**6. Purification of phytoconstituents**

The extracts, which contain numerous phytoconstituents, must be separated and purified further to obtain the fraction or pure phytoconstituents. The techniques utilized for isolation and purification from the extract are determined by the physical and chemical properties of the component to be separated. The physical approaches employed for this goal are as follows.

#### **6.1 Fractional crystallization**

The point of supersaturation in the solvent in which phytopharmaceuticals are soluble causes them to crystallize. The processes involved in the crystallization of phytoconstituents are slow concentration, slow evaporation, and chilling. Crystallization is an ideal purification procedure. It is operationally easy, very inexpensive, and may be done in quantities ranging from a few micrograms to hundreds of kilograms. The results are normally highly pure (unlike the mixes that can sometimes be obtained with distillation). Using chromatography to purify that much material is a nightmare. Another key point to remember about crystallization is that X-ray crystallography can be used to discover the structure of unknown molecules. With very few exceptions, X-ray crystallography is the gold standard for structure determination: if you can get a substance to crystallize, you can determine its structure. The only issue is that not all compounds crystallize, and finding circumstances that can preferentially recrystallize one chemical can take a long time [43].

#### **6.2 Fractional distillation**

This is a process of purifying phytoconstituents from a mixture. It's commonly used to separate hydrocarbons like crude oil, citral, and eucalyptol. Purification is accomplished by comparing the boiling points of the different substances. When heat is applied, the fractional distillation equipment is built in such a way that each chemical evaporates and separates at its boiling point. As a result, each fractionated chemical will condense and be collected separately via numerous syphons coupled to fractional distillation apparatus [44].

The fractional distillation method is based on differences in compound volatility and is affected by physicochemical properties of the components, as well as the pressure and temperature of the distillation process. The mass and energy transition between the fluid and vapor stages of the mixture has an impact on separation efficiency. Most terpenes are thermally unstable, dissolving, or oxidizing when exposed to high temperatures, light, or oxygen. As a result, the distillation technique is typically used at vacuum pressures to lower the vaporization temperature of the volatile mixture. Due to the boiling temperature reduction, the vacuum also slows processes such as thermal deterioration in temperature-sensitive chemicals. In the chemical industry, vacuum fractional distillation is used to separate compounds with extremely high boiling points that would need a lot of energy to separate under atmospheric pressure [45].
