Chlorobenzene solvent

Ranganathan, S. et al., Tetrahedron Lett., 1985, 26, 4955-4956 Although a stable crystalline compound (m.p. 217-221°C), its oxidation potential approximates to that of ozone, and it should only be used in a suitably inert solvent (chlorobenzene or nitrobenzene). 

The same authors also studied recently the preparation of substituted vinyl -lactams 14, with efficient stereocontrol [11], by use of limited amounts of solvent (chlorobenzene) (Scheme 8.7). Microwave oven-induced reaction enhancement (MORE) chemistry techniques have been used to reduce pollution at the source and to increase atom economy. 

A11 reactions were carried out under N2, using anhydrous conditions, with 5% nucleophile. Mole % relative to substrate. Isolated Yields. Toluene solvent. Chlorobenzene solvent. o-Dichlorobenzene solvent. 

A common and effective direct approach to unsubstituted or multiply substituted oxazolines is the Lewis acid catalyzed reaction of nitriles with amino alcohols in an alcoholic or aromatic solvent (chlorobenzene) at reflux. The most common Lewis acids employed include ZnCl2, ZnBr2, NiBr2, CuCl2, and kaolinitic clay. Microwave irradiation has also been reported to facilitate the transformation. Alternatively, the condensation can be carried out in the presence of catalytic amounts of potassium carbonate. The method works well for both aliphatic and aromatic nitriles, with retention of stereochemistry. Some representative examples from the recent literature are listed in Table 8.16 (Scheme 3 40),2 35.2oi-2i3... 

As far as equilibrium constant is concerned, differences between metal ions are perhaps more important than those between ligands. Thus, in the solvent chlorobenzene (41), the equilibrium constant [Eq. (7)] for MC12 and pyridine favors the octahedral configuration for Ni(Il) over that for Co(II) y a factor of 1500 to 2000. In the same solvent, there is no clear evidence that any octahedral zinc compound is formed. The Ni-Co difference cited is actually less than the difference between chloride and thiocyanate against... 

Gielen and Nasielski43 suggested that reaction (37) proceeded through a cyclic transition state of the SE2(cyclic) type, for which we may write (X) as a possible structure. In view of later work35 on the related brominolysis of tetraalkyltins in solvent chlorobenzene, it would seem possible that reaction (37) might proceed by mechanism SE2(co-ord) (cf reactions (41) and (42), p. 158). 

SECOND-ORDER RATE COEFFICIENTS (l.mole-. SeC ) FOR THE BROMINOLYSIS OF TETRAALKYLTINS BY BROMINE IN SOLVENT CHLOROBENZENE AT 20 °C 3... 

RELATIVE VALUES OF kt (REACTIONS (42) AND (44)) FOR THE TRANSFER OF ALKYL GROUPS FROM TIN TO BROMINE IN SOLVENT CHLOROBENZENE AT 20 °C... 

The order is moderated in the slightly polar solvent chlorobenzene by a counteracting sequence in the order... 

Again, a moderating effect in the slightly polar solvent chlorobenzene takes place in the sense... 

It is clear that these bromodemetallations, proceeding by the SE mechanism in the non-polar solvent chlorobenzene, are extremely complex and that a variety of transition states (e.g. (XII), (XIII), and (XV)) are possible. The main function of the more complicated transition states seems to be that of providing a route for bromodemetallation such that collapse of the transition state yields uncharged molecules and not ionic species. In addition, the transition states also serve to distribute any charge separation over a molecular aggregate. 

Table 24. Faleschini and Tagliavini36 stated that for all of the unsymmetrical tetraalkyls they studied, only the smaller alkyl group in each tetraalkyl was split off as RBr. Such selectivity is rather unexpected in view of the poor selectivity observed for brominolysis in solvent chlorobenzene. Indeed, Gielen and coworkers37 have shown that in the brominolysis of EtSnBu"3 in carbon tetrachloride at 35 °C, both the ethyl and the n-butyl groups are split off as alkyl bromides, with a ratio EtBr/Bu"Br of 0.43. Similarly, the ratio Pr"Br/BunBr was 1.3 in brominolysis of Pr"SnBu"3. In view of this work, the rate coefficients recorded by Faleschini and Tagliavini are valid only as overall rate coefficients and (until further work is done) cannot be used as rate coefficients for the cleavage of particular alkyl-tin bonds. Only for the two sets of compounds examined by Gielen and co-workers37 can the rate coefficient data be used to deduce these alkyl-tin rate coefficients, and values calculated by the author are given in Table 24.

