Coal methylene bridges

The Effect of Phenol. Three types of phenol compounds have been identified in the fractions derived from the product of the phenol ati on reaction (.1,2) alkyl phenols and alkyl-aryl ethers, both formed by combining phenol with alkyl side chains cleaved from the coal molecule, and compounds made up of aromatic fragments attached to phenol by a methylene bridge, formed by... 

Table II contains a list of the aliphatic bridges detected in the toluene extract. Compounds with methylene bridges were predominant in the products from the fresh coal. This is consistent with the results of Benjamin et al. . It is interesting to note that several branched chain bridges appear in the transalkylation products from both the fresh and oxidized coals.

Relationship Between Number of Methylene Bridges and Degree of Depolymerization. A relationship between the number of methylene bridges in a coal and the extent of depolymerization was mentioned briefly by us (3) in a recent publication. The data were based on NMR analysis of the benzene ... 

NMR Spectra. Figure 4 shows NMR spectra for fractions A, B, C, and E (as mentioned earlier, fraction D and the whole coal were virtually insoluble in pyridine-dg, and spectra from them are not representative). Table II shows the forms the protons are present in, as determined from these spectra. The unrepresentative data for the small soluble parts of fraction D and the whole coal are shown in brackets. This table demonstrates the difficulties the coal chemist faces in trying to use NMR on physical solutions of coal e.g., the soluble part of the whole coal shows no hydrogen-bonded protons despite the evidence of Table I it shows no triaromatic or methylene bridge protons, despite the presence of appreciable amounts of these in the fractions on the other hand, it shows far more methylene a and methyl P than do the fractions. 

The NMR data confirm and amplify the IR data hydrogen-bonded protons are presented from phenolic and carboxylic groups in the coal and phenol groups added with the chemically combined phenol. The monoaromatic content (of fractions A and B especially) is high, also because of added phenol, but two-ring aromatic material also is present in all fractions (even triaromatic in C), which must have come from the original coal. The aliphatic material observed in the IR spectra of A, B, and C now is seen to consist principally of methylene bridges and short, branched aliphatic chains (a- and P-methyl predominate). 

The reaction is second order, first order in phenol and first order in the methylene-bridged aromatic (27), Presumably the mechanism involves ipso protonation of the aromatic followed by attack of phenol on the cationic intermediate (27). When applied to coals, it renders them almost completely extractable into pyridine, and the number average molecular weights of the extractable material generally range between 300 and 750 (24). 

Studies of coals of different ranks have shown that the proportion of aromatic hydrogen varies from 20% to 30% of the total hydrogen and that no simple relationship appears to exist with rank. Beta-paraffinic naphthenic hydrogen comprised 38%-66% of the nonaromatic hydrogen while the most striking variation in the structures of the coals was in the number of methylene bridges (Calkins and Spackman, 1986). 

Depolymerization of coal is a technique which, it is claimed, solubilizes coal by cleaving methylene bridges in the coal. The methylene chains joining aromatic groups can be cleaved at the ring and the free alkyl group and then alkylate another aromatic substrate (Larsen et al., 1981 Mastral-Lamarca, 1987 Sharma, 1988) ... 

Thus, the depolymerization of coal (Heredy et al., 1965 Heredy, 1981 Wender et al., 1981 Given, 1984) by means of a phenol/boron trifluoride mix is reputed to proceed by the cleavage of aryl-alkyl-aryl systems (Figure 12.11). On this basis, the extent of the polymeric nature of coal is proportional to the number of methylene bridges in the coal, which can be determined from the concentration of di(hydroxyphenyl)methane in the reaction products. 

While the organic coal matrix contains methylene bridges of the 9,10-dehydroanthracene type (54), the compounds of nitrogen, oxygen and sulfur are also constituents of coal and their presence affect the nature of the coal and the liquid fuel produced from it. 

Heredy, L.A., A.E. Kostyo and M.B. Neuworth. "Chemical Identification of Methylene Bridges in Bituminous Coal." Fuel 43 (1964) 414. 

Such bridges in coal structure have been reported only recently. Alkyl substituted methylene and ethylene bridges have been detected in a Wyodak coal by Benjamin et al.. In the present study, some of the branched chain bridges may have been formed by rearrangement of the straight chain bridges during transalkylation. ... 

The relative concentrations of several types of hydrocarbon bridges, namely methylene(-CH2-), ethylene(-CH2-CH2-), methyl methylene (-CH(CH3)-), methyl ethylene(-CH(CH3)-CH2-), ethyl methylene (-CH(CH2CH3)-), and propyl methylene (-CH(CH2CH2CH3)-) in the fresh and oxidized San Juan coal are compared in Table... 

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