The base catalysed hydrolysis of trans-dichlorobis-(1,2-diaminoethane)-cobalt(III) and -(1,3-diaminopropane)cobalt(III) cations: rate-limiting proton transfer

1987 ◽  
pp. 1775 ◽  
Author(s):  
Christine Blakeley ◽  
Martin L. Tobe
Keyword(s):  
Proton Transfer ◽  
Rate Limiting ◽  
Hydrolysis Of

Concerted rate-limiting proton transfer to sulfur with nucleophilic attack at phosphorus — A new proposed mechanism for hydrolytic decomposition of the P=S pesticide, Diazinon, in moderately acidic sulfuric acid media

2007 ◽  
Vol 85 (6) ◽  
pp. 421-431 ◽  
Author(s):  
Doreen Churchill ◽  
Julian M Dust ◽  
Erwin Buncel
Keyword(s):  
Proton Transfer ◽  
Organophosphorus Pesticide ◽  
Nucleophilic Attack ◽  
Acid Media ◽  
Hydronium Ion ◽  
Neutral Aqueous Solution ◽  
Region Product ◽  
Rate Limiting ◽  
Hydrolysis Of ◽  
Acid Region

We report herein the first kinetic study of a P=S containing organophosphorus pesticide, Diazinon (1), in the moderately concentrated acid region. Product analyses (31P NMR) show that reaction occurs only at the P centre. The rate-acidity profile (kobs vs. molarity of H2SO4) appears as a curve in which the initial slight downward trace (molarity = 1 to ca. 5) is followed by sharper upward curve (molarity ca. 5 to 14). Using treatments involving the excess acidity (X) method, the A-1 and A-2 mechanistic possibilities were found to be inoperative over the full acidity range. A novel mechanism is proposed for the higher acidity (X ca. 2–6) region. This mechanism involves proton transfer to P=S from hydronium ion with concomitant proton transfer from water, which effectively delivers hydroxide to the P centre in a variant of the A-SE2 process. A putative A-2 mechanism in this region is supplanted by the proposed A-SE2 variant where the cyclic array results in proton transfer being efficiently coupled with nucleophilic attack involving water. This constitutes the first report of rate-limiting proton transfer at the P=S functionality in acid hydrolysis of this class of organophosphorus neutroxins. A 600 000-fold acceleration in the decomposition of Diazinon is associated with the change of medium from neutral aqueous solution to the most acidic medium studied (X ca. 6). Key words: phosphorothioate ester hydrolysis, acid catalysis, rate-limiting proton transfer at P=S, excess acidity analysis, new A-SE2 variant mechanism.

Proton transfer is not rate-limiting in buffer-induced non-enzymic glucation of hemoglobin

1988 ◽  
Vol 110 (24) ◽  
pp. 8265-8266 ◽  
Author(s):  
Herminia. Gil ◽  
Julio F. Mata-Segreda ◽  
Richard L. Schowen
Keyword(s):  
Proton Transfer ◽  
Rate Limiting

The hydrolysis and biogas production of complex cellulosic substrates using three anaerobic biomass sources

2013 ◽  
Vol 67 (2) ◽  
pp. 293-298 ◽  
Author(s):  
C. Keating ◽  
D. Cysneiros ◽  
T. Mahony ◽  
V. O'Flaherty
Keyword(s):  
Biogas Production ◽  
Positive Role ◽  
Diverse Range ◽  
Factors Affecting ◽  
Rate Limiting Step ◽  
Solid Substrates ◽  
Different Temperatures ◽  
Anaerobic Biomass ◽  
Rate Limiting ◽  
Hydrolysis Of

In this study, the ability of various sludges to digest a diverse range of cellulose and cellulose-derived substrates was assessed at different temperatures to elucidate the factors affecting hydrolysis. For this purpose, the biogas production was monitored and the specific biogas activity (SBA) of the sludges was employed to compare the performance of three anaerobic sludges on the degradation of a variety of complex cellulose sources, across a range of temperatures. The sludge with the highest performance on complex substrates was derived from a full-scale bioreactor treating sewage at 37 °C. Hydrolysis was the rate-limiting step during the degradation of complex substrates. No activity was recorded for the synthetic cellulose compound carboxymethylcellulose (CMC) using any of the sludges tested. Increased temperature led to an increase in hydrolysis rates and thus SBA values. The non-granular nature of the mesophilic sludge played a positive role in the hydrolysis of solid substrates, while the granular sludges proved more effective on the degradation of soluble compounds.

Potential of anaerobic digestion of complex waste(water)

2001 ◽  
Vol 44 (8) ◽  
pp. 115-122 ◽  
Author(s):  
G. Zeeman ◽  
W. Sanders
Keyword(s):  
Waste Water ◽  
Anaerobic Digestion ◽  
Order Relation ◽  
Organic Substrates ◽  
Reactor Technology ◽  
Rate Limiting Step ◽  
Treatment Technologies ◽  
Transport Complex ◽  
Rate Limiting ◽  
Hydrolysis Of

Although they differ greatly in origin complex waste(water)s mainly consist of proteins, lipids, carbohydrates and sometimes lignin in addition. Hydrolysis is the first and generally rate-limiting step in the process of anaerobic digestion of particulate organic substrates. Hydrolysis of particulate polymers can be described by Surface Based Kinetics, but for use in practice the empirical first order relation is advised. Unlike the hydrolysis of protein and carbohydrate, lipid hydrolysis is hardly occurring in the absence of methanogenesis. The latter is probably a physical rather than a biological process and affects the choice for either a one- or a two-step (phase) anaerobic reactor. In the chain of collection and transport, complex wastes often become complex wastewaters simply because of dilution. Dilution not only changes the reactor technology to be applied but also complicates the post-treatment and possibilities for resource recovery. Combining concentrated with diluted waste streams will almost always end up in much more complicated treatment technologies.

scholarly journals Study of Kinetics, Equilibrium and the Influence of Steric Effects on Proton-Transfer in the Reactions of 2, 2, 4- and 2, 6- Substituted Anilines with 2-Phenoxy-3,5-dinitropyridine in DMSO

2010 ◽  
Vol 7 (1) ◽  
pp. 253-259 ◽  
Author(s):  
Basim H. Asghar
Keyword(s):  
Proton Transfer ◽  
Steric Effect ◽  
Nucleophilic Attack ◽  
Steric Effects ◽  
Substituted Anilines ◽  
Phenoxy Group ◽  
Kinetics Studies ◽  
Zwitterionic Intermediate ◽  
Rate Limiting ◽  
Step Mechanism

Kinetic and equilibrium results for the reactions of 2-phenoxy-3,5-dinitropyridine (1), with a series of 2, 2, 4- and 2, 6- substituted anilines (2a-f), in the presence of DABCO in DMSO are reported. The reactions yield the 2-anilino derivatives (5), without the accumulation of intermediates. Kinetics studies are compatible with a two-step mechanism involving initial nucleophilic attack by amine at the ring carbon substituted by phenoxy group followed by either base-catalyzed or uncatalyzed conversion to the product. The base-catalyzed pathway is likely to involve rate-limiting proton-transfer from the zwitterionic intermediate to base. This work indicates a steric effect to proton transfer in reactions involving 2, 6-disubstituted anilines. The results were compared with those for reactions of 1, 3, 5-trinitrobenzene with anilines.

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