heat of reaction for dehydrogenation of paraffins in the asphalt is calculated to be about 25 kcal. per gram mole. Composition changes which result from both air-blowing and sulfurization of asphalt also are being studied at Florida. Particular emphasis is on carbon structures. Empirical methods based on molecular weight, carbon hy drogénation, chemical reactivity studies, NMR, and gel permeation chromatography have yet to give completely satisfactory results, according to Dr. Schweyer.
Chlorobenzene polymerizes with aluminum chloride and cupric chloride catalysts
Hto +AICI$ ^±:H a o
ΑΙΟ^^^ΑΚ^βΗίΓ
Halobenzenes polymerize with AICI3-CuCI2 catalyst RD
ACS NATIONAL MEETING Polymer Chemistry
Halobenzenes polymerize under the combined influence of aluminum chloride and cupric chloride. Although evidence points to chlorobenzene and fluorobenzene following similar polymerization paths, bromobenzene appears to undergo an initial debromination step, Dr. Peter Kovacic of Case Western Reserve University told the Special Topics Symposium. The object of the study was to extend the scheme of the polymerization of benzene and other aromatics to the halobenzenes, Dr. Kovacic notes. He and his coworkers, Dr. Li-chen Hsu at the National Aeronautics and Space Administration, Cleveland, and John T. Uchic of Duquesne University, Pittsburgh, Pa., examined the polymerization under a variety of reaction conditions. They settled on a monomer-AlCl 3 CuCl 2 molar ratio of 6:1:0.5 interacting at 60° C. for one hour. Yield isn't high, being about 14% (by weight) for chloroand fluorobenzene. Molecular weight determination of the chloroform-soluble portion of the product shows that there is an average of 12 monomer units in the oligomers. In all cases, the halobenzenes polymerize to solid products that vary from orange to deep red. A variety of analytical techniqueselemental analysis, molecular weight determination, infrared and ultraviolet spectroscopy, oxidative degradation, dehalogenation, and solubility—were used to characterize the oligomers. Evidence points to an ortho-polyphenyl backbone for the chlorobenzene and fluorobenzene oligomers. In contrast, the benzene oligomer has a para configuration. In the initiation step of the reaction, a proton from an aluminum chloride-cocatalyst complex apparently attaches itself to either the ortho or
CI
para position of the halobenzene. During the subsequent propagation steps, data indicate attack at the para position of the chlorobenzene. In contrast, there seems to be some ortho attack as well in the case of fluorobenzene. The oxidative cationic mechanism for the polymerization follows the general pattern that Dr. Kovacic and his coworkers found in earlier work. IR analysis of the chlorobenzene oligomer shows absorption maxima in the aromatic region of 865 cm. - 1 and 820 cm. - 1 , indicating a 1,2,4-substitution mode. The same interpretation expains the broad IR absorption band that the fluorobenzene oligomer exhibits. UV analysis also points to an ortho-polyphenyl structure. Oxidative degradation of the chlorobenzene oligomer with chromic acid in acetic acid, and subsequent esterification, yields dimethyl 4-chlorophthalate and methyl p-chlorobenzoate. The latter very likely arises
Cl
through oxidation of the end groups of the chain. Appearance of the 4-chlorophthalate is further indication of 1,2,4-substitution. Contrary to expectation, methyl mchlorobenzoate failed to show up as an oxidation product. Dr. Kovacic attributes the absence of this product to the presence of polynuclear sites in the chains that can occur, theoretically, at any stage following trimerization through the loss of hydrogen. The color of the polymerized material is also indicative of polynuclear regions, since the polynuclear moiety is a much more potent chromophore than the analogous polyphenyl entity. In addition, he finds that the hydrogen content of the oligomer falls short of the theoretical amount. He also construes this to indicate the presence of some polynuclear sites. The results of the oxidative degradation of the fluorobenzene oligomer are generally similar to those of its chlorobenzene counterpart. APRIL 17, 1967 C&EN 55
Dr. Kovacic and his coworkers removed chlorine from the chlorobenzene oligomer with sodium in mesitylene. The material they recovered shows a much smaller degree of IR absorption in the 1,2,4-substitution region. But there is a pronounced increase in the absorption band between 740 cm. -1 and 750 cm.-1, which is further evidence for the ortho-polyphenyl structure, they say. In contrast to the path followed by the polymerization of chlorobenzene and fluorobenzene, bromobenzene, Dr. Kovacic believes, first undergoes disproportionation followed by preferential polymerization of the benzene to a partially brominated para-polyphenyl. Backing up this contention is the fact that the bromobenzene oligomer has an IR spectrum very similar to that of para-polyphenyl. Additional evidence for this mode of polymerization comes from the fact that brominated para-polyphenyl and the bromobenzene oligomer have essentially identical IR spectra.
