Chemical classification of herbicides
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This document provides a summary of a presentation on the chemical classification of herbicides. It discusses the major categories of herbicide classification including inorganic, organic, phenoxy, triazine, urea, and others. The presentation covers the history and development of each classification group, examples of common herbicides that fall within each group, and basic information on their chemical structures and modes of action. The presentation aims to explain the importance and basis of chemically classifying herbicides according to their molecular structures.
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Chemical classification of herbicides
- 1. A PRESENTATION ON CHEMICAL CLASSIFICATION OF HERBICIDES COURSE NAME:WEED MANAGEMENT COURSE NO:AGRON-503 COURSE CREDIT HOURS:3(2+1) SESSION:2017-18 PRESENTED TO: DR. N.K CHOUBEY DEPARTMENT OF AGRONOMY COLLEGE OF AGRICULTURE,RAIPUR PRESENTED BY: DEBASIS PANDA MSc.(Agronomy)Previous COLLEGE OF AGRICULTURE,RAIPUR
- 3. What is chemical classification ? Grouping of herbicides having similarity in chemical structure provides the basis for chemical classification Most herbicides are classified into groups (chemical families) according to common chemistry Chemical groups will have a common base structure and substitutions on the base molecular structure will determine the specific herbicide
- 4. Why there was need of chemical classication ? As we all know chemistry affects herbicidal properties. The chemistry of a compound determines how the herbicide will act in biological and physical systems such as plants, animals, soils, and water.
- 5. By whom it was done ? Anonymously from mid 20th century gradually the classification groups increased to a significant number. Presently WSSA( weed science society of America )is a pioneer institution from where HERBICIDE HANDBOOK releases which accounts these type of classification based on chemistry(structural chemistry).
- 6. Is chemical classification very much essential and is it 100 % correct ? We classify the herbicides according to similar structures and they have quite common mode of action or the same mechanism by which they kill the targeted weeds but sometimes it contradicts . I M EXPLAINING ONE CHEMICAL BASED EXAMPLE(NOT FROM HERBICIDE BUT HAVING THE SAME LOGIC ). TESTOSTERONE and PROGESTERONE almost having same structure but we cant place them with in one group because one is having male desirability and other is having female desirability LIKEWISE HRBICIDES CLASSIFICATION ARE NOT STRICTLY FORMED
- 8. Inorganic herbicide era starts from late 19th to mid 20th century SERENDIPITY:Accidental discovery 1880:Salt first inorganic herbicide (reason:salt acts as an osmotically active inducing substance to plant vegetation) PROCESS:EXOSMOSIS 1897:Sulphuric acid/H2SO4(very strong acid ,it burns all the things which comes in its way )
- 9. HIGH AMOUNT OF PRODUCT NEEDED WHICH IS QUITE UNECONOMICAL NON SELECTIVE IN NATURE HIGH MAMALIAN TOXICITY PERSISTENT IN NATURE
- 10. SOME OTHER EXAMPLES ARE Ash : Best natural herbicide (even used in present time) Kerosine oil Ammonium sulphamate Potassium cyanate Calcium cyanamide borax Sodium chlorate Copper sulphate Ferrous sulphate Thiocyanate compounds Mercuric compounds Sodium arsenite
- 11. Breakthrough as selective weed chemical control Today dominant in almost all areas Most effective and selective Started around 40 years ago
- 12. In chemistry, organic means that a molecule has a carbon backbone with some hydrogen thrown in for good measure. Living creatures are made of various kinds of organic compounds. Inorganic molecules are composed of other elements. They may contain hydrogen or carbon, but if they have both, they are organic.
