REACTIONS OF SIMPLE AROMATIC HYDROCARBONS

In short, while the overall features of OH-alkyne reactions are understood, more research needs to be done, especially on the alkynes larger than acetylene. 

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Hashimoto, S. and Akimoto, H. (1989). UV absorption spectra and photochemical reactions of simple aromatic hydrocarbons in the cryogenic oxygen matrix. J. Phys. 

The reactions of simple aromatic hydrocarbons with OH provide a classic example of how kinetics can be used to elucidate reaction mechanisms. Figure 6.10 shows a semilogarithmic plot of the decay of OH in the presence of a great excess of toluene from 298 to 424 K at 100 Torr total pressure in argon. While one would expect such plots to be linear (Chapter 5.B.1), this is only observed to be the case at temperatures below 325 K and above about 380 K at the intermediate temperatures, the plots are clearly curved. 

As seen in Table 6.1, the reactions of the nitrate radical with the simple aromatic hydrocarbons are generally too slow to be important in the tropospheric decay of the organic. However, one of the products of the aromatic reactions, the cresols, reacts quite rapidly with NO,. o-Cresol, for example, reacts with N03 with a room temperature rate constant of 1.4 X 10 " cm3 molecule-1 s-1, giving a lifetime for the cresol of only 1 min at 50 ppt N03. This rapid reaction is effectively an overall hydrogen abstraction from the pheno-... 

Deamination ofRNHI.t> A new method for reductive deamination of primary amines (1) involves conversion to an aromatic imidoyl chloride (2), which is converted to the hydrocarbon by Bu,SnH and AIBN (10, 412-413). Yields are satisfactory in the deamination of benzylamine, but are only moderate in the reaction of simple alkylamines. 

To conclude this chapter we will be occupied with an old, long-known reaction The Elbs reaction130, suited for a simple preparation of polycyclic aromatic hydrocarbons containing the anthracene moiety, by heating diarylketones with an ortho-placed methyl group at 400-450°. Our mechanistic proposal, applied to the cycliza-tion of the 2-naphthyl-(2 -methylnaphthyl-l )ketone (365) which yields the dibenzo-(a,h)anthracene (369) may involve an electrocyclic step followed by an elimination ... 

Nitrations are highly exothermic, ie, ca 126 kj/mol (30 kcal/mol). However, the heat of reaction varies with the hydrocarbon that is nitrated. The mechanism of a nitration depends on the reactants and the operating conditions. The reactions usually are either ionic or free-radical. Ionic nitrations are commonly used for aromatics many heterocycHcs hydroxyl compounds, eg, simple alcohols, glycols, glycerol, and cellulose and amines. Nitration of paraffins, cycloparaffins, and olefins frequentiy involves a free-radical reaction. Aromatic compounds and other hydrocarbons sometimes can be nitrated by free-radical reactions, but generally such reactions are less successful. 

Cesium forms simple alkyl and aryl compounds that are similar to those of the other alkah metals (6). They are colorless, sohd, amorphous, nonvolatile, and insoluble, except by decomposition, in most solvents except diethylzinc. As a result of exceptional reactivity, cesium aryls should be effective in alkylations wherever other alkaline alkyls or Grignard reagents have failed (see Grignard reactions). Cesium reacts with hydrocarbons in which the activity of a C—H link is increased by attachment to the carbon atom of doubly linked or aromatic radicals. A brown, sohd addition product is formed when cesium reacts with ethylene, and a very reactive dark red powder, triphenylmethylcesium [76-83-5] (C H )2CCs, is formed by the reaction of cesium amalgam and a solution of triphenylmethyl chloride in anhydrous ether. 

Although many of the aromatic compounds based on benzene have pleasant odors, they are usually toxic, and some are carcinogenic. Volatile aromatic hydrocarbons are highly flammable and burn with a luminous, sooty flame. The effects of molecular size (in simple arenes as well as in substituted aromatics) and of molecular symmetry (e.g., xylene isomers) are noticeable in physical properties [48, p. 212 49, p. 375 50, p. 41]. Since the hybrid bonds of benzene rings are as stable as the single bonds in alkanes, aromatic compounds can participate in chemical reactions without disrupting the ring structure. 

In complex organic molecules calculations of the geometry of excited states and hence predictions of chemiluminescent reactions are very difficult however, as is well known, in polycyclic aromatic hydrocarbons there are relatively small differences in the configurations of the ground state and the excited state. Moreover, the chemiluminescence produced by the reaction of aromatic hydrocarbon radical anions and radical cations is due to simple one-electron transfer reactions, especially in cases where both radical ions are derived from the same aromatic hydrocarbon, as in the reaction between 9.10-diphenyl anthracene radical cation and anion. More complex are radical ion chemiluminescence reactions involving radical ions of different parent compounds, such as the couple naphthalene radical anion/Wurster s blue (see Section VIII. B.). 

Similarly, trityl cation in aromatic hydrocarbons initiates the fragmentation of simple tetraalkyl plumbanes and stannanes yielding the plumbyl or stannyl cationic species, e.g. 11, and alkenes. The reaction is thought to proceed via plumbyl-or stannyl-substituted carbocations 12, which in a second step eliminate the al-kene. This approach was used in the synthesis of norbornyl cations of the elements tin and lead, e.g. 13, (Scheme 5). ... 

Non-chlorinated Lewis acids, such as scandium triflate, were found to be good catalysts for Friedel-Crafts alkylation reactions (167). Although no aromatic hydrocarbon alkylation occurred in CH2CI2, [BMIMJPFg, Sc(OTf)3 catalyzed the alkylation of benzene with high yields of the monoalkylated product. The lower acidity of the ionic liquid led to fewer byproducts and therefore higher yields. The products were separated by simple decantation and the catalyst was reused. 

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