the
edited by
loborotory Microscale Svnthesis of cis
a Corresponding trans Isomer. A Rapid and Convenient Method of Preparing Cisplatin-An Anticancer Drug A Laboratory Experiment for Inorganic and Bioinorganic Chemistry Mono M. Slngh, Zvl Szafran, and Ronald M. Plke Merrimack College N. Andover, MA 01845
Following thediscovery in 1969 by Rosenberg et al. that square planar cis-platinum(I1) complexes possess good antitumor activity, more than 2000 platinum(I1) complexes have been prepared. Many of them have been studied as potential anticancer chemotherapeutic agents. One particularly effective anticancer drug is eis[Pt(NH3JzC12]. cis-diamminedichloroplatinum(II), commonly called cisplatin. This laboratory fulfills several learning objectives: (a) synthesis of a drug, cisplatin, (b) illustration of a laboratory for bioinorganic chemistrv. (c) aoolication of the trans efk t , and ( d ) preparation and charanertza. trvn of wmcra under d~fferentreactmn nmditions.
..
Experimental Sectlon Part A: Preparation of cisDiamminediiodoplatinum(II)(1) Safety Recommendations: Potassium tetrachloroplatinate(I1) [CAS# 10025-99-7) is harmful if swallowed, inhaled, or absorbed through theskin. It is classifiedas an anticancer agent. IPR-MUS LD50: 45 mgl kg. Potassium iodide [CAS# 168-1-11-01 is harmful if swallowed, inhaled, or absorbed through the skin. No toxicity data is available. I t has been shown to have deleterious effects on newborns and on pregnancy. Note: Avoid bright light to minimize decomposition of the products. Prepare a solution of 125 mg (0.301 mmol) of potassium tetraehloroplatinate(I1)in 200 pL of water in a 10-mL beaker containing a magnetic stir bar. (Note: If potassium tetrachloroplatinate is not available, it can he prepared from chloroplatinic acid hy reduction with a stoiehiometrie amount of hvdraPre~emma1 the 1991n ACS National Meeting. Boslon. Am l 22-27. 1990 For aelsl s. see SraIran. 2.;Pfke.R M.; Smgh, M. M. Mmoscale Inorganic Chemistry: A Comprehensive LaboratoryEXperien~ Wiley: New York. 1990.
ARDEN P. ZIPP SUNY-Conland Conland. NY 13045
zine sulfate in aqueous solution, in the presence of KC1 (1)). Heat the solution, with stirring, on a sand bath to 40 OC. To this mixture add a solution of 300 mg (1.81 mmol) of KI dissolved in 500 a L of warm water. Upon the addition of KL, the solution changes from red-brown to dark brown in color. Heat the mixtwe to 70 "C with continuous stirring. As soon as this temperature is reached, cool the mixture to room ternperatwe. Do not ouerheat the solution! Suction-filter the solution using a Hirsch funnel to removeany solid impurities. Use a few drops of water to make the transfer as quantitative as possible. Transfer the filtrate to a 25-mL beaker and, dropwise, add 400-500 pL (1mmol) of -2.0 M NH3 solution (automatic delivery pipet) to the filtrate with constant stirring. As soon as the ammonia is added, fine yellow crystals of (1) should precipitate. If the supernatent liquid is still dark yellow in color, add a few more drops of ammonia to complete the reaction. Allow the beaker to stand for an additional 20 min s t room temperature. Suction-filter the yellow crystalline compound using a Hirsch funnel. Wash the filter cake with 500 a L of ice-cold ethanol, followed by 1.0 mL of ether. Air-dry the product and determine the percentage yield.
