Abstract:
S-n-butyl-N,N-diisopropyl thiocarbamate which has the structural formula ##STR1## which is useful as a selective herbicide in sugarbeets, carrots and cabbage.

Description:
BACKGROUND OF THE INVENTION 
     An herbicide is a compound which controls or modifies plant growth, e.g. killing, retarding, defoliating, desiccating, regulating, stunting, tillering, stimulating, and dwarfing. &#34;Plants&#34; refer to all physical parts, including seeds, seedlings, saplings, roots, tubers, stems, stalks, foliage, and fruits. &#34;Plant growth&#34; is meant to include all phases of development from seed germination to natural or induced cessation of life. 
     Herbicides are generally used to control or eradicate weed pests. They have gained a high degree of commercial success because it has been shown that such control can increase crop yield and reduce harvesting costs. 
     Herbicidal effectiveness is dependent upon several variables. One of these is the time or growth related method of application. In the past, the most popular methods of application included: pre-plant incorporation into the soil, pre-emergence surface treatment of seeded soil, and post-emergence treatment of the plant and soil. 
     The most important determinant of herbicidal effectiveness is the susceptibility of the target weed. Certain herbicidal compounds are phytotoxic to some weed species but not to others. 
     The manufacturer of the herbicide recommends a range of rates and concentrations calculated to maximize weed control. The range of rates varies from approximately 0.01 to 50 pounds per acre (0.0112 to 56 kilograms per hectare (k/ha)), usually from 0.1 to 25 pounds per acre (0.112 to 28 k/ha). The actual amount used depends upon several considerations, including particular weed susceptibility and overall cost limitations. 
     Thiocarbamate herbicides are known to be particularly effective in the control of grassy type weeds which interfere with the cultivation of a wide variety of crops, e.g., barley, corn, lentils, peanuts, peas, potatoes, soybeans, spinach, tobacco, sugarbeets, carrots, cabbage and tomatoes. 
     Unfortunately, the thiocarbamates, like many other herbicides, are not selective exclusively off weed species. Many are toxic to both weeds and the intended crop beneficiary. Therefore, a particular herbicide&#39;s use may be proscribed by its injurious effect on the cultivated crop even though it may otherwise provide excellent control of weeds plaguing that crop. 
     SUMMARY OF THE INVENTION 
     The present invention pertains to the discovery that the S-n-butyl-N,N-diisopropyl thiocarbamate has the remarkable effect of controlling nutsedge, watergrass and other weeds when applied at certain rates in a pre-emergence manner, while at the same rate exhibiting essentially no adverse effect to sugarbeets, carrots and cabbage. 
     The selectivity toward sugarbeets, carrots and cabbage that is possessed by the compound of this invention is quite unexpected and surprising in light of the fact that homologous compounds are not nearly as effective. 
     DESCRIPTION OF THE INVENTION 
     This invention is directed to the use of S-n-butyl-N,N-diisopropyl thiocarbamate as a selective herbicide for use on sugarbeets, carrots and cabbage crops. Sugarbeets, carrots and cabbage show a high degree of tolerance to S-n-butyl-N,N-diisopropyl thiocarbamate. 
     The above herbicidal compound and those to which it is compared can be prepared by the general methods described in Thiolcarbamates--Preparation and Molar Refractions, American Chemical Society, 81, 714 (1959). The thiocarbamate compounds are known herbicides and their method of synthesis is well known. See U.S. Pat. Nos. 2,913,327, 2,983,747, 3,133,927, 3,175,897, and 3,185,720, for example. However, in general the thiocarbamates produce unacceptable injury to sugarbeets, carrots and cabbage. Therefore, it is quite unexpected to discover the high degree degree of tolerance exhibited toward S-n-butyl-N,N-diisopropyl thiocarbamate. 
     It has been discovered that S-n-butyl-N,N-diisopropyl thiocarbamate is particularly effective in control of nutsedge and other weeds. This is particularly unexpected in that extremely close prior art homologs show no such superior control. 
    
    
     The compound of the present invention can be prepared according to the teaching of the following example. 
     EXAMPLE 
     S-n-Butyl-N,N-diisopropyl thiocarbamate ##STR2## 
     A sodium dispersion in xylene was prepared by blending 75 grams (g) of finely divided sodium into 300 g (345 cubic centimeters (cc)) of anhydrous xylene. The experimental equipment was an argon-flushed 1 liter, 4-neck flask provided with a truebone stirrer, constant pressure dropping funnel air condenser and thermometer. 
