GB2074871A - Urea Prills Having Surface Impregnation of Certain Thiolcarbamate Sulfoxides - Google Patents

Abstract

A solid herbicidal composition comprising urea prills having impregnated into the surface thereof from 0.1 to 10.0 percent by weight of a thiolcarbamate sulfoxide of the formula <IMAGE> wherein R is alkyl C2-C8, or benzyl; and R<1> and R<2> together with the nitrogen atom to which they are attached form piperidino, hexamethyleneimino, 2,5-dimethylpiperidino or 5-ethyl-2-methylpiperidino. The composition shows increased thermal stability of the sulfoxide and may be used directly as a herbicide.

Description

SPECIFICATION Urea Prills Having Surface Impregnation of Certain Thiolcarbamate Sulfoxides This invention relates to stabilized thiolcarbamate sulfoxide compositions.

Thiolcarbamate sulfoxides of the type stabilized in accordance with the present invention are disclosed in U.S. Patent No.

3,989,684. While these compounds exhibit excellent herbicidal activity, they have been found to be somewhat thermally unstable. A study on the thermal stability of these comounds is reported in The Journal of Chemistry and Industry, March 1, 1975, "On the Thermal and Chemical Stability of Carbamoyl Sulfoxides" by Gozzo, Masoero, Santi, Galluzzi and Barton. U.S. Patent No. 3,975,180 describes solid crystalline adducts of carbamyl sulfoxide and urea in a 1:3 mole ratio which have improved thermal stability compared to the corresponding sulfoxide. The patent teaches that the adducts are prepared by adding carbamoyl sulfoxide to a solution of urea in a suitabie solvent, and in concentrating said mixture. The adduct precipitates and is then collected and dried.

It has now been found that the thermal stability of certain thiolcarbamate sulfoxides can be improved by impregnating the sulfoxide into the surface of urea prills. Accordingly, one embodiment of this invention relates to a novel composition of matter comprising: urea prills having impregnated into the surface thereof from 0.1 to 10.0 percent by weight, preferably from about 4.0 to about 6.0 percent by weight, of a thiolcarbamate sulfoxide of the formula:

wherein R is alkyl C2-C8, preferably C2-C4, or benzyl, most preferably R is alkyl C2-C4; and R1 and R2 together with the nitrogen atom to which they are attached form piperidino, hexamethyleneimino, 2,5-dimethyl-piperidino or 5-ethyl-2-methylpiperidino, preferably hexamethyleneimino.

The term "alkyl" as used herein refers to straight or branched chain saturated aliphatic hydrocarbon groups, i.e., methyl, ethyl, propyl, propyl, n-butyl, s-butyl, and t-butyl.

The thiolcarbamate sulfoxide herbicides within the scope of the present invention include both liquids and solids. The urea prills can be impregnated with liquid herbicide compounds by directly applying the herbicide by any conventional manner such as by spraying or dripping the herbicide onto the urea prills.

Normally, the urea prills have a low absorptivity for the herbicide and it will be necessary to mix the two components for several hours. Mixing can be accomplished in any conventional equipment such as a tumbling drum, ribbon mixer or the like.

Herbicides which are solid at ambient temperatures can be melted and combined as described above for liquid herbicides.

If desired, the herbicide component can be dissolved in a solvent such as methanol before being impregnated into the surface of the urea prills. Thereafter, the solvent is evaporated from the prills.

Since the urea carrier has a limited absorptivity, only relatively small quantities of herbicide can be impregnated into the surface of the prills. A quantity ranging from about 0.1 to about 10.0 percent by weight of urea prill is useful, and the preferred amount is from about 4.0 to about 6.0 percent by weight of urea prill.

Urea is obtained from commercial synthesis routes as a 70-75 weight percent aqueous solution. Such urea is further processed to a solid form which is more economical for shipping and distribution. Two different routes are used to reduce urea to its solid form. The first route is by evaporation of water from steam-heated urea solution or by a process of atmospheric air-sweep evaporation. The urea evaporation route is utilized for the production of agriculture grade urea.

