''p''-Menthane-3,8-diol, also known as ''para''-menthane-3,8-diol, PMD, or menthoglycol, is an

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...

classified as a diol and a terpenoid. It is colorless. Its name reflects the hydrocarbon backbone, which is that of ''p''-menthane. A total of eight stereoisomers are possible, based on the three stereocenters of the ring. Depending on the source, one or more may predominate.

Use as insect repellent

''p''-Menthane-3,8-diol is the active ingredient in some insect repellents. Its odor and chemical structure are similar to

menthol Menthol is an organic compound, more specifically a monoterpenoid, made synthetically or obtained from the oils of corn mint, peppermint, or other mints. It is a waxy, clear or white crystalline substance, which is solid at room temperature ...

and has a cooling feel. Its repellent effect was discovered in the 1960s by the industry. There are eight possible stereoisomers of PMD; the exact composition is rarely specified and is commonly assumed to be a complex mixture. PMD is found in small quantities in the

essential oil An essential oil is a concentrated hydrophobic liquid containing volatile (easily evaporated at normal temperatures) chemical compounds from plants. Essential oils are also known as volatile oils, ethereal oils, aetheroleum, or simply as the o ...

from the leaves of '' Corymbia citriodora'', formerly known as ''Eucalyptus citriodora''. This tree is native to

Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...

, but is now cultivated in many warm places around the world. ''C. citriodora'' oil, when refined to increase its PMD content for use in insect repellents, is known in the United States as ''oil of lemon eucalyptus'' (OLE). Some commercial PMD products are not made from ''C. citriodora'' oil, but rather from synthetic

citronellal Citronellal or rhodinal ( C10 H18 O) is a mono terpenoid aldehyde, the main component in the mixture of terpenoid chemical compounds that give citronella oil its distinctive lemon scent. Citronellal is a main isolate in distilled oils from the ...

. Refined OLE contains approximately up to 70% PMD (a mixture of the ''cis'' and ''trans''

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. Is ...

s of ''p''-menthane-3,8-diol). OLE has been notified under the European Biocidal Products Directive (BPD) 98/8/EC (now BPR Regulation (EU) No. 528/212) under its generic name "PMD rich botanic oil" and is currently proceeding through the registration process with the

Health and Safety Executive The Health and Safety Executive (HSE) is a UK government agency responsible for the encouragement, regulation and enforcement of workplace health, safety and welfare, and for research into occupational risks in Great Britain. It is a non-depar ...

in the UK. It is also registered with Canada's Pest Management Regulatory Agency under the generic name "PMD and related oil of lemon eucalyptus compounds". PMD can be synthesized by a Prins reaction of

. This 2011 study also shows that ''C. citriodora'' oil contains only 1–2% PMD and is therefore different from OLE as registered with the U.S. EPA which has up to 70% PMD. A 2006 study showed that PMD is as effective as

DEET ''N'',''N''-Diethyl-''meta''-toluamide, also called DEET () or diethyltoluamide, is the most common active ingredient in insect repellents. It is a slightly yellow oil intended to be applied to the skin or to clothing and provides protection a ...

when used in like quantities.

References

{{DEFAULTSORT:Menthane-3, 8-Diol, P- Insect repellents Monoterpenes Diols Cyclohexanols Isopropyl compounds