Chemistry of herbicides

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Herbicides, also commonly known as weed killers

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 mimics of natural plant hormones . Herbicides

used to clear waste ground, industrial sites, railways and railway

embankments are not selective and kill all plant material with which they come into contact. Smaller quantities are used in forestry,

pasture systems, and management of areas set aside as

wildlife habitat. Some plants produce natural herbicides, such as

the genus Juglans (walnuts), or the tree of heaven ; such action of

natural herbicides, and other related chemical interactions, is

called allelopathy.

Herbicides are widely used in agriculture and landscape turf

management. In the US, they account for about 70% of all

agricultural pesticide use.This slides has been made By : Mahmoud Galal Zidan Farag

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Aromatic Acid Compound

Dicamba

MCPA

Chloramben

Amide Compounds

CDDA

CDEA

Propachlor

Phenolic Nitro Compounds

DNOC

DinitroAniline Compounds

Trifluralin

Heterocyclic Compounds

S-Triazine

Diazine

This slides has been made By : Mahmoud Galal Zidan Farag


IUPAC Name : 3,6-Dichloro-2-methoxybenzoic

acid

Structure :

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Preparation


Uses And Affection : The most versatile group of herbicides.

it is used to control brush and bracken in pastures, as well as legumes and cacti .

It kills broadleaf weeds before and after they sprout. In combination with a phenoxy herbicide or with other herbicides.

Dicamba is used in pastures, range land, and noncrop areas (fence rows, roadways, and wastage) to control weeds

Dicamba is toxic to conifer species but is in general less toxic to grasses

Some weed species have developed resistance to Dicamba. Dicamba resistance in kochia was discovered in 1994 and has not been explained by common modes of resistance such as absorption, translocation, or metabolism.

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Toxicity : Dicamba does not present unusual handling hazards. It is moderately toxic by ingestion and slightly toxic by inhalation or dermal exposure (oral LD50 in rats: 757 mg/kg body weight, dermal LD50 in rats: >2,000 mg/kg, inhalation LC50 in rats: >200 mg/L).

In a 3-generation study, Dicamba did not affect the reproductive capacity of rats. When rabbits were given doses of 0, 0.5, 1, 3, 10, or 20 (mg/kg)/day of technical Dicamba from days 6 through 18 of pregnancy, toxic effects on the mothers, slightly reduced fetal body weights, and increased loss of fetuses occurred at the 10 mg/kg dose. U.S. Environmental Protection Agency (EPA) has set the NOAEL for this study at 3 (mg/kg)/day.

In dog tests, some enlargement of liver cells has occurred, but a similar effect has not been shown in humans.


The Properties


IUPAC Name : (4-Chloro-2-

methylphenoxy)acetic acid

Structure :


Preparation :

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Uses :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 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.

Chemical useBecause it is inexpensive, MCPA is used in various chemical applications. Its carboxylic acid group allows the formation of conjugated complexes with metals (see above). The acid functionality makes MCPA a versatile synthetic intermediate for more complex derivatives


http://en.wikipedia.org/wiki/Carboxylic_acid

Hazard And

physical

Properties


IUPAC Name :

3-Amino-2,5-dichlorobenzoic acid

Structure :


Pharmaco Kinetics of Choramben :

Adsorption :

Choramben is rabidly adsorbed from the

gastro intestinal track of Sprague dawley

female rate .

Metabolism :

It rats dosed by gavage , the parent

compound accounted for 70% of the

applied dose in 24 h Urine .


Andrawes (1984) identified 5 of 24 urinary

metabolism .


Uses :used to control the seedlings of broadleaf

weeds and annual grasses. It is mostly used

for soybeans , but also for dry beans

, peanuts , sunflowers , peppers , cotton

, sweet potatoes, squash, hardwood trees

, shrubs , and some conifers.

Chloramben is considered practically

nontoxic



Hazard And

physical Properties


1- CDEAIUPAC Names: N,N-diethyl chloro acetamide

Structure :

2- CDDAIUPAC Names: N,N-diallyl chloro acetamide

Structure :


3- PropachlorIUPAC Names: 2-cholor-N-isopropyl acetaniline

Structure:



Uses of Amide Group :The preparation acts on annual grasses and on some broadleaf plants.

Between 1987 and 1996, about 2.1 million pounds of its active ingredient were used in the United States. 75% was applied to sorghum crops and 24% to maize.

Monsanto voluntarily discontinued its manufacture in 1998. It is currently listed in the U.S. Environmental Protection Agency's Toxics Release Inventory. In 2008, the European Commission issued a decision withdrawing its approval for use as of March 18, 2009, citing the presence of its metabolites in groundwater. Propachlor was added toCalifornia's Proposition 65 list as a carcinogen in 2001



Properties

Non of them properties is known .



IUPAC Names: 4,6 dinitro – 2 methyl phenol

Common Name : DNOC – Dinitro-o-Cresol

Structure :

Preparation :


Applications and safety

This toxicant interferes with adenosine

triphosphate (ATP) production , So it’s high

mammalian toxic

Symptoms of dinitro-ortho-cresol poisoning,

due to ingestion or other forms of exposure,

include confusion, headache, shortness of

breath, and sweating.



IUPAC Name: 2,6-Dinitro-N,N-dipropyl-4-(trifluoromethyl)aniline .

