First, two p-xylylene molecules con­dense on a surface to form a linear diradical. A linear polymer forms as p-xylylene units attach to each end of the diradical. Growth is finally terminated when end groups of the growing polymer react with reactive sites on other growing polymer mole­cules. Growth can also be terminated by chain transfer agents or by the re­active end groups getting buried in the polymer matrix.

This concept of linear molecules growing by a free-radical mechanism is supported by the high concentra­tion of free electrons in these poly­mers, Dr. Gordon says. Poly-p-xylyl-enes made from di-p-xylylenes contain from 5 to 10 X 1 0 - 4 moles of free electrons per mole of xylylene.

Xenon Trioxide Oxidizes Plutonium

149TH ACS NATIONAL MEETING

Nuclear Chemistry

Xenon trioxide can be used to oxidize plutonium ( III ) to plutonium ( IV ). Scarcity of xenon and the high price of its compounds probably rule out their large-scale use in plutonium process­ing. But they offer one advantage over conventional oxidizing agents: The reduction product (xenon) is a relatively insoluble gas and inert under most conditions. It does not contami­nate the solution, according to Dr. J. M. Cleveland of Dow Chemical's Rocky Flats division.

In his work, Dr. Cleveland prepared plutonium (III) solutions by dissolving high-purity plutonium metal in per­chloric acid. The xenon trioxide— prepared at Argonne National Labora­tory—was standardized by adding ex­cess potassium iodide and titrating the iodine produced by xenon trioxide oxidation with sodium thiosulfate. Disappearance of plutonium ( III ) and appearance of plutonium (IV) were followed spectrophotometrically.

The oxidation follows this path: 6Pu+ 3 + XeO s + 6H+ -> 6Pu+ 4 + Xe + 3 H 2 0 (AF ^ - 1 1 3 kcal. per mole). Dr. Cleveland concludes that the reaction is first order for pluto­nium (III) and xenon trioxide, and zero order in hydrogen ion in 0.5M to 2M perchloric acid.

Xenon trioxide also oxidizes plu-

Dr. J. M. Cleveland Xe03 offers advantages

tonium(IV). This reaction was kept at a minimum by selecting conditions so that plutonium (IV) concentra­tion was always much lower than plutonium ( III ) concentration. Sec­ond-order kinetics indicate that the rate-determining step is the reaction of plutonium (III) with xenon trioxide to produce an unstable, lower-valent xenon species and an oxidized plu­tonium species. The plutonium (III) may be oxidized directly to pluto­nium (IV) ; or, possibly, it is oxidized to plutonyl(V), which then reacts with plutonium (III) to form plutonium-(IV) .

Orange Peels Contain «-Tocopherol Chemical is a potent natural antioxidant and vitamin Ε factor

149TH ACS NATIONAL MEETING Agricultural and Food Chemistry

A potent natural antioxidant has been isolated from orange peels and identi­fied as α-tocopherol at the University of Florida agricultural experiment station, Lake Alfred. For Dr. William F. Newhall and Dr. S. V. Ting, the identification caps a search for the natural antioxidant of oranges, a search which began with the idea that, being natural, the antioxidant

was not likely to be toxic. The isola­tion has taken on added importance with the recent incorporation, by the National Academy of Sciences, of α-tocopherol in its recommended dietary allowances. The compound is a vitamin Ε factor. NAS says it's essential to the health and well-being of most animals.

Most scientists believe that autoxi-dation is one of the main paths to off-flavors in citrus fruit. During au-toxidation, terpenes in citrus fruit are oxidized. Citrus oils are used com­mercially in flavor extracts, soaps, and perfumes.

Over the years, various workers have found that many antioxidants will prolong storage life of citrus oils; α-tocopherol is one. Others are nordihydroguaiaretic acid, butylated hydroxyanisole, butylated hydroxy-toluene, gallic acid esters, wheat germ oil, and hydroquinone.

There have been various indica­tions that citrus peel contains an anti­oxidant. In 1949, other workers dis­closed that citrus peel and pulp stabilize animal fats against rancidity. Processors operate with the rule-of-thumb that cold-pressed citrus oil keeps better than steam-distilled oil. Also, high-yield extracting methods yield more stable oils.

In light of this situation, Dr. Ting and Dr. Newhall set out to determine the relative antioxidant activity in various parts of the citrus fruit and, if possible, where this activity is con­centrated. In a study of oranges, lemons, and limes last year, they found most activity in the orange and little in lemons and limes. Except for the juice vesicles of Valencia oranges, most of an orange's antioxidant is concentrated in the outer peel skin. To get at the active agent, Dr. New­hall and Dr. Ting took the dried outer peel through a variety of ex­traction and chromatographic pro­cedures.

