BIMOLECULAR SUBSTITUTION REACTIONS

The large rate enhancements observed for bimolecular nucleophilic substitutions m polai aprotic solvents are used to advantage m synthetic applications An example can be seen m the preparation of alkyl cyanides (mtiiles) by the reaction of sodium cyanide with alkyl halides... 

The apphcation of bimolecular, nucleophilic substitution (S ) reactions to sucrose sulfonates has led to a number of deoxhalogeno derivatives. Selective displacement reactions of tosyl (79,85), mesyl (86), and tripsyl (84,87) derivatives of sucrose with different nucleophiles have been reported. The order of reactivity of the sulfonate groups in sucrose toward reaction has been found to be 6 > 6 > 4 > 1. ... 

Nucleophilic Substitution. The kinetics of the bimolecular nucleophilic substitution of the chlorine atoms in 1,2-dichloroethane with NaOH, NaOCgH, (CH2)3N, pyridine, and CH COONa in aqueous solutions at 100—120°C has been studied (24). The reaction of sodium cyanide with... 

The preceding Sections illustrate several experimental features of heteroaromatic substitutions. It is now intended to comment on some of these features which are most significant in terms of reaction mechanism. As stated in the Introduction, a possible mechanism of nucleophilic bimolecular aromatic substitution reactions is that represented by Eq. (14), where an intermediate of some stability... 

Sfj2 reaction (Section 11.2) A bimolecular nucleophilic substitution reaction. 

If the water content of the diazotization system is too high, the halogen atom in halogen-substituted mono- and dinitroanilines may be replaced by a hydroxy group in a bimolecular aromatic substitution. Analogous behaviour was observed in the diazotization of pentafluoroaniline, where the 4-fluoro substituent became hydrolysed (Brooke et al., 1965). As already mentioned in Section 2.1, this side reaction does not take place if the diazotization is conducted in a dichloromethane-aqueous sulfuric acid two-phase system in the presence of tetrakis[3,5-bis(trifluoromethyl)-phenyl]borate (Iwamoto et al., 1983a, 1984). 

The reaction of Sn2, that is, the bimolecular nucleophilic substitution with allyl rearrangement... 

The mechanism of these bimolecular nucleophilic substitution reactions is shown in Scheme 11.3 for the reaction between a primary amine and the intermediate dichlorotriazine. A corresponding scheme can be drawn for reaction of a secondary amine, an alcohol or any other nucleophile in any of the replacement steps. It follows from this mechanism that the rate of reaction depends on ... 

As can be seen from the data presented, the high energies of complex formation decrease sharply the endothermicity of the retro-Wittig type decomposition and, moreover, fundamentally change the reaction mechanism. As has been shown for betaines (")X-E14Me2-CH2-E15( + )Me3 (X = S, Se E14 = Si, Ge E14 = P, As), the reaction occurs as bimolecular nucleophilic substitution at the E14 atom. For silicon betaines, the transition states TS-b-pyr with pentacoordinate silicon and nearby them no deep local minima corresponding to the C-b complexes can be localized in the reaction coordinate. 

The catalysis of hydrocarbon liquid-phase autoxidation by transition metals is the result of the substitution of the slow bimolecular reaction (Ek 100 kJ mol-1, see Chapter 4)... 

In this section, we sketch the nature of the three VB state framework as a template to describe bimolecular nucleophilic substitutions ( S. -2)[7, 12, 13], Although it remains to be seen if three VB states are sufficient to describe the title reaction system in solution, this is still a useful additional exercise to expose the reasoning underlying the practical application of our theory. The wave function to describe the Sa/2 reaction... 

At pH < 7 the nitroxyl radicals do not undergo an observable heterolysis (khs 10 s ), but decay by bimolecular reactions. However, in basic solution an OH -catalyzed heterolysis takes place to yield the radical anion of the nitrobenzene and an oxidized pyrimidine. In the case of the nitroxyls substituted at N(l) by H (i.e. those derived from the free bases), the OH catalysis involves deprotonation at N(l) which is adjacent to the reaction site [= C(6)] (cf. Eq. 15) [26] ... 

Homolytic substitution reactions including homolytic allylation, radical [2,3]-migrations and stereochemical reactions been reviewed. The review also highlights the possible applications of homolytic substitution reactions. ni reactions at silicon (by carbon-centred radicals in the a-position of stannylated silyl ethers) are efficient UMCT reactions producing cyclized alkoxysilanes. Bimolecular reactions can also be facilitated in good yield (Schemes 32 and 33). ... 

Chlorination and chloramination of a widely used antibacterial additive, triclo-san, which is used in many household personal care products, results in the formation of chloroform, 5,6-dichloro-2-(2,4-dichlorophenoxy)phenol, 4,5-dichloro-2-(2,4-dichlorophenoxy)phenol, 4,5,6-trichloro-2-(2,4-dichlorophenoxy)phenol, 2, 4-dichlorophenol, and 2,4,6-trichlorophenol [119]. The reaction of triclosan with monochloramine is slow, however, compared to chlorine [120]. The chlorophenox-yphenols are formed via bimolecular electrophilic substitution of triclosan. 

Further, Takahashi et al. [57] reported no spectral change in an air atmosphere between 200 nsec and 2 msec for 6-nitro-BIPS in methanol and acetonitrile, a result that is consistent with Lenoble and Becker s findings [56]. Kaliskey and co-workers [58] collected data for a nitro-substituted BIPS in acetonitrile with many similarities to that of Lenoble and Becker and further noted that the buildup of the 560 nm absorption is concentration dependent, which implies a bimolecular reaction such as aggregation leads to the absorption changes in this spectral region. 

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