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A Kinetic Study of the Acid Hydrolysis of a Bunte Salt
Kice,John
J. Org. Chem.
Vol.28(4) 1963 pp.957–961
DOI: 10.1021/jo01039a019 Abstract:http://pubs.acs.org/doi/abs/10.1021/jo01039a019
Abstract
The acid hydrolysis of sodium S-ethyl thiosulfate to ethyl mercaptan has been examined kinetically in aqueous perchloric and hydrochloric acids. Although the mechanism is almost certainly given by equation 4, the rate (log K) shows an excellent correlation with H2. THis presumably occurs because the log K actually varies as to log - H-1, and for the values of 10 to about three this function changes with acid concentration in almost exactly the same way as H2, at least over the range of acidities employed in the present study.
The Mechanism of the Acid Hydrolysis of Bunte Salts (S-Alkyl and S-Aryl Thiosulfates)
Kice,John;Anderson,James,Pawlowski,Norman
J. Am. Chem. Soc.
Vol.88(22) 1966 pp.5245–5250
DOI: 10.1021/ja00974a039
Abstract:http://pubs.acs.org/doi/abs/10.1021/ja00974a039
Abstract
The rates of acid-catalyzed hydrolysis (eq1) of a series of S-aryl and s-alkyl thiosulfates (Bunte salts) have been measured under a variety of reaction conditions in water and various dioxane-water mixtures. The data on the variation of the hydrolysis rate with the acidity of the medium and on the increase in rate accompanying an increase in the dioxane content of dioxane-water mixtures have been compared with corresponding data for two closely related acid-catalyzed hydrolyses: (1) that of sodium aryl sulfates (a reaction thought to proceed through an A-1 mechanism) and (2) that of sodium methyl selenate (a reaction presumably proceeding through an A-2 mechanism). This comparison shows that the response of the Bunte salt hydrolysis to these particular reaction variables is very closely comparable to that of the sulfate hydrolysis and very different to that of the selenate hydrolysi, and it strongly suggests that the Bunte salt hydrolysis proceeds by an A-1 mechanism. It is shown that the observed solvent isotope effect of the Bunte salt hydrolysis (kD20/KH20 = 1.4) and the variation of rate with Ar for ArSSO3- (p=~ - 0.5) are also comparable with the particular A-1 mechanism shown in eq 3. This mechanism involves na initial reversible protonation of the Bunte salt on the divalent sulfur followed by rate-determining unimolecular dissociation of the zwitterion intermediate to thiol and sulfur trioxide. It is thus the same type of mechanism proposed for the sulfate hydrolysis. A tentative explanation is advanced to explain why the Bunte salt and sulfate hydrolyses, although proceeding from the same basic mechanism, show somewhat different response of rate to changes in alkyl or aryl group structure.
Structure-Activity Relationships of Phenylalkylamines as Agonist Ligands for 5-HT(2A) Receptors
Blaazer,Antoni;Smid,Pieter;Kruse,Chris
Chem Med Chem
Vol.3(9) 2008 pp.1299-1309
DOI: 10.1002/cmdc.200800133
Abstract:http://www3.interscience.wiley.com/journal/121357186/abstract
Abstract
Agonist activation of central 5-HT(2A) receptors results in diverse effects, such as hallucinations and changes of consciousness. Recent findings indicate that activation of the 5-HT(2A) receptor also leads to interesting physiological responses, possibly holding therapeutic value. Selective agonists are needed to study the full therapeutic potential of this receptor. 5-HT(2A) ligands with agonist profiles are primarily derived from phenylalkylamines, indolealkylamines, and certain piperazines. Of these, phenylalkylamines, most notably substituted phenylisopropylamines, are considered the most selective agonists for 5-HT(2) receptors. This review summarizes the structure-activity relationships (SAR) of phenylalkylamines as agonist ligands for 5-HT(2A) receptors. Selectivity is a central theme, as is selectivity for the 5-HT(2A) receptor and for its specific signaling pathways. SAR data from receptor affinity studies, functional assays, behavioral drug discrimination as well as human studies are discussed.
Keywords:SAR;Phenylalkylamines;Agonist ligands;5-HT2A Receptors;Phenethylamines;indolealkylamines;piperazines
Oxidation of Aromatic Acids. IV. Decarboxylation of Salicylic Acids
Kaeding,Warren
J. Org. Chem
Vol.29 (9) 1964 pp.2556–2559
DOI: 10.1021/jo01032a016
Abstract:http://pubs.acs.org/doi/abs/10.1021/jo01032a016
Abstract
Pseudo-first-order rate constants for the decarboxylation of salicylic acid and a number of derivatives, in benzoic acid solutions, were measured. ortho and para substituents which tended to enrich the electron density of the aromatic ring produced an increase in rate. The converse was observed with electron-withdrawing groups. The decarboxylation rate also increased when soluble metal salts of benzoic acid were added. A difference in the ability of various metals to promote decarboxylation was observed. The mechanism is discussed in terms of an attack by a proton on the ring carbon atom which is bonded to the carboxylate group.
Keywords:Decarboxylation;Copper;Phenol;Benzoic Acid;Salicylic Acid
Insight into Friedel-Crafts acylation of 1,4-dimethoxybenzene to 2,5-dimethoxyacetophenone catalysed by solid acids—mechanism, kinetics and remedies for deactivation
Yadav,Ganapati;Pimparkar,Ketan
J.Mol. Cat. A: Chemical
Vol.264(1) 2007 pp.179-191
DOI: 10.1016/j.molcata.2006.07.075
Abstract:http://tinyurl.com/2c3xyk6
Abstract
Friedel-Crafts acylation of aromatic ethers is challenging, which frequently encounters rapid catalyst deactivation by the ether. Although H-Y and H-? are known to perform better, there is still deactivation due to both the ether and the acylated ether. In the current work, the synthesis of 2,5-dimethoxyacetophenone, an intermediate used in the production of fine chemicals, was carried out via acylation of 1,4-dimethoxybenzene with acetic anhydride over various solid acid catalysts such as sulfated zirconia, UDCaT-1, UDCaT-5, 20% w/w H3P12W40/K10, 20% w/w Cs2.5H0.5P12W40/K10, Amberlyst-15 and Indion-125. The cation exchange resins, Amberlyst-15 and Indion-125, were superior to other inorganic solid acids. A systematic study was undertaken to understand the reaction mechanism and catalyst functioning with Indion-125. The catalyst gets deactivated slowly over repeated use and this was studied independently. The adsorption of reactants and products was studied from pure component solutions and mixtures. The experimental data so generated were used to develop a model, incorporating deactivation. The model fits the experimental data very well. The current work gives an insight into choice of catalyst, kinetic modeling, studies in catalyst deactivation and methods to avoid deactivation.
Keywords:Friedel Crafts;Acylation;1,4-dimethoxybenzene;2,5-dimethoxyacetophenone;catalysis
jo01052a026[1].pdf
