Plant growth regulator
ethylene generator



NOMENCLATURE
Common name ethephon (ANSI, Canada); chorethephon (New Zealand)

IUPAC name 2-chloroethylphosphonic acid 

Chemical Abstracts name (2-chloroethyl)phosphonic acid 

CAS RN [16672-87-0]  EEC no. 240-718-3 

PHYSICAL CHEMISTRY
Mol. wt. 144.5  M.f. C₂H₆ClO₃P  Form Colourless solid; (tech. is a clear liquid).  M.p. 74-75 ºC  B.p. c.  265 ºC (decomp.)  V.p. <0.01 mPa (20 ºC)  K_OW logP <-2.20 (25 ºC, unstated pH)  Henry <1.55 × 10^-9 Pa m³ mol^-1 (calc.)  S.g./density 1.409.02 (20 ºC) (tech.)  Solubility In water c. 1 kg/l (23 ºC). Readily soluble in methanol, ethanol, isopropanol, acetone, diethyl ether, and other polar organic solvents. Sparingly soluble in non-polar organic solvents such as benzene and toluene. Insoluble in kerosene and diesel oil.  Stability Stable in aqueous solutions having pH <5. At higher pH, decomposition occurs with the liberation of ethylene. Sensitive to u.v. irradiation.  pKa pKa₁ 2.5, pKa₂ 7.2

APPLICATIONS
Mode of action Plant growth regulator with systemic properties. Penetrates into the plant tissues, and is decomposed to ethylene, which affects the growth processes.  Uses To promote pre-harvest ripening in apples, currants, blackberries, blueberries, cranberries, morello cherries, citrus fruit, figs, tomatoes, sugar beet and fodder beet seed crops, coffee, capsicums, etc.; to accelerate post-harvest ripening in bananas, mangoes, and citrus fruit; to facilitate harvesting by loosening of the fruit in currants, gooseberries, cherries, and apples; to increase flower bud development in young apple trees; to prevent lodging in cereals, maize, and flax; to induce flowering of Bromeliads; to stimulate lateral branching in azaleas, geraniums, and roses; to shorten the stem length in forced daffodils; to induce flowering and regulate ripening in pineapples; to accelerate boll opening in cotton; to modify sex expression in cucumbers and squash; to increase fruit setting and yield in cucumbers; to improve the sturdiness of onion seed crops; to hasten the yellowing of mature tobacco leaves; to stimulate latex flow in rubber trees, and resin flow in pine trees; to stimulate early uniform hull split in walnuts; etc.  Formulation types EC; SL.  Compatibility Incompatible with alkaline materials and with solutions containing metal ions, e.g. iron-, zinc-, copper-, and manganese-containing fungicides. 

ANALYSIS
Product analysis by measuring the ethylene produced on treatment with concentrated alkali. Residues determined by conversion to the dimethyl ester, measured by glc with NPD or FPD (Pestic. Anal. Man., Vol. II; Anal. Methods Residues Pestic., 1988, Part II; W. P. Cochrane, J. Assoc. Off. Anal. Chem., 1976, 59, 617).

MAMMALIAN TOXICOLOGY
Reviews FAO/WHO 80 (see part 2 of the Bibliography). G. Hennighausen et al., Pharmazie, 32, 181 (1977).  Oral Acute oral LD₅₀ for rats 3030 mg/kg (tech.).  Skin and eye Acute percutaneous LD₅₀ for rabbits 1560 mg/kg (tech.). Irritating to skin and eyes.  Inhalation LC₅₀ (4 h) for rats 6.26 mg/l (tech.).  NOEL (2 y) for rats 3000 ppm diet.  ADI (JMPR) 0.05 mg/kg b.w. [1997].  Toxicity class WHO (a.i.) III (Table 5); EPA (formulation) I (tech.)  EC hazard Xn; R20/21| C; R34| R52, R53: for preparations containing ≥25%, C; R20/21, R34: for 25%>concn.≥10%,C; R34: for 10%>concn.≥5%, Xi; R36/37/38

ECOTOXICOLOGY
Birds Acute oral LD₅₀ for bobwhite quail 1072 mg/kg (tech.). Dietary LC₅₀ (8 d)  for bobwhite quail >7000 ppm in diet (tech.).  Fish LC₅₀ (96 h) for carp >140, rainbow trout 720 mg/l (tech.).  Daphnia EC₅₀ (48 h) 577.4 mg/l.  Algae EC₅₀ (24-48 h) for Chlorella vulgaris 32 mg/l.  Other aquatic spp. Low toxicity.  Bees Not toxic to bees.  Worms Not toxic to earthworms.

ENVIRONMENTAL FATE
Animals In animals, ethephon is rapidly excreted intact via the urine, and as ethylene via the expired air.  Plants In plants, ethephon rapidly undergoes degradation to ethylene.  Soil/Environment Rapidly degraded in soil, and strongly adsorbed; unlikely to leach.