H. W. Schneiderl
Varniton Company North Palm Springs, California 922.58
A New, Long-Lasting Luminol Chemiluminescent Cold Light
O n l y a few organic and inorganic compounds are known to emit appreciable amounts of visible cold light. Very few chemicals are reasonably efficient in producing cold light for prolonged periods of time (longer than one hour) and a t present there are about five chemiluminescent reactions which are outstandingin their performance as follows 1. The oxidation of luminol (3-aminophthalhydranide) (5amino-2,3-dihydro-l,4 phthalaeinediane) 2. lucigenin 3. oxalyl peroxide chloride and its esters 4. tetrakis-(dimethylsminoethylene) 5. calcium disilicide (CrsSi.)
Of the five chemicals, luminol has been considered one of the most valuable light producers. Luminol has been known since the year 1928 when H. 0. Albrecht first studied its reactions and wrote a thesis on it (1). I t has the following formula
&l& II
0
Ever since its discovery by chemists in Germany, much effort has been put forth t,o extend the longevity of this very beautiful and striking chemiluminescent light producer. I n 1934 a practical method of synthesis for luminol was published by E. H. Huntress and co-workers and luminol has been manufactured by this method with some modifications for over 28 years (2). Its primary sale has been to high schools and colleges for demonstration in chemistry courses under the subject of oxidation in which an oxidation reaction is shown that produces light without heat. However, because of its limited longevity, no commercial applications for luminol have ever been found. The normal method of demonstrating luminol is in a water solution containing approximately 0.1 g luminol per liter of water with 10 ml of 5% sodium hydroxide and 10 ml of 3% hydrogen peroxide. Small amounts of iron, copper, or cobalt compounds act as catalysts and initiate a brilliant display of light. The ferricyanides are also efficient light starters for this reaction. When mere traces of copper, cobalt, or iron compounds are present as contaminants in chemicals, water, or on
the surface of glassware, an extremely weak light in the presence of hydrogen peroxide is produced which is just visible to the eye for many hours. However, small amounts (0.050 g) of organo-cobalt compounds or dry hemin produce a very rapid decomposition of hydrogen peroxide in the presence of luminol which results in the liberation of cold light. But the energy of the luminol reaction is still given off in about two minutes, and no more chemiluminescence can be generated. Over the past 40 years, numerous attempts have been made, especially by the Russians, to produce derivat'lves of luminol in hopes that these derivatives would lead to the key of increased longevity for luminol chemiluminescence. Japanese chemists attacked this problem from the direction of controlling light longevity by using the proper catalyst to start a very slow oxidation of the 3-aminophthalhydrazide-peroxide reaction. As a result of their excellent work, many organic derivatives of copper, cobalt, nickel, and iron were prepared and tried as catalysts. However, no increase in luminol chemiluminescence longevity has ever been described in the literature as a result of any new derivative or new catalyst. Basic Studies of the Luminol Reaction
For a number of years E. H. White of the Johns Hopkins University chemistry department and his students have carried out brilliant investigations concerning the theory of the formation of luminol chemiluminescence. E. H. White writes the following concerning the mechanism of the luminol reaction (3) Practically the only facts available for a discussion of the mechanism are the following: (1) oxygen is required (6); ( 2 ) the anion of luminol is the reactant (K, for luminol is 10-6); (3) free radicals are involved; and (4) nitrogen is a product of the reaction. The requirements for radical intermediates is based largely on the observrttion that radical chain stoppers inhibit the chemiluminescence (5b, 23, 26, and on experiments suoh 8s the following: a basic aqueous solution of luminol (pH about 11) is dark bath a t room temperature and at 75°C. When a small amount of a free-radical-forming compound such as azoisobutyronitrile, or better, benzoyl peroxide is added to the hot solution, light is emitted. The emission meximum is a t the same wave length (430 mu) as the emission from the hydrogen-peroxidebased chemiluminescence. Oxygen gas is required for light production, and this system is therefore very similar to the oxygenferricyanide system mentioned earlier. Our working hypothesis for the chemiluminescence in the water systems, based on these facts, is given [below].
