Toluene Reaction Rate

The rate expression for toluene is determined in a similar manner as that for benzene. The concentration of toluene in the system is a function of two competing reactions one where toluene is a product, and the other where toluene is a reactant. A one-to-one molar relation exists between the consumption of benzene and the production of toluene in reaction 1, and in general, the reaction rates for all species that participate in reaction 1 may be determined simply by stoichiometry, where the rate of formation for toluene must be equal to the rate of reaction for benzene by mass balance.  

Ethylene may also combine with toluene by reaction 2. An additional half mole of ethylene may be reacted with toluene to form xylene. The form of this expression is specified as follows  

Similar to that of benzene, the overall rate of reaction for toluene is found by the summation of the individual reaction rate contributions as follows  

This expression is the negative complement of the benzene reaction rate for reaction 1. 

If a rate of reaction is known for a particular component in a reaction, then the rates of reaction for all other species present in the reaction are also known by stoichiometry. If this were not the case, then the rate of a particular species would outbalance the rate of another and violate the conservation of mass in the reactor. Consider the following hypothetical reaction  

---

There are several kinetic and product studies on Cl atom gas phase reactions of hydrocarbons [16-42], Though the various kinetic studies show more consistency on Cl-I-toluene reaction rates [41], the reactions of Cl- -benzene has been shown to be quite contradictory. Indeed, six existing published studies on the Cl -l- benzene reaction rates vary by more than 5 orders of magnitudes, ranging from 1.3 x 10 to 1.5 X 10 cmV(molecules) [16,17,19,24,27,42],... 

The final product ArCH ONO is formed in further oxidation of ArCH/ to ArCH/ by CAN and the subsequent reaction with NOj . For toluene derivatives with electron-donating substituents such as the methoxy group, the electron transfer reaction (Equation 4.73) was confirmed by the laser flash photolysis method [44]. For toluene, there is a probability for direct H-atom abstraction (Equation 4.72) with a highly polar transition state. Furthermore, for toluene derivatives with electron-withdrawing substituents, the addition ability of NO3 to phenyl 7t-bonds can be considered on the basis of data for reactions with phenols [41] and furan [45]. To clarify the interchanges in the reaction paths by the substituent in toluene, reaction rate constants for various toluene derivatives were evaluated by flash photolysis [44]. The substituent effect of the rate constants for toluene derivatives was correlated with ionisation energies (lEs) of these substances. The reaction rate for anisole is too fast to obtain accurate rate constants, and only lower limits of the rate constants are obtained (anisole) >310 M -s h For p-nitrotoluene, the rate constant is 2.3T0 M -s IE = 9.5 eV. A deuterium kinetic isotope effect of 1.6 was observed for the reaction of NO3 with toluene and toluene - dg. This indicates that NO3 predominantly abstracts the H atom from methyl groups. In the case of p-xylene, the deuterium isotope effect was not observed [43]. The rate constant forp-xylene (> 2 x 10 M/s) is close to the diffusion-controlled limit in acetonitrile, and consequently selectivity becomes low. 

The reaction rate is increased by using an entraining agent such as hexane, benzene, toluene, or cyclohexane, depending on the reactant alcohol, to remove the water formed. The concentration of water in the reaction medium can be measured, either by means of the Kad-Eischer reagent, or automatically by specific conductance and used as a control of the rate. The specific electrical conductance of acetic acid containing small amounts of water is given in Table 6. 

The PMBs, when treated with electrophilic reagents, show much higher reaction rates than the five lower molecular weight homologues (benzene, toluene, (9-, m- and -xylene), because the benzene nucleus is highly activated by the attached methyl groups (Table 2). The PMBs have reaction rates for electrophilic substitution ranging from 7.6 times faster (sulfonylation of durene) to ca 607,000 times faster (nuclear chlorination of durene) than benzene. With rare exception, the PMBs react faster than toluene and the three isomeric dimethylbenzenes (xylenes). 

Noncatalytic ring chlorination of toluene in a variety of solvents has been reported. Isomer distributions vary from approximately 60% ortho in hydroxyhc solvents, eg, acetic acid, to 60% para in solvents, eg, nitromethane, acetonittile, and ethylene dichloride (49,50). Reaction rates are relatively slow and these systems are particularly appropriate for kinetic studies. 

In contrast to the hydrolysis of prochiral esters performed in aqueous solutions, the enzymatic acylation of prochiral diols is usually carried out in an inert organic solvent such as hexane, ether, toluene, or ethyl acetate. In order to increase the reaction rate and the degree of conversion, activated esters such as vinyl carboxylates are often used as acylating agents. The vinyl alcohol formed as a result of transesterification tautomerizes to acetaldehyde, making the reaction practically irreversible. The presence of a bulky substituent in the 2-position helps the enzyme to discriminate between enantiotopic faces as a result the enzymatic acylation of prochiral 2-benzoxy-l,3-propanediol (34) proceeds with excellent selectivity (ee > 96%) (49). In the case of the 2-methyl substituted diol (33) the selectivity is only moderate (50). 

