April 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
Empirical tests-temperature of ethylene evolution, temperature rise with water, and colors with isophorone and with alcoholic methyl orange-are described as useful in classifying typical commercial products. ACKNOWLEDGMENT
Acknowledgment is made to E. H. Siegler and%. F. Smith of t h e Bureau of Entomology and Plant Quarantine, and t o J. B. DeWitt of the U. S. Fish and Wildlife Service, for their work on t h e biological aspects of these products. Results of their investigations are reported elsewhere. LITERATURE CITED (1) Arbuzov, A. E., and Arbuzov, B. A., J . pra&. Chqm., 130, 10332 (1931); Ber., 65, 195-9 (1932). (2) Balarev, D., 2.anorg. Chem., 88,145 (1914). (3) Ibid., 99, 191 (1917). (4) Bronson, T.E., and Hall, S. A., Am. Chemicals.. 1.. 19 (1946) . , (5) Cavalier, J., Compt.rend., 142,885 (1906). (6) Clark, E. P., “Semimicro Quantitative Organic Analysis,” pp. 68-72,7842, New York, Academic Press, 1943. (7) Clermont, P, de, Ann. Chim., 44,330 (1855). (8) Fleitmann, T.,and Henneberg, W., Ann., 65,304-34 (1848). (9) Hall, 8. A., 77.8. Dept. Commerce, OTS,PB. 252 (1945). (10) Jacobson, M., and Hall, S. A., Anal. Chem., to be published. (11) Jones, W. J., Davies, W. C., and Dyke, W. J. C., J . Phys. Chem., 37, 583-96 (1933). I
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(12) Kilgore, L. B., Soap S a n k Chemicals, 21, 138,169 (1945). (13) Ludvik, G. F., and Decker, G. C., J . Econ. Entomol., 40, 97-100 (1947). (14) McCombie, H., Saunders, B. C., and Stacey, G. J., J . Chem. SOC., 1945,380-2. (15) Nylbn, P., 2. unorg. Chem., 212, 182-6 (1933). (16) Partridge, E. P., Hicks. V.. and Smith. G. W.. J . Am Chem. Soc.,63, 454-66 (1941). (17) Rakunin, M. A,, and Arsenyev, A. A., J . Russ.Phys. Chem. Soc., 53,376-7 (1921) ; Chem-Ztg., 47,195 (1923). (18) Roark, R. C., U. S. Dept. Agr., Bur. Entomol. and Plant Quarantine, E-721 (1947). (19) Rosenheim, A., and Pritze, M., Ber., 41,2708-11 (1908). (20) Schrader, G. (to I. G. Farbenindustrie) German Patent 720,577 (1942) (vested in Alien Property Custodian) U. S. Patent 2,336,302 (1943). (21) Siegler, E. H., and Hall, S. A., J . Econ. Entomol., 40, 722-4 (1947). (22) Smadel, J. E., and Curtis, F. J., U. S. Dept. Commerce, OTS, P B 240 (1945). (23) Smith, F. F., Fulton, R. A., Lung, P. H., and Brierley, P., Florists’ Rev., 99, 31-55 (1947). (24) Snell, F. D., and Snell, C. T.,“Colorimetric Methods of Analysis,’’ Vol. 11,p. 24, New York, D. Van Nostrand Co., 1937. (25) Thurston, J. T., U. S. Dept. Commerce OTS,PB 60890 (1946). (26) Wagner-Jauregg, T., and Griesshaber, H., Ber., 70B,1-11 (1937). (27) Woodstock, W. H., U. 6. Patent 2,402,703 (1946). R E C E I V November ~D 22, 1947.
Propellents for Low-Pressure Liquefied Gas Aerosols R . A. Fulton Bureau of Entomology and Plant Quarantine, United States Department of Agriculture, Beltsville, M d .
A study has been made of a number of mixtures of lique6ed gases as low-pressure propellents suitable for use in liquefied gas aerosols. They include chloro- and fluoroderivatives of methane and ethane such as methylene chloride, dichlorodifluoromethane (Freon 12), difluoroethane (Genetron loo), and monochlorodifluoroethane (Genetron 101).
