Bayer EX1026 (Part 1 of 2)
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`Bayer EX1026 (Part 1 of 2)
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` Bayer EX1026 (Part 1 of 2)
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`Bayer EX1026 (Part 1 of 2)
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`PREFACE
`
`This is the first of a two volume set detailing the properties, chemistry, analysis,
`environmental pollution, and biology of the herbicidal chlorinated phenoxyalkanoic
`acids and their compounds. It is strange that this is one of the first book of its kind
`for these compounds since they are the most widely used herbicides. Perhaps it is not
`too strange after all since Chemical Abstracts, Biological Abstracts, and Index Medicus
`list well over 50,000 entries, and the task of sifting and fusing this vast literature is
`(and was) gargantuan.
`This first volume details the physical and chemical properties and environmental
`impact of the herbicidal chlorinated phenoxyalkanoic acids and related compounds,
`including contaminants. This book does not claim to be exhaustive in its coverage of
`the literature. We have elected to concentrate on the decade 1967 to 1980 inclusive,
`citing other important references when we deemed it necessary. We have endeavored
`to give overviews where possible, spiced with the appropriate detail. We have also tried
`to cite many foreign language sources in the hope of making the information accessible
`to scientists in all countries, and have cited the Chemical Abstracts reference for East(cid:173)
`ern European, South American, and Asian sources.
`There is a general paucity of information on the physical properties and chemistry
`of the phenoxys, and we have tended to go into more detail on these aspects than on
`other better known facets such as pollution and analysis. However, we have also pre(cid:173)
`sented methods for analysis in the hope this first volume can be used as a methods
`manual as well as a handbook for physical and chemical properties, and for pollution
`control. With regard to phenoxy residues, it is obviously futile to tabulate all of these
`since the list is literally endless. When necessary, we have referenced the reader for the
`appropriate sources. We have included sections on the fundamental principles of such
`properties as vapor pressure, droplet impingement and retentivity, adsorption etc. to
`make this a complete reference book.
`We have also endeavored to suggest areas of profitable research potential.
`T he authors would like to thank Gail Gair for her excellent typing, as well as Mrs(cid:173)
`Lois Carpenter for her typing contributions.
`In addition., we would like to acknowledge the support of Dr. R. R. Suskind, Direc(cid:173)
`tor, Institute of Environmental Health, Kettering Laboratory, University of Cincin(cid:173)
`nati, Ohio.
`We wish to thank the Department of Biomedical Communications of the University
`of Cincinnati MedicaJ Center for their expert artwork.
`
`Shane S. Que Hee
`Ronald G. Sutherland
`January, 1981
`Cincinnati, Ohfo
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`B.
`
`Amides .. ......... ... ... ... ........ . . . .. . . .. . . ......... 41
`4.
`IR Spectra ...... . ..... .. ..................... . .. . .. . .. . ... . . .41
`1.
`Free Acids . .............. . . . ......... . . . .. . ....... . . . .. 41
`2.
`Esters ..... ... .. . ............................. ... . .. ... 41
`3.
`Salts ... . . .. . .... . .......... ... .. . ...... . ...... . . . .. . .. 42
`4.
`Amides .. •............... .. ................ . ...... . .... 42
`C 13 and Proton NMR .. . ...... . ................ . . . ... . .. . ..... .42
`C .
`D. Mass Spectrometry ................................ . .......... .43
`Free Acids . . ..... . .............. . ...................... 43
`1.
`2 .
`Esters . . .......... .. ................................... 45
`3.
`Salts ................. . ........ .. ..... .. . . . . . . .. .... . .. 47
`a .
`Alkali Salts ... . .................... . ............ .47
`Amine Salts .... . ....... . .... • ....... ... .... . . . . . .47
`b.
`Amides ............ . . . ... .. ...... . . .... . . . ....... . ..... 47
`4.
`Fluorescence and Phosphorescence .................. . .......... .48
`1.
`Free Acids .... . .... . ................................... 48
`2.
`Esters ...... . . . .......... . ...... .. ..... . .. . ..... . ...... 49
`3.
`Salts ...................... . ........................... 50
`Miscellaneous ... . . .. . .. .. . .. ....... . . .. .... . . . .. . .... . ....... 50
`F.
`Appendixes . • .. . . .. ... . ........ . .. . .. . ............................. .. ... . 51
`References . . ...... . .............................. . .... . . . .... . ... .. . . ... 101
`
`E.
`
`III.
`
`Chapter 2
`Synt hesis ... . ................ . .. . .............. . ............... . .. . ..... 107
`I.
`Free Acids . ...... .. .. . ...... . ... . .. . .. .. . .. .... . . . ... . ...... ... ... 107
`II.
`Esters ... . ............ . .. . . . .......... . .. . ....... . ................ 112
`A.
