Chemistry for Everyone
Mustard Gas: Its Pre-World War I History Ronald J. Duchovic* Department of Chemistry, Indiana University Purdue University, Fort Wayne, IN 46805-1499; *
[email protected] Joel A. Vilensky Department of Anatomy and Cell Biology, Indiana University School of Medicine, Fort Wayne, IN 46805-1499 In July 1917 the English troops near Ypres were fired upon by the Germans with shells which contained an oily liquid. Those who came into contact with this oil developed a few hours later symptoms previously unknown. The new chemical warfare agent caused burns on the skin that were slow to heal; it quickly penetrated clothing and it contaminated the ground. A new stage began in chemical warfare; the use of persistent chemical warfare agents of long-lasting effect. (1)
Mustard gas, the common name for bis(2-chloroethyl) sulfide, 1,1-thiobis(2-chloroethane), or β,β´-dichloroethyl sulfide (ClCH2CH2SCH2CH2Cl), is the oily liquid referred to in the quote. It is the most well-known chemical warfare agent, and one that appears regularly in the popular press because of its potential use by terrorists or by the military of rogue nations. For example, a Google search of 4500 news sources (newspapers, news magazines, broadcast media, Internet) done on March 25, 2006, for “mustard gas” covering only the previous month yielded 109 “hits”. Mustard gas was used in military conflicts throughout the 20th century beginning with the German attack on July 12–13, 1917, and ending with its use by Iraq during its war with Iran during the 1980s (2, 3). As recently as March 2004, the New York Times reported that Libya announced the stockpiling of some 23 tons of mustard gas (4). Although mustard gas, similar to most of the earlier agents used during World War I, is a respiratory system irritant, its main attraction to the German Army during World War I was its vesicant properties, which were effective whether or not the enemy used gas masks. Furthermore, a peculiar characteristic of mustard’s1 vesicancy is that its effect is delayed for at least a few hours, depending on dosage. This had both advantages and disadvantages militarily, but the disadvantages propelled the United States to develop during World War I a similar but immediately painful and more deadly vesicant, lewisite (ClC2H2AsCl2) (3). When mustard gas is described, its history is typically traced to World War I and to its use by both sides during that war. However, mustard gas was actually first synthesized almost 100 years prior to the start of World War I and the basic approaches used to manufacture it by both sides during World War I (and later) were based on methods pioneered by European chemists of the 19th century. It is likely that reports in the popular news media about mustard gas will continue to appear because it is often identified as a “weapon of mass destruction” that could be used by rogue nations or terrorists. The efficacy of mustard gas as such a weapon is certainly open to debate. However, the use of a chemical agent on a dense population of human beings clearly satisfies the term “mass”. The more central point addressed by an analysis of the history of mustard gas has two dimensions. First, knowledge of this history will equip both chemical profes944
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sionals and students of chemistry to speak with greater understanding when discussing mustard gas as a chemical warfare agent. Second, it is important that students of chemistry recognize that, very often, the basic scientific investigations leading to a weapon were undertaken long before any individual or organization had decided to build a weapon. The history of the mustard agent demonstrates this and stands in contrast to more recent history in which science and technology have been expressly focused on the development of weapons. The French Connection César-Mansuète Despretz (1798–1863), a Belgian-born professor at the Ecole Polytechnique in Paris, described some of his research at a meeting of the Commission l’Académie Royale des Sciences, which occurred in December 1822 (5). Despretz outlined his combination of sulfur dichloride and ethylene, presumably the following reaction (6, 7):
SCl2 + 2(C2H4)
(ClCH2CH2)2S
(1)
