Organic chemistry lab report - steam distillation
Methods and Background
I. Relevant Equations
II. Steam Distillation of Caraway Seeds
III. Thin Layer Chromatography of Caraway Seeds
Smell: spearmint Smell: Caraway
Optical rotation = [a]D = 61o Optical rotation = [a]D = -61o
The purpose of this lab was to isolate an essential oil, carvone, from caraway seeds using steam distillation. We can analyze and identify the oil using Thin-Layer Chromatography (TLC) and IR spectroscopy. We can compare the obtained IR and TLC plate of the oil to the known IR and Rf value of authentic carvone.
(S)-(+) Carvone, found in caraway seeds, and (R)-(-)Carvone, found in spearmint leaves are enantiomers of each other. Enantiomers are superimposed images of each other, which mean that these two compounds have identical physical properties except with respect to their effect on plane-polarized light. Hence, they have optical rotations of the same magnitude but in different directions. They also have same chemical properties except that they undergo chemical changes at different rates if the reaction occurs in a stereochemically asymmetric environment. For example, (R)-(-)Carvone smells like spearmint; however, (S)-(+)Carvone smells like caraway seeds even though that look almost alike. The reason for this
Based on the observation and results of this lab, we can conclude that steam distillation is a useful technique for isolating a volatile oil like (S)-(+)-Carvone from caraway seed and (R)-(-)-Carvone from spearmint leaves when they are mixed with water. We made this conclusion because the Rf value for the experimental sample of oil was about the same as that of the standard sample of (R)-(-)Carvone. This similarity indicates that the oil obtained from spearmint leaves was (R)-(-)Carvone. Thus, we can expect that the oil obtained from caraway seeds would be similar to (S)-(+)-Carvone. Furthermore, the IR spectra graph should have indicated that the presence of a ketone and an alkene. In our case, the peak of C=O (carvone) was observed at 1672.76 cm-1. Also, the peak of C=C, which represent the alkene, was observed relatively at the upper part of the peak range because there was no conjugation involved around this C=C double bond. The IR for the spearmint leaves was almost same except different intensity
Gilbert, J.C., Experimental Organic Chemistry, Saunders Publishing, New York, 2006, 4th Ed, pp. 123-125; 127-130; 192-202.