Polyanion , coal with reactions

In principle, the reductive alkylation of coal involves treatment of coal with an alkali metal in tetra-hydrofuran in the presence of naphthalene whereby a coal polyanion is produced that is capable of undergoing further reaction with, say, an alkali halide. The resnlting product has been presumed to be the alkylated coal but the relatively straightforward chanistry is, in fact, a complex sequence of reactions. For example, ether bridges are also cleaved under the conditions of the reaction as are carbon bonds. That the former can happen makes the resulting product mix somewhat more complex than if ethers were not cleaved but the cleavage of carbon-carbon bonds ensures the complexity of the product mix as well as the chemistry involved in the process. 

The rich chemistry of the coal polyanion and the presumably close relationship between the structures of the coal polyanion and the initial coal molecules prompted us to study the reaction conditions and the reaction products carefully and then to examine the reaction of the coal polyanion with 90%-enriched butyl-l- C iodide. 

Coal Alkylation with Butyl-1- C Iodide. Potassium (26.1 mmol) was added to a stirred solution of naphthalene (3.14 mmol) in tetrahydrofuran (45 mL) under argon. After 45 min, -325 mesh coal (1.00 g) and an additional wash quantity of tetrahydrofuran (10 mL) were added. The mixture was stirred for 5 days. The excess potassium (2.98 mmol) was removed. A small quantity of insoluble coal (0.041 g) was unavoidably lost in the removal of the metal. A solution of 90%-enriched butyl-1- C iodide (6.88 g) in tetrahydrofuran (10 mL) was added to the stirred solution in 15 min. This quantity corresponds to a twofold excess of the amount of reagent needed for the alkylation of a coal polyanion with 21 negative charges per 100 carbon atoms and naphthalene dianion. Potassium iodide began to precipitate from the reaction mixture almost immediately. The alkylation reaction was allowed to proceed for 2 days. Potassium iodide rapidly settled from the reaction mixture when stirring was interrupted. 

The rates of reduction of tetrahydrofuran (Curve A), naphthalene in tetrahydrofuran (Curve B), and a mixture of naphthalene and Illinois No. 6 coal in tetrahydrofuran (Curve C) are shown in Figure 1. These preliminary experiments established that potassium reacted only very slowly with tetrahydrofuran under the experimental conditions used for the formation of the coal polyanion. Naphthalene was rapidly converted to a mixture of anion radicals and dianions under the same conditions. The initial reaction between the electron transfer reagent and the Illinois No. 6 coal was quite rapid. However, the reaction slowed to nearly constant rate after about 12 hr. During the last 4 days of reaction the coal molecules acquired about 0.1 negative charge per 100 carbon atoms per hour. 

The reaction of the. coal polyanion with methyl iodide occurs at least fivefold more rapidly than the reaction with butyl or octyl iodide, as judged by the rate of precipitation of potassium iodide. However, the results shown in the table reveal that there are only very minor differences in the solubility of the reaction products. In addition, we observed that the coal polyanions prepared from the insoluble residues of the first alkylation reaction were considerably more reactive. These polyanions reacted very rapidly with methyl iodide and reacted with butyl iodide to produce butene-1. 

The reactions of the potassium-coal polyanion with the butylation reagents differed markedly. Both the percentage of soluble product and... 

In another experiment we tested the utility of 1,2-dimethoxyethane as a solvent for the reaction. The results obtained in this experiment revealed that the coal polyanion was formed to the same extent as in tetrahydrofuran. In addition, the alkylation of the polyanion with butyl mesylate gave the same quantity of soluble product in 1,2-dimethoxy-ethane as it did in tetrahydrofuran. Hence both solvents are equally useful for the alkylation reaction. 

The alkylation reactions of the coal polyanions also were investigated. The reactions of the polyanion with methyl, butyl, and octyl iodide were compared in tetrahydrofuran. The reaction could be monitored quite readily by the rate at which potassium iodide precipitated from solution. We estimate that methyl iodide is at least fivefold more reactive than butyl or octyl iodide under these conditions. This result, of course, suggests that the Sj 2 reactions of the coal polyanion are more... 

As already mentioned, several investigators have pointed out that naphthalene or tetrahydrofuran may be incorporated into the coal product (9, 10, 11), In this work we found that chromatographic procedures could be used to separate unbound naphthalene and its reductive alkylation products from the coal alkylation products. The spectroscopic work indicates that the principal resonances of naphthalene and tetrahydrofuran are absent from the butylated coals. Moreover, the mass balance shows that no important quantity of naphthalene or tetrahydrofuran could be incorporated. We supplemented this negative evidence by a comparison of the reaction products obtained from the same coal in a reaction in liquid ammonia. In the most pertinent case the Illinois No. 6 coal was treated with potassium in liquid ammonia. The polyanion was alkylated with butyl iodide. The product distribution obtained by GPC and the spectroscopic properties of these fractions were very closely related to the properties of the reaction products obtained in the reaction with naphthalene in tetrahydrofuran. Recently Larsen and his group found that neither " C-labeled naphthalene nor tetrahydrofuran was incorporated in chemically significant amounts in the coal products separated from the reaction mixture by chromatography (12). 

The resonances in the butyl ether region occur in three distinct bands. Chemical shift data for the a carbon atom resonances in about 20 ethers indicate that the resonances centered about 872.9 may result from hindered aryl ethers, for example, butyl 2,6-dimethylphenyl ether, butyl benzyl ethers, or butyl n-alkyl ethers, for example, dibutyl ether. The resonances in this region could arise from tetrahydrofuran residues in the coal product. However, the results obtained in this laboratory and in Larsen s laboratory are much more compatible with interpretations that exclude the involvement of tetrahydrofuran and focus on the reactions of the labeled butylation reagent with 2,6-disubstituted phenoxides, benzylic oxides, and primary alkoxides liberated in the formation of the coal polyanion. The most intense resonance centered at... 

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