Lab Documentation
Ionic Liquids and Green Chemistry: A Lab Experiment
Authors names
Annegret Stark Denise Ott Dana Kralisch Guenter Kreisel Bernd Ondruschka
Institutional address
Friedrich-Schiller University of Jena Institute for Technical Chemistry and Environmental Chemistry Lessingstrasse 12 07743 Jena Germany
In the following, some useful information can be found which may be also adjusted to serve as a student handout.
Background Information and Further Reading
Ecological and economic metrics To assess products and processes regarding ecological and economic objectives, life cycle approaches (life cycle analysis (LCA), life cycle costs (LCC)) are often used. The results obtained are well-founded and comprehensive; however, their application is very time-consuming and needs an extensive database. Especially during the R&D phase, data and time are limited, making LCA/LCC methodologies hardly feasible. Nevertheless, a fundamental change from end-of-pipe to inherent environmentally benign strategies can only be realized if the rethinking starts during the R&D stage, since at this stage the ecological and economic impacts of products or processes will be defined. To implement an ecological as well as an economic assessment at this
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stage, single or only a few simple metrics can be used to compare different synthetic pathways, equipment, reactants etc. For instance, Sheldon suggested the environmental factor, E-factor (1-4), which characterizes the mass of waste produced per unit mass of product. The reaction mass efficiency describes the amount of product per amount of starting materials and reagents used (5). A similar approach is the calculation of mass loss indices, considering all substances used in a process in relation to the product mass. In addition, environmental and economic metrics such as the environmental index EI (input- and output oriented) and economic/cost index (CI) have been suggested by Hungerbühler and coworkers (6,7). Further important metrics for daily use in chemistry are e.g. the atom economy developed by Trost (8-10) as well as the mass index established by Eissen (11). In most cases, these indices are mass-based, easy to calculate and therefore widely used.
NOP A web-based, open-access tool has been developed, dedicated to the dissemination of Green(er) Chemistry laboratory experiments (12,13). The name of the platform – NOP – stands for “Nachhaltigkeit im Organischchemischen Praktikum” (German title), i.e. “Sustainability in the Organic Chemistry Laboratory Course”. It offers course material free of charge in various languages, and is open for further contributions. Experiments, e.g. the oxidation of anthracene or nitration of phenol, are evaluated regarding aspects of ecological sustainability, e.g. (eco)toxicity and consumption of energy and resources. Furthermore, the NOP gives background information on sustainability, evaluation methods for chemical substances and reactions and specification of the chemicals used. The NOP employs the metrics yield, atom economy, energy and mass efficiency and E-factor. Furthermore, it integrates a qualitative assessment of the (eco)toxicity of educts, auxiliaries and products. In the style of the NOP, the lab experiment presented herein considers the yield, atom economy, energy efficiency, reaction mass efficiency and E-factor and integrates a qualitative assessment of the (eco)toxicity of educts, auxiliaries and products. Besides mass-based (yield, energy efficiency, reaction mass efficiency, Efactor) and reaction type-based key objectives (atom economy), the assessment of the ecological impacts of the starting material and products as well as prices of chemicals is desirable in order to compare the reactions in a more holistic way. Since life cycle assessment approaches are too complex to deal with in even an advanced lab course, the next section introduces the relevant literature for further studies concerning the assessment of ionic liquids via a life cycle approach.
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Assessing Ionic Liquids: Literature In an ongoing effort, we have set out to elucidate the factors influencing the synthesis of ionic liquids, taking into account also an ecological point of view (14,15). The method proposed by Kralisch et al. (15), namely the ECO method (Ecological and Economic Optimization Method), employs a Simplified Life Cycle Assessment approach and is a screening tool to assess all life cycle stages (supply of reactants, solvents etc., synthesis, work-up, recycling and disposal) of ionic liquids, and products and processes in general. The method consists of three main objectives: the energy factor (EF) describing the energy demand, the risk factor concerning environment and human health (EHF) and the cost factor (CF). By varying and comparing different process parameters at each process step (e.g. T, t, solvent, and reactant alternatives), the optimization potential can be identified to find the most efficient combinations for the synthesis of ionic liquids. Furthermore the method can be used to evaluate the ecological and economic performance of ionic liquids in comparison to molecular solvents (16). Using such a life cycle approach, the search for sustainable chemical compounds, synthesis pathways or processes can already be applied during R&D stage. Also Zhang et al. (17) investigated the use of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4]) as a solvent for a Diels-Alder reaction and for the manufacture of cyclohexane via a life cycle approach (‘from cradle to gate’). The lack of data, errors and possible variation of data were negotiated with the help of a sensitivity analysis. The authors demonstrate that the life cycle environmental impact of the processes using ionic liquids is larger than in the case of conventional methods; furthermore, they emphasize the difficulties and uncertainties accompanied by the assessment of ionic liquids and the importance of life cycle considerations during early stages of decision making in general.