The reaction rates of toluene and benzene with i-propyl chloride in nitromethane fit a third-order rate law ... 

The kinetics and activation parameter of the alkylation reaction of PS and toluene as a model compound with EC in the presence of BF3-0(C2H5)2 catalysis are given in Table 2. The initial rate and reaction rate constant was increased with increasing temperature as... 

Kinetic studies at 25 °C showed that for benzene, toluene, o-, m-, and p-xylene, /-butylbenzene, mesitylene, 4-chloroanisole, and p-anisic acid in 51 and 75 % aqueous acetic acid addition of small amounts of perchloric acid had only a slight effect on the reaction rate which followed equation (100). At higher concentrations of perchloric acid (up to 0.4 M) the rate rose linearly with acid concentration, and more rapidly thereafter so that the kinetic form in high acid concentration was... 

In the absence of added mineral acid, the effective chlorinating species was concluded to be chlorine acetate. Like the catalysed chlorination, the rate of chlorination (of toluene) falls rapidly on changing the solvent from anhydrous to 98 % aqueous acetic acid, passes through a shallow minimum and thence to a maximum in 50 % aqueous acid this was thus attributed to a combination of the decrease in concentration of chlorine acetate as water is added and a solvent effect. By correcting for the change in concentration of chlorine acetate in the different media it was shown that the reaction rate increases as the water content of the media increases. 

The lower reaction rates obtained with this catalyst permitted measurements of the reaction rates of benzene and toluene with a range of alkyl halides including /-propyl and /-butyl bromides, the rate being followed in some cases by the... 

Finally, rates of mercuration have been measured using mercuric trifluoro-acetate in trifluoroacetic acid at 25 °C450. The kinetics were pure second-order, with no reaction of the salt with the solvent and no isomerisation of the reaction products rate coefficients (10 k2) are as follows benzene, 2.85 toluene, 28.2 ethylbenzene, 24.4 i-propylbenzene, 21.1 t-butylbenzene, 17.2 fluorobenzene, 0.818 chlorobenzene, 0.134 bromobenzene, 0.113. The results follow the pattern noted above in that the reaction rates are much higher (e.g. for benzene, 690,000 times faster than for mercuration with mercuric acetate in acetic acid) yet the p factor is larger (-5.7) if the pattern is followed fully, one could expect a larger... 

The importance of the inductive effect in controlling the reaction rates was further shown by Streitweiser and Humphrey596, who measured the rates of dedeuteration of toluene (a, a-d2), (a, 2,4,6-g 4), and (a, 2,3,4,5,6-g 6) by lithium cyclohexylamide at 50 °C and found the rate to be reduced by 0.4 %, 0.4 %, and 1.8 % for a deuterium atom in the ortho, meta and para positions respectively. The retardation is consistent with the +1 effect of deuterium but the differential positional effect could not be rationalised in simple and general terms. 

Rate constants and thermodynamic activation parameters. The rate constant for the reaction between C2H4 and HCN catalyzed by a nickel(0) complex was studied over a range of -50 to -10 °C in toluene.31 These authors give the activation parameters A//1 = 36.7kJmor andAS = -145 J mol-1 K I when the reaction rate was expressed using concentrations in the units molL-1 and time in the unit seconds. 

Absorption rates of carbon dioxide were measured in organic solutions of glycidyl methacrylate at 101.3 kPa to obtain the reaction kinetics between carbon dioxide and glycidyl methacrylate using tricaprylylmethylammonium chloride(Aliquat 336) as catalysts. The reaction rate constants were estimated by the mass transfer mechanism accompanied by the pseudo-first-order fast reaction. An empirical correlation between the reaction rate constants and the solubility parameters of solvents, such as toluene, A-methyl-2-pirrolidinone, and dimethyl sulfoxide was presented. 

In this study, the absorption rates of carbon dioxide into the solution of GMA and Aliquat 336 in such organic solvents as toluene, N-methyl-2-pirrolidinone(NMP), and dimethyl sulfoxide(DMSO) was measured to determine the pseudo-first-order reaction constant, which was used to obtain the elementary reaction rate constants. 

