Bimolecular Electrophilic Substitutions

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. 

Bimolecular Electrophilic Substitutions at Carbon-Hydrogen Bonds... 

BIMOLECULAR ELECTROPHILIC SUBSTITUTION via AN OPEN TRANSITION state Se2, Se2(open)... 

Ingold3 has used the term SE2 to describe these bimolecular substitutions which proceed via open transition states (as shown in reaction (4)), but Reutov4 uses the symbol SE2 to describe all bimolecular electrophilic substitutions, including those in which cyclic transition states are formed as well as those in which the transition state is open. More recently, Abraham et at.6 have suggested that bimolecular electrophilic substitutions in which an open transition state is formed could more explicitly be denoted by the term SE2(open). 

The nomenclature used in describing bimolecular electrophilic substitutions involving cyclic transition states reflects, in part, the above-mentioned difficulty. Ingold3 has adopted the nomenclature of Winstein et al.1 and refers to such substitutions as SEi, but to the present author this is not a particularly appropriate choice since it does not indicate the bimolecular nature of the substitution. Dessy et al.8 have used the term SF2 to describe a mechanism, such as that in reaction (5), in which a four-centred transition state is formed, but not only is such a term too restricted, it also provides no indication that the mechanism is one of electrophilic substitution. The view of Reutov4 is that the cyclic, synchronous mechanism is very close to the open mechanism and that both can be described as SE2 mechanisms. Dessy and Paulik9 used the term nucleophilic assisted mechanisms to describe these cyclic, synchronous mechanisms and Reutov4,10 has recently referred to them in terms of internal nucleophilic catalysis , internal nucleophilic assistance , and nucleophilic promotion . Abraham, et al,6 have attempted to reconcile these various descriptions and have denoted such mechanisms as SE2(cyclic). 

BIMOLECULAR ELECTROPHILIC SUBSTITUTION WITH REARRANGEMENT Se2, [Se2 (open)]... 

BIMOLECULAR ELECTROPHILIC SUBSTITUTION, via A CYCLIC TRANSITION STATE, WITH REARRANGEMENT SEi [SE2 (cyclic)]... 

ENTROPIES OF ACTIVATION (cal.deg" .mole- ) FOR SOME BIMOLECULAR ELECTROPHILIC SUBSTITUTIONS AT SATURATED CARBON... 

KINETIC SALT EFFECTS IN SOME BIMOLECULAR ELECTROPHILIC SUBSTITUTIONS INVOLVING NEUTRAL REACTANTS... 

If kn > fe I proton transfer from H30+ to S is slow and ratedetermining. This mechanism is designated A-SE2 [13] (acid catalysis, bimolecular electrophilic substitution). If fen k lt the intermediate SH + is formed relatively fast in a pre-equilibrium step, and the second step is slow and rate-determining. (In most cases, the pre-equilibrium is far on the... 

To drive the reaction over to the sulfonic acid, an excess of sulfuric acid is generally employed which also assists the forward reaction by removing the water formed. Sulfonation is a bimolecular electrophilic substitution (Se2) reaction and is therefore facilitated by the presence of electron-donating substituents on the aromatic nucleus and is made more difficult by the introduction of electron withdrawing groups (see chapter 7, p. 98). 

Sulfonation is a bimolecular electrophilic substitution reaction (SE2) and the electrophile is sulfur trioxide.3a Sulfur trioxide is a powerful electrophile because of the electron-withdrawing effect of the three double-bonded oxygen atoms. Consequently, oleum (fuming sulfuric acid), which contains approximately 10% of excess sulfur trioxide, is a much more powerful sulfonating agent than concentrated sulfuric acid. Sulfur trioxide is a sufficiently powerful electrophile to attack benzene (23) directly. The mechanism of the sulfonation of benzene by hot concentrated sulfuric acid to give benzenesulfonic acid (24) is shown in Scheme 15.4a... 

Tetradifon is a valuable acaricide for the control of phytophagous mites on a wide range of crops the last step in the synthesis is an example of the Friedel-Crafts reaction, and can be likened to the reaction between t-butylbenzene (62) and a sulfonyl chloride (51) in the presence of aluminium trichloride catalyst to give the sulfone (62) (see Chapter 10, p. 196) (Scheme 37). This reaction is a bimolecular electrophilic substitution reaction(SE2) and... 

The reaction of alkylcobalamins with metal electrophiles, such as Hg(II), has been studied extensively since MeBjj may be responsible for formation of highly toxic meth-ylmercury(II) compounds under environmental conditions ". The reaction mechanism has been studied for both alkylcobaloximes and alkylcobalamins " . Reaction of alkylcobaloximes with Hg(II) salts can be described as a bimolecular electrophilic substitution (Se2), which takes place with inversion of configuration . 

Low-density lipoprotein Tosylate (y>-toluenesulfonate) Unimolecular electrophilic substitution Bimolecular electrophilic substitution Aromatic electrophilic substitution Intramolecular electrophilic substitution... 

Notes-. Most used reactions are SEAr (iododemetallation) and SNAr (halogen exchange, copper assisted). SeI, unimolecular electrophilic substitution Se2, bimolecular electrophilic substitution SeAp aromatic electrophilic substitution SeI, intramolecular electrophilic substitution S l, unimolecular nucleophilic substitution 3 2, bimolecular nucleophilic substitution S Ar, aromatic nucleophilic substitution. 

Sulfonation is a bimolecular electrophilic substitution reaction (Se2) which may be depicted in general terms as shown (Equation 1) ... 

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