Illinois Institute
Cadet's Fuming Liquid
of Technology Chicago
An historical survey
John 5. Thayerl
Cadet's fmingliquid was accidently discovered during an investigation in a completely unrelated area. Spontaneously inflammable, toxic, and extremely malodorous, this unprepossessing mixture nevertheless occupied the attention of many prominent chemists. The isolation and characterization of its compontluts by Bunsen provided a model for later studies on organic compounds and led directly to the still-expanding field of organometallic chemistry, as well as materially aiding the development of bonding theory. Cadet's liquid arises from the heterogenous fusion of potassium acetate with arsenic trioxide, giving various organoarsenic compounds along with numerous organic and inorganic by-products. The only review on the history of this material appeared in a book by G. T. Morgan ( I ) , published in 1918 and now out of print. This paper is intended to provide a developmental study of Cadet's liquid from its origin to the present time. I n 1760, Cadet,, a Parisian military apothecary, presented a paper on cobalt-rontaining "sympathetic inks" (2), a follow-up of previous work hy Hellot (3) on derivatives of "roholt" (either smaltite, CoAsz, or cobaltite, CoAsSz). The A&O1, formed as a byproduct, was heated with "terre foliee de tartre" (potassium acetate) in a glass retort and a completely unexpected reaction occ~irred:~ I heated the reaction vessel slowly. After some time, a faintly colored liquid, having an extremely penetrating odor of garlic, distilled over, followed by a red-brown fluid that filled the flask with a thick vapor ( 8 ) .
The two-layer liquid had an extremely persistent, nauseating stench and fumed in air, bursting spontaneously into flame if poured from its container. Cadet himself did no further work on this reaction, but "Cadet's fuming arsenical liquid" attracted the attention of other chemists. Guyton de IMorveau and his two associates in Dijon, France, investigated this material further and discussed it in their printed lectures (4). They separated the two liquids and found that the heavier one was the more reactive: The red liquid retains, even after cooling, the property of fuming every time its container is emptied, giving off the same atrocious odor that nothinp, - can destroy and which persists for several days even in the most aerated rooms. . .we removed, as precisely as onssihle. the sunernatant liauid and ~ o u r e dthe remainder
-
Department of Chemistry, University of 1 Present address: Cmcinnati, Cincinnati, Ohio 45221. The literature excerpts quoted herein were originally written in French or German, and are translated by the author, who takes full responsibility for any errors.
594 / Journal of Chemical Education
cation of boiling around the edges, and then appeared a beautiful rose-colored flame that lasted far several seconds (4).
Next to investigate this uninviting mixture was Thenard (6),whose paper extended and amplified earlier work. He fonnd that the lighter liquid was a solution of the heavier in acetic acid and water, and that COz, K2CO1, ASH%,and various hydrocarbons were formed as by-products. Oxidation with chlorine indicated that the oily red-brown liquid showed the properties of carbonic acid, acetic acid, and inorganic arsenic. Thenard concluded: This liquid is a compound of oil, acetic aoid, and arsenic that resembles the metallic state and shonld be regarded as a type of soap of acid and arsenic, or as a type of oleo-arsenical acetate (6).
The detailed naturc of Cadet's liquid and its components was clarified by Bunsen (6a-e). He called the brown oil "alkarsin," from the initial letters of alkohol and amen, sinre he considered the substance as containing the elemrnts of alrohol, with the oxygen replaced by arsenic. Rnnsen's first two papers discussed the preparation and properties of alkarsin (fia, b) : Cadet's liquid can he obtained in moderately large smounts if about one kilogram of starting material in a glass retort is slowly warmed to red heat in a. sandbath. Three layers of products are found. At the bottom is a not inconsiderable quantity of reduced amenic; above that is a brown oily liquid consisting mostly of alkarsin and another compound. The top layer is a mare watery liquid which is a. solution of alkarsin in acetone, water, and acetic acid.. .No arsine is fprmed, but there are quantities of carbon dioxide, methane, and 'ethylene evolved, m d potassium carbonate is left in the reaction ves~el.. . (fia)
He carefully purified samples and, on the basis of its molecular composition, assigned alkarsin, the formula CsHl&O. This was independently confirmed by Dumas (7), who gave the following analytic figures (in percent): C, 23.60; H, 5.66; As, 69.00; Total, 98.26. Table 1.
Cacodyl and Derivatives Reported by Bunsen (6c-e)
Name
Formula
Cacodyl Cacodyl Oxide Cacocyl Chlonde Caeodyl Bromide Cacodyl Iodide Cacodyl Cyan~de Cacadyl Solfide Cacodyl Disolfide Cwodylic Acid
Bunsen's other three papers discussed the chemical reactions of alkarsin (6c-e). The products obtained (see Table I) were postulated as derivatives of the radical CaHIAsn. Berzelius, who had followed Bunsen's work with great interest, considered this species as a compound radical:
. . .probably the most accurate theoretical view of these compounds is that they include a compound radical, C4H,.As., of the type found in organic compounds, for which I suggested to Bunsen the name "kakadyl," became of the extremely repulsive odor of all its derivatives. . . (8).