Ionic Liquids in Education: A Literature Review Although ionic liquids have received increasing attention in both academia and industry, a thorough literature review revealed that the development of these neoteric solvents is not reflected appropriately in laboratory courses, although many of our colleagues do indeed cover them in diverse undergraduate lectures. Since learning-by-doing is a well-recognized didactic strategy, especially in the natural sciences, in the following we will summarize the available teaching material on ionic liquids for high-school, undergraduate chemistry and chemical engineering students. It should be noted here that more lab experiment materials, which have not been published in printed journals, may be accessible on the internet from colleagues throughout the world.
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A very good general introduction on high-school and undergraduate level has been published by Endres (18), which demonstrates the potentials of ionic liquids on the examples of electrodeposition of aluminum on a steel screw, and processing of cellulose. In the latter experiment, cellulose material, such as filter paper, is dissolved in the ionic liquid 1-butyl-3-methylimidazolium chloride ([C4mim]Cl), and then injected into water using a syringe, leading to the precipitation of cellulose fibers. Alternatively, interesting structures are achieved by casting; Figure S1 shows a cellulose film with a Euro imprint obtained after spreading a solution of cellulose in [C4mim]Cl on a coin, and careful immersion in a slowly agitated water-bath.
Figure S1 Cellulose imprint of a Euro coin obtained from an ionic liquid – cellulose solution.
This experiment can be used to demonstrate that ionic liquids as solvents are ideal substitutes in some process which - up to now - use environmentally harmful liquids such as CS2 in the viscose process. Both experiments should prove to be quickly adaptable to a teaching lab or demonstration. Additionally, an industrial application of ionic liquids, the BASIL (Biphasic Acid Scavenging using Ionic Liquids) process, highlights engineering advantages which lead to an increase of the process efficiency by a factor of 80,000 (18). Mak et al. (19) presented comprehensive materials on the synthesis of ionic liquids and their use as solvents in the Mannich reaction, including spectroscopic analysis (1H NMR and mass spectroscopy). The supplementary material contains student handouts and instructor’s notes. The lab experiments were designed for groups of three students in an advanced undergraduate synthetic course, and required approximately four times four hours in the lab. The reaction is carried out in both 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4]) and ethanol, and the performance is compared with regard to conversion and solvent recycling (19). Bowman showed how solvent effects on SN2 reactions can be demonstrated to first-year organic chemistry students using ionic liquids. For this purpose, Hughes-Ingold solvent effect rules and some Kamlet-Taft solvent parameters are introduced to the students (20).
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Timetable Depending on the length of the laboratory modules of the course in which this experiment is to be implemented, one of three modes can be chosen: Mode 1 is carried out as a conventional lab experiment, mode 2 as a research project, and by employing mode 3 (“homework assignment”), most teaching goals (Table 2) can be achieved even without any time spent in the laboratory. Chart S1 details the requirements for each mode.
Chart S1
Specifications of the three modes in which the experiment can be conducted.
Group size Laboratory time Home work /report writing Background information (ionic liquids, reaction mechanism, micro-wave assisted synthesis) Data retrieval from literature Experimental data provided
Mode 1 “lab experiment”
Mode 2 “research project”
2-4 students 2x4h Approx. 8 h per student
1-2 students 3x8h Approx. 16 h per student
Mode 3 “homework assignment” 1-2 students 0h Approx. 16 h per student
Lecture
Lecture and/or literature search
Lecture and literature search
R + S codes toxicological data market prices Yields, energy requirements and analytical data for reactions III, IV and V
R + S codes toxicological data market prices None
R + S codes toxicological data market prices Yields, energy requirements and analytical data for reactions I, II, III, IV, V
Chart S2 details the timetable for mode 1. In this instance, a lecture should introduce the students to the background of ionic liquids and their preparation, and microwave-assisted synthesis. The preparation of safety sheets (R + S codes) is recommended as homework assignment prior to the first lab session. In this mode, only experiment I and II are conducted. The data of experiments III, IV and V (compare Table S2) are provided by the instructor, as are the 1H NMR spectra or HPLC chromatograms. Both, the calculation of the results as well as the preparation of the report are carried out as homework assignment.
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Chart S2
Timetable for mode 1: “lab experiment”. 1
Lab Session 1: Reactions I and II Set-up of reactions I and II, conduct reactions 2 Work-up of reactions I and II Lab Session 2: Reactions I and II Drying of the products of reactions I and II Research on toxicological data and market prices Determination of yields Preparation of samples for analysis (1H NMR, HPLC) Obtain data for experiments III, IV and V from instructor Chart S3 presents the proposed timetable of mode 2, which in our experience will require one week (5x8 hours). In dependence on the available time, this mode can be reduced (depending on the priority of some experiments) or extended (e.g. by further syntheses or application examples).
