Hexazinone is an

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The ...

that is used as a broad spectrum

herbicide Herbicides (, ), also commonly known as weedkillers, 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 fo ...

. It is a colorless solid. It exhibits some solubility in water but is highly soluble in most organic solvents except alkanes. A member of the

triazine Triazines are a class of nitrogen-containing heterocycles. The parent molecules' molecular formula is . They exist in three isomeric forms, 1,3,5-triazines being common. Structure The triazines have planar six-membered benzene-like ring but ...

class herbicides, it is manufactured by

DuPont DuPont de Nemours, Inc., commonly shortened to DuPont, is an American multinational chemical company first formed in 1802 by French-American chemist and industrialist Éleuthère Irénée du Pont de Nemours. The company played a major role in ...

and sold under the trade name Velpar. It functions by inhibiting photosynthesis and thus is a nonselective herbicide. It is used to control grasses, broadleaf, and woody plants. In the United States approximately 33% is used on alfalfa, 31% in forestry, 29% in industrial areas, 4% on rangeland and pastures, and < 2% on sugarcane. Hexazinone is a pervasive groundwater contaminant. Use of hexazinone causes groundwater to be at high risk of contamination due to the high leaching potential it exhibits.

History

Hexazinone is widely used as a herbicide. It is a non-selective herbicide from the triazine family. It is used among a broad range of places. It is used to control weeds within all sort of applications. From sugarcane plantations, forestry field nurseries, pineapple plantations to high- and railway grasses and industrial plant sites. Hexazinone was first registered in 1975 for the overall control of weeds and later for uses in crops.

Structure and reactivity

Triazines like hexazinone can bind to the D-1 quinone protein of the electron transport chain in photosystem II to inhibit the photosynthesis. These diverted electrons can thereby damage membranes and destroy cells.

Synthesis

Hexazinone can be synthesized in two different reaction processes. One process starts with a reaction of methyl chloroformate with

cyanamide Cyanamide is an organic compound with the chemical formula, formula carbon, Cnitrogen, N2hydrogen, H2. This white solid is widely used in agriculture and the production of pharmaceuticals and other organic compounds. It is also used as an alcoho ...

, forming hexazinone after a five-step pathway: Hexazinon1

A second synthesis starts with methyl

thiourea Thiourea () is an organosulfur compound with the formula and the structure . It is structurally similar to urea (), except that the oxygen atom is replaced by a sulfur atom (as implied by the ''thio-'' prefix); however, the properties of urea ...

Degradation

The degradation of hexazinone has long been studied. It degrades approximately 10% in five weeks, when exposed to artificial sunlight in distilled water. However, degradation in natural waters can be three to seven times greater. Surprisingly, the pH and the temperature of the water do not affect the

photodegradation Photodegradation is the alteration of materials by light. Commonly, the term is used loosely to refer to the combined action of sunlight and air, which cause oxidation and hydrolysis. Often photodegradation is intentionally avoided, since it destroy ...

significantly. It is mainly degraded by aerobic microorganisms in soils.

Mechanism of action

Hexazinone is a broad-spectrum residual and contact

, rapidly absorbed by the leaves and roots. It is tolerated by conifers, and therefore it is a very effective

for the control for

annual Annual may refer to: * Annual publication, periodical publications appearing regularly once per year **Yearbook ** Literary annual * Annual plant * Annual report * Annual giving * Annual, Morocco, a settlement in northeastern Morocco * Annuals (b ...

and

perennial A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also wide ...

broadleaf weeds, some grasses, and some woody species. Hexazinone works as rain or snowmelt makes it possible for the

to move downward into the soil. There the hexazinone is absorbed from the soil by the roots. It moves through the conductive tissues to the leaves, where it blocks the

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...

of the plant within the

chloroplast A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in ...

s. Hexazinone binds to a protein of the

photosystem II Photosystem II (or water-plastoquinone oxidoreductase) is the first protein complex in the light-dependent reactions of oxygenic photosynthesis. It is located in the thylakoid membrane of plants, algae, and cyanobacteria. Within the photosystem ...

complex, which blocks the electron transport. The result are multiple following reactions. First triplet-state

chlorophyll Chlorophyll (also chlorophyl) is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words , ("pale green") and , ("leaf"). Chlorophyll allow plants to a ...

reacts with

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

to form

singlet oxygen Singlet oxygen, systematically named dioxygen(singlet) and dioxidene, is a gaseous inorganic chemical with the formula O=O (also written as or ), which is in a quantum state where all electrons are spin paired. It is kinetically unstable at ambie ...

. Both

and

then remove

hydrogen ion A hydrogen ion is created when a hydrogen atom loses or gains an electron. A positively charged hydrogen ion (or proton) can readily combine with other particles and therefore is only seen isolated when it is in a gaseous state or a nearly particle ...

s from the unsaturated

lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include ...

s present in de cells and the organelle membranes, forming lipid radicals. These radicals will oxidize other lipids and proteins, eventually resulting in loss of the membrane integrity of the cells and organelles. This will result in a loss of

, leakage of cellular contents, cell death, and eventually death of the plant. Woody plants first show yellowing of the leaves before they start to defoliate, eventually they will die. Sometimes plants are able to refoliate and defoliate again during the growing season.

References

External links

DuPont webpage on Velpar
* {{Herbicides Herbicides Toxicology DuPont Triazines Lactams Cyclohexyl compounds