R
ECENTLY there has been considerable interest in the development of low-pressure aerosol formulas (1, 3 ) with the same efficiency as those using dichlorodifluoromethane (Freon 12) as the propellent. The high-pressure formulas in general use require a special container t o meet regulations of the Interstate Commerce Commission. The containers approved for aerosol use are ICC 9 (a refillable container) and ICC 40 (a nonrefillable container). The manufacture of these containers is a n expensive process and increases the cost of the insecticide. Can manufacturers are now (2) developing low cost containers for use with reduced-pressure formulas. Most of t h e aerosol formulas in use contain 2% pyrethrum extract (20% pyrethrins) and 3% DDT. These formulas were thoroughly tested for the armed forces, and at the close of hostilities, containers bearing commercial labels appeared on the market. The propellent gas i n all the so-called high-pressure containers is dichlorodifluoromethane (Freon 12). This liquefied gas exerts a pressure of approximately 85 pounds per square inch gage at room temperature. If the pressure of the aerosoI formuIa is reduced t o below 25 pounds per square inch at 70 O F. an approved ICC container is not required. Tariff No. 4 of the Interstate Commerce Com-
mission, par. 300, defines a liquefied gas as one exerting a total pressure exceeding 25 pounds per square inch at 70” F. An exemption request filed with the Interstate Commerce Commission t o permit a n aerosol formula with a gage pressure not exceeding 40 pounds per square inch a t 70 ’ F. t o be used in light containers was granted July 28, 1947. A number of combinations of solvents and liquefied gases were studied t o determine the pressure characterization of the resulting solution. Several combinations of liquefied gases were found t o be effective as propellents. However, some did not produce aerosols which would meet all requirements of the U. S. Department of Agriculture for acceptable formulas. The more effective of the combinations tested were as follows: trichlorofluoromethane (Freon 11) and dichlorodifluoromethane (Freon 12); methylene chloride and dichlorodifluoromethane (Freon 12); pentane, Freon 11, and Freon 12; deodorized kerosene (Deobase) and Freon 12; propane and methylene chloride; methylene chloride, Freon 12, and carbon dioxide; 1,l-difluoroethane and Freon 11; and l,l,l-chlorodifluoroethaneand Freon 12. Combinations of Freon 11and Freon 12 were tested in a number of low-pressure formulas, 25 t o 40 pounds per square inch a t 70’ F., containing pyrethrum extract and DDT in various ratios, and the resulting aerosols appeared t o be satisfactory. Freon 11 was a better solvent for DDT than Freon 12, and the amount of auxiliary solvent, such as cyclohexanone and unsaturated hydrocarbons, could be reduced. With mixtures of Freon 11 and Freon 12 it was necessary t o avoid the use of the high-boiling fractions of t h e unsaturated hydrocarbons which caused such mixtures t o separate; this increased the vapor pressure in proportion to the amount of solvent added. ’
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INDUSTRIAL AND E N G I N E E R I N G C H E M I S T R Y
Methylene chloride plus Freon 12 constituted a satisfactory propellent. A 50-50 mixture of the two liquids gave a vapor pressure of 41 pounds per square inch a t 70” F., and after the addition of the pyrethrum extract, DDT, and solvents, the vapor pressure of the solution was approximately 37 pounds per square inch a t 70” F. Less solvent was required for the DDT when methylene chloride TT-as used instead of Freon 11. Pentane was incorporated with the mixture of the two Freons t o lower the vapor pressure, but there appeared t o be no advantage in its use because of its poor solvent properties. Deobase was used to lower the vapor pressure of Freon 12. Approximately 70y0was necessary t o reduce the pressure below 40 pounds per square inch gage, and the resulting mixture was oily and produced a very coarse mist. Propane (15yo)plus methylene chloride (85%) made a good propellent for aerosols, but a fire hazard could be caused by the stratification of the two vapors. Carbon dioxide added to methylene chloride containing approximately 5% Freon 12 increased the pressure of the solution. The high percentage of methylene chloride eliminated the necessity for auxiliary solvents. However, if the carbon dioxide is lost by faulty mechanism before the contents are used, the performance of the remaining portion of liquid will be unsatisfactory.