Chart S3
Timetable for mode 2: “research project”.1
Day 1: Theoretical preparation Reading of background on ionic liquids Reading of background on microwave energy input Preparation of safety sheets (R + S codes) Research type of reaction investigated Research on toxicological data available Research on market prices (chemical catalogue) Preparations in lab for next day Day 2: Experimental: conductively heated experiments Set-up of reactions I, III, IV and V, conduct reactions Work-up of reactions I, III, IV and V Preparation of samples for analysis (1H NMR, HPLC) Day 3: Experimental: microwave heated experiment Introduction to microwave oven Set-up of reaction II, conduct reaction Work-up of reaction II Preparation of sample for analysis (1H NMR, HPLC) Day 4: Analysis of results Analysis of 1H NMR data and/or HPLC data 3 Calculation of results Preparation of table of results Day 5: Preparation of report2 If the experiment is carried out in mode 3, i.e. without any laboratory time, a lecture should introduce the students to the background of ionic liquids and their preparation, and microwave-assisted synthesis. The data of
1
Each square equals one hour. The times during the reactions should be used to start with the preparation of the report. 3 Data acquisition may be performed by the students themselves. Alternatively, spectra and chromatograms may be supplied by the lab assistant. 2
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experiments I, II, III, IV and V (Table S2) and 1H NMR spectra or HPLC chromatograms are provided. Both, the calculation of the results as well as the preparation of the report are carried out as homework assignment.
Experimental Information
Equipment and Glass-ware Required 250-mL 2-neck round-bottom flask, oil bath 4 , thermometer, reflux condenser,
I, III, IV, V
magnetic stirrer, rotary evaporator, separatory funnel, graduated cylinder, 100-mL round-bottom flask, energy monitoring socket. II
250-mL 2-neck round-bottom flask, microwave apparatus, internal temperature sensor, 5 reflux condenser, magnetic stirrer, rotary evaporator, separatory funnel, graduated cylinder, 100-mL round-bottom flask, energy monitoring socket.
Chemicals Required Table S1 Exp. Procedure I, II, III, V IV Extraction 1
H NMR HPLC
Chemicals required and their properties (CAS, amount, R + S codes). Chemical substance 1-methylimidazole 1-chlorohexane 1-methylimidazole 1-bromohexane diethyl ether water (dist.) D2O acetonitrile NaH2PO4*2H2O
CAS No. 616-47-7 544-10-5 111-25-1 60-29-7 7789-20-0 75-05-8 13472-35-0
Amount 17.24 g 25.33 g 17.24 g 34.66 g 75 mL 20 mL
R codes 21/22-34 10
S codes 26-36-45 24
10-38-51/53 12-19-22-66-67
25-61 9-16-29-33
11-20/21/22-36 -
16-36/37 -
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Alternatively, a heating mantle can be used. For safety reasons, a technical microwave apparatus (not a household microwave) should be used, e.g. a START (MLS GmbH, Germany) or Discover, Mars (CEM, USA). Internal temperature control using a temperature sensor, which measures the temperature IN the reaction vessel, is important to obtain meaningful results.
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Experimental Procedures Notes: 1.
The experiments are to be carried out on the same scale, using reactors of similar shape. Furthermore, the oil bath should be chosen to be in reasonable relation to the reactor volume, and the oil level has to be the same. Hence, the loss of thermal energy over the oil bath surface is minimized. For similar reasons, other reaction and work-up conditions, e.g. stirrer speed, temperature of cryostat should be kept constant for a better comparison, especially concerning the energy demand of different experiments. Furthermore, for the evaluation, students should be advised that a theoretical scale-up of this kind is only permissible for similar scales.
2.
Before starting the lab experiment, students should be briefed with respect to safety (fume hood, safety goggles, gloves and protective clothing is required). We usually require students to look up and comment on safety cautions of the chemicals used (MSDS-sheets, R + S codes).
3.
Especially regarding the exothermic reaction of 1-bromohexane and 1-methylimidazole to [C6MIM]Br, caution is recommended! Students have to be advised to heat the reaction mixture slowly, and set the starting time once the required temperature is reached. The internal temperature is regulated in all cases via a temperature sensor!
Scheme S1 summarizes the experimental procedures for this lab experiment.
Scheme S1 Reaction parameters in the synthesis of ionic liquids investigated in the lab experiment.
