Benzene molecule reactions

This is a nifty little way to turn catechol or guaiacol into protocate-chualdehyde or vanillin using what is called the Riemer-Tiemann reaction [137 p824, 138], It is a really ancient reaction and only works on benzene molecules that have an OH group. One needs to use KOH instead of NaOH because it is better at promoting para substitutions (don t ask). And if one is going to make vanillin from guaiacol then there needs to be a little ethanol in the reaction as well. 

The most intriguing hydrocarbon of this molecular formula is named buUvalene, which is found in the mixture of products of the reaction given above. G. SchrOder (1963, 1964, 1967) synthesized it by a thermal dimerization presumably via diradicais of cyciooctatetraene and the photolytical cleavage of a benzene molecule from this dimer. The carbon-carbon bonds of buUvalene fluctuate extremely fast by thermal Cope rearrangements. 101/3 = 1,209,6(X) different combinations of the carbon atoms are possible. 

It should be noted, however, that this reaction sequence may be different from what may actually be occurring in the reactor. The reactions proceed at different rates depending on the process variables. Hydrodesulfurization of complex sulfur compounds such as dibenzothiophene also occurs under these conditions. The desulfurized product may crack to give two benzene molecules ... 

It is interesting to mention here that Dewar and Storch (1989) drew attention to the fact that ion-molecule reactions often lack a transition state barrier in theoretical calculations related to the gas phase, but are known to proceed with measurable activation energy in solution. Szabo et al. (1992) made separate calculations at the ab initio Hartree-Fock 3/21 G level for the geometry of the nitration of benzene with the protonated methyl nitrate by two mechanisms, not involving solvent molecules. Both calculations yielded values for the energy barriers. 

The catalytic system used in the Pacol process is either platinum or platinum/ rhenium-doped aluminum oxide which is partially poisoned with tin or sulfur and alkalinized with an alkali base. The latter modification of the catalyst system hinders the formation of large quantities of diolefins and aromatics. The activities of the UOP in the area of catalyst development led to the documentation of 29 patents between 1970 and 1987 (Table 6). Contact DeH-5, used between 1970 and 1982, already produced good results. The reaction product consisted of about 90% /z-monoolefins. On account of the not inconsiderable content of byproducts (4% diolefins and 3% aromatics) and the relatively short lifetime, the economics of the contact had to be improved. Each diolefin molecule binds in the alkylation two benzene molecules to form di-phenylalkanes or rearranges with the benzene to indane and tetralin derivatives the aromatics, formed during the dehydrogenation, also rearrange to form undesirable byproducts. 

Reaction with a benzene molecule produces acetophenone and HCl and regenerates the AICI3 catalyst. 

Unlike the alkanes, however, the reaction of benzene with the halogens is catalyzed by iron. The relative lack of reactivity in aromatic hydrocarbons is attributed to delocalized double bonds. That is, the second pair of electrons in each of the three possible carbon-to-carbon double bonds is shared by all six carbon atoms rather than by any two specific carbon atoms. Two ways of writing structural formulas which indicate this type of bonding in the benzene molecules are as follows ... 

The negative AS was explained in terms of the solvation of the transition state by the reaction medium. Dimerisation reduces the polar nature of acetic acid. Hence, in 1% acetic acid the polar transition state is thought to freeze the benzene molecules, thus producing a negative AS (—5.8 e.u./mol). When the acetic acid concentration is increased, the monomers of acetic acid solvate the transition state preferentially and the... 

Dehydrogenation of substituted benzene molecules has also been observed, thus Sc+ and Ti+ react with toluene (129) to form adduct ions involving loss of a hydrogen molecule, [MC7H6]+. Simple addition occurs in the reaction of V+ with toluene, [VC7H ]+, similar to the reaction of V+ with benzene. The reactions of many of the lanthanide ions, Sc+ and Y+, with 1,3,5-tri-terf-butylbenzene produce ions showing that dehydrogenation has occurred (130). 

In contrast to the addition of only one benzene molecule to even large niobium cluster anions, small niobium cluster anions react by the addition of up to 5 N2 molecules and up to 15 CO molecules (229). The reactions of the niobium cluster anions Nb (n = 2-7) were qualitatively similar to the reactions of the cluster cations and in both cases CO was more reactive than N2. The rates of reaction generally increased with increasing size of the cluster but in many cases extensive fragmentation of the clusters was observed. 

