Acidizing mechanisms

Stir 15 ml. of concentrated sulphuric acid mechanically in a wide-necked 50 ml. flask with external ice-water cooling until the temperature of the acid is about 5°. 

The ionization of (E)-diazo methyl ethers is catalyzed by the general acid mechanism, as shown by Broxton and Stray (1980, 1982) using acetic acid and six other aliphatic and aromatic carboxylic acids. The observation of general acid catalysis is evidence that proton transfer occurs in the rate-determining part of the reaction (Scheme 6-5). The Bronsted a value is 0.32, which indicates that in the transition state the proton is still closer to the carboxylic acid than to the oxygen atom of the methanol to be formed. If the benzene ring of the diazo ether (Ar in Scheme 6-5) contains a carboxy group in the 2-position, intramolecular acid catalysis is observed (Broxton and McLeish, 1983). 

The Feulgen Nucleai Reaction. Acid Degradation of Sperm Deoxynucleic Acid. Mechanism of the Feulgen Nucleai Reaction, Chong-fu Li, W. G. Overend, and M. Stacey, Nature, 163 (1949) 538-540. 

It is well known also that higher alkanes suffer radical gas phase oxidation above 723 K. Therefore, their use requires catalysts active and selective for deNOx at lower temperatures. The mechanism of NOx elimination is still debated a redox mechanism involving Cu ions is probable, and isolated Cu cations exchanged into MFI [4,5] or mordenite [6] have been found to be more active than CuO clusters. It must be emphasized, however, that acid zeolites exhibit good activity at high temperature, and acid mechanisms have been proposed [7-10]. In presence of Cu this acid mechanism disappears probably due to the decrease of the acidity of mordenite upon Cu exchange [6]. According to... 

Sasaki et al. [8] this acid mechanism could proceed by nitration of a product of the oxidation of the hydrocarbon, followed by autoreduction of this intermediate to nitrogen. 

Quantum mechanical/molecular mechanical study on the Favorskii rearrangement in aqueous media has been carried out.39 The results obtained by QM/MM methods show that, of the two accepted mechanisms for Favorskii rearrangement, the semibenzilic acid mechanism (a) is favored over the cyclopropanone mechanism (b) for the a-chlorocyclobutanone system (Scheme 6.2). However, the study of the ring-size effects reveals that the cyclopropanone mechanism is the energetically preferred reactive channel for the a-chlorocyclohexanone ring, probably due to the straining effects on bicycle cyclopropanone, an intermediate that does not appear on the semibenzilic acid pathway. These results provide new information on the key factors responsible for the behavior of reactant systems embedded in aqueous media. 

Horrocks, L. A. and Farooqui, A. A. NMDA receptor-stimulated release of arachidonic acid mechanisms for the Bazan effect. In Municio, A. M. and Miras-Portugal, M. T. (eds), Cell Signal Transduction, Second Messengers, and Protein Phosphorylation in Health and Disease. New York Plenum Press, 1994, pp. 113-128. 

Stulnig, T.M., Immunomodulation by polyunsaturated fatty acids Mechanisms and effects, Int Arch Allergy Immunol, 132, 310, 2003. 

Rates of the Rh(m) complex were highest in water-ethanol mixtures of a 22 3 ratio. Rate dependence data, provided in Table 21, suggested the metallo-carboxylic acid mechanism (not unlike that of Darensbourg,61 Scheme 20 or Tanaka,75 Scheme 27) depicted in Scheme 37, and the kinetic equation in the lower pH region where Pco >0.3 atm was found to be ... 

Note This reaction involves a polar acidic mechanism, not a free-radical mechanism It is a Friedel-Crafts alkylation, with the slight variation that the requisite carbocation is made by protonation of an alkene instead of ionization of an alkyl halide. Protonation of C4 gives a C3 carbocation. Addition to Cl and fragmentation gives the product. 

Step 3. The numbering of the atoms in this polar acidic mechanism is not straightforward, because it is... 

Little is formally known about the toxicity of amanita use. Ibotenic acid is a potent neurotoxin, through excitatory amino acid mechanisms (Steiner et al. 1984 Schwarcz et al. 1984). It has been used extensively in animal research to create discrete neuroanatomical lesions. For example, it has been used to lesion the basal forebrain nuclei to create a putative animal model of Alzheimer s disease (Arbogast and Kozlowski 1988). 