Summary: Experimental Using chlorohexane, both a microwave and a conductively heated experiment are conducted for 3 hours at 100 °C (Experiments I and II). Additionally, the reaction is carried out for 6 hours (oil bath, experiment V) and at 70 °C for 6 hours using either chloro- or bromohexane (experiments III and IV, respectively). This set of experiments allows for comparing the effect of a) the method of energy input (microwave-assisted vs. conductive heating, I Æ II), b) the reactivity of the alkylating agent (III Æ IV), c) the reaction time (I Æ V), and d) the reaction temperature (III Æ V). After the times indicated, the reaction mixtures are dissolved in small amounts
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of water (20 mL), extracted three times with diethyl ether (3x25 mL) 6 , and dried at 80 °C for 1.5 hours under reduced pressure (10 mbar). In our hands, the ionic liquids were obtained as clear, pale-yellow oily liquids with the yields detailed in Table S3. The yield is determined by weighing the crude material, and deducting water (determined by Karl-Fischer titration) and residual 1-methylimidazole (determined by 1H NMR spectroscopy or HPLC, vide infra). The energy requirements of the reaction (heating, stirring) and work-up (removal of volatiles on the rotary evaporator) are measured using an energy monitoring socket.
A.
Synthesis of [C6mim]Cl and [C6mim]Br 7
Conductively Heated Reactions (oil bath); Experiments I, III, V [C6MIM]Cl: The reaction is performed in a 250-mL 2-neck round-bottom flask, fitted with a reflux condenser. Connect an energy monitoring socket to the magnetic stirrer to measure the energy demand during the synthesis. The mixture of 0.21 mol (17.24 g) 1-methylimidazole and 0.21 mol (25.33 g) 1-chlorohexane is allowed to stir for 3 h and 6 h (100 °C, I and V), and 6 h (70 °C, III) respectively, afterwards cooled down to room-temperature. The work-up procedure is carried out by dissolving the crude reaction mixture in water (20 mL), followed by an extraction of the remaining 1-methylimidazole with diethyl ether (3x25 mL). The yield is determined after removal of all volatiles in vacuo (rotary evaporator, water bath T = 80 °C, t = 1.5 h, p = 10 mbar). Because of a small amount of remaining diethyl ether, do not start evaporating at a pressure lower than 600 mbar! Caution: Approach 10 mbar in small pressure steps to avoid bumping of the water-containing mixture. After reaching 10 mbar, connect an energy monitoring socket to measure the energy demand for 1.5 h. Determine the remaining water content by Karl-Fischer titration and the purity by 1H NMR-spectroscopy or HPLC.
Conductively Heated Reactions (oil bath); Experiment IV [C6MIM]Br: The reaction is performed in a 250-mL 2-neck round-bottom flask, fitted with a reflux condenser. Connect an energy monitoring socket to the magnetic stirrer to measure the energy demand during the synthesis. The mixture of 0.21 mol (17.24 g) 1-methylimidazole and 0.21 mol (34.66 g) 1-bromohexane is allowed to stir for 6 h (70 °C, IV), afterwards cooled down to room-temperature. The work-up procedure is carried out by
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Extracting three times with diethyl ether is not sufficient to provide a pure ionic liquid. In our experience, the extraction efficiency of diethyl ether is low, and hence requires often > 10 extractions for purities > 95 %. Hence, we have opted to investigate the efficiency of the work-up by extraction in a latter contribution to this journal. 7 The reactions can be scaled down if required.
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dissolving the crude reaction mixture in water (20 mL), followed by an extraction of remaining 1-methylimidazole with diethyl ether (3x25 mL). The yield is determined after removal of all volatiles in vacuo (rotary evaporator, water bath T = 80 °C, t = 1.5 h, p = 10 mbar). Because of a small amount of remaining diethyl ether, do not start evaporating at a pressure lower than 600 mbar! Caution: Approach 10 mbar in small pressure steps to avoid bumping of the water-containing mixture. After reaching 10 mbar, connect an energy monitoring socket to measure the energy demand for 1.5 h Determine the remaining water content by Karl-Fischer titration and the purity by 1H NMR-spectroscopy or HPLC.
Microwave-Assisted Reaction; Experiment II [C6MIM]Cl: The reaction is performed in a 250-mL 2-neck round-bottom flask, fitted with a reflux condenser. Connect an energy monitoring socket to the microwave oven plug to measure the energy demand during the synthesis. The mixture of 0.21 mol (17.24 g) 1-methylimidazole and 0.21 mol (25.33 g) 1-chlorohexane is allowed to stir for 3 h (100 °C, II), afterwards cooled down to room-temperature. The work-up procedure is carried out by dissolving the crude reaction mixture in water (20 mL), followed by an extraction of the remaining 1-methylimidazole with diethyl ether (3x25 mL). The yield is determined after removal of all volatiles in vacuo (rotary evaporator, water bath T = 80 °C, t = 1.5 h, p = 10 mbar). Because of a small amount of remaining diethyl ether, do not start evaporating at a pressure lower than 600 mbar! Caution: Approach 10 mbar in small pressure steps to avoid bumping of the water-containing mixture. After reaching 10 mbar, connect an energy monitoring socket to measure the energy demand for 1.5 h. Determine the remaining water content by Karl-Fischer titration and the purity by 1H NMR-spectroscopy or HPLC. Microwave programme (for example, multimode, type “Start”, Mikrowellen Laborsysteme MLS GmbH): heating-up to 100 °C at 500 W (approx. 1 min. required); maintain the temperature for 3 h at 100 °C.
