Preparation of substantially dust-free tetrahydro-3,5-dimethyl-1

Details Preparation of substantially dust-free tetrahydro-3,5-dimethyl-1 Preparation of substantially dust-free tetrahydro-3,5-dimethyl-1

1994-06-13

1996-02-27

Ford, John M.

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

C07D28534

Patent

active

054950171

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/EP92/02907, filed Dec. 15, 1992. The present invention relates to a process for the preparation of substantially dust-free granules of tetrahydro-3,5-dimethyl-1,3,5-thiadiazine-2-thione (I) by reacting methylamine (II) with carbon disulfide (III) and formaldehyde (IV) or by reacting the methylammonium salt of N-methyldithiocarbamic acid (V) with formaldehyde (IV).
The invention also relates to substantially dust-free granules of tetrahydro-3,5-dimethyl-1,3,5-thiadiazine-2-thione and to methods of soil decontamination and of controlling nematodes, germinating plants and soil fungi using these granules.
Tetrahydro-3,5-dimethyl-1,3,5-thiadiazine-2-thione (I) (common name: dazomet) is used in agriculture and horticulture for soil decontamination (against nematodes, germinating plants and soil fungi) (U.S. Pat. No. 2,838,389).
In the known preparation processes, the active ingredient is obtained in the form of a fine powder which furthermore has a high content of active ingredient as dust. Such a product is not suitable for the safe use of the active ingredient, which releases methyl isothiocyanate on decomposition.
The literature discloses that thiadiazine derivatives, such as tetrahydro-3,5-dimethyl-1,3,5-thiadiazine-2-thione (I), are obtained in the form of granules if the reaction of the starting materials is carried out in the presence of an emulsifier (Emulgen PP150) and zinc sulfate (JP-A 84/210 073=Chemical Abstracts 102 (19), 166 783 g). The granules thus prepared contain 10% of particles having a diameter of from 200 to 300 .mu.m, 79% of particles having a diameter of from 100 to 200 .mu.m and 11% of particles having a diameter of less than 100 .mu.m.
However, problems with the disposal of the aqueous mother liquors may occur in this process, owing to the use of the inorganic salt and of the emulsifier.
It is an object of the present invention to provide a simpler process for the preparation of tetrahydro-3,5-dimethyl-1,3,5-thiadiazine-2-thione (I) in the form of granules.
We have found that this object is achieved by a process for the preparation of substantially dust-free granules of tetrahydro-3,5-dimethyl1,3,5-thiadiazine-2-thione (I) by reacting methylamine (II) with carbon disulfide (III) and formaldehyde (IV) or by reacting the methylammonium salt of N-methyldithiocarbamic acid (V) with formaldehyde (IV), wherein the reaction is carried out in the presence of at least one diaminoalkylene of the formula VI C.sub.1 -C.sub.4 -alkyl and A is a 1,2-ethylene, 1,3-propylene or 1,4-butylene bridge and these bridges may carry from one to four C.sub.1 -C.sub.4 -alkyl groups.
The reaction is carried out according to the following reaction scheme: ##STR1##
The process may be based on the fact that small amounts of the diaminoalkylene compound compete with methylamine in the reaction and, if R.sup.1 and R.sup.2 are simultaneously hydrogen, for example "dimers" of the formula VII or higher "polymers" of the active ingredient may thus be formed. ##STR2##
The diaminoalkylene compounds in which R.sup.1 or R.sup.2 is not hydrogen my result in the formation of, for example, