HaCKeRz KrOnIcKLeZ 3/HaCKeRz_KrOnIcKLeZ.iso/drugs/cyclic.reactions

Text File | 1996-05-06 | 15KB | 315 lines

Psychedelic Chemistry - LITERALLY. Making repeating lightshows using
CYCLIC REACTIONS: They look pretty.

Collected notes.

From [e-mail]
Subject: Re: Cool Reaction(Ithink)
[e-mail] (Scott Runyon) writes:
>I recently saw a reaction demonstrated on television as follows:
>   Chemical solutions(3 I believe) are poured into a large beaker
>   with a spin bar at bottom.
>   Spin bar is turned on and withina minute or so, the clear liquid
>   turns red....another minute or so and the liquid turns blue...
>   another minute or so and the liquid turns clear again...you get
>   the point...
>   The gentleman demonstrating referred to the reaction by its
>   name, the Briggs-Roucher cyclic reaction...I may have heard
The Briggs-Raucher reaction is carried out as follows:
     in a 250ml beaker, mix equal volums (about 10ml) of each of the following:
                 A   6% H2O2
                 B   4.3g KIO3 dissolved in 100 ml H2O + 1.5 ml 6M H2SO4
                 C   1.56g malonic acid + 0.34g MnSO4.H2O dissolved in 100ml H2O
                       + 3 mL of fresh 1% soluble starch solution
     swirl beaker gently to mix.  Several seconds after last ingrediant is added
     the mixture turns yellow, then blue, colorless, yellow, ...
The reaction which you refer to is probably the Belousov_Zhabotinskii reaction, I could give you that recipe also if you wish.  It is a bit more difficult how-
ever because it is somewhat tempermental.  The colors are red and blue and are
both spacial as well as time resolved.  For this reaction, you must have a
source of deionized water because it is very sensitive to chloride.

***************************************************************************

>From [e-mail]
Subject: Re: !**EXPERIMENT BACKGROUND**!
>     I need some information about the Briggs-Rauscher reaction.  This
> reaction starts with thre colorless solution, then it turns amber
> and latter turns blue-black.  This process repeats itself for about 5-10
> minutes.  Here is my dilema: I want to know what causes these color
> changes and why? The chemicals involved are:
> potassium iodate, sulfuric acid, malonic acid, manganese(II) sulfate
> monohydrate, starch and sodium thiosulfate.
The first fast answer is "Yellow/amber is due to I2, blue-black is due to
iodine-starch complex".  I did this reaction in slightly different way -
instead of thiosulphate I used H2O2.  I think what's going on is very
similar, so I'll show what I did then and a scheme involved.  This is a
great stuff, very impressive, and a great demonstration.  I remember when
I finally mixed solutions and it started blinking, I was about to jump
around the apartment ;-) (I was a high school junior then).  The reaction
was lately described in Sept. 1984 issue of Russian "Chemistry and Life"
magazine, p.56, and I'm copying from there now.  The make-up was as
follows:

Solution 1.  Dilute 102.5ml of 30% H2O2 by water to the total volume 250ml.

Solution 2.  Dissolve 1.1 ml of concentared H2SO4 (HClO4 works as well)
in 10 ml of water, add water to make the volume about 50-60ml, dissolve
4.28g KIO3 (slightly heating it) and add the water till the total 100ml
of solution.

Solution 3.  Make a solution of 0.08 g of starch in a small amount of
water (heating needed), dissolve there 3.9 g of malonic acid and 0.85 g
of MnSO4, and add water to form 250ml of solution.

Add 100ml of solution 2 in the big beaker, and 100ml of solutions 1 and 3
in smaller ones.  Than simultaneously add solutions 1 and 3 to the big beaker
(stiring).  Then sit and start staring on it ;-).  First it'll be
colourless, but in several seconds starts changing.

What's going on is the oxidation of malonic acid by H2O2 in the presence
of iodate ions and mmanganese ions (which are the catalyst), and starch
works as an indicator.  The summary equation is

CH2(COOH)2 + 4H2O2  ---> 3CO2 + 6 H2O,

But the reaction stoichiometric concentration ratios are different of ones
that can be found from this equation.  The conditions when the color
changes are well seen by human eye were found experimentally. The magazine
says that they were found to be: 0.067M KIO3, 1.2M H2O2, 0.053M H2SO4,
0.05M malonic acid, 0.0067M MnSO4.  Starch is added in minor amounts -
0.01%, and Iodide-starch complex formes only when I- concenration reaches
10E-4 M.  And after full oxidation of malonic acid the reaction stops ;-)

If the scheme will be hard to read in ASCII, email me and I can send you
.PCX or hardcopy.