It is noticeable that the substitution of tetraalkyltins by bromine in solvent chlorobenzene (No. 31, Table 7) follows a much more steric sequence than does the substitution of the same series of substrates by bromine in solvent carbon tetrachloride (No. 36, Table 7) or by chromium trioxide in solvent acetic acid (No. 37, Table 7), and on this basis it could be suggested that the substitutions in series No. 31 (Table 7) follow mechanism SE2(cyclic) rather than mechanism SE2(co-ord). 

Waste generated in the laboratory can often be characterized from knowledge of the starting materials (e.g., hydrocarbon mixture, flammable laboratory solvents, chlorobenzene still bottoms). Professional expertise, common sense, judgment, and safety awareness of trained professionals performing chemical operations in the laboratory usually put them in a position to judge the type and degree of chemical hazard. 

Solvent, chlorobenzene (C4H7NiCl)2, 3 mmoles/liter butadiene, 2.5M. 

Conditions toluene (3.0mL) Ln (lOpmol) [Ph3C][B(C6F5)4] (lOpmol) TIBA (lOOpmol) Hexane as solvent Chlorobenzene as solvent... 

Figure 3. Residual solvent (chlorobenzene) in 1 yarn P(MMA) film on silicon wafer vs. prebaking time B - 85°c.,...

Benzofuran (99.5%) and the solvent chlorobenzene (99%) were purchased from Aldrich. Acetic anhydride (99%) was purchased from Janssen. 

A standard procedure was defined in which the solvent (chlorobenzene) was added to the zeolite followed by the acylating agent (acetic anhydride). Stirring was turned on, and the mixture was heated to the reaction temperature (60 C) for 15 min before starting the addition of the substrate (benzofuran). Typical quantities of the ingredients were the following zeolite, Ig chlorobenzene, 30 ml (295 mmol) acetic anhydride, 5.5 ml (58 mmol) benzofuran, 0.5 to 5.4 ml (4.7 to 50 mmol). Samples of 0.3 ml were withdrawn and analyzed by gas chromatography... 

Materials. The reagents Mo(CO)e, W(CO)6, iodine, tetrapropyl-ammonium bromide, tetrabutylammonium iodide, propionic acid, benzoic acid, pivalic acid, and 1,2-dibromoethane were obtained from commercial sources and used without purification. The solvents chlorobenzene, 1,2-dichloroethane, o-dichlorobenzene, toluene, decahydronaph-thalene (decalin), and cyclohexane were purged 10-30 min with a stream of dry nitrogen prior to use. Acetonitrile was dried over molecular sieves (4A) and also purged with nitrogen prior to use. Benzene used in the preparation of MoW(02CC( 113)3)41 was carefully dried and stored over calcium hydride, then vacuum distilled into the reaction vessel when needed. 

A different source of arenesulphenyl cations has been reported by Montevecchi and coworkers . They showed that the BFs-promoted reaction of 4 -nitrobenzenesulphena-nilide (35) with aryl-substituted alkynes in poorly nucleophilic solvents such as chlorobenzene generally led to bissulphides (36) and sulphimides (37) in addition to diphenyl disulphide and 4-nitroaniline. In acetonitrile as solvent, products of capture of the thiirenium ion by the solvent were also observed (equation 22). The thiirenium ion from phenylacetylene reacted even with the poorly nucleophilic solvent chlorobenzene to ( )-PhSCH=CPhC6H4Cl. With alkyl-substituted alkynes in chlorobenzene as solvent, a small amount of ( )-2-fluorovinyl sulphide PhSC(R )=CF(R ) was also detected. The yield of this sulphide could be increased when the reaction was performed in the presence of tetrabutylammonium tetrafluoroborate. Terminal alkynes gave the corresponding 2-fluorovinyl sulphides in 35-55% and internal alkynes in 65-87% yield. The procedure was unsuccessful for di-tcrt-butylacetylene and gave low yields for arylacetylenes. In acetic acid as solvent the thiirenium ion was captured as ( )-PhSC(R )=CR (OAc). 

Fig. 2.5 Conversion of pent-2-ene (0.5 M) into metathesis products at 40°C for different pre-irradiation times (t,) in the system W(CO)5 (0.5 x 10 MyiiCU (0.5 x 10 m) solvent chlorobenzene (Vanwijnsberghe 1987).

Solvent chlorobenzene at 25°C except where indicated, initial values. 0°C. In octane. Corrected for 4% trans isomer in the initial pent-2-ene.- Pre-irradiated. In benzene. Also see Quignard 1985a, 1986. 

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