     Anhydrous xylene (100 cc) and 18.2 cc (0.119 mole) of the sodium dispersion was added to the reaction flask producing a purplishhued dispersion. n-Butyl mercaptan (13.4 g, 0.149 mole) dissolved in 25 cc of xylene was added to the flask over a period of 4.5 minutes while the temperature of reaction mixture rose from 35° C. to 76° C. The reaction mixture was heated to reflux and 19.5 g (0.119 mole) of diisopropylcarbamyl chloride was reacted with the reaction mixture over 7.5 minutes. The resultant reaction mixture was then heated at reflux for 1.5 hours, cooled and allowed to stand for 2 days. The mixture was then filtered through super-cell. The filter cake was washed with 25 cc of toluene and the filtrate combined and evaporated on a steam bath to produce 25.4 g of a liquid. The fraction from 142° C. to 143.5° C. was recovered as product. The product was 17.72 g of a liquid having an n D   30  of 1.4753. Yield was 68.6% of theoretical of the title compound. The structure was confirmed by infrared spectrascopy. This compound will be referred to as Compound No. 1. 
     Compound No. 1 was comparatively tested with other thiocarbamate herbicides for selectively controlling watergrass [Echnichloa crusgalli (L.) Beauv.], foxtail (Seteria sp.), Johnsongrass (Sorghum halepense), wild cane (Sorghum bicolor), and nutsedge (Cyperus spp.) by pre-emergent application on these weeds and sugarbeets, carrots and cabbage. 
     The additional herbicides tested are S-tert-butyl N,N-dipropyl thiocarbamate, described in U.S. Pat. No. 2,913,327 (Compound No. 2) and S-n-propyl N,N-di-n-butyl thiocarbamate, described in U.S. Pat. No. 2,913,327 (Compound No. 3). 
     Pre-Emergence Herbicide Screening Test 
     A mini field test carried out in which Compounds 1, 2, and 3 were pre-plant incorporated (PPI) at 6 lb/A approximately 3 inches deep in a loam soil and two rows of yellow nutsedge tubers were planted 1 inch apart and 1.5 inches deep through the plots which werew 11 feet long and 4 feet wide. Compound No. 1 was also applied PPI at 3 lb/A. Each plot also contained four rows of cotton planted 1.5 inch deep and rows of yellow foxtail, watergrass, johnsongrass, wild cane, sugarbeets, cabbage and carrots, planted 0.5 inch deep. The results taken 3 weeks after treatment are shown in Table I. 
     The percent control of the weeds is based on the total injury to the plants due to all factors of injury. The rating system is from 0 to 100 percent, where the value represents percent control. For example, 0 represents no herbicidal effect with growth equal to untreated controls and 100 represents complete control. The results are reported in Table I. 
     
                                           TABLE I__________________________________________________________________________   % Injury or Control 21 Days After TreatmentComp.    Rate   Nut-      Yellow          Water-              Johnson                   Wild                      SugarNo. (lb/A)   grass      foxtail          grass              grass                   cane                      beets                          carrots                              cabbage__________________________________________________________________________1   3   58 70  90  60   35 0    0   0    6   100      90  97  85   40 0   10   02   6   40 90  94  95   90 0    0  1003   6   50 80  70  90   94 90  30  90__________________________________________________________________________ 
    
     The compound of the present invention is useful as an herbicide, especially as a pre-emergence herbicide, and can be applied in a variety of ways at various concentrations. The compound is applied to the soil where control of undesirable vegetation is desired. Preferably, the pre-emergence application is made a day or two before planting of the sugarbeets, carrots, cabbage or crop, on the data of planting or a day or two after planting of the sugarbeets, carrots or cabbage. 
     In the preferred practice, the compound herein defined is formulatd into herbicidal compositions, by admixture, in herbicidally effective amounts, with the adjuvants and carriers normally employed for facilitating the dispersion of active ingredients for agricultural applications, recognizing the fact that the formulation and mode of application of a toxicant may affect the activity of the material in a given application. Thus, the active herbicidal compound may be formulated as granules of relatively large particle size, as wettable powders, as emulsifiable concentrates, as powdery dusts, as solutions or as any of several other known types of formulations, depending upon the desired mode of application. 
