Abstraction of hydride

Experimental Procedure 2.1.3. Preparation of an Iron Carbene Complex by a-Abstraction of Hydride Dicarbonyl(T 5-cyclopentadienyl)(phenylthiocarbene) iron hexafluorophosphate [179]... 

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]. 

The key propagation step in the mechanism is abstraction of hydride from the starting alkyl mercury. In the propagation step anything will do to cleave the weak Hg-H bond but once the chain is running it is an alkyl radical that does this job, just as in tin hydride chemistry. 

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. 

The rate-determining step in the ionic hydrogenation reaction of carbon-carbon double bonds involves protonation of the C==C to form a carbocation intermediate, followed by the rapid abstraction of hydride from the hydride source (equation 45). ° There is a very sensitive balance between several factors in order for this reaction to be successful. The proton source must be sufficiently acidic to protonate the C—C to form the intermediate carbocation, yet not so acidic or electrophilic as to react with the hydride source to produce hydrogen. In addition, the carbocation must be sufficiently electrophilic to abstract the hydride from the hydride source, yet not react with any other nucleophile source present, i.e. the conjugate anion of the proton source. This balance is accomplished by the use of trifluoroacetic acid as the proton source, and an alkylsilane as the hydride source. The alkene must be capable of undergoing protonation by trifluoroacetic acid, which effectively limits the reaction to those alkenes capable of forming a tertiary or aryl-substituted carbocation. This essentially limits the application of this reaction to the reduction of tri- and tetra-substituted alkenes, and aryl-substituted alkenes. 

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. 

Common error alert The abstraction of hydrogen atom IT. which has a low activation energy, is not to be confused with the abstraction of hydride anion ... 

The stabilisation of a carbocation by hyperconjugation by a P-C-Sn bond is sometimes referred to simply as the P-tin effect. It is apparent in the abstraction of hydride by Ph3C+ BF4 from alkyltin compounds.19 Tetramethyltin is unreactive, but ethyltin compounds undergo elimination. 

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. 

Abstraction of hydride by ozone results in an intimate ion pair which was originally thought to collapse exclusively to the covalent hydrotrioxide,... 

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>. 

Once cyclization has occurred, aromatization can occur through abstraction of hydride. 

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