Substituted 2,3-Dihydro-,4-Oxathiin Plant Growth Stunting Agents

Powdered 2-phenylacetophenone (1021 g., mp. 55.degree.-57.degree.) was charged into a three-necked flask equipped with a strong mechanical stirrer, a reflux condenser and a dropping funnel. Sulfuryl chloride (430 ml.) was added in a continuous stream, over 10 minutes, with vigorous stirring. The reaction mixture was kept molten by heating on a steam bath for 1/2 hour. Benzene (2.5 l.) was added to the reaction mixture and a portion (300 ml.) of the solvent was removed under reduced pressure to remove excess sulfuryl chloride. The reactor was cooled to 20.degree. in an ice bath and a stream of ammonia was bubbled into the solution. After 15 minutes, 2-mercaptoethanol (385 ml.) was added during 1/2 hour (the reaction mixture temperature remained below 50.degree.). The ammonia sparge was continued for four additional hours and the reaction mixture was left at room temperature overnight. A cold solution of hydrochloric acid (1500 ml.). prepared by pouring 37% acid (600 ml.) over crushed ice (900 ml.), was poured into the reactor with stirring. After 15 minutes, stirring was stopped and the reaction mixture separated into two layers. The benzene layer was separated, p-toluenesulfonic acid (20 g.) was added and the reaction mixture was heated under reflux for 4 hours with azeotropic water removal. After cooling, the benzene solution was successively washed with 1.0 N sodium hydroxide solution (1000 ml.), water (500 ml.), filtered, and evaporated under reduced pressure. The warm syrup was then poured slowly into isopropyl alcohol (2.5 l.) with vigorous stirring, left overnight, the solid filtered off, and dried. The light tan coloured product (1062 g., 80% yield) melted at 61.degree.-63.degree..

Anal. Calc. for C.sub.16 H.sub.14 OS: C, 75.57; H, 5.55. Found: C, 75.58; H, 5.74.

A mixture of 1-mercapto-2-propanol (19.2 g.) and triethylamine (10.1 g.) in benzene (25 ml.) was added dropwise to a stirred, cooled (20.degree.), solution of 2-chloro-2-phenylacetophenone (23.0 g.) in benzene (200 ml.). The reaction mixture was left at room temperature overnight, washed with water (200 ml.), then with aqueous 5% hydrochloric acid (100 ml.). p-Toluenesulfonic acid (1.0 g.) was added to the benzene solution and the reaction was refluxed for 3 hours with azeotropic water removal. After cooling, the benzene solution was successively washed with 1.0 N sodium hydroxide solution (100 ml.), water (100 ml.) and the benzene removed under reduced pressure. The residue was crystallized from absolute ethanol to give light tan-colored crystals (16 g., 60% yield) melting at 68.degree.-69.degree..

Anal. Calc. for C.sub.17 H.sub.16 OS: C, 76.10; H, 6.01. Found: C, 76.14, H, 6.05.

To a stirred suspension of 2,3-dihydro-5,6-diphenyl-1,4-oxathiin (63.5 g., 0.25 mole) in glacial acetic acid (200 ml.) was added dropwise 30% hydrogen peroxide (30 ml., 0.26 mole). During the addition the temperature of the reaction mixture was maintained below 25.degree. by cooling in an ice bath. After standing for 12 hours at room temperature, the reaction mixture was filtered and the filtrate was poured, with stirring, into water (1,400 ml.). The crystalline precipitate was filtered, washed with water, and recrystallized from methanol to give colorless crystals (59.6 g., 88% yield) melting at 157.degree.-159.degree. with decomposition.

Anal. Calc. for C.sub.16 H.sub.14 O.sub.2 S: C, 71.10; H, 5.22. Found: C, 71.22; H, 5.11.

To a stirred mixture of 2,3-dihydro-5,6-diphenyl-1,4-oxathiin (12.7 g., 0.05 mole), toluene (25 ml.) and formic acid (4 ml.) was added dropwise 30% hydrogen peroxide (12.5 ml., 0.1 mole). The mixture was refluxed on a steam bath for two hours, cooled, and the solid product was filtered off. The product was recrystallized from absolute ethanol to give colorless crystals (12.5 g., 87%) melting at 178.degree.-179.degree..

