Solvent effect dinitrobenzenes

The kinetics of the reactions of 1-halo-2,4-dinitrobenzenes with aliphatic amines have been used to probe solvent effects in mixtures of chloroform or dichloromethane with polar hydrogen-bond acceptors, such as DMSO. In these reactions, nucleophilic attack is rate limiting. Attempts to correlate reactivity with the empirical solvent... 

During the last two decades, our group has smdied solvent effects on the process development in different molecular solvents (aprotic and protic, polar and non-polar) or in their binary mixtures, correlating the kinetic data of this reaction with empirical solvent parameters (E, n, a and 3) through Linear Free Energy Relationship s - LFER s - simple and multiparametric equations. The principal S Ar reactions studied comprise l-halo-2,4-dinitrobenzene or l-halo-2,6-dinitrobenzene as substrates and primary and secondary amines as nucleophiles. For the 1-fluoro-dinitrobenzenes derivatives, the reaction can exhibit base catalysis, which is normally solvent dependent. In general, solvent effects were related to reaction rates, mechanisms and catalysis. These studies were extented employing ILs as reaction media. 

Mancini PME, Fortunato G, Adam C, Terenzani A, Vottero LR (2002) Specific tmd nonspecific solvent effects on aromatic nucleophilic substitutions. Kinetics of the reaction of 1-fluoro-2,6-dinitrobenzene and homopiperidine in binary solvent mixtures. J Phys Oig Chem 15 258-269... 

Martinez RD, Mancini PME, Vottero LR, Nudelman NS (1986) Solvent effects on aromatic nucleophilic substitutions. Part 4. Kinetics of the reaction of l-chloro-2,4-dinitrobenzene with piperidine in protic solvents. J Chem Soc Perkin Trans 2 1133-1138... 

By far the most evidence for electrophilic sulphur is found in the sulphenyl halides (RSCl, RSBr) Although these compounds may in theory react either as sources of RS or X (X = halogen), none of the observed reactions of the sulphenyl halides indicate the latter mode of heterolysis. Kharasch et have presented good evidence for the existence of the 2,4-dinitrobenzene-sulphenium ion (Ar ) in strongly acidic media evidence has also been presented of a strong solvent effect upon the rate of reaction of 2,4-dinitroben-zenesulphenyl chloride and cyclohexene - and of a definite substituent effect in the reaction of this sulphenyl chloride with some substituted styrenes in acetic acid . Such observations are entirely consistent with an electrophilic heterolytic ad tion mechanism involving attack by the sulphenyl chloride in the sense iC -Cl. 

In acetonitrile the reaction is partially inhibited (A obs/ o = 0.74). When the substrate is electron acceptor it cannot be complexed by another acceptor. Therefore this latter is acting only by its polarity and polarizability (general solvent effect) catalyzing thereby the reaction. When the substrate is an electron donor it can form a complex with 1,3-dinitrobenzene. The charge-transfer is in a direction favorable to the reaction. However in more polar medium (acetonitrile) the complexation excludes from... 

Brand and co-workers (36) used aromatic nitro compounds as indicator bases to extend the scale far into the oleum region and obtained basicity values which, because of solvent effects, disagree slightly with earlier ones that he obtained. The validity of these results is supported by very careful ciyoscopic and conductometric measurements of Gillespie and Solomoi (138). The mono- and dinitrobenzenes and toluenes are useful Hammett indicators over the whole oleum range and the fact that 1,3,5,-trinitrobenzene shows no basic character towards HjSjOr (40,73), a medium of sufficient acidity to protonate sulfur and iodine, means that we still have this nitro compound in reserve for the exploration of more acidic media when they are available. 

Control of the regioselecdvity of VNS is important. It is governed by three major factors the stnicture of the nitroarene the nature of the nucleophile, and the reacdon condidons, especially solvent and base. The different effect of methoxy and hydroxy groups is interesdng the reacdon of Tmethoxy-2,4-dinitrobenzene vdth cbloromethyl phenyl sulfone proceeds in... 

The Kus can be estimated as follows an extrapolation of the Kus for the CT complex formed by any one donog such as mesitylene or hexamethylbenzene, with 1,3,5-trinitrobenzene and 1,4-dinitrobenzene to PhN02, and an extrapolation from solvent CC14 to one of DC > ca. 10 (Foster, 1969) shows that for our system Kus is very unlikely to be greater than 0.01 hmol"1. Therefore, with m = 1 mold"1, and [Sv] = 10 mold"1, [MSv] < 0.1 mold 1. This means that for styrene and other 7t-donors effectively all the monomer is free. For n-donor monomers such as the VE, however, the fraction of uncomplexed monomer may be somewhat smaller. Therefore it appears that the formation of CT complexes probably did not affect significantly at least the results for the three hydrocarbon monomers. 

When the decomposition of the zwitterionic intermediate is rate-determining, the effect of the solvent is crucial since it may produce changes in the mechanisms and in the rate-determining step. A recent study of the kinetics of the reactions of 1-chloro-, 1-fluoro- and l-phenoxy-2,4-dinitrobenzene with piperidine, n-butylamine and benzylamine in ethyl acetate and THF indicated that these reactions resemble those in dipolar aprotic solvents when primary amines are the nucleophiles (i.e. that shown in equation 1, with... 

A new assumption to be discussed in this section is that the fourth-order kinetics in SatAr by amines in aprotic solvents is due to the formation of the substrate-catalyst molecular complex. Since 1982, Forlani and coworkers149 have advocated a model in which the third order in amine is an effect of the substrate-nucleophile interaction on a rapidly established equilibrium preceding the substitution process, as is shown in Scheme 15 for the reaction of 4-fluoro-2,4-dinitrobenzene (FDNB) with aniline (An), where K measures the equilibrium constant for ... 

Addition of an alkali metal ion to 23 should also make this host molecule a better binder of aromatic guest molecules. In the aa conformation unlike the as conformation-the 7r-electron rich naphthalene walls are capable of sandwiching rc-electron poor molecules (see Fig. 12). Indeed, upon addition of a potassium salt to a solution of 23, the for binding of 1,3-dinitrobenzene increases by a factor of 2 to 6, depending on the solvent systems [26]. Consistent with the proposed structure of the complex of 23 with sodium ions, addition of these ions has no effect on the of 23 with 1,3-dinitrobenzene. 

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