Despretz reported that the resulting malodorous liquid was viscous and was difficult to burn. He did not describe any irritating properties of the compound, which perhaps suggests that the presumed reaction producing mustard never completely occurred. However, two French chemists argued strongly in the 1930s that Despretz should be credited with discovering the compound (8, 9). Approximately 30 years later, in 1854, and again in France, chemist Alfred Riche (1829–1908) apparently repeated Despretz’s experiments (without citing him) and reported this work in an article titled, “Recherches sur des combinaisons chlorées dérivées des sulfures de méthyle et d’éthyle” (Research on the combinations of chlorine derivatives of sulfur with methyl and ethyl) (10, 11). Riche was studying the condensation products of the halogens and of halogenated sulfur compounds with methyl and ethyl radicals. In the article, Riche did not provide the details of his synthetic pathway to mustard or an analysis of any reaction intermediates. Riche also did not attribute any irritant properties to the resulting yellow liquid that he described as boiling at 185–200 ⬚C. Interestingly, Riche in 1859 prepared chloroacetone (ClCH2COCH3), another chemical agent that was used, primarily by the French, during World War I (12). The Early German Connection Albert Niemann (1834–1861) was a German chemist who died at the young age of 27 years. However, while a graduate student at the University of Göttingen he was able to isolate a white, odorless, crystalline substance from the Peruvian coca leaf that he subsequently named cocaine. This
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Chemistry for Everyone Table 1. Relative Atomic Weights of Hydrogen, Carbon, and Oxygen Scientist
H
C
O
Berzelius
1
12
16
Liebig
1
06
08
Dumas
1
06
16
work, for which he is well-known and which was submitted as his doctoral thesis, was described in the Journal of Pharmacy in 1861, the same year he died (13). Less well-known is an article by Niemann that appeared in 1860 in Annalen der Chemie und Pharmazie titled, “Ueber die Einwirkung des braunen Chlorschwefels auf Elaygas” (About the effect of brown chlorosulfide on ethylene gas) (14). In this article, Niemann, following the work of Despretz (attributing to Depretz the observation that sulfur chloride, SCl2, is converted by ethylene into an “evil-smelling . . . liquid”), describes the reaction between ethylene and the “brown” chloride of sulfur (a mixture of sulfur monochloride and sulfur dichloride). As translated, he states, The most characteristic property of this oil is also a very dangerous one. It consists in the fact that the minutest trace which may accidentally come in contact with any portion of the skin, though at first causing no pain, produces in the course of a few hours a reddening and on the following day a severe blister, which suppurates for a long time and is very difficult to heal. Great care is therefore requisite in working with this compound. (15)
Thus, Niemann was the first to describe mustard’s toxic characteristics. It should be noted that Niemann used the formulas S2Cl for the sulfur monochloride and SCl2 for the sulfur dichloride. The modern understanding of the bonding between sulfur and chlorine requires the formula S2Cl2 for the monochloride. The dichloride is not stable but readily dissociates within a few hours: 2SCl2
S2Cl2 + Cl2
(2)
Niemann was aware of the instability of SCl2, noting that it is “volatile”. He further concluded, agreeing with Woehler’s observation (16) that the reaction takes place only between the SCl2 and the ethylene gas. It appears that Niemann’s oil had a boiling point between 190 and 200 ⬚C, was completely insoluble in water, only dissolved with difficulty in alcohol, and was easily dissolved in ethers. Niemann concluded his report by presenting an elemental analysis of the products that he considered to be insufficiently pure to provide a reliable formula. He did, however, suggest the chemical formula, C4H4ClS2. The reader will note that Niemann’s empirical formula differs significantly from the modern molecular formula for mustard gas, ClCH2CH2SCH2CH2Cl. This disparity reflects the fact that in the mid-19th century there was still little agreement among chemists on appropriate values of atomic weights (masses).2 As early as 1814, Berzelius had assigned oxygen a relative atomic weight of 100 (17). In 1826 he published a table (18) of atomic weights in which oxygen was again assigned a relative mass of 100. The lack of consensus, reflecting the situation at the end of the 1830s, is illustrated www.JCE.DivCHED.org
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in Table 1 (19). Consequently, at this point in the 19th century, chemical formulas carried no meaning unless the atomic weight system utilized by a particular chemist was specified along with the formula. While many readers of these pages are well-aware of this historical perspective (20), the lack of agreement among chemists on the values of atomic weights is often not recounted in modern general chemistry texts. The emergence of the concept of the periodicity of elemental properties is usually described without reference to the lack of agreement on specific values of atomic weights. The subsequent discussions of empirical formulas and percent yields in these texts also rarely include an elaboration of this lack of agreement that is so evident in the 19th century chemical literature. Consequently, we take this opportunity to briefly elaborate on the critical meeting that led both to the emergence of the modern periodic