/aFeku !an the k
edited by MALCOLMM. RENFREW University of Idaho Moscow, ldaho 83843
More on the Mlcroscale Laboratory
Editor's Note: Readers who find this article interesting will also want to know that a new feature column entitled The Microscale Laboratory, edited by Arden P. Zipp, makes its debut in this issue on page 956. In addition, four laboratory experiments that have mierascale components and are nuitahle for the organic lab appear on pages938.Y58,96l, nnd 965. A mrenwale experimrnt that al. lows students in general chemistry to do himhemistry studies is on page 944. Twonotes, on pages 964 and 967, give instructions for new microscale laboratory techniques and equipment, respectively.
The Microscale Inorganic Laboratory Safety, Economy, and Versatility Zvi Szatran, Mom, M. Singh, Ronald M. Pike Merrimack College, North Andover, MA 01845 Until recently, there has been an increasine " tendenev toward elimination of laborstorim in all areas ofrhemistry, particularly in inoqnnic chemistry. 'l'hrrc are a number of cogent reasons for this trend. One of the more serious problems is the cwt associated with the disposal of hazardous chemicals, due to current governmental regulations. I t is generally more expensive to dispose of inorganic (and organic, for that matter) wastes than it is to purchase the chemicals themselves. T h e traditional method of chemical waste disposal, flushing the waste materials down the drain or burial in landfills, has resulted in damage to the surrounding environment and t o concerns
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about public health. These methods of waste disposal are now illegal or tightly regulated. Many compounds of toxic metals (such as lead, mercury, cadmium, and barium) have been largely eliminated from instructional laboratory use due to the environmental toxicity considerations. Based on current trends, it is clear that all chemical users can look faward to a rising tide of legislation and litigation in this area. Lahoratorv air oualitv, and exoosure of students u, toxic chemical$ is also an areaof grwing cmcarn. Colleges and universities are faced wtih an eaprn~iveretrofit of exist-
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ing laboratories to meet current air quality regulations (I). Insurance costs are also rising sharply, not only for the students but for the instructors as well. While the current level of litigation seainst chemistrv, denart., menu and laboratory in~trurmrais low, it was of wffirient concern to the American Chemical Society to offer liability insurance for a short time and to reintroduce it recently. Chemical costs have also escalated prohibitively, even more sharply limiting the number and varietv of exueriments that can he used in the ina&udi&al lahoratorv. In the traditional inorganic laboratory, the high costs asaoeinred wrrh macrwrale preparations have limited experiments tu the use of only the least expensive metals (chromium and cobalt, for example). These high costs, coupled with declining chemistry enrollments, have persuaded many colleges and universities to conclude that the inarganic lahoratory is no longer a viable option. Current ACS guidelines for chemistry departments include a much greater emphasis on inorganic chemistry, both a t the introductory and advanced levels (2). This must, of necessity, include a larger inorganic laboratory component in the student's undergraduate training. The difficulty hecomes reconciling the ACS recommendations with the ~rohlemsoutlined ahove. The fallawine diurwsion will outline what we I~elbveto he the moat practirol d u t i o n : the irnplernentation of the microscale concept in the inorganic laboratory. ~~
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W a s t e Disposal Regulatlons Many of the materials used in the traditional inorganic chemistry lahoratory pose significant health and ecological risks. All lahoratory programs, whether in the academic or industrial sector, should be designed with consideration of waste disposal. There are three types of waste disposal that are Likely to be encountered within the instructional laboratory, as exemplified by the 12 reagents listed in Tahle 1.These compounds were selected at random from current inorganic laboratory textbooks. Generally, products from the reactions of the above reagents, as well as reagent wastes will have to be divided into three categories for disposal. The simplest method covers hulk inorganics and consists of loosely packing the original bottles of chemicals (however full they are) in 50-gallon drums. In addition to the cost of the drum and packing material, there is a "landfill"castof approximatelv $7-10Ab bulk rate. Even after the m a t e r k s are delivered to the waste disomnl rompany, theoriginating inrtitutiun (generator) is not frer from liability should pmhlems develop at the landfill site of the disposer. The disposer must often maintain several types of insurance relative to the chemicals (51, as listed in Table 2. In thewordsof a typicaldisposal contract, the Generator must aeree to "indemnifv. >. save harmless and defend the Diaposrr from and against any and all liahilit~es,rlnims. prnaltirr, furfeitures, suits and the costs ~~
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Table 1.
Cosis and Waste Dlsporal Types lor Common lnorganlc Reagents
Original Chemical
o w m i used
~ o s t / 1 0 0g (3
Chromi~m(iii)chiwide Cobaqii) nitrate Triphenyiphosphine Phosphorus penlachloride Antimony pentachloride iron pentacarbonyl lodlne Sliver nitrate Mercuric iodide Capper(ii)chloride Sodium metal spheres Methyiene chloride
10 9 15 9 2.6 g 2.2 g 2.0 g 15 9 7.5 g 553 10 9 13 9 29 50 mL
$10.20 516.30 $13.75 $13.40 $32.00 $30.00 $19.70 $79.50 $21.60 5 3.00 $26.80 $11.75
Table 2.
