F. C. Hentz, Jr. and G. G. Long North Corolino State University Raleigh, 27607
Synthesis, Properties, and Hydrolysis of Antimony Trichloride
Ever since chemistry and alchemy parted ways, SbC4 and SbrOjClz have been prepared and studied by numerous chemists whose names are notable on the pages of the history of chemistry. Paracelsus (1493-1541) prepared SbCla by distillation from a mixture of Sb& and HgCIz and was familiar with the reaction of SbC13 with water. Since a mercury compound was used in the preparation, it was long thought that both SbC13 and its hydrolysis product were compounds of mercury. Paracelsus referred to them, respectively, as cinnabaris antimonii and mercurius uitae. As was suggested by the name mercurius vitae, wonderful medicinal powers were ascribed to the compound, and Paracelsus expounds on these virtues in Archidoxies.' After this, numerous others prescribed various antimonial preparations as cures for a multitude of ailments. F'robably the most famous of these was the author who wrote a volume entitled, "The Triumphal Chariot of Antimony" dating from at least 1604. Glauher in "Novis Furnis Philosophicis" (1648) showed that neither cinnabaris antimonii nor mercurius uitae contained mercury, and that the former substance was simply the chloride of antimony which he referred to as butyrum antimonii (butter of antimdny). Glauber also reported the preparation of butyrum antimonii by distillation from a mixture of Sbz03 and spirit of salt (hydrochloric acid). ShrOsClz still was frequently enthusiastically prescribed by many medical practitioners. A particular proponent of its medicinal value was V. Algarotto who referred to the compound as puluis angelicus in his work "Compendio della natura, virtu e mod0 d'usare una uolve quint'essenza d'oro medicinale" published in ~ e r o n ain 1667. Shortly thereafter, others referred to the compound as powder of Algaroth. Throughout the 19th and early 20th centuries it was noted that the reaction of SbC18 with water did not always yield consistent results and a wide variety of compositions have been claimed, e.g. SbOC1, SbzOClr, Sh403 (OH)&13, S~SOIICIZ,SbsOClzz, etc. The product(s) obtained depend upon variables such as the amounts of water, acidity, chloride ion, etc. and quite a number of rather well known chemists spent some time investigating the problem. The most famous of these probably was H. LeChatelier (1885) who was interested in the reversibility of the reaction. In the following experiment we prepare antimony trichloride in the same manner as Glauber, examine one of the chemical equilibria that was investigated by LeChatelier a t about the time he expounded the principle that
now bears his name, and determine antimony in the mercurius vitae of Paracelsus. The experiments illustrate equilibrium shifts due to mass action in that a t one extreme, readily hydrolyzable SbC13 is prepared and isolated from an aqueous solution, and at the other, a hydrolysis reaction of ShC4 is studied and the hydrolysis product isolated and identified. This hydrolysis product is of particular interest since its composition is not readily anticipated by the students. Indeed, general chemistry texts frequently list only SbOCl as the product of hydrolysis of SbCb even though the usual hydrolysis conditions lead instead to Sb405C12. The entire reaction sequence is indicated schematically below
.Fraction Il Fraction El Fraction I 10 ml, llO0C 110-215°C 5 ml, 215-220°C Deter. density
1 Filtrate
H?dmW=
Fraction IV 220-221°C fp and solubility tests
+ White Solid
male HCL mole WCI,
% ~ b
Our second semester freshman chemistry majors carry this out in three 3-hour laboratory periods; the first period is devoted to the synthesis of SbC13, the second to the study of the hydrolysis, and the third t o the determination of Sh in the hydrolysis product. If less laboratory time is available, one might elect to do only one or two parts of the experiment, e.g., rather than prepare SbCla, the hydrolysis can be carried out using the commercial reagent, or the antimony determination on SbrOaClz can be omitted, and the student, on the basis of the titration of
Volume 52, Number 3. March 1975 / 189
the liberated acid, would readily be able t o determine
Student Results and Comparative Values
+
which of t h e following hypothesized reactions is best in accord with t h e d a t a
If earlier in t h e term, the student has carried out acidbase and redox tritrations, t h e study of t h e hydrolysis reaction a n d product m a y he assigned as a small project in which t h e student needs t o recall these techniques a n d p u t them t o practical use. Experimental Synthesis a n d Properties of Antimony Trichioride Synthesis. Caution!l Twenty grams of SbzOs, 35-50 ml of concentrated hydrochloric acid, and 2-3 glass beads are placed in a 125-ml distilling flask and swirled gently until most of the solid dissolves. The flask is fitted with a 250°C thermometer and the mixture is then distilled directly into receivers. As indicated in the schematic (uide supm), four fractions are collected: Fraction I is the first 10 ml of distillate and is essentially constant boiling hydrachloric acid; Fraction JJ is a mixture of hydrochloric acid and SbCls; Fraction ID is collected in an accurately weighed graduated tube (possibly, a 15-ml conical tipped, graduated centrifuge tube) and consists of -5 ml of SbCla which one starts to collect a t 215'C and is used for density measurement and the hydrolysis experiment; and Fraction N, collected in a tared test tube, is the remainder of the SbCI3 which will be used for the melting point determination and solubility tests. Both Fractions IIl and N should be tightly stoppered and immediately stored upright to solidify. The temperature a t which these fractions are ohtained is taken as an estimate of the normal boiling point of SbC13. The SbClz so obtained is nearly colorless unless the reflux has been allowed to come in contact with the rubber stoooer holding the thermometer. The total mass of Fractions 111 a n i r ~ is used to compute the % yield of SbCb. Properties. The melting point of SbCls is obtained from temperature versus time measuremerits for the cooling of Fraction N. This may he done before solidification of this fraction, or alternatively, the solid may be remelted. Estimates of solid and liquid (near mp) densities are made by noting the volume of Fraction ID along with the massof this fraction. Small portions of Fraction IV are added, respectively, to 1ml of water, benzene, CClr, etc. to qualitatively obtain an idea of the solubility of SbCls in these solvents. After the effect of water on SbCls is noted, small portions of Fraction I and ll are diluted with water tosee if SbC4 is present here also. ~
