Indian Journal of Chemistry Vol. 4513. October 2006, pp. 2353-2360 Within the portals of green chemistry: Green strategies to manage curriculum induced hazards in chemistry laboratories S Bh:llllllllat(" & Harsh Deep" "Chemistry Department, Garg! College (Delhi University), Siri Fort Road. New Delhi 110049. India E-mail: sbhnnurnutiticrcdiffmail.com bM se (Biotechnology), I'TU. India E-Illail: har;;hdeep(vnic.in Received 12 June 2006 There arc several chemistry reactions prescribed in the undergraduate syllabi that nearly hall' the pupil population dread performing (chcmophobia), To feel safe and comfortable both physically and psychologically, while working in the laboratories is a legitimate right of every student. The tutors and the instructors share this responsibility. Some green procedures arc being suggested here to establish a doer-friendly atmosphere in the laboratories. The work entails (i) working in meso/micro scale quantities (ii) olTmering an alternative chcrnical/procedurc/roure for achieving the same results. Two in one economically viable volumetric titrations are proposed which focus on better learning in lesser time. Using the interplay of physical and chemical principles, desired results can bc achieved for the preparation of many organic derivatives and often with bcuer yield and purity. Some classical procedures arc modified in a green way. Typical organic derivatives have been prepared with minimum energy requirements at ambient temperature avoiding the use of auxiliary substances and avoiding multiple steps in accordance with Green Principles 5, 6 and g. Two in one derivatives are also prepared for convenience. bGIIGr quality (even unncccssitariug recrystallization) and of-course ill improved yields. Atom economy is critically handled for practical purpose. Keywords: Chcmophobi.r. mcaso/micro chemical/procedure. aux i Iiary economy. green chemistry JPC Code: Int. ci.' C07B scale. alternative substances. atom Chemistry is perceived as a subject involving risks and pollution. To make the subject more substantial and meaningful, teachers' efforts are desired. Students, fears "Chernophobia" needs to be handled critically. Simplifying practical procedures with discretion, evolving two in one experiments, using microscale techniques to minimize waste and pollution, finding alternative chemicals and reagents to downscale risks are the suggested steps towards making chemistry an environmentally benign subject. Results and Discussion A survey conducted through a cross section or students revealed that students fear the toxic fumes the most (Table I). If chemists increasingly direct their strength to contributing to a sustainable civilization, chemistry will become more interesting and compel Iing to people and may lose its toxic image. It will become more worthy of public support and spawn exciting economic enterprises that nurture sustainability'. Derivatization in organic practicals is a challenging task for students. An ideal deri vati ve should: (i) be obtained under mild conditions, (ii) consume less time and energy in preparing, (iii) preferably be a solid with a reasonable melting point (60°-160°C), (iv) be formed in good yield so as to facilitate submission of the sample, (v) use less toxic reagents, solvents etc, (vi) involves minimum steps and be a single pot reaction if possible. Benzaldehyde and propanone both gi ve products with Brady's reagent. The products (i) have melting points 237°C and 128°C respectively, (ii) are light and heavily stick to the filter paper, (iii) yield 70%, time taken 20 minutes heated on water-bath. The students are tempted to use large quantities of Brady's reagent to have sufficient sample for submission because the product is sticky. Table I- Survey of students who tear toxic fumes I fear chemistry practical because or in ('Ic) a) Fi re hazards IS b) Poisonous chemicals 14 c) Brittle glass apparatus and breakage fires 22 d) Toxic fumes 34 Total 85 Not answered Ol) No fears 06
Transcript
Indian Journal of ChemistryVol. 4513. October 2006, pp. 2353-2360
Within the portals of green chemistry: Greenstrategies to manage curriculum induced
hazards in chemistry laboratories
S Bh:llllllllat(" & Harsh Deep""Chemistry Department, Garg! College (Delhi University),
Siri Fort Road. New Delhi 110049. India
E-mail: sbhnnurnutiticrcdiffmail.com
bM se (Biotechnology), I'TU. India
E-Illail: har;;hdeep(vnic.in
Received 12 June 2006
There arc several chemistry reactions prescribed in theundergraduate syllabi that nearly hall' the pupil population dreadperforming (chcmophobia), To feel safe and comfortable bothphysically and psychologically, while working in the laboratoriesis a legitimate right of every student. The tutors and the instructorsshare this responsibility. Some green procedures arc beingsuggested here to establish a doer-friendly atmosphere in thelaboratories. The work entails (i) working in meso/micro scalequantities (ii) olTmering an alternative chcrnical/procedurc/rourefor achieving the same results. Two in one economically viablevolumetric titrations are proposed which focus on better learningin lesser time. Using the interplay of physical and chemicalprinciples, desired results can bc achieved for the preparation ofmany organic derivatives and often with bcuer yield and purity.Some classical procedures arc modified in a green way. Typicalorganic derivatives have been prepared with minimum energyrequirements at ambient temperature avoiding the use of auxiliarysubstances and avoiding multiple steps in accordance withGreen Principles 5, 6 and g. Two in one derivatives are alsoprepared for convenience. bGIIGr quality (even unncccssitariugrecrystallization) and of-course ill improved yields. Atomeconomy is critically handled for practical purpose.
