Benzene equilibrium constants

Chlorination is carried out m a manner similar to brommation and provides a ready route to chlorobenzene and related aryl chlorides Fluormation and lodmation of benzene and other arenes are rarely performed Fluorine is so reactive that its reaction with ben zene is difficult to control lodmation is very slow and has an unfavorable equilibrium constant Syntheses of aryl fluorides and aryl iodides are normally carried out by way of functional group transformations of arylammes these reactions will be described m Chapter 22... 

Unionized mercuric acetate is also a mercurating species, for the second-order rate coefficient for mercuration of benzene by mercuric acetate in acetic acid at 25 °C is 0.41 x 10"7. If mercuration took place via ionized acetate ion pairs HgOAc+OAc" for which AT, the equilibrium constant can be estimated at 2 x 10"8, then since the rate of mercuration by this ion pair will be approximately the same as by the acetoxymercury perchlorate ion pair for which k2 the second-order rate coefficient has been determined (above) as 0.37x10"3 at 25 °C, the observed second-order rate should be 2 x 10"8 x0.37 x 10"3 = 0.74xl0-11. This is so different from the rate actually observed that mercuration by the ion pair can be eliminated which leaves ionized mercurcy acetate as the only possible mercurating species439. 

The lack of a substrate isotope effect suggests very extensive internal return and is readily explained in terms of the fact that conversion of the hydrocarbon to the anion would require very little structural reorganisation. Since koba = k 1k 2/(kLl+k 2) and k 2 is deduced as > k2, then kobs = Kk 2, the product of the equilibrium constant and the rate of diffusion away of a solvent molecule, neither of the steps having an appreciable isotope effect. If the diffusion rates are the same for reactions of each compound then the derived logarithms of partial rate factors (above) become pAT differences between benzene and fluorobenzene hydrogens in methanol. However, since the logarithms of the partial rate factors were similar to those obtained with lithium cyclohexylamide, a Bronsted cor-... 

The symbol k or K is the rate or equilibrium constant, respectively, for a side-chain reaction of a meta- or para-substituted benzene derivative, and k° or K° denotes the statistical quantity (intercept term) approximating to k or K for the parent or unsubstituted compound. The substituent constant a measures the polar (electronic) effect of replacing H by a given substituent (in the meta- or para-position) and is, in principle, independent of the nature of the reaction. The reaction constant p depends on the nature of... 

As both state variables are measured, the output vector is the same with the state vector, i.e., yi=x, and y2=x2. The feed to the reactor was pure benzene. The equilibrium constants K and K2 were determined from the run at the lowest space velocity to be 0.242 and 0.428, respectively. 

Here X denotes lb-moles of benzene per lb-mole of pure benzene feed and x, denotes lb-moles of diphenyl per lb-mole of pure benzene feed. The parameters k, and k2 are unknown reaction rate constants whereas K, and K2 are known equilibrium constants. The data consist of measurements of Xi and x2 in a flow reactor at eight values of the reciprocal space velocity t. The feed to the reactor was pure benzene. The experimental data are given in Table 6.2 (in Chapter 6). The governing ODEs can also be written as ... 

The Hammett equation is the best-known and most widely studied of the various linear free energy relations for correlating reaction rate and equilibrium constant data. It was first proposed to correlate the rate constants and equilibrium constants for the side chain reactions of para and meta substituted benzene derivatives. Hammett (37-39) noted that for a large number of reactions of these compounds plots of log k (or log K) for one reaction versus log k (or log K) for a second reaction of the corresponding member of a series of such derivatives was reasonably linear. Figure 7.5 is a plot of this type involving the ionization constants for phenylacetic acid derivatives and for benzoic acid derivatives. The point labeled p-Cl has for its ordinate log Ka for p-chlorophenylacetic acid and for its abscissa log Ka for p-chloroben-zoic acid. The points approximate a straight line, which can be expressed as... 

Although anation and aquation rates of vitamin B12 are not affected appreciably by aqueous micelles, the solubilized water in reversed micelles, in contrast, influences the rate and equilibrium constants for the formation and decomposition of glycine, imidazole, and sodium azide adducts of vitamin Bl2 (Fendler et al., 1974). A vitamin B12 molecule is conceivably shielded from the apolar solvent (benzene) by some 300 surfactant molecules. 

One of the oldest and most familiar quantitative relationships for relating the structure of substituted benzene derivatives to both equilibrium constants and rate constants is the "Hammett Equation." See Louis Hammett, Physical Organic Chemistry, 184199. 