            Mn2+          Mn2+ -----------\           Mn2+
               \        /              H2O2 \        /
            H2O2 \    /                       \    /
                  Mn3+                         Mn3+
CH2(COOH)2 + HIO3 ----> ICH(COOH)2 + CO2 + H2O ----> HI + CO2
(colorless)   ^         (colorless)                  | (colorless)
              |                                      |
              |        This is the main cycle.       |
              |                                      |
             H2O2                                   H2O2
              |                                      |
              |                      starch, I-      v
       I-*I2*starch complex  <---------------------- I2
              (blue)                              (yellow)


I reproduced the scheme as it was in the article, but actually I have some
doubts about the validity of the first stage
  CH2(COOH)2 +HIO3 --> ICH(COOH)2 + CO2 + H2O
                       ^^^^^^^^^^^^^^^^
Maybe it's a typo and the author meant ICH2-COOH + CO2 ?

Anyways, hope this helps.

Lev.

****************************************************************************
Subject: Re: Belosov-Zhabotinsky reaction

"Oscillations and Traveling Waves in Chemical Systems" edited by
Richard Field is one of the comprehensive treatments on oscillating
systems. It covers bromate-driven oscillations and a number of models of
BZ reaction.

Alexander Varvak
Brandeis University
Dept. of Chemistry
email: [e-mail]
***************************************************************************

From: [e-mail]
You can start by checking Ilya Prigogine's books:
Exploring Complexity,  (don't remember the publisher, sorry :(   )
Self-organization in Non-equilibrium Systems.  This book has a section
specifically devoted to the Briggs-Rausch rx'n.  Lots of references.
Both books were co-authored with G. Nicolis.

***************************************************************************

From: Kinsley William <[e-mail]>
    Sorry I haven't thanked you sooner for the Briggs-Raucher recipe and
explanation.  It looks easy and friendly and I hope that it will interest
the students who have been intimidated by Shakhashiri.
    The Liesegang rings preparation has been based on R. Sassen,
Scientific American 220:131(1969) and B. Z. Shakhashiri, "Liesegang
Rings," in Chemical Demonstrations, Vol. 2, Univ. Wisconsin: Madison WI
(1985).
    A reference which has come up from this query but not yet checked
out is A. H. Sherbaugh III and A. H. Sherbaugh Jr., J. Chem. Educ. 66:589(1989)
References are mushrooming, all very scholarly but none with the spectacular
pictures stuck in my memory.  On the other hand, we're now spurred to try
dynamic oscillations.  Thanks again for your help.
Therese

***************************************************************************
>From [e-mail] May 16 14:51:37 1995
Reply to: [e-mail]
> Are there any reactions that oscillate? Are there any that do not need other
> chemicals than those I have in my kitchen? I'd like to know about a _really_
> simple reaction, one that I could not possible fail to make, that
> illustrates a very simple diff.eqation. Could anyone _please_ help me to
> find one?

There aren't any known oscillating reactions which are simple or use only
chemicals in your kitchen.

The known oscillating reactions are one of three types:

(1) An enzyme is involved.
--------------------------

It has to be purified from a bioligical system. Horseradish peroxidase is one.
The enzyme PFK of glycolysis is another. These reactions can usually be
modelled with simple differential equations, but the oscillations come from
the very complex kinetics of the enzyme.

(2) Oxyhalogens, an organic acid, and a transition metal.
---------------------------------------------------------

This group makes up practically all the experimental oscillating systems
people work on.

In these reactions there is a very oxidized halogen like HBrO3, and an organic
acid like malonic acid which reduces the HBrO3. The halogen forms a series of
ions having a single halogen atom and various numbers of oxygen atoms, and the
oxidation states are all odd or even. For example, Br in HBrO3, HBrO2, HBrO
and HBr has oxidation states 5, 3, 1, -1.

The organic acid cannot reduce the oxyhalogen directly. Instead, it passes a
single electron to a transition metal such as Fe or Mn which acts as an
intermediary. The metal must have adjacent oxidation states, such as Fe+2 and
Fe+3. This metal ion must pass two electrons to the oxyhalogen in order to
change the oxidation state by two, from +5 to +3 (say). However, this can only
be done by forming a small quantity of the relatively unstable in-between
oxidation state, which is +4 (in BrO2). Being unstable, two of these
in-between molecules spontaneously change into the stable +3 and +5 states in
the reaction

 2 BrO2 + H2O --> HBrO3 + HBrO2

When you combine this reaction with twice (times 2) the reaction where the
metal ion gives an electron to the higher oxidation state to form the
in-between state:

  Fe+2 + HBrO3 + H+ --> Fe+3 + BrO2 + H2O

you get the combined reaction:

 BrO2 + 2 Fe+2 + HBrO3 + 2 H+ --> 2 Fe+3 + 2 BrO2 + H2O

This reaction has a important feature: the in-between substance BrO2
reproduces itself AUTOCATALYTICALLY.

