Presentation on theme: "Temperature Controlled Rate Studies of Co(salen) Reversible Oxygen Binding By Philip Chuang."— Presentation transcript:
1 Temperature Controlled Rate Studies of Co(salen) Reversible Oxygen Binding By Philip Chuang
2 Background Information Co(salen) is Cobalt N,N’-bis (salicylaldehyde) ethylenediamineAbility to reversibly bind oxygen discovered by Tsumaki in 19381A square planar dioxygen carrierExists in both an Active and Inactive stateInterested in Effect of Temperaturee on Rate in:Oxygenation of Inactive Co(Salen) in DMSO[(DMSO)Co(Salen)]2 + O2 [(DMSO)Co(Salen)]2O2Deoxygenation of Active Co(salen) in CHCl3Co(Salen)O2 Co(Salen) + O2
3 Active State vs. Inactive State Active State binds Oxygen readilyDimeric Form coordinates between Cobalt centers.2Binds Oxygen in polar aprotic solventsDimeric Form coordinates Co and O.3Diagram from Reference 2Diagram from Reference 3
4 HypothesisThe Rate of Oxygen Binding and Dissociation increases with Higher Temp. More specifically:The Rate of Inactive Co(salen) Oxygenation will Increase with Temperature in DMSO.Rate of Active Co(salen) Deoxygenation will Increase with Temperature in chloroform.
5 Synthetic Method Synthesis of Inactive Co(salen) 1 eq. ethylenediamine added to 2 eq. Salicylaldehyde in boiling ethanol, for 4 min.1 eq. Salen product (from above) refluxed in ethanol under Argon, 1 eq. Cobalt Acetate in H2O added via addition funnelStirred and kept in 700C Water bath for 1 hourSynthesis of Active Co(salen)Same methods as Inactive, but no hot water bathProcedure derived from Reference 4
6 UV-VisUV-VIS of Inactive Co(salen) in DMSO in atmosphereUV-Vis of Inactive Co(salen) in DMSO in N2 from literature5The UV spectra indicates that the Inactive product was obtained.Differences between UV spectra likely due to availability of Oxygen in the DMSO solution
7 H-NMR -The H-NMRs did not correspond to predicted H-NMRs H-NMR of Active Product in dDMSOH-NMR of Inactive Product in dDMSO-The H-NMRs did not correspond to predicted H-NMRs-Conclusive Identification from H-NMR unobtainable-Future improvement: prepare H-NMR in inert atmosphere, include C13 NMR
8 IR SpectraIR Spectra of inactive Co(salen) from Unniversity of Wimona6IR spectra of Inactive Co(salen)With the exception of the C-H peak at 3000, and the nujol peaks at 1500, 1400 and 700 cm-1 look similarFurther reinforces likelihood of obtaining Inactive Product
9 UV-Vis Kinetics Results pt.1 Absorbance vs Time graph of oxygenated Co(salen) in CHCl3 at 150CAbsorbance vs. Time graph of oxygenated Co(salen in CHCl3 at 150C, excluding first 8 data pointsThe first 8 data points were removedNot enough time given to allow temperature to equilibrate
10 UV-Vis Kinetics Results pt. 2 Absorbance vs. Time graph of oxygenated Co(salen) in CHCl3 at 500CAbsorbance vs. Time graph of oxygenated Co(salen) in CHCl3 at 500C without first 8 data pointsAgain, the first 8 data points were discarded.Not enough time was given for temperature to equilibrate
11 UV-Vis Spectra Results pt. 3 -LN Absorbance vs Time plot for 150C deoxygenation of Inactive Co(salen)-LN Absorbance vs. Time plot for 500C deoxygenation of Inactive Co(salen)The slope of the –LN Absorbance vs. Time plot yields the rate constant of a first order reaction.
12 UV-Vis Kinetics Results pt. 4 Absorbance vs. Time plot for Inactive Co(salen) in DMSO at 150C-LN Absorbance vs. Time plot for Inactive Co(salen) in DMSO at 150CNo Data points were removedFor the DMSO runs, temperature was allowed to equilibrate
13 UV-Vis Kinetics Results pt. 5 Absorbance vs. Time graph of inactive Co(salen) in DMSO at 500CResult was not workable, rate could not be calculatedPossible explanations in Discussion Section
14 DiscussionWhen LN Absorbance vs. LN Time plotted (not pictured), linearity observedIndicated a first order reaction:R = k[A] -d[A]/dt = k[A]-d[A]/[A] = k Integrate to get LN [A] = -ktThus k = -LN [A] /tThis method used to attain reaction rates from resultsDecreasing absorbance indicative of oxygen complex formation5
15 Discussionk = /s for oxygenated Active Co(salen) in CHCl3 at 150C in atmospheric conditionsValidity in question due to low correlation coefficientk = /s for oxygenated Active Co(salen) in CHCl3 at 150C in atmospheric conditionsk = /s for inactive Co(salen) in DMSO at 150Ck could not be determined for inactive Co(salen) in DMSO at 500CPossible Reason: Reaction has finishedSupported by the lower absorbance compared to the 150C sample.
16 ConclusionsData supports hypothesis for increased rate of Oxygen Dissociation for Oxygenated Co Active Co(salen) at increased temperaturesNot enough data to support or disprove hypothesis for increased rate of Oxygen uptake in Active form of Co(salen at increased temperatures.Future Considerations:Prepare NMRs and UV-Vis solutions in an inert glovebox using a sealable cuvetteTake the C13 NMR to better characterize productsRun more samples at different temperatures to give better overall picture
17 References T. Tsumaki, Bull. Chem. Soc. Jpn., 13, 252 (1938). Schaefer, W. P., and Marsh, R. E., Acta Crystallogr., B25, 1675 (1969)Bruckner, S.,Calligaris, M., Nardin, G., and Randaccio, L., Acta Crystallogr., B25, 167 (1969)Bailes, R. H., and Calvin, M., J. Amer. Chem. Soc., 69, 1886 (1947)B. Ortiz, and Park, S., Bull. Korean Chem. Soc. 21, 4, (2000)
18 AcknowledgementsI’d like to thank Ankur for always being available to help me at all hours of the daySimone for being a big help during the lab sessions and being ridiculously funnyProfessor Roth for allowing me to use her temperature controlled UV-Vis and giving us a cool, albeit hard final project that taught us to make use of the journal articles available to usFinally my fellow students for being ever supportive and cheery