Paper presented s t Internrttional Chemiluminesoenee Conference. Desert Hot Sorines. California. March 17-19. 1969. (Information presented is pert of a patent pending, U S . Patent Office, January, 1969.) 'Present address: 2827 Corning St., Apt 4A, Los Angeles, California 90034.
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C-N-0-4 C-N-H
11
NH,
0
SEVERAL, UNKNOWN STEPS
h.
+
PmdUCtS
A major change in the ehemiluminescent reaction ocours, however, when certain weakly acidic, highly polar orgmic solvents are used; only luminal, oxygen, and a hase are reqrdred, and t,he light emission is superior to that observed in water. Dimethyl sulfoxide is the best of the mlvents that we have tested and dimethyl farmamide is the second best. The advantage of wing solvents of this l,ype is that b a s e stronger than hydroxide ion can he used. We normally use l-butoxide ion (prepared from the alcohol and potsssium metal); with this base, the dianion of luminol is formed and, as will be shown later, this ion can react directly with oxygen. Luminol plus O2
+ base
-
Light
The reaction is thus similar in general outline to a number of other chemiluminescent reactions . . . These equations illustrate the interesting fact that in most, if not all, ehemiluminescent and bioluminescent reilctions at room temperature, oxygen is a reactant. The ground state of oxygen is a triplet state, and bhe significance of the oxygen requirement may he that in these eases, adducts of oxygen and the organic molecules are formed with no reversal of an electron spin; i.e., the adducts may be formed directly in a triplet excited state.
oxygen is used rapidly; because of the presence of caustic, this then becomes a way to produce nearly pure nitrogen. I t was also noted that lowering the temperature to 13°C did not stop the chemiluminescence reaction, but that at lO0C no light was visible to the eye. I n order to increase the light brightness of the normal blue light it is necessary to add small amounts of fluorescein and then approximately 500 times the regular brightness was achieved. The color was changed to yellow. An attempt to use rhodamine "B" and many other organio coloring agents failed to produce other colors because none of these coloring substances are able to resist alkaline oxidation conditions. Conditions for Forming Luminol Dianion and Peroxides
It is fortuitous that the need for an ionic reacting medium for luminol chemiluminescence was recognized. A demonstration of the reaction will show that an aqueous caustic solution requires time to initiate conditions for the triplet excited state of oxygen which can react with the soluble dianion of luminol. This takes about two minutes. A system that constantly forms and replenishes soluble luminol peroxide derivatives will lead to light longevity as follows
.
As a result of E. H. White's work in identifying all the important chemical intermediate products involved in the luminol chemiluminescence, it is now possible to pinpoint the exact chemical compositions responsible for emitting cold light (4). Following White's observations of the efficacy of organic solvents in increasing light emission our lahoratory tests indicated quickly that it was only necessary to add a saturated sodium or potassium hydroxide solution to a DMSO luminol solution a t room temperature, and to shake the solution vigorously for 1-2 minutes to initiate the chemiluminescent reaction. It was then found that when air (0%) is admitted slowly through a sealed Mylar plastic bag, the system released light from the initial luminol concentration for as long as 30 days. The liberated light progressively decreases in brightness until on the 30th day the brightness is equivalent to that of light given off by bioluminescent bacteria.