Anal. Calc. for C.sub.16 H.sub.14 O.sub.3 S: C, 67.12; H, 4.93. Found: C, 66.91; H, 4.93.

Using the procedures of the previous examples and appropriate starting materials, the substituted 1,4-oxathiins shown in TABLE I are prepared. TABLE I gives the systematic name for each product and identifies the method used, and also gives melting point data. In subsequent examples the compounds are identified by the example numbers given in TABLE I.

To illustrate effectiveness of the described oxathiins as preemergent herbicides, 600 mg chemical is dissolved in 10 ml organic solvent (e.g., acetone) to which 30 mg conventional emulsifying agent (e.g., isooctylpolyethoxyethanol, "Triton X 100" trademark) is added. The solution is diluted to 100 ml with distilled water. Twenty ml of this 6000 ppm solution is diluted to 250 ppm with distilled water. The chemical is applied at the rate of 10 lbs/A (pounds per acre) by drenching 46 ml of the 250 ppm solution on the surface of soil in 41/2 inch plastic pots which had been planted with the following weeds: rough pigweed (Amaranthus retroflexus L.), purslane (Portulaca oleracea L.), tall morningglory (Ipomea purpurea L. Roth), crabgrass (Digitaria ischaemum (Schreb.) Muhl.), Barnyardgrass (Echinochloa crusgalli (L) Beauv.) and giant foxtail (Setaria faberi Herrm.). The percent control of the weeds compared to untreated checks is determined 2 weeks after treatment. TABLE II shows the results with the preemergence herbicides of the invention prepared in accordance with the above examples.

Selectivity of a herbicide is desirable since it allows control of weeds growing among desirable crop plants. To illustrate the usefulness of the oxathiins of the invention as selective preemergence herbicides, 15 mg chemical is dissolved in 5 ml organic solvent containing 25 mg conventional emulsifying agent (e.g., isooctylpolyethoxyethanol) and this solution diluted to 300 ml with distilled water. The chemical is applied at the rate of 2 lbs/A by drenching the surface of soil containing weed and crop seeds in 6-inch plastic pots with 80 ml of the 50 ppm solution. The percent weed control and crop injury are evaluated two weeks after emergence of the crops. TABLE III illustrates the usefulness of these chemicals as selective preemergence herbicides.

Listed below are non-limiting examples of formulations which can be prepared with chemicals of this invention.

Four crop species are planted in regular potting medium contained in 12 oz styrofoam cups. The four crops are Pinto Beans -- Phaseolus vulgaris; Cotton -- Gossypium hirsutum; Soybeans -- Glycine max and Wheat -- Triticum aestivum L. Six hundred mg chemical is dissolved in 10 ml acetone, 1-3 ml toluene and 30 mg of isooctylphenylpolyethoxyethanol (Triton X100; trademark). This mixture is diluted to a volume of 100 ml with distilled water. This mixture contains 6000 ppm active ingredient by weight. The mixture is sprayed to runoff on the four species aforementioned. The plants are sprayed with a DeVilbiss atomizing sprayer at the following stages of growth.

Plant growth regulant observations were made from 5 days after spraying throughout the next 3 weeks. These observations included retardation, formative effects and phytotoxicity. These data are presented in TABLE IV, wherein "retd" stands for retardation, "phyto" stands for phytotoxicity, "N.G." stands for new growth, "trif" stands for trifoliate, and "n.e." stands for no effect.

To further illustrate the utility of these chemicals, data are presented in this Example on the growth retarding properties of soybeans (Corsoy variety). Seventy-five mg chemical is dissolved in 10 ml acetone, 2 ml toluene and 30 mg of Triton X100 (isooctyl phenyl poly ethoxyethanol). This mixture is diluted to a 50 ml volume with distilled water. This mixture is equivalent to 1500 ppm. In some cases a lower rate of 750-800 ppm is used, thus only 38-40 mg are used respectively for the mixture. This mixture is sprayed to runoff on three pots each containing two soybean plants in the early first trifoliate leaf stage. The spray is applied with a DeVilbiss atomizing sprayer. The first height measurement is taken at spraying time and the second when the control plants began to pod or approximately 4 weeks after spraying. A percent growth figure is obtained by using the following formula ##EQU2## where G.C. stands for growth of control plants in cm, and G.T. stands for growth of treated plants. TABLE V shows the unique growth retarding properties of the chemicals on soybeans.