     Preferred formulations of pre-emergence herbicidal applications are wettable powders, emulsifiable concewntrates and granules. These formulations may contain as little as about 0.5% to as much as about 95% or more by weight of active ingredient. 
     Crop injury and herbicidal effectiveness depends upon several factors, including the nature of the soil where control is desired and the types of seeds or plants to be controlled. Therefore, the rate of which dispersion readily in water or other dispersants. The wettable powder is ultimately applied to the soil either as a dry dust or as a dispersion in water or other liquid. Typical carriers for wettable powders include fuller&#39;s earth, kaolin clays, silicas and other readily wet organic or inorganic diluents. Wettable powders normally are prepared to contain about 5% to about 95% of the active ingredient and usually also contain a small amount of wetting, dispersing, or emulsifying agent to facilitate wetting and dispersion. 
     Emulsifiable concentrates are homogeneous liquid compositions which are dispersible in water or other dispersant, and may consist entirely of the active compound with a liquid or solid emulsifying agent, or may also contain a liquid carrier, such as xylene, heavy aromatic naphthas, isophorone and other non-volatile organic solvents. For herbicidal application, these concentrates are dispersed in water or other liquid carrier and normally applied as a spray to the area to be treated. The percentage by weight of the essential active ingredient may vary according to the manner in which the composition is to be applied, but in general comprises about 0.5% to 95% of active ingredient by weight of the herbicidal composition. 
     Granular formulations wherein the toxicant is carried on relatively coarse particles, are usually applied without dilution to the area in whih suppression of vegetation is desired. Typical carriers for granular formulations include sand, fuller&#39;s earth, bentonite clays, vermiculite, perlite and other organic or inorganic materials which absorb or which may be coated with the toxicant. Granular formulations normally are prepared to contain about 5% to about 25% of active ingredients which may include surface-active agents such as heavy aromatic naphthas, kerosene or other petroleum fractions, or vegetable oils; and/or stickers such as destrins, glue or synthetic resins. 
     Typical wetting, dispersing or emulsifying agents used in agricultural formulations include, for example, the alkyl and alkylaryl sulfonates and sulfates and their sodium salts; polyhydric alcohols; and other types of surface-active agents, many of which are available in commerce. The surface-active agent, when used, normally comprises from 0.1% to 15% by weight of the herbicidal composition. 
     Dusts, which are free-flowing admixtures of the active ingredients with finely divided solids such as talc, clays, flours and other organic and inorganic solids which act as dispersants and carriers for the toxicant, are useful formulations for soil-incorporating application. 
     Pastes, which are homogeneous suspensions of a finely divided solid toxicant in a liquid carrier such as water or oil, are employed for specific purposes. These formulations normally contain about 5% to about 95% of active ingredient by weight, and may also contain small amounts of a wetting, dispersing or emulsifying agent to facilitate dispersion. For application, the pastes are normaly diluted and applied as a spray to the area to be affected. 
     Other useful formulations for herbicidal applications include simple solutions of the active ingredient in a dispersant in which it is completely soluble at the desired concentration, such as acetone, alkylated naphthalenes, xylene and other organic solvents. Pressurized sprays, typically aerosols, wherein the active ingredient is dispersed in finely divided form as a result of vaporization of a low boiling dispersant solvent carrier, such as the Freons, may also be used. 
     The phytotoxic compositions of this invention are applied to the plants in the conventional manner. Thus, the dust and liquid compositions can be applied to the plant by the use of power-dusters, boom and hand sprayers and spray dusters. The compositions can also be applied from airplanes as a dust or a spray because they are effective in very low dosages. In order to modify or control growth of germinating seeds or emerging seedlings, as a typical example, the dust and liquid compositions are applied to the soil according to conventional methods and are distributed in the soil to a depth of at least 1/2 inch below the soil surface. It is not necessary that the phytotoxic compositions be admixed with the soil particles since these compositions can also be applied merely by spraying or sprinkling the surface of the soil. The phytotoxic compositions of this invention can also be applied by addition to irrigation water supplied to the field to be treated. This method of application permits the penetration of the compositions into the soil as the water is absorbed therein. Dust compositions, granular compositions or liquid formulations applied to the surface of the soil can be distributed below the surface of the soil by conventional means such as discing, dragging or mixing operations. 
     The herbicide can also be applied in the crop furrow or it can be applied by injection along-side the crop and furrow in rows spaced several inches from the seed.