Chlorobenzenes, accelerated solvent

Note It is reported that the use of chlorobenzene as solvent is essential when the reagent is to be used to detect aromatic amines [1]. In the case of steroids, penicillins, diuretics and alkaloids the reaction should be accelerated and intensified by spraying afterwards with dimethylsulfoxide (DMSO) or dimethylformamide (DMF), indeed this step makes it possible to detect some substances when this would not otherwise be possible [5,9-11] this latter treatment can, like heating, cause color changes [5,9]. Penicillins and diuretics only exhibit weak reactions if not treated afterwards with DMF [10, 11]. Steroids alone also yield colored derivatives with DMSO [9]. Tlreatment afterwards with diluted sulfuric acid (c = 2 mol/L) also leads to an improvement in detection sensitivity in the case of a range of alkaloids. In the case of pyrrolizidine alkaloids it is possible to use o-chloranil as an alternative detection reagent however, in this case it is recommended that the plate be treated afterwards with a solution of 2 g 4-(dimethyl-amino)-benzaldehyde and 2 ml boron trifluoride etherate in 100 ml anhydrous ethanol because otherwise the colors initially produced with o-chloranil rapidly fade [12]. 

Hubert et al. [101] state that accelerated solvent extraction compared to alternatives such as Soxhlet extraction, steam distillation, microwave extraction, ultrasonic extraction and, in some cases, supercritical fluid extraction is an exceptionally effective extraction technique. Hubert et al. [ 101 ] studied the effect of operating variables such as choice of solvent and temperature on the solvent extraction of a range of accelerated persistent organic pollutants in soil, including chlorobenzenes, HCH isomers, DDX, polychlorobiphenyl cogeners and polycyclic aromatic hydrocarbons. Temperatures ofbetween 20 and 180 °C were studied. The optimum extraction conditions use two extraction steps at 80 and 140 °C with static cycles (extraction time 35 minutes) using toluene as a solvent and at a pressure of 15 MPa. 

In polar solvents, this reaction is fast. For instance, at 333 K/ -methoxyphenol is oxidized by cumyl hydroperoxide in chlorobenzene and a mixture of chlorobenzene tert-butanol = 4 1 with kn = 3.5 x 10-6 and 2.5 x 10-4 Lmol-1 s 1, respectively [124]. The acceleration of this... 

In non-polar solvents such as benzene, toluene, chlorobenzene and diisopropyl ether (called solvent set B), a mild acceleration is observed, and the reactions are slower than in hexane. A molecular complex (see below) is proposed to explain the results for the reactions in solvent set B. 

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-... 

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