Aromatic compounds anisole

The authors of this work were concerned chiefly with additions to alkenes, and evidence about the mechanism of aromatic nitration arises by analogy. Certain aspects of their work have been repeated to investigate whether the nitration of aromatic compounds shows the same phenomena ( 5-3-6). It was shown that solutions of acetyl nitrate in acetic anhydride were more powerful nitrating media for anisole and biphenyl than the corresponding solutions of nitric acid in which acetyl nitrate had not been formed furthermore, it appeared that the formation of acetyl nitrate was faster when 95-98% nitric acid was used than when 70 % nitric acid was used. 

Zeroth-order nitrations. The rates of nitration at 25 °C in solutions of acetyl nitrate (6xio —0-22 mol 1 ) in acetic anhydride of 0- and jw-xylene, and anisole and mesitylene were independent of the concentration and nature of the aromatic compound provided that... 

The best-known equation of the type mentioned is, of course, Hammett s equation. It correlates, with considerable precision, rate and equilibrium constants for a large number of reactions occurring in the side chains of m- and p-substituted aromatic compounds, but fails badly for electrophilic substitution into the aromatic ring (except at wi-positions) and for certain reactions in side chains in which there is considerable mesomeric interaction between the side chain and the ring during the course of reaction. This failure arises because Hammett s original model reaction (the ionization of substituted benzoic acids) does not take account of the direct resonance interactions between a substituent and the site of reaction. This sort of interaction in the electrophilic substitutions of anisole is depicted in the following resonance structures, which show the transition state to be stabilized by direct resonance with the substituent ... 

Through a study of the influence of thiophene and other aromatic compounds on the retardation and chain transfer on the polymerization of styrene by stannic chloride, the relative rates of attack of a carbonium-ion pair could be obtained. It was found that thiophene in this reaction was about 100 times more reactive than p-xylene and somewhat less reactive than anisole. ... 

Arenediazonium ions are relatively weak electrophiles, and therefore react only with electron-rich aromatic substrates like aryl amines and phenols. Aromatic compounds like anisole, mesitylene, acylated anilines or phenolic esters are ordinarily not reactive enough to be suitable substrates however they may be coupled... 

Aromatic compounds that do not contain meta-directing groups can be converted to diarylamines by treatment with aryl azides in the presence of phenol at — 60°C ArH -f- Ar N3 —> ArNHAr. Diarylamines are also obtained by the reaction of N-arylhydroxylamines with aromatic compounds (benzene, toluene, anisole) in the presence of F3CCOOH ArH -f Ar NHOH ArNHAr. ... 

Electron-rich aromatic compounds such as durene, p-dimethoxybenzene, mesitylene, anisole, thiophene, and fluorene can be benzoylated or acetylated by the corresponding Af-acylimidazole in trifluoroacetic acid to give the corresponding benzophenone or acetophenone derivative in good yield (Method A). As the actual acylating agent, a mixed anhydride of trifluoroacetic acid and benzoic acid has been proposed 1973... 

Diathiadiphosphetane disulfides are probably the most studied and the most thermally and hydrolytically stable of all the phosphorus-chalcogen heterocycles. They contain a central four membered P2S2 ring and can be prepared from heating phosphorus pentasulfide with aromatic compounds. The most well-known of these is Lawesson s reagent (43), which is made from anisole and phosphorus pentasulfide,92 and is used extensively in organic synthesis procedures (see Section 5.4.1). Other dithiadiphosphetane disulfides of note are 44 and 45, formed from the reaction of phosphorus pentasulfide with ferrocene or 1 -bromonaphthalene respectively.93... 

Chain-Transfer with anisole. The phenomenon of chain-transfer, especially with aromatic compounds, has been extensively investigated for the polymerisation of styrene, but there is only one such study with isobutene [13]. Isobutene (0.1 mole/l) was polymerised by titanium tetrachloride (3 x 10 3 mole/l) in methylene dichloride with a constant, low, but unknown concentration of water in the presence of anisole (0.02 to 0.15 mole/l) over the temperature range -9° to -90°. The reactions were stopped at 10-20 per cent conversion by the addition of methanol. 

