RESEARCH
at 10,1 microns. This band, tentatively assigned to cyclic structures, is probably cyclopentane or cyclohexane rings, says Williams. This b a n d does not a p p e a r if t h e polyethylene is irradiated in a molten state at 140° C , a n d then cooled to room temperature. End linking also apparently changes the polyethylene crystallinity on cooling after melting. Material irradiated at room temperature has no change in crystallinity with irradiation up to 10 1 5 m.e.v. p e r gram, says Williams. B u t if a sample is irradiated, heated, a n d cooled, a definite decrease in crystallinity results. Williams, Dole, and H . Matsuo d e rived a relation between increase of amorphous content and number of cross and end links formed b y irradiation. From it, they estimate t h a t t h e degree of disorder introduced per branch is about 30 methylene groups.
Wineries OK ion Exchange Clarity, color, and flavor of more and more wines a r e being preserved by treatment with resins
H. Matsuo ( left ) and T. F . Williams of Northwestern find that vinyl unsaturation in irradiated linear polyethylene disappears at a r a t e proportional to concentration
End Linking Polyethylene C h a i n - e n d vinyl u n s a t u r a t i o n in l i n e a r p o l y e t h y l e n e cross links with g a m m a i r r a d i a t i o n EVlDENCE
THAT
RADIOSENSITIVE
GROUPS in high polymers can disappear by a first order concentration relation comes from work of T. F . Williams, Malcolm Dole, a n d coworkers at Northwestern. They find that gamma radiat i o n causes vinyl unsaturation at one end of a linear polyethylene chain to disappear (cross link) at a rate proportional to the unsaturation concentration. Describing t h e group's work to the A C S Division of Physical and Inorganic Chemistry in San Francisco, Williams says that vinylidene unsaturation in a l o w density polyethylene and vinyl unsaturation in a Ziegler-type polyethyle n e disappear similarly. The relation p r o v e d interesting for t h e Ziegler-type material because it contains less initial vinyl unsaturation than does t h e linear polyethylene they tested. # End Linking. Williams says the 42
C&EN
MAY
5,
1958
unsaturation disappearance mechanism could not be correlated with known direct effects of irradiation, such as hydrogen evolution, or by isomerization to another t y p e of unsaturated group. The possibility of free radical reactions involving addition to unsaturated groups also appears unlikely because no dose rate effect on vinyl decay results, he adds. Furthermore, there is evidence that the free radicals produced are frozen in the crystalline matrix. However, Williams, Dole, and coworkers suggest one possible mechanism. Irradiation energy may excite the end vinyl group to a biradical. It, in turn, then reacts with a neighboring chain to form an e n d link. Williams theorizes the latter reaction occurs with a very low activation energy. W h e n they irradiate Phillips Marlex50 a t room temperature, the infrared spectrum reveals a n e w absorption band
USE
O F ION EXCHANGE resins to
in-
crease t h e stability of wines is making increasing headway. Although the idea of applying ion exchange methods in wine making is not new, it gained relatively little acceptance until fairly recently. Now Wente Brothers Winery in Livermore, Calif., a n d a number of other wine producers are relying on this technique to help preserve t h e clarity, color, and flavor of their products. This use for ion exchange got a b i g boost with recent rulings of t h e Alcohol and Tobacco Tax Division of t h e U. S. Treasury Department and t h e California Department of Health. They have given the go-ahead to treating certain wines by various ion exchange resins. Until recently, government agencies have had a wait-and-see policy on this development o n the grounds that it might cause fundamental changes in the character of wines (C&EN, Jan. 13, page 4 6 ) . Many of t h e major wine companies now h a v e development programs under w a y on the use of ion exchange resins. They also want to be sure t h a t this t y p e of treatment will h a v e no ad-
