The hydrolysis of thioacetic, thiobenzoic, and three substituted thiobenzoic acids in perchloric and sulfuric acids

1978 ◽  
Vol 56 (7) ◽  
pp. 935-940 ◽  
Author(s):  
John T. Edward ◽  
Graeme Welch ◽  
Sin Cheong Wong
Keyword(s):  
Sulfuric Acid ◽  
Activity Coefficients ◽  
Acid Concentration ◽  
Perchloric Acid ◽  
Transition States ◽  
Sulfuric Acid Concentration ◽  
Thiobenzoic Acid ◽  
The Difference ◽  
Different Response ◽  
Hydrolysis Of

The rates of hydrolysis of thioacetic, thiobenzoic, and three substituted thiobenzoic acids increase with concentration of solvent sulfuric or perchloric acid to a maximum in 30–40% acid and then decrease. Yates–McClelland r, Bunnett–Olsen [Formula: see text], and Hammett ρ parameters, and entropies of activation indicate an AAC2 mechanism over this range of acid concentrations. In acid concentrations above 50–60% the rates increase sharply and the same mechanistic criteria now indicate an AAc1 mechanism. The difference between the rate–acidity profile of thiobenzoic acid and that of ethyl thiolbenzoate can be explained by the different response of the activity coefficients of their transition states to increase in sulfuric acid concentration.

Studies of azo and azoxy dyestuffs. Part 18. Kinetics and mechanism of the hydrolysis of 3- and 4-(p′-methoxyphenylazo)pyridines in aqueous sulfuric acid media

1986 ◽  
Vol 64 (11) ◽  
pp. 2115-2126 ◽  
Author(s):  
Erwin Buncel ◽  
Ikenna Onyido
Keyword(s):  
Sulfuric Acid ◽  
Transition States ◽  
Activation Parameters ◽  
Nucleophilic Attack ◽  
Acid Solutions ◽  
Acid Media ◽  
Charge Delocalization ◽  
Leaving Group ◽  
The Difference ◽  
Hydrolysis Of

The kinetics of hydrolysis of 4-(p′-methoxyphenylazo)pyridine, 1, and its 3-isomer, 2, have been studied in moderately concentrated sulfuric acid media at 25 °C. In all the acid solutions investigated, 1 reacted faster than 2; rate differences between the two compounds varied from ca. 1000-fold in the dilute region of acidity to ca. 250-fold in the more concentrated acid solutions. The observed first-order rate constants, kψ, for both substrates exhibit a maximum, at ca. 42% H2SO4 and 47% H2SO4 for 1 and 2 respectively. Activation parameters have also been determined. The pKa values for the second protonation equilibria of 1 and 2 have been evaluated and structures of the diprotonated species are discussed. Hydrolysis is shown to occur from the diprotonated substrates and two main mechanisms are operative. The first is an A-2 type mechanism, which involves rate-limiting attack of H2O on the aryl carbon center giving delocalized transition states and intermediates in which the pyridinium and azonium functions are involved in charge delocalization. Subsequent transfer of a proton and detachment of the leaving group are fast processes. In the second A-SE2 type mechanism, nucleophilic attack and transfer of the proton are fast steps preceding the slow general acid catalyzed separation of the leaving group. The difference in reactivity of the two compounds is attributed to differences in extent of charge delocalization in the transition states of the reactions: for 1 both the pyridinium and protonated azonium functions are involved whereas for 2 only the azonium function participates in charge delocalization.

The Belousov-Zhabotinskii Oscillatory Reaction Involving Some Organic Chiral Substrates

1997 ◽  
Vol 62 (5) ◽  
pp. 739-745 ◽  
Author(s):  
Ľubica Adamčíková ◽  
Katarína Kučárová ◽  
Peter Ševčík
Keyword(s):  
Sulfuric Acid ◽  
Induction Period ◽  
Acid Concentration ◽  
Perchloric Acid ◽  
Organic Substance ◽  
Sulfuric Acid Concentration ◽  
Oscillatory System ◽  
Oscillatory Reaction ◽  
Oscillatory Systems ◽  
Active Substrate

Oscillatory systems of the Belousov-Zhabotinskii (BZ) type were studied using the following substrates: D-gluconic and D-galactonic acids, their lactones, and D-glucose and D-galactose. The systems were either nitrogen purged or left undisturbed. It is suggested that during the induction period (IP), reactions occur giving rise to the active substrate in the BZ system which need not be identical with the organic substance with which the oscillatory system starts up. A special dependence of the IP on sulfuric acid concentration was measured, exhibiting a minimum and a maximum; the dependence on perchloric acid concentration displayed a minimum.

