Add Catalyzed Reactions

Taft showed that LEER can also be established for aHphatic systems [8]. Taft compared the hydrolysis of substituted aliphatic methyl esters under basic conditions with the corresponding add-catalyzed reactions. 

Non-catalyzed and protonic add-catalyzed reactions are by far the best known. However, many studies have been carried out under conditions where kinetic values and relative mechanisms have no meaning. 

Are the promotion effects of hydrogen on the typycal add-catalyzed reaction observable for Pt/S042--Zr02 and the other catalysts ... 

Scheme 5. Add Catalyzed Reactions 1n HydroxyHc or Non1on1c Media...

Stoichiometric Organic Reactions and Add-Catalyzed Reactions in Ionic Liquids... 

Barclay, L. R. C. Sonawane, H. R. MacDonald, M. C. Sterically hindered aromatic compounds. III. Add-catalyzed reactions of 2,4,6-Iri-I-bulyl and 2-methyl-4,6-di-t-butylbenzyl alcohols and chlorides. Can. J. Chem. 1972, 50, 281-290. 

In 1997, the controversial mechanism of the Biginelli reaction was reinvestigated by Kappe using NMR spectroscopy and trapping experiments [94], and the current generally accepted process was elucidated (see Scheme 9.23). The N-acyliminium ion 9-112 is proposed as key intermediate this is formed by an add-catalyzed reaction of an aldehyde with urea or thiourea via the semiaminal 9-111. Interception of 9-112 by the enol form of the 1,3-dicarbonyl compound 9-113 produces the open-chain ureide 9-114, which cyclizes to the hexahydropyrimidine 9-115. There follows an elimination to give the final product 9-116. 

High-resolution Si NMR spectroscopy was used to study the hydrolysis and condensation kinetics of monomeric and dimeric species in the silicate sol-gel system. Peak assignments for the kinetics experiments were determined by comparing add-catalyzed reaction solutions prepared with limited amounts of water with the synthetically prepared dimeric, trimeric, and tetrameric species. Si NMR peaks were assigned for 5 of the 10 possible dimeric species. The temporal evolution of hydrolysis and condensation products has been compared with a kinetic model developed in our laboratory, and rate constants have been determined. The results indicate that the water-producing condensation of dimeric species is approximately 5 times slower than the water-producing condensation of the monomeric species. The alcohol-producing condensation of dimeric species is comparable with that of monomeric species. 

S5 Aldehydes and ketones underg o add-catalyzed reaction with alcohols to yield hemi-acetals, compounds that have one alcohol-like oxygen and one ether-like oxygen bonded to the same carbon. Further reaction of a hcmiacetal with alcohol then yields an acetal, a compound that has two ether-like oxygens bonded to the same carbon. (See Section 19.11.)... 

A problem present in the refinery is that, due to its fast transport in water and low biodegradabUity, MTBE addition to gasoline pool has been banned in some countries (from 2003 in Cahfomia). MTBE is formed by add-catalyzed reaction of isobutene with methanol. Other alcohols could be used to form different oxygenated additives, as discussed below, but the alternative is to use isobutene for conversion into another high octane number component such as isooctane, which could substitute in part the need of the alkylation process and related environmental/safety problems. 

A specifically kinetic effect may derive from the nature of the transition state. For a cydization reaction the transition state is a ring with one partial covalent bond (for example, 5.2). This may be formed almost completely, as in some lactonisa-tions moderately, as in Sn 2-type processes or to a very minor extent, as perhaps in the hard-to-detect cyclisation reactions of acetals (see 3.29, above). Observed EMs for cydization reactions fall in this order [36]. For a general base catalyzed reaction, by contrast, there is no formal equilibrium free energy of cydization, because the product is not a ring rather - at best - a cycle interrupted by an intramolecular hydrogen bond, set up for the reverse, intramolecular general add catalyzed reaction (5.5, Scheme 2.41). In this situation it is clear that stronger... 

Synthesis of a-hydroxycarboxamides by add catalyzed reaction of an isocyanide with an aldehyde or ketone (see 1st edition)... 

In this paper, pyridine adsorption was utilized to investigate the hydrogen spillover phenomenon from metal to acidic centers of zeolite by observing hydrogenation of chemisorbed pyridine on B or L acid sites of USY zeolite using hybrid catalyst composed of USY zeolite and Pt/SiOo. To give insight into spill-over process in the hybrid catalyst system, isomerization of n-pentane, which is one of the typical add catalyzed reaction, was also studied. 

Moreova, the hydrolysis of phosphite AOs is a handling problem that can be influenced by blended co-additives. Since hydrolysis is an add-catalyzed reaction, hydrotaldte antadds blended in a pellet with the phosphite tends to help slow down hydrolysis [3-9]. 

Application of MW irradiation in the solid add-catalyzed reaction of resorcinol and phloroglucinol with ethyl acetoacetate and propenoic and propynoic acid resulted in the formation of corresponding hydroxy coumarins in very high yields, avoiding the acidic waste associated with aqueous and Lewis adds (De la Hoz et al. 1999). 

As usual, this base-catalyzed reaction has its add-catalyzed counterpart. For the add-catalyzed reaction the catalyst is not hydroxide, but H30, and the active ingredient is not the enolate anion, but the enol itself The first step in the reaction is acid-catalyzed enol formation, the keto-enol tautomerization we have come to know (Fig. 19.67). 

The most important source of acetone is the Hock process for phenol production. In this process acetone is obtained as stoichiometric coupling product. If acetone needs to be produced deliberately, it can be obtained by oxidative dehydrogenation or dehydrogenation of isopropanol. Oxidative dehydrogenation proceeds at 400-600 °C at silver or copper contacts, direct dehydrogenation is carried out at 300-400 °C using zinc contacts. Alternatively, acetone can also be obtained by a Wacker-Hoechst oxidation of propylene. Acetone is used industrially as solvent. Moreover, the aldol condensate products of acetone (diacetone alcohol) are used as solvents. Acetone is also converted in an add catalyzed reaction with two moles of phenol for the synthesis of bisphenol A. Bisphenol A is an important feedstock for the production of epoxy resins and polycarbonates. 

Excellent sensitivity of polymer 3e with rert-alcohol units suggests the add catalyzed reaction as shown in Scheme 6. 

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