- 13. Chemically these are Caboxylic acids (We can say aromatic carboxyllic acid as they contain one Aromatic ring structure ) 2,4-Dichlorophenoxyacetic acid, a Phenoxy herbicide 1 2 3 4 5 6
- 14. Various subtitutions –Cl,-CH3,-NH2, -NO2 replacing hydrogen atom on the ring or aliphatic side chain or both Cl Cl CLEARLY INDICATING THE CHLORINE SUBSTITUTION IN 2,4-D
- 15. This group developed during 1940 Britain dicovered MCPA USA discovered 2,4-D Phenoxy herbicides (or "phenoxies") are a family of chemicals related to the growth hormone - indoleacetic acid (IAA). When sprayed on broad-leaf plants they induce rapid, uncontrolled growth ("growing to death"). When sprayed on monocotyledonous (grass) crops such as wheat or corn, they selectively kill broad-leaf weeds, leaving the crops relatively unaffected.
- 16. The wide variety of phenoxies in use today can be grouped into the phenoxyacetic, phenoxybutyric and phenox ypropionic subtypes, the latter containing the aryloxyphenoxypropionic subtype with the greatest number of commercial variants. Chemically, they are carboxylic acids, typically applied in an ester or salt form. First introduced in 1946, these herbicides were in widespread use in agriculture by the middle of the 1950s
- 17. The best known phenoxy herbicides are MCPA, 2,4-dichlorophenoxyacetic acid (2,4- D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5- T). 2,4,5-T was later found to be inherently contaminated with the dioxin 2,3,7,8- tetrachlorodibenzo-para-dioxin (TCDD), and has since been banned in most countries. 2,4-D may also contain dioxin impurities, depending on the production method.
- 18. Agent Orange is an herbicide and defoliant chemical. It is widely known for its use by the U.S. Military as part of its herbicidal warfare program, Operation Ranch Hand, during the Vietnam War from 1961 to 1971. It is a mixture of equal parts of two herbicides, 2,4,5-T and 2,4-D. In addition to its damaging environmental effects, the chemical has caused major health problems for many individuals who were exposed.
- 19. AGENT ORANGE SPRAYING DURING VIETNAM WAR
- 20. HOW CAN WE KNOW BY KNOWING THE SUFFIX ? SUFFIX OF –PYR,-PROP SOME OTHER EXAMPLES AREMECOPROP DICHLORPROP 2,4-D MCPA 2,4,5-T FLUROXYPYR TRICLOPYR MCPB 2,4-DB
- 21. Effective against annual and prennial broad leaf weeds and sedges Absorbance by root or foliage Translocated through transpiration and photosynthetic streams. Accumulates in growing meristem Persists for 2-4 weeks Longer persistence in cold condition Decomposition in soil by microbes At low rates act as growth regulators
- 22. FIRST HERBICIDE-2,3,6-TBA(1954)=Trichloro benzoic acid ARYL CARBOXYLIC ACID BENZOIC ACID 2,3,6-TBA DICAMBA CHLORAMBEN PICOLINIC ACID CHLOPYRALID PICLORAM PTEREPTHALIC ACID CHLORTHAL- DIMETHYL
- 23. Except cholramben and chlorthal dimethyl all others having post emergence activity Usually used as a component of mixture CHLORAMBEN 3-amino,2,5-dichlorobenzoic acid
- 24. Otherwise called as Diphenoxy carboxyllic acid These substances contain a chiral centre and the r (+) enantiomer is the most active herbicidally Each of a pair of molecules that are mirror images of each other
- 25. They are sold as active isomer or recemates a racemic mixture.
- 26. Some examples are FLUOZIFOP-BUTYL HALOXYFOP-ETHOXY ETHYL QUIZALFOP-ETHYL
- 27. Readily absorbed by both roots and shoots May be apoplastic pathway may be symplastic or may be both Examples are: Trichloroacetic acid TCA Dalapon
- 28. HALOGEN GROUPS
- 29. First introduced herbicide –Simazine First discovered in 1952, introduced commercially in 1957, by Geigy Ltd. in Switzerland. SYMMETRICAL TRIAZINES ASYMMETRICAL TRIAZINES
- 30. A triazine is class of nitrogen- containing heterocycles. The parent molecules' molecular formula is C3H3N3. They exist in three isomeric forms, 1,3,5-triazines being common.
