The Synthesis And Characterization Of Ferrocene Essay

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A Modern Iterative Approach to a Classical Organometallic Laboratory ExperimentPamela S. Tanner, Gennady Dantsin, Stephen M. Gross, Alistair J. Lees, Clifford E. Myers, M. Stanley Whittingham and Wayne E. Jones, Jr. [ 1 ]

State University of New York at Binghamton, Binghamton, New York 13902

( Funded by the National Science Foundation ) ( Submitted to J. Chemical Education )

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Since ferrocene is credited with the rapid acceleration of modern organotransition metal chemical science ( 1,2 ) and the cyclopentadienyl group is extensively used as a stabilizing ligand, it is merely suiting that the synthesis of ferrocene be incorporated into an advanced undergraduate inorganic research lab. In our four recognition class, the pupils work in braces and have the chance to choose six experiments from a sum of nine. Three of these experiments must be selected from the country of stuffs chemical science and the subjects include the synthesis of anhydrous CrCl3, a high temperature superconductor, the ZSM-5 zeolite and the lithium embolism of WO3. Three wet experiments are besides selected. These include the synthesis of W ( CO ) 4, metal composites of DMSO, a tris ( bipyridyl ) Ru composite, ferrocene, and the acetylation of ferrocene. If ferrocene is selected, it must be done in concurrence with the acetylation of ferrocene and these labs make up two of the three moisture labs that are done by the pupil. Each lab incorporates an unfastened ended inquiry that the pupil may reply with the assistance of library research or CAChe molecular mold package with the Project Leader extension. This iterative attack physiques assurance in the pupils ability to research the unknown and reinforces the basic thought of the scientific method.

The ferrocene synthesis has been an highly successful and popular choice. The pupils enjoy the diverse proficient accomplishments acquired during this experiment. These are techniques that a pupil may non be introduced to once more as an undergraduate and include the usage of air-less glasswork while working on a vacuity line, cyclic voltammetry, bulk electrolysis, thin-layer and column chromatography. In add-on, the compounds are characterized by standard methods such as runing point finding, IR and UV-Vis spectrometries.

ExperimentsPreparation of FerroceneFerrocene is synthesized with a alteration of the readying reported by Jolly ( 3 ) . The output in the reported synthesis was 93 % ( 3 ) . Cyclopentadiene undergoes a 4+2 cycloaddition to organize dicyclopentadiene. For this ground, cyclopentadiene is normally purified before usage. Dicyclopentadiene boils at 170C and cyclopentadiene furuncles at 42.5 C. For efficiency, the dicyclopentadiene dimer is thermally cracked utilizing a fractional distillment setup in progress by the instruction helper. While this is normally done on the twenty-four hours of the experiment, we have found that cyclopentadiene may be stored without important dimerization in a foil covered container in a deep-freeze for several yearss. At the beginning of the lab period, the pupils grind KOH in a howitzer and rapidly reassign it to a tared phial. KOH is hygroscopic and should be land in little parts ( 2 g ) . A nitrogen baseball mitt bag is a worthwhile investing for this measure in the process. In add-on to protecting the pupils from the caustic KOH, it ensures that the KOH is dry. The FeCl2.4H20 will besides travel into solution more efficaciously if it is finely land. It is so placed in a tared vial.The pre-weighed KOH ( 15 g ) is placed in a 100 milliliter ( 14/20 ) three-neck unit of ammunition underside flask equipped with a magnetic stirring saloon.

1,2-Dimethoxyethane ( 30 milliliter ) is added with stirring to the KOH. One side of the cervix is stoppered and the other is connected to a vacuity line through a gas arranger. While the mixture is easy stirred and the flask is being purged with a watercourse of N, the cyclopentadiene ( 2.75 milliliter ) is added. The resulting solution is rose colored. The chief cervix is so fitted with a force per unit area equalising dropping funnel ( 25 milliliter ) with its turncock unfastened. In a 2nd one cervix unit of ammunition underside flask that is fitted with a septum, FeCl2.4H20 ( 3.25 g ) and DMSO ( 12.5 milliliter ) are stirred under a N atmosphere to fade out the FeCl2.4H20.

