MCPA
Encyclopedia
MCPA or 2-methyl-4-chlorophenoxyacetic acid is a powerful, selective, widely-used phenoxy herbicide
. The pure compound is a brown-colored powder.
s Jealott's Hill
research centre into the effects of synthetic hormones on plant growth looking specifically for a way to kill weeds without harming crops such as corn.
Synthesis of MCPA was first reported by Synerholme and Zimmerman in 1945 and by Templeman and Foster in 1946. Templeman and Foster were searching for compounds with similar or greater selective activity than 1-naphthaleneacetic acid
in inhibiting the growth of weeds while not adversely affecting the growth of cereal
grains. They synthesized MCPA from the corresponding phenol by exposing it to chloroacetic acid
and dilute base in a straightforward substitution reaction
:
s, including thistle
and dock
, in cereal crops and pasture
. It is selective for plants with broad leaves, and this includes most deciduous
trees. Clover
s are tolerant at moderate application levels. It is currently classified as a restricted use pesticide
in the United States
. Its toxicity and biodegradation are topics of current research. One formulation is described by its manufacturer as "designed for specific markets that require the safest possible phenoxy product, primarily for use in the Pacific Northwest". Though not extremely toxic, it has recently been determined that MCPA can form complexes with metal ions and thereby increase their bioavailability, though there is also work being done to utilize this ability.
group allows the formation of conjugated complexes with metals (see below). The acid functionality makes MCPA a versatile synthetic intermediate for more complex derivatives.
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...
. The pure compound is a brown-colored powder.
History
In 1936 investigations began at ICIICI
ICI or Ici may mean:* ICI programming language, a computer programming language developed in 1992* Ici , an alternative weekly newspaper in Montreal, CanadaICI is also an abbreviation which may mean:...
s Jealott's Hill
Jealott's Hill
Jealott's Hill is a village in Berkshire, England, within the civil parish of Warfield.The settlement lies near on the A3095 road and is approximately north-east of Bracknell. It is home to Syngenta's largest R&D site in the world, and houses Europe's largest greenhouse at 4,000 square metres...
research centre into the effects of synthetic hormones on plant growth looking specifically for a way to kill weeds without harming crops such as corn.
Synthesis of MCPA was first reported by Synerholme and Zimmerman in 1945 and by Templeman and Foster in 1946. Templeman and Foster were searching for compounds with similar or greater selective activity than 1-naphthaleneacetic acid
1-Naphthaleneacetic acid
1-Naphthaleneacetic acid, commonly abbreviated NAA, is an organic compound with the formula C10H7CH2CO2H. This colourless solid is soluble in organic solvents...
in inhibiting the growth of weeds while not adversely affecting the growth of cereal
Cereal
Cereals are grasses cultivated for the edible components of their grain , composed of the endosperm, germ, and bran...
grains. They synthesized MCPA from the corresponding phenol by exposing it to chloroacetic acid
Chloroacetic acid
Chloroacetic acid, industrially known as monochloroacetic acid is the organochlorine compound with the formula ClCH2CO2H. This carboxylic acid is a useful building-block in organic synthesis.-Production:...
and dilute base in a straightforward substitution reaction
Substitution reaction
In a substitution reaction, a functional group in a particular chemical compound is replaced by another group. In organic chemistry, the electrophilic and nucleophilic substitution reactions are of prime importance...
:
- 2-methyl-4-chlorophenol + ClCH2CO2H + baseBase (chemistry)For the term in genetics, see base A base in chemistry is a substance that can accept hydrogen ions or more generally, donate electron pairs. A soluble base is referred to as an alkali if it contains and releases hydroxide ions quantitatively...
→ MCPA + base·HCl
Commercial use
MCPA is used as an herbicide, generally as its salt or esterified forms. Used thus, it controls broadleaf weedWeed
A weed in a general sense is a plant that is considered by the user of the term to be a nuisance, and normally applied to unwanted plants in human-controlled settings, especially farm fields and gardens, but also lawns, parks, woods, and other areas. More specifically, the term is often used to...
s, including thistle
Thistle
Thistle is the common name of a group of flowering plants characterised by leaves with sharp prickles on the margins, mostly in the family Asteraceae. Prickles often occur all over the plant – on surfaces such as those of the stem and flat parts of leaves. These are an adaptation that protects the...
and dock
Rumex
The docks and sorrels, genus Rumex L., are a genus of about 200 species of annual, biennial and perennial herbs in the buckwheat family Polygonaceae....
, in cereal crops and pasture
Pasture
Pasture is land used for grazing. Pasture lands in the narrow sense are enclosed tracts of farmland, grazed by domesticated livestock, such as horses, cattle, sheep or swine. The vegetation of tended pasture, forage, consists mainly of grasses, with an interspersion of legumes and other forbs...
. It is selective for plants with broad leaves, and this includes most deciduous
Deciduous
Deciduous means "falling off at maturity" or "tending to fall off", and is typically used in reference to trees or shrubs that lose their leaves seasonally, and to the shedding of other plant structures such as petals after flowering or fruit when ripe...
trees. Clover
Clover
Clover , or trefoil, is a genus of about 300 species of plants in the leguminous pea family Fabaceae. The genus has a cosmopolitan distribution; the highest diversity is found in the temperate Northern Hemisphere, but many species also occur in South America and Africa, including at high altitudes...
s are tolerant at moderate application levels. It is currently classified as a restricted use pesticide
Restricted use pesticides
Because of safety concerns, some pesticides are not available to the general public in the United States. The "Restricted Use" classification restricts a product, or its uses, to use by a certificated pesticide applicator or under the direct supervision of a certified applicator. This means that a...
in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. Its toxicity and biodegradation are topics of current research. One formulation is described by its manufacturer as "designed for specific markets that require the safest possible phenoxy product, primarily for use in the Pacific Northwest". Though not extremely toxic, it has recently been determined that MCPA can form complexes with metal ions and thereby increase their bioavailability, though there is also work being done to utilize this ability.
Chemical use
Because it is inexpensive, MCPA is used in various chemical applications. Its carboxylic acidCarboxylic 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...
group allows the formation of conjugated complexes with metals (see below). The acid functionality makes MCPA a versatile synthetic intermediate for more complex derivatives.
Brand names
The following commercial products contain MCPA.- Agritox, Agroxone, Chiptox, Chwastox, Cornox, Methoxone, Rhonox, Spurge Power, Tigrex, Verdone Extra (UK), Weed-Rhap, Weed'n'Feed, Weed-B-Gone, Zero Bindii & Clover Weeder (Aus)