Chapter 6
Formulation, Structure, and Properties
Physical
Factors Affecting the Rate of Penetration of Yellow Foxtail Cuticle by a Series of Aryloxyphenoxypropionate Herbicides Arlene Hamburg and Philip J. McCall
Downloaded by UNIV LAVAL on July 12, 2016 | http://pubs.acs.org Publication Date: June 24, 1988 | doi: 10.1021/bk-1988-0371.ch006
Agricultural Chemistry R&D Laboratories, Dow Chemical Company, 9001 Building, Midland, MI 48640 The c u t i c u l a r penetration behavior i n yellow f o x t a i l as measured by a penetration rate constant ( k p e n ) f o r s i x aryloxyphenoxypropionates was found to be dependent primarily on the s t r u c t u r a l class (pyridinyloxy, quinoxalinyloxy and phenoxy) and secondarily on formulation. Correlations of kpen with the physical properties melting point, log P, vapor pressure and water s o l u b i l i t y were examined and determined to be unreliable because separation of the penetration behavior of the s i x compounds into s t r u c t u r a l classes reduced the number of compounds available f o r such c o r r e l a t i o n s . The rate constant, kpen, was extracted by mathematically modeling the d i s t r i b u t i o n of the 14C-aryloxyphenoxypropionate herbicides in the relevant environmental and plant compartments over a 24- to 48-hour period. For each herbicide, the two formulations used were 0.1% Ortho X-77 in 50% acetone/water with (+COC) and without (-COC) 0.3% Agri-dex crop oil concentrate.
The transport of a f o l i a r l y applied herbicide through the plant c u t i c l e i s the f i r s t process a f f e c t i n g the o v e r a l l e f f i c a c y of the chemical. In t h i s study the factors influencing f o l i a r absorption of a series of s i m i l a r h e r b i c i d a l compounds i n simple formulations w i l l be examined. This work w i l l provide i n s i g h t into the relationships among chemical, plant c u t i c l e and adjuvant that control c u t i c u l a r penetration. This information w i l l a i d more sophisticated formulation e f f o r t s and herbicide discovery research. The s u i t a b i l i t y of the aryloxyphenoxypropionate family of herbicides f o r t h i s study l i e s i n 1) the d i v e r s i t y of structures (three classes) within t h i s family ( s i x compounds) showing h e r b i c i d a l a c t i v i t y (Table I) and 2) the importance of t h i s new group of chemicals i n the post-emergent grass control market. The objective of t h i s work was to examine how structure, physical properties and/or the nature of the adjuvant a f f e c t c u t i c u l a r penetration i n yellow f o x t a i l as measured by a c u t i c u l a r 0097-6156/88/0371-0056$06.25/0 ° 1988 American Chemical Society
Cross and Scher; Pesticide Formulations ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
6. HAMBURG AND McCALL Table I.
Structures of the Aryloxyphenoxypropionate Herbicides
COMPOUND Pvridinvloxy: Haloxyfop Haloxyfop-ME Haloxyfop-EE Fluazifop-BE Phenoxv: Diclofop-ME
a
Downloaded by UNIV LAVAL on July 12, 2016 | http://pubs.acs.org Publication Date: June 24, 1988 | doi: 10.1021/bk-1988-0371.ch006
Rate of Penetration of Yellow Foxtail Cuticle
X
Y
Z
R
CF3 CF3
N N N N
H
CF3
CI CI CI H
CI
CI
CH
CFs
CH3 CH2CH2OCH2CH3 CH2CH2CH2CH3
CH3
Quizalofop-ME
OCH
See Legend of Symbols f o r the abbreviations used.
penetration rate constant, k p e n . The a v a i l a b l e aryloxyphenoxypropionates include pyridinyloxy, quinoxalinyloxy and phenoxy. The physical properties of the aryloxyphenoxypropionates which p o t e n t i a l l y could correlate with k p e n are water s o l u b i l i t y , vapor pressure, melting point and log P, which i s a measure of the hydrophobicity of the chemical. The range i n these physical parameters f o r the aryloxyphenoxypropionate s e r i e s i s s u f f i c i e n t (Table II) to detect any correlations i f they exist. In these experiments the amount of herbicide d i s t r i b u t e d on the plant surface, beneath the plant c u t i c l e , and i n the a i r was monitored at 7-9 time points over a 24- to 48-hour period. The value of k p e n was then extracted from the compound-distributionversus-time data using a reasonable k i n e t i c model and mathematical modeling. Extracting a parameter d i r e c t l y r e l a t e d to the time course of penetration, i.e. k p e n , rather than using a penetration value determined at one time point gives a more r e a l i s t i c view of penetration rates. The one-time-point method levels the penetration value of fast penetrators to the same number which i s r e l a t e d to the experimental time period chosen rather than to any physical or chemical property of the system. If strong c o r r e l a t i o n s exist between k p e n and structure or physical properties, etc. then they should be derivable from the s i x compounds used i n t h i s study.
Cross and Scher; Pesticide Formulations ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
57
58
PESTICIDE FORMULATIONS: INNOVATIONS AND DEVELOPMENTS Table I I . Physical Constants f o r the Aryloxyphenoxypropionate Herbicides
COMPOUND
Log P°
0
Haloxyfop Haloxyfop-ME Haloxyfop-EE Fluazifop-BE* Quizalofop-ME Diclofop-ME* c
d
Downloaded by UNIV LAVAL on July 12, 2016 | http://pubs.acs.org Publication Date: June 24, 1988 | doi: 10.1021/bk-1988-0371.ch006
Range:
h
Water Solubility, ppm
4.316 4.642 5.149 5.761 4.529 5.521
43.4 9.3
1.4
43
v
0.3 3 1
Vapor Pressure, mm Hg
Melting Point, °C
6.9E-7
106 56 57 5 92 40
>100
101
AIR PEN
