Corymbia citriodora (Hook.) K.D. Hill & L.A.S. Johnson - syn. Eucalyptus citriodora Hook. - Myrtaceae \\ spotted gum, lemon-scented gum, **Zitroneneucalyptus** \\

"On favourable sites, these species grow to 45 m in height and 1.3 m in stem diameter, but attain only half these dimensions on poorer sites. They have straight, slender trunks with smooth bark. The bark is shed in patches, giving the species its characteristic spotted appearance. Colour tones range from pink to grey-blue." [[http://www.daff.qld.gov.au/forestry/using-wood-and-its-benefits/wood-properties-of-timber-trees/spotted-gum]]

"...tall tree, growing to 35 metres in height (but sometimes taller), from temperate and tropical north eastern Australia...The essential oil of the lemon-scented gum mainly consists of citronellal (80%), produced largely in Brazil and China. While unrefined oil from the lemon eucalyptus tree is used in perfumery, a refined form of this oil is used in insect repellents. The refined oil's citronellal content is turned into cis- and trans- isomers of p-menthane-3,8-diols (PMD), a process which occurs naturally as the eucalyptus leaves age. This refined oil, which includes related compounds from the essential corymbia citriodora, is known widely by its registered tradename, "Citriodiol", but also by generic names which vary by country or continent: "oil of lemon eucalyptus" or "OLE"(USA); "PMD rich botanic oil" or "PMDRBO"(Europe); "PMD and related oil of lemon eucalyptus compounds" (Canada); Extract of Lemon Eucalyptus (Australia). Pure PMD is synthesized for commercial production from synthetic citronellal." [[http://en.wikipedia.org/wiki/Corymbia_citriodora]]

"The chemical composition of decanted (obtained directly by steam distillation of the leaves) and recovered (extracted from distillation water using hexane) essential oils of Eucalyptus citriodora were examined. The decanted oil was richer in citronellal (70.3%), citronellol (8.8%), citronellyl acetate (1.3%) and β-caryophyllene (2.6%). The recovered oil was richer in isopulegol (53.0%), borneol (10.0%), menthol (5.3%), neral (6.9%), geraniol (1.4%) and eugenol (4.6%). Citronellal, the major constituent of the decanted oil, was absent in the recovered oil." \\
[Rajeswara Rao, B. R., et al. "Comparative composition of decanted and recovered essential oils of Eucalyptus citriodora Hook." Flavour and fragrance journal 18.2 (2003): 133-135]

| {{:citronellal.jpg|citronellal}} \\ [[https://en.wikipedia.org/wiki/Citronellal|citronellal]] | {{:p_menthan38diol.jpg|p-menthane-3,8-diols}} \\ p-menthane-3,8-diols |

"In all, 19 constituents were identified in oil from juvenile and senescent leaves compared to 23 in adult leaves and 20 in leaf litter, respectively. Citronellal, a characteristic monoterpene of the oil reported hitherto was found to be more (77-78%) in the juvenile and senescent leaves compared to 48 and 54%, respectively, in the adult leaves and leaf litter. In the adult leaves, however, the content of citronellol - another important monoterpene - was very high (21.9%) compared to other leaf types (7.8-12.2%)." \\
[Chemical composition and phytotoxicity of volatile essential oil from intact and fallen leaves of Eucalyptus citriodora., Batish DR, Singh HP, Setia N, Kaur S, Kohli RK., Z Naturforsch C. 2006 Vol.61(7-8), 465-71] [[http://znaturforsch.com/ac/v61c/s61c0465.pdf]]

"A simple and efficient method was developed for the synthesis of para-Menthane-3,8-diol (PMD), a well-known repellent active against mosquitoes, from Eucalyptus citriodora essential oil by a treatment of citric acid in a biphasic medium (H2O/essential oil). The E. citriodora contains as main component (+)-citronellal (74% in the present case), which cyclises (Prins reaction) to form cis/trans PMD isomers. As an example, an emulsion containing an aqueous solution of 7% citric acid and E. citriodora oil at 50°, conducted after 15h stirring to 82% conversion of (+)-citronellal with a selectivity of 80% with the remaining presence of monoterpenes and sesquiterpenes in the medium. Investigations of lasting protection on human volunteers are carried out using a cage test bioassay protocol and Aedes aegypti mosquitoes. At 20% in iPrOH, the new reaction mixture showed a complete protection of 303 min compared to 22 min with the pure essential oil. The modified oil was compared with N,N-diethyl-m-methylbenzamide (DEET), the most popular active used in repellent formulations. Thermogravimetric analyses (TGA) of E. citriodora, the modified oil, PMD, DEET, and (+)-citronellal were performed and showed a slow evaporation rate for PMD and DEET as well as for the modified oil, which may explain their long lasting protection action." \\
[Drapeau, Jeremy, et al. "Green synthesis of para-Menthane-3, 8-diol from Eucalyptus citriodora: Application for repellent products." Comptes Rendus Chimie 14.7 (2011): 629-635]

{{http://www.hear.org/molokai/kalaupapa/herbarium/images/originals/corymbia_citriodora_kala_13369.jpg?700}} \\
Corymbia citriodora, Kalaupapa HNP herbarium, from www.hear.org [[http://www.hear.org/molokai/kalaupapa/herbarium/vouchers/corymbia_citriodora_kala_13369.htm]]