Drug Detection and analysis

Drug Isolation and Purification In the synthesis of drugs, the product usually contains a mixture of compounds formed, as well as unreacted components, including reactants, solvents and catalysts. SO, ISOLATION OF THE DESIRED PRODUCT IS AN ESSENTIAL PART OF THE SYNTHESIS PROCESS. To achieve isolation, the differences between the physical properties of the desired product and the other components in the mixture are used. Two properties used in this process are: Difference in solubility in different solvents. Difference in volatility

Organic structure and solubility The solubility of a solute depends on how it interacts with the solvent. Organic molecules that dissolve well in non-polar solvents, such as benzene and hexane, are generally non-polar. These solute have a high hydrocarbon content (long carbon chains) and smaller proportion of polar functional groups. Organic molecules that dissolve well in water have a higher proportion of polar functional groups. These functional groups include hydroxyl (-OH), carboxyl (-COOH), and amino (-NH2) groups. Functional groups in aldehydes and ketones, amides, and esters also provide some polarity in the molecule. Solutes with ionic groups (salts) have high solubility in water.

Solubility is an important factor in determining the ability of drugs to reach their target in the body, which is the reason drugs like aspirin are modified to increase their solubility. Another example is fluoxetine, which is made more soluble by reacting it with HCl

During isolation processes, solubility differences can be used to separate the components of a mixture. Solvent Extraction – a process that takes advantage of the fact that a solute may be more soluble in one solvent than another, in order to separate it. When placed in a mixture of two immiscible solvents, a solute will become unequally distributed between the two, this is known as partition.

Recrystallization is another important technique that can be used in the purification of drug product mixtures. This process also exploits differences in solubility between required product and impurities.

Organic Structure and volatility The boiling point of an organic compound is determined by the strength of the intermolecular forces. In order for a substance to boil, the intermolecular forces must be broken. The stronger the intermolecular forces, the higher the boiling point and the less volatile a substance is. IMF depend on: 1. Molecular size: increasing the molecular size lowers volatility because London forces increases as the number of electrons increases. 2. Polarity: the more polar the functional groups cause lower volatility because they can form hydrogen bonding or dipole-dipole interactions.

Fractional distillation- a separation technique which exploits differences in volatility. This process uses a fractionating column to separate a mixture of liquids with boiling points close to each other. Fractional distillation is based on Raoult’s law. To understand this concept we must understand two concepts: mole fraction and vapor pressure. a. Mole fraction - refers to the fraction of the substance in a mixture.

b. Vapor pressure – the pressure exerted by the vapor on the liquid at equilibrium, at a given temperature in a closed system.

The more the equilibrium lies to the right, the more molecules in the vapor state and the higher the vapor pressure. The higher the vapor pressure, the more volatile the substance and the lower the boiling point. So in a mixture of A and B, the vapor above the liquid will contain molecules of A and B. The more volatile substance will have more vapor molecules and will therefore contribute more to the total vapor pressure. The total vapor pressure of a mixture is equal to: Where, The partial pressure of each component in the solution depends on the mole fraction and the vapor pressure of the pure substances

Drug Detection