MadSci Network: Chemistry

Re: What products can be made with the use of catalysts (ex/pesticides)and how?

Date: Tue May 12 03:23:45 1998
Posted By: Jeremy Starr, Grad Student, Chemistry, California Institute of Technology
Area of science: Chemistry
ID: 892879481.Ch

Hi Christine,

	What a fantastic question! Catalysis is a 
tremendously complex subject and its 
importance extends into virtually every area of 
chemistry. There is more than one meaningful 
definition of a catalyst. One I learned as an 
undergraduate is that a catalyst is a chemical 
species which participates in a chemical reaction 
but is not consumed in the reaction. This 
definition doesn't allude to the real value of 
catalysts: their ability to lower the "activation 
energy" of a reaction. The activation energy is 
the energy "invested" in the reaction to make it 
go. When the reaction is done that energy is 
returned (and then some) if the reaction is 
exothermic (products are lower energy than 
starting materials). The figure below is a 
graphical representation of this principle:

	It is important to understand that the rate of 
a reaction is directly related to its activation 
energy. A higher activation energy requires a 
greater energetic investment and therefore slows 
the rate of the reaction. It is important , also, to 
know that most reactions are reversible and a 
catalyst will act to lower the activation barrier 
between products and reactants such that the 
reverse reaction is catalyzed as well. An 
example of a simple, reversible, catalyzed 
reaction is the acid catalyzed hydrolysis of an 

	In the forward direction, the ester 
associates with an acidic proton (H+) to form an 
"activated" intermediate that is attacked by a 
water molecule to form the next intermediate that 
can then lose a proton and decompose to the 
carboxylic acid and alcohol products of 
hydrolysis. The proton is catalytic because it is 
consumed and regenerated, then can be reused 
in the reaction cycle. The catalyst does not 
determine which direction the reaction goes, but 
that can be influenced by other factors 
(temperature, pressure, and reactant 

	The most important catalysts on earth are 
enzymes. Without them there would be no 
living things (and thus no man-made catalysts!). 
The products of enzyme catalysis are proteins, 
DNA, RNA, simple to complex organic 
products, and enzymes themselves. In fact there 
is nothing in your body except water and simple 
inorganic salts (like NaCl) that isn't the product 
of a catalytic process. Chemicals like diatomic 
oxygen, vitamins, and some amino acids are not 
made in your body but are products of catalytic 
processes in plants and other organisms. 
Enzyme catalysts possess the ability to perform 
selective catalytic reactions beyond anything 
currently possible in a laboratory with a non 
proteinogenic catalyst. Your body possesses 
enzymes called "esterases" which perform the 
identical ester hydrolysis reaction as shown 
above but have the ability to select a specific 
ester and only lower the activation energy of 
hydrolysis of that ester! In contrast, an ordinary 
acid catalyst will catalyze any ester hydrolysis. 

	The most important industrial catalytic 
processes produce polymers (plastics), 
methanol, ammonia, hydrogen, and carbon 
monoxide. This is by no means a complete list 
but these few simple compounds are the starting 
materials for an uncountable number of 
consumer products (how many plastic things do 
you use each day?) from fertilizers to 
pharmaceuticals to bulk construction materials. 
Hoola-hoops would not have been possible 
without a special polymerization catalyst that 
produces the stereo-regular plastic required for 

	A special class of catalysts that is growing 
in importance in the pharmaceutical industry is 
stereoselective catalysts. These catalysts have 
the ability to catalyze reactions to give optically 
active products. These products can be the 
precursors of optically active pharmaceuticals 
that are free of the ineffective (and sometimes 
dangerous) stereoisomer present in a racemic 
mixture. (see my Madsci post 891001341.Ch 
for more detailed information on the importance 
of optical activity in pharmaceuticals). One 
example of this is the Noyori asymmetric 
hydrogenation catalyst used in the industrial 
preparation of the OTC drug sodium naproxin.

I hope this information was helpful!


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