`Esteri fication of Free Acids ................................... 112
`Production of Esters by Routes Other Than Direct Esterification .... 116
`B.
`Salts ... . ... . .. . . . .. . ... . .. .. .. . . .. . . . ........................... . 116
`A. Metal Salts and Organometallic Compounds ............... . . . .. . 116
`B.
`Amine Salts ...................... . ................ . ........ . 117
`IV. Amides ..... . .. . .................. .. ... . .. . ..... . .... . .... .. .. . .. 118
`V. Miscellaneous Compounds . . .. . . ..... . .. . .................. .. .... . .. 119
`Impurities in Reaction Products .................... . ................. 121
`VI.
`VII. Radiolabeled Materials ... .. . .. ......... . ................... .. ...... 123
`VIII. Industrial Manufacture and Uses ......... . .......................... . 124
`IX. Government Regulations .. . .. . .............. . .. • .... . .... . ....... .. 126
`Appendixes .. . ...... . .. . .. .. ......... . . .... . ...... . . . .... . ... .. ....... .. 128
`References ................ . ... . . . ............................ . .......... 140
`
`Chapter 3
`Chemistry ............. . ... . . . ... . ................................. . .... 149
`I.
`Reactions of the Free Acids ... . ....... . . .. ... .... ... .. . .. .. . . . . .. ... 149
`A.
`Introduction ....... . ............ . ........................... 149
`B.
`T hermodynamics ...... . .... .. .. ...... .... ... ... . .... . .. .. ... 149
`C.
`Typical Carboxylic Acid-Type Reactions ............... . ..... . .. 149
`Salt Formation .. . . .. .. . . . . . .. . .. . ....... .. . ... ........ 149
`1.
`Condensation Reactions with Unlike Molecules ............ 151
`2.
`3.
`Influence of Ring Substitution of Self-Condensation . .. ... . . 151
`4.
`Ether Link Cleavage ... . .............. . ......... , ... .. . 153
`5.
`Substitution at the Aromatic Ring .... . ... . .. . ......... .. . 155
`6.
`Side Chain Oxidation . . ............. . ...... . ....... . ... 156
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`4
`
`The Phenoxyalkanoic Herbicides
`
`II. NOMENCLATURE AND TRADE NAMES
`
`This section lists the more common phenoxyalkanoic acids and their commercial
`.formulations and manufacturers. The following acronyms will be used:
`
`Registralion of common names and nomenclature
`ANSI
`American National Standards Jnstitute
`BSI
`British Standards lnstitution
`IUPAC
`International Union of Pure and Applied Chemistry
`Weed Science Society of America
`WSSA
`
`CIBA-GEIGY
`
`DiamondS.
`
`DOW
`DuPont
`
`Fisons
`I.C.l.
`Kanesha
`
`Manufacturers and addresses
`Ansul
`The Ansul Company, 1 Stanton St.. Marinette, Wis. 54143
`Boots
`The Boots Pure Drug Company, Station Street, Nottingham, England
`Chipman, Division of Rhodia, lnc., 120 Jersey Avenue, New Brunswick, N. J.
`Chipman
`08903
`Research and Development Department, Agricultural Division, CIBA-GEIGY
`Corp., P.O. Box 1142.2, Greensboro, N.C. 27409
`Diamond Shamrock Corporation, Commercial Development Agriculcure.l Chemi(cid:173)
`cals Division, 1100 Superior Ave., Cleveland, Ohio 44114
`Tile Dow Chemical Company, Midland, Mich. 48640
`E. I. duPont de Nemours and Company, Biochemicals DepartmenL, Wilmington,
`Del. 19898
`Fisons Pest Control, Ltd., Harston, Cambridge, England
`LC.I. Plant Protection, Lid., Femhurst, Haslemere, Surrey, England
`Kanesha Company, Ltd., Room 333, Marunouchi Building, Maunouchi, Chiyoda-
`ku, Tokyo, Japan
`Mallinckrodt Chemical Works, 360 North 2nd St., St. Louis, Mo. 63160
`May and Baker, Lld., Room 10, Dagenham, Essex 7XS, England
`E . Merck, AG, 61 Darmstadt, Frankfurter Strasse 250, Germany
`Nor-Am Ag Products, l 1710 Lake Avenue, Woodstock, Ill. 60098
`Pepro, B.P. 139, 69 Lyon, R.P. • France
`Rhone-Poulenc, Boite Postale N753.08, Paris - Se• France
`
`Mallinckrodt
`M&B
`Merck
`Nor-Am
`Pepro
`Rhone-Poul-
`enc
`Stauffer
`
`Transvaal
`Union Carbide
`Uniroyal
`
`U.S. Borax
`Velsicol
`ViI1eland
`
`Stauffer Chemical Company, Agricultural Chemical Division, Westport, Conn.