They first extracted the peel with n-hexane for 24 hours. They then removed the n-hexane on a film evap­orator and dewaxed the viscous residue with anhydrous methyl alco­hol. This procedure yielded almost 25 grams of dark, viscous oil (the work started with 1400 grams of dried peel from 1350 pounds of oranges). The oil was separated into 77 frac­tions by chromatography on alu­minum oxide. Tests showed anti­oxidant activity in fractions 48 through 69. These were combined

52 C&EN A P R I L 12, 1965

8 10 12 Wave length (microns)

Infrared absorption (in chloroform) spectrum of an authentic sample of d-a-tocopherol (upper curve) and the IR absorption of the compound isolated from orange peels (lower curve) are identical, Florida chemists find

and evaporated to yield 1.5 grams of dark, oily material.

Further chromatography yielded a light yellow, viscous oil. Thin-layer chromatography showed spots with Rf values similar to α-tocopherol. When subjected to infrared analysis, the yellow oil yielded a spectrum identical with an authentic sample of d-a-tocopherol.

Oxygen Reduces to Superoxide Anion Major reaction in aprotic solvents is one-electron reduction

149TH ACS NATIONAL MEETING

Analytical Chemistry

The major reaction occurring during the first oxygen reduction process in aprotic solvents such as dimethyl-formamide and dimethylsulfoxide (DMSO) is a one-electron reduc­tion to the superoxide anion, accord­ing to Dr. D. L. Maricle and Dr. W. G. Hodgson of the Stamford Re­search Laboratories of American Cyanamid (Stamford, Conn.). In aqueous solvents, two electrons per oxygen molecule are consumed, pro­ducing either H 2 0 2 or H 0 2 " (de­pending on p H ) . To demonstrate the one-electron oxygen reduction process, the Cyanamid chemists used

techniques such as polarography and cyclic voltammetry.

Cyclic voltammetric experiments show a quasi-reversible reoxidation ©f the first oxygen reduction product. Any reduction involving the consump­tion of protons should not occur re-versibly in a solvent with such a low proton availability. Therefore, Dr. Maricle and Dr. Hodgson con­clude that the usual two-electron re­duction to H0 2 ~ doesn't hold. This suggests that the initial reaction is a one-electron reduction to super­oxide:

0 2 + e ^±02L

rather than the two-electron reduc­tion:

0 2 + 2e- + H 2 0 H 0 2 - + OH-

Also supporting the one-electron reduction equation is an analysis of the dropping mercury electrode polarogram of the aerated DMSO solution. Two waves were observed (the second of which varies in dif­ferent experiments) which may re­flect differences in the level of acidic impurities in the solvent. The slope of the plot (E vs. log id — i/i) for the rising portion of the first wave is 0.070 volt. This agrees more closely with the predicted slope for a one-electron reduction (0.059 volt) than

with that of a two-electron reaction (0.030 volt).

Moreover, when the Cyanamid sci­entists added phenol (a proton source) to aerated DMSO, the first oxygen reduction process became a normal two-electron process:

0 2 + C6H5OH + 2e - -> H 0 2 - + C 6 H 5 0 -

Preparative. Dr. Maricle and Dr. Hodgson substantiated the electro­chemical data by independent product identification. They used preparative-scale reductions to make K0 2 , a known superoxide. Since the superoxide anion is paramagnetic, electron spin resonance was used to study the reduc­tion product. The ESR evidence sup­ports the formation of superoxides without leading to a definite identifica­tion of the species produced.

The two scientists speculate that electrolytic generation of the super­oxide anion might lead to a variety of new superoxide salts. The cation in­volved need not be derived from a strongly reducing metal, as is true in usual methods of preparing well-known alkali metal superoxides. In principle, any salt may be prepared as long as the cation is nonacidic and is not reduced by 0 2

_ . Attempts to prepare several new superoxides are under way.

One-Electron Process Is Quasi-reversible

These cyclic voltammograms support the conclusion that the first oxygen reduction process in aprotic solvents is a quasi-reversible, one-electron reduction (top curve) and that addition of a proton source converts the reduction to a normal two-electron process (lower curve). In the one-electron process (aerated dimethylsulfoxide, O.lM in tetrabutylammonium perchlorate, platinum electrode), the potential separat­ing the cathodic and anodic peaks is 0.19 volt. The reduction is in the quasi-reversible category 02 + e ~^± 0 - 2 . Adding phenol shifts thé reduction peak potential anodically (from —0.88 to —0.84), the 0 - 2 oxidation peak disappears, and a new oxidation peak appears at 0.15 volt. Phenol addition converts the first oxygen reduction to 02 + C6H5OH + 2er - » HO"2 + CeHsO"

A P R I L 12, 1965 C & E N 53

Electrical Discharge Aids Synthesis Laboratory work may shed new light on role of porphine-like molecules during Pre-Cambrian evolutionary period

149TH ACS NATIONAL MEETING

Physical Chemistry

Chemists at the University of Detroit have synthesized α,β,γ,δ-tetraphenyl-porphine (TPP) from an aqueous sus­pension of pyrrole and benzaldehyde. Dr. Anton Szutka and Ronald H. Radzilowski (now at the University of Michigan, Ann Arbor) produced elec­trical discharge between an electrode (connected to a Tesla coil) and the surface of the aqueous suspension to accomplish the synthesis. In one set of experiments, they used a reductive atmosphere; in another, they applied an oxidative atmosphere.