Waste Type (Q landfill landfill landfill landfill reacts with water reacts with water
landfill landfill landfill landfill reacts with water incineration
Insurance Coverage Requirements for Chemlcal Waste Dfsposal
Wwkm's Compensation Employer's Liabiiliy Public Liability (bodily injury) Public Liabiiii (propertydamage) Automobile Liability ( M i i y injury) Aulambiie Liability ( p r o p l y damage)
Table 3. Roduct
Sla~ory $500,000 each occvrence $5,000.000 combined $5.000.000 combined $200.000 each person a $500,000 each occurrenca $50,000
Product Generation Relative to Product Need
Appx. Am. Oenerated
NHIBFl Sni4 ~NHMbCls CpFe(COkCH3 (C~HS~~S~ CuiNH&SO. . . . .
BFa
5.0 g 2.7 g 5.0 g 2.0 g
10 t g 15 g 40
Am. Needed for Analysis 0.1 g via leF-NMR 5 mg for n
2gfwsta 5 mg for n 0.1 g for 'I 10 mg for I1 0.1 g for ' I 50mgfws
% Dispwed 96%
.% b b
b .%
mum used in published explmem.~ u c less h a u l d have been used to do the -me analysis a reaction st me m1n00caIe. a Some pmduct laed in m d reaction, also at large scale a
and expenses incident thereto, (including costs of defense, settlement and reasonable attorney's fees)" (5).In addition, the Generator is responsible for bodily injuries to any person, destruction or damage to any property, contamination or adverse effect to the environment, or for any violation of governmental Law. In short, the Generator islegally responsible for the waste from the moment of original generation to the end of time.
The Mlcroscale Solution The introduction of microscale organic chemistry by Mayo, Pike, and Butcher (6) has created a revolution in the manner in which organic laboratory instruction is carried out. First implemented in 1983 a t Merrimaek College, Bowdoin College, and BrownUniversity, microscaleorganic cbemistry laboratories are now in place at over 400 colleges and universities in the United States alone. I t has been estimated that by
1992 over 80% of all organic instructional labaratories will he conducted at the mierolevel (7). The microscale technique promises to have an even larger impact on inorganic chemistry than an organic chemistry. Before microscale, mast colleges and universities continued to offer organic chemistry laboratories, with the recognition of the problems involved. This is not true in the area of inorganic chemistry, where fewer than 305% of academic institutions offer a dedicated inorganic laboratory a t other than the general chemistry level (8). The major difficulties associated with the offering of an inorganic instructional laboratory are largely eliminated at the microscale level as summarized below. (1) Quantities of wastes generated are (Continued on page A266) Volume 66
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hack to the starting material hy merely heatine it in the hood. and releasine- NHaF into a water trap, thus recovering the HrF, sulrting material ( 9 ) . If desired, the NH4F can he recovered by evaporation and used in the following year's synthesis. drastically reduced. Recycling hecomes a more viable option. (2) Laboratory safety is markedly improved, as is laboratory air quality. (3) A much wider variety of chemicals may he economically and safely employed. (4) Laboratories are less time-consuming, due to faster and less cumbersome workups. These areas are discussed in more detail helow.
1. Microscale Impact on Waste G e n e r s
tion In any well-thought-out lahoratory experiment, the product must he used in various characterization tests or have utility in a subsequent reaction. Given current analytical techniques, the amount of product needed is therefore quite small. Tahle 3 lists the amounts of product generated in experiments found in several published inorganic lahoratory textbooks and the amounts used in further characterization or reaction. I t is clear from Tahle 3 that most of the product generated in the lahoratory is never employed for any useful chemical purpose. The microscale technique sharply reduces the percentage of product disposed. The obvious lesson to be learned is "never make more product than is required for suhsequent work or characterization". The disposal data further dramatically illustrates the necessity for using small quantitiesof all reagents, and for recycling to the maximum degree possible for toxic materials. This recycling aspect is especially critical when designing new experiments for the chemical lahoratory. Most inorganic laboratories not only exclude the use of such well-known toxic metals as lead or beryllium hut have also excluded essentially all metalcontaining compounds. This is due to the environmental hazards posed by disposal of the wastes and to a Lesser demee due to dancers =n m d to the chemist iLthe lahoratory. This, in turn, rliminsws the poaarhility ofofferrng acumprrhrnaive inorganic chemistry lahoratory. By reducing the quantities of toxic compounds used, the students' exposure to these compounds is also reduced. Therefore, with suitable safety precautions and judicious selection of reagents, the mieroscale technique allows the interesting area of metal chemistry to he reintroduced to the lahoratory. The products, in many cases, could then he easily recycled back to the original startingmaterials by the laboratory instructor or by the students. An example of the use of recyclahlelead in the laboratory is the microscale synthesis of ammonium hexachloroplumhate(IV), (NH&PhCLj, from PhClz (50 mg starting material used) (9).The stability of this camplex can he compared to the analogous tin complex, serving as an illustration of the "inert pair effect". The lead complex can he recycled to the original starting material by thermal reduction. A more extreme example of such a reaction is in the (advanced lahoratory) synthesis of (NHhBeF4 from BeFz and N H 9 . The product can be recycled ~~~~