Vol. 40, No. 4
1,l-Difluoroethane added t o Freon 11 for use as a propellent required the use of auxiliary solvents. l,l,l-Difluorochloroethaneand Freon 12 formed a satisfactory propellent with auxiliary solvents to hold the D D T in solution. A number of possible propellents for lon--pressure aerosols will produce satisfactory insecticidal aerosols. I n developing new formulas it is necessary t o make a thorough study of the complete formula in regard to compatibility, pressure characteristics, and action on the valve mechanism. I n the production of an effective low-pressure aerosol the use of a release device suited t o the particular formula will be a requirement. LITERATURE CITED (1) Goodhue, L. D., Schulte, F. S., and Wilkins, P. W., Chem. Ind., 60, 602-4 (1947). (2) Peterson, H. E., “Low Pressure Aerosols,” Bull. 14, Continental Can Co., 1947. (3)
Rhodes, M7, W., and Goodhue, L. D., Soap Sanit. Chemicals, 23, NO. 10, 122-3, 151 (1947).
RECEIVED S o v e m b e r 22, 1947. .I portion of this research was conducted as p a r t of a programsupported by transfer of funds from the Office of Quartermaster General, U. 9. Army, to t h e Bureau of Entomology a n d Plant Quarantine.
Surface Active Agents in Foliage S Frank Wilcoxon and R . L. Morgan American Cyanamid Company, Stamford, Conn. Surface-active agents are used i n . foliage sprays to render powdered solids wettable, or to promote emulsification. They increase the tendency of the spray to wet the leaves and insects. Their presence usually decreases the amount of actual deposit, because of increased runoff. Their effect on rain resistance is variable, and there is often an optimum concentration for best results. The effectiveness of contact sprays is increased by surface active agents, but that of residual type sprays may be increased, decreased, or not affected depending on materials and concentrations used. The spreading coefficient is a fairly satisfactory measure of wetting tendency; whereas the surface tension of the spray is inadequate for this purpose. The value of addition agents in promoting rain resistance is best determined by actual rain or washing tests.
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UKGICIDES and insecticides are generally applied to foliage in the form of aqueous emulsions or suspensions, or as dusts. It is a fact, however, that leaves of many species, as well as the integument of insects are not readily wetted by water. Moreover, water, on account of its high surface tension, appears t o be unable to penetrate small capillaries such as the tracheal system of insects. For these reasons entomologists and plant pathologists have for a long time been interested in surface active agents which could be added to a spray suspension or emulsion to modify its physical properties. There are at least three ways in which such agents affect the spray. I n the preparation of the spray, they are used to form an emulsion in the case of a liquid toxicant, and to render a powder wettable in the case of a solid toxicant, When the spray is applied to leaves or fruits, surface active agents may influence the wetting and spreading power of the spray with a consequent change in effectiveness. Finally, where it is desirable to maintain a protective coating on leaves or fruits for a considerable
period of time, the presence or absence of surface active agents may affect both the amount of initial deposit per unit area, and its resistance to rain and weathering, Early work on addition agents t o sprays stressed the importance of lowering the surface tension of the spray fluid to obtain good netting, but as early as 1912, TTermoreland Dantony ( I S ) concluded that surface tension of the spray was not the sole criterion of netting poxer; they observed that two diffcrent sprays of equal surface tension might exhibit diffe1en.t wetting properties for different species of leaves, whereas two diffcrent sprays with widely different surface tension values wetted the leaves of a given species equally well. SPREADIhG COEFFICIEST
The work of Harkins and others (6) on the spreading of one liquid over another has led to the concept of the spreading coefficient as a measure of spreading tendency. This is simply the diffeience between the vork done in separating one liquid from another to produce 1 sq. em. of each, and the work done in separating the first liquid from itself to produce 2 sq. em. of surface. I n the first case the work is TL, TLz = TLIL2, and in the second case the work is ~ T L ~The . difference TL2- TL, = TLiL,expresses the spreading coefficieiit in terms of the surface tension of the two liquids and the interfaoial tension between them, all quantities accessible t o measurement. I n the case of an aqueous liquid spreading over a solid surface, presumably, a similar relation would hold, but the only quantity susceptible t o measurement is the surface tension of the aqueous liquid. However, if the aqueous liquid meets the solid a t a definite angle of contact, the spreading coefficient may be expressed in terms of the surface tension of the liquid and the cosine of the coniact angle is expressed by the formula: -S. C. = TLI(cos. 8 - 1). Many attempts have been made to determine the spreading coefficient of spray liquids on the surface of leaves and insects by measurement of contact angles ( l a , 16). Difficulties are
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