The rate constants in organic reaction in a solvent generally reflect the solvent effect. Various empirical measures of the solvent effect have been proposed and correlated with the reaction rate constant [5]. Of these, some measures have a linear relation to the solubility parameter of the solvent. The logarithms of kj and k2/ki were plotted against the solubility parameter of toluene, NMP and DMSO[6] in Fig. 2. As shown in Fig.2, the plots satisfied the linear relationship. The solvent polarity is increased by the increase of solubility parameter of the solvent. It may be assumed that increase of unstability and solvation of Ci due to the increase of solvent polarity make the dissociation reaction of Ci and the reaction between Ci and COisuch as SNi by solvation[7] easier, respectively, and then, k2/ki and ks increases as increasing the solubility parameter as shown in Fig. 2. 

Direct esr evidence for the intermediacy of radical-cations was obtained on flowing solutions of Co(III) acetate and a variety of substituted benzenes and polynuclear aromatics together in glacial acetic acid or trifluoroacetic acid solution . A p value of —2.4 was reported for a series of toluenes but addition of chloride ions, which greatly accelerated the reaction rate, resulted in p falling to —1.35. Only trace quantities of -CH2OAC adducts were obtained and benzyl acetate is the chief product from toluene, in conformity with the equation given above. 

For toluene, a less significant impact of temperature (exceeding 70 °C) on reaction rates was observed than for benzene [31]. 

OS 32] ]R 16a] ]P 23]Toluene nitration rates determined in the capillary-flow reactor were generally higher than benzene nitration rates [31, 97]. This is not surprising, as it stems from the higher reactivity of toluene towards electrophilic substitution owing to its more electron-rich aromatic core. For instance, at a reaction temperature of 60 °C, rates of 6 and 2 min were found for toluene and benzene nitration, respectively. However, care has to be taken when quantitatively comparing these results, since experimental details and tube diameters vary to a certain extent or are not even listed completely. 

OS 32] ]R 16a] ]P 23] On increasing the ratio of flows in favor of the acid content, the toluene nitration reaction rate decreases, especially at low temperature (25 °C ... 

Table 4.1 Influence of reaction temperature and acid-to-organic flow rate on the reaction rate of toluene nitration [31, 97].

The catalyst anion has also been shown to have a large influence on the reaction rate. The extraction constant of tetra-n-butylammonium salts between water and chloroform decreases with different anions as follows picrate CIO4 > T > toluene sulphonate > NO.-i > Br > benzoate > Cf > acetate > OH (Esikova, 1997 Dehmlow, 1993). 

Very significant acceleration in the rate of deprotonation of 2-methylcyclohexanone was observed when triethylamine was included in enolate-forming reactions in toluene. The rate enhancement is attributed to a TS containing LiHMDS dimer and triethylamine. Steric effects in the amine are crucial in selective stabilization of the TS and the extent of acceleration that is observed.18... 

The Rh(COD)(BoPhoz)/PTA/C (AHC-2) was prepared and used to promote the hydrogenation of DMIT. Data for 5,000 TON and 10,000 TON reactions are given in Table 3. In the first set of reactions, the four hydrogenations had identical rates (TOF hr"1). With the 10,000 TON reactions the first three runs had the same reaction rate while the fourth and fifth showed about a 20% decrease, probably because the catalyst was exposed to hydrogen too long after mn number three was completed. These reactions were all run using 3% toluene in methanol. The toluene was used as a co-solvent in these reactions in order to... 

Enantioselective hydrogenation of 2,3-butanedione and 3,4-hexanedione has been studied over cinchonidine - Pt/Al203 catalyst system in the presence or absence of achiral tertiary amines (quinuclidine, DABCO) using solvents such as toluene and ethanol. Kinetic results confirmed that (i) added achiral tertiary amines increase both the reaction rate and the enantioselectivity, (ii) both substrates have a strong poisoning effect, (iii) an accurate purification of the substrates is needed to get adequate kinetic data. The observed poisoning effect is attributed to the oligomers formed from diketones. 

Pt/Al2C>3-cinchona alkaloid catalyst system is widely used for enantioselective hydrogenation of different prochiral substrates, such as a-ketoesters [1-2], a,p-diketones, etc. [3-5], It has been shown that in the enantioselective hydrogenation of ethyl pyruvate (Etpy) under certain reaction conditions (low cinchonidine concentration, using toluene as a solvent) achiral tertiary amines (ATAs triethylamine, quinuclidine (Q) and DABCO) as additives increase not only the reaction rate, but the enantioselectivity [6], This observation has been explained by a virtual increase of chiral modifier concentration as a result of the shift in cinchonidine monomer - dimer equilibrium by ATAs [7],... 

The direct chemical evidence clearly indicates that either (26) or (27) can be involved depending on the circumstances. Thus in the benzoylation of toluene, the same mixture of products (1 % m-, 9% o-and 90% p-) is obtained no matter what the Lewis acid catalyst is, and with either benzoyl chloride or benzoyl bromide, though the reaction rates do of course differ this suggests a common attacking... 

---