The major absorption in the 31P n.m.r. spectrum of an equimolar solution of penta-phenoxyphosphorane and sodium phenoxide in DMF-acetonitrile is due to the hexaphenoxyphosphate anion, as predicted from the low equilibrium constant estimated for equation (2) (page 35).27 Catechol and phosphorus oxychloride in refluxing benzene gave the spirophosphorane(108), which with triethylamine gave the salt (109).45 On the basis of its 31P chemical shift in DMF solution, (108) was formulated86 as the free six-co-ordinate acid (110), but it seems probable that DMF is... 

Table 9 gives the results of this calculation. In order to achieve a consistent formulation of the equilibrium we use the reciprocal of the dissociation constant given by Brown and Brady (1952) multiplied by ko- Since the measurements show that Henry s law is very well obeyed, the equilibrium mole fractions in Table 9 were given as above, computed with the aid of the Henry s law constants k and As may be seen from the equilibrium constants in the last column of the table, the stability of the complexes increases with the number of methyl groups in the benzene nucleus, which implies that the basicity of the aromatic substances also increases in the same sense. 

Ogimachi et al. (1955) also investigated in more detail the steric effect on the equilibrium constants of the complex formation of ICl with various benzene derivatives. The basicity decreases greatly on substitution of bulky groups, e.g. the t-butyl group. This effect is particularly pronounced for 1,3,5-tri-t-butylbenzene. 

Pertechnetate in neutral and alkaline media can be extracted into solutions of tetra-alkylammonium iodides in benzene or chloroform. With tetra-n-heptylammo-nium iodide (7.5 x 10 M) in benzene distribution coefficients up to 18 can be obtained . A solution of fV-benzoyl-iV-phenylhydroxylamine (10 M) in chloroform can be used to extract pertechnetate from perchloric acid solution with a distribution coefficient of more than 200, if the concentration of HCIO is higher than 6 M The distribution of TcO between solutions of trilauryl-ammonium nitrate in o-xylene and aqueous solutions of nitrate has been measured. In 1 M (H, Li) NOj and 0.015 M trilaurylammonium nitrate the overall equilibrium constant has been found to be log K = 2.20 at 25 °C. The experiments support an ion exchange reaction . Pertechnetate can also be extracted with rhodamine-B hydrochloride into organic solvents. The extraction coefficient of Tc (VII) between nitrobenzene containing 0.005 %of rhodamine-B hydrochloride and aqueous alcoholic " Tc solution containing 0.0025 % of the hydrochloride, amounts to more than 5x10 at pH 4.7 . 

The solution electron affinities of a series of monosubstituted benzenes were measured by the ESR method (Stevenson et al. 1991b). The equilibrium constant for the electron transfer in XCgHj + XCgDj = XCgHj + XCgDj, where X = H, tert-Bu, OMe, Ph, CN, was found to be less than unity for all cases (entries 1-6 in Table 2.1). These equilibrium constants are in linear correlation to the appropriate constants o of the substituents. 

Under similar conditions, cw-azobenzene could be oxidized to cw-azoxy-benzene. Evidently the only major precaution to be taken in this preparation is the exclusion of ultraviolet light (by carrying the reaction out in a dark room) [24]. Whether this precaution is truly required is open to some doubt since cis-azoxybenzenes were prepared more recently by oxidation while warming with a heating lamp [28]. The isomerization by ultraviolet light is probably an equilibrium process in which equilibrium constants have a pronounced dependence on the chemical constitution of the materials involved. Therefore variations in the observations of the stability of the products are not entirely surprising. 

Even if the addition of DMSO to protic solvents has a dramatic effect on the rate and equilibrium constants for adduct formation, to a first approximation it does not affect the relative stability of adducts formed from the same substrate. As already observed in the chemistry of Meisenheimer adducts in the benzene series, the ratios Kk/Kt, kf/kj, and k /k] are practically independent of the composition of the medium.46 Under such circumstances it is possible to obtain approximate kinetic or thermodynamic data for a given adduct in a particular medium whenever kinetic and... 

State, the charge density on oxygen is leduced and a reasonable charge density is now found on ortho- and meta-positions. Therefore, excited phenol is more acidic and is also ortho-meta-directing towards substitution fa benzene ring. The protolytic equilibrium constant pK for the reaction is 10.0 and 5.7 in the ground and excited states, respectively, a difference 6f 4.3 pK units. 

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