Figure S2 shows the equipment necessary for both, the conductively heated and the microwave-assisted set-ups.
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Figure S2 Experimental set-up and equipment necessary for the experimental procedures. Left and middle: conductively heated experiments (I, III – V); right: microwave-assisted experiment (II).
Demonstration: Reaction Performance as Function of Time (Microwave-Assisted vs. Conductively Heated Experiment) Figure S3 demonstrates that indeed, no difference in conversion 8 is observed using the microwave-assisted or conductively heated set-up. Hence, there is no “microwave effect” in this reaction and both reactions are activated thermally.
Figure S3
Alkylation of 1-methylimidazole with 1-chlorohexane (1:1) at 100 °C. Reaction carried out in
an oil bath (squares) or microwave oven (triangles). 8
Since the selectivity of the reaction equals 1, yield = conversion.
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Energy Demand (Synthesis and Work-up) For the determination of the energy demand for heating and stirring (Table S2) energy monitoring sockets (e.g. Energy Monitor 3000, Voltcraft) are used. The round-bottom flask is heated up to the reaction temperature using a conventional oil (alternatively: heating mantle) bath as well as a microwave apparatus. The recycling of diethyl ether is simulated using a rotary evaporator by placing 500 g of the solvent in a 1000-mL round-bottom flask. Diethyl ether is distilled at T = 40 °C (water bath) at ambient pressure. The electrical current necessary to heat the water-bath and for condensation (cryostat) is measured using an energy monitoring socket. The energy demands for attaining operating conditions (rotary evaporator) are not taken into account, since the demand is equal for each experimental procedure. We assume that approximately 90 % of the solvent can be recycled; hence only 10 % of the used diethyl ether is taken into consideration for the inputanalysis. The work-up by drying in vacuo is carried out using a rotary evaporator fitted with a water-bath at 80 °C (real solvent mixture). The pressure decay is adjusted slowly, till 10 mbar are reached without bumping of the watercontaining mixture. The electrical current necessary to run the vacuum pump, to heat the water-bath and for condensation (cryostat) are measured using an energy monitoring socket. The energy demands for attaining operating conditions (rotary evaporator) are not taken into account, since the demand is equal for each experimental procedure.
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B. Analytical Characterization
Product Characterization by 1H NMR Sample preparation: approx. 0.1 g of the ionic liquid are dissolved in 0.7 mL of D2O and measured via 1H NMR spectroscopy. Exemplarily, a spectrum of [C6MIM]Br containing 1-methylimidazole is shown in Figure S4 (measured at 200 MHz, D2O).
Figure S4
1
H NMR sprectrum of 1-hexyl-3-methylimidazolium bromide.
The following signals are detected: 1
H NMR (200 MHz, D2O): δ [ppm] 0.78 (t, 3H, 12), 1.24 (m, 6H, 9/10/11), 1.81 (m, 2H, 8), 3.85 (s, 3H, 6), 4.14
(t, 2H, 7), 7.40 (dd, 2H, 4/5), 8.68 (s, 1H, 2). Additionally, the spectrum shows a signal at 4.66 ppm (D2O, DHO) and at 3.73 ppm (s, 3H, N-CH3 of 1methylimidazole).
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To calculate the 1-methylimidazole content remaining in the ionic liquid, the peaks at 3.73 ppm and 3.85 ppm, belonging to the N-CH3 group of 1-methylimidazole and the ionic liquid, have to be integrated. Afterwards, the mole fraction x of 1-methylimidazole in 1-hexyl-3-methylimidazolium bromide is determined (Eq. S1)
xi =
ni ntotal
(Eq. S1)
The calculation is exemplarily shown below. Peak integral (MIM) 3.73 ppm
7
a
Peak integral (IL)
x (MIM)
x (IL)
3.85 ppm
300
0.023 =7/(7+300)
0.977 =300/(300+7)
m (crude product)a
M (mixture)
n (mixture)
n (IL)
Yield
[g]
[g/mol]
[mol]
[mol]
[%]
50.22
243.370 =0.023*82.102 g/mol + 0.977*247.166 g/mol
0.206 =50.22 g/243,37 g/mol
0.201 =0.206 mol*0.977
96 =100*0.201 mol/0.21mol
mass of crude product after correction by water content (as determined by Karl-Fischer titration).