Method determines metals in organics at less than 1 p.p.m. RD
ACS NATIONAL MEETING Analytical Chemistry
Less than 1 p.p.m. metal in petroleum and organic chemicals can be accurately determined by ion exchange concentration followed by x-ray fluorescence (XRF). The technique, developed by Dr. J. G. Bergmann and his coworkers at American Oil Co., has been used to determine 0.1 to 1.0 p.p.m. nickel and vanadium in petroleum and less than 2 p.p.m. iron, nickel, chromium, manganese, calcium, cobalt, titanium, and molybdenum in terephthalic acid. The method fills the petroleum industry's need for a rapid, simultaneous analysis of feedstocks for 0.1 p.p.m. nickel and vanadium to within 0.01 p.p.m. Such sensitivity is needed because trace amounts of metals can adversely affect the catalytic cracking process. Existing methods, such as emission spectroscopy, XRF, neutron activation analysis, atomic absorption, and electron paramagnetic resonance, can qualitatively detect 0.1 p.p.m. of metals in ashed 10-gram samples, but they can't determine the concentrations with 10% accuracy. To do so would require a tenfold increase in sample size. The method developed by the American Oil workers consists of igniting a 10-gram sample of petroleum in the presence of sulfur, concentra56 C&EN APRIL 17, 1967
ION EXCHANGE DISK. Joseph L. Janik (left) and John G. Bergmann hold ion exchange disks which will be analyzed by the x-ray fluorescence apparatus in the background. The ring stand holds apparatus for absorption of samples onto disks
ting the metals on a small disk of cation exchange paper, and determining the collected metals by XRF. The ash from the ignition is treated with hydrochloric acid and perchloric acid before being taken up in dilute perchloric acid. This solution is adjusted to pH 2.5 ± 0.5 and passed through the 9/i6~mcri-diameter disk. Accurate geometry of the apparatus for absorbing the sample on the disk is critical. The disk is held in a sandwich of two Teflon rings. A slight depression in the lower ring precisely centers the disk. The rings' close tolerances ensure a snug fit and the exposition of a reproducible area to the solution. The resulting thin layer of metals gives a high yield of secondary x-ray emission during XRF and greatly reduces the background scatter. The XRF analysis uses the Ka lines and a tungsten tube. Dr. Bergmann and his coworkers found no interelement effects between nickel, vanadium, and iron. Relative errors are 5 to 10% between 0.1 and 1.0 p.p.m., and the limit of detection for a 10-gram sample is 0.005 p.p.m. (0.05 microgram). The analysis takes four hours. The method as applied to terephthalic acid is not so simple. Ignition doesn't require the presence of sulfur, but the ash must be treated with hydrofluoric acid, followed by hydrochloric acid, perchloric acid, and hydrochloric acid again before taking up the residue with perchloric acid. This series of treatments allows the cation exchange disk to pick up iron, nickel, cobalt, manganese, calcium,
and most of the chromium and titanium. The remaining chromium and titanium, as well as the molybdenum, are caught by evaporating the cation exchange eluant, converting the metals to the ammonium salts, and passing the solution through an anion exchange disk. The Ka lines were used in the XRF of all elements except molybdenum, for which the L^, line was used. A tungsten tube was used for all elements except calcium and molybdenum, for which a chromium tube was used. The mean error in the 1to 2-p.p.m. range is 0.2 p.p.m.
Disulfide cross-links relate to cotton properties RD
ACS NATIONAL MEETING Cellulose, Wood, a n d Fiber Chemistry
Chemical analysis of disulfide crosslinked cotton after successive cross-link cleavages and reformations helps to relate the eflFect of cross-linking to the fiber's physical properties, according to Dr. Giuliana C. Tesoro and Dr. Stephan B. Sello of J. P. Stevens & Co/s central research laboratory, Garfield, N.J. Speaking at the Symposium on Recent Advances in the CrossLinking of Cellulose Fibers, Dr. Tesoro indicated their results confirm the fact that changes in physical properties such as crease recovery are proportional to the extent of cross-linking. She pointed out, however, that the proportionality is rough and does not
