Hydroaromatic molecules

Two PAH molecules disproportionate into one hydroaromatic molecule and one free-radical molecule. 

The hydroaromatic molecules cleave to produce liquid and gas-phase species. 

Direct Liquefaction Kinetics Hydrogenation of coal in a slurry is a complex process, the mechanism of which is not fully understood. It is generaly believed that coal first decomposes in the solvent to form free raclicals which are then stabilized by extraction of hydrogen from hydroaromatic solvent molecules, such as tetralin. If the solvent does not possess sufficient hydrogen transfer capability, the free radicals can recombine (undergo retrograde reactions) to form heavy, nonliquid molecules. A greatly simplified model of the liquefaction process is shown below. 

Palladium is the most active and most frequently used catalyst in transfer hydrogenations.77 78 Cyclohexene, a cheap, readily available, highly reactive molecule, is the preferred donor compound. Alternatively, tetralin and monoterpenes and, in general, any hydroaromatic compound, may be used. Mainly alcohols are employed as the donor with Raney Ni. 

Leslie Reggel Could you say more about the structure of the coal molecule you showed us Is enough hydroaromatic hydrogen included ... 

Coals are macromolecular, —i.e., low rank coals, at least, appear to be able to absorb certain molecules such as methanol and hydrocarbons. In low and medium rank coals the ultimate units are linked by chemical and physical forces, and in high rank coals physical forces predominate. The presence of hydroaromatic structures in low rank coals must lead to rather distorted frameworks. Although it is not difficult to visualize that spaces exist in which foreign... 

Promotion of Hydrogen Exchange The radicals derived from the coal molecules by simple thermal homolyses and by molecule-induced homolyses initiate exchange reactions between tetralin-d, and the donors in the reaction system—principally diphenyl-methane and the hydroaromatic compounds in the macerals (2. ... 

Molecular Weight. Aromatization of hydroaromatic structures, rather than removal of aliphatic substituents, was suggested because the weight per molecule remained approximately constant with increasing temperature up to 900°C. The shift to solid products at 1100°C probably represents a significant increase in molecular weight. 

Multiple intramolecular ring closures of aryl-substituted unsaturated long chain alcohols, acids, acid chlorides and ethers in the presence of Friedel-Crafts catalysts have been extensively employed to synthesize polynuclear hydroaromatic hydrocarbons and polycyclic ketones. This is illustrated by two examples shown in equations (112) and (113). The application of stereospecific cycloalkylations in approaching the synthesis of complex organic molecules has been reviewed by Barclay. ... 

Treatment of certain hydroaromatic compounds and steroids with DC1 leads to the known rearrangements of the carbon skeleton,12 which here occur with labeling although the chlorine is not retained in the molecule.13... 

A majority of the proposed models suggest coals to consist of several ring aromatic and hydroaromatic structural units, cross-linked through aliphatic and ether bridges to form the three dimensional structure and in the pores and cavities of this structure reside weakly linked smaller molecules which are easily extracted by solvents. The model proposed by Solomon and Shinn are representative examples of this macromolecular model. 

Additional molecules entering into the reactions lead to a further complexity of possibilities. Highly important is the transfer of hydrogen, such as occurs from hydroaromatics to form paraffins and aromatics. Transfer reactions occur most rapidly with tertiary carbonium ions. 

Aqueous solutions of certain salts, such as those of benzoic, salicylic, benzene-sulfonic, naphthoic, and various hydroaromatic acids, possess the power of dissolving certain substances otherwise not soluble in water. These substances, known as hydrotropes, are structurally similar to surfactants in that they have hydrophilic and hydrophobic moieties in the same molecule, but the alkyl chain is shorter. A few typical hydrotropes are listed in Figure 26.8. When solubilization... 

The flexibility of coal structure and mobility of loosened molecules are responsible for the successive extraction of coal in solvents having different chemical characteristics. In fact, coal has a heterogeneous structure having different structural units, that is, polyaromatic, hydroaromatic, and paraffinic units linked through C-C, C-N-C, C-O-C, and C-S-C linkages. 

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