For synthesis of benzil from benzoin I need help for blued question... You may n
ID: 303723 • Letter: F
Question
For synthesis of benzil from benzoin
I need help for blued question...
You may need to work to induce crystallization. DO NOT DISCARD the reaction if crystals do not form! Wash the crystals with two portions of cooled water (10 mL). The benzil obtained often contains small amounts of unreacted benzoin which needs to be removed. Take a TLC of the crude crystals. If benzoin is observed it must be removed. Several purification protocols can be followed. Recrystallization is a good purification method however your technique must be excellent due to the fact that benzoin is less soluble in most solvent systems than is benzil (does this make sense to you?). So if one is not careful, the crystals that form will be of the less soluble benzil! Chromatography is also a valid purification method that can be utilized here. A new lechnique that can also work well in situations where the desired material is more soluble than the impurity is called "Irituration". This is essentialy a solld-liquld extraction which involves treating a solld with a solvent (hot; roomt temp,; or cold) that will dissolve one component but not both. One can hen effect a separation via filtration. Ifthe less soluble component of the mixture is desired, the solid is retained If the more soluble is desired, he filtrate is concentrated to dryness. To find sucha solvent, one can fest the solubilities of benzoin (that you made) and benzil (anthentic) in some common lab solvents using TLCExplanation / Answer
Trituration is also a purification technique which is based upon the differences in solubility of the compound and its impurities. The process can be executed in the lab stepwise as mentioned below:-
1) First of all, a solvent has to be selected in which the compound is soluble and impurities are not and it can be vise versa too. This step is proceeded by checking the solubility of the compound in various solvents. (In this case ethanol can be used as the solvent as benzil is soluble in ethanol but benzoin is soluble in hot ethanol)
2) The product and the solvent are allowed to stand for sometime to ensure the complete dissolution of the product.
3) After that the mixture is filtered and benzil which is the desired product will be in the solvent and solid left is the benzoin. A small quantity of fresh ethanol is also added durig filtration to completely extract the desired product.
4) Further, the solvent obtained after filtration is concentrated to dry benzil powder by rotavapour or heating.
5) To confirm whether benzoin has been completely removed or not, dissolve small amount of obtained product in ethanol and add a drop of 10% NaOH. If purple colour appears, this is due to the presence of benzoin. If no colour appears that means product is free from benzoin.