table and to the common agreement among chemists on the values of atomic weights. In September 3–5, 1860, the First International Scientific Congress was attended by approximately 140 of the leading European chemists in Karlsruhe, Germany. The three day meeting attempted to reach a consensus about the nature of atoms and molecules and to establish a scale of atomic weights acceptable to all those in attendance. However, the Congress produced no universally accepted conclusions. The most significant consequence of the Congress was the impact of the presentation by Italian chemist Stanislao Cannizzaro on the thinking of the young chemists attending the meeting. Cannizzaro argued strongly that the hypothesis of Amedeo Avogadro provided a basis on which to develop a consistent set of atomic weights. While an increasing number of chemists (but not all!) accepted Dalton’s atomic theory, the hypothesis by Amedeo Avogadro in 1811 (21) that equal volumes of gases (at the same pressure and temperature) contain equal numbers of particles had been largely rejected or ignored by the vast majority of chemists. In 1814, Andre Marie Ampère (22) had restated Avogadro’s hypothesis. However, his attempt was no more successful than Avogadro’s initial proposal. Cannizzaro’s presentation was based on his article of 1858 (23) in which he described a much simplified approach to teaching chemistry based on Avogadro’s hypothesis. At the conclusion of the Congress, Angelo Pavesi, professor of chemistry at the University of Pavia and a friend and supporter of Cannizzaro, distributed copies of the 1858 article. The manuscript affected the thinking, in particular, of Lothar Meyer and Dimitri Mendeleev. Meyer’s text of 1864, Die modernen Theorien der Chemie und ihre Bedeutung für die chemische Statik (24) used Avogadro’s hypothesis as the basis of theoretical chemistry. This book was significant in influencing chemists to apply the hypothesis and focusing attention on the physical aspects of chemistry. The systematic approach to a scale of atomic weights that emerged in the last third of the 19th century resulted in modern empirical formulas. The Early British Connection Frederick Guthrie (1833–1886) is most known for his work in physics but in 1860 he synthesized and described the properties of mustard gas (25). Guthrie studied chemistry at University College London before pursuing additional
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studies in Germany under, among others, the chemist Robert Bunsen. In 1860 he published two articles, both entitled “On Some Derivatives from the Olefines” (26, 27). Guthrie was interested in those hydrocarbons that have equal numbers of equivalents of hydrogen and carbon, for which, ethylene is the “historical prototype”. Interestingly, he noted that ethylene combines “… with two equivalents of chlorine, bromine, and iodine…” to yield the compounds C4H4Cl2, C4H4Br2, and C4H4I2. Our modern scale of atomic weights would give the formulas C2H4Cl2, C2H4Br2, and C2H4I2. The discrepancy between Guthrie’s formulas and the modern formulas again reflects the lack of agreement among chemists on the scale of atomic weights utilized in the mid-19th century. In his article, Guthrie described the slow bubbling of ethylene in an ordinary bulb wash tube3 immersed in cold water and containing chloride of sulfur (S2Cl2 or SCl; Guthrie allowed both possibilities, while our modern understanding requires S2Cl2.) As saturation was approached in an exothermic reaction (after approximately 12 hours, using a bubbling rate of one bubble per second and 2–3 ounces of sulfur chloride), the liquid in the tube changed color from the garnet red of chloride of sulfur to the straw yellow of the bisulfide of chlorine (S2Cl in Guthrie’s nomenclature). Completion of the reaction and the removal of possible impurities required heating the wash tube bulb in a water bath to 100 ⬚C while increasing the flow rate of the ethylene for a period of one to two hours. Finally, to remove the unreacted chloride of sulfur, the bulb wash tube was cooled to 80 ⬚C, vigorously shaken multiple times with fresh water at that temperature, and then allowed to stand for an unspecified number of days in contact with caustic soda (NaOH). Guthrie’s elemental analysis allowed him to conclude that the substance produced by this reaction has the formula of C4H4S2Cl2. One should again note that this formula differs from the modern formula for mustard (ClCH2CH2)2S. He referred to this product as the bichlorosulfide of ethylene. Its smell is pungent and not unpleasant, resembling that of the oil of mustard; its taste is astringent and similar to that of horseradish. The small quantities of vapor which it diffuses attack the thin parts of the skin, as between the fingers and around the eyes, destroying the epidermis. If allowed to remain in the liquid form on the skin, it raises a blister. (26)