We are being somewhat disingenuous here. If performed and interpreted correctly and with the appropriate ancillary phase-change enthalpy information, the enthalpy of formation of an arbitrary species by ion-molecule reaction chemistry and by combustion calorimetry must be the same. That the ionization potential of quinuclidine is higher than l,4-diazabicyclo[2.2.2]octane simply says that there is a stabilizing effect in the radical cation of the latter not found in the former. This information does not say that there is a stabilizing effect in the neutral molecular form of the latter not found in the former. After all, we trust the reader is not bothered by the fact that the ionization potential order of the cyclohexenes increases in the order 1,3-diene < 1,4-diene < 1-ene < 1,3,5-triene (benzene). 

Many other ion-molecule reactions involving highly unsaturated hydrocarbon ions and neutral olefins or the equivalent strained cycloalkanes have been studied by mass spectrometry98. For example, we may mention here the addition of ionized cyclopropane and cyclobutane to benzene radical cations giving the respective n-alkylbenzene ions but also isomeric cyclodiene ions such as ionized 8,9-dihydroindane and 9,10-dihydrotetralin, respectively. Extensive studies have been performed on the dimerization product of charged and neutral styrene4. 

The associative mechanism resembles a conventional radical (hydrogen atom) substitution reaction where the 7T-bonded benzene molecule is attacked by a hydrogen atom formed by the dissociative adsorption of water or hydrogen gas. The activation energy in this process is essentially due to the partial localization of one tt electron in the transition complex 21, 31). The transition state differs, however, from conventional substitution reactions by being 77-bonded to the catalyst surface ... 

The postulated transition state of the tt—a bond conversion occurs when the plane of the rotating benzene molecule is approximately at 45° to the catalyst surface. The electronic hybridization changes involved in this process (Fig. 4) are similar to those proposed by Melander 22) for homogeneous substitution reactions and show how resonance interactions may achieve a lowering in the activation energy. This aspect has previously been discussed in terms of the Lennard-Jones theory where the activation energy is lowered more effectively by resonance effects... 

Benzene and hydrogen in excess of whats needed are fed cold into the pressurized, catalyst-filled reactor. The hydrogenation reaction that takes place, attaching six hydrogen atoms each to the benzene molecules, is exothermic. 

The Friedel-Crafts reaction has one major drawback. It doesn t stop at the mono-substitution stage. That is, the catalyst works so well, that the benzene will pick up two, three, or more ethylene molecules, forming diethylbenzene, triethylbenzene, or higher polyethylbenzenes. See Figure 8 2.) The problem is that chemically its easier to alkylate EB than it is benzene. One way to control the problem is to carry out the reaction in the presence of a large excess of benzene. When an ethylene molecule is in the neighborhood of one..EB molecule and 20 benzene molecules, chances are that the ethylene will hook up with benzene, even though it prefers EB. 

When hydrogen atoms are added to the benzene molecule (hydrogenation), the chemical reaction gives offbeat (exothermic). 

Hanmura, T. Ichihashi, M. Kondow, T. Reaction of Benzene Molecule on Size-Selected Nickel Cluster Ions. J. Phys. Chem. A 2002, 106, 4525-4528. 

The growth of such structures is possible only from a gas phase and probably occurs as a result of dehydropolymerisation (polycondensation) [4,11 ]. Under more harsh reaction conditions multi-walled nanotubes grow as a loop on ceramic reactor walls (Fig. 3.4). We suggest that the benzene molecule could be the main fragment in the graphene network formation. At temperatures >600°C benzene rapidly undergoes dehydrogenation followed by diphenyl formation that can be considered... 

The dependence of IjG of the formation of products 56 and 19, plotted against the reciprocal concentration of 55, are differently curved, i.e., the ratio of the yields of 56 and 19 changes with the concentration of 55. This points out that at least two different excited states of the donor (benzene) are transferred, differing in k /k, values (km — rate constant of energy transfer from an excited benzene molecule to 55, kq = over-all constant of deactivation of excited benzene molecule by other pathways) which influence the reactions of the acceptor 55 in different ways. 

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