxidative decarboxylation by enneamolybdomanganate(IV) in a rate determining step generating phenol. Further oxidation of phenol by another oxidant molecule gives the final product p-benzoquinone in a fast step. The mechanism of oxidation of salicylic acid was also studied under identical conditions as that of aspirin and found to be similar except its prior hydrolysis. A plausible mechanism was proposed and the rate laws for both the substrates were derived. In order to understand the intervention of free radicals the reaction was studied in presence of added acrylonitrile. The formation of copious precipitate due to polymerization of added acrylonitrile was not observed and the values of kobs also remain constant in presence of added acrylonitrile. The formation of MnIII was also studied in presence of added tetrasodium pyrophosphate, which did not affect the values of kobs. Therefore, the formation of free radical and MnIII was excluded while proposing mechanisms for both the substrates. The effect of added products Mn2+ and molybdate also did not have any effects indicating no prior equilibria involving these two products. The effect of ionic strength and solvent polarity are in favour of the reaction between two neutral molecules. The activation parameters were determined and support an outer sphere reaction with formation of a weak precursor complex between the reactants was proposed for both aspirin and salicylic acid.

산 촉매 가수분해에 의한 자이란 분해속도 연구

본 연구는 산 촉매에 의한 자이란 분해속도를 분석하는 것으로 <TEX>$120^{\circ}C$</TEX>에서 60분 동안 가수분해를 수행하여 자이란 분해속도를 조사하였다. 산 촉매로는 황산, 옥살산, 말레산을 사용하였다. 자이란 분해에 관여하는 분해속도상수(<TEX>$k_1$</TEX>)는 산 농도에 비례하여 증가하였으며 이것은 산 농도가 증가할수록 자이란 가수분해가 빠르게 진행된다는 것을 의미한다. 황산, 옥살산, 말레산 중에서 자이란에서 자이로스로 분해되는 속도는 황산을 촉매로 사용하였을 때 가장 높았다. 하지만 수소농도인 pH를 기준으로 하였을 때, 즉 같은 pH 조건에서 가수분해를 수행하였을 때 자이란에서 자이로스로 분해되는 속도는 옥살산, 말레산과 같은 dicarboxylic acid 촉매에서 황산을 사용하였을 때 보다 높은 분해속도상수를 나타냈다. In this study, we investigated the kinetics of acid-catalyzed hydrolysis of xylan over a 60 min at <TEX>$120^{\circ}C$</TEX>. Sulfuric, oxalic and maleic acids were used as acid catalyst for hydrolysis. The calculated degradation rate constants (<TEX>$k_1$</TEX>) showed a correlation with the acid concentration, meaning that the stronger the acid, the higher the xylan degradation rate. Among sulfuric, oxalic and maleic acid catalyzed hydrolysis, the xylan degradation rate to xylose was highest with sulfuric acid. At equivalent solution pH, acid catalyzed hydrolysis was proportional to <TEX>$H^+$</TEX> concentration. The <TEX>$k_1$</TEX> of dicarboxylic acid such as oxalic and maleic acid was higher than that of sulfuric acid at same pH values during hydrolysis.

The solution phase complexing of atrazine by fulvic acid: Equilibria at 25°c

Abstract The solution phase complexing equilibria of atrazine by fulvic acid at 25°C±1.° have been investigated over the pH range of 1.3 to 6.0. Experiments with 0.1MKC1 and chelated Cu(II) are compared with those without metal ions. The use of a fulvic acid having calibrated acidic and Cu(II) chelation properties has made it possible to obtain stoicheometricly “exact”; chemical information. This is correlated with previous hydrolysis kinetics work. It is concluded that atrazine is hydrogen bonded in a labile equilibrium, to an identifiable set of protonated carboxyl groups, which act as Brönsted acid catalysts for hydrolysis. 0.1M KC1 changes (1‐αA), the degree of protonation of the carboxyl groups, without otherwise affecting the atrazine complexing. Cu(II) chelation both reduces and weakens the complexing through a combination of carboxyl group blocking, and fulvic acid aggregation. Simple equations are presented for predictive calculations.

Determination of neutral and amino sugars in glycoproteins by gas chromatography.

A gas chromatographic method for the determination of neutral and amino sugars in glycoproteins was developed by using trifluoroacetyl derivatives of sugar alcohols and by selecting trifluoroacetic acid as acid catalyst for hydrolysis. The method is as follows : As the hydrolytic condition, 2.5 N TFA, 100°, 7 hr was common to obtain excellent recovery of neutral and amino sugars in many glycoproteins. In the case of having enough sample, it was recommendable to select 4 and 7 hr for hydrolysis of neutral sugars and 7 and 10 hr for amino sugars. In sample preparation for gas chromatography, sugars were reduced with sodium borohydride to corresponding sugar alcohols and trifluoroacetylated with trifluoroacetic anhydride in ethyl acetate. This method was further improved for micro-analysis of sugars in glycoproteins, taking full advantage of the sensitivity of an electron capture detector (ECD) to trifluoroacetyl derivatives. Consequently, it was suggested to be able to analyze constituent neutral and amino sugars in microgram amounts of glycoproteins.