`06880
`Transvaal Inc., P.O. Box 69, Marshall Road, Jacksonville, Ark. 72076
`Union Carbide AgricuJ tural Product Company, Jnc. South Charleston, W. Va.
`Uniroyal Chemical, Agriculcural Chemical Division, Amity Road, Bethany, Conn.
`06525
`U.S. Borax Research Corporation, 3075 Wilshire Blvd., Los Angeles, Calif. 90010
`Velsicol Chemical Corporation, 341 East Ohio Street, Chicago, ru. 60611
`Vineland Chemical Company, West Wheat Road, Vineland, N.J. 08360
`
`The information presented here comes from the Herbicide Handbook of the Weed
`Science Society of America, 4th edition, 1979; Agricultural Chemicals: Book II -
`Herbicides, 1975-1976 Revision, by W. T. Thomson, and the Pesticide Manual, 2nd
`edition, British Crop Protection Council, Boreley, Worcester, England, 1971.
`
`Common name
`(BSl:WSSA)
`2,4-D
`(2,4-Dichlorophenoxy)
`acetic acid
`
`lUPAC name
`
`(2,4-Dichlorophenoxy)
`ethant>ic acid
`
`Ci-@--0-CH2-COOH
`
`Cl
`c, H. Cl,O~
`MW:221.0
`
`Origin; Amchem, 1942 (U.S.)
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`6
`
`The Phenoxyalkanoic Herbicides
`
`Amine salts
`Amine4T
`Brush - Rhap A-4T
`Veon 245
`Weedar® 2,4,5-T
`Esters
`Brush - Rhap LV-OXY-4T
`Esteron® 245
`LO-VOL4T
`2,4,5-T Low Volatile Ester 6L
`Wcedone® 2,4,5-T
`
`Mixtures wilh other herbicides
`Dinoxol (2,4-D/2,4,5-T)
`Semparol 1167 (Atrazine/MCPP/2,4.5-T)
`Tordon 155 (picloram/ 2.4,5-T esters)
`
`Manufacturer
`Diamond S.
`Transvaal
`Dow
`Union Carbide
`
`Transvaal
`Dow
`Diamond S.
`Chipman
`Union Carbide
`
`Union Carbide
`CIBA-GEIGY
`Dow
`
`Other names
`Dacamine 4T, Envert-T, Phortox, Reddon, Tippon, Tribulon, Trinoxul, Veon
`
`Common name
`(BSI, WSSA)
`MCPA,MCP
`(2-Methyl-4-chlorophenoxy)
`acetic acid
`
`IUPAC nam e
`
`(2-Methyl-4-chlorophenoxy)
`ethanoic acid
`
`MW:200,6
`
`Origin: Plant Protection Ltd .• England, 1945
`
`Amine salts
`Dow MCP Amine Weed Killer
`'Rhomene
`
`Esters
`Chiptox
`Rhonox
`
`Sodium salt
`WeedarSodium MCPA
`
`Mixtures with other herbicides
`Aniten (fluorenol-n-butyl es1er/ MCPA)
`Banlene Plus (Dicamba/mecoprop/MCPA)
`Bencornox (Dicamba/MCPA)
`Brominal, Brominal Industrial, Brorninal M (Canada) (bromoxynil/MCPA)
`Brominal Plus (bromoxynil/MCPA)
`Bronate (bromoxynil/ MCPA)
`Buctril F (bromoxynil/MCP A)
`Cam bilene (Dicamba/TBA/ mecoprop/ M CPA)
`Fisons 18-15 (TBA/ MCPA)
`Legumex-DB (2.4-DB/ MC:PA)
`Ley-Cornox (Benazolin/ 2,4-0B/ MCPA)
`Lcy-Comox BN (benazolln/ MCPB/MCP A)
`Mondak (dicamba/ MCPA)
`New Legumex (MCPB/ MCPA)
`Rawl (dicamba/ mecoprop/MCPA)
`Tri-Cornox (benazolin/dicamba/ MCPA)
`Tri-Cornox Special (benazolin/ dicarnba/2,4-0P/ MCPA)
`
`Manufacturer
`Dow
`Chipman
`
`Chipman
`Chipman
`
`Union Carbide
`
`E. Merck A.G.
