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Formation and Kinetics of Dissociation of Some Pentaaquotrihalomethyl Chromium(Iii) Ions

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Formation and Kinetics of Dissociation of Some Pentaaquotrihalomethyl Chromium(Iii) Ions University of the Pacific Scholarly Commons University of the Pacific Theses and Dissertations Graduate School 1973 Formation And Kinetics Of Dissociation Of Some Pentaaquotrihalomethyl Chromium(Iii) Ions. Sher Khan Malik University of the Pacific Follow this and additional works at: https://scholarlycommons.pacific.edu/uop_etds Part of the Chemistry Commons Recommended Citation Malik, Sher Khan. (1973). Formation And Kinetics Of Dissociation Of Some Pentaaquotrihalomethyl Chromium(Iii) Ions.. University of the Pacific, Dissertation. https://scholarlycommons.pacific.edu/ uop_etds/3049 This Dissertation is brought to you for free and open access by the Graduate School at Scholarly Commons. It has been accepted for inclusion in University of the Pacific Theses and Dissertations by an authorized administrator of Scholarly Commons. For more information, please contact [email protected]. FDRMATION AND KINEriCS.OF DISSOCIATION OF SOME PENTAAQUOTRIHAL0~1ETHYLCHROMIUM( III) IONS. +-----------------------------~A-Dissert-a~1o~n~----------------------------------­ Presented to The Faculty of the Graduate School University of the Pacific In.Partial Fulfillment of the Requirement for the Degree Doctor of Philosophy .. by Sher Khan Malik May 1973 ACl'J-J'Ovli.EDGFJl!Ei'~"T The author wishes to thank Dr. Larry 0. Spreer, the Director of Research program, for his supervision and support of this project. The author further thanks Dr. Wilfred Scrt~ddt (Aerojet General Corporation, Sacramento) for his help in Mass Spectrometry work of organic products; Dr. Emerson Cobb for his help in rraking the arrange­ ments for this period at the University of the Pacific; and the merr:bers of the Cherrrrstry Department for their help and hospitality . .. ._.__ . ____________________________________....... _ This dissertation, written and submitted by Sher Khan Malik is approved for recommendation to the Committee on Graduate Studies, University of the Paciflc Dean of the School or Department Chairman: Dissertation Co ittee: Chairman Dated~------------------------------------- . I Formation and Kinetics of Dissociation of Some Pentaaquotrihalomethy lchrotnium( III) Ions. The present.study was an investigation of the formation and kinetic stability of sotre conplexes conta.ir)ing a chromium-carbon bond in an aqueous rredium. An orange-bi'CMJ1 pentaaquotrifluoromethylchromium(III) ion was ob­ tained by the. reduction of trifluororrethyl,iodide with Cr(II) and is the most inert of any organochrotnium(III) COI'lfJlex known. The initial aquation rates. of trifluororrethylchromium(III) ion were described by the differential rate aw 2+ + -dln [(H o) crCF ]/dt = ko + k (H) 2 5 3 1 The products of the initial reaction were hexaaquochromium(III), cart>on monoxide and HF. The values of k and k1 at 45°C were 5~21 x l0-7se.::-l and 9. 38 x lo-1t·1-lsec-1 respectively. 0 The activation pararreters for the acid independent and acid dependent pathway~ were: ~ = 19.7 kcal/~le, As+ = -27.4 cal-defliOOle-1; and ..c.w- =· 23.4 kcWrrole and AS = -12. 