Product Characterization by HPLC (21) 1-Methylimidazole is determined from a linear calibration curve (between 0 and 500 mgL-1 1-methylimidazole in buffer) obtained on a reversed-phase C-8 (e.g. Hyperchrome 125-4, Prontosil 120-5-C8-SH) HPLC with UV detection at 208 nm using 30 % v/v acetonitrile and 70 % v/v 0.02 M aqueous NaH2PO4 (pH=5) as isocratic eluent (column temperature: 30 °C, flow rate: 1.2 mL min-1, programme length: 8 min). For the sample preparation, approximately 150 mg ionic liquid product is weighed into a 25-mL volumetric flask and dissolved in the eluent mixture. The solution is transferred to a sample vial and analyzed by injecting 5 μL. The retention times of 1-hexyl-3-methylimidazolium cation and 1-methylimidazole are approximately 2.24 and 1.00 min, respectively.
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List of Abbreviations BASIL
Biphasic Acid Scavenging using Ionic Liquids
CF
Cost factor
CI
Cost index
[C4MIM][BF4]
1-Butyl-3-methylimidazolium tetrafluoroborate
[C6MIM]Br
1-Hexyl-3-methylimidazolium bromide
[C6MIM]Cl
1-Hexyl-3-methylimidazolium chloride
ECO
Ecological and economic optimization
EF
Energy factor
E-factor
Environmental factor
EHF
Factor concerning environment and human health
EI
Environmental Index
Et2O
Diethyl ether
GK
Swiss poison class
1
1
HPLC
High pressure liquid chromatography
KF
Karl-Fischer titration
LCA
Life cycle assessment
LCC
Life cycle costs
MAC
Maximum allowable concentration
MIM
1-Methylimidazole
MSDS
Material Safety Data Sheet
NOP
Nachhaltigkeit im Organisch-chemischen Praktikum (German title), i.e. Sustainability in the
H NMR
H nuclear magnetic resonance spectroscopy
Organic Chemistry Laboratory Course R&D
Research and development
S N2
Nucleophilic Substitution
WGK
German water hazard class
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Literature Cited in the Supplemental Material
1.
Sheldon, R. A. Chemistry & Industry (London) 1992, 903-906.
2.
Sheldon, R. A. CHEMTECH 1994, 3, 38-47.
3.
Sheldon, R. A. Chemistry & Industry (London) 1997, 12-15.
4.
Sheldon, R. A. Green Chemistry 2007, 12, 1261-1384.
5.
Curzons, A. D.; Mortimer, D. N.; Constable, D. J. C.; Cunningham V. L. Green Chemistry 2001, 3, 1-6.
6.
Heinzle, E.; Weirich, D.; Brogli, F.; Hoffmann, V.H.; Koller, G.; Verduyn, M. A.; Hungerbuehler, K. Industrial & Engineering Chemistry Research 1998, 37, 3395-3407.
7.
Koller, G.; Weirich, D.; Brogli, F.; Heinzle, E.; Hoffmann, V. H.; Verduyn, M. A.; Hungerbuhler, K. Industrial & Engineering Chemistry Research 1998, 37, 3408-3413.
8.
Trost, B. M. Science 1991, 254, 1471-1477.
9.
Trost, B. M. Angewandte Chemie-International Edition in English 1995, 34, 259-281.
10.
Sheldon, R. A. Pure and Applied Chemistry 2000, 72, 1233-1246.
11.
Eissen, M.; Metzger, J. O. Chemistry-A European Journal 2002, 8, 3580-3585.
12.
Ranke, J.; Bahadir, M.; Eissen, M.; König, B. Journal of Chemical Education 2008, 85, 1000-1005.
13.
Web Page: NOP - Sustainability in the organic chemistry lab course. http://www.oc-praktikum.de (accessed July 2008).
14.
Kralisch, D.; Stark, A.; Körsten, S.; Kreisel, G.; Ondruschka, B. Green Chemistry 2005, 7, 301-309.
15.
Kralisch, D.; Reinhardt, D.; Kreisel, G. Green Chemistry 2007, 9, 1308-1318.
16.
Reinhardt, D.; Ilgen, F.; Kralisch, D.; König, B.; Kreisel, G. Green Chemistry 2008, 10, 1170-1181.
17.
Zhang, Y.; Bakshi, B. R.; Demessie, E. S. Environmental Science & Technology 2008, 42, 1724-1730.
18.
Endres, F. Praxis der Naturwissenschaften 2007, 5, 9-12.
19.
Mak, K. K. W.; Siu, J.; Lai, Y. M.; Chan, P. Journal of Chemical Education 2006, 83, 943-946.
20.
Bowman, D. C. The Chemical Educator 2006, 11, 64-66.
21.
Stark, A.; Behrend, P.; Braun, O.; Müller, A.; Ranke, J.; Ondruschka, B.; Jastorff, B. Green Chemistry 2008, 10, 1152-1161.