Guthrie further noted, consistent with the observations of Niemann, that this product is soluble in (boiling) ether but only slightly soluble in hot alcohol. It is almost insoluble in cold alcohol and “quite insoluble” in water. Finally, Guthrie argued that the product is a definite compound and does not consist of a mixture of bisulfide of chlorine and dissolved chlorine. Guthrie, in the second article, described the formation of a compound that he named the bisulfochloride of ethylene and to which he assigned the formula C4H4S2Cl (again note the variance from the modern formula). While acknowledging the observation of Niemann that ethylene and the bisulfide of chlorine (S2Cl) are virtually unreactive under “ordinary circumstances of temperature…”, the observed product was produced over a period of twenty hours in a boiling water bath. Describing this compound, he stated, “Like the 946
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bichlorosulfide of ethylene, its annoying effect upon the eyelids is very enduring.” When applied to the tongue, Guthrie noted that this substance destroyed the epidermis and caused soreness that persisted for “many days”. The properties described by Guthrie suggest that this substance is again mustard. Further, Guthrie described the liquid as pale yellow in color with a specific gravity of 1.341 at 19 ⬚C, properties that are consistent with the mustard manufactured by the British during World War I (15). The Second German Connection The German chemist Robert Bunsen, who taught Guthrie, was also responsible for stimulating a young German acting student Victor Meyer (1848–1897) to change his career path to chemistry. Meyer completed his doctoral studies at the young age of 19 years at the University of Heidelberg in 1867. Meyer described his synthesis of mustard gas while a professor at University of Göttingen in 1886, exactly 26 years after Niemann had also described its synthesis while also a chemistry professor at this same university (28). Perhaps because Meyer’s synthesis began with different reagents, it appears that he was unaware of Niemann’s work or that of Despretz, Riche, or Guthrie. Meyer was a renowned organic chemist who, with his students, published more than 300 articles during his career; many of these articles were fundamentally significant (29). Meyer’s description of his synthesis of mustard was published in the journal, Berichte der Deutchen Chemischen Gesellschaft in an article titled, “Ueber Thiodiglykolverbindungen” (About thiodiglycol reactions) in 1886 (30). In this article Meyer describes forming mustard gas by reacting ethylene chlorohydrin with aqueous potassium sulfide and treating the resulting thiodiglycol with phosphorus trichloride:
K2S + 2 ClCH2CH2OH (HOCH2CH2)2S + 2KCl
(3)
3(HOCH2CH2)2S + 2PCl3 3 (ClCH2CH2)2S + 2H3PO3
(4)
This method produced a purer product than the earlier processes (11). Meyer described mustard as being a heavy, oily fluid with a faint sweetish smell that is slightly suggestive of sulfur compounds and with a boiling point of 217 ⬚C (2). Meyer further reported in the article that the resulting oil is intensely poisonous, producing wounds that heal with great difficulty. Meyer indicated that the lesions do not appear immediately after the product is applied to the skin, but rather, only appear some hours later. Toward the end of his life Meyer, believing in the need for a comprehensive treatise on organic chemistry that did not exist in German or any other language, began work with his assistant, Paul Jacobson, on the voluminous Textbook of Organic Chemistry (31). The 1913 edition of volume 1, part 2 contained a discussion of β,β´-dichloroethyl sulfide, noting that its physiological effects are remarkable. The textbook indicated that even dilute solutions produce skin inflammation and that its vapor produces inflammation and death in rabbits by pneumonia. Meyer and Jacobson’s comment on
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rabbits dying from mustard gas refers to some testing Meyer had done after his initial synthesis. When Meyer’s assistant first reported that the oil had caused him to develop a blister and conjunctivitis, Meyer was very surprised because the compound’s precursors are fairly innocuous. Thus, he thought that his assistant perhaps had a mental problem (32). Nevertheless, Meyer sent some of the synthesized oil to the local medical school and asked that its effects on rabbits be examined experimentally (33). At the medical school, two medium-sized rabbits were confined in a cage and mustard-saturated air was instilled. The animals became restless and their noses and eyes reddened. The next day both eyes were inflamed, lids “glued” shut by secretions, and noses and ears inflamed. Both animals died of pneumonia on the third day. Further experiments on rabbits were conducted resulting in even more rapid deaths, leading Meyer to conclude that the most severe action of mustard occurs only after it enters the blood (2). Meyer wrote, The intended work with the chloride was not continued on account of the extremely poisonous qualities of the compound. It is striking that the apparently harmless substance which is only slightly volatile, is almost insoluble in water, and has a very slight odor as well as a perfectly neutral reaction, should exert a specific toxic effect. Its chemical constitution would never lead one to expect its aggressive properties. (33)