After approximately five proceedingss, the turncock is closed and the FeCl2 solution is added to the force per unit area equalising dropping funnel. The reaction mixture in the three-neck flask is stirred smartly and the purge with N is continued. After about 10 proceedingss, the stopper is placed on the dropping funnel, the N flow is reduced and drop-by-drop add-on of the FeCl2 solution is begun. The rate of add-on is adjusted so that the full solution is added in 30 proceedingss. Then the dropping funnel turncock is closed and vigorous stirring of the dark green solution is continued for an extra 30 proceedingss. Finally, the N flow is stopped and the mixture is added to a mixture of 6M HCl ( 45 milliliter ) and crushed ice ( 50 g ) . Some of the ensuing slurry may be used to rinse the reaction flask to maximise the merchandise output. The slurry is stirred for approximately 15 proceedingss and the orange precipitate is collected on a Buchner or Hirsch funnel and washed with four 5-mL parts of H2O. The moist solid is spread out on a big ticker glass and dried in the air. The compound is so purified through sublimation in a big glass petri dish that is placed on a warm hot home base ( 100 C ) . Care is used to avoid coaling the ferrocene. The purified ferrocene is so characterized by runing point finding, UV-Vis and IR spectrometries, and cyclic voltammetry. We are integrating a majority electrolysis to bring forth the ferrocenium cation.

Preparation of AcetylferroceneAcetylferrocene is synthesized under mild conditions with a alteration of the process reported by Bozak ( 4 ) . The pupils are supplied with ferrocene during the 2nd research lab period so that the acetylation of ferrocene may take topographic point at the same time with the purification of ferrocene. This encourages pupils to develop multi-tasking skills.A mixture of ferrocene ( 1.5 g ) and acetic anhydride ( 5 milliliter ) is prepared in a little Erlenmeyer flask. To this mixture, 85 % H3PO4 ( 1 milliliter ) is added dropwise with changeless stirring. This add-on is exothermal and is accompanied by a alteration in colour. Following the add-on of the phosphorous acid, the Erlenmeyer flask is fitted with a CaCl2 drying tubing. The dark green solution is so heated in a beaker of H2O on a hot home base for 10 proceedingss ( 50 C ) . During this clip, the solution becomes rose colored. The mixture is so poured over ice ( 20 g ) into a big beaker that will suit the gas ( CO2 ) formed during the NaHCO3 neutralisation. Water is used to rinse the reaction flask and maximise the merchandise output. When the ice has melted, little measures of Na hydrogen carbonate are added until gas development Michigans. The pH may be tested with pH paper to see that neutrality is achieved. This is followed by chilling the ensuing orangish solution in an ice bath for 30 proceedingss during which clip a brown precipitate signifiers. This precipitate is collected by suction filtration utilizing a coarse fritted funnel. The dark brown solid is so washed with distilled H2O to take drosss until it is pale orange in colour. It is so dried in air for 15 proceedingss.

Thin bed chromatography is used to optimise the conditions for column chromatography of acetylferrocene. TLC plates ( silica gel ) are provided for pupil usage. Alternatively, microscope slides may be used as TLC home bases by using a slurry that consists of silicon oxide gel ( 40 g ) and trichloromethane ( 100 milliliter ) . A little sum of the petroleum acetylferrocene, which is a mono- and diacetylferrocene/ferrocene mixture, is dissolved in a phial in methylbenzene ( 2-3 beads ) . A little sum of ferrocene is besides dissolved in a separate phial in methylbenzene. A line is penciled on each slide about 1 centimeter from the underside of the TLC home base. The home bases are spotted utilizing a all right capillary applier about on the pencil line. Each home base will incorporate two musca volitanss, one is ferrocene and one is rough acetylferrocene. The musca volitanss are allowed to aerate dry and so a 2nd topographic point is applied at the same location to obtain a concentrated country of compound. The individuality of the topographic point is indicated with a pencil grade. The home bases are separately placed with the patched terminal in the dissolver in five developing Chamberss. The Chamberss contain the undermentioned solutions: crude oil quintessence, methylbenzene, ethyl ether, ethyl ethanoate and a mixture of 10 % ethyl ethanoate and 90 % crude oil quintessence. The pencil grade should be above the solvent degree. The solvent containers are covered while the home bases are developing. The home bases are removed when the dissolver forepart has traveled about 3/4 of the distance of the home base. The home bases are air dried. The TLC home bases may be developed in an iodine chamber. This will ensue in brown musca volitanss that can be marked and identified so that the home bases may be included in a laboratory study. The solutions that provide maximal separation of the two constituents are chosen as column chromatography solutions. For case, ferrocene may elute with methylbenzene while the acetylferrocene remains on the column and is so eluted with a toluene/ethyl ethanoate mixture. The colour of the musca volitanss is helpful to spot the single sets that elute from the column. The petroleum acetylferrocene is dissolved in the solution that is selected to elute the first constituent.

