Answer

• Chirality- Isolation of Limonene from Citrus Fruits

  INTRODUCTION

  The purpose of this experiment is two-fold: (i) to obtain Limonene from citrus fruits through steam distillation and (ii) to analyze the optical rotation and enantiomeric excess (optical purity) of the fruits using polarimetry.

  Limonene belongs to a class of aromatic compounds, mainly terpenoids in composition and characterized by several isoprene repeat units (Ludwiczuk, Skalicka-Woźniak & Georgiev, 2017). These include monoterpenes which comprise 2 isoprene units, sesquiterpenes with three isoprene units, diterpenes containing 4 isoprene units and triterpenes with 6 isoprene units (Asia, Nicholas, Segui & Ballivian, 2020).

  Limonene is extracted by steam distillation, as aromatics are thermally decomposable under high temperatures (Valderrama & Ruiz, 2017). Subsequently, polarimetry is deployed to determine the chirality of the limonene. Chirality is the “direction of rotation” of the substance (Telo, 2016). Additionally, chirality confirms optical activity and the presence of a chiral center, a carbon attached to four other groups (Weldegirma, 2016; Telo, 2016). Polarimetry is a necessary tool for establishing optical purity through measurement of enantiomeric excess (ee), or optical purity.

  Findings from the experiment show the specific rotation to be about “half of the literature value” (Asia, Nicholas, Segui & Ballivian, 2020). Many studies associate this outcome with a high concentration of limonene in the samples being investigated. Similarly, the optical rotation of the sample was found to be 11 (Asia, Nicholas, Segui & Ballivian, 2020). The ee was found to be 11.34%, one possibility for this result could be that our sample was not pure, therefore accounting for the low percentage. A percentage of 100% means a pure enantiomer (Weldegirma, 2016).