1. Crystal Seeding

In GSK, crystal seeding is an important part of the process to get solid crystals of organic compounds out from liquid or aqueous solutions. In this process, seed crystals are inserted to provided to pre-formed basis for nucleation to occur in a saturated solution of the selected compound. This reduces the time taken for the crystals to develop.

This step also offers a chance to control the size of the crystals formed. By adding more seeds, the average amount of compounds that crystallize on the seeds is lesser as compared to when less seeds are added. Thus, the size of the crystals formed are lesser. The control of the size of the crystals formed is important so that delivery of the drugs can be successful.

Here is a video on growing copper sulfate crystals using a household chemical:

As seen from the video above, the copper(II) sulfate seed crystal is placed into a saturated solution of copper(II) sulfate solution. The copper(II) sulfate crystal grows bigger as nucleation takes place.


2. Reversible Reaction and Equilibrium

In a reversible reaction, the reaction is never complete. The end product will consist of both the reactants on both sides of the equation. This reaction occurs to a point where the rate of the forward reaction is equal to the rate of the backward reaction.

An example of a reversible reaction:

One extremely famous reversible is the Haber process.

Equilibrium often occurs during chemical reactions carried out in pharmaceutical plants, such as GSK. There is a set of principles which help define factors which will affect the degree of completion of the reversible reaction. This principle is called the Le Chatelier's Principle.

external image LeChatelier.jpg

The Le Chatelier's Principle states that:
"If a chemical system at equilibrium experiences a change in concentration, temperature,
volume or partial pressure, then the equilibrium shifts to counteract the imposed change
and a new equilibrium is established."
It also helps to look at the equilibrium constant to decide on optimal conditions to achieve maximum yield, as seen below:

external image kc.png

In order to increase the yield of the desired product, the pressure, temperature reaction vessel, and the concentration of the reactants need to be varied and controlled so that, at the equilibrium, the amount of the intended product is the greatest. At the same time, one will need to balance this with the cost of maintaining the conditions.

Thus, concepts like Le Chatelier's Principle and equilibrium constants are needed to optimize the reaction conditions. Equipment, such as thermal blanket for the reaction vessels, is installed to control the tmperature to increase the yield and rate of reaction.