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2. Laboratory Safety Oneof themajor advantagesof microscale chemistry is the greatly rnhanred rnfety nspeet of the laboratory. It is obvious that air quality is markedly upgraded, as the quantity of solvents and other volatile substances is reduced by a factor of 1CK-1CKO from the conventional laboratory work scale. This is especially beneficial to those laboratories that do not possess high efficiency ventilation svstems and have limited funds for uograding their present facilities. As a historic now, this was the overriding factor that led to the initial development r d the mirro~calr concept for organic chemistry a t Bowdain and Merrimack Colleges (10). Another important advantage is the reduced risk of fire and explosion afforded by the reduced quantities of chemicals used. Over the past sir years of o b s e ~ a t i o nof mieraseale organic and inorganic lahoratories, there have been no reports of accidents of this type received. 3. Use of Wider Varieties of Reagents There are additional reasons for recycling products to reclaim starting materials. Many reagents that could he used in interesting inorganic laboratory preparations are prohibitively expensive. Converting to the microscale level lowers the reagent costs significantly on a per-student hasis. Recycling the product brings the net cost of the enperimental procedure down to nearly zero, with the only losses corresponding to problems of technique and overall yield. Microscale inoreanic chemistm was first ~~
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offered tosoph~~morechemistr). major%l ' h ~ first "all-micro" inorganic Inborntory was offered in 1987. The downsizing of the lahoratory enabled us to use materials that were prohibitively expensive forthe conventional laboratory we had offered in prior years. Several examples to illustrate this m i n t follow. Over the past quarter century, the area of organometallic chemistry has experienced an extensive growth. I)cspiw this, there have been few educational lahoratory experiments available in this area, due to prohibitively high reagent costs. The microscale inorganic lahoratory approach allows the use of such important metals as rhodium, palladium, and platinum in arganometallic chemistry experiments. In our lahoratories, students synthesize trans-chlorocarhonylhis(triphenylphosphine)rhodium(I) from rhodium(II1) chloride hydrate (55Ilg) and dimethylformamide (11). Each student is given 25 mg of the rhodium starting material, and sufficient product is obtained for two suhsequent reactions (formation of sulfur dioxide adduct and oxidative addition with halogens). A second reaction involves the synthesis of dichlorohis(henzonitrile)palladium(II) and di-p-ehlaradiehlorodiethylenedipalladium(I1) from PdClz ($25/g) and benzonitrile, followed by displacement of the benzonitrile ligand with ethylene (11). Once again, 25 mg per student of the starting material is sufficent for these reactions.
A third and final illustration is in the synthesis of tetrakis-(tripheny1phosphine)plat i n u d o ) , an interesting complex with the metal in the 0 oxidation state, from PtCh ($54/g) and triphenylphosphine (11). A sample of 25 to 50 mg of starting material is used in this synthesis, depending an haw many subsequent transformations will be carried o u t 4. Laboratoty Efficiency Due to the reduced amounts of material used in t h e lahoratory experiment, the length of time necessary for process manipulationa is substantially reduced. For example, chromatography, filtration, crystallization, sublimation, distillation, and dissolution are all more readily accomplished. The net effect is that the amount of time required for laboratory workupr is reduced, allowing the student toconc~nrratemore on the actual chemistry involved. Reaction times are also somewhat shortened, due to factors including greater relative surface area for reaction, and reduced mass transfer requirements. ~
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costs. Overall liability is thereby decreased in two ways: reduced toxic wastes and reduced chances of lahoratory accidents.
Literature Cned 1. (4Butcher, S. 6.; Mayo, D. w.:Pike, R.M.:F&.
C. M.; Hotham, J. R.: Page, D. S. J. Cham. Educ.
1985,62,141.
lb) Bufeher,S.S.:Mayo,D.W.;Hebnf,S.M.:Pikc.R M. J. Chsm. Educ. 1985.62,AUS. 2. 1588 Exfensian of the Guiddinos for Udndndgraduoto PlofessiomIEducolion in Chemlarn; ACS Commit.
teean Pmfessionsl Trainine. American Chemical%-
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Conclusion The adoption of the mimoseale technique in the introductory and advanced inorganic chemistry laboratory solves a wide range of problems hitherto associated with the offering of such a laboratory s t the conventional scale. The major benefit is a safer laboratory environment, both for the student and instructor, due to decreased exposure to toxic chemicals and solvents. Costs are sharply reduced, both in terms of initial outlay (purchase cost of the chemicals) and disposal
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