Keywords: Chcmophobi.r. mcaso/microchemical/procedure. aux iIiaryeconomy. green chemistry
JPC Code: Int. ci.' C07B
scale. alternativesubstances. atom
Chemistry is perceived as a subject involving risksand pollution. To make the subject more substantialand meaningful, teachers' efforts are desired.Students, fears "Chernophobia" needs to be handledcritically. Simplifying practical procedures withdiscretion, evolving two in one experiments, usingmicroscale techniques to minimize waste andpollution, finding alternative chemicals and reagentsto downscale risks are the suggested stepstowards making chemistry an environmentally benignsubject.
Results and DiscussionA survey conducted through a cross section or
students revealed that students fear the toxic fumesthe most (Table I).
If chemists increasingly direct their strength tocontributing to a sustainable civilization, chemistrywill become more interesting and compel Iing topeople and may lose its toxic image. It will becomemore worthy of public support and spawn excitingeconomic enterprises that nurture sustainability'.
Derivatization in organic practicals is a challengingtask for students. An ideal deri vati ve should:
(i) be obtained under mild conditions,
(ii) consume less time and energy in preparing,
(iii) preferably be a solid with a reasonable meltingpoint (60°-160°C),
(iv) be formed in good yield so as to facilitatesubmission of the sample,
(v) use less toxic reagents, solvents etc,
(vi) involves minimum steps and be a single potreaction if possible.
Benzaldehyde and propanone both gi ve productswith Brady's reagent. The products
(i) have melting points 237°C and 128°Crespectively,
(ii) are light and heavily stick to the filter paper,
(iii) yield 70%, time taken 20 minutes heated onwater-bath.
The students are tempted to use large quantities ofBrady's reagent to have sufficient sample forsubmission because the product is sticky.
Table I - Survey of students who tear toxic fumes
I fear chemistry practical because or in ('Ic)
a) Fi re hazards ISb) Poisonous chemicals 14c) Brittle glass apparatus and breakage fires 22d) Toxic fumes 34
Total 85Not answered Ol)
No fears 06
2354 INDIAN J CIIEM. SEC n, OCTOBER 2006
Brady's Reagent is:
(i) a potent skin and eye irritant,(ii) harmful if inhaled/ingested or skin absorbed.
Preparation or dibcnzalpropunone ' which
(i) has melting point 112DC,(ii) is obtained in 94% yield,(iii) needs no healing only manual shaking takes
10-15 minutes,
For dibenzalpropanone:
(iv) is a copious, non sticky product.
FOI"details refer to the experimental section.
The concept of atom economy applied to the abovecase:
Barry Trost' from Stanford University suggestedthis concept or atom economy, which reflects howcfficientl y atoms or the reactants are used in asynthesis i.e. how much of the reactants end up in thefi nal product.
So theoretically while atom economy is as under forthe three derivatives
(1) Dibenzalpropanone
(2) 2,4-DNP of Propanone
(3) 2,4-DNP of Benzaldehyde
86.6
93.0
94.0
In practice the first product is found to be muchsuperior due to the following reasons:
(i) It is a five minute reaction with no energyrequirements. Only manual shaking does the job,
(ii) The product obtained is copious, nonsticky andpure enough with a m.p, 112°C, ,
(iii) The derivative being common for tworepresentative compounds acetone andbenzaldehyde is easy for the pupil to registermentally,
(iv) 2,4-DNP being a skin and eye irritant withadditional toxic effects is better avoided thanliberally used.
Teachers and demonstrators own thisresponsibility of suggesting less harmful and easyderivatives to students after evaluating thempractically.Using simple procedure of physical
homogenization of the reactants a host of derivativescan be prepared on micro scale within minutes andwith the least energy requirement. whilesimultaneously.relating to the reduction in chemicalpollution. ':.;
For macerating the reagents a self designed pestleand mortar can be used as under:
(i) A small china dish (or a toycup) as mortar and athick glass rod with a flattened end (students canmake this in the lab) as pestle,
(ii) A china dish as mortar and a pyrex boiling tubecontaining some hot water as pestle.