RESEARCH verse effects on the flavor, aroma, and other properties of wines. In this industry, with its long-standing traditions, n e w operating techniques are often accepted only v e r y slowly. In the past few years, ion exchange resins have b e e n improved to make them more suitable for use by the wine industry, Β Ν . Dickinson of Chemical Process told t h e ACS Division of Agri cultural and F o o d Chemistry in San Francisco. I m p r o v e d methods of ap plying these resins and a n increasing knowledge of the precautions to be taken to retain the distinctive quality of wines h a v e helped promote their use. According to several recent stu dies, taste experts frequently find that wines h e a t e d b y ion exchange taste as good as, if not better than, wines treated in t h e conventional way. • Sources of Instability. One of the biggest problems in wine making, espe cially with w h i t e wines, is that, after extended chilling, potassium bitartrate precipitates. T h e wine develops an un sightly haze. T h e conventional way to minimize this is for the wine maker to store the w i n e s for long periods in large refrigerated vats and then filter out the precipitated bitartrate. This requires large storage space, expensive cooling, and also delays production. A simpler procedure is to treat the wine with a cation exchanger such as the Chemical Process's Duolite C-3 or C-25, says Dickinson in a report coauthored with G. F. Stoneman. These resins can b e either in the hydrogen or sodium form a n d may b e used either in a continuous column or batchwise. Sodium cation exchangers of the sul fonic acid t y p e convert the bitartrate salts into t h e relatively soluble sodium form. A sodium exchanger also reduces somewhat t h e acidity of wines. A hydrogen cation exchanger, on the other hand, increases the acidity of wines. It also converts the bitartrate salts into t h e more soluble acid. Some wine treatments call for the combined use of both sodium and hydrogen cat ion exchangers. • Added Problems. Other sources of instability in wines can be partly or completely eliminated by ion exchange. Among these are heavy metals such as copper and iron, which form precipi tates with tannâtes and phosphates. Ion exchange resins or resinous absorbents can also remove proteins, tannins, and oxidized colored material that would otherwise precipitate on chilling.
CH 3 CH 3 I
H3C
CH 3 1
Fe(CO) 5 -+• m -+" H I C C I I CH 3 CH 3
CO
hι/
Fe—CO H3C CO
When iron pentacarbonyl and dimethylacetylene are exposed to sunlight, new carbon-carbon bonds are formed; iron tricarbonyl-duroquinone complex results
N e w Mechanism of Bond Formation Quînone-iron carbonyl complex gives new synthetic route a n d new explanation of some Reppe reactions EVIDENCE
FOR A NEW MECHANISM o f
carbon-carbon b o n d formation, a n e w organometallic complex, a new m e t h o d for preparing quinones and h y d r o quinones, and a simple synthesis for benzene rings labeled in the 1,4 position—these are the outcome of a n experiment involving the action of sunlight on a mixture of iron pentacarbonyl and dimethylacetylene. Heinz W. Sternberg, Raymond Markby, a n d Irving W e n d e r of t h e U. S. Bureau of Mines told the Division of Inorganic Chemistry at the ACS meeting in San Francisco that they tried the experiment in an effort t o d e termine whether t h e reaction of iron pentacarbonyl with acetylenes was analagous to that of cobalt octacarbonyl. Since this iron compound is practically insoluble in organic solvents, they formed it in situ by exposing iron pentacarbonyl to sunlight. An analysis of t h e reaction p r o d u c t showed, to their surprise, that one mole of iron pentacarbonyl reacted with t w o moles of dimethylacetylene. T h e infrared spectrum showed two types of carbonyl groups: terminal carbonyls such as those in iron pentacarbonyl and ketonic carbonyls such as those in quinones. The authors postulate t h a t two moles of dimethylacetylene join under the reaction conditions with t w o carbonyl groups to form a new ligand—
duroquinone. This then forms a complex with iron tricarbonyl. T h e y find strong support for this postulate in their finding that t h e complex, w h e n treated with hydrochloric acid, decomposes to one mole of durohvdroquinone and three moles of carbon monoxide. Furthermore, w h e n the complex is exposed to radioactive carbon monoxide for two weeks and then decomposed, all of the radioactivity is found in the evolved carbon monoxide. T h u s , they reason, only the terminal carbonyl groups can exchange, not those in the quinone ring. W h e n the iron complex is exposed to air, the iron tricarbonyl unit is oxidized, a n d duroquinone is formed in high yield. H e r e , then, is a new synthesis for substituted quinones and hydroquinones. Also, benzene rings labeled in the 1,4 position can be obtained easily in marked contrast to their laborious preparation by other methods. Just expose radioactive iron pentacarbonyl (readily obtainable) and a suitable acetylene to sunlight and acidify the reaction product. W h a t , then, is the structure of the new complex and what is the type of bonding involved? Fortunately, a theory is ready at hand to fit this particular case. T w o years ago, studies based on molecular orbital theory led Longuet-Higgins and Orgel to predict MAY
5,
1958
C&EN
43
