Reaction mechanism scheme

A P NMR study of stoichiometric reactions using the di-primary phosphine H2PCH2CH2CH2PH2 provided more information on the reaction mechanism (Scheme 5-12, Eq. 2). Norbornene was displaced from Pt(diphosphine)(norbornene) by ethyl acrylate. Reaction with the diphosphinopropane was very fast this gave the hydrophosphination product, which, remarkably, did not bind Pt to give Pt(diphos-phine), instead, Pt(diphosphine)(norbornene) was observed [12]. 

The proposed reaction mechanism (Scheme 7-2) comprises (1) oxidative addition of ArSH to RhCl(PPh3)3 to give Rh(H)(Cl)(SPh)(PPli3)n, (2) coordination ofalkyne to the Rh complex, (3) ris-insertion of alkyne into the Rh-H bond with Rh positioned at terminal carbon and H at internal carbon, (4) reductive elimination of 16 from the Rh(III) complex to regenerate the Rh(I) complex. 

Carbonylation of aromatic halides is of great industrial interest and several efforts were made to produce the corresponding benzoic acids in aqueous (biphasic) reactions. The tendency of an aromatic C-X bond to react in an oxidative addition onto Pd(0) as required by the reaction mechanism (Scheme 5.4) decrease in the order X = I > Br > Cl so much that chloroarenes are notoriously unreactive in such reactions. 

The reaction mechanism (Scheme 6.25) involves formation of a cationic 7t-allylpalladium complex by the oxidative addition of the substrate onto the catalyst. In case of a dimethylallyloxycarbonyl protecting group this step is disfavoured compared to Alloc and therefore the removal of dimethylallyl groups is slower or requires more catalyst. Accordingly, in homogeneous CH3CN/H2O solutions deprotection of (allyl)phenylacetate proceeded instantaneously with 2 mol % [Pd(OAc)2]/TPPTS while it took 85 min to remove the dimethylallyl group (cinnamyl is an intermediate case with 20 min required for complete deprotection). The reactivity differences are... 

The rate-determining first step is the reaction of the isocyanate with phosphane oxide, resulting in the formation of isocyanate and CO2. Once the isocyanate is formed, it reacts with additional isocyanate to give carbodi-imide and regenerate the catalyst. A more detailed investigation of the reaction mechanism (Scheme 25) followed years later (69ACSA2697 72ACSA1777). 

For the photolysis of ferf-butyl nitrite a possible reaction mechanism (Scheme 6) consists of the production of ferf-butoxy radicals (equation 3), followed by their decomposition to give acetone and methyl radicals (equation 4). The latter are trapped by the nitric oxide liberated in the first step (equation 5). However, the absence of ethane production in the actual experiments suggested that an intramolecular formation of nitrosomethane is unlikely ". ... 

An interesting reaction related to the ring expansions of penicillin S-oxides (208) was observed in the thermal rearrangement of 2,2,4A-tetramethyl-thiethan-3-one 1-oxide to the five-membered thiolane ring 209. Oxidation attempts of these thermally unstable thietanone oxides led via ring opening to the more stable heterocycle. The reaction mechanism (Scheme 11) was... 

We conclude that the neutral substrate enters 1 to form a host-guest complex, leading to the observed substrate saturation. The encapsulated substrate then undergoes encapsulation-driven protonation, presumably by deprotonation of water, followed by acid-catalyzed hydrolysis inside 1, during which two equivalents of the corresponding alcohol are released. Finally, the protonated formate ester is ejected from 1 and further hydrolyzed by base in solution. The reaction mechanism (Scheme 7.7) shows direct parallels to enzymes that obey Michaelis-Menten kinetics due to the initial pre-equilibrium followed by a first-order rate-limiting step. 

Bienayme34 reported the formation of substituted isonitriles by treatment of a dialkyl amine with imidazole diethylacetal and methyl isocyanoacetate. This forms dialky-lamino propenoates via a three-component cascade reaction mechanism (Scheme 5.18). 

