Dichlorprop
Encyclopedia
Dichlorprop is a chlorophenoxy herbicide
similar in structure to 2,4-D 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
.
and is therefore a chiral
molecule, however only the R-isomer is active as an herbicide. When dichlorprop was first marketed in 1960s, it was sold as racemic mixture of stereoisomers, but since then advances in asymmetric synthesis 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 in the United States.
Dichlorprop is a carboxylic acid
, and like related herbicides with free acid groups, it is often sold as a salt or ester
. 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
salt is still available, while the diethanolamine salt is no longer used.
According the United States Environmental Protection Agency
(EPA), "2,4-DP-p is thought to increase cell wall
plasticity, biosynthesis of proteins, and the production of ethylene
. 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."
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
(IARC) ranked this class of compounds as group 2B "possibly carcinogenic to humans". The EPA classifies the R-isomer as “Not Likely to be Carcinogenic to Humans.”
Herbicide
Herbicides, also commonly known as weedkillers, are pesticides used to kill unwanted plants. Selective herbicides kill specific targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic "imitations" of plant...
similar in structure to 2,4-D that is used to kill annual and perennial broadleaf weeds. It is a component of many common weedkillers. About 4 million pounds
Pound (mass)
The pound or pound-mass is a unit of mass used in the Imperial, United States customary and other systems of measurement...
of dichlorprop are used annually in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
.
Chemistry
Dichlorprop possesses a single asymmetric carbonAsymmetric carbon
An asymmetric carbon atom is a carbon atom that is attached to four different types of atom or four different groups of atoms. Knowing the number of asymmetric carbon atoms, one can calculate the maximum possible number of stereoisomers for any given molecule as follows:As an example, malic acid...
and is therefore a chiral
Chirality (chemistry)
A chiral molecule is a type of molecule that lacks an internal plane of symmetry and thus has a non-superimposable mirror image. The feature that is most often the cause of chirality in molecules is the presence of an asymmetric carbon atom....
molecule, however only the R-isomer is active as an herbicide. When dichlorprop was first marketed in 1960s, it was sold as racemic mixture of stereoisomers, but since then advances in asymmetric synthesis 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 in the United States.
Dichlorprop is a carboxylic acid
Carboxylic acid
Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...
, and like related herbicides with free acid groups, it is often sold as a salt or ester
Ester
Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
. Currently, the 2-ethylhexyl
2-Ethylhexanol
2-Ethylhexanol is a fatty alcohol, an organic compound is a branched, eight-carbon chiral alcohol. It is a colorless liquid that is nearly insoluble in water but soluble in most organic solvents...
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
Dimethylamine is an organic compound with the formula 2NH. This secondary amine is a colorless, flammable liquified gas with an ammonia-like odor. Dimethylamine is generally encountered as a solution in water at concentrations up to around 40%...
salt is still available, while the diethanolamine salt is no longer used.
According the United States Environmental Protection Agency
United States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...
(EPA), "2,4-DP-p is thought to increase cell wall
Cell wall
The cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to...
plasticity, biosynthesis of proteins, and the production of ethylene
Ethylene
Ethylene is a gaseous organic compound with the formula . It is the simplest alkene . Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant hormone...
. 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."
Health effects
The EPA rates the oral acute toxicityAcute toxicity
Acute toxicity describes the adverse effects of a substance that result either from a single exposure or from multiple exposures in a short space of time...
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
International Agency for Research on Cancer
The International Agency for Research on Cancer is an intergovernmental agency forming part of the World Health Organisation of the United Nations....
(IARC) ranked this class of compounds as group 2B "possibly carcinogenic to humans". The EPA classifies the R-isomer as “Not Likely to be Carcinogenic to Humans.”