Leon M. Stock

A Quantitative Treatment of Directive Effects in Aromatic Substitution

Publisher Summary This chapter focuses on the quantitative treatment of directive effects in aromatic substitution. The observations for the electrophilic substitution reactions of the monosubstituted benzenes are examined for adherence to a linear free-energy relationship. The selectivity relationship, or the extended selectivity relationship, correlates the data for aromatic substitution simply and accurately. Comparison of the correlations of substitution reactions with side-chain reactions illustrates the more precise nature of the selectivity treatment. This result must be a reflection of the greater similarity of transition states for all aromatic substitution reactions as contrasted to the large variations in the character of the equilibrium states and activated complexes encountered in ordinary and electrophilic side-chain reactions. The introduction of additional parameters in the correlation equation does not yield a significant improvement in the correlation of substitution data. The discrepancies found are not associated with the more apparent properties of these reactions—that is, with influences, such as the charge on the electrophile or variations in resonance interactions as a consequence of the modification of selectivity of the reagent.

Ruthenium tetroxide catalysed oxidation of illinois no.6 coal and some representative hydrocarbons

Abstract The use of ruthenium tetroxide for the catalytic oxidation of coal molecules under mild conditions has been examined. The selectivity of the reagent for aromatic nuclei has been assessed by a study of the oxidation of selected benzene, naphthalene and phenanthrene derivatives. The catalysed oxidation of Illinois No.6 coal has been studied. The preliminary results described in this report suggest that this oxidant is effective for the selective oxidation of the aromatic structures in this coal.

Solid state magnetic resonance spectra of Illinois No. 6 coal and some reductive alkylation products

Abstract Illinois No. 6 coal and its reductive methylation and butylation products have been studied by magnetic resonance techniques. Conventional CP-MAS13Cn.m.r. spectroscopy indicates that 62% of the carbon atoms in the coal are aromatic and that about 6% of the carbon atoms are carbonyl. Esters are more abundant than carboxylic acids. The resonances of methoxy groups and other novel etheric carbon atoms are apparent in the high field region. Dipolar dephasing experiments suggest that methyl carbon atoms constitute no more than 16% of the carbon, methylene and methine carbon atoms about 14% and quaternary aliphatic carbon atoms about 2%. The dipolar dephasing experiments in conjunction with previous work also permit estimates of the hydrogen atom distribution. The THF-insoluble products obtained in the reductive alkylation reactions with13C-enriched alkylating agents contain paramagnetic and ferromagnetic substances that adversely influence the solid state n.m.r. spectra. However, good 13C n.m.r. spectra were obtained after these substances were extracted with aqueous hydrochloric acid. The O:C alkylation ratios are 1.2 and 1.0 for methylation and butylation, respectively. Dipolar dephasing experiments establish that the decay constants of functional groups in the whole coal and of C- and O-methyl-13C and C- and O-butyl-1 -13C nuclei in the labelled coal molecules are very similar to those of reference compounds. These findings suggest that the decay constants measured for the 13C nuclei in coals and coal-derived solids provide reliable information about their degree of substitution.

Ruthenium tetroxide catalysed oxidation of coals: The formation of aliphatic and benzene carboxylic acids

Abstract Ruthenium tetroxide was used as a reagent for the oxidation of several different coals. Significant quantities of aliphatic, di-, tri- and tetracarboxylic acids as well as benzene di-, tri-, tetra- and pentacarboxylic acids were produced in these oxidation reactions. More than 100 products have been identified by g.c.-m.s. The yields of three abundant products, butanedioic acid, 1,2-benzenedicarboxylic and 1,2,4,5-benzenetetracarboxylic acid, were determined quantitatively by an isotope dilution technique and the yields of eleven other relatively abundant products were measured semiquantitatively by g.c.-m.s. A striking array of carboxylic acids are formed in this reaction, which selectively preserves the aliphatic portion of the coal. The product distribution depends upon the rank of the coal. Texas lignite, for example, produces the most diverse group of aliphatic acids, but the higher rank bituminous coals also provide significant quantities of these acids. The structural implications of the observations are discussed.

Aspects of the chemistry of donor solvent coal dissolution. The hydrogen-deuterium exchange reactions of tetralin-d12 with Illinois No. 6 coal, coal products and related compounds

Abstract The exchange of hydrogen and deuterium atoms between Illinois No. 6 coal and tetralin-d 12 and naphthalene-d 8 has been studied at 400 °C. These exchange reactions are readily reversible and the evidence suggests that the same kinds of hydrogen atoms exchange with tetralin as with naphthalene. The influence of illinois No. 6 coal, selected coal products and other compounds representative of the structural elements in Illinois No. 6 coal on the rate of the exchange reaction between diphenylmethane and tetralin-d 12 has been studied also. The results indicate that the exchange reaction is initiated by compounds which have labile linkages or reducible structures but not by the weak acids or weak bases. The reactions are initiated by single-bond homolyses and by molecule-induced homolyses.

