Separation and purification
A mixture of benzoic acid, benzaldehyde and butylamine. What kind of experiment should you design to obtain each of the three compounds in a pure state.
Just need ideas in order to start this experimental design.
Thanks!!!
Put the mixture in a separatory funnel containing pH9 aqueous solution and Et2O.
This way will selectively carry benzoic acid into the water phase, while leaving both amine and aldehyde in the ether phase.
Split the 2 phases and work on them separately.
Organic phase: add an acidic water solution at pH around 2-3. This will transform the amine in amonium ion, soluble in water. Split the 2 phases again. The organic one will contain only aldehyde and you need to get it dry through rotavapor. The aqueous one will have to be basified at pH 9 and re-extracted with Et2O in order to recover the purified amine as a free base.
Let come back to the first aqueous phase containing sodium (or K) salt of benzoic acid: add an acidi solution to bring the final pH at around pH 2, thus, the undissociated benzoic acid will precipitate. Filter it out and get it dry at max 60 °C. If you need it purer, you may it recristallize through hot water and filter it again and finally dry it into an oven at around 60 °C.
remove the solvent from the remaining 2 ethereal phases containing the other 2 chemicals.
To obtain each of the three compounds (benzoic acid, benzaldehyde, and butylamine) in a pure state from the mixture, you can design a separation and purification experiment using various techniques such as extraction, distillation, and recrystallization. Here's a step-by-step guide to designing the experiment:
1. Preliminary assessment: Begin by determining the physical properties of the compounds, such as melting/boiling points, solubilities, and acid/base properties. This information will help you decide which methods to utilize for separation.
2. Selective extraction: Based on the solubility properties of the compounds, you can perform liquid-liquid extraction using solvents that selectively dissolve one of the compounds. For example, benzoic acid is soluble in aqueous sodium hydroxide (NaOH) solution, while benzaldehyde is soluble in organic solvents like diethyl ether. Butylamine, being a base, can be liberated by adding a suitable acid. Utilize these solubility differences to separate the compounds.
3. Acid-base separation: After the selective extraction, you may need to further separate the benzoic acid and butylamine. This can be achieved by converting the benzoic acid to its sodium salt through acid-base reaction with sodium hydroxide, while the butylamine can be converted to its hydrochloride salt through reaction with hydrochloric acid. The salts can then be recovered by filtration or extraction.
4. Distillation: Next, you can separate benzaldehyde from the organic solvent (diethyl ether) that was used during the extraction process. Distillation involves heating the mixture, vaporizing the more volatile compound (benzaldehyde), and then condensing it back to liquid form, while leaving behind the non-volatile diethyl ether.
5. Recrystallization: To obtain pure benzoic acid and the corresponding benzoate salt, perform recrystallization. Dissolve the solid mixture obtained previously in a suitable solvent (such as water for benzoic acid or ethanol for benzoate salt) and then cool the solution slowly. The desired compound will crystallize out, leaving impurities behind. Filter the crystals and wash them with a small amount of cold solvent to obtain pure compounds.
Throughout this experimental design, it is important to consider safety precautions, such as wearing appropriate protective equipment and working in a well-ventilated area. Make sure to consult literature references or seek guidance from a chemistry instructor to ensure accurate execution of the experiment and handling of the compounds involved.