Electrophilic aromatic substitution 2-naphthol

The azo coupling reaction proceeds by the electrophilic aromatic substitution mechanism. In the case of 4-chlorobenzenediazonium compound with l-naphthol-4-sulfonic acid [84-87-7] the reaction is not base-catalyzed, but that with l-naphthol-3-sulfonic acid and 2-naphthol-8-sulfonic acid [92-40-0] is moderately and strongly base-catalyzed, respectively. The different rates of reaction agree with kinetic studies of hydrogen isotope effects in coupling components. The magnitude of the isotope effect increases with increased steric hindrance at the coupler reaction site. The addition of bases, even if pH is not changed, can affect the reaction rate. In polar aprotic media, reaction rate is different with alkyl-ammonium ions. Cationic, anionic, and nonionic surfactants can also influence the reaction rate (27). 

The y-nitrogen atom of a sulfonic acid azide is electrophilic and reacts in an electrophilic aromatic substitution with an activated benzene or naphthalene derivative, e.g., a phenoxide ion, forming a l-tosyl-3-aryltriazene (2.47). The 1,4-quinone diazide is obtained by hydrolysis (Scheme 2-30, Tedder and Webster, 1960). The general applicability of this reaction seems to be doubtful. With 1-naphthol the 1,2-naphthoquinone diazide was obtained, not the 1,4-isomer. 

The coupling reaction is probably that electrophilic aromatic substitution which is characterized to the highest degree by its sensitivity to orientation. In practically all cases the aromatic substrate reacts only if a strong electron donor (O, NH etc.) is present. The reaction takes plare exclusively at the o- and p-positions m-sub-stitution has never been observed nor a reaction at the 3-position of 2-naphthol and 2-naphthylamine (in contrast to, for example, sulfonation). 

Reaction with phenols and naphthols are usually carried out in the pH range 8-11, when the coupling species is the phenoxide ion. A cold, acidic solution of the diazonium salt is added to an alkaline solution of the phenol, when a fast electrophilic aromatic substitution occurs at the 4-position (Scheme 8.25). If this position is already occupied, attack occurs at the 2-position. 2-Naphthol couples at the 1-position. 

Scheme 16. Comparison of TADDOL with BINOL and Future Goals. Derivatives of (R,R)-TADDOLs and of (P)- or (S)-BINOL, when employed in the same reaction, often give the same product enantiomer preferentially (cf. the Cj-symmetrical structural similarity). While TADDOLs are much easier to prepare and to modify, they are many orders of magnitude less acidic than BINOLs (TADDOLates are less polar ligands to a metal). Some TADDOL derivatives contain CPh2X groups which are labile to (undesired) nucleophilic substitution the dioxolane group of TADDOLs, on the other hand, is surprisingly stable to hydrolysis. BINOL (a naphthol derivative ) can be very sensitive to oxidation and (undesired) electrophilic aromatic substitution, and there are conditions under which it may racemize. Some goals to increase the usefulness of the TADDOL system are shown at the bottom of the Scheme other P derivatives, more acidic derivatives, reagents for enantioselective protonation, deprotonation,...

Highly reactive methylene iminium chlorides 250 were used by Kaupp for carbon-carbon formation in arylaminomethylations of 2-naphthol in a ball mill (Scheme 2.79) [67], Due to susceptibility of iminium chlorides to moisture, reagents were handled under an argon atmosphere. After milling, electrophilic aromatic substitution products 252 were dissolved in dihloromethane and recrystallized. The... 

Historically, sulfonation has been one of the most important electrophilic aromatic substitutions, particularly in the production of 1- and 2-naphthol, as well as alizarin. Unlike the previously mentioned electrophilic reactions, it is frequently reversible. SO3, which occurs in low concentration in sulfuric acid, acts as the electrophilic agent. 

NaOH deprotonates CHCI3, and will give dichlorocarbene by an a-elimination reaction. This intermediate is very electrophilic, and will rapidly react with suitable nucleophiles. Under these conditions, naphthol is also deprotonated to the alkoxide, and this makes it very susceptible to electrophilic aromatic substitution. 

Electrophilic aromatic substitution 3t C-1 of 2-naphthol with dichlorocarbene gives the dichloromethyl product. Elimination of chloride generates an enone which is intercepted by hydroxide this regenerates the aromatic ring. Collapse of the intermediate so formed generates the aldehyde product. 

Electrophilic and nucleophilic substitution in aromatic systems ring fission to yield the more familiar 1-naphthol (104) ... 

Friedel-Crafts alkylation is one of the most frequently used and widely studied reactions in organic chemistry. Since the initial discovery by Charles Friedel and James Mason Crafts in 1877, a large number of applications have emerged for the construction of substituted aromatic compounds. Friedel-Crafts alkylation processes involve the replacement of C—H bond of an aromatic ring by an electrophilic partner in the presence of a Lewis acid or Bronsted acid catalyst. Particularly, catalytic asymmetric Friedel-Crafts alkylation is a very attractive, direct, and atom-economic approach for the synthesis of optically active aromatic compounds. However, it took more than 100 years from the discovery of this reaction until the first catalytic asymmetric Friedel-Crafts (AFC) alkylation of naphthol and ethyl pyruvate was realized by Erker in 1990. Nowadays, owing to continued efforts in developing... 

Similarly, naphthols and other phenolic aromatics also undergo substitution with the same set of electrophilic reagents as phenol and simple substituted phenols. Thus, as shown in Equation 8.32,1-naphthol (a-naphthol) reacts with the potent electrophilic benzenediazonium ion (generated from aminobenzene [aniline] and sodium nitrite [NaN02] in acid solution and is written here as the tetralluoroborate [BF4 ] salt) to produce the corresponding brightly colored phenyldiazonaphthale-nol, in which substitution has occurred para to the hydroxyl. 

The existence of S /ace-N=N-aryl bonds are more difficult to establish because azo bonds are also formed during the growth of the film. A C(OH)-C-N=N-C6H5 has been observed by TOF-SIMS [126] and assigned to an electrophilic attack of the diazonium cation on an -OH-substituted aromatic ring at the surface of carbon. This is the well-known azo coupling reaction between diazonium salts and, for example, naphthol that has been the basis of the dye chemistry. It is different from the reaction of Figure 3.1 that involves a radical. 

The role played by dihydrodiols in the metabolic formation of phenols and their conjugated derivatives from aromatic substances is at present undecided. In theory, upon dehydrating a dihydrodiol, the phenolic hydroxyl should remain at that carbon most activated toward electrophilic substitution (14,625). This criterion of mechanism is satisfied in some instances (i.e., the halogenobenzenes (379, 682) and benzonittile (681). Furthermore, compounds that arise from the metabolism of aromatic hydrocarbons also arise from metabolism of dihydrodiols which are formed from them (94,163). However, hver slices and Uver microsomes capable of forming dihydrodiol from naphthalene form neg%ible amounts of naphthol (95,558). 

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