`Fisons
`Boots
`Union Carbide
`Union Carbide
`Chipman
`Chipman
`Fisons
`Fisons
`Fisons
`Boots
`Boots
`Vel.sicol
`Fisons
`Fisons
`Boots
`Boots
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`10
`
`The Phenoxyalkanoic Herbicides
`
`As sole active ingredient
`Ku ron® (low-volatile esters)
`Weedone® 2,4,5-TP (low-volatile esters)
`
`Other names
`2.4.5-TP, Fenormone, Oarlon, Kurosal, Propon
`
`Manufacturer
`Dow
`Union Carbide
`
`III. THE STRUCTURE OF HALOPHENOXY ALKANOIC ACID
`COMPOUNDS
`
`A. Free Acids
`Recent years have seen the active interest of at least one X-ray crystallographic group
`in the structure of various phenoxyacetic acids. 3H•.•• The bond lengths and angles as
`well as the dimensions of the crystallographic unit cells are presented in Tables I , 2.
`and 3, respectively. Noting that o-chlorophenoxyacetic acid (2-CPA) and 2,4,6-trich(cid:173)
`loropbenoxyacetic acid (2,4,6-T) are not auxins, the following conclusions can be
`made:
`
`1.
`
`2.
`
`The free acids all form dimers held together by van der Waals' interactions by
`H-bonds of approximately the same length, approximately 268' pm, apart from
`the 2-CP A (approximately 245 pm).
`There are few clear-cut differences in the bond lengths be.tween corresponding
`atoms of nonherbicidal and herbicidal members (see Table 1). The average length
`for the c.-c6 bond in herbicidal members is approximately 160.1 pm, compared
`with 136.0 pm with that for nonauxins. However, the latter figure includes the
`very_ low 130.2-pm value for 2-CPA, and the length for 2,4,5-T and 2,4,6-T is
`the same. The bond lengths of C6-H• do show variations in that the bond for
`Silvex (100 pm) and 2,5-0 (97 pm) are much shorter than for 2,4-D and 2,4,6-T.
`There is one clear-cut difference. The Cs-C• bond length does appear to be
`shorter for nonauxins (<150 pm) than for auxins {151 to 152 pm).
`The same nondiscriminating differences between herbicidal and nonherbicidaJ
`members can be discerned in the corresponding bond angles (see Table 2). The
`steric hindrance in 2,4,6-T is clearly evident, and the aromatic rings of 2,4,5-T
`and MCP A are much flatter than the others.
`Consideration of the crystallographic systems for each does reveal some differ(cid:173)
`ences (see Table 3). All but the 4-CPA acid fall into the triclinic system, Space
`Group Pl, while 2-CPA acid belongs to the monoclinic system. The angle be(cid:173)
`tween the normals to the planes of the benzene ring and the carboxy groups varies
`widely. The angles for 2,4,6-T and 2,4,5-T are much lower than tb.e rest. How(cid:173)
`ever, even though the dihedral angles of 2,4-D, 2,5-D, and Silvex are similar,
`that for 2,4,5-T is 4 to 15°; this means the 2,4,5-T dimer has all atoms, except
`a behavior similar to that
`the methylene group lying approximately in a plane -
`shown by most other substituted aromatic carboxylic acids. In addition, the ben(cid:173)
`zene rings of 2,4-D, 2,5 -D, and Sil vex do not lie on top of one another.
`5. The distance between the o- of the carboxyl group and the fractional positive
`charge induced on a specific ring C is 420, 429, 417, and 428 pm for 2,4-D, 2,4,5-
`T, 2,5-D, and 2,4,6-T, respectively, compared to 412 pm for IAA.
`For comparison with most other carboxylic acids:••
`
`3.
`
`4.
`
`6.
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`12
`
`The Phenoxyalkanoic Herbicides
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`Table2
`BOND ANGLES IN DEGREES BETWEEN THE DESIGNATED ATOMS ABOVE
`TABLE l FOR PHENOXYALKANOIC ACIDS. THE DIHEDRAL L REFERS TO
`THE ANGLE BETWEEN THE NORMALS TO THE BENZENE RING AND THE
`CARBOXYL GROUP
`
`Angles
`
`2,4-D'"·"
`
`2,4,5-T"
`
`2,s-0• 1
`
`Silvex"
`
`2-CPA"
`
`2,4,6-T"
`
`Bo nd angles ( 0
`
`)
`
`c.-c,-c,
`c,-c,-c.
`c,-c.-c.
`c,-c.-c.
`c.-c.-c.
`c.-c,-c,
`C,-0 .. -H,.
`o,.-c.-o,,
`A-C,-C,
`A-C,-C,
`B-C,-C,
`B-c.-c.
`c-c.-c.
`c- c.-c.
`o-c.-c,
`o-c.-c.
`c,-c,-o,
`c.- c,-o,
`c,-o,-c.
`o,-c.- c,
`c.-c.-o,.