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Table S2 Exp. Procedure
I II III IV V
Protocol of the energy demands and masses depending on the reaction procedure: Example results. Reaction Conditions (temperature, reaction time, energy source, starting material)
Energy demand (reaction) [kWh] ([MJ])
Energy demanda (distillation of Et2O) (3*25 mL) [kWh] ([MJ])
Energy demand (1.5 h vacuo) [kWh] ([MJ])
m (crude product) [g]
Water content (KF) [%]
MIM content (1H NMR) [g]
m (product) [g]
m (reactants, solvent for extraction)b [g]
m (non-reacting starting material, solvents) [g] 47.90
100 °C, 3 h, oil bath, 0.083 (0.30) 0.023 (0.083) 0.875 (3.15) 25.60 2.68 4.92 19.99 67.89 1-chlorohexane 100 °C, 3 h, microwave, 0.943 (3.39) 0.023 (0.083) 0.875 (3.15) 29.35 1.65 5.63 23.24 67.89 44.65 1-chlorohexane 70 °C, 6 h, oil bath, 0.124 (0.45) 0.023 (0.083) 0.875 (3.15) 8.80 0.20 5.68 3.10 67.89 64.79 1-chlorohexane 70 °C, 6 h, oil bath, 0.117 (0.42) 0.023 (0.083) 0.875 (3.15) 50.57 0.69 0.39 49.83 77.22 27.39 1-bromohexane 100 °C, 6 h, oil bath, 0.165 (0.59) 0.023 (0.083) 0.875 (3.15) 38.27 3.70 2.75 34.10 67.89 33.79 1-chlorohexane a The energy demand for the distillation of 1 kg diethylether (excluding operation conditions) in our laboratory course was 0.430 kWh. b 17.24 g MIM, 25.33 g C6H13Cl / 34.66 g C6H13Br, 20 g H2O, 5.32 g diethyl ether (10 %) [assumption: only 10 % of the total amount of diethyl ether is considered, since 90 % can be recycled by distillation (to separate from the extracted non-reacting starting materials)].
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Protocol of the metrics atom economy, reaction mass efficiency, E-factor and energy
Table S3
efficiency investigated: Example results. Exp. Procedure
I II III IV V
I II III IV V a
Atom economy [%]
47 55 7 96 80
100 100 100 100 100
Reaction mass efficiency [kg/kg] 0.29 0.34 0.05 0.65 0.50
E-factor [kg/kg]
Energy efficiency [10-3 kg/MJ]
2.4 1.9 20.9 0.5 1.0
5.7 3.5 0.8 13.6 8.9
Determination of the prices of the chemicals used: Example results
Table S4 Exp. Procedure
Yield [%]
m (MIM) [g]
m (diethyl ether) [g]
Price (MIM)a [€]
17.24
m (C6H13X) X = Cl, Br [g] 25.33
5.33
2.68
17.24
25.33
5.33
2.68
17.24
25.33
5.33
2.68
17.24
34.66
5.33
2.68
17.24
25.33
5.33
2.68
Price (C6H13X)a [€]
Price (diethyl ether)a [€] 0.06
Price of chemicals (summation) [€/kg]a 2.73 5.47 €/20 g 273.5 €/kg 2.73 0.06 5.47 €/23.4 g 233.8 €/kg 2.73 0.06 5.47 €/3 g 1823.3 €/kg 1.77 0.06 4.51 €/49.9 g 90.4 €/kg 2.73 0.06 5.47 €/34.1 g 160.4 €/kg of June 2008 (diethylether: www.vwr.com as of
Prices compiled from www.sigma-aldrich.com as February 2008). 500 mL 47.40 € (Aldrich), density = 0.88 g/mL C6H13Cl 500 g 25.60 € (Aldrich) , density = 1.18 g/mL C6H13Br Diethyl ether 25 L 202.00 € (VWR), density = 0.71 g/mL 1-Methylimidazole 500 mL 80.10 € (Aldrich) , density = 1.03 g/mL
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Student Handouts
Questions to Help Preparing the Research Report
From a chemical point of view: 1.
What are ionic liquids? Give an example from catalysis and one from another area of application and outline in which way they act. Are they advantageous for the application? What (potential) drawbacks can you think of?
2.
Discuss the difference between 1-hexyl-3-methylimidazolium bromide and chloride, if the respective application is a) as a reactant (e.g. as carbene ligand), b) a solvent.
3.
What type of reaction are you dealing with? Which factors influence generally this type of reaction, and in which way? What is the difference between 1-bromo- and 1-chlorohexane? Please consult your organic text book.
From a technical point of view: 1.
What are microwaves and by which mechanism do they activate the reaction mixture? What advantages/disadvantages can you think of? Research examples of applications! In which cases are microwaves suitable tools for heating chemical reactions?
2.
Why is it vital to conduct the experiments at the same scale, using reactors of similar shape?
3.
Why should the oil bath be of the same volume and surface, and always be filled with similar amounts of oil?
4.
Why should you not use a household microwave oven?
5.
Why is internal temperature measurement important?
From an ecological point of view: 1.