9 cal-deg-lrrole- . 1 1 The acceleration in ·the aquation with tirre was observed indicating l+ autocatalysis by a product of. the reaction. An internediate, ( Cr( OH ) FCrCF ) , 2 4 was separated from the aquation reaction solution; this sarre ion was also 3 formed immediately when fluoride ion was added to the (H 2o) crCF~2+ ion in 0.051·1 perchloric acid. The. added fluoride ion also increased5 thi:i rate of. aquation. Rapid formation of (Cr(OH 2 )1JFCrCF~l+) ion was attributed to the strong labilizing effect of the trifluorometfiyl ligand on water rrolecules in the inner coordination sphere of chromium( III) . A sol vent'-assisted mechanism for the aquation of pentaaquotrifluoromethyl­ chrotnium(III) ion was proposc!'d in which an activated co~lex was formed which dissociated in a concerted manne.· to give the products. Also, a reaction sequence was proposed for the co~lete aquation reaction which was consistent with the rate laws, the effect of added fluoride ion and the activation pararreters . Pink organochrotnium(III) species of 2+ charge was isolated in the reduction of carbon tetrachloride and carbon tetrabrotnide with chromium( II). 'rhe pink species have ·chromium:carbon:halide ratios of 1:1:1 and their uv-visible spectra showed unusually higp absorbancy values in the 500 nm region. The pink organochromii..un(III) reacted very rapidly with oxygen. 'l'lic products of dis:1ociation were carbon rronoxide, formic acid, formaldehyde, !Jr:x:wquochromiwn(III), chromium( II) nhd halide ion::;. 'l'he kineticn of a11uatlon wuroe :.;tudicd, and initial rate coefficients and activation pnr­ ruretem were obt.ained. The· identity dt these organochromium(III) species was not established but roost possible structures· were proposed. --~ TABLE OF CONTENTS PAGE I INTRODUGriON . 1 II EXPERJJVJENTAL... • • • • • • • • • • • • • • • 4 A. Reagents . • . • • . 4 Sodium perchlorate solution . • . 5 Formaldehyde Solution . • . 5 Formic Acid Solution . • 5 Ion-exchange resin . • . • . 5 il-------~B""'-'--. _.,..Synthesis . ,_____._,_,_,_,_._,_._._._,_,_,_:__._,_,_,_,_,_,__ 6, _______ ---i ChY~mium(II) perchlorate solution . 6 Pentaaquotrifluoromethylchromium(III) . 6 Ion-exchange chromatography . 6 Fluorotetraaquotrifluoromethylchromium(III) ion 7 Pentaaquochloroorganochromium(III) ion 8 Pentaaquomonobromoorganochromium(III) ion . • • . 8 Separation of monohalogenoorganochromium(III) ion . 9 Hexaaouochromium(III) ion . 10 Fluoropentaaquochromium(III) ion . • . • 10 C. Analyses . • . • • • . • • • • • 10 Chromium(III) . • • . • • . • • . • 10 F~oti~ioo . • . • • . U Bromide and Chloride . • . 17 Carbon monoxide and Carbon dioxide • . • . 1~ Formaldehyde . • • • . • . • . • 18 Formic Acid . 20 Sodium perchlorate . • • • 22 D. Procedures . 2 4 Determination of Isosbestie for Hexaaquochromium(III) and Fluoropentaaquochromium(III) ion . 24 E. Kinetic Measurements • . • • • • 24 Pentaaquotrifluoromethylchromium(III) ion . 24 Pentaaquomonohalogenoorganochromium(III) ion • • • • • 26 Measurements of Fluoropentaaquochromium( III) ion in Aquation and Anation Reactions • • • • • 28 .Constant temperature bath • • • 28 :::rr. RESULTS . • • • • 29 A. Pentaaquotrifluoromethylchromium(III) ion . 