~
~
~
Hydrolysis of SbCia Exactly 250 ml of distilled water is measured into a 500-ml Erlenmeyer flask. The tube containing the accurately weighed Fraetion III is carefully lowered into the water and the flask tightly stoppered. The flask is gently swirled, and agitation is continued until the SbCh has completely reacted to farm a white milky slurr ~ . ~ The mixture is filtered through a tared, medium-porosity fritted-glass filter and the filtrate (aqueous HCI) is collected in a clean, dry filter flask. After 100 ml or so of filtrate have been collected, this portion of the filtrate is transferred to a clean, dry Erlenmeyer flask and saved for the titrations with base. The filter is replaced on the filter flask and as much of the precipitate as is practical is collected. The solid is rinsed with several small portions of deionized water and dried at 110" C until the next laboratory period (see Analysis of the Hydrolysis Product section). The dried product is finally weighed. Twenty-five-milliliter aliquots of the filtrate are titrated with 0.5xx.x M NsOH to determine the HCI content. Assuming the total volume of filtrate to be 250 ml., the total HCI produced by the hydrolysis and the mole ratio, HCI produced/SbC13 reacted, are calculated. The equation that best represents the hydrolysis reaction may he inferred from these data. Analysis o f the Hydrolysis Product Further verification of the hydrolysis reaction suggested hy the results of the above is accomplished by titrating the dried, white solid with permanganate. The fallowing titration conditions have heen found satisfactory: 0.2rxr g of.sample is dissolved in 10 ml 190
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Journal of Chemical Education
~ o u n d standard ~eviatio~ Melting point Boiling point (740-755 to=) Density of liquid Mole HCI produced Mole WCI. reacted %Sb in Hydrolysis Product
70.2 1: 2.3OC 220 + 1'C 2 . 6 1:0.1 g/ccC
Comnaratiw values
72. 221 (7M)tom)"
2.441 g/cc (178°C)"
+ 0.05
2.50b
76.45 1: 0.31
76.346
2.45
'Dodd, R. E., and Robiosoioso, P. L., "ErperLnental Inorganic Chemistry,'' Ekevier Publishing Co., New York, 1861, p. 216. %esn. (3). Caled for SbaOGl.. (Near inelting point
of concentrated HCI and then this is diluted with 45 ml of 3 M HzSO, and 45 ml of deionized water. The solution is cooled to about 10"C and titrated with 0 . 0 2 0 ~MKMnO*. ~ Students are asked to write a balanced equation for the titration reaction. The percent Sb determined from the titratian is compared with the theoretical percent SB for various possible products. The weight of dried hydrolysis product is compared with the weight calculated on the basis of the amount of ShC13 which was reacted with water.
Discussion T h e table shows representative results ohtained by well over 75 freshman chemistry majors who have worked on this project at North Carolina S t a t e University. These results strongly suggest t h a t eqn. (3) best represents t h e hydrolysis reaction under these conditions. Students have found t h e project of particular interest in view of t h e historical significance of these substances and their reactions, t h e quality of t h e products, a n d t h e definitive results ohtained. We have found it quite desirable in terms of t h e application of standard general chemistry lahoratory techniques t o what in reality is a small (and openended) research problem; furthermore, since t h e results are contrary t o those most frequently cited in freshman texts (usually ShOCl and, t o some extent, ShzOs, or Sh(OH)s), students have benefited from seeing first-hand the experimental basis on which the equations of "descriptive chemistry" rest. 'The following excerpt is given by Mellar, J. W., "A Comprehensive Treatise on Inoreanic and Theoretical Chemistrv." Lone0 ~ : "-~~ '~ou~h mans, Green & Co.. N& York. Vol. IX. 1929.. o. 5~~and its powers do not fail on account of bld age, but these exist equally in the old as in the young. The corruption, however, which grows up with youth is so strengthened that it takes away the powers, whence old age is recognized . . . The mercurius uitoe separates corruption . . . . So powerful is it in man, that, after the eonuption shall have been separated from him, the quintessence is again excited, and lives as in youth . . . . The aged life then recovers most effectually its powers as they were before.. . . and corMercurius vitae restores ruption cannot demonstrate old age the defective and lost powers so that in old women the menses and the blood flow naturally as in young ones; for it brings back aged women to the same perfection of nature as the younger ones." -Arehidoxies. Wue to hydrochloric acid vapors, the synthesis is best carried out in a hood. SbCh can severely burn the skin even at roam temperature and is markedlymore hazardous a t 220°C. Anytime there is a chance that a little SbCI3 has gotten an the skin, immediately wash with water. The same caution should be exercised with hydrochloric acid and its vapors. Also, he careful in handling distillation receivers to avoid thermal burns. It is well to have the side arm of the flask 1-2 in. into the receiver and attach the clamp near the mouth of the test-tube receiver. Antimony residues may be cleaned from equipment by rinsing with 3-6 M HCI in the hood. 3Agitation of the flask and its contents must be gentle to avoid breaking the flask, but one must make sure that all of the SbC13 gets in contact with water. Actually, this is a good place to stop after the first laboratory period. If the tube of SbCls stays in contact with water for several days, all of the SbCla reacts without much agitation being necessary and the precipitate becomes more crystalline and easier to filter.
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