1. What is the difference between Citriodiol® and “a mixture of cis- and trans-p-menthane-3,8-diol/Citriodiol” (also known as PMDRBO)?
Citriodiol® is Citrefine's trade name for the generic active ingredient PMDRBO (PMD Rich Botanic Oil) which is listed with the European authorities as "a mixture of cis- and trans-p-menthane-3,8-diol/Citriodiol", a naturally sourced active substance containing p-menthane-3,8-diol (PMD) and other naturally occurring components from the Eucalyptus citriodora tree’s oil (common name: Lemon eucalyptus).
Please contact us to understand how to reference Citriodiol® on your labels, or if you have any further questions about this.
2. Is Citriodiol® the same as Citronella?
No, while Citriodiol® is made from an essential oil, it is very different from citronella oil. Firstly citronella oil is obtained from the leaves and stems of different species of Cymbopogon, or lemongrass, whereas the oil for Citriodiol® is obtained from the Eucalyptus citriodora tree.
The other fundamental and biggest difference is that Citriodiol® contains at least 64% of the naturally occurring constituent PMD (p-menthane-3,8-diol) whereas Citronella oil contains only trace quantities of PMD. This is an important distinction because PMD is the constituent primarily responsible for the efficacy of Citriodiol® in repelling insects and biting arthropods. In side-by-side independent comparisons, Citriodiol® products repel biting insects, such as mosquitoes, 4 to 8 times longer than citronella oil products (Barnard 2004).
Citronella can no longer be marketed as an insect repellent active ingredient in the EU, as it is not being supported under the EU Biocidal Products Regulations (BPR). In addition, the Canadian PMRA is currently considering a ban on Citronella based repellent products due to a lack of safety data and concerns surrounding some of the oils components. By contrast, Citriodiol® is being supported under the BPR (with inclusion expected in 2019) and the Canadian authorities have approved Citriodiol® (registered in Canada under the generic name “Oil of lemon eucalyptus, hydrated, cyclized") for use as a repellent with products supporting 4-6 hours of complete protection time claims against mosquitoes at 30% w/w concentration.
3. Is naturally sourced PMD the same as synthetic PMD?
No. The PMD in Citriodiol® is sourced directly from essential oils. The PMD created from this oil sits along-side the other naturally occurring constituents in a product with 100% purity. This naturally sourced PMD product, which is sometimes called PMD rich botanic oil (PMDRBO) or Oil of Lemon Eucalyptus (OLE) has been notified under the BPR as “Eucalyptus citriodora oil, hydrated, cyclized” and is about 50% more effective in repelling insects than like quantities of synthetic PMD.
By comparison, what is commonly referred to as synthetic PMD is not derived from an essential oil, but rather is typically is a product of far more complicated multi-step chemical processes, for example making menthol. The resulting material contains only PMD and has no essential oil co-constituents.
4. Why is naturally sourced PMD better than synthetic PMD?
Simply put, in our view it is better for the consumer and better for the environment. Consumers benefit because naturally sourced PMD (i.e. Citriodiol®) performs significantly better than synthetic PMD in efficacy tests. An independent study (Drapeau 2011) published comparing synthetic PMD with PMDRBO shows that with like amounts of PMD, it performed 50% better in repelling the target organism (in that case Aedes mosquitoes). In this study a 20% PMDRBO (which at a min 64% PMD contained ca. 13% PMD) alcohol spray offered over 5 hours complete protection against Aedes mosquitoes whereas the 13% synthetic PMD product provided only 3¼ hours of protection.
While both forms of PMD are rapidly biodegradable, the real benefit to the environment from Citriodiol® is that it actually exists in nature in its final form. This means nothing is being added to the environment that has the potential to upset its natural order and balance. In addition, because the material used to make Citriodiol® is Eucalyptus citriodora oil, and this oil is distilled just from the leaves and twigs of the tree, allowing the tree to continue growing, using Citriodiol® actually encourages the growth and maintenance of healthy trees.
5. Why was Citriodiol® notified under the CAS number for PMD if it is being treated as a pure substance?
The history of the registration of Citriodiol® in Europe has been complex, in part because it has forged new ground for the approval of botanicals as biocides. One complication has been how to identify naturally sourced PMD e.g. Citriodiol®. At the time of its notification and in the absence of a CAS Registry Number specific to Citriodiol®, the Commission advised that its main constituent in Citriodiol® is PMD, and it should be notified using the CAS RN for pure PMD (42822-86-6). We have since applied for, and been given, a unique CAS RN for Citriodiol®, which applies to the substance as a whole. This CAS RN is 1245629-80-4 and will be the number under which it is formally listed following an inclusion decision.
As of April 2017, the Art 95 list of approved suppliers includes the active substance EC Oil (H/C) but also ties this to prior name PMD. It may be helpful for customers who are working with Member State authorities unfamiliar with this change, to direct them to this listing. We now recommend notifying/registering products in Europe under the new CAS RN 1245629-80-4, since this is a substance readily found on the Art 95 list of supported substances. It is also appropriate to register products containing Citriodiol® in Canada, the USA and Australia under the new CAS number. Please check with us for products in other countries.
7. How is Citriodiol® made?
As the essential oil in the leaves of the Eucalyptus citriodora tree matures, the main constituent of the oil, citronellal, gradually converts into PMD. Indeed, what we know as Citriodiol® (i.e. a high PMD content oil with minor isopulegol, citronellol and acetal co-constituents) is merely an acceleration of nature’s process.
However, steam distillation is required to extract the oil. Because PMD crystallises, distillation of oil containing PMD is not feasible. We therefore harvest the leaves at a younger age when there is only a very small amount of PMD present and the citronellal content is highest. We then use a dilute aqueous catalyst to convert the citronellal content to PMD, with small amounts of isopulegol and acetal as by-products. Finally, we wash out the catalyst. The result is a product that contains a minimum of 64% PMD and only a negligible amount of citronellal. In this way we are effectively mimicking nature’s own aging process. The other components in the Eucalyptus citriodora oil remain unaffected by process and are found in the same relative quantities in Citriodiol®