When up to 5% water DMSO solution was employed, excellent results for the chemiluminescent reaction were obtained, but as the water concentration increased towards 20%, the chemiluminescent light became quenched. Water concentrations above 20% also quench light output completely. Sodium or potassium hydroxide react with luminol in a regulated DMSO water solution to form the dianion of luminol as follows
Some Reaction Properties
When'the DINSO, luminol, water, and caustic solution are shaken in the presence of oxygen from air, an oxidation reaction produces considerable bright bluegreen light and as the reaction uses up the dissolved oxygen, light intensity decreases in about one minute to a low level resembling the light output of micro-organisms as noted above. This low level light is continuously produced at the air-liquid interface for many days. Passing large amounts of air or pure oxygen into the fluid quickly quenches the light and when the excess oxygen has dissipated, light is again evolved. Even heating the fluid to 100°C does not prevent the normal reaction of light generation from taking place. The light, however, does go out faster because all the 520 / Journal of Chemical Education
The Chemiluminescence of Luminol in DMSO
I n the presence of air, the entire fluid bursts into light. Best results are achieved by using about five milligrams of luminol per ml of fluid. The exact number of light minutes given off from each milligram of
luminol, either when the solution is agitated or quiescent, is easily measured. Laboratory tests have shown that when the concentration of luminol goes to 10 mg/ml of liquid medium, the reactivity of luminol with air is extremely rapid and all oxygen in the container is quickly used up, leaving almost pure nitrogen. A superior light producing luminol derivative, 4diethyl amine phthalhydrazide has been described by Gundermann and Drawert (6). It is claimed that this derivative is the strongest chemiluminescent phthalhydrazide compound yet produced. Although it was not tested in our laboratory, it should also give excellent results in a dimethyl sulfoxide, caustic, water solution. Similarly, improved chemiluminescence is anticipated by using dimethoxy and trimethoxy luminol derivatives as prepared by E. H. White (4). These compounds are listed as being more efficient than luminol (by 13 and 30%, respectively, in dimethyl sulfoxide). Various forms of the long-lasting luminol chemiluminescent composition can he prepared, such as a glowing inert powder made from diatomaceous earth, a paste, crayon, tape, or impregnated fabric. Relationship to Bioluminescence
The chemiluminescent light produced from DMSO, water, caustic, and luminolsolution followsE. H. White's observation that in nearly all chemiluminescent and bioluminescent reactions at room temperature, oxygen is the reactant. The described DMSO composition is especially unique and extraordinary for a chemical reaction because it simulates exactly the formation of bioluminescent light. For example, it is known that certain sea dinoflagellates give off light continuously while floating in the ocean (E. N. Harvey) (6) and that their light is visible as a low level glow. When these dinoflagellates are disturbed, as when a ship passes through the waters containing them, oxygen of the air is forced into their system and they liberate a hioluminescent glow. The presently discovered dimethyl sulfoxide (DMSO) luminol composition simulates bioluminescent light production a t room temperature, and produces light under reacting conditions similar to bioluminescent organisms, hut vastly improves on nature because this system causes the liberation of light even a t temperatures as low as 13°C and as high as 100°C. I t is douhtful if any living system can produce light a t such extremes of temperature. Also i t is of interest to note that when bioluminescent bacteria are exposed to air samples contaminated with smoke, smog, toxic warfare agents, or gases such as methane, they quickly dim their lights and only recover when fresh air is admitted. Although chemists have not yet isolated the active chemicals responsible for the light produced by the dinoflagellates or luminescent bacteria, it can be demonstrated that the chemiluminescent reaction for the light production is a chemiluminescent system. A New Chemical Reacting Medium
The 2% water, DMSO, strong caustic solvent composition could be used as a medium for the synthesis of other organic compounds to make organic dyes, pharmaceuticals, and polymers with those chemicals capa-
ble of forming a mono or disodium salt soluble in the medium. Because the rate of reaction and the time of completion of the luminol reaction can he determined by measuring the light output, so in a similar way other non-chemiluminescent organic reactions fitting into this scheme could be monitored for completion; such a method should result in a 90% improvement in synthesis yields. Practical Applications for the DMSO Chemiluminescence System
The following practical applications are now possible 1. The preparation of a plastic (Mylar) package of portable cold
light for use anywhere a t any time, which does not deteriorate prior to use for many years. I t can be used under the sea, in the air a t low temperetures, and a t temperatures as high as 100°C to release light far 6 to 30 days. I t is recommended for home uses in times of power failures, in the car, for civil defense shelters; for use as a light somee in hazardous areas where flammable gsses, vapors, and stored explosives may he present. I t can be lowered into tanks of gasoline or other flammable liquids in order to inspect the tank or the fluid a t night. 2. The new light source is an ideal emergency light of flameless Draoertv for
3. 4.
5.