The column is assembled by puting a little piece of glass wool into the underside of the column ( 50 milliliter buret ) . The glass wool is so covered with a little sum of sand and the buret is filled with the dissolver that was chosen to fade out the petroleum mixture. A pulverization funnel is used to slowly make full the column with dry silicon oxide gel to a tallness of about 30 centimeter. The column is ne’er allowed to dry. Alternately, the column may be prepared by the traditional slurry method. A little sum of silica gel may be added to the petroleum acetylferrocene solution to do a slurry that is so added to the top of the column and covered with a little sum of sand. The two solutions ( or mixtures ) are so used to sublimate the petroleum acetylferrocene. The ferrocene set is discarded and the dissolver is removed from the acetylferrocene set by rotary vaporization. It may so be recrystallized from trichloromethane. The acetylferrocene is characterized by runing point finding, IR and UV-Vis spectrometries, and cyclic voltammetry.

DiscussionThe experimental process for the synthesis of ferrocene provided above was adopted after several failed efforts to

incorporate newer microscale techniques that utilize ethylene ethanediol ( 5 ) as the dissolver instead than 1,2-dimethoxyethane. When ethylene ethanediol was used, an highly syrupy reaction mixture resulted that was incapable of being stirred efficaciously in the micro-glassware. Our success rate with the revised readying is 100 % .Our advanced undergraduate inorganic lab is taught in the semester format with two three-hour hebdomadal categories. The pupils learn to multi-task to carry through their lab duties expeditiously. We have provided the undermentioned suggested format ( Table 1 ) to carry through the synthesis and word picture of ferrocene and acetylferrocene in two and a half hebdomads. This format is non provided to the pupils. They are advanced and are required to subject their ain agendas before get downing work. The format allows teachers and learning helpers to flexibleness in the method of guaranting that the pupils use their clip expeditiously.

Table 1. Suggested Time Management Schedule Day Program1 Synthesis of Cp2Fe ; learning helper to supply cyclopentadiene2 Sublimation of Cp2Fe ; pupils are given Cp2Fe to execute the acetylation3 Thin bed and column chromatography of acetylferrocene followed by rotary vaporization ; get down word picture of Cp2Fe ( runing point, UV-Vis, IR ) 4 Word picture of acetylferrocene ( runing point, UV-Vis, IR ) ; CAChe modeling5 Finish word picture including cyclic voltammetry and majority electrolysis