Electron-rich aromatic compounds, such as phenol, anisole and A,./V-dimethylaniline, add to bis(2-trichloroethyl) azodicarboxylate under the influence of lithium perchlorate, boron trifluoride etherate or zinc chloride to yield para-substituted products 74, which are transformed into the anilines 75 by means of zinc and acetic acid86. Triflic acid (trifluoromethanesulphonic acid) catalyses the reactions of phenyl azide with benzene, toluene, chlorobenzene and naphthalene, to give TV-arylanilines (equation 34)87. 

A similar reaction occurs with electron-rich aromatic compounds, such as toluene or anisole, under tin(IV) chloride catalysis, e.g. equation 131 ... 

Samajdar et al. (2000) performed nitration of aromatic compounds by bismnth nitrate on catalysis with montmorillonite KSF. The reaction develops in THF suspension on steering dnring 10 min. Nitration of anisole proceeds strictly in the para position (91% yield after 10 min), bnt in case of phenol, the reaction occnrs to be nonregioselective and 3 1 mixture of para and ortho nitro prod-nets is formed with a common yield of 89%. Nitration of estrone (the steroid phenol) also leads to 1 1 mixtnre of para and ortho nitrophenolic steroids in 94% yield. 

It was realized that the mechanism of Birch reduction involves protonation of the anion-radical formed by the addition of one electron to the reacting aromatic compound. This is followed by rapid addition of a second electron and protonation of the forming carbanion to yield nonconjugated alicyclic products. Protonation of the anion-radical by added alcohol is the rate-limiting stage. Recent calculations show that the ortho and meta positions in anisole are most enhanced in density by electron introduction. The para position is not appreciably affected (Zimmerman and Alabugin 2001 Scheme 7.9). 

Okamoto and co-workers noted that N-phenylhydroxylamine gave predominately diphenylamine on treatment with benzene in TFA but mostly 4-aminobiphenyl and 2-aminobiphenyl in the stronger acid trifluoromethane-sulfonic acid (TFSA). Similar results were obtained if benzene was replaced by toluene or anisole. The authors suggested that the reaction in TFA proceeded through O-protonated hydroxylamine either via a direct Sn2 displacement on N by the aromatic nucleophile or via attack of the aromatic compound on the N of a nitrenium ion. In TFSA they favored a mechanism in which the diprotonated hydroxylamine lost water to generate an iminium-benzenium dication (11, Scheme 5), a protonated nitrenium ion. " This... 

The fluorination of other activated aromatic compounds, such as anisole and phenol, undergo monofluorination mainly in the ortho and para positions, whereas the fluorination of deactivated aromatics, such as nitrobenzene, trifluoromethylbenzene and benzoic acid, give predominantly the corresponding meta fluoro-derivatives which is consistent with a typical electrophilic substitution process. Also, fluoro-, chloro- and bromo-benzenes are deactivated with respect to benzene itself but are fluorinated preferentially in the ortho and para positions [139]. At higher temperatures, polychlorobenzenes undergo substitution and addition of fluorine to give chlorofluorocyclohexanes [136]. 

Substituted 1-fluoropyridinium triflates have been used for substitution of hydrogen by fluorine in aromatic compounds (Table 3).46"50 Thus benzene is transformed to fluorobenzene (56 % yield, l-fluoro-2,6-bis(methoxycarbonyl)pyridinium triflate), Af-ethoxycarbonylaniline gives Al-ethoxycarbonyl-2- and -4-fluoroaniline (60 and 27% yield, respectively, 1-fluoropyridinium triflate), and phenylurethane also gives the products of fluorination at position 2 (47%) and 4 (32%) of the aromatic ring [l-fluoro-2,6-bis(methoxycarbonyl)pyridinium triflate]. In the case of fluorination of anisole, 1-fluoropyridinium tetrafluoroborate gives 19% 2- and 17% 4-fluoroanisole.46... 

