Chlorobenzene: acylation

FIGURE 3.22 Degradation involving dioxygenation via acyl chlorides of (a) chlorobenzene, (b) y- hexachlo-rocyclohexane, and (c) pentachlorophenol. 

Sulphated zirconia catalysts can be acidic or superacidic depending on the method of treatment. A variety of acid-catalysed reactions, referred to earlier in this section, can be carried out with sulphated zirconia. Yadav and Nair (1999) have given a state-of-the art review on this subject. Examples of benzylation of benzene with benzyl chloride / benzyl alcohol, alkylation of o-xylene with. styrene, alkylation of diphenyl oxide with 1-dodecene, isomerization of epoxides to aldehydes, acylation of benzene / chlorobenzene with p-chloro benzoylchloride, etc. are covered in the review. 

A variety of other reactions such as acylation of toluene, anisole, and chlorobenzene to give selectively p-isomer, alkylations, etc. have been conducted with IL. 

In 1991 Bose described the synthesis of ot-vinyl /1-lactams by reaction of ,/l-unsa-turated acyl chlorides with a Schiff base in chlorobenzene under microwave irradiation (an example of the eco-friendly MORE chemistry, in which only a limited amount of solvent is used) [20b]. Under these conditions, a-vinyl /1-lactam formation can be achieved in 65-70% in approximately 5 min (classical conditions require several hours and lead only to modest yields). 

A catalytic effect that may be of the same type as the mimicry of acyl transferase enzymes is reported by Gandour et al. (1978). They describe the rate enhancement of the aminolysis of p-nitrophenyl acetate in the presence of bis(2,6-pyridinyl) crown ethers [328] and [329] in chlorobenzene. The rate of... 

Ammonolysis. Reactions involving ammonia. Ammonolysis of esters, acyl chlorides, and anhydrides give amides aniline is produced by ammonolysis of chlorobenzene. The reaction is analogous to hydrolysis, with ammonia substituted for water. 

Seddon and coworkers studied the Friedel-Crafts acylations of toluene, chlorobenzene and anisole with acetyl chloride in [emim][Al2Cl7] and obtained excellent regioselectivities to the para isomer, Scheme 9. Similarly, the fragrance chemical, traseolide, was obtained in 99% yield as a single isomer. Scheme 10. It should be noted, however, that the question of product recovery from the reaction medium still needs to be addressed in these systems. 

The activity of 42%STA/silica catalysts for the acylation of related aromatic reactants with iso-butyric anhydride was investigated. In the presence of anisole and veratrole, 100% anhydride conversion was observed, leading to the expected para-acylation products. No reaction was observed in the presence of chlorobenzene and other deactivated aromatic systems. 

The wide scope of application of the electrophilicity index of Parr, Szentpaly, and Liu has been reviewed.1 Applications to electrophilic aromatic substitutions discussed are few. However, some alkylation and acylation reactions do correlate well with electrophilicity values. In the case of the nitration of toluene and chlorobenzene, correlation is not very good and it is suggested2 that electrophilicity is a kinetic quantity with inherent thermodynamic information. 

Decomposition of Aromatic Acyl Peroxides. The decomposition of aromatic acyl peroxides in liquid aromatic compounds is similar to the decomposition of nitrosoacetylarylamines and appears to involve the intermediate formation of free radicals. When dibenzoyl peroxide is heated in benzene, biphenyl, benzoic acid, and small amounts of phenyl benzoate, p-terphenyl, and quaterphenyl are produced. 4 That the second component enters into the reaction is shown by the formation of 4-chlorobiphenyl from the decomposition of di-p-chlorobenzoyl peroxide in benzene 84 and of dibenzoyl peroxide in-chlorobenzene 86... 

The typical reaction with benzoic anhydride as acylating agent was carried out as follows a solution of 20 mmol of aromatic substrate in 50 ml dry chlorobenzene were introduced in the flask and magnetically stirred under nitrogen atmosphere. 

Acyl isocyanates. SnCl4 is the best catalyst for preparation of these products by reaction of ArCOCI and NaOCN, with ZnCl2 being a close second. 1,2-Di-chlorobenzene is the preferred solvent. Yields are lower in reactions of aliphatic acyl chlorides. 

Figure 2. Catalytic activities of SO /ZrCK prepared by use of HiSOj ( ) and (NH4) S04 ( >) vs calcination temperature. Yield % of dichlorobenzophenone in acylation of chlorobenzene with o-chlorobenzoyl chloride at 403 K in 3 h.

Acylation of aromatics which had been known to be catalyzed only by AICI3 was found to be effectively catalyzed by solid superacids. As shown in Table 4, SO4 /ZrCL exhibited a high activity for the acylation of chlorobenzene with o-chlorobenzoyl chloride in the liquid phase. The yield is 100% at 406 K in lOh, while the yields over H-ZSM-5 and SiC -ALOj are 0 and 0.17%, respectively [9]. 

The starting material is obviously available by a Friedel-Crafts acylation of chlorobenzene and the rest of the synthesis follows. Note that the nitrile can be converted directly into the ester with acidic ethanol and that an excess of Grignard reagent is needed because the free OH group destroys some of it. 

As would be expected, high rate accelerations can result when reactions proceeding through ionic intermediates, e.g. carbocations, are performed in ionic liquids. For example, Seddon and coworkers [100] studied the Friedel-Crafts acylation of toluene, chlorobenzene (Fig. 7.30) and anisole with acetyl chloride in [emi-m][Al2Cl7], whereby the ionic liquid is acting both as solvent and catalyst. They ob-... 

Phthalimidoaziridines can be cleaved by hydrazinolysis to give 1-aminoaziridines, which decompose slowly at room temperature, and rapidly above 48 C, regenerating the starting alkene with stereochemistry intact. There would appear to be some unexploited potential for phthalimidoaziridines to be used for alkene protection. Phth imidoaziridines are stable to reflux in chlorobenzene (132 C) for 24 h. A/-Aminoaziridines can be acylated to yield )V-acylaminoaziridines of varying thermal stability (34 ti/2 = IS min at 37 C) is a ready thermal source of benzamidonitrene from which new aziridines can... 

Keto esters. When ethyl acetoacetate (1) is heated with a nitrile in benzene or chlorobenzene in the presence of stannic chloride a tin(IV) complex (2) is formed. When 2 is hydrolyzed by acid, the acyl group is cleaved preferentially to give a new i3-keto ester (3). 

Chloromethylation and the Friedel-Crafts alkylation and acylation take place normally at the ortho and para positions. The insecticide DDT (43, dichlorodiphenyltrichloroethane) is prepared from chlorobenzene and chloral (trichloroethanal). 

In the Friedel-Crafts acylation of benzene, the above procedure gave only poor yield, whereas a new catalyst system, Hf(OTf)4 and CF3SO3H, was found to catalyze the reaction of even deactivated benzenes, e.g. chlorobenzene and fluorobenzene (Eq. 13) [20]. 

Friedel-Crafts acylation. This new catalyst system is effective for the acylation of benzene, chlorobenzene, and fluorobenzene. 

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