Free Radical Fragments Research Articles

Lignin depolymerizes coal at 300 °C

Liquefaction of coal requires thermal rupture of its carbon–carbon bonds to form free-radical fragments. Before these radicals can recombine or polymerize they must be stabilized by hydrogen atoms usually supplied by a hydrogen-donating solvent or by gaseous hydrogen. The conditions required for such liquefaction reactions are usually temperatures ≳400 °C and hydrogen pressures of several hundred atmospheres1,2. Often catalysts can be used to accelerate the breaking of carbon–carbon bonds and the transfer of hydrogen. Ouchi et al.5 reported that p-toluenesulphonic acid catalysed the depolymerization of coal. Darlage and Bailey6 investigated various solvents and Friedel–Crafts catalysts and found that repolymerization of the coal radical fragments was a predominant reaction when coal liquefaction was conducted in non-phenolic solvents such as toluene, xylene or tetralin. Heating coals in phenol at 425 °C was reported7 to cause extensive depolymerization accompanied by rearrangement of hydrogen to form a hydrogen-rich soluble fraction and a hydrogen-poor insoluble fraction. We now report that bituminous coal can be depolymerized at 300 °C by using, instead of phenol, the abundant, renewable raw material lignin which is a major component of all vascular plants. When a mixture of coal and lignin is reacted in a solvent in the presence of an acid catalyst both the coal and the lignin depolymerize in relatively mild conditions to form a filterable liquid product. The presence of the lignin increases substantially the amount of the coal that can be so liquefied.

The Photolyses of Fully Aromatic Amides

The 254 nm photolyses of ethanol solutions of four fully aromatic amides were followed by liquid chromatography and u.v. spectroscopy, and quantum yields for the major products calculated. The photolysis of benzanilide was examined in detail at various wavelengths and in several solvents, both in the presence and absence of oxygen. Quantum yields for 2- and 4-aminobenzophenones and products from free radical precursors decreased with increasing solvent polarity and with increasing incident wavelength of irradiation. Oxygen had no affect on aminobenzophenone formation but produced benzoic acid from free radical fragments which escaped the solvent cage. The results are tentatively interpreted in terms of an energy dependent radiationless conversion to a reactive 1π*-carbonyl which then cleaves the N—C bond to give caged free radicals, rather than by a concerted, nonradical rearrangement.

Laser Heating of Coal Particles in the Source of “Time-of-Flight” Mass Spectrometer

DURING general investigation of the processes that occur in the combustion of pulverized coal, experiments have been undertaken to develop methods for determining the nature of products formed by the rapid thermal decomposition of coal particles, especially those evolved in the very early stages of decomposition. In previous work1 the yields of the stable decomposition products evolved from small coal particles during the first millisecond of flash heating were determined by quenching the products in an inert atmosphere. Using this method, however, it was not possible to determine whether free radical fragments constituted part of the primarily evolved species. Recent work on the pyrolysis of lump coal using a laser beam has suggested that free radicals of molecular weight of about 100 are evolved2, but in these experiments the products arose both from complete vaporization within the crater formed by the direct beam and from relatively slow low-temperature pyrolysis around this crater.

Electron Spin Resonance of Irradiated DNA

The electron spin resonance (ESR) spectra of free radicals formed in-the sodium salt of desoxyribonucleic acid (DNA) by 1-Mev electrons were examined. Dry samples were irradiated at approximates 200°K and examined at 77°K at microwave power levels below approximates 0.1 mw. At levels below 1 Mrad only a single, rather broad absorption line was seen. At around this dosage, an additional spectrum containing several resolved hyperfine satellites was found. A free radical fragment compatible with the results was - C (CH 3)CH 2--. This free radical postulated must come from thymine which contains the only methyl group in DNA.

Complex Cyclotron Resonance in Dilute Gases

An X-band electron spin resonance spectrometer has been used to analyze the products of an electrodeless discharge in flowing gases at low pressure. During a search for polyatomic free radical fragments, a multiple signal was found near g=2.0000. Three poorly resolved peaks were found for a variety of paraffins and olefins, while methane, ammonia, methylamine, and sulfur dioxide yielded doublets. The structure was best resolved at low pressure. The spacing of the peaks increased with ESR microwave power. Evidence is presented that the signal is caused by cyclotron resonance of photo-ionized electrons. It is suggested that this multiple resonance is more apparent than real, and arises from either a velocity-dependent capture process or from dephasing of electrons upon collision with gas molecules.

Reaction of Sulfur, Hydrogen Sulfide, and Accelerators With Propylene and Butadiene.

As part of a study of vulcanization, propylene as a model compound for natural rubber has been reacted with sulfur alone, with hydrogen sulfide alone, and with each of these materials in the presence of certain accelerators. Butadiene as a model compound for intermediate conjugated systems found in vulcanized rubber by means of infrared studies has been similarly studied. Results of mass spectrometer analyses of the volatile portions of the reaction products indicate the formation of sulfides, disulfides, and carbon-to-carbon bonds. Zinc dimethyl dithiocarbamate (ZnDMDC), a vulcanization accelerator, facilitates the formation of hydrogen sulfide from the olefin or diolefin in the presence of sulfur, and in turn promotes the reaction of hydrogen sulfide with the olefin and diolefin. The ZnDMDC-accelerated reaction of hydrogen sulfide and sulfur with the diolefin may account for the reduced conjugation observed in vulcanizates accelerated with ZnDMDC. Studies with free radical accelerators show that a mechanism other than a free radical chain mechanism is involved in the formation of diisopropyl sulfide in the reaction of propylene with sulfur (or hydrogen sulfide) and certain substances that facilitate the reactions. The same conclusion applies to the formation of a nonvolatile residue in the ZnDMDC-accelerated reaction between propylene and sulfur. Other phases of the reactions involve the formation of compounds from what appear to be free radical fragments of the original molecule. In most of the reactions, appreciable portions of the reaction products are nonvolatile.