Common Name : Trifluralin

Structure:


Preparation :


Application and toxicity

Trifluralin is a commonly used pre-

emergence herbicide . With about 14 million

pounds used in the United States in 2001, it is

one of the most widely used herbicides .

Trifluralin is generally applied to the soil to

provide control of a variety of annual grass

and broadleaf weed species. It inhibits root

development by interrupting mitosis, and thus

can control weeds as they germinate.

Trifluralin has been banned in the European

Union since 20 March 2008, primarily due to its

high toxicity to fish and other aquatic life.This slides has been made By : Mahmoud Galal Zidan Farag


Hazard And

physical

Properties



Simazine

Propazine

Atrzine

S-Triazine

Bentazone

Bromacil

Diazine


Triazine compounds have been synthesized by reacting

cyanuric chloride with alkyl amine .


Properties and uses

Simazine is an off-white crystalline compound which is sparingly soluble in water. It is a member of the triazine-derivative herbicides, and was widely used as a residual nonselective herbicide, but is now banned in European Union states.Like atrazine, a related triazineherbicide, it acts by inhibiting photosynthesis. It remains active in the soil for 2-7 months after application.


Properties and uses Atrazine is an herbicide that is used to stop pre and post-

emergence broadleaf and grassy weeds in crops such as sorghum, maize, sugarcane, lupines , pine and eucalyptplantations, and Triazine tolerant (TT) canola .

In the United States as of 2014, atrazine was the second most widely used herbicide after glyphosate, with 76 million pounds of it applied each year. Atrazine continues to be one of the most widely used herbicides in Australian agriculture.

Its use is banned in the European Union.

Its effect on corn yields has been estimated from 8% to 1%, with 3–4% being the conclusion of one economics review .

In another study looking at combined data from 236 university corn field trials from 1986–2005, atrazine treatments showed an average of 5.7 bushels more per acre than alternative herbicide treatments.

Effects on sorghum yields have been estimated to be as high as 20%, owing in part to the absence of alternative weed control products that can be used on sorghum.


Common Name : Bromazil, Borea, Bromax

4G, Cynogan, Uragan and Hyvar .

IUPAC Name : 5-bromo-3-(butan-2-yl)-6-

methylpyrimidine-2,4(1H,3H)-dione or 5-

bromo-3-sec-butyl-6-methyluracil

Structure :


Applications

Bromacil is applied mainly by sprayers including boom, hand-held, knapsack, compressed air, tank-type, and power sprayers. Bromacil is also applied using aerosol, shaker, or sprinkler cans. Solid forms of bromacil are spread using granule applicators and spreaders. Application using aircraft is allowed only for Special Local Need registrations to control vegetation on the Department of Defense’s Yakima Firing Center in the state of Washington.


SafetyThere are quite a few safety precautions that should be taken when dealing with Bromacil. Dry formulations containing bromacil must bear the word "Caution" and liquid formulas must signal "Warning." Care should be exercised when spraying Bromacil on non-target plants because it will also stop the photosynthesis of the adjacent plants therefore killing them. Bromacil should never be used in residential or recreation areas for risk of exposure. Bromacil is slightly toxic if individuals accidentally eat or touch residues and practically nontoxic if inhaled. Bromacil is a mild eye irritant and a very slight skin irritant. It is not a skin sensitizer. In studies using laboratory animals, bromacil is slightly toxic by the oral, dermal, and inhalation routes and has been placed in Toxicity Category IV (the lowest of four categories) for these effects. This herbicide should be stored in a cool, dry place and after any handling a thorough hand-washing is advised.

In regards to occupational exposure, the National Institute for Occupational Safety and Health has recommended workers handing bromacil not exceed an exposure of 1 ppm (10 mg/m3) over an eight-hour time-weighted average.



Pharmaco Kinetics of Bromacil :

Adsorption

workers who exposed to bromacil during

production and packing excreted uncharged

bromacil and 5-bromo-3-sec-butyl-6-

hydroxymethylurine metabolite in urine.

uncharged bromacil and metabolite were also

detected in the rats fed bromacil .

Metabolism

Unchanged bromacil and 5-bromo-3-sec-butyl-6-

hydroxymethylurine metabolite present as

glucuronide and/or sulforate conjugated in urine


Five Minors detected in urine


Common Name : Bentazone, Basagran,

Herbatox, Leader, Laddock

IUPAC Name : 3-Isopropyl-1H-2,1,3-

benzothiadiazin-4(3H)-one 2,2-dioxide

Structure :


UsageBentazon is a selective herbicide as it only damages plants unable to metabolize the chemical. It is considered safe for use on alfalfa, beans (with the exception of garbanzo beans ), corn, peanuts, peas (with the exception of blackeyed peas ), pepper , peppermint , rice , sorghum soybeans and spearmint; as well as lawns and turf. Bentazon is usually applied aerially or through contact spraying on food crops to control the spread of weeds occurring amongst food crops. Herbicides containing bentazon should be kept away from high heat as it will release toxic sulfur and nitrogen fumes.

Bentazon is currently registered for use in the United States in accordance with requirements set forth by the United States Environmental Protection Agency. However as of September 2010, the herbicides Basagran M60, Basagran DF, BasagranAG, Prompt 5L and Laddock 5L are currently under review for pending requests for voluntary registration cancellation.


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