A second major mode of photocydoaddition involves 1.2-addition to the aromatic ring, and this predominates if there is a large difference in electron-donor/acceptor capacity between the aromatic compound and the alkene. It is therefore the major reaction pathway when benzene reacts with an electron-rich alkene such as 1,1-dimethoxyethylene (3.43) or with an electron-deficient alkene such as acrylonitrile (3.441. When substituted benzenes are involved, such as anisole with acrylonitrile (3.45), or benzonitrile with vinyl acetate (3.46), reaction can be quite efficient and regioselective to give products in which the two substituents are on adjacent carbon atoms. 

The oxidative carbonylation of arenes to aromatic acids is a useful reaction which can be performed in the presence of Wacker-type palladium catalysts (equation 176). The stoichiometric reaction of Pd(OAc)2 with various aromatic compounds such as benzene, toluene or anisole at 100 °C in the presence of CO gives aromatic acids in low to fair yields.446 This reaction is thought to proceed via CO insertion between a palladium-carbon (arene) allyl chloride, but substantial amounts of phenol and coupling by-products are formed.447... 

Formylation of the less reactive phenol and anisole with CO in HF-BF3 was found to require at least stoichiometric amount of the acid for effective transformation (50 equiv. of HF, 2 equiv. of BF3, 50 bar CO, 45°C).445 Conversion increases with increasing reaction time but results in decreasing paralortho ratios suggesting a change from kinetic control to thermodynamic control and the reversibility of formylation. Furthermore, the amount of byproducts (mainly diphenylmethane derivatives) originating from reactions between substrates and products also increases. Additional studies in ionic liquids showed that imidazolium cations with increased chain lengths—for example, l-octyl-3-methylimidazolium salts—are effective in the formylation process. This was attributed to the enhanced solubility of CO in the ionic liquid medium. Tris(dichloromethyl)amine, triformamide, and tris (diformylamino)methane have recently been applied in the formylation of activated aromatic compounds in the presence of triflic acid at low temperature (— 10 to 20°C) albeit yields are moderate.446... 

There is no standard, universal, procedure for the Birch reduction. Experiment 7.19 illustrates some of the variants which have been reported in the literature. The original Birch procedure is to add small pieces of sodium metal to a solution of the aromatic compound in a mixture of liquid ammonia and the proton source (ethanol).18 After completion of the reaction, which is usually indicated by the disappearance of the blue colour, it is quenched by the addition of ammonium chloride and the ammonia allowed to evaporate before the cautious addition of water, and isolation of the product by ether extraction. In a modified procedure a co-solvent (ether, tetrahydrofuran, etc.) is initially added to the solution of aromatic compound/liquid ammonia prior to the addition of metal lithium metal is often used in place of sodium.19a,b In general these latter procedures are used for substrates which are more difficult to reduce. Redistilled liquid ammonia is found to be beneficial since the common contaminant iron, in collodial form or in the form of its salts, has a deleterious effect on the reaction.20 A representative selection of procedures is given in Expt 7.19 for the reduction of o-xylene, anisole, benzoic acid, and 3,4,5-trimethoxybenzoic acid. 

A correlation for less structurally related compounds was also developed by Amalric et al. (1996). To develop this correlation, meta- and para-substituted anisoles were studied. These aromatic compounds were substituted with F, Cl, N02, OH, and NH2 groups. The first-order degradation rate constant, kapf was predicted with the octanol/water partition coefficient (log Kow), Brown s constant (o+), and molar refractivity (MR) used as descriptors. The following correlation was developed ... 

The correlation was developed with a correlation coefficient of 0.903. The correlation was able to accurately predict the first-order degradation rate constants as a function of Brown s constant, the octanol/water partition coefficient, and molar refractivity. This correlation held for a broader class of aromatic compounds substituted at the meta and para positions, as compared to a simple substitution at one position on the aromatic ring. Table 9.6 lists the experimental and predicted values for the first-order degradation rate constants of substituted anisoles. 

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