Alkylation hydrogen transfer

The main reactions of the MTG/MTO process can be summarized as follows the first is the dehydration of methanol to DME on acidic zeolite catalysts. The equilibrium mixture of methanol, DME, and water is then converted to light alkenes, which react further to form higher alkenes, n- and Ao-alkanes, aromatics, and naphthenes by hydrogen transfer, alkylation, polycondensation, isomerization, and other secondary reactions. 

The aromatization of propane and butanes is a thermodynamically feasible endothermic reaction (35-45 Kcal/mole). Aromatization in the Cyclar process includes a series of distinct reaction steps, including dehydrogenation, olefin oligomerization, cyclization, hydrogen transfer, alkylation, dealkylation, and cracking. 

Keywords Hydrogen transfer Alkylation Alcohol Metal halide Methanol Guerbet reaction... 

According to Refs. [21,56], over an acid catalyst, methanol (MeOH) is first dehydrated to DME (Fig. 7). Next, the equilibrium mixture of MeOH, DME, and Hp is further converted into light olefins (step 2). The following step (step 3) is the formation of n/iso paraffins, higher olefins, aromatics, and naphthenes by hydrogen transfer, alkylation, and polycondensation. 

Propylene. Propylene alkylation produces a product that is rich in dimethylpentane and has a research octane typically in the range of 89—92. The HF catalyst tends to produce somewhat higher octane than does the H2SO4 catalyst because of the hydrogen-transfer reaction, which consumes additional isobutane and results in the production of trimethylpentane and propane. 

Some hydrometalation reactions have been shown to be catalyzed by zirconocene. For instance, CpiZrCf-catalyzed hydroaluminations of alkenes [238] and alkynes [239] with BU3AI have been observed (Scheme 8-34). With alkyl-substituted internal alkynes the process is complicated by double bond migration, and with terminal alkynes double hydrometalation is observed. The reaction with "PrjAl and Cp2ZrCl2 gives simultaneously hydrometalation and C-H activation. Cp2ZrCl2/ BuIi-cat-alyzed hydrosilation of acyclic alkenes [64, 240] was also reported to involve hydrogen transfer via hydrozirconation. 

Saponification of Ionized Esters by Intramolecular Hydrogen Transfer Cleavage of the Alkyl/Oxygen Bond... 

Termination Reactions / -Hydrogen Elimination, Alkyl Chain End Transfer, and fi-Methyl Elimination... 

Intramolecular Hydrogen Transfer Reactions in Peroxyl, Alkoxyl, and Alkyl Radicals. 

INTRAMOLECULAR HYDROGEN TRANSFER REACTIONS IN PEROXYL, ALKOXYL, AND ALKYL RADICALS... 

This method gave a primary hydrogen-deuterium kinetic isotope effect of 1.3 for the reaction between the aryl radical and tributyltin hydride. This isotope effect is smaller than the isotope effect of 1.9 which San Filippo and coworkers reported for the reaction between the less reactive alkyl radicals and tributyltin hydride163 (vide infra). The smaller isotope effect of 1.3 in the aryl radical reaction is reasonable, because an earlier transition state with less hydrogen transfer, and therefore a smaller isotope effect164, should be observed for the reaction with the more reactive aryl radicals. 

TABLE 9. The primary hydrogen-deuterium kinetic isotope effects for the hydrogen transfer reactions between alkyl radicals and tributyltin hydride (deuteride)... 

With hydrofluoric acid (23,50), and to a lesser degree also with zeolites (14,81, 87-89), a significant fraction of the product stems from self-alkylation, which is sometimes also termed hydrogen transfer. The importance of this mechanism depends on the acid, the alkene, and the reaction temperature. Self-alkylation... 

K. Manabe, Asymmetric Phase-Transfer Alkylation Catalyzed by a Chiral Quaternary Phosphonium Salt with a Multiple Hydrogen-Bonding Site , Tetrahedron Lett. 1998, 39, 5807-5810. 

K. Manabe, Synthesis of Nobel Chiral Quaternary Phosphonium Salts with a Multiple Hydrogen-Bonding Site, and Their Application to Asymmetric Phase-Transfer Alkylation , Tetrahedron 1998, 54, 14465-14476. 

High pressure free radical process is not suitable for propylene due to extensive hydrogen transfer to free radical which results in resonance stabilised alkyl radicals with reduced tendency to... 

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