The second process involves crystallization with crystal remelt and produces a relatively purer product well suited for industrial uses. Here water is removed from the solution in a vacuum crystallizing with heating. A slurry containing about 30 weight percent urea crystals in suspension is formed. These urea crystals are separated from the mother liquor in a continuous pusher type centrifuge washed with water and dried. Next, the crystals are remelted in a steamheated crystal melter in the top of a prilling tower.

Molten urea obtained by either the evaporation process or the crystal melting process is sprayed as droplets down from the top of a tall cylindrical tower about 50 meters high and allowed to fall countercurrently to a stream of ambient air. The urea-droplets freeze into small spherical particles about 1.5 to about 3.0 millimeters (MM) in diameter.

Larger prills of about 2-3 mm in diameter or larger have been prepared in another system in which granulation is effected by spraying the urea melt onto a cascading bed of recycling fines in an inclined, rotating pan granulator.

Any urea prill including both the smaller and larger prills discussed above are useful in the practice of this invention.

The following example illustrates the stabilizing effect by impregnating urea prills with representative thiolcarbamate sulfoxide.

Example I 93.06 grams (g) urea prills (reagent grade) were placed in a stainless steel mixing beaker (4 inches in diameter and 5.5 inches deep). 6.94 g of the technical grade S-iso-propyl-hexahydro-1 H azepine- 1 -carbothioate sulfoxide (75.7% purity) were melted by heating at 50-550C and added to the prills with an eyedropper. The stainless steel beaker was inclined at about 300 horizontally and revolved for two hours to tumble the wetted prills. At the end of this time period, an examination of the urea prills showed that almost all the sulfoxide had impregnated the prills to a slight depth below the surface. The center portion of the prills were not so impregnated. Some sulfoxide remained coated to the inside surface of the stainless steel beaker.About 10 g of the impregnated urea prills were aged at 41 0F for four weeks and a like sample was aged at 1 250F for four weeks.

At the end of the one month aging period, the samples were subjected to analytical analysis to ascertain the degree of thermal decomposition of the thiolcarbamate sulfoxide contained in the samples of the prills impregnated with the thiolcarbamate sulfoxide and aged at 41 OF and 1250F.

Analysis was run with a Hewlett Packard Model 1084 high pressure liquid chromatograph equipped with a microparticulate silica column and ultraviolet light detector operated at a wave length of 254 nm. The mobile phase for the analysis was a solvent mixture containing hexane, dichloromethane and methanol in volumetric ratios of 25:5:1, respectively.

Test samples were prepared for analysis by mixing one milligram (mg) thiol carbamate sulfoxide per milliliter (ml) of the mobile phase and shaking the mixture for at least 30 minutes to ensure thorough mixing. The solution was filtered and analyzed.

Sufficient amounts of samples were weighed such that one mg sulfoxide per ml of mobile phase resulted. Thus, for the above aged prilis, which were assumed to contain 5.0 percent by weight sulfoxide, 800 mg of prills were added to 40 mi mobile phase.

To calibrate the instrument, at least three injections of a calibration solution were made and UV response noted. The calibration solution was prepared by dissolving 40 mg of thiolcarbamate sulfoxide of known purity in 40 ml of mobile phase. Purity of this standard thiolcarbamate sulfoxide was maintained by storage at OOC.

A test sample solution was then injected into the chromatograph and UV response noted. If large numbers of samples were run, the instrument was periodically recalibrated. The weight percent of thiolcarbamate sulfoxide in a test sample was found by directly comparing the instrument UV response for the test sample solution versus the response of the calibration solution. The coefficient of variation was ascertained to be approximately two percent.

The impregnated urea prills that were aged for four weeks at 41 OF were found to contain 4.8 weight percent thiolcarbamate sulfoxide.

The impregnated urea prills that were aged for four weeks at 1 250F were found to contain 4.3 weight percent thiolcarbamate sulfoxide. Thus, it was ascertained that only about 10 percent of the thiolcarbamate sulfoxide that was impregnated into the urea prills decomposed during the four week heat aging at 1 250F.