Study on Sugar Production Conditions of Dilute Sulfuric Acid Hydrolysis of Corn Straw

2014 ◽  
Vol 1008-1009 ◽  
pp. 97-100
Author(s):  
Qing Sun ◽  
Shu He Huang ◽  
Bo Wang ◽  
Xiao Run Deng ◽  
Jia Sheng Yi ◽  
...  
Keyword(s):  
Sulfuric Acid ◽  
Reaction Time ◽  
Acid Hydrolysis ◽  
Acid Concentration ◽  
Sulfuric Acid Concentration ◽  
Sugar Yield ◽  
Corn Straw ◽  
Experimental Conditions ◽  
Dilute Sulfuric Acid ◽  
Hydrolysis Of

In this paper, through the study of reducing sugar conditions of corn straw hydrolysis under acidic condition, looking for the production of experimental conditions relatively reasonable. Mainly by dilute sulfuric acid hydrolysis of corn straw by single factor test, effects of sulfuric acid concentration, temperature, reaction time, particle size, ratio of solid to liquid five factors, effects on sugar yield of corn straw. The dilute sulfuric acid concentration 5%, ratio of solid to liquid was 1:14, when the reaction time is 140 min, particle fineness of 120 mesh, the reaction temperature is 100 °C, corn stalk sugar yield reached a maximum 20.11%.

scholarly journals HIDROLISIS SELULOSA DARI SEKAM PADI (Oryza sativa) MENJADI GLUKOSA DENGAN KATALIS ARANG TERSULFONASI

KOVALEN ◽  
2016 ◽  
Vol 2 (3) ◽  
Author(s):  
Adeks Pramana ◽  
Abdul Rahman Razak ◽  
Prismawiryanti Prismawiryanti
Keyword(s):  
Oryza Sativa ◽  
Sulfuric Acid ◽  
Acid Concentration ◽  
Rice Husk ◽  
Contact Time ◽  
Sulfuric Acid Concentration ◽  
Cellulose Hydrolysis ◽  
Hydrolysis Reaction ◽  
Rice Husks ◽  
Hydrolysis Of

Cellulose hydrolysis from rice husk (Oryza sativa) into glucose with sulfonated charcoal catalyst was conducted. The aim of this research was to determine sulfuric acid concentration and contact time on the sulfonation process of charcoal which would produce the highest glucose rendement from cellulose hydrolysis of rice husk. Sulfuric acid concentrations in this experiment were 8, 10, and 12 N with variation of contact time of 4, 6, 8, 10 and 12 hours respectively.  Rice husk was delignified with NaOH 10% to produce cellulose which was hydrolyzed by sulfonated charcoal catalyst. Hydrolysis reaction with the ratio cellulose/aquadest 1:25 (w/v) was conducted in autoclave with temperature 130 oC for 3 hours. The result showed that 8 N concentration of sulfuric acid and 12 hours of contact time produced the highest glucose rendement 17,9%. Keywords : rice husks, cellulose, glucose, sulfonated charcoal

scholarly journals Optimization of hydrolysis conditions for xylans and straw hydrolysates by HPLC analysis

2021 ◽  
Author(s):  
Alexander Beckendorff ◽  
Anne Lamp ◽  
Martin Kaltschmitt
Keyword(s):  
Sulfuric Acid ◽  
Acid Concentration ◽  
Hplc Analysis ◽  
Degradation Products ◽  
Sulfuric Acid Concentration ◽  
Corn Cob ◽  
Hydrolysis Time ◽  
Conversion Rates ◽  
Hydrolysis Temperature ◽  
Hydrolysis Of

AbstractOligosaccharide analysis is commonly done by acid hydrolysis and following HPLC analysis. A major problem is the incomplete hydrolysis of oligosaccharides and disaccharides and the increasing formation of volatile furfural from pentose monomers and hydroxymethylfurfural (HMF) from hexose monomers. This paper optimizes the conditions of hydrolysis approaches and proposes a method for oligosaccharide quantification. The optimal condition for hydrolysis of model xylan from corn cob was found to be for 100 °C hydrolysis temperature, 120 min hydrolysis time, and 2 wt% sulfuric acid concentration. Under these conditions, the total free and bound xylose yield was 77.4% and hemicellulose conversion 87.4% respectively; no degradation products were found. The optimal conditions for hydrolysis of model xylan from beech wood were found to be for 120 °C hydrolysis temperature, 120 min hydrolysis time, and 2 wt% sulfuric acid concentration. Under these conditions, the total free and bound xylose yield was 65.1% and hemicellulose conversion 70.5% respectively; no degradation products were found. For pentosan hydrolysate, conditions were further optimized (110 °C, 60 min, 2 wt% H2SO4). Standard addition of xylan from the corn cob for hydrolysation showed similar conversion rates (< 2% deviation); no matrix effects were detected.

Sign in / Sign up

Export Citation Format

Share Document