29 Uv-visible spectrum • • • • • • • 29 Composition • . • • • • • · +. • • • • • • • • • • • 29 Aquation Products of CrCF 2 • • • . 3 33 Kinetics of CrCF32+ • • • • • • . • • • • • . • • • • • 34 Aquation of CrCF~2+ in the presence of halide ions • • 65 Effect of.Fluoriae ions on other complexes containing chromium-carbon bonds • • • . • . • • • • • • • • • • . 69 - CHAPI'ER PAGE B. Fluorotetraaquotrifluoromethylchromil.IDl(III) ion 71 Uv-visible spectrum . 71 Composition . • . 71 Equilibrium constant 71 Activation parameters .•....•. 77 C . Monohalogenoorganochrorni1.ID1( III) ions 79 Characterization . 79 Reaction with Oxygen . • . • . 79 Products in the Absence of Oxygen . 85 Kinetics . 85 lV. DISCD0-siON • • TO? A. Pentaaquotrifluoromethylchrornium(III) ion .. 105 B. Pentaaquomonohalogenoorganochromium(III) ion 117 BIBLIOGRAPHY . 122 ·~· n--- - LIST OF TABLES TABLE PAGE 1. Standardization of Lanthanwn Nitrate with Sodiwn Fluoride 14 2. Titration of Free Fluoride with Lanthanwn Nitrate . • . 15 3. Aquation Products for the Aquation of CrCF 2+ in the Absence of Ozy gen . 3. 32 4a Chromiwn(III) Products vs Time in the Aquation of CrCF 2+ il-----I-oi-r . • . • • . • • • • • . • . • • • • • • • . • 3.'-.------;35 4b Chromium(III) Products vs Time During the Reaction of Fluoride with Hexaaquochromium(III) Ion . 36 5-7. Absorbance vs Tilne for the Aquation of Pentaaquotrifluoro­ methylchromium(III) Ion • . • . • • , . • ~7-63 8. Initial Rate Coefficients for the Aquation of Pentaaquotrifiuoro­ methylchromium(III) as a Function of-Temperature and Hydrogen Ion . 66 9. Hydrogen Ion Dependent and Independent Initial Rate Coefficients for the Aquation of Pentaaquotrifluororrethylchromium(III) Ion . 67 10. IPitial Rate Coefficients for the Aquation of CrCF 2+ Ion with Added Fluoride • • . • • . • . • . • 3• . • • 70 11. Product Analysis for the Aquation of Fluorotetraaquotrifluoro- methylchromium(III) Ion • • • • • • • . • • . 74 12. Equilibrium Quotient for crCF 2+ and FCrCF 1+ Ions at 25°C 76 3 3 13. Activation Parameters for CrCF 2+ Ion • • • . • . 78 3 14. Reaction Products of MonohalogenoorganochromiU!n(III) Ions ·in the Presence of Oxygen • • • • • • • • • • . • • • • • • . • 84 15. Aquation Products of Monohalogenoorganochromium(III) Ions in the Absence of oxy·gen • • • • . • • • •· • . • • • • • • • 86 - 16-18. Absorbance vs Time for the Aquation of Pentaaquomonochloro­ organochromium(III) Ion in the Absence of Oxygen •.•••• 88-93 19. Initial Rate Coefficients for the Aquation of Pentaaquomono­ . chloroorganochromium(III) as Function of Temperature and Hydrogen Ion Concentration • • . • • • • • • • • • • . • • • • 95 TABLE PAGE 20-22. Absorbance vs Time for the Aquation of Pentaaquomonobrorno­ organochromium(III) Ion . • . • . 96~101 23. Initial Rate Coefficients for the Aquation of Pentaaquomonobromo­ organochromium(III) Ion as Function of Temperature and Hydrogen Ion Concentration . • . • . .104 '....,. LIST OF FIGURES FIGURE PAGE 1. Plot of ~mv/b'rnl) vs. Milliliters of Lanthanum Nitrate 13 2. Contmstion Apparatus . • . • 19 3. Beer's Law Plot for Formaldehyde . 21 4. Beer's Law Plot for Formic Acid 23 5. Isosbestic Points for Hexaaquochromium(III) and Fluoropenta- {\-------caquoehromi:ttm(-I-I-I--)-I-on~ . • • . • • . • . • . • • • • • . • • 25 . 2+ 6. ln(At-Aoo)
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