Parl B: Preparation of cis-Diammine (2) dichloro~latinum(ll), . . Cisolatin . .. Safety Recommendations: Potassium chloride [CAS# 7447-40-71 is not normally considered dangerous. ORL-RAT LD50: 2600 mglkg. Silver sulfate [CAS# 1029426-51. No toxicity data is available for this compound. I t would be prudent to follow the normal precautions as silver salts have been found to act as heavy metal poisons. To a solution of 63 mg (0.202 mmol) of silver sulfate in 10 mL of water in a 25-mL beaker containing a magnetic stir bar, add 100 mg (0.207 mmol) of ( I ) as prepared in Part A, in small portions. Heat the suspension, with stirring, on a sand hath (70-80 'C) for 10-12 min. Suction-filter the mixture on a Hirsch funnel to separate the precipitated Agl. Transfer the filtrate to a 10-mL beaker (Pasteur pipet), and concentrate it to a volume of about 2.0 mL on a sand hath. Add 330 mg (4.43 mmol, a large excess) of KC1 with stiring. Heat the mixture at 70-80 *C far %3 min. Bright yellow crystals of cisdiamminedichloraplatinum(II), cisplatin, should precipitate. The heating is continued for an additional 5-8 min. Cool the mixture to 0 OC in an ice-water bath. Suction filter the product using a Hirsch funnel. Wash the crystals with 500 pL of ethanol, followed by 1 mL of ether. Dry the product under suction in air. Determine the percentage yield. Obtain the mid- and far-infrared (IR) spectra of [2]. Determine the decomposition point of the product (270 'C). Volume 67
Part C: Preparation of trans-Diamminedichloroplatinum(ll) (3) Carry out t h e reaction in a hood. Dissolve 42 mg (0.1 mmol) of K2PtC14in asolution of 25 pL of conc. HCI and 150 FL of water in a 10-mL beaker containing a magnetic stir bar. Heat the solution to a gentle boil using a sand bath set atop a magnetiestirrine-hot .late. Slowlv. ..add 100 uL of conrentrated aqucoua ammonia 1,. the boiling solution. The solutwn at chlr stage is straw rulurrd. Avuid nddmg excess ammonra 11, prevent the formation of a green product, [Pt(NH$nl[PtCL] (Magnus's green salt). If any green precipitate forms, filter it using a Pasteur pipet filter. Reduce the volume of the solution almost to dryness, cool the mass and add 4 mL of 6M HC1. Evaporate the mixture to about 200-4M) aL, coal the mass in an ice-salt bath. Light yellow crystals of the trans isomer separate out. Suction-filter the fine crystals using a Hirsch funnel; airdry the crystals on a clay tile. The average yield is 40-60s. Determine the deeomposition temperature of the product (270 'C). Run the mid- and far-IR spectra of (3) using Nujol mull.
Discussion Potassium tetraiodoplatinate(I1) is prepared from potassium tetrachloraplatinate(I1) by a metathesis reaction (2):
Two of the iodide Ligands are then replaced with ammonia (or any other ammine ligand) formine cis-diamminediiodo~latinum(I1). The iod;de ligands hare a high;, trans effect than amrnonio, resulting in the formntion uf the cis isomer. K,Pt14
+ 2am = cis-[Pt(am),l,] + 2K1
The trans effect, commonly observed in ligand exchange reactions in square planar complexes, may be considered as the ability of a lieand to facilitate substitution in the position trans to itself. Ligands can be arranged in order of their decreasing tendency of trans effect (3): CO, CN- > H- > NOZ-, IF, SCN- > Br-, C1- > NH3, H20. I t is because of this effect that the cis geometry is maintained in subsequent steps.' The platinum complex is then treated with silver ion, which precipitates the remaining iodide ligands which are replaced hy water:
Silver sulfate is used instead of the more
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Number 10
October 1990
A261
the microscala laboratory obvious choice of silver nitrate, as formation of the ehloroplatinum complex from the sulfate species is more favorable than from the analogous nitrate derivative. This results in a higher yield of the final product. Finally, the water ligands are easly replaced with an alkali halide or alternatively, any salt of a hidentate anion: cis-[Pt(am)2(H,O),IZt + 2X= cis-[Pt(am);X,]
+ 2H20
Appropriate soluble hsrium salts can also be used to isolate various cis-diamminedianionicplatinum(1I) complexes (4). This is not desirable in the case of the synthesis of cisplatin, as insoluble Bas01 will precipitate, necessitating an additional fitration step in the process. The cis and trans isomers may be identified by their IR spectra or by the difference in reactivity toward aqueous solution of thiourea. YR.c,(c~-') YR.N(c~-') ci~-[Pt(NH~)~Cizl 330, 323 trans-[Pt(NHahCi21 365
510 572
With thiourea the cis isomer forms yellow needles of tatrakis(thiourea)platinum(II) chloride. On the other hand, the trans isomer yields colorless crystals of bis(thiourea)diammineplatinum(I1) chloride. The cis isomer is an effective anticancer agent: the trans isomer is not. The reasons for such activity for the cis isomer have been the topic of extensive study (5).
