Dichlorprop is a chlorophenoxy

herbicide Herbicides (, ), also commonly known as weed killers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page f ...

similar in structure to

2,4-D 2,4-Dichlorophenoxyacetic acid is an organic compound with the chemical formula . It is usually referred to by its ISO common name 2,4-D. It is a systemic herbicide that kills most broadleaf weeds by causing uncontrolled growth, but most gra ...

that is used to kill annual and perennial broadleaf weeds. It is a component of many common weedkillers. About 4 million pounds of dichlorprop are used annually in the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

Chemistry

Dichlorprop possesses a single

asymmetric carbon In stereochemistry, an asymmetric carbon is a carbon atom that is bonded to four different types of atoms or groups of atoms. The four atoms and/or groups attached to the carbon atom can be arranged in space in two different ways that are mirror ...

and is therefore a

chiral Chirality () is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek language, Greek (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is dist ...

molecule, however only the ''R''-isomer is active as an herbicide. When dichlorprop was first marketed in the 1960s, it was sold as

racemic mixture In chemistry, a racemic mixture or racemate () is a mixture that has equal amounts (50:50) of left- and right-handed enantiomers of a chiral molecule or salt. Racemic mixtures are rare in nature, but many compounds are produced industrially as r ...

stereoisomer In stereochemistry, stereoisomerism, or spatial isomerism, is a form of isomerism in which molecules have the same molecular formula and sequence of bonded atoms (constitution), but differ in the three-dimensional orientations of their atoms in ...

s, but since then advances in

asymmetric synthesis Enantioselective synthesis, also called asymmetric synthesis, is a form of chemical synthesis. It is defined by IUPAC as "a chemical reaction (or reaction sequence) in which one or more new elements of chirality are formed in a substrate molecul ...

have made possible the production of the enantiopure compound. Today, only ''R''-dichlorprop (also called dichlorprop-p or 2,4-DP-p) and its derivatives are sold as

pesticides Pesticides are substances that are used to pest control, control pest (organism), pests. They include herbicides, insecticides, nematicides, fungicides, and many others (see table). The most common of these are herbicides, which account for a ...

in the United States. Dichlorprop is a

carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an Substituent, R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl ...

, and like related herbicides with free acid groups, it is often sold as a

salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...

ester In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...

. Currently, the 2-ethylhexyl ester is used commercially. The butoxyethyl and isooctyl esters were once popular, but are no longer approved for agricultural use. For the salts, the

dimethylamine Dimethylamine is an organic compound with the formula (CH3)2NH. This secondary amine is a colorless, flammable gas with an ammonia-like odor. Dimethylamine is commonly encountered commercially as a solution in water at concentrations up to around ...

salt is still available, while the

diethanolamine Diethanolamine, often abbreviated as DEA or DEOA, is an organic compound with the formula HN(CH2CH2OH)2. Pure diethanolamine is a white solid at room temperature, but its tendencies to absorb water and to supercool often results in it being foun ...

salt is no longer used. According to the

United States Environmental Protection Agency The Environmental Protection Agency (EPA) is an independent agency of the United States government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it began operation on De ...

(EPA), "2,4-DP-p is thought to increase

cell wall A cell wall is a structural layer that surrounds some Cell type, cell types, found immediately outside the cell membrane. It can be tough, flexible, and sometimes rigid. Primarily, it provides the cell with structural support, shape, protection, ...

plasticity, biosynthesis of

proteins Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, re ...

, and the production of

ethylene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon–carbon bond, carbon–carbon doub ...

. The abnormal increase in these processes result in abnormal and excessive cell division and growth, damaging vascular tissue. The most susceptible tissues are those that are undergoing active cell division and growth."Reregistration Eligibility Decision (RED) for Dichlorprop-p (2,4-DP-p)
US EPA, August 29, 2007]

Health effects

The EPA rates the oral

acute toxicity Acute toxicity describes the adverse effects of a substance that result either from a single exposure or from multiple exposures in a short period of time (usually less than 24 hours). To be described as ''acute'' toxicity, the adverse effect ...

of dichlorprop as "slight" based on a rat of 537 mg/kg, and its derivatives are even less toxic. It is, however, considered to be a severe eye irritant. There has been concern that chlorophenoxy herbicides including dichlorprop may cause cancer, and in 1987 the

International Agency for Research on Cancer The International Agency for Research on Cancer (IARC; ) is an intergovernmental agency forming part of the World Health Organization of the United Nations. Its role is to conduct and coordinate research into the causes of cancer. It also cance ...

(IARC) ranked this class of compounds as group 2B "possibly carcinogenic to humans".CHLOROPHENOXY HERBICIDES (Group 2B)
International Agency for Research on Cancer (IARC), 1987 The EPA classifies the ''R''-isomer as “Not Likely to be Carcinogenic to Humans.”

References

External links

{{Herbicides Carboxylic acids Organochlorides IARC Group 2B carcinogens Phenol ethers Auxinic herbicides