Reaction 3a is well known in organic chemistry. Pyrolysis of acetone usually gives ketene, which breaks down further (15); methyl radicals have also been detected. Cadet's reaction, it should be noted, must be carried out at fairly high temperatures. Arsenic Kakodyl, or cacodyl, was coined from the Greek roots, oxide is probably reduced by carbon monoxide (possibly x or x or, evil, pernicious, and o odor; the name also by methyl radicals) to elemental arsenic, which referred specifically to the radical postulated by Bunthen reacts with methyl radicals forming [CH3As] sen and Berzelius; other compounds were named as radical. This in turn reacts by themechanism of Valeur derivatives (e.g., C4H12As20,cacodyl oxide). and Gaillot to form the products isolated. Breakdown Later research on Cadet's liquid brought out strucof ketene and/or methyl radical would give the obtural and mechanistic details. Kolbe (9) and Frankserved hydrocarbon products. Fuson and Shive (17, land (10) suggested that cacodyl was the dimethyl18) have reported a process for the continuous producarsenic radical. Cahours and Riche ( l l ) , and Baeyer tion of racodyl oxide from Asz03and acetlc acid. Sub( I S ) , established the true constitution of cacodyl as stitution of propionic acid for acetic acid gives ethyl tetramethyldiarsine, (CH3)sA~A~(CH3)2, and discovcacodyl oxide (C2H&AsOAs(C2H& in good yields. ered alternative methods of preparation. Baeyer also Little or no by-products are formed in this particular found that pure cacodyl oxide, (CH&ASOAS(CH~)~, process. Cadet's reaction has also been suggested for was not inflammable; i t was cacodyl that caused the use in the qualitative detection of acetate ion (19). liquid to inflame in air. Since the "classical" equation Acknowledgment
does not really indicate the reaction mechanism nor explain the complex mixture of products obtained (see Table 11),the most recent work has concentrated on this aspect of Cadet's reaction. Valeur and Gaillot made detailed studies on the react,ion products (13a-c)
I wish to acknowledge the invaluable assistance of the John Crerar Library and the Rare Book Department of the University of Wisconsin. I am also grateful to Dr. Aaron J. Ihde and Dr. Robert West, University of Wisconsin, for their advice and encouragement.
Table 2.
Literature Cited
Organoarsenic Components o f Cadet's Liquid
(134 Name
Percentaee
Cseodyl Caeodyl Oxide Trimethvlnrrine
-+- +- + + -+ -
and postulated the following mechanism (13c) : a. 2CHaCOzK b. 4ICHaAsl
c. 2(CHa),Az d. 2(CHa)sAs e. 21CHaAsl f. 5ICHaAsl
+
As3O 2LCHaAsI K&Ol 2As (CH3)4As? [CHaAs] (CH,)aAs [CHaAs] (CH,XAr;a (CH&As (CHa):Asa (CHsAs)&
+ CO1 (2)
They account for the presence of the hypothesized intermediate Am0 (no such compound has ever been isolated) as arising from the reduction of As203. A more complex mechanism for Cadet's reaction in aqueous solution, involving the intermediate CH2(As02)%, has been proposed by Titov and Levin (14). Neither n~echanisn~ is entirely satisfactory, considering the very complex nature of the react,ion. A third possiblemechanisn~is shown in eqn. (3).
--A
0
+ + + + +
2cH.coa K2co. cH.!xHs A CHaCOCHa CH!=C=O CH& CHaCOCH3 5 2[CHa.l CO A d. CH3=C=0 CHF=CH~ CO e. 2A.310. 6CO As4 6C01 41CH..l 4[CHaAs1etc. f. As,
a. h. c.
+
+
-
(3)
(1) MORGAN, G. T., "Organic Compounds of Arsenic and Antimony," Longmans, Green, and Co., London, 1918, pp. xii-xiv, 1-17. L. C., Memaires de MathAmatique (2) CADETDE GASSICOURT, et de Physique. PrAsentOs a 1'Academie Royale des Sciences par divers Savans et 1;s dans ses .4ssembl6es, 3, 623 (1760). (3) HELLOT,J., Histoire de 1'AcadAmie Royale des Sciences, 1, 101 (1737). D E MORVE.~U, L. B., MARET,H., AND DURANDE, (4) GUYTON J. F., ElEmens de chyme thboriqne et pratiqne, Dijons (France), 1778,111, 41. (5) THEXARD, L. J., Annales de Chimie, 52,54 (1804). R. W., Annalen 24, 271 (1837); b. ihid. 31, (6) it. BUNSEN, 175 (1839); c. ibid. 37, I(1841); d. ibid. 42, 14 (1842); e. ihid. 46, l(1843). J. B., Annalen 27,148 (1838). (7) DUMAS, J. J., Jahwsbwicht 20, 526 (1841). (8) BERZELIUS, (9) KOLRE,H., Annalen 65, 288 (1848). (10) FR.~NKL.~ND, E.,J . Chem. SOc. 2, 297 (1850). (11) CAHOURS, A,, AND RICHE,A,, Compt. l a d . 39, 541 (1854). (12) B.AEYER, A,, Annalen 107,257 (1858). (13) a. ~ ~ L E U RA.,, AND GAILLOT,P., Conpi. rend 184, 1559 (1927); h. ibid. 185, 779 (1928); c. ibid., 185, 956 11928). ~- - , (14) TITOV,A. I., AND LEVIN,B. B., Shornik Ohshchez Khim. 2, 1473 (1953) [C.A. 49, 4504 (1055)l. M., Y u k i Qosei Kagaku Kyokaishi 20, 730 (1962) (15) DEHAYA, [C.A. 58, 4412 (1963)l. (16) RADICH, I., KR~VCHUK, I. P., AND M.ARDALEISHYILI, R. E., Dokledg Akad. Nauk S S S R 136, 657 (1961). (17) F u s o ~ R. , C., .4ND SKIVE,W., J. Am. Chem. Soe. 6 9 , 559 (1947). (18) FasoN, R. c., A N D SAIVE,W., US 2,756,245 [C. d. 51, 2020 (1958)l. (19) BR~NTLEY, L. R., CROMWELL, T. M, AND MEAD,J. F., J. CHEM.EDUC.24, 353 (1947).
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