MCPA

Chembox new
Name = MCPA
ImageFile = MCPA structure.png ImageSize = 200px
IUPACName = (4-Chloro-2-methylphenoxy)acetic acid
OtherNames = 4-Chloro-"o"-tolyloxyacetic acid
MCPA
Name = Hazards
Section1 = Chembox Identifiers
SMILES = Cl-C1=CC=C(OCC(=O)O)C(C)=C1
CASNo = 94-74-6
Section2 = Chembox Properties
Formula = C₉H₉ClO₃
MolarMass = 200.62 g/mol
Appearance = white to light brown solid
Density = 1.18-1.21 g/cm³
Solubility = Virtually insoluble,
amine salt: 866 g/L
ester: 5 mg/L
MeltingPt = 114-118 °C (387-391 K)
BoilingPt =
pKb =
Viscosity =
Section3 = Chembox Structure
MolShape =
Coordination =
CrystalStruct =
Dipole =
Section7 = Chembox Hazards
ExternalMSDS = [http://www.agrimor.com/mcpa.htm External MSDS]

MCPA or 2-methyl-4-chlorophenoxyacetic acid is a powerful, selective, widely-used phenoxy herbicide. The pure compound is a brown-colored powder.

History

Synthesis of MCPA was first reported by Synerholme and Zimmerman in 1945 and by Templeman and Foster in 1946. [cite book | author=S. Budaver, ed. | title=The Merck Index (11th ed.) |publisher=Merck & Co, Inc. | year=1989 ] Templeman and Foster were searching for a 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: [cite journal | author=W.G. Templeman, W.A. Sexton| title=The Differential Effect of Synthetic Plant Growth Substances upon Plant Species. I. Seed Germination and Early Growth Responses to α-Naphthylacetic Acid and Compounds of General Formula arylOCHCOO| journal=Proceedings of the Royal Society of London| volume=133| issue=872| year=1946| pages=300–313] :2-methyl-4-chlorophenol + ClCH₂CO₂H + base → MCPA + base·HCl

Chemical use

Because it is inexpensive, MCPA is used in various chemical applications. Its carboxylic acid group allows the formation of conjugated complexes with metals (see below). The acid functionality makes MCPA a versatile synthetic intermediate for more complex derivatives. [cite journal | author=A. R. Prasad, T. Ramalingam, A. B. Rao, P. V. Diwan and P. B. Sattur| title=Synthesis and biological evaluation of 3-aryloxyalkyl-6-aryl-7H-s-triazolo3,4-b [1,3,4] thiadiazines*| journal=European Journal of Medicinal Chemistry | volume=25| issue=2| year=1989| pages=199–201| doi=10.1016/0223-5234(89)90116-5]

Commercial use

MCPA is used as an herbicide, generally as its salt or esterified forms. Used thus, it controls broadleaf weeds, including thistle and dock, in cereal crops and pasture. It is selective for plants with broad leaves, and this includes most deciduous trees. Clovers are tolerant at moderate application levels. It is currently classified as a restricted use pesticide. 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". [cite web|url=http://www.nufarm.com/USAg/Chiptoxr|title=Chiptox|publisher=Nufarm] Though not extremely toxic, [http://pmep.cce.cornell.edu/profiles/extoxnet/haloxyfop-methylparathion/mcpa-ext.html Extoxnet listing of MCPA] ] it has recently been determined that MCPA can form complexes with metal ions and thereby increase their bioavailability, [cite journal | author=J. Kobylecka, B. Ptaszynski, R. Rogaczewski, A. Turek| title=Phenoxyalkanoic acid complexes. Part I. Complexes of lead(II), cadmium(II) and copper(II) with 4-chloro-2-methylphenoxyacetic acid (MCPA)| journal=Thermochimica Acta| volume=407| issue=1-2| year=2003| pages=25–31| doi=10.1016/S0040-6031(03)00287-9] though there is also work being done to utilize this ability. [cite journal | author=R. Kruszynski, T.J. Bartczak, B. Ptaszynski and A. Turek| title=A Novel Lead- bis (4-Chloro-2-Methylphenoxy)- Acetate Polymeric Complex| journal=Journal of Coordination Chemistry| volume=55| issue=9| year=2002| pages=1079–1089| doi=10.1080/0095897021000010035]

Brand names

The following commercial products contain MCPA.
*Agritox
*Agroxone
*Chiptox
*Chwastox
*Cornox
*Methoxone
*Rhonox
*Tigrex
*Verdone Extra (UK)
*Weed-Rhap
*Weed'n'Feed [ [http://www.yates.com.au/Products/Lawncare/PestDiseaseWeedControl/WeednFeedLiquidHoseOn.asp Yates Weed'n'Feed information page] ]
*Weed-B-Gone
*Zero Bindii & Clover Weeder (Aus)

References