The Second British Connection Hans T. Clarke (1887–1972) was born of a German mother and American father in Harrow, England. In 1905 Clarke entered University College London and began studying chemistry. In 1911 he was awarded an 1851 Exhibition Scholarship, allowing him to study with German chemist Emil Fischer in Berlin. Upon returning to England he received a doctoral degree from University College London (34). In 1913 Clarke published an article in The Journal of the Chemical Society titled, “4-Alkyl-1,4-thiazans” (35), that discusses various alkyl derivatives of a heterocyclic six-member carbon ring containing sulfur at position 1 and nitrogen at position 4 (thiazan). This compound is the sulfur analogue of morpholine. In this article, Clarke reported that he used Meyer’s method to prepare β,β´-dichloroethyl sulfide, the precursor of thiazan; however, he found that the conversion of the glycol to its dichloride (the second step in Meyer’s synthesis) can be effected by warming a solution of the thiodiglycol in HCl with a water bath. This conversion is rapid and quantitative. Meyer had accomplished this step using PCl3 (35). Clarke paraphrased Meyer’s description of the effects of mustard, noting that they are delayed for a few hours after initial skin contact. Further, mustard’s lack of a pungent odor indicates that it is actually a toxic substance and not just a skin irritant. However, Clarke also observed that mustard can be handled “with perfect safety” provided that one does not breathe its vapor or allow it to contact the skin. Although Clarke considered β,β´-dichloroethyl sulfide safe to handle, Clarke suffered a severe injury to his leg while working in Fischer’s Berlin laboratory, the result of a broken flask. The associated burns required two months of hospitalwww.JCE.DivCHED.org
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ization to heal. Clarke, who later immigrated to the United States, becoming a biochemistry professor at Columbia University, believed that Fischer’s reporting of this mishap in 1915 to the German Chemical Society led to Germany’s use of mustard during World War I (33). World Wars I And II The German process for large scale production of mustard gas during World War I was based on the Meyer–Clarke synthetic method. Germany was able to produce mustard in this manner because the large manufacturing infrastructure of the dye industry provided an easily accessible supply of ethylene chlorohydrin (6, 33). In contrast, although the Allies were immediately able to identify mustard as the product described by Meyer, they could not produce it using his synthetic scheme. This caused almost a year’s delay between the Allies’ initial identification of the mustard agent and their first use of it on the battlefield of World War I (6). Britain, France, and the United States all struggled to manufacture β,β´-dichloroethyl sulfide using the Despretz–Niemann– Guthrie process based on the monochloride, a synthetic route that did not produce as pure a product (36). The British chemist Sir William Pope is often credited with perfecting, near the end of the war, what became known as the Levinstein process for producing the mustard agent based on sulfur monochloride. The historical significance of Pope’s contribution was challenged by Green in two brief articles that appeared immediately after the end of World War I (15, 37). The Levinstein process was used again by the Allies to produce mustard during World War II (33). Thus, the processes used to make mustard during both World Wars of the 20th century, and possibly the one still employed by some countries today, is more than 150 years old and is based on experiments conducted by European chemists in the 19th century. Notes 1. The term mustard, short for sulfur mustard, refers to a large class of chemical warfare agents that are cytotoxic and that possess distinctive vesicant properties. Sulfur mustard may smell like garlic, onions, or mustard and sometimes has no odor. It can exist as a vapor, an oily liquid, or a solid. In this article we focus on the compound bis(2-chloroethyl)-sulfide, colloquially called mustard gas, mustard agent. 2. The term “atomic weights” is conventionally used to discuss atomic masses. 3. A diagram of a bulb wash tube is provided in Guthrie’s article (26). It appears to be a series of spherical bulbs made of glass linked together, looking much like a rigid string of beads.