Photoinduced electron transfer from the amine to the fullerene core leading to a radical ion pair is suggested to be the initial step in the reaction mechanism (Scheme 39). Formation of the bis-[6,6] closed adduct proceeds via [3 + 2] cycloaddition of the tertiary amine followed by a [2 + 2] cycloaddition of the vinyl group and the C6o double bond adjacent to the previously formed ring connection leading to a structure analogous to 1,2,3,4-C6oH4-... 

Roberts had reported that the low reactivity of alkyl and/or phenyl substituted organosilanes in the reduction processes can be ameliorated in the presence of a catalytic amount of alkanethiols (vide supra)49. The general reaction mechanism (Scheme 11) shows that alkyl radicals abstract hydrogen atom from thiols and the resulting thiyl radicals abstract hydrogen from the silane. This procedure has been applied in dehalogenation, deoxygenation and desulphurization reactions. This approach has also been extended by the same... 

The unusual coimectivity pattern of the dipoles 247 and 248, whereby the isocyanide nitrogen is linked to the a-carbon of the azine, suggests a markedly distinct reaction mechanism (Scheme 37) to that of the Ugi-Reissert reaction. A reasonable mechanistic proposal may involve the formation of the A-acylazinium salt I, which would then be attacked at its a-position by the isocyanide, then leading to the Amdtsen-type dipoles 249 (which have been isolated in some cases). Alternatively, the isocyanide can attack the activated carbonyl group in I, triggering a cascade leading to the generation and subsequent transformation of intermediate... 

In the photoaddition of acetone and other ketones to 1-, 2- and 1,2-di-methylimidazoles the products sire a-hydroxyalkylimidazoles (153) which are derived from the selective attack of excited carbonyl oxygen at C-5. In the case of 2-methylimidazole the products are the 4-mono- (8%) and 4,5-di- (14.5%) substituted compounds, but imidazole itself does not react. The suggestion that it is not a sufficiently electron-rich substrate is not particularly convincing. The reaction mechanism (Scheme 72) may reflect the greater radicd reactivity at C-5, and the comparative stabilities of the radical intermediates derived from carbonyl attack at this position. Hiickel calculations of radical reactivity indices show that, indeed, C-5 is more reactive, and the radical intermediate at C-5 is more stable than that at C-4, but a concerted cycloaddition could also give rise to the oxetane (152). Such an oxetane can be isolated in the photochemical addition of benzophenone to 1-acetylimidazole. 

The effect of phenyl substitution on the rate of Grignard addition to IV-benzylidinetmiline has been examined. The reaction rate in ether for ethylmagnesium bromide conforms to r = it[R 2Mg-MgX2][Schiff base]. A four-centered reaction mechanism (Scheme 3) has been suggested. ... 

The Periana system is currently the most active catalytic system for the C-H activation of methane. The proposed reaction mechanism (Scheme 6) is also based on three steps, C-H activation, oxidation, and functionalization. An important feature of the overall process is that the methyl ester is less reactive with the catalyst than methane. This is attributed to greater inhibition of the presumed electrophilic reaction of the C-H bonds of methylbisulfate in comparison with methane as a result of the electron-withdrawing ability of the bisulfate group... 

Ester formation is a standard organic reaction between an alcohol and a carboxylic acid, which is an equilibrium reaction that has been shown to occur under catalysis by either acid or base. In polyesterification involving an organic acid, the substrate is itself the catalyst. It has been noted (Pilati, 1989) that, among the many reaction mechanisms, Scheme 1.1 is the most likely for acid-catalysed esterification, with the second reaction being the rate-determining step. 

In the case of a single-step reaction such as the reduction of Fe to Fe " (in the absence of diffusion control), no assumptions are required about a rate-determining step in the usual sense (although microscopically, for such redox reactions in solution, consideration can be given to solvent reorganization in the formation of the transition state associated with electron transfer). Correspondingly, no intermediate (except the transition state itself ) need be considered in the reaction mechanism scheme. 

From our study reported here, from our earlier studies of divalent metal molybdates [10-11], and oxidation literature in general [1], we can postulate a reaction mechanism (Scheme 2) which takes all of these factors into account and is consistent with them. Accordingly,... 

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