`c.-c.-o,,
`
`l 19. l
`122.2
`l 17.3
`122.7
`l 19.1
`1.19.6
`111 .5
`123. I
`118.9
`118.8
`117.6
`I 19.6
`
`l 16.2
`124.7
`118.8
`I 11.1
`123.2
`112.2
`
`119.8
`121.1
`l 19.5
`119.5
`121.9
`l l 8.1
`114.8
`124.4
`l 19.9
`119.l
`1J9.0
`121.6
`121.4
`116.6
`
`I 16.l
`124.0
`117.0
`106.7
`122.9
`112.7
`
`117.1
`121.9
`121.7
`117.0
`122.4
`119.9
`
`123.8
`I 17.l
`121.0
`
`118.8
`118.7
`
`l 17.8
`125. l
`J 18.9
`111.9
`124. l
`112.0
`
`118.8
`120.0
`119.8
`120.9
`ltO.O
`118.8
`llJ.9
`124.1
`119.5
`119. 7
`118. 7
`121.5
`120.9
`118.8
`
`119.7
`125.5
`I 18.3
`110.4
`123.9
`111. 9
`
`121.0
`122.6
`113.J
`126.2
`119.9
`116.7
`
`125.3
`122.2
`115.2
`
`116.9
`122.1
`115.5
`107.0
`121.4
`l 13.2
`
`115.9
`126.2
`139.4
`139.S
`136.J
`138.5
`
`136.5
`140.2
`137.8
`136.5
`137.8
`107.0
`115.9
`126.2
`
`In Silvex E
`
`c,o
`H,C.,.,.H
`
`a)~~
`
`c7
`
`a
`b
`Dihedral
`angle
`
`85.23
`
`4.15
`
`81-2
`
`105.0
`109.4
`77.8
`
`6.6
`
`32.03
`
`O·-H-0
`C-R
`R-C 0\
`"o-H--0~
`
`1c
`
`"
`
`Cl'
`
`122°
`
`R-C
`
`C=O
`
`146-154 pm
`
`112-+ 126 pm
`
`C-0
`
`126 ..... 13 7 pm
`
`0-H
`
`261-+ 264 pm
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`16
`
`The Phenoxyalkanofc Herbicides
`
`J. Sales
`The .mps for some amine salts of 2,4-D, of 2,4,5-T, and miscellaneous salts are
`presented in Appendixes 3, 4, and 6, respectively.
`
`a. Alkali and Metal Salts
`The sodium and potassium salts have high mps since they are ionic. The sodium salt
`of 2,4,5-T melts at 268°C with very little decomposition°1 and exists in at least two
`crystalline forms; it always recrystallizes from the melt into characteristic spberulites
`which are indefinitely stable at room temperature, but transform to the fibrous needles
`of the thermodynamically stable form when heated above 200°C. The potassium salt
`of 2,4,5-T, however, decomposes on heating above 300°C and is almost insoluble in
`molten 2,4,5-T, whereas lbe sodium salt is much more soluble. The potassium salt
`exhibits medium birefringence, but no similar studies have been reported for 2,4-D
`salts, even though the mp of the sodium salt is only 217°C. The 2,4-D potassium salt
`melts above 300°C The mp behavior may seem anomalous, since the mp order is
`usually Li> Na>K>Rb>Cs, but the phenoxy acid salts appear to act like typical fatty
`acid salts, where potassium salts have higher mps and water solubilities than the cor(cid:173)
`responding sodium salts. 73
`DTA of various (2,4,5-T)1 ·M·nH20 systems, where M = Cu, Zu,Cd, Co, Ni, and
`Mn and n = 2 or 4, and of (2,4,5-Th · Fe have been reported. 10 Most of these salts
`lost water of crystallization at "-'40°C, and the thermal stability of the anhydrous salts
`ranged from 20°C for Cd to 130°C for the Zn salt. All salts formed stable oxides at
`high temperatures, excepting CdO, which was unstable:
`
`b. Amine Salts
`The phenoxyalkanoic acids are weak acids and the alkylamines are weak bases; their
`salts are weakly ionic and so have low mps (see Appendixes 3 and 4, respectively).
`Generally, the salt is converted to its corresponding amide between 150 to 200°C, but
`the latter's formation can be detected well beneath the mp of the salt. 6~ The mp Litera(cid:173)
`ture is difficult to evaluate, since the temperature used in salt synthesis is often not
`given; also, there are many stoicbiometries that are possible other than 1: 1 as well as
`polymorphic forms.
`DSC of several 1: 1 amine salts of 2,4-D was investigated by Que Hee and Suther(cid:173)
`land. 65 The aH, values for the dimethyl, methyl, .n-butyl, n:-dodecyl, and n-tetradecyl
`salts were 11.20, 6.53, 15.0, 31.2, and 39.2 kcal/mo!, respectively. There is a linear
`relationship between llH1 and molecular weight obeying aH, = 0.1445 mol wt -27.4.
