Mesitylene, acetyl

The ability of iron(III) chloride genuinely to catalyze Friedel-Crafts acylation reactions has also been recognized by Holderich and co-workers [97]. By immobilizing the ionic liquid [BMIM]Cl/FeCl3 on a solid support, Holderich was able to acetylate mesitylene, anisole, and m-xylene with acetyl chloride in excellent yield. The performance of the iron-based ionic liquid was then compared with that of the corresponding chlorostannate(II) and chloroaluminate(III) ionic liquids. The results are given in Scheme 5.1-67 and Table 5.1-5. As can be seen, the iron catalyst gave superior results to the aluminium- or tin-based catalysts. The reactions were also carried out in the gas phase at between 200 and 300 °C. The acetylation reac-... 

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... 

Fig. 5.1. Zeroth-order rates of nitration with acetyl nitrate compared with those for other systems, (a) HNOa/ sulpholan, (i) HNO3/CCI4, (c) AcONOj/AcjO/O % AcOH, (d) AcONOj/AcaO/O % AcOH/[mesitylene] = o-8 mol l-i,n (e) AcONOj/AcaO/ [AcOH] = 2-2moll-i,ii >(/)AcONOa/AcaO/[AcOH] = 1-96 mol l-i and (g) AcONOa/ AcaO/[AcOH] 3 9i mol l-i/[mesitylene] = o-8 mol 1-i H.

Nitrations of the zeroth order are maintained with much greater difficulty in solutions of acetyl nitrate in acetic anhydride than in solutions of nitric acid in inert organic solvents, as has already been mentioned. Thus, in the former solutions, the rates of nitration of mesi-tylene deviated towards a dependence on the first power of its concentration when this was < c. o-05-o-i mol 1 , whereas in nitration with nitric acid in sulpholan, zeroth-order kinetics could be observed in solutions containing as little as 10 mol 1 of mesitylene ( 3.2.1). 

Acetoxylation and nitration. It has already been mentioned that 0- and m-xylene are acetoxylated as well as nitrated by solutions of acetyl nitrate in acetic anhydride. This occurs with some other homologues of benzene, and with methyl phenethyl ether,ii but not with anisole, mesitylene or naphthalene. Results are given in table 5.4. 

Table 5.1-5 The acylation of aromatics in batch reactions at 100 °C, for 1 hour. Ratio of aromatic compound to acetylating agent = 5 1, mes. = mesitylene.

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... 

Dr. Mawby In w-hexane, the reaction of CHsMn(CO)5 with cyclohexylamine was first-order in both reactants, suggesting that a concerted mechanism, involving simultaneous attack by the amine and rearrangement to form the acetyl group, is operating. In mesitylene, which has a slightly higher dielectric constant, we observed a more complicated state of affairs. Both mechanisms appeared to operate side by side, and we obtained rate constants for both the two-step and the concerted mechanisms. Certainly a nonpolar solvent appears to favor the concerted mechanism. 

Competition experiments with benzocyclic aromatics show that arsabenzene is considerably more reactive than benzene. Arsabenzene is acetylated at approximately the same rate as mesitylene, that is about 103 faster than benzene. Deuterium exchange takes place at a rate comparable to that of p-xylene, again about 103 faster than benzene. 

In the Sc(0Tf)3-LiC104-system, wider substrate scope was observed as is shown in Table 8. Each acylation reaction in the Table gave a single acylation product and formation of other isomers was not observed. Acetylation of anisole (1) resulted in excellent yield of the product (entry 1). Mesitylene (3) and xylenes were transformed to 2,4,6-trimethylacetophenone and dimethylacetophenones, respectively, in moderate yields (entries 2-5). It is noteworthy that toluene was acylated by the Sc(0Tf)3-LiC104 system to give 4-methylacetophenone in 48 % yield (entry 6) but the acylation did not proceed in the absence of LiC104. Furthermore, recovery and reuse of the RE(0Tf)3-LiC104 system were performed successfully. As shown in Table 9, the yields of 6 in the second and third uses of the catalyst system were almost the same as that in the first use. 

Derivatives of durene and mesitylene— In Chapter 9 it was pointed out that in derivatives of durene and mesitylene stcric factors due to the methyl groups may hinder the resonance of the substituent group with the ring system. In Tables Cl and C//the dipole moments of these compounds are compared with the corresponding aromatic and aliphatic derivatives. The dipole moments of the acetyl derivatives of durene and mesitylene are very similar to the value for acetone but lower than that for acetophenone, where resonance with the ring occurs. In aldehydes, on the other hand, where apparently there is no steric hindrance, the moment is almost identical with that of benzaldehyde. 

Catalytic acylation of electron-rich aromatics is achieved with a combination of InCls and silver perchlorate (Scheme 8.114) [157]. Acetic anhydride, acetyl chloride and isopropenyl acetate serve as satisfactory acyl donors. By using an InCl3-impreg-nated Si-MCM-41 catalyst at low concentration, acylation of aromatic compounds (benzene, toluene, p-xylene, mesitylene, anisole, naphthalene, methylnaphfhalene, and methoxynaphfhalene) by acyl chlorides (benzoyl chloride, phenylacetyl chloride, propionyl chloride, or butyryl chloride) can be accomplished rapidly (3 h) at 80 °C in high yield, even in the presence of moisture in the aromatic substrate or solvent (dichloroethane) (Scheme 8.115) [158], In(OTf) j is an efficient catalyst in the sulfonylation of both activated and deactivated aromatic compounds (Scheme 8.116) [159]. 

Figure 7. Ratios of the amount of catalyst (AICI3 or acid-treated clays) to the amount of acetyl chloride or acetic anhydride in the acylation of mesitylene (for the latter catalyst the same value was obtained with both acylating reagents) [62].

Figure 11. Catalytic activity as a function of the nature of the pillaring element for some pillared montmorillonites in the acylation of mesitylene with acetyl chloride (reaction temperature = 473 K reaetion time = 15 min AZA and FAZA supported by Concerted European Action-Pillared Layered Structures (CEA-PLS) EXM-534 and EXM-551 provided by Slid Chemie) [62].

PILC have also been investigated in the acylation of mesitylene with acetyl chloride [62], showing in comparison with the starting clays (i) higher activities related to the presence of additional Lewis acid sites in the pillars... 

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