Example of reaction being performed regularly:
(i)
(i i)
(i ii)
Benzoylation of aniline/phenol,
Acetylation,
Oxidation of benzaldehyde.
Using the interplay of physical and chemicalprinciples-i.e. physical homogenization ofchemicals, several other derivatives can beprepared on microscale with least hassles.
Try two-in-one experiments for:
(i)
(i)
Reducing the steps of a reaction,
Putting together two almostexperiments for valid reasonscompromising on the results.
identicalwithout
2356 INDIAN J CHEM, SEC B, OCTOBER 2006
(i) Potassium iodide, potassi urn bromide andbromate all are reasonably expensive anddemand wastage minimization.
(ii) Hypo solution, an intermediate, needs to bestandardized either with a standard potassium
--- dichromate or a copper sulphate solutions asprescribed in standard text books.
Present Approach:(i) Standardize hypo with a standard (known)
phenol/aniline solution and then estimate theunknown phenol/aniline within a singleexperiment.
Two examples which form the integral part ofalmost all undergrad B.Sc. honours syllabi of Indianuniversities are cited below.
Estimation of Glucose by
a) Benedict method.b) Fehling solution method.
The two methods are identical in principle exceptfor the type of reagents used.
(i) For a group of 10 students in three differentburettes keep Fehling A, Fehling BandBenedicts reagents,
(ii) Students withdraw the required quantities of thereagent and perform titration with glucosesolution taken in their individual burettes, asprescribed under boiling hot conditions,
(iii) Once with the standard glucose (knownsolution) titrations with the two reagents areperformed one after the other, till concordantvalues are obtained,
(iv) In the next set individual burettes are filled withthe unknown glucose solution and the procedurerepeated as in the first case.
In a live situation, the time consumed for theexercise was practically half while the range oferror in results was considerably minimized.
The principle and procedure for the two estimationare identical.
Advantages:(i) Use of additional solutions (potassium
dichromate or copper sulphate) is avoided,(ii) Students get better opportunity to learn the
experiment in question,(iii) Time and chemicals are saved considerably.
The products of titration were invariably filteredthrough a filter funnel, washed, dried and storedfor future use for detecting bromine and nitrogenas extra elements in other classes.
A significant way to reduce the chemical pollutionin chemistry labs is through downscaling techniques.
"Microscale chemistry and Green Chemistry arecomplementary pedagogies'"
(i) Eliminating glass wares selectively, in favour ofplastic eguipments has a major advantage inperforming micro scale chemistry,
(ii) In academia with limited funds, the saved grantscan be diverted towards instrumentation (IR,Ge, etc.).
Scrap that makes sense
BHANUMATI & DEEP: GREEN EDUCTATION
"Sweet are the uses of adversity which like a toadugly and venomous wears yet a precious stone inhead"
(Shakespeare)
The paradigm of green chemistry gears towardspollution prevention. Its premise is the fact that abenign process and product present no risk.
A valuable substitute, sodium acetate tri-hydrate forthe hazardous sodium metal was experimented for thepreparation of sodium fusion extract used fordetecting the presence of extra elements in organiccompounds using usual procedure. Enlisted are thecompounds which gave satisfactory results:
Novel use of sodium salts of benzoic, oxalic,succinic and phthalic acids for fusion in place ofsodium metal has been equally successful.
(i) This work is in progress as some representativecompounds (amino- and nitro benzene, etc.) didnot give satisfactory answer for nitrogen despiteall efforts,
(ii) The procedure was extended towards inorganicsalts and selective results were obtained.
1. . Sulphides, sulphites and thiosulphates gavepositive test for S
2357
2. Sulphates gave transient violet color withsodium nitorprusside
3. Nitrites answered for N
4. Halogens gave positive answers.
The humble synthesis of alkali metal cyanide bythe fusion of urea and sodium/potassium ethanoate isnoteworthy because both the reagents are organiccompounds by nature.
A green tip for reducing the pangs of inorganicmixture analysis
Remove anions by way of preparing the sodiumcarbonate extract and use· the residue for cationanalysis. (Cu, As, Sb, etc form complex soluble saltswith Na2C03 so treat these as exceptions).
Materials and Methods
Items used in Micro Scale Chemistry
2358 INDIAN J CHEM, SEC B, OCTOBER 2006
Glass items fabricated by women under the project"Waste Glass Recycling" at Gargi College funded byDST: Principal Investigator S Bhanumati.
Innovative tools devised by the author for MicroScale Chemlstry''"
WIT (Welled investigation Tray)
Use push out tablets packs, blistered packs as tinywells equivalents to microtitre plates. With pinsmount on the thermocole block to stabiles and rendera white background for assessing the color change ofthe contents.