`At a heating rate of 10°C/ min and for a nitrogen furnace atmosphere, 72 the methylam(cid:173)
`ine salt sbowed endotbermal transitions at 103 to 117, 139 to 157, and 165 to 182°C,
`after which decomposition set in. The dimethylamine salt had one peak from 64 to
`74°C, a glass transition 134 to 136°C, and decomposed above 157°C. The a-butylam(cid:173)
`ioe salt had transitions from 98 to 111 and 162 to 195°C, with subsequent decomposi(cid:173)
`tion. The a-tetradecyl salt produced peaks between 57 to 64.5 and 163 to 202°C, with
`subsequent decomposition. The higher transitions correspond to the elimination of
`water in the formation of the corresponding amide, which is decomposed65 beyond
`200°c.
`
`4. Amides
`The melting points of various 2,4-D amides, 2,4-D amino acid amides, and miscel(cid:173)
`laneous amides are in Appendixes 3, 5, and 6, respectively. No OTA or DSC studies
`have been reported.
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`18
`
`The Phenoxya/kanoic Herbicides
`
`) . Phillips'~
`high dilutions. Often mixed solvents were utilized (van Oberbeek et al. ' 5
`showed that the pK. of 2,4-D at I l'\,0.001 was 2.86 at 20°C, but was 4. IO in l: I
`ethanol/water (I 'v 0.005). The major criticism of the spectroscopic method of Phillips
`is that the molar absorptivity vs. wavelength curve has a very steep slope in the far
`UV rc::gioo, even though the:: pK value:: cited is the average of pK.s done at four wave(cid:173)
`lengths. However, the discrepancy between the value of Nelson and Faust77 and that
`of Phillips is not great. To check whether the solubility and pK. data are compatible,
`the maximum possible pK. value can be calculated from the solubility of 2,4-D (2.36
`>< 10-, Mat 25°C). 1• Since this represents the maximum (H•), the lowest pK. at 25°C
`should be around 2.63. The observed pK. is 2.73 (K. = 1.86 x 10-a), and this implies
`79o/o of the acid is dissociated, and 21 % is solvated without dissociation at saturation.
`It is also interesting that the degree of chlorination of the ring does not affect the
`pK. in a marked way, even though 4-CPA and 2-CPA have larger pK.s than 2,4-D, as
`does 2,4,5-T.1
`• Even the pK. of MCPA is not very different from that of 4-CPA, but
`MCPB, however, does have a much larger pK. than MCPA.
`Phillips' spectroscopic work is highly suggestive of the following relationships: '"
`
`I.
`
`2.
`
`3.
`
`4.
`
`The negative inductive effect of the phenoxy group (pK. 'v3 .12) I = 0.00 l re(cid:173)
`sponsible for the acid strengthenjng relative to acetic acid (pK. l'\,3. 74) is of the
`order of the iodo group and much greater than that of either the phenyl or hy(cid:173)
`droxyl groups.
`Chloro substitution in the phenyl ring generally enhances acid strength; the mag(cid:173)
`nitude depends on the number of chlorines, the distance of separation between
`the aromatic ring and the ionizing group, and solvent effects. In the phenoxy(cid:173)
`acetic acids, the effects of chloro substitution are swamped by solvent effects,
`e.g., pK. values in water vs. those in I :1 water to ethanol. The acid weakening
`effect of ethanol is due to the fact that open-chain H - bonded dimers are favored
`
`(B--H-0--H-O)
`I
`I
`R'
`R'
`
`in alcohol, whereas water allows other arrangements thus promoting greater dis(cid:173)
`sociation. Also, ethanol can be regarded as preferring to sol'vate the undissociated
`molecule rather than the dissociated form.
`The insertion of methylene groups between the phenoxy and ionizing group in(cid:173)
`creases the pK. as expected from inductive effects. Thus, /3-(2,4-DP) is 1.5 pK
`units weaker than the corresponding acetic or a,-substituted propionic acid. The
`insertion of another methylene group weakens it by a further 0.4 pK unit, so that
`the pK. is the same as that for butyric acid, i.e., the phenoxy group does not
`affect the ionization at all and its effect is almost eliminated by the insertion of
`two methylene groups.
`2,6-Disubstituted derivatives, usually inactive as auxins, are much weaker acids
`than their parent acids, and this is attributable to steric hindrance which prevents
`the phenoxy group from interacting with the carboxyl group. interestingly, al(cid:173)
`though 2,6-dichloro and 2,4,6-txichlorophenoxyacetic acids are not auxins, 2-flu(cid:173)
`oro-4,6-dichloro- and 2,4-dichloro(6-fluoro)-pbenoxyacetic acids are, and these
`also show greater acidity than their sterically hindered analogues.