The study was third in a series of porphine syntheses to shed light on the probable role of porphines during chemical evolution in the Pre-Cam­brian period.

The Detroit chemists exposed the samples to electrical discharge in semi-darkness for two and four hours. The reductive atmosphere consisted of methane, ammonia, and hydrogen, with water and organic vapors. The oxidative atmosphere was air. Tem­perature during the experiments varied between 40° and 60° C ; pH changed between 4 and 6.

After electrical discharge treatment, they stored the samples in darkness up to 100 days. During storage, the sam­ples were agitated.

The Detroit scientists identified TPP from the samples by:

• Separation of the compound by thin-layer chromatography.

• Comparison of the visible spec­trum of the free base with that of the reference TPP.

• Comparison of the visible spec­trum of the zinc chelate of the base with that of the reference TPP.

They calculated yield from the known value of molar extinction co­efficient of TPP.

The two scientists find that electri­cal discharge for two hours in a reduc­ing atmosphere gives the sample latent ability for synthesis during extended storage. Dr. Szutka thinks that this

ability is provided by autocatalysis— the system is self-perpetuating.

Exposure to electrical discharge for two hours in an oxidative atmosphere is also conducive to autocatalysis, he says. But the rate of synthesis is lower in this case, he adds. And four hours of exposure to electrical discharge in oxidative atmosphere just about pre­vents synthesis by autocatalysis.

Intermediate. Dr. Szutka thinks that the synthesis of TPP proceeds through the formation of a labile in­termediate which can be easily de­stroyed by longer exposure to electrical discharge in an oxidative atmosphere. Four hours of exposure apparently de­stroy most of the intermediate, he concludes.

Dr. Szutka, who was born and raised in the Ukraine, believes that his syn­thesis of TPP by electrical discharge

provides evidence for hypotheses of chemical evolution advanced by others. Four years ago, Dr. Melvin Calvin of the University of California (Berkeley) suggested that if iron porphyrin struc­tures turn out to be better catalysts than iron itself for the abiogenetic syn­thesis of more complex molecules (con­taining tetrapyrrole ring) from simple (primitive) molecules, then the proc­ess becomes self-perpetuating. His ex­periments, Dr. Szutka believes, prove that porphine-like substances can be autocatalytic. Therefore, they can be effective in abiogenesis of complex molecules.

The Detroit scientist has been work­ing in the abiogenesis of porphine-like substances since 1957. His previous investigations included studying the synthesis of these compounds by gamma, visible light, and ultraviolet light irradiation.

Dr. Szutka believes, as do others, that the primeval atmosphere on earth consisted of methane, ammonia, water, and hydrogen, and hence was reduc­tive in character. At some time in the Pre-Cambrian era, it started to change into an oxidative atmosphere, owing to

Autocatalysis Increases Tetraphenylporphine (TPP) Yield

Samples made by intermixing 2 ml. of pyrrole, 4 ml. of benzaldehyde, and 4 ml. of distilled water were exposed to electrical discharge for two and four hours. In one experiment, a reductive atmosphere was used; in the other, air was introduced to the sample. In a separate (control) run, no discharge was applied. The yield of tetraphenylporphine from equal amounts of samples was studied as a function of storage time after electrical discharge. Electrical discharge in a reductive atmos­phere seems to give the system an autocatalytic, self-perpetuating nature, explains Dr. Anton Szutka; after a slow start, the yield rises rapidly. If an oxidative at­mosphere is applied, the yield increase with time is lower, and four hours of ex­posure reduces the yield increase to almost zero

54 C & E N A P R I L 12, 1965

Dr. Anton Szutka Porphine synthesis in evolution

the accumulation of molecular oxygen formed by the photolysis and radioly-sis of water vapor. The action of UV radiation and electrical discharges on molecular oxygen produced ozone in the atmosphere which shielded the earth's surface from short (high-energy) UV radiation. Also, photol­ysis and radiolysis of water vapor pro­duced large quantities of hydrogen peroxide which could destroy the more complex organic compounds.

The Detroit scientist subscribes to the theory that a vital need existed during the chemical evolutionary pe­riod for a compound that would:

• Utilize visible instead of UV radia­tion for the continuation of chemical evolution to more complex compounds.

• Destroy the accumulated hydro­gen peroxide.

The metalloporphines, role in chem­ical transformations (such as electron transfer) is well known. They are colored substances, hence are capable of absorbing visible light and utilizing this energy for chemical reactions. And metalloporphines are effective catalysts for decomposing hydrogen peroxide to water and oxygen.

Dr. Szutka feels his work adds proof to the concept that porphyrins or porphine-like substances could be syn­thesized from simple compounds which were available during the chemical evolutionary period. These complex materials, however, were vulnerable to high-energy solar radiation and electrical discharges. Therefore, they had to be protected some way. He thinks that they were buried deep in the oceans to survive.

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