Experiment 7

Experiment 7 Esterification: Banana Oil Discussion

Esters have low molecular weight that makes them have characteristic flavours and  pleasant odours associated with essential oils. They occur prevalently in nature and often have fruity fruity taste or odour. Ester functional functional group group can be synthesied synthesied by many different different methods. methods. !implest of these methods is the "isher esterification done by reacting a carboxylic acid and an alcohol in the presence of a concentrated acid catalyst. #sopentyl acetate$ known as banana oil$ is an example of an ester. #n this experiment$  banana oil is synthesied by direct esterification of acetic acid with isopentyl alcohol in the  presence of sulfuric acid as catalyst. %eneral reaction occurs as below. below.

&echanism of the reaction above involves initial protonation of the carbonyl group in acetic acid  by '(!O) . The hydroxyl hydroxyl group of the alcohol alcohol adds to the carbonyl carbonyl carbon via nucleophili nucleophilicc attack. * proton tranfer and loss of water followed followed by the loss of acid catalyst are the the remaining steps before isopentyl acetate is formed.

The reaction stated is a slow and so reflux of reactants is needed to aid completion. This is done in order to prevent loss of reactants. 'eat was employed to thermodynamically thermodynamically control

the reflux process and form the most stable ester. The boiling chips added played a significant role in the process. #t allowed smooth heating of the process preventing violet heating from occuring. To furthermore push reaction e+uilibrium to product formation$ ,e chatelier-s principle is exploited by adding excess of any of the two reactants. *cetic acid was added in excess and not isopentyl alcohol to favor product formation. The reason for this is that it is hard to separate residual isopentyl alcohol from banana oil because they have comparable solubility. Bothare soluble in organic media. &eanwhile$ acetic has poor solubility of organic solvents making it easier to separate from banana oil. Excess acetic acid is removed by adding sodium bicarbonate.  a(/O0 converts acetic acid to its con1ugate base forming sodium acetate. !odium acetate is easily removed from the organic layer because it is not soluble on organic compounds but soluble in water. /ontinues acidity measurement of the mixture determines whether all of the acetic acid is removed. Basic solution indicates that all of the acetic acid is removed and converted to sodium acetate. *ddition of saturated a/l enables separation of water from the organic layer. Because of strong intermolecular attractive between water molecules and a/l ions$ water is pulled from the synthesied banana oil and thus$ can be discarded. *lso$ unreacted salts present can be carried by water reducing impurities from the crude sample. *ddition of anhydrous magnesium sulfate furthemore removes remaining water in the sample during drying. /harged &g(2 and !O)(3 ions have high affinity to water molecules and therefore effective in removing residual water from the sample. 4urification of banana oil was carried through distillation. "igure 5 shows the "T#6 analysis of the synthesied isopentyl acetatem as compared to literature data.

4rominent peak at around 0 cm35 corresponds to /3' bond functionality while  peak at 57 cm35 corresponds to the carbonyl functionality. This two results coincide with the

structural functional groups present in isopentyl acetate. &oreover$ it is seen that experimental #6 analysis 8left figure9 has comparable results with the literature data 8right figure9

Conclusion

Banana oil or isopentyl acetate is synthesied from esterification of acetic acid with isopentyl alcohol. /rude sample was isolated by extraction method using sodium bicarbonate solution while purification was carried through distillation. Because esterification process is slow$ reflux of reactants is needed as the reaction is thermodynamically controlled. !ynthesied  banana oil has comparable #63spectrum with literature data$ having peaks at 0 cm35 and at 57 cm35 depicting /3' and carbonyl functionalities respectively.

References

 !mith$ . Organic Chemistry; &c%raw3hill: ew