Abstraction of hydride ions

B2H6 from BHg. The simplest reaction observed involves the abstraction of hydride ion from BHi by a boron halide to generate BH3 units which combine to form B2H6. Reaction (16) represents the general reaction observed. 

An initial step Involves abstraction of hydride ion from B3H8 to generate the unstable intermediate [B3H7]. Transfer of a BH3 unit from one [B3H7] molecule to another would generate BitHio and a residue of empirical composition (BH2). Thus the following sequence with resulting stoichiometry (17) is envisioned. 

H-NMR spectral studies. Moreover, the mechanism of ferricyanide oxidation of 166 has been established (78JOC1132). The rate-determining abstraction of hydride ion by ferricyanide leads to isoquinolone 169 and a species [HFe(CN)6] that rapidly reacts with a second ferricyanide ion to give two ferrocyanide ions. This mechanism is contrary to the results in the pyridine series (cf Section 1I,A,2 and II,A,3). 

The parent ion 5 and its naphtho[6] analogue have been generated by treatment of 1 and 11, respectively, with trityl tetrafluoroborate. The cations so formed are captured by water and the final product of reaction is the ring opened aryl aldehyde (equation 24)230 231. Kinetic measurements have shown230 that abstraction of hydride ion from 1 is first order and displays a deuterium isotope effect of 6.5. To the best of the author s knowledge, the isolation and spectroscopic characterization of an unsubstituted cycloproparenyl cation has yet to be achieved. 

Goble and Lawrence attributed the high isomerization activity of chlorinated platinum-alumina catalyst to the creation of a localized dual site comprising a Lewis acid site and an adjacent platinum site. However, as has since been pointed out by Asselin et al. (88), carbonium ion intermediates over low-temperature isomerization catalysts are probably created by the same process as that observed for Friedel-CrEifts catalyst abstraction of hydride ion from the paraffin by a strong Brdnsted acid according to the equation... 

Abstraction of hydride ions from tropylidenes by nitrosyl or trityl tetra-fluoborates leads to 2-imino-3-arylthiazolotropylium salts like 640a,b [94H(38)2691] and to cycloheptaazaazulenium salt 643 or (unstable) 14-77-electronic pyrrolotropylium salt 647 [Scheme 173 94JCS(P1)2579]. 

Isobutane-to-Olefin Ratio with Propylene Feed. The isobutane-to-olefin ratio has long been recognized as an important process variable in the alkylation of isobutane with either butenes or pxopylene (Phillips Petroleum Company, 1946). By maintaining a sufficiently high concentration of isobutane in the reaction zone, the abstraction of hydride ions from isobutane is favored over abstraction from product isoparaffins. 

The presence of catalyst is necessary in the catalytic cracking process. Acid cracking catalysts produce carbonium ions by protons addition to olefins or abstracting of hydride ions from hydrocarbon molecules ... 

Catalytic cracking generally proceeds through a carbenium ion, which is considered to occur by the abstraction of hydride ion from polymer or the addition of proton on the polymer macromolecule in the initial step of the reaction (Figure 9.1). 

The acid cracking catalysts produce carbonium ions by the addition of protons to polyolefin chains or by abstraction of hydride ions from hydrocarbon molecules. This is followed by chain scission, which yields C30-C50 oligomeric hydrocarbons. Secondary cracking by P-scission of the C30-C50 hydrocarbons yields liquid (C10-C25) hydrocarbon fuel. Specific advantages of the Polymer-Engineering Process include ... 

The need for an oxidant is shown by the failure of the colour to develop if insufficient m-dinitrobenzene is used [202], although addition of a substance like lead dioxide causes rapid appearance of colour in such a mixture [igg]- w-Nitro-aniline is always formed in reactions using excess of m dinitrobenzene as the oxidant [203]. It is uncertain at present whether the abstraction of hydride ion and proton occurs as a synchronous termolecular process, or as two discrete steps in one order or the other. 

Although Able et al. (2, 8) had originally set out to prepare 7r-cyclo-heptatrienyl complexes of metals, the cycloheptatriene complexes they actually obtained served as key intermediates in forming the former complexes. In 1958 Dauben and Honnen (61) reported that cycloheptatriene-molybdenum tricarbonyl reacted with triphenylmethyl tetrafluoroborate in methylene chloride solution with abstraction of hydride ion from the molybdenum complex. The reaction products, obtained in nearly quantitative yields, were triphenylmethane and the 7r-cycloheptatrienyl complex [(7r-C7H7)Mo(CO)3]+BF4 . 

The first two steps are identical with those of the dimerization reaction. In step (3) a carbonium ion abstracts a hydrogen atom with its pair of electrons (a hydride ion, essentially) from a molecule of alkane. This abstraction of hydride ion yields an alkane of eight carbons, and a new carbonium ion to continue the chain. As we might expect, abstraction occurs in the way that yields the tert-butyl cation rather than the less stable (P) isobutyl cation. 

The abstraction of hydride ion from R3SnH by Ph3C+ has been used as one approach for preparing cations R3Sn+ (Section 7-2)74 76... 

The reaction scheme involves initial formation of an ammine complex that can provide amide ions for reaction with benzyl carbonium ions formed by hydride ion abstraction from toluene. The resulting coordinated benzylamine is displaced from the complex by NH3, and subsequently rapidly dehydrogenated to benzonitrile. In support of this mechanism, it has been demonstrated that the events depicted in Eq. (6) occur very rapidly over ZnX catalyst at 500°. In addition, the use of an olefin to provide carbonium ions for abstraction of hydride ions from toluene enhances the overall reaction rate. 

The synthesis of 2,4,6-triaryl-l,3,5-thiadiazinium tetrafluoroborates (e.g. (94)) by abstraction of hydride ion from 2,4,6-triaryl-4//-l,3,5-thiadiazines (e.g. (93)) with triphenylcarbenium tetrafluoroborate has been reported (Equation (3)) <73BCJ3902, 80BCJ3369, 81JAP(K)5657778, 81JAP(K)5657779>. 

Benzannulation of bridged bicyclic systems has been reported [13], The reaction involves in situ reduction of bridged bicyclic hexa-3-yn-l,5-diene to 1,3,5-hexatriene and electrocyclization to dihy-droaromatic intermediate. Lewis acid-mediated dehydrogenation gave the benzannulated bridged bicychc compound as the product (Scheme 16.10) [13]. Although the mechanism of Lewis acid-mediated dehydrogenation in the presence of benzaldehyde is not fuUy understood, it is presumed to occur by the abstraction of hydride ion from the dihydroaromatic intermediate by the Lewis acid-activated aldehyde. 

Ion cyclotron resonance studies of 3-methoxyalkanethiols and homologous sulphides MeO(CH2) SMe (n = 1—3/ have provided information on the reactivity profile of the methoxymethyl cation towards alcohols, thiols, and amines, and on the preferential abstraction of hydride ion from the carbon atoms that are alpha to sulphur (confirming that, in gas-phase reactions, S is more able than O to stabilize a neighbouring carbonium ion). Gas-phase acidities of dimethyl sulphoxide and representative aliphatic sulphones reveal a lower degree of stabilization of the cr-sulphonyl carbonium ions. ... 

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