Rainer Glaser, ChemistryMLS Proseminar, November 16, 2009

(with updates)

Complexity of Growth & DeclineDelayed Consequences and Oscillations

Chemical Reaction KineticsLandolt Iodine Clock Reaction (Chem. Ber., 1885)Belousov-Zhabotinsky Reaction (Nature, 1970)

Briggs-Rauscher Reaction (J. Chem. Educ., 1973)

Organization of Activities1. Meeting, 11/16: Chemistry Background, Lecture, Dr. Glaser

2. Meeting, 11/30: Experiments by 4 Student Groups, Dr. Glaser & Ms. Miller 2 Student Groups perform Landolt and Briggs-Rauscher Reactions

2 Student Groups perform Landolt and Belousov-Zhabotinsky Reactions3. Meeting, 12/7: Mathematical Simulation, Dr. Chicone

Focus on Lengyel Reaction, a Briggs-Rauscher-type Reaction

Simple Chemical Kinetics: Differential Form

http://www.chm.davidson.edu/vce/Kinetics/index.html

Zero-Order Reaction (red)The rate of reaction is a constant. When the limiting reactant is completely consumed, thereaction abruptly stops.

Differential Rate Law: r = kUnit of k: mole L-1 sec-1

First-Order Reaction (green)The rate of reaction is directly proportional to the concentration of one of the reactants.

Differential Rate Law: r = k [A]Units of k: sec-1

Second-Order Reaction (blue)The rate of reaction is directly proportional to the square of the concentration of one of thereactants.

Differential Rate Law: r = k [A]2

Units of k: L mole-1 sec-1

Simple Chemical Kinetics

Organic Chemistry Demonstration Experiments on Video Chemistry Visualized

Peter Keusch, University of Regensburg

http://www.chemie.uni-regensburg.de/Organische_Chemie/Didaktik/Keusch/D-Video-e.htm

Landolt Iodine Clock Reaction

How to recognize starch in your food…

And then my friendly local chemist reminded me of the easy test for starch: simply drop iodine onto the suspect food. If it contains starch, the color of the iodine will darken from orange to shades ranging from inky blue to black.

http://easyweb.easynet.co.uk/~design.machine-tanya/irritable.bowel/test.htmhttp://www.webelements.com/iodine/

The Element Iodine

Iodine is a bluish-black, lustrous solid. It volatilizes at ambient temperatures into a pretty blue-violet gas with an irritating odor.

Landolt Iodine Clock Reaction

http://www.elmhurst.edu/~chm/vchembook/548starchiodine.html

Starch

Amylose and AmylopectinGlucose Polymers

Landolt Iodine Clock Reaction

Bisulfite reduces Iodate to Iodine (Overall)

5 HSO3- + 2 IO3

- + 2 H+ 5 HSO4- + I2 + H2O

If this were a simple reaction, then one would expect that iodine is formed as soon as the bisulfite and iodate solutions are mixed.

Instead, the experiment shows that the iodine concentration [I2] remains below detection limit until [I2] builds up, quite suddenly, after a delay time t.

Now watch the video (requires Real Player).

Landolt Iodine Clock Reaction

Bisulfite reduces Iodate to Iodide (LR1)3 HSO3

- + IO3- 3 HSO4

- + I-

Iodate reacts with Iodide to Iodine (LR2)5 I- + IO3

- + 6 H+ 3 I2 + 3 H2O

Bisulfite reduces Iodine to Iodide (LR3)I2 + HSO3

- + H2O 2 I- + HSO4- + 2 H+

Iodine-Iodide-Starch Complex Formation (LR4, fast!)x I2 + y I- + amylose blue complex

Symproportionation

Landolt Iodine Clock Reaction

Iodate (+V) Iodine (0) Iodide (-I)

IO3- I2 I-

LR2 - fast

LR3 - very fast

LR1 - slow

While LR1 and LR3 occur:[1] Iodate concentration continuously decreases

[2] Iodide concentration increases, then collapses [3] Iodine concentration cannot build up until bisulfite consumed

Landolt Iodine Clock Reaction

Stoichiometry: 5 bisulfite for every 2 iodate.

Solution A (1 L) contains 1.16 g NaHSO3. Solution B (1 L) contains 4.3 g KI.MW(NaHSO3) = 104 g/mol; MW(KI) = 166 g/mol

50 mL of solution A contain 1.16/20 g NaHSO3, or 0.56 mmol. 50 mL of solution B contain 4.3/20 g KI, or 1.3 mmol.

25 mL of solution B contain 0.65 mmol.

Our conditions: Not stoichiometric. Excess of iodate. We will run out of bisulfite for sure!

The slow reaction LR1 depends on the concentration of iodate.Rate of reaction LR1 = kLR1 [HSO3

-]m [IO3-]

The faster LR1, the faster we will run out of bisulfite!

Landolt Iodine Clock Reaction

Church-Dreskin Induction PeriodOn the Kinetics of Color Development in the Landolt (“Iodine Clock”) Reaction.

Church, J. A.; Dreskin, S. A. J. Phys. Chem. 1968, 72, 1387-1390.

€

P = 0.0037secmol2 L−2

[KIO3] [NaHSO3]

Refs from Sobel, 2006.

Rings or Spirals!

Belousov-Zhabotinsky Reaction“unstirred”

http://www.youtube.com/watch?v=bH6bRt4XJcwhttp://www.youtube.com/watch?v=GEF_NtTNeMc&feature=related

Click here to see the video of the “stirred” BZ Reaction

(requires Real Player).