For stirring use the tip of ST (sponge tip, plastictooth pick with a sponge head) and for drying thesponge head.
Wit is sensitive to cone. alkali and pure organicsolvents (which you hardly use in titrations!).
Glass WIT and BUD
For plastic sensitive chemicals 'compact' providestiny glass cups which can be embedded in athennocole block to serve as WIT. Glass BUD's areequivalent to Beral pippets.
For Iodometry and titration under hot conditionsmicro bottles with stoppers are used.
Micro bottles with glass stoppers are generallysuited for performing experiments such as Iodometryand Iodimetry. ,..•
Experimental Section
Fabrication of BUD (Bhanu's Utility Droppers)Use flexible plastic/glass droppers as
burettes/pipettes/dispensers, after drawing the tip to acapillary (use a flame, candle or soldering iron fordrawing. Cut the capillary leaving 10 mm lengthintact.Use a common bud for analyte and titrant to avoidcalibration (rinse very well each time).
Label a calibrated bud to avoid confusion.Use vertical delivery for best results.
Calibration of bud:
1. Fix a burette or a calibration tube (a piece ofbroken burette converted into a tube) and fill itwith distilled water up to any whole numbermark.
2. Withdraw distilled water in a BUD. Squeeze theteat gently to expel any air bubble.
3. Reject the first few drops and hold the BUDvertically over the burette or calibration tube andstart counting freefalling drops till the increasein the meniscus is by 1 mL.
4. Repeat the process till concordant values areobtained
5. To obtain the drop value of BUD, divide I mLby the number of drops.
6. Place the drop value as a label on the BUD.
BHANUMATI & DEEP: GREEN EDUCTATION 2359
List of experiments possible using WIT and BUD
1. Acid-alkalimetry.2. Redox titration (dilute solutions of these
chemicals have no reaction on plastic WIT andBUD. One can also use the class alternativementioned earlier.
3. Complexometric titrations-estimation ofdivalent cation (calcium and magnesium ions)using EDTA.
4. Analysis of water quality parametersexperiments.
5. Testing various anions and cation qualitatively.6. Testing S, Cl, Br and I in Lassaignes extract.7. Performing Spot tests in organic and Inorganic
analysis, food adulterants, etc.8. Viewing biological micro specimen under a
microscope.
Use Drop Bottles (DROBO) for various purposes:
Use colorless, ophthalmic medicine bottles as
(1) gas reactions vessels(2) Filtration flasks(3) mini Kipps assembly(4) mini desiccator
For filtrationInsert a 15 mrn funnel into the centre of plastic
nozzle cap of DROBO, use a nail for filter paper andan injection syringe (without needle) as suctiondevice.
Preparation of dibenzalpropanone10 drops (0.25 mole) of benzaldehayde, 4 drops
(0.126 mole) of acetone and 15 drops of methylatedsprit were shaken together in a microtube.Now 20 drops of 10% sodium hydroxide were
added and the mixture was shaken vigorously for 5-7minutes with simultaneous pressure release. The
mixture was cooled in ice. The pale yellow copiousproduct was filtered through a small button andwashed with water, dried collected and weighed. m.p.was determined.
Eco Gloves
ConclusionUsing the strategies illustrated in this paper and
adopting these at school and junior college levels,pollution, wastage and risks in a chemistry lab can beminimized. A huge chunk of money spent on glassapparatus and chemicals can be saved in educationalinstitutions and the same can be diverted to a numberof more meaningful projects of national importanceand relevance. It is suggested that NCERT utilizes thecontent of this education oriented paper for greeningeducation and promoting hands on experience forstudents.
AcknowledgementThe author gratefully acknowledge thanks to UGC
and DST for a research grant. Thanks are also due to
2360 INDIAN J CHEM, SEC B, OCTOBER 2006
the lab staff of Chemistry Department, Gargi Collegefor needful help and to the previous and presentprincipals Dr. Hema V. Raghavan and Dr. MeeraRamachandran respectively for their encouragementand support. The work on Green Chemistry is rapidlyprogressing with the support and grant extended asGargi College is honored as a college with a potentialfor excellence by UGC, Delhi.
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References1 Terry Collins, Carneigi Mellon University, Science, 291
(5501),2001,48.2 Claisen-Schmidt condensation (a) Claisen L & Claparede A,
Ber, 14, 1981,2460; (b) Schmidt J, Ber, 14, 1881, 1459.J Trost B M, Science, 254,1991, 147l.4 Mono M Singh, Zviazafran & Ronald M Pike lCE, 76, 1999,
1684.5 Bhanumati S, International News Letter on Chemical
EducationlUPAC, 45,1997, P 11-15.6 Interview incorporated in BBC film on Survival in Science .