Literature Clted 1, Livingstone,S.E. Syn.Inorg. Msforg.Chem. 1971.1.1. 2. Dhara,S. C.lndionJ. Chem. 1970,8,193. 3. Cotton. F. A.; Wi1kinson.G. Advancedlnorgvnic Chemistry.5Lhed.; Wiley: New York, 1988: p 1299. 4. Harrison, R. c . : McAuiiffe, C. A ; Zaki. A. M. Inor#. Chirn. Acto 1380.46, L15. 5. 2ioo.A. P.:. Zion. .. S. G. J. Chem.Educ. 1971.54.739and referenceatherein.
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7 We thank the edltw of this column. A. P. Zipp. for his suggestions to incorporate this and omer
changes.
Rapid Semimicro Extraction and pkification of Caffeine from a Commercial Product E. F. Neuzll Western Washington University Beilingham. WA 98225
An experiment that is frequently performed in a first-year general chemistry course is the separation and purification of components of a mixture. Often the mixture is an artificial concoction such as sand and salts and is performed on a macroscale level. The experiment is usually haring and seemingly without real purpose because an unreal starting material is used. We have developed an extraction of a well-known sub-
A262
Journal of Chemical Education
stance, caffeine, from a real mixture using semimicro techniques. The experiment is easily performed in 2-h laboratory period by students who have had no previous chemistry experience. The amounts of chemicals are such that hazardous waste is kept to a minimum.
The Experlrnent 1. One-half of a No Doz tablet is placed in a mortar and ground to a powder. The powder is ~ l a e e din a250-mL beaker, and 50 mL of water is added and stirred well with aglass rod. With gentle stirring 6 M aqueous NH3 is added dropwise until red litmus turns blue. 2. The solution is placed in a 125-mL separatory funnel, and 5 mL of methylene chloride is added. The caffeine extracted into the methylene chloride layer is allowed to settle out and drain off through a small (grape-size) bit of cotton in a small funnel into a 40-mL conical-bottom test tube. The extraction is repeated with a second portion of 5 mL of methylene chloride. 3. The combined methylene chloride solutions are centrifuged and the lower waterless layer removed using a dry, clean Pastkur pipet. This lower layer is placed in a second clean, dry 40-mL centrifuge tuhe. 4. A small wooden dowel is placed in the methylene chloride solution in the centrifuge tuhe and the solution is evaporated to dryness in a warm60 'C water bath in a hood to reveal the crude caffeine. 5. Ten drops of anhydrous methanol are added to the crude caffeine warmed in 60 'C water to dissolve the caffeine. This methanol solution is transferred using another clean, dry Pasteur pipet into a small (10- x 75-mm) test tube. The solution is cooled in an ice bath to crystallize the purified caffeine. The crystallized caffeine is centrifuged to compact the product (if there is not enoughliquid layer after centrifuging, more methanol is added to redissolve the caffeine, the solution is cooled and centrifuged again). 6. The methanol solution is drawn from the caffeine and may be saved in order to recover more caffeine. Five drops of methanol are added to the caffeine, warmed again to dissolve the residual caffeine. Using a Pasteur pipet, the solution is placed on a clean, dry watch glass, and the methanol is allowed to evaporate a t room temperature. 7. The melting point of the recovered caffeine is determined. T h e instructor should demonstrate the loading of the capillary tube. Students then compare their mp to the literature value (238 'C) for a generalized evaluation of product purity. For more capable students, 1W mL of a cold drink may be used, hut the caffeine yields ere much smaller, and more care is needed during the extraction.