Click here for a great video (requires Real Player).

http://www.youtube.com/watch?v=PI2Y7wzhjVA

Belousov-Zhabotinsky Reaction

Bromate (+V), BrO3-

Bromite (+III), BrO2-

Hypobromite (+I), BrO-

Bromide (-I), Br-

[Fe(o-phen)3]2+

Ferroin

[Fe(o-phen)3]3+

Ferriin

Oscillations in Chemical Systems. I. Detailed Mechanism in a System Showing Temporal Oscillations. Noyes, R. N.; Field, R. J.; Koros, E. J. Am. Chem. Soc. 1972, 94, 1394-1395.

[(Ce3+)(NH4+)2(NO3

-)5]

Bromination of Malonic Acid with Bromate and in the presence of Bromide

BrO3- + Br- + 2 H+ HBrO2 + HOBr (R3)

slow HBrO2 + Br- + H+ 2 HOBr

(R2) HOBr + Br- + H+ Br2 + H2O

(R1) Br2 + MA BMA + HBr

(R8)

BrO3- + 2 Br- + 3 MA + 3 H+ 3 BMA + 3 H2O (A)

[HBrO2]A = k3/k2 [BrO3-][H+] = 510-10 [BrO3

-][H+] (1)Lots of Br-, lots of Br2 production.

Belousov-Zhabotinsky ReactionNoyes-Field-Koros Model

Bromination of Malonic Acid with Bromate and in the absence of Bromide

BrO3- + HBrO2 + H+ 2 BrO2 + H2O (R5)

slowBrO2 + Ce3+ + H+ HBrO2 + Ce4+ (R6) 2 HBrO2 BrO3

- + HOBr + H+ (R4) HOBr + MA BMA + H2O (R8a)

BrO3- + 4 Ce3+ + MA + 5 H+ BMA + 4 Ce4+ + 3 H2O (B)

[HBrO2]B = k5/2k4 [BrO3-][H+] = 110-4 [BrO3

-][H+] (2)[HBrO2] is 100,000 times higher compared to process A!Independent of [Br-].

Belousov-Zhabotinsky ReactionNoyes-Field-Koros Model

The Bromide Switch

BrO3- + 2 Br- + 3 MA + 3 H+ 3 BMA + 3 H2O (A)

[HBrO2]A = k3/k2 [BrO3-][H+] = 510-10 [BrO3

-][H+] (1)Lots of Br-, lots of Br2 production. Keeps [HBrO2] low.

BrO3- + 4 Ce3+ + MA + 5 H+ BMA + 4 Ce4+ + 3 H2O (B)

[HBrO2]B = k5/2k4 [BrO3-][H+] = 110-4 [BrO3

-][H+] (2)Independent of [Br-].

[Br-]crit = k5/k2 [BrO3-] = 310-6 [BrO3

-] (3)

Now we know why solutions reacting by (A) will turn themselves into solutions reacting by (B).

Belousov-Zhabotinsky ReactionNoyes-Field-Koros Model

The Back-Switch

6Ce4+ + MA + 2H2O 6Ce3+ + HCOOH + 2CO2 + 6H+ (9)4Ce4+ + BMA + 2H2O 4Ce3+ + Br- + HCO2H + 2CO2 + 5H+ (10)

Early: Mostly MA present, no bromide is formed. Later: BMA is present, bromide is formed. Process (B) shuts down when [HBrO2] drops below [HBrO2]crit.

Now we know why solutions reacting by (B) will turn themselves into solutions reacting by (A).

Belousov-Zhabotinsky ReactionNoyes-Field-Koros Model

Belousov-Zhabotinsky ReactionNFK Model Modifications: COx

Iodination of Malonic Acid with Chlorite and in the presence of Iodide

I2 + MA IMA + HI (L3) slow

r3 = -d[I2]/dt = 410-3 [MA] [I2] / {110-4 + [l2]} (L3’)

Lengyel Reaction

Batch Oscillation in the Reaction of Chlorine Dioxide with Iodine and Malonic Acid.Lengyel, I.; Rabai, G.; Epstein, I. R. J. Am. Chem. Soc. 1990, 112, 4606-4607.

Iodine consumption rate via reaction L3Involves MA enolization and subsequent rxn with iodine

Iodination of Malonic Acid with Chlorite and in the presence of Iodide

I2 + MA IMA + HI (L3) slow ClO2 + I- 0.5 I2 + ClO2

- (L4)

ClO2- + 4 I- + 4 H+ 2 I2 + Cl- + 2 H2O (L5)

r4 = 6.3103 [ClO2] [I-] (4’)

r5 = 4.6102 [ClO2-] [I-][H+] + 2.6510-3 [ClO2

-][l2]/[I-] (5’) r5 = 4.6102 [ClO2

-] [I-][H+] + 2.6510-3 [ClO2-][l2][I-]/(u+[I-]2) (5”)

u = 10-13

Lengyel Reaction

Iodine formation rates via reactions L4 & L5

This term reflects self-inhibition by iodide

Avoid div. by zero

Mathematical Evaluation: Numerically.Start with initial conditions and evolve concentrations over small times.

Mathematical Evaluation: Analytically.Keep constant: [MA], [I2], [ClO2] Remaining variables: [I-] = X; [ClO2

-] = Y; [ClO2] = Z.

Lengyel Reaction

Taube's Influence on the Design of Oscillating Reactions – CIO2 Radical-Driven CIO2-Anion Iodine Oscillator and TuringStructures. Irving R. Epstein, Kenneth Kustin, and Istvan Lengyel, 1997.

Lengyel Reaction

Taube's Influence on the Design of Oscillating Reactions – CIO2 Radical-Driven CIO2-Anion Iodine Oscillator and TuringStructures. Irving R. Epstein, Kenneth Kustin, and Istvan Lengyel, 1997.

Lengyel ReactionExcel Simulation programmed by Dr. Montgomery-Smith

Series 1: X; Series 2: Y

0 5 10 15 20 250

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0 1 2 3 4 5 6 70

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