`
`2. Esters
`These compounds are gener.ally immiscible. or insoluble in water, but gradual hydro(cid:173)
`lysis does occur (see Chapter 3).
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`21
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`aqueous pH below the pK. of of the free acid was necessary to extract the latter. Table
`5 shows the expenrnental conditions and p values obtained for some chlorophenoxy
`alkanoic acids atnd esters. These p values agree with those calculated from other liter(cid:173)
`ature sources (see Reference 95). It can be seen that the more polar the herbicide the
`smaller is its p •value and that different kinds of water make no significant difference
`to the observed! p values. However, suspended particulates do affect recovery, but
`more so at pH 7 to 8 than at pH 2 (see Section IV.F). Water should be filtered before
`any solventextr.action is attempted .
`The best solv,ents for extraction of the free acids are ethyl acetate and diethyl ether.
`Hexane is very poor. Diethyl ether and ethyl acetate are best for 2,4-D compounds,
`and benzene is ,optimal for 2,4,5-T. Benzene is a poor solvent for 2,4-D and MCPA.
`Thus, to separate a mixture of esters and free phenoxyacetic acids, one would use rr
`hexane to extract the esters, and then use ether or ethyl acetate to isolate the free acid.
`This procedure would not work for the propionjc or butyric acids, although pH ad(cid:173)
`justment would most likely solve this problem. A two-step procedure with 200 and 50
`ml of ethyl acetate was demonstrated to extract 99% of 2,4-D from 1 £ of aqueous
`solution adjusted before extraction to pH 2 with 0.2 Mphosphate buffer.
`Appendix l 1 compares the literature of the recovery (F.) of various herbicidal com~
`pounds from aqueous solution. Again, consistent recoveries of at least 99% are ob(cid:173)
`tained with diethyl ether, confirming p-value predictions, even if the pH was adjusted
`by HCl or H,SO. instead of phosphate buffer.
`
`E. Vapor Pressmes and Volatility
`1. Introduction
`A compound with a low vapor pressure (P) is often said to be ''nonvolatile".
`Pis a thermodynamic property, and no time scale can be inferred, but volatilization
`is a kinetic pro(~ess. Thus, although kinetic steady states are common. thermodynamic
`equilibrium is hardly ever attained. The atmosphere acts as an infinite reservoir, with
`the wind as a dlispersing agent. The amount of material volatilized is then a function
`of wind speed, ,contact volume, exposed surface area, temperature, type of compound,
`and variety of flow, as well as vapor pressure. There are several distinct available
`approaches which are used to predict volatilization rates.
`
`a. Ideal Gas Mc:tbod
`Since most phenoxy herbicides have a P < 10-2 mmHg, the vapors can be described
`as ideal gases olf volume, V, mass, m, and molecular weight, M, at a given temperature,
`T. Thus,
`
`M;
`mi
`,oi = 7 = Pi RT
`
`(7)
`
`where Q1 is the vapor density of component i, and p1 is its partial pressure; R is the gas
`constant in appiropriate units.
`When p, = P,, P, is the maximum mass of the compound per unit volume able to
`be contained in the vapor phase at a given temperature under ideal conditions.
`lf the air is s:ampled at Z 1/min and if the vapor .is sampled for t minute~, the mass
`of the compounid i that can be collected from a saturated atmosphere is
`
`z
`~m- = IP·Z = t p. M- -
`I RT
`I
`I
`I
`
`(8)
`
`where 2m, is the total mass collected.
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`Schuylkill River water
`River water (filtered)
`Wissahickon Creek water (high organic load)
`
`0.925
`0.91 I
`0 .920
`
`0.007
`0.007
`
`13
`2
`
`0.996
`0.997
`0.998
`
`0.0005
`0.0010
`
`II
`3
`1
`
`Note: All values are the average of at least three determinations except those in parentheses, with a water:solvent ratio of
`10: I.
`
`• Amchem Products, Inc., analytical grade. All solids were recrystallized before use.
`• After Nelson and Faust."
`• All compounds are soluble at these concentrations.
`• All UV analyses on the water phase after solvent evaporation step.
`• Water:solvent ratio changed to 5: l.
`Water:solvent ratio changed to l: 1.
`
`Reprinted with permission from Suffet, l. H., J. Agric. Food Chem., 21,591, 1973. Copyright by the American Chemical
`Society.
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`32
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`The Phenoxyalkanoic Herbicides
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`2 Mo
`pd
`ln - = ' - -
`pl' RTdr
`
`(53)
`
`where P • is the vapor pressure of the droplet, PP is the vapor pressure from a plane
`surface, r is the droplet radius, dis the surface tension, and dis the fluid density.
`
`2. Data for Chlorinated Phenoxyalkanoic Acid Herbicides
`a.Acids
`Very little work has been done on the volatility or vapor pressures of the free acids.