Crude ferrocene and acetylferrocene were synthesized in 51-79 % and 27-58 % output severally. An experimental thaw point scope of 169-171 C was obtained for ferrocene. The reported thaw point scope is 173-174 C ( 3 ) . For acetylferrocene, the experimental thaw point scope was 80-83 C as compared with the reported scope of 81-83 C ( 7 ) . Infrared spectrometry was performed by the pupils on ferrocene and acetylferrocene both as a KBr pellet and as a Nujol mull on NaCl home bases. The infrared spectra were comparable to those reported for ferrocene ( 3 ) and acetylferrocene ( 8 ) . The chief difference between the spectra of ferrocene and acetylferrocene is of class the visual aspect of a carbonyl stretch at 1736 cm-1 that is present in the acetylferrocene and absent in the ferrocene. Some pupils besides observed a extremum at 893 cm-1 that is attributed to the monoacetylferrocene pealing. They did non detect extremums that could be attributed to the 1,2-diacetylferrocene composite at 917 cm-1 or a doublet due to the 1,3-diacetylferrocene composite at 922 and 905 cm-1 ( 8 ) . The experimental UV-Vis spectra of ferrocene and acetylferrocene were obtained in acetonitrile and Beers jurisprudence was used to cipher the molar absorption factor. The UV spectrum for ferrocene shows maxima at 330 nanometers ( 2 = 52 ) and 440 nanometer ( 2 = 90 ) , and a lifting short-wavelength soaking up at 225 nanometers ( 2 = 5051 ) . This is comparable with the reported spectrum in ethyl alcohol ( 3 ) . The UV spectrum for acetylferrocene shows maxima at 219 nanometers ( 2 = 2.2 ten 104 ) , 266 nanometer ( 2 = 5268 ) and 320 nanometer ( 2 = 1124 ) . Except for the deliberate molar absorption factor of the extremum at 219 nanometer, this is comparable with the reported spectrum in 95 % ethyl alcohol ( 8 ) . The pupils besides observed extremums assigned to ferrocene in their acetylferrocene samples.

The electrochemistry constituent of this research lab was the first clip that most pupils were exposed to cyclic voltammetry and the majority electrolysis technique. An Amel System 5000 Potentiostat was used for all measurings. For cyclic voltammetry, the electrochemical cell was a 100 milliliter beaker equipped with a Ag/AgCl mention electrode ( pupil prepared ) , a BAS ( West Lafayette, IN ) platinum-disk working electrode ( 2 mm diameter ) and a big ( 1 cm2 ) Pt flag counter electrode. After holding verified a level background of tetrabutylammonium hexafluorophosphate ( 0.01 M ) back uping electrolyte in acetonitrile in the scope 0.0 to 1.0 V vs. Ag/AgCl, cyclic voltammograms of ferrocene and acetylferrocene ( about 3.2 ten 10-3 M ) were obtained at scan rates of 100 500 mV/sec. A typical cyclic voltammogram of ferrocene showed a reversible oxidization at E1/2 = +0.35 V vs. Ag/AgCl with Ep/2 = 0.057V. A typical cyclic voltammogram of acetylferrocene besides showed a reversible oxidization at E1/2 = +0.58 V vs. Ag/AgCl with Ep/2 = 0.044V. Small extremums for ferrocene were besides seeable in the acetylferrocene cyclic voltammogram. These consequences are comparable to the reported E of acetylferrocene at +0.27 V vs. the ferrocene/ferrocenium twosome ( 6 ) .

A 2nd new electrochemical constituent that was late introduced into this research lab is the bulk electrolysis of ferrocene to ferrocenium. The electrochemical cell was a 100 milliliter beaker equipped with an Ag/AgCl mention electrode ( pupil prepared ) , a BAS ( West Lafayette, IN ) reticulated vitreous C ( RVC ) working electrode and an highly big Pt flag counter electrode. After holding verified a level background of tetrabutylammonium hexafluorophosphate ( 0.01 M ) back uping electrolyte in acetonitrile in the scope 0.0 to 1.0 V vs. Ag/AgCl, the majority electrolysis of ferrocene ( about 7.5 ten 10-4 M ) was achieved on several occasions. As expected, a new extremum in the UV-Vis was observed at 620 nanometers and the solution changed colour from orange to blue. Unfortunately to day of the month, these experimental conditions are non consistent.

As a addendum to their standard chemical word picture, pupils used the CAChe molecular patterning plan to construct a ferrocene molecule in both the eclipsed and staggered conformations and to take an negatron to obtain information about the ferrocenium cation. The consequences of this mold were so discussed in relation to their experimental observations.