 BrO2 ... ---> 2 BrO2 ...

When the in-between species can reproduce itself, an explosive growth in the
concentration of that species is possible. This is the source of instability
that causes the oscillations. BrO2 will only grow autocatalytically if the
rate of the above reaction is faster than the rate of all reactions where
something reacts with BrO2 and removes it. To have oscillations, other
parts of the mechanism must provide negative feedback which limits the
autocatalytic explosion. The negative feedback occurs when the mechanism
generates something that reacts with BrO2 and removes it faster than it can
reproduce itself. This inhibiting substance must disappear if BrO2 stops
reproducing itself, so that the reproduction of BrO2 will resume.

Because chlorine, bromine and iodine form a large number of ions and molecules
with oxyen, and many of the oxidation states differ by two, there are many
possible ways for a transition metal to pass a single electron twice to one of
the higher oxidation states. This often produces an autocatalytic reaction and
can result in oscillations under the right experimental conditions.

I once wrote some software that counted the number of different ways a series
of 2-electron species could be unstable when reacting with 1-electron species
and got over 500 different ways.

As a result, there are a large number of oscillators that are variations on
this idea. They use various transition metals, various organic acids, and a
number of different oxidized halogens. Taking into account all the
combinations we there are about 200 oscillators.

The problem for you is, you don't have oxyhalogens or transition metal ions
in your kitchen.


(3) Like the above (case 2) but using Group VI instead of Group VII.
--------------------------------------------------------------------

There are a few very rare examples where a Group VI element plays the role
that the Group VII element usually plays. For example, there is an oscillator
where peroxydisulfate, S2O8-2 acts as the oxidized state analogous to bromate.
It is reduced from the +7 state to the +5 state in SO4- by silver acting as an
intermediary. The intermediary has to have two important oxidation states. In
this case, the mechanism that fits the experimental data uses Ag+ and Ag+2.
The organic acid is oxalic acid.

You can read about this oscillator in my paper in the Journal of Chemical
Physics, vol 97, pages 2459-2472 (1992).

This example has an unusually complex mechanism. When Ag+ donates electrons
to S2O8-2 (+7 state) to reduce it to SO4- (+5 state), the in-between state
is sulfate SO4-2 and is stable. The instability does not follow the above
pattern where the unstable inbetween state reproduces itself autocatalytically.

Instead, the instability comes from the way Ag+2 and SO4- work together to
gain electrons from oxalate and the CO2- radical. This system is problbly the
most complex oscillator that is well understood.

As a general rule, when everything reacts with everything, chemistry is stable
and oscillations are not possible. Oscillations tend to occur when the
possible reactions are restricted due to only certain pathways being catalyzed
by enzymes, or only certain pathways being possible because one-electron
reducing agents and two-electron oxidizing agents are only able to react via a
metal intermediate. When the pathways are restricted, the greater the
complexity, the greater the chance of oscillations.

Since you wanted simple differential equations, the oscillator invented by
Lotka in 1909 is one of the simplest. Keep A and P fixed and integrate X and Y
using mass action kinetics for the following mechanism:

A + X --> 2 X
X + Y --> 2 Y
    Y --> P

This has two autocatalytic steps, and as I've explained, it takes a complex
mechanism in real chemistry to get an autocatalytic step. Hence, it is
extremely unlikely that any real chemical system has this mechanism; however,
with a lot of approximations a complex chemical system might yield this
mechanism. It also has a mathematical flaw. The oscillation disappears if you
put in the reverse of any of these reactions, no matter how small the rate
constant. Since all real reactions are reversible, even a real system with
this mechanism wouldn't ocillate.


--
---------------------------------------------------------------------
Bruce Clarke                 | internet:   [e-mail]
Department of Chemistry      | compuserve: 70740,3135
University of Alberta        | phone voice [phone]
Edmonton AB, T6G 2G2         | phone fax   [phone]
Canada                       | WWW server: www.chem.ualberta.ca

***************************************************************************

>From [e-mail] Jun  2 19:49:25 1995
Date: 2 JUN 1995 23:57:10 GMT
From: "Vincent J. Perricelli" <[e-mail]>
Newsgroups: sci.chem
Subject: Re: Chaos in chemistry?

Here are a few articles that are probably generally available:

"Clocks and Chaos in Chemistry" by Stephan Scott, _New Scientist_, v 124,
2 Dec 1989, pp. 53ff.

"Controlling Chaos in the Belousov-Zhabotinsky Reaction" by V. Petrov,
V. Gaspar, J. Masere, and K. Showalter, _Nature_, v 361, no 6409,
21 Jan 1993, pp. 240-243.