Alkyl Thiourea Miticides

Included among the many insecticidal and miticidal compounds available are various substituted thioureas. Such compounds and their biological properties are discussed in Hoskins, W. M., et al., J. Econ. Ent., 33:6, 875-881 (1940), and Schroeder, D. C., Chem. Reviews, 55, 181-228 (1955).

This invention relates to a class of substituted thioureas and to their use as miticides when used in a miticidally effective amount. More specifically, this invention relates to alkyl thioureas having the formula ##STR2## wherein --R is selected from the group consisting of benzhydryl, 3'-(2'-ethylhexoxy)-propyl, allyl, cyclohexyl, cycloheptyl, 1',3'-dimethylbutyl, and alkyl containing from 7 to 13 carbon atoms, inclusive; and where R is benzhydryl, R.sub.1 is alkyl containing from 7 to 11 carbon atoms, inclusive; where R is 3'-(2'-ethylhexoxy)-propyl, R.sub.1 is alkyl containing from 1 to 12 carbon atoms, inclusive; where R is allyl, R.sub.1 is alkyl containing from 9 to 13 carbon atoms, inclusive; where R is cyclohexyl, R.sub.1 is dodecyl; where R is cycloheptyl, R.sub.1 is heptyl; where R is 1',3'-dimethylbutyl, R.sub.1 is n-heptyl or dodecyl; where R is heptyl, R.sub.1 is alkyl containing from 6 to 8 carbon atoms, inclusive; where R is octyl, R.sub.1 is alkyl containing from 6 to 10 carbon atoms, inclusive; where R is nonyl, R.sub.1 is alkyl containing from 3 to 9 carbon atoms, inclusive; where R is decyl, R.sub.1 is alkyl containing from 3 to 7 carbon atoms, inclusive; and where R is undecyl, dodecyl, or tridecyl, R.sub.1 is alkyl containing from 2 to 7 carbon atoms, inclusive.

The term "alkyl" is intended to include both straight chain and branched chain hydrocarbons -- for example, n-heptyl, s-heptyl, isobutyl, t-octyl. This definition extends to both R and R.sub.1 and applied wherever the term "alkyl" is used or wherever the prefix denoting the chain configuration for an alkyl of a specified number of carbon atoms is not given--for example, hepty, octyl, nonyl, decyl.

By "miticidally effective amount" is meant the amount of the herein disclosed miticidal compounds which when applied to the habitat of mites in any conventional manner will kill or substantially injure a significant portion of the population thereon.

The compounds of the present invention are manufactured by reacting the properly selected isothiocyanate with the properly selected amine. A variety of non-reactive solvents can be used, such as benzene and other aromatic hydrocarbons, ether, dioxane, tetrahydrofuran, and in some instances, alcohols. The time and temperature requirements for the reaction will depend on the reactivities of both the isothiocyanate and the amine used. Normally, a complete reaction will occur with a few hours of reflux. The examples shown herein are illustrative of the method of preparation of the compounds of the invention.

7.9 g (0.05 mole) n-heptylisothiocyanate was dissolved in 50 ml of benzene. To this solution was added 7.2 g (0.05 mole) of n-nonylamine. The resultant mixture was heated on a steam bath for 1 hour with reflux. The solvent was then removed in a rotary evaporator under vacuum leaving 15.2 g of a waxy solid. The structure, as confirmed by infrared spectroscopy, was that of 1-heptyl-3-nonyl-2-thiourea. The theoretical yield was 15.0 g.

9.25 g (0.05 mole) of n-dodecylamine was dissolved in 50 ml of benzene. To this solution was added 5.75 g (0.05 mole) of n-butylisothiocyanate. An exothermic reaction took place. When a temperature rise could no longer be detected, the reaction mixture was heated with reflux on a steam bath for 2 hours. The solvent was then removed under vacuum in a rotary evaporator, leaving a residue of 14.5 g of a waxy solid, of melting point 49.degree. to 55.degree. C. The structure, as confirmed by infrared spectroscopy, was that of 1-n-dodecyl-3-n-butyl-2-thiourea. The theoretical yield was 14.2 g.

Other compounds, such as those included in the following table, can be prepared in a manner analogous to that shown in the examples above, starting with the appropriate materials. The compounds in the table are representative of those embodied in the present invention. Compound numbers have been assigned to them for purposes of identification throughout the balance of this specification.

Miticidal activity of each of the above compounds was evaluated for efficacy on the two-spotted mite ›Tetranychus urticae (Koch)! as follows:

Pinto bean plants (Phaseolussp.), approximately 10 cm tall, are transplanted into sandy loam soil in 3-inch clay pots and thoroughly infested with two-spotted mites of mixed ages and sexes. Twenty-four hours later the infested plants are inverted and dipped for 2-3 seconds in 50--50 acetone-water solutions of the test chemicals. Treated plants are held in the greenhouse, and 7 days later mortality is determined for both the adult mites and the nymphs hatching from eggs which were on the plants at the time of treatment. Test concentrations range from about 0.2% down to that at which 50% mortality occurs (LD-50).

Test chemicals are dissolved in acetone and aliquots are diluted in 200 cc of water in glass bottles. Two pinto bean plants (Phaseolus sp.), with expanded primary leaves, are supported in each bottle by cotton plugs, so that their roots and stems are immersed in the treated water. The plants are then infested with 75-100 two-spotted mites of various ages and sexes. One week later the mortality of the adult mites and nymphs is recorded. Test concentrations range from 10 ppm down to that at which 50% mortality occurs (LD-50).

The results of the above test procedures, indicating the effective concentration at which LD-50 control effect was achieved, are listed in Table II.

Neither the examples nor the tables above are intended to limit the invention in any manner.

The compounds of this invention are generally embodied in a form suitable for convenient application. For example, the compounds can be embodied in miticidal compositions in the form of emulsions, suspensions, solutions, dusts, and aerosol sprays. In addition to the active compounds, such compositions generally contain the adjuvants which are normally found in miticide preparations. One such composition can contain either a single miticidally active compound or a combination of miticidally active compounds. The miticide compositions of this invention can contain as adjuvants organic solvents such as sesame oil, xylene, or heavy petroleum; water; emulsifying agents; surface active agents; talc; pyrophyllite; diatomite; gypsum; clays; or propellants such as dichlorodifluoromethane; or a combination of these. If desired, however, the active compounds can be applied directly to feedstuffs, seeds, or other such matter upon which the pests feed. When applied in such a manner, it will be advantageous to use a compound which is not volatile. In connection with the activity of the presently disclosed miticidal compounds, it should be fully understood that the compounds need not be active as such. The purposes of this invention will be fully served by a compound which is rendered active by an external influence such as light, or by some physiological action which the compound induces when it is ingested into the body of the pest.

The precise manner in which the miticidal compounds of this invention should be used in any particular instance will be readily apparent to a person skilled in the art. The concentration of the active miticide in a typical composition can vary within rather wide limits. Ordinarily, the miticide will comprise not more than about 15.0% by weight of the composition. The preferred range of concentration of the miticide is about 0.1 to about 1.0% by weight.