The occurrence of elemental sulphur in coals

Abstract Elemental sulphur is present in many coals and sometimes constitutes as much as 5% ot the total amount of sulphur in the sample. However, three pristine samples obtained from the Premium Sample Bank at the Argonne National Laboratory are free of elemental sulphur within the detection limit (0.0005%) of a sensitive analytical method. These initial observations suggest that sulphur is not a natural constituent of coal, but that significant quantities are produced after exposure to air.

Proton and carbon n.m.r. spectra of butylated coal

Abstract The proton and carbon n.m.r. spectra of butylated Illinois No. 6 coal which has been fractionated by gel-permeation chromatography (GPC) are reported. The chemical shifts and spin-lattice relaxation times of model compounds provide the bases for the assignment of the spectroscopic results. The spectra of the various molecular weight fractions are clearly different. There are significant variations in the degree of aromaticity, the presence of linear alkanes, the ratio of C-butylation to O-butylation, the extent of butylation on aliphatic and aromatic carbon atoms, and the amount of carbonyl and vinyl derivatives. The results suggest that electron transfer, proton abstraction, ether cleavage, and elimination reactions are important under the conditions of the Sternberg process and that both nucleophilic and free-radical substitution reactions occur. The results also strongly suggest that the distribution of functional groups in coal is not uniform.

Ruthenium tetroxide catalysed oxidation of Illinois No. 6 coal. The formation of volatile monocarboxylic acids

Abstract Ruthenium tetroxide selectively oxidizes activated aromatic compounds under mild conditions and has been used for the catalytic oxidation of several different coals. The quantities of the volatile monocarboxylic acids with 2–6 carbon atoms have been determined by an isotope dilution technique. The amount of ethanoic acid ranges from 1 to 3mol/100C and the quantities of propanoic acid, and butanoic acid exceed 0.1 mol/100C. Methylpropanoic, pentanoic, 2-methylbutanoic, 3-methylbutanoicand hexanoic acid are formed in lesser amounts. The outcome of the experiment depends upon whether or not the coal has been extracted prior to oxidation. The results for Illinois No. 6 coal expressed in moles of ethanoic acid produced/l00C illustrate this feature: raw whole coal, 1.9; coal extracted by the method of Hayatsu and co-workers, 1.0. Dehydrogenation with benzoquinone prior to oxidation increases the yield of ethanoic acid to sol1.5mol 100C. The amounts of ethanoic acid obtained from the other extracted coals are 1.0 for Texas lignite, 1.2 for Rawhide subbituminous, 3.4 for Pittsburgh No. 8, 3.3 for a higher ranking bituminous coal (PSOC 726) and 0.7 for an anthracite (PSOC872). The results obtained in this study are compared with related information concerning the distribution of alkyl groups within coal by other methods.

Aspects of the chemistry of donor solvent coal dissolution. The role of phenol in the reaction

The relative reactivity of phenol in exchange reaction with tetralin-d12 and naphthalene-d8 indicates that hydrogen exchange occurs by a free radical process rather than by an electrophilic substitution reaction at 427 °C. Substances such as benzyl phenyl ether that initiate free radical reactions increase the rate of the exchange reaction between phenol and tetralin-d12 whereas weak acids have only a modest influence on the exchange. Phenol and 1 -naphthol accelerate the rates of decomposition of some ethers and amines in tetralin. These results suggest that phenolic compounds enhance thermal coal dissolution reactions in donor solvents via their influences on the rates of the homolytic cleavage of carbon-oxygen and carbon-nitrogen bonds.

Aspects of the chemistry of donor solvent coal dissolution: Promotion of the bond cleavage reactions of diphenylalkanes and the related ethers and amines

Abstract The influences of Illinois No. 6 coal, benzyl phenyl sulphide, 9, 10-anthraquinone, tetracene, phenol and benzoic acid on the rates of decomposition of 1,2-diphenylethane, 1,3-diphenylpropane, 1, 4-diphenylbutane, benzyl phenyl ether, dibenzyl ether, N-benzylaniline, and dibenzylamine in tetralin have been investigated. Radical initiators such as benzyl phenyl sulphide enhance the rate of decomposition of the compounds that form benzylic radicals which can decompose via β-scission reactions. Weak organic acids enhance the reaction rates of the compounds, for example, benzyl phenyl ether and N-benzylaniline, that undergo the homolysis reaction via polar transition states. Among the reactive initiators considered in this Paper, benzyl phenyl sulphide is the only compound which, in small quantities, accelerates the conversion of Illinois No. 6 coal to pyridine-soluble products in tetralin at 400 °C. The facile reactions of Illinois No. 6 coal with tetralin and the accelerating effects of benzyl phenyl sulphide, anthraquinone, tetracene and phenols on the decomposition of the diphenylalkanes and the related heteroatom analogues are discussed.