Example II 2-3 ml technical grade S-iso-propyl-hexahydro- 1 H-azepine-1-carbothioate sulfoxide (75.7% purity) were melted by heating at 50-550C and added to 5 cc glass ampoule. The ampoule was sealed and placed in a constant temperature oven at l250Fforfour weeks. The amount of decomposition was ascertained by the method described in Example I, and the compound was found to be almost completely decomposed.

It has been found that the admixture of the urea with the thiolcarbamate suifoxide has no adverse effect on the herbicidal activity of the thiolcarbamate sulfoxide, that is, the mixture of the thiolcarbamate sulfoxide and the urea is herbicidally as active as the thiolcarbamate sulfoxide alone.

The solid compositions of the present invention are easy to prepare, stable in storage and can be directly used as a herbicide without formulation with other ingredients.

The solid compositions of the present invention are useful in controlling the growth of undesirable vegetation by pre-emergence or post-emergence application to the locus where control is desired, including pre-plant and post-plant soil incorporation as well as surface application.

In general, any conventional method of application can be used. The locus of application can be soil, seeds, seedlings, or the actual plants, as well as flooded fields. Soil application is preferred and can be achieved by conventional ground or air application equipment. In typical application, the compositions are applied to the soil surface.

The amount of the present composition which constitutes a herbicidally effective amount depends upon the nature of the plants to be controlled. The rate of application of active ingredient varies from about 0.01 to about 50 pounds per acre, preferably about 0.1 to about 25 pounds per acre with the actual amount used depending on the overall cost and the desired results.

Claims (13)

Claims

1. A solid herbicidal composition comprising urea prills having impregnated into the surface thereof from 0.1 to 10.0 percent by weight of a thiolcarbamate sulfoxide of the formula

wherein R is alkyl C2-C8, or benzyl; and R1 and R2 together with the nitrogen atom to which they are attached form piperidino, hexamethyleneimino, 2,5-dimethyl-piperidino or 5-ethyl-2-methylpiperidino.

2. A composition as claimed in claim 1 in which from 4.0 to 6.0 percent by weight of the thiolcarbamate sulfoxide is impregnated into the surface of the urea prills.

3. A composition as claimed in claim 1 or claim 2 in which R is alkyl C2-C8 and R' and R2 together with the nitrogen atom to which they are attached form hexamethyleneimino.

4. A composition as claimed in any of claims 1 to 3 in which R is alkyl C2-C4.

5. A composition as claimed in claim 1 or claim 2 in which R is isopropyl and R' and R2 together with the nitrogen atom to which they are attached form hexamethyleneimino.

6. A composition as claimed in claim 1 substantially as herein described with reference to the Examples.

7. A process for preparing a solid herbicidal composition as claimed in claim 1, comprising impregnating the surface of urea prills with from 0.1 to 10.0 percent by weight of a thiolcarbamate sulfoxide of the formula

wherein R is alkyl C2-C8, or benzyl; and R1 and R2 together with the nitrogen atom to which they are attached form piperidino, hexamethyleneimino, 2,5-dimethyl-piperidino or 5-ethyl-2methylpiperidino.

8. A process as claimed in claim 7 in which the thiolcarbamate sulfoxide is a solid at ambient temperatures and it is melted prior to impregnating the surface of the urea prills.

9. A process as claimed in claim 7 or claim 8 in which the impregnating is done with from 4.0 to 6.0 percent by weight of a thiolcarbamate sulfoxide in which R is alkyl C2-C4 and P1 and R2 together with the nitrogen atom to which they are attached form hexamethyleneimino.

10. A process as claimed in claim 7 substantially as herein described with reference to the Examples.

11. Solid herbicidal compositions when prepared by a process as claimed in any of claims 7to 10.

12. A method of controlling undesirable vegetation which comprises applying to the area where control of said vegetation is desired a herbicidally effective amount of a solid herbicidal composition comprising

wherein R is alkyl C2-C8, or benzyl; and R' and R2 together with the nitrogen atom to which they are attached form piperidino, hexamethyleneimino, 2,5-dimethyl-piperidino or 5-ethyl-2methylpiperidino.

13. A process as claimed in claim 12 in which the solid herbicidal composition is a composition as claimed in any of claims 1 to 6 or 11.