6.
to carry out hospital operations under a non-sparking flameless light, - . and in field medical h o s ~ i t a lmilitarv ten&; I t can be stored in public buildings, air-raid shelters, trains, aircraft, and automobiles for emergency light. As a camping light, i t prevents fires and explosions from conventional lanterns and can he set up in minutes. For night survival sea rescue in the sea or in life boats. The packaged light can be used for emergency lighting in submarines, thus eliminating the need for flashlights and the need for using the storage battery system to provide electric lieht. Since i t is possible to circulate the chemiluminescent fluid in plastic or glass tubing, the potential exists for replacing electric lighting with this system which because of its portability can be carried anywhere in the world without need for batteries, wires, and other lighfgenerating paraphernalia. The cost of making luminol can be drastically reduced and the DMSO can he recovered, thus making it entirely possible in the future to compete with electric lighting for many purposes. There is no shack hazard or failures due to corrosion, and it is not necessary to lay miles of wire to transport power for lighting. In addition, strategic metals such as copper can he saved for other uses. A brief mention of the other uses for DMSO luminol chemiluminescence follows Detects trace amounts of oxygen. Indicates the presence of an anaerobic environment for microbiologists. Useful in snow areas for night rescue work. Can be made quiescent in the event enemy aircraft approach life rescue boats. Colored light compositions for use in identifying friendly (from enemy) scuba divers. The light photographs in color easily even under water. Can be used to mark the position a t night of icebergs. Marks a position on the ocean a t night for aircraft for the purpose of fixing a spot on the sea surface, thus enabling drift measurements to be made, and therefore allows accurate estimating of sircraft height above the sea surface. Marking of enemy submarine positions during wsr time. Marking temporary landing area5 for deployment of friendly ses. planes a t night. Allowing helicopters to fly in formation a t night by in-
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dicrtting their proximity to each other without exposing them to enemy fire. Provides limited light duration for limited distances during war time to prevent the enemy from taking ~ d v a n t a g eof information for friendly planes. Does not throw a beam of light visible for long distances. Enables small boab to maintain formation without disclosing t,heir presence to the enemy. llecommended for lighting aircraft cockpits during extended night-t.ime missions h e c a ~ ~it s eproduces no eye strain when viewed for many hours. Submarine commanders could illuminate selected areas of the sea just below sea surface without being spotted by aircraft. Useful for illuminating, for short periods, remote sections of aircraft carrier lsnding decks. Plastic bags of the chemiluminescent composition, when laced on beach sands or in the ~ e r i m e t e rof a base, instantly identify persons walking on them a t night by releasing light. Useful for over-theside illumination when persons board large vessels from small boats while a t sea, because no glare blinds the person coming aboard. This chemiluminescent light is easily detected by the cadmium sulfide photo diodes, and numerow ligh6 sensitive electronic detecting circuits are possible.
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The chemiluminescent light is easily carried by the new light pipe systems and lends itself to applications where electric light is not easily used for piping to remote spots.
Chronic oral toxicity reports show that at a dosage of 1 g/kg a slight toxic effect, mainly upon the liver, with a slight toxic effect upon the kidneys, results. The acute oral toxicity report states that the test substance is Llo for 5.5 g/kg and may be classified as ''Class 111, moderately toxic." Literature Cited (1) A f i n n ~ c a H ~ . 0.. Phyrik. chem. Leiprio. 129, 321 (1928). (2) Hurrmess, E. H.,S T A N L L. ~ , N., A N D PARYER, A. S.. J. CAEI. EDUC., 84, 241 (1934). (3) WXLTE.E. H. in "Light and Life" (Editor*: MoEmor. A N D G'*ss), John Hopkins Press. Baitimor8. Md., 1961, 8. 189. (4) WXITE,E. H., ZAFIRIOU, O . , KLGI,a.H.. A N D HILL I. H. M., Chemiluminescence of Luminol: The Chemical Reaotion, Abatraots: 134th National Meeting of the Amerioan Chemiosl Society, Chicago. Ili.. Sept. 1958, p. 94p. J . A m . Chem. Soc. 86, 940 (1984); also W m n , E. H.. A N D Bonsmr. M. M.. "Chemiiumineseenee of Luminol and Related Hydrasides: The Light Emission Step." ( 5 ) G u ~ m n r m K. ~ , D., A N D DRAWERT. M . , Chemische Bcrirhle, 95, 2018 (1962). ( 6 ) H ~ n v ~F. r .N., "A IIistory of Luminesoenoe," American Philosophical Society, Independence Square, Philadel~ltia,Pa.
