Substitution reactions aromatic compounds

Other well-known reactions are those offluorinated olefins with fluoride ion and negatively substituted aromatic compounds leading to the formation of per-fiuoroalkylated aromatic compounds The reaction may be considered an amonic version of a Fnedel Crafts process and can result in introduction of one or several perfluoroalkyl substituents [/ /] Aromatic substrates include substituted and unsuhstiluled perfiuorobenzenes [J3l, 212, 213, 214], fiuorinated heterocycles [131, 203, 215, 216, 217, 218, 219, 220, 221, 222, 223],perchlorinated heterocycles [224] (equation 44), and other activated aromatic compounds [225] (equation 45) The fluonnated olefins can be linear or cyclic [208] (equation 46)... 

The difference in position of attack on primary and secondary aromatic amines, compared with phenols, probably reflects the relative electron-density of the various positions in the former compounds exerting the controlling influence for, in contrast to a number of other aromatic electrophilic substitution reactions, diazo coupling is sensitive to relatively small differences in electron density (reflecting the rather low ability as an electrophile of PhN2 ). Similar differences in electron-density do of course occur in phenols but here control over the position of attack is exerted more by the relative strengths of the bonds formed in the two products in the two alternative coupled products derivable from amines, this latter difference is much less marked. 

It has been shown that when nucleophilic aromatic photo-substitution reactions are carried out in non-deoxygenated solutions of aprotic solvents, such as DMSO and acetonitrile, destructive superoxide anions may be formed from aromatic radical anions. Such solvents are best avoided. There has been a review of mechanistic aspects of photo-substitutions of the cyano group in aromatic compounds. ... 

Figure 8-10 shows another pair of reactions for the halogenation of an aromatic compound. The reaction of the side chain is a free-radical substitution. Figure 8-11 shows the mechanism of this free-radical substitution. 

Electrochemical reduction of TNT led to the formation of TAT-3HC1 selective acidic hydrolysis of this compound led to the formation of 2,6-diamino-4-hydroxytoluene dihydrochloride, which was neutralised to 2,6-diamino-4-hydroxytoluene [38, 40, 46]. The interaction of the last product with perfluorotoluene using aromatic nucleophilic substitution reactions led to the formation of 3,5-diamino-4-methyl-2, 3, 5, 6 -tetrafluoro-4-trifluoromethyldiphenyl ether [38, 47] (Scheme 4.17). 

On the other hand, a pure Eley-Rideal mechanism, in which the aromatic compound in the liquid phase reacts with the adsorbed acylating agent was first proposed by Venuto et alP1,22] and more recently by others.[23] However, for acylation reactions of polar substrates (anisole, veratrole), chemisorption of the latter must be taken into account in the kinetic law. A modification, the modified Eley-Rideal mechanism, has been proposed 114,24-26 an adsorbed molecule of acylating agent should react with a nonadsorbed aromatic substrate, within the porous volume of the catalyst. However, the substrate is also competitively adsorbed on the active sites of the zeolite, acting somehow as a poison of the acid sites. That is what we checked through different kinetic studies of various aromatic electrophilic substitution reactions.[24-26]... 

A second limitation is that aromatic compounds substituted with moderately or strongly deactivating groups cannot be alkylated. The deactivated ring is just too poor a nucleophile to react with the unstable carbocation electrophile before other reactions occur that destroy it. 

Meta-cyclizations are often called meta-bridging reactions, since they yield polycyclic meta-bridged structures (74ACR181). In the series of aza-aromatic compounds, these reactions are mostly found with 3-nitro-substituted azines or with 1,3-diazines, as illustrated by Scheme 54 (77JOC2589). 

Aromatic compounds undergo many reactions, but relatively few reactions that affect the bonds to the aromatic ring itself. Most of these reactions are unique to aromatic compounds. A large part of this chapter is devoted to electrophilic aromatic substitution, the most important mechanism involved in the reactions of aromatic compounds. Many reactions of benzene and its derivatives are explained by minor variations of electrophilic aromatic substitution. We will study several of these reactions and then consider how substituents on the ring influence its reactivity toward electrophilic aromatic substitution and the regiochemistry seen in the products. We will also study other reactions of aromatic compounds, including nucleophilic aromatic substitution, addition reactions, reactions of side chains, and special reactions of phenols. 

Strong nucleophiles such as organolithium or organomagnesium derivatives do not react with substituted or unsubstituted phosphabenzene or arsabenzene (Y = P or As) by nucleophilic substitution as in the case of pyridines, but by addition to the heteroatom forming intermediate anions. These anions can then be converted into non-aromatic compounds by reaction with water yielding 1-alkyl-1,2-dihydro-derivatives, or they can be alkylated by an alkyl halide with the same or a different alkyl group, when two products may result a l,2-dialkyl-l,2-dihydro-derivative, or a 2 -derivative (Figure 17). The former products are kinetically controlled, whereas the latter compounds are thermodynamically controlled. 

The Heck reaction was discovered independently in the end of 1960s by T. Mizoroki and R. F. Heck . But Heck developed it into a synthetically useful reaction. Since then it has become one of the most important reactions for the synthesis ° of aromatic compounds substituted with alkenes. 

Metal /3-diketonates, particularly acetylacetonates, will undergo electrophilic substitution at the central methine carbon atom in a similar way to aromatic compounds. Known reactions of this sort include bromination, nitration, acylation, and the Mannich reaction. 

Electrophilic aromatic substitution is the mechanism suggested in both cases the initial step being attack of the cation radical on the aromatic compound (ArH) (reaction 101), followed by deprotonation of the intermediate (reaction 102) and further oxidation of the radical to the resulting arsonium or stibonium ion (reaction 103). 

An example of using sonication and PTC to improve an aromatic nucleophilic substitution reaction has been provided by Wu et al. [56]. Nine diphenyl ether compounds were synthesized from chloronitrobenzene and alkyl-substituted phenols with higher yields and shorter reaction period (Equation 7). 

Fluorination of aromatic compounds. The reaction of various indoles takes place at room temperature in aq MeCN to afford 3-fluoroxindoles. 4-Substituted phenols are converted to 4-fluoro-2,5-cyclohexadienones. ... 

Easic Principles Practical Photochemistry General Considerations Carbonyl Compounds a-Cleavage Carbonyl Compounds Hydrogren Abstraction Steroids Carbonyl Compounds Cycloaddition Enone and Dienone Rearrangements Alkenes Isomerisation and Rearrangement Alkenes Cycloaddition Alkenes Photo-Cxidation Terpenoids Aromatic Compounds Isomerisation and Cycloaddition Practical Photochemistry Scale-up Aromatic Compounds Substitution and Cydisation Alkaloids Photoinitiated Free-radical Chain Reactions. 

CHEMICAL PROPERTIES stable under ordinary conditions of use and storage hazardous polymerization has not been reported organic portions of compound have typical aromatic chemical properties chemical activity is intermediate between phenol and anisole undergoes a wide variety of aromatic ring substitution reactions, including Friedel-Crafts acylation, arylation and sulfonation sublimes above 100°C (212°F) resists pyrolysis at 400°C (752°F) molecule is diamagnetic dipole moment is effectively zero not decomposed by high temperature, air, water, dilute acids or bases, when the central metal atom is in a stable oxidation state FP (data not available) LFL/UFL (data not available) AT (data not available) HC (data not available),... 

---