`mainly because they are hardJy ever used in spraying. However. it has been found that
`2,4-D has a p of 1.05 X 10· 2 mmHg at 25°C and boils at 160°C at 0.4 mmHg. 10
`'
`
`b. Esters
`It is instructive to compare the calcuJated values of P at 25°C for various esters
`calculated from the equations of Jensen and Schall'°0 and those of Flint et al., 101 who
`both utilized the same GC technique (see Chapter 1, Section TV. E.l.c) to find Ps of
`2.4-D esters at high temperatures, as well as the same internal reference (see Appendix
`12). It can be seen that the values for the 2-ethylhexyl, 2-octyl, and the 2-propyl esters
`of 2,4-D differ by more than an order of magnitude, witn Jensen and SchalJ's values
`being higher. Some of tne assumptions may be responsible for the contradictions (see
`Chapter I, Section E.1.c). Consjderation of the data of Jensen and Schal1100 leads to
`the conclusion that, as expected, the corresponding esters of 2,4,5-T have smaller Ps
`than those of 2,4-D, and branched isomers of the same acid have a higher vapor pres(cid:173)
`sure than the normal esters. The relevant calculated values are also compared with Ps
`found experimentally (see Appendix 13). The latter show that there are still many con(cid:173)
`tradictions. lt can be concluded, however, that the calculated values of Flint et al. ,oi
`are too low. The values for the 2,4-D n-butyl ester at 25°C range from 10-s to 4.0 x
`J0-<3 mm Hg, with the correct value probably between 3.90 x 10-• and 3.90 x 10-a mmHg.
`The P of the methyl ester of 2,4-D at 25°C varies from 3.3 x 10-• to 1.27 x 10·1 mmHg.
`The correct value is probably between 2 x 10-• to I. 3 x 10·2 mmHg. The values for the
`i-propyl ester also range from 4 x 10-s to 1.05 x 10-2 mmHg at 25°C, with the true
`value probably between 1.2 x 10-3 to 10· 2 mmHg.
`In general, the transpiration technique91 produces higher P values than the other
`methods, although the method used by Que Hee et al. 9
`6 and by Grover98
`99 does not,
`•
`4-9
`since the contact volume was always less than the nominal volume of air flowing over
`the surface deposit. Appendix 13 aJso presents the available fi.H. data. As expected the
`values for the liquid esters are lower than ~H, for solid 2,4-D (see Appendix 1). The
`various equations developed through Section E. l can then be utilized to find U values.
`Clearly, reliable P values have to be known before this is possible.
`The volatility of the esters has also been measured directly on a number of surfaces.
`Pyrex is less adsorptive than is the cuticle of a plant, so that volatilization from glass
`surfaces should be a good model system for the worst field conditions at comparable
`temperature, surface/mass ratios (Q) and flow rates. A major difficulty with many of
`these kinetic studies is that the crucial parameters were not often specified. Thus, Que
`Hee and Sutherland9" ·95 showed that only under the same conditions of Q., flow rate,
`and temperature did the volatilities of the 2,4-D esters follow the vapor pressures, i.e.,
`as chain length decreased so does volatility. Grover,96 using technical grade butyl esters
`of 2,4-D in a transpiration method, found that 238 ng/cm1/hr of butyl esters volatil(cid:173)
`ized at 14 £/hr at 30°C, whereas 447 ng/ cm2 /hr was the rate at 57.6 11hr. Que Hee
`and Sutherland found an evaporation rate of 4.45 t,tg/cm2/hr at 38°C for n-butyl ester
`at 56.4-Ubr flow rate and a Q" of 3.28 cm2 /g. If it is remembered that each 10°C rise
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`34
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`The Phenoxyalkanoic Herbicides
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`as well as the free acid, did not affect bean and tomato plants, and volatilities of many
`esters were reduced compared with the pure compounds when they were dissolved in
`diesel, corn, 1)r cottonseed oil. 111 The latter effect is explainable by consideration of
`Raoult's Law which predicts a partial pressure above a homogeneous solution of con(cid:173)
`stituents. Not only plants are affected by herbicides in the vapor phase. The germina(cid:173)
`tion of air-dried seeds was inhibited by "volatile" esters of 2,4-D and 2,4,5-T (C, to
`C 3 esters inhibiting more than C, to C$ esters), when exposed to vapors for 30 to 60
`days. 118 lt was found that the vapor did not permeate the seed coats, bul entered during
`inhibition of water early in the germination process. Cotton plants were also sensitive,
`as well as bean and tomato. 120 The designation "high volatile" and "low volatile" was
`122 and Zimmerman et al,,." 6 ,u using the
`first formulalted by Baskin and Walker11
`• ·
`tomato stem o:urvature test. rt was shown that the C