When the pupils have synthesized and derivatized ferrocene, they have an experimental background for comparing of the unsubstituted ferrocene versus the acetylated ferrocene. They besides have a clear apprehension of the possible R groups that are chemically practical. This is particularly meaningful if the pupil has completed organic chemical science and is able to associate the familiar benzine substituents with the ferrocene molecule. We have found that if a pupil returns through the iterative inquiry before understanding the acetylation experiment, they design unusual, fantastic and impractical molecules with the assistance of the CAChe system. It must be stressed that molecular mold is merely a tool. The input is influenced to a big grade by the apprehension of the operator which may be enhanced with counsel from the teacher.

A natural patterned advance at the completion of the two syntheses is the debut of the iterative inquiry. Students are asked to plan a ferrocene with specific belongingss such as a different coloured ferrocene. This inquiry is answered with the assistance of CAChe patterning where electronic spectra of the gas stage ferrocene and the substituted ferrocene may be generated by ZINDO ( Zerners Intermediate Neglect of Differential Overlap ) . A more comprehensive iterative undertaking involves both library work and molecular mold. The pupils are asked to happen the readying of a substituted ferrocene in the library. They may besides plan a synthesis and corroborate the synthesis with the assistance of library mentions. They so model the complex and predict its spectroscopic features based upon what they are able to cipher from the molecular theoretical account and their cognition of general chemical tendencies.

Since the pupils became familiar with cyclic voltammetry, one tendency of involvement involves the ionisation potency of the substituted ferrocenes. One pupil undertaking involved a comparing of several known substituted ferrocenes ( 6 ) and their gas stage theoretical accounts ( Figure 1 and Table 2 ) . The gas stage theoretical accounts were used since the expected dissolver dependance has non been observed utilizing the CAChe system due to initial restrictions with undertaking leader. The initial deliberate ionisation potencies were adjusted by deducting 7.647 electron volt. This sets the ferrocene/ferrocenium twosome at nothing as is customary ( 6 ) . These values and a least squares arrested development secret plan were so plotted. In general, a downward tendency in the least squares arrested development is observed with the more easy reduced ferrocenes incorporating negatron retreating substituents holding positive ionisation potencies. Conversely, the more easy oxidized ferrocenes with negatron donating substituents are calculated with negative ionisation potencies. Deviations from experimental informations may be accounted for since the pupil was comparing gas stage ferrocene theoretical accounts and acetonitrile ferrocene electrochemistry ( 6 ) .

Fig. 1. Student CAChe Project

Table 2 Student CAChe Project

ConclusionThe incorporation of an iterative inquiry into each of our advanced inorganic undergraduate research labs has allowed pupils to plumb the deepnesss of their chemical cognition and to get new tools that improve their usage of the scientific method. The pupils enjoy the high success rate of the ferrocene/acetylferrocene lab. They besides appreciate the opportunity to get new man-made techniques such as the usage of Schlenk techniques. In add-on, the usage of fresh instrumental analysis such as electrochemistry is good to their overall undergraduate instruction. They seem to boom on the diverse exposure and the chance to stretch themselves. This allows them to go aroused about chemical science and like the experiment that they are carry oning, they come full circle and position chemical science in a new visible radiation as a utile, valuable tool. The add-on of the iterative inquiry to a classical research lab can therefore supply an extra profusion to the traditional wet chemical science.

AcknowledgmentsResearch supported by NSF under Grants # DUE-9452023 and DUE-9452131.

Literature Cited1. Kauffman, George B. J. Chem. Educ. 1983, 60, 185.2. Kealy, T. J. ; Pauson, P. L. Nature 1951, 168, 1039.3. Reasonably, W. L. , The Synthesis and Characterization of Inorganic Compounds, Prentice-Hall: New Jersey, 1970.4. Bozak, R. E. J. Chem. Educ. 1966, 43, 73.5. Szafran, Z. ; Pike, R. M. ; Singh, M. M. , Microscale Inorganic Chemistry, Wiley: New York, 1991.6. Geiger, William E. J. Organomet. Chem. 1990, 22, 142.7. Wade, Leroy G. J. Chem. Educ. 1978, 55, 208.8. Rosenblum, Myron, Chemistry of the Iron Group Metallocenes: Ferrocene, Ruthenocene, Osmocene Part One, Interscience Publishers: New York, 1965.

The Synthesis And Characterization Of Ferrocene Essay

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