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

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

classified as a diol and a

terpenoid The terpenoids, also known as isoprenoids, are a class of naturally occurring organic compound, organic chemicals derived from the 5-carbon compound isoprene and its derivatives called terpenes, diterpenes, etc. While sometimes used interchangeabl ...

. 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. PMD is the active ingredient in some

insect repellent An insect repellent (also commonly called "bug spray" or "bug deterrent") is a substance applied to the skin, clothing, or other surfaces to discourage insects (and arthropods in general) from landing or climbing on that surface. Insect repellent ...

s. Its odor and chemical structure are similar to

menthol Menthol is an organic compound, specifically a Monoterpene, monoterpenoid, that occurs naturally in the oils of several plants in the Mentha, mint family, such as Mentha arvensis, corn mint and peppermint. It is a white or clear waxy crystallin ...

, and it has a cooling feel. It 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 ...

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 country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

, 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). ''C. citriodora'' oil contains only 1–2% PMD, while refined OLE contains approximately up to 70% PMD. Some commercial PMD products are not made from ''C. citriodora'' oil, but rather from synthetic citronellal.

Effectiveness

A 2006 study showed that PMD used as a repellent is as effective as

DEET ''N'',''N''-Diethyl-''meta''-toluamide, also called diethyltoluamide or DEET (, from DET, the initials of di- + ethyl + toluamide), is the oldest, one of the most effective, and most common active ingredients in commercial insect repellents. ...

when used in like quantities.

Contraindications

PMD should not be used on children under 3 years of age.

Interactions

Few if any studies have evaluated possible interactions when using PMD with sunscreens.

Chemistry

There are eight possible stereoisomers.PubChem Compound Search
/ref> The exact composition is rarely specified and is commonly assumed to be a complex mixture. PMD can be synthesized by a Prins reaction of citronellal. 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 formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the exi ...

s of ''p''-menthane-3,8-diol.

History

Its repellent effect was discovered in the 1960s by the industry. 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 British public body responsible for the encouragement, regulation and enforcement of workplace health, safety and welfare. It has additionally adopted a research role into occupational risks in Great B ...

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".

References