The unique property of these chemicals to inhibit axillary growth is exhibited in this Example. Four hundred mg chemical is dissolved in 10 ml solvent (e.g. toluene, acetone, or mixture thereof) containing 3% surfactant (e.g., isooctylphenylpolyethoxyethanol [Triton X100; trademark], polyoxyethylene sorbitan monolaurate [Tween 20; trademark] or AH831 [trademark] blend of anionic and nonionic surfactants). This mixture, diluted to 100 ml with distilled water, is equivalent to 4000 ppm chemical. Lower dosages may be made by diluting the 4000 ppm formulation or by dissolving less chemical in the solvent mixture. Twenty ml of one of the mixtures described above is sprayed on tobacco plants (Nicotiana tabacum Xanthii variety) at the early flowering stage, but with flowers removed to force axillary growth. The spray is directed to the terminal growing areas in order to facilitate wetting each node as the mixture runs down the central stalk. Percent sucker control data are calculated on the green weight of the suckers which are plucked approximately 4 weeks after spray application. The following formula is used to calculate percent sucker control: ##EQU3## where S.W.C. stands for sucker weight in grams for the control and S.W.T. stands for sucker weight in grams for the treated plant. TABLE VI shows the unique ability of the chemicals to inhibit sucker or axillary bud growth.

To explain more clearly the activity of this invention on flowering, the following test on chrysanthemum is described. A sprayable formulation is made by emulsifying 1.06 g of a 4 lb active gallon (see Example 54 formulation 3 for composition) containing 2,3-dihydro-5,6-diphenyl-1,4-oxathiin and diluting this mixture to 100 ml volume with water. This mixture is equivalent to 5000 ppm. A respective dosage of 2500 is made by diluting the 5000 ml emulsion. This sprayable formulation is applied to Fred Shoesmith mums that had been exposed to 16 and 23 Short Days (10 hours) to induce flowering. The spray is applied to runoff with a DeVilbiss atomizing sprayer. The plants are placed back in the growth chamber until the total short day period of 6 weeks is completed. They are then removed and placed in a greenhouse until flowering. Data are taken by counting the number of axillary flower buds 1/2 inch or longer below the terminal flower. These data are presented in TABLE VII. The date in TABLE VII illustrate the unique properties of this invention in reducing the number of flower buds that would ordinarily require hand removal.

To illustrate further the growth regulating properties of the chemicals on the metabolic activity of plants, 45.6 cc of chemical (formulated as a four pound active gallon -- see Example 54 formulation 3 for composition) were brought up to an 1,892 ml volume with water. This solution was applied at a 3 lb per acre rate in 30 gallons of water to sugarbeets, Beta vulgaris, three weeks before harvest.

The yield data were determined by hand harvesting each of three treatment replicates which consisted of one row 15 feet long. The sugar content was determined by measuring the sucrose content of beets that were randomly selected from each plot.

The data are given in TABLE VIII illustrating the increase in sugar content due to the chemical application. Based on an average yield of 40,000 pounds of beets per acre, the one percent increase would add 400 pounds of extra sugar per acre.

To illustrate further the unique growth regulating properties of the chemicals on flowering, 8.5 g. of the chemical of EXAMPLE 1 (formulated as a four pound active gallon -- see EXAMPLE 54 for composition) was brought up to a 400 ml volume with water. This emulsion was applied to four replicate branches of Red Haven peaches that were in the second year of bearing. The flower buds at this time were in the tight bud stage. The chemical emulsion was applied to the branches to the point of run off, with a 1/2 inch brush. The buds were counted and recorded for each branch. Each branch had an average of 35 flower buds. The number of flower buds open were counted 28 and 33 days after application and compared to the original bud count. The percent flowers open figure was established from these two counts, with the results shown in TABLE IX.

A peach farmer is often faced with yield losses due to late frost. The chemicals herein described inhibit flower opening and hence flower kill.