- 31. The triazines have planar six-membered benzene- like ring but with three carbons replaced by nitrogens. The three isomers of triazine are distinguished by the positions of their nitrogen atoms, and are referred to as 1,2,3-triazine, 1,2,4-triazine, and 1,3,5-triazine. Other aromatic nitrogen heterocycles are pyridines with one ring nitrogen atom, diazines with 2 nitrogen atoms in the ring and tetrazines with 4 ring nitrogen atoms.
- 32. GENERAL COMMENTS. 1. Large, very important family: Symmetrical triazine and asymmetrical triazinones will both be dealt with together in this chapter. 2. First discovered in 1952, introduced commercially in 1957, by Geigy Ltd. in Switzerland. 3. Atrazine introduction revolutionized maize production when it was introduced in the late 1950's to early 1960's. 4. Cyanazine was introduced by Shell Co. in 5. Herbicides in this family are used to control many annual broadleaf and grassy weeds.
- 33. 6. Applied in many ways: early preplant, pre emergence, pre plant incorporated and post emergence. 7. Triazine herbicides are used in maize, sorghum, sugarcane, pineapple, etc.s Metribuzin is used in soybeans, potatoes, transplanted tomatoes and other crops. 8. Atrazine is an important herbicide for quackgrass control and other perennial weeds. 9. Cyanazine does not control quackgrass but is used were persistence in the soil is a concern and for the control of fall panicum and crabgrass, weeds atrazine often does not control.
- 34. CHEMISTRY S-TRIAZINE FAMILY 1. Herbicidal properties limited to chlorine, methoxy and methylthio substitutions on carbon 2 of ring. 2. Examples of commercial s-triazines a. chlorinated s-triazines: atrazine, cyanazine, cyprozine, simazine, procyazine, propazine b. methoxy s-triazines: atraton, prometon, secbumeton, simeton c. methylthio s-triazines: ametryn, prometryn, terbutryn, simetryn, desmetryne. 3. Atrazine: 6-chloro-N-ethyl-N'-(1-methethyl)-1,3,5-triazine-2,4- diamine a. "-azine" means the that nitrogen is substituted for carbons in the 6-Carbon ring. b. "Tri-" means that 3 nitrogens occur in the ring. c. Diamino means the "-N=" moiety occurs twice in the molecule.
- 35. 4. Symmetrical refers to the nitrogens arranged N-C-N- C-N-C. 5. Asymmetrical (triazinones) refers to the nitrogens arranged C-C-N-N-C-N. 6. Generalized family structure: Chlorinated: R1 = -Cl Methoxy: R1 = -O-CH3 Methylthio: R1 = -S-CH3
- 36. SYMMETRICAL TRIAZINES • Heterocyclic nitrogen molecules with 3 N –atoms alternating with 3 carbon atoms in the central ring.There are two amino substituents at two of the ring carbon atoms • ATRAZINE,SIMAZINE,AMETRYN ASYMMETRICAL TRIAZINES • The position of N-atoms do notalternate with those of carbon atoms • METRIBUZIN,HEXAZINONE PROMETRYN,AZIPROTRYN, CYANAZINE,DESMETRYN
- 37. ATRAZINE
- 38. METRIBUZIN 3 NITROGEN ATOMS DON’T ALTERNATE WITH 3 CARBON ATOMS
- 39. -TRYN -TONE -AZINE
- 40. First introduction –Monouron (1952) Its actually urea derivatives Mainly soil activae herbicides At higher concentration they can be USED AS total killer Resists leaching Effective against grassy and blw Less toxic to man and animals Mostly microbial degradation Poor control of weeds in dry field
- 44. Introduced around 1980 Remarkable for their high potency Application rates very low Generally 5-20 gram/ha wide margin of selective
- 46. First introduced herbicide-Propham Developed during 1945 Next carbamate grp.herbicide comes after 15 years Sulphonyl carbamates and asulam were the next Largely used to control grassy weeds Some broad leaved weeds are sensitive