Venkitasubramanian, P., Daniels, L. and Rosazza, J.P.N., Biocatalytic reduction of carboxylic acids mechanism and application. In Biocatalysis in the Pharmaceutical and Biotechnology Industries, Patel, R. (ed). CRC Press LLC Boca Raton, FL, 2006, pp. 425-440. 

Capon et al. considered three possible mechanisms [equation (47)] for hydrolysis of o-methoxymethoxybenzoic acid. Mechanisms (a) and (b) involve nucleophilic attack by the carboxylate anion on the protonated acetal, and mechanism (c) proceeds with intramolecular gener2il acid catalysis. Capon was able to rule out mechanisms (a) and (b) since the synthetically prepared intermediate in (a) is stable under the reaction conditions. That in (b) leads to products at... 

Liu, X., Yamada, N., Maruyama, W., and Osawa, Y. (2008b). Formation of dopamine adducts derived from brain polyunsaturated fatty acids Mechanism for Parkinson s disease.. Biol. Chem. 283,34887-34895. 

Derrick BE, Martinez Jr JL (1996) Associative, bidirectional modifications at the hippocampal mossy fibre-CA3 synapse. Nature 381 429-434 Dickenson A (1997) Mechanisms of central hypersensitivity excitatory amino acid mechanisms and their control. In Dickenson A, Besson JM (eds) Pharmacology of pain. Springer-Verlag, Berlin, pp 167-210... 

Many catalysts do not use metals in their pure reduced metallic forms. Anchored organometallic complexes are often analogs of homogenous catalysts fixed on a solid support. In particular, titanate complexes both in solution and in supported form have been found to be especially active in transesterifications of simple esters.It was proposed that titanates catalyze the transesterification reaction through a Lewis acid mechanism where the reactant ester and metal form a Lewis complex activating the carbonyl groups for a nucleophilic attack by the reactant alcohol. The tetrahedral intermediate that is formed breaks down into the product alcohol and an ester-metal Lewis... 

The major part of isomers (> 90%) are formed by an acid mechanism, according to the consecutive scheme odCB mdCB pdCB, as in homogeneous phase (ref.6). However, the small odCB pdCB direct interconversion, and the appearance of CB and TCBs, evidenced a dechlorination/chlorination process initiated on Fe + impurities by a radical mechanism (ref.6). 

In a 3-I. round-bottom flask, fitted with a reflux condenser, is placed 650 cc. of absolute alcohol (Org. Syn. 5, 56) and to it 46 g. (2 moles) of sodium is added as rapidly as possible without loss of material through the condenser. If all the sodium does not dissolve, heat is applied. To the hot sodium ethylate solution 312 g. (2.1 moles) of ethyl oxalate (Org. Syn. 2, 23 5, 59) is added as rapidly as possible. Then, immediately, 234 g. (2 moles) of benzyl cyanide (Org. Syn. 2, 9) is added. The reaction mixture is allowed to stand overnight. The solution is transferred to a 3-I. beaker and treated with 250-300 cc. of water (Note 1). It is then warmed to 350, and made strongly acid to litmus with concentrated hydrochloric acid. Mechanical stirring is used during the acidification. On cooling to ordinary... 

The absorption of C02 by copper(I) amides [Eq. (36)] most likely also proceeds via a carbamic acid mechanism (101). 

Modification of zeolites, based on chemisorption of silane or diborane and subsequent hydrolysis of the chemisorbed hydride groups can also be applied for encapsulating gas molecules in zeolites. For example, krypton and xenon can be encapsulated in mordenite combining the modification process with a physical adsorption of the noble gases at moderate pressures and temperatures (e.g. 100 kPa, 300 K). The encapsulates are homogeneous and stable towards acids, mechanical grinding and y-irradiation. By controlling the pore size reduction however, the thermal stability can be controlled. 

Carboxylic Acids Mechanism of Hydrolysis of an Ester by Base (page 816)... 

The regio- and enantioselective pentadienylation of aldehydes is also catalyzed by the BINAP/silver complex.312 The reaction of dienylstannanes 351 with various aldehydes takes place in the 7-position exclusively to afford the products 352 with good to high enantioselectivities (Scheme 100). The reaction was proposed to occur either via a Lewis acid mechanism (transition state 353) or by transmetallation (transition state 354). 

The following processes are used commercially for the separation of such fatty acids mechanical pressing, solvent crystallization, and hydrophilization. 

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