Aromatic compounds nucleophilic substitution reactions

The most widely used approach to the preparation of PESs in both academic research and technical production is a polycondensation process involving a nucleophilic substitution of an aromatic chloro- or fluorosulfone by a phenoxide ion (Eq. (3)). Prior to the review of new PESs prepared by nucleophilic substitution publications should be mentioned which were concerned with the evaluation and comparison of the electrophilic reactivity of various mono- and difunctional fluoro-aromats [7-10]. The nucleophilic substitution of aromatic compounds may in general proceed via four different mechanism. Firstly, the Sni mechanism which is, for instance, characteristic for most diazonium salts. Secondly, the elimination-addition mechanism involving arines as intermediates which is typical for the treatment of haloaromats with strong bases at high temperature. Thirdly, the addition-elimination mechanism which is typical for fluorosulfones as illustrated in equations (3) and (4). Fourthly, the Snar mechanism which may occur when poorly electrophilic chloroaromats are used as reaction partners will be discussed below in connection with polycondensations of chlorobenzophenones. 

UNIMOLECULAR NUCLEOPHILIC SUBSTITUTION OF AROMATIC COMPOUNDS THE REACTIONS OF DIAZONIUM SALTS WITH SIMPLE NUCLEOPHILES... 

Kinetics of Nucleophilic Substitution Reactions of Polyfluoro Aromatic Compounds (Russ) Rodionov, PP, Funn, G G hv Sib Old Akad NaukSSSR 3-26 87 B- [Pg.21]

Arynes are intermediates in certain reactions of aromatic compounds, especially in some nucleophilic substitution reactions. They are generated by abstraction of atoms or atomic groups from adjacent positions in the nucleus and react as strong electrophiles and as dienophiles in fast addition reactions. An example of a reaction occurring via an aryne is the amination of o-chlorotoluene (1) with potassium amide in liquid ammonia. According to the mechanism given, the intermediate 3-methylbenzyne (2) is first formed and subsequent addition of ammonia to the triple bond yields o-amino-toluene (3) and m-aminotoluene (4). It was found that partial rearrangement of the ortho to the meta isomer actually occurs. 

Compound 40 has not yet been synthesized. However, there is a large body of synthetic data for nucleophilic substitution reactions with derivatives of 41 [synthesized from aliphatic and aromatic aldehydes, pyridine, and trimethylsilyl triflate (92S577)]. All of these experimental results reveal that the exclusive preference of pathway b is the most important feature of 41 (and also presumably of 40). 

The Ullman reaction has long been known as a method for the synthesis of aromatic ethers by the reaction of a phenol with an aromatic halide in the presence of a copper compound as a catalyst. It is a variation on the nucleophilic substitution reaction since a phenolic salt reacts with the halide. Nonactivated aromatic halides can be used in the synthesis of poly(arylene edier)s, dius providing a way of obtaining structures not available by the conventional nucleophilic route. The ease of halogen displacement was found to be the reverse of that observed for activated nucleophilic substitution reaction, that is, I > Br > Cl F. The polymerizations are conducted in benzophenone with a cuprous chloride-pyridine complex as a catalyst. Bromine compounds are the favored reactants.53,124 127 Poly(arylene ether)s have been prepared by Ullman coupling of bisphenols and... 

The synthesis of nitro dyes is relatively simple, a feature which accounts to a certain extent for their low cost. The synthesis, illustrated in Scheme 6.5 for compounds 140 and 141, generally involves a nucleophilic substitution reaction between an aromatic amine and a chloronitroaromatic compound. The synthesis of C. I. Disperse Yellow 14 (140) involves the reaction of aniline with l-chloro-2,4-dinitroaniline while compound 141 is prepared by reacting aniline (2 mol) with compound 144 (1 mol). 

Arylations of nitro compounds can be achieved by aromatic nucleophilic substitution using aromatic nitro compounds, as discussed in Chapter 9.100 Komblum and coworkers reported displacement of the nitro group of nitrobenzenes by the anion of nitroalkanes. The reactions are usually carried out in dipolar aprotic solvents such as DMSO or HMPA, and nitroaromatic rings are substituted by a variety of electron-withdrawing groups (see Eq. 5.63).101... 

Anodic side chain substitution is a competing reaction to nuclear substitution of aromatic compounds. In side chain substitution, the first formed acidic radical cation is deprotonated at the a-carbon atom of an alkyl group to form a radical. This is further oxidized to a benzyl cation, which reacts with a nucleophile (Scheme 9, path d). The factors that influence the ratio of nuclear to side chain substitution have been described in 5.4.1. 

Apart from nucleophilic substitution reactions, the chemistry of the halo derivatives of the 7r-deficient heterocycles is fairly similar to that of aromatic halides. Thus, heterobiaryls can be prepared by the Ullman reaction, and Grignard reagents and organolithium compounds can be prepared, although in many instances, and especially with Grignard reagents,... 

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). 

Kinetics of Nucleophilic Substitution Reactions of Polyfluoro Aromatic Compounds ... 

The methylenedioxy group is obtained from a 1,2-dihydroxy aromatic compounds in a double nucleophilic substitution reaction. 

Nucleophilic substitution reactions via an SN2 reaction are not possible in aromatic compounds because the configuration at the reacting C atom cannot be inverted. 

The last two examples in Table 8.5 have the leaving group bonded to an. s/r-hybridized carbon, either a vinylic carbon or an aromatic carbon. Under normal conditions, both of these types of compounds are inert to nucleophilic substitution reactions because of the stronger C—L bond, the difficulty in forming carbocations at s/r-hybridized carbons, and the extra steric hindrance to approach of the nucleophile from the side opposite the leaving group. (Under particularly favorable circumstances, SN1 reactions of these compounds can be forced to occur.)... 

Next, three different mechanisms for nucleophilic substitutions on aromatic rings are presented. These are followed by several other reactions that are useful in synthesis because they interconvert groups attached to aromatic rings. Finally, the use of combinations of all of these reactions to synthesize a variety of substituted aromatic compounds is discussed. 

On the other hand, if only catalytic amounts of A1C13 are added, the acetyl group of the acetophenone is brominated. Under these conditions a catalytic amount of HC1 is first formed. It allows the acetophenone to equilibrate with the tautomeric enol. This is a better nucleophile than the aromatic compound because it is brominated elec-trophilically without intermediate loss of the aromaticity. HBr is the stoichiometric byproduct of this substitution. Just like the HC1 that is formed initially, it catalyzes the enolization of unreacted acetophenone and thus keeps the reaction going. 

This synthesis shows how important electrophilic substitution in aromatic compounds is in industrial processes. It involves four separate such reactions as well as three nucleophilic aromatic substitutions. The chemistry of Chapters 22 and 23 is well represented here. 

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