- 48. Thiocarbamates are a family of organosulfur compounds First member of this group –EPTC(1954) Soil applied herbicides Sufficiently volatile so required soil incorporation Those used in rice are generally used in irrigation water Generally control annual grasses and broad leaf weeds
- 49. EPTC BUTYLATE DIALLATE TRIALLATE MONILATE THIOBENCARB General structural formulae of O-organyl(1) and S-organyl (2) thiocarbamates FOR THIS SULPHUR PART THIO WORD CAME
- 50. Being volatile they need direct incorporation These are stronglyadsorbed on soil clay and organic matter highly selective forbroad leaved weeds Generally we can know its group by its suffix – Ralin Mainly used as pre-emergence herbicide Most common herbicides
- 54. ISOXABEN NAPROPAMIDE PROPAYZAMIDE DIPHENAMIDE AMIDE PART DIPHEN=TWO PHENYL GROUP ATTACHED
- 55. DIVIDED INTO 3 SUB GROUPS (A)2-CHLORO ACETAANILIDES (B)ESTERS OF N-ARYL ALANINES (C)MISCALLANEOUS ANILIDES
- 57. BENZOYL PROP-ETHYL FLAMPROP -METHYL
- 58. Diflufenican Naptalam Pentanochlor Propanil EXAMPLES OF OVERALL ANILIDES ALACHLOR PROPACHLOR METOLACHLOR PRETILACHLOR PROPACHLOR BUTACHLOR
- 59. Historic interest as they have been now mostly replaced by compounds with better selectivity and lower mamalian toxicity One of the first organic herbicides-dnoc(1933) Example….. DINOSEB DNOC
- 60. PHENOL GROUP
- 61. Compounds in this group are Nitro-diphenyl ethers They are usually applied as pre-emergence to control germinating annual weeds They mostly used in broad leaved crops like soyabean,rapeseed,and mustard,cottonetc but some are used in rice and wheat also……
- 62. BIFENOX NITROFEN OXYFLUROFEN BASIC STRUCTURE OF DIPHENYL ETHER
- 64. Nitrile is any organic compound that has a −C≡N functional group. the prefix Cyano- is used interchangeably with the term Nitrile in industrial literature. Control annual broad leaf weeds Usually mixed with ohenoxy alkanoic acid for cereals exmples DICHLORBENYL BROMOXYNIL IOXYNIL
- 66. Introduced during 1963 Mostly soil active nature Foliar activity can also occur Control germinating annual weeds BROMACIL LENACIL TERBACIL
- 68. First of the quternary ammonium compound was introduced during 1957 Post emeregence ,foliar activity with no soil activity Nonselective Used for zero tillage farming Weed control in plantations Used for preharvest desication of leaves
- 69. PARAQUAT BIPYRIDINIUM COMPOUND DIQUAT PYRAZINEDIUM COMPUND
- 71. AMITROLE BENTAZONE FLURIDONE
- 72. Most important –glyphosate as total killer Foliar applied translocated herbicide with no foliar activity Zero till herbicide Highly mobile in phloem Examples Gluphosinate ammonium Glyphosate
- 74. IMAZAMETHABENZ-METHYL IMAZAPYR IMAZAQUIN IMAZATHAPYR
- 77. CARFENTRAZONE
- 78. This herbicide has selective pre- emeregence activity against both dicot and monocot weeds Oxadiargyl
- 79. Das TK, Weed Science Basics and Applications, Jain Brothers Publication Walia US, Weed Management, Kalyani Publishers Rao VS, Principle of Weed Science, Oxford and IBH Publishing Co. Pvt. Ltd., New Delhi Gupta OP 1998. Weed Management-Principle and Practices, Agrobotanical Publishers, Bikaner agriinfo.in irri.org Weed science related book
- 80. ORGANIC CHEMISTRY ,MORRISON AND BOYD,PEARSON PUBLICATION ADVANCED ORGANIC CHEMISTRY BY S.CHAND DR.O P TONDON ORGANIC CHEMISTRY ,GRB PUBLICATION Organic chemistry book