Acknowledgments Margaret Mettler, Matt Weber, and Jeanette Clausen are acknowledged for translation help. Literature Cited 1. Franke, S. Manual of Military Chemistry; Chemistry of Chemical Warfare Agent; United States Department of Commerce,
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2. 3. 4.
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7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.
National Bureau of Standards, Institute for Applied Technology: Washington, 1968; Vol. I; This is a complete translation of Lehrbuch der Militärchemie, Deutscher Militärverlag, Berlin [East], 1967. Warthin, A. S.; Weller, C. V. The Medical Aspects of Mustard Gas Poisoning; C. V. Mosby Company: St. Louis, MO, 1919. Vilensky, J. A. Dew of Death: Lewisite, America’s World War I Weapon of Mass Destruction; Indiana University Press: Bloomington, IN 2005. Miller, J. The New York Times. http://query.nytimes.com/gst/ fullpage.html?res=9D06EFD61630F930A15750C0A9629C8B63 (accessed Mar 2007). Despretz, M. Ann. Chim. Phy. 1822, 21, 437–438. Jones, D. P. The Role of Chemists in Research on War Gases in the United States during World War I. Ph.D. Thesis, University of Wisconsin, Madison, WI, 1969. Sloane, T. O. New Advent. http://www.newadvent.org/cathen/ 04755b.htm (accessed Mar 2007). Peronnet, M. M. J. Pharm. Chim. 1936, 8, 290–292. Cattelain, M. E. J. Pharm. Chim. 1935, 8, 512–514. Riche, A. Ann. Chim. Phy. 1854, 5, 283–304. Medema, J. NBC Defense &Technology International, 1986, 1, 66–71. Sartori, M. The War Gases; D. Van Nostrand Company: New York, 1943. Albert Niemann. http://www.whonamedit.com/doctor.cfm/ 603.html (accessed Mar 2007). Niemann, A. Ann. Chem. Pharm. 1860, 113, 288–292. Green, A. G. J. Soc. Chem. Ind. 1919, 38, 363R–364R. Woehler, F. Ann. Phys. Chem. 1828, 13, 297–299. Berzelius, J. J. Annals of Philosophy, 1814, 3, 353–364. Berzelius, J. J. Jahres–Bericht, 1828, 7, 73.
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19. Ihde, A. J. The Development of Modern Chemistry; Dover Publications, Inc.: New York, 1984; p 191. 20. Gordin, M. A. J. Chem. Educ. 2006, 83, 561–565. 21. Avogadro, A. J. de Physique, 1811, 73, 58–76. 22. Ampère, A. M. Ann. Chim., 1814, 90, 43–86. 23. Cannizzaro, S. Il Nuovo Cimento, 1858, 7, 321–366. 24. Meyer, L. Die modernen Theorien der Chemie und ihre Bedeutung für die chemische Statik, 1st ed.; Maruschke & Berendt: Breslau, Prussia 1864. 25. Stilwell, D. Physics World 1999, 12, 33–35. 26. Guthrie, F. Quart. J. Chem. Soc. Lond. 1860, 12, 109–126. 27. Guthrie, F. Quart. J. Chem. Soc. Lond. 1860, 13, 129–135. 28. Harrow, B. Eminent Chemists of Our Time; Books for Libraries Press: Freeport, NY, 1968. 29. Parthasarathy, R. The Hindu. http://www.hinduonnet.com/ thehindu/2001/10/04/stories/0804000a.htm (accessed Mar 2007). 30. Meyer, V. Ber. Deut. Chem. Ges. 1886, 12, 3259–3266. 31. Meyer, V.; Jacobson, P. Lehrbuch der Organischen Chemie; Verlag Von Veit & Company: Lepzig, 1913. 32. Croddy, E. Chemical and Biological Warfare; Springer–Verlag: New York, 2002. 33. Senior, J. K. Armed Forces Chem. J. 1958, 12, 12. 34. Vickery, H. B.; Clarke, H. T. In Biographical Memoirs; National Academies Press: Washington, DC, 1975. http:// www.nap.edu/openbook/0309022401/html/3.html (accessed Mar 2007). 35. Clarke, H. T. J. Chem. Soc. 1913, 101, 1583–1590. 36. Haber, L. F. Chemical Warfare in the First World War; Clarendon Press: Oxford, 1986. 37. Green, A. G. J. Soc. Chem. Ind. 1919, 38, 469R.
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