Which ecological factors/impacts are disregarded? Think about the up- and downstream chains, and give a few examples.
2.
What will happen with the unreacted starting materials in the laboratory/industrial processes?
3.
Formulate rules which contribute to more sustainable, optimized and safer work in the lab.
4.
Research reactions/reaction types in which the atom economy differs from 100 %.
5.
Describe a mathematical correlation between the E-factor and reaction mass efficiency.
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6.
Which parameters influence the reaction mass efficiency and E-factor and how can they be optimized? Why is water for reflux and ice for cooling disregarded? What will happen with the cooling water in the laboratory/industrial processes?
7.
The metrics reaction mass efficiency, E-factor, energy efficiency and price are related to the product mass, and reciprocal of the product mass respectively. Calculate the metrics with regard to the molarity of the product, in order to get a better comparison of the different ionic liquids obtained.
8.
The cumulative energy demand sums up the required energies for all life cycle stages. Which energy demands are to be considered in a life cycle assessment, in addition to the energy demand for the synthesis considered?
9.
The required energy demand for synthesis and work-up can be expressed in CH4-equivalents, when assuming that the electrical current necessary is only derived from the oxidation of methane (as model for natural gas), described by the following equation
CH 4 + 2O2 → CO2 + 2H 2O + energy ↑
(Eq. S2)
The maximum availability of the released energy is given by the net calorific value, defined as the quantity of heat liberated by the complete combustion of 1 kg methane, which amounts to approximately 50 MJ/kg. 9 Estimate the theoretically necessary amount of methane for the energy demand you have determined, according to the equation above and with the assumption that 100 % of the chemical energy can be converted into electrical energy. In addition, research the real efficiency of converting the chemical energy of natural gas into electrical energy.
9
Web Page: The Egineering Toolbox , Fuel Gases - Heating Values.
http://www.engineeringtoolbox.com/heating-values-fuel-gases-d_823.html (accessed July 2008).
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Student Handout Table 1
Protocol of the energy demands and masses depending on the reaction procedure.
Energy demanda (reaction) [kWh] ([MJ])
Energy demandb (distillation of Et2O) (3*25 mL) [kWh] ([MJ])
Energy demandc (1.5 h vacuo) [kWh] ([MJ])
m (crude product) [g]
Water content (KF) [%]
MIM content (1H NMR) [g]
m (product) [g]
m (reactants, solvent for extraction)d [g]
m (nonreacting starting material, solvents) [g]
Exp. Procedure
Reaction Conditions (temperature, reaction time, energy source, starting material)
I
100 °C, 3 h, oil bath, 1-chlorohexane 100 °C, 3 h, microwave, 1-chlorohexane 70 °C, 6 h, oil bath, 1-chlorohexane 70 °C, 6 h, oil bath, 1-bromohexane 100 °C, 6 h, oil bath, 1-chlorohexane a The energy demands for heating and stirring are determined using an energy monitoring socket (Energy Monitor 3000, Voltcraft), and the round-bottom flask is heated up to reaction temperature using a conventional oil bath. b The work-up by recycling of diethyl ether is carried out using a rotary evaporator fitted with a water-bath by placing 500 g of the solvent in a 1000-mL roundbottom flask. Diethyl ether is distilled at T = 40 °C. The electrical current necessary to heat the water-bath and for condensation (cryostat) is measured using an energy monitoring socket. The energy demands for attaining operating conditions (rotary evaporator) can be excluded, since the demand is equal for each experimental procedure. c The work-up by drying in vacuo is carried out using a rotary evaporator fitted with a water-bath at 80 °C (real solvent mixture in a 100-mL round-bottom flask). The pressure decay has to be adjusted slowly, till 10 mbar are reached without bumping of the water-containing mixture. The electrical current necessary to run the vacuum pump, to heat the water-bath and for condensation (cryostat) is measured using an energy monitoring socket. The energy demands for attaining operating conditions (rotary evaporator) can be excluded, since the demand is equal in each experimental procedure. d Cooling water can be excluded; assumption for the solvent loss: only 10 % of the total amount of diethyl ether have to be considered, since 90 % can be recycled by distillation.
II III IV V
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Student Handout Table 2
Protocol of the metrics atom economy, reaction mass efficiency, E-
factor and energy efficiency investigated. Exp. Procedure
Yield [%]
Atom economy [%]
Reaction mass efficiency [kg/kg]
E-factor [kg/kg]
Energy efficiency [10-3 kg/MJ]
I II III IV V
Student Handout Table 3 Exp. Procedure
m (MIM) [g]
m (C6H13X) X = Cl, Br [g]
Determination of the prices of the chemicals used. m (diethyl ether) [g]
Price (MIM) [€]
Price (C6H13X) [€]
Price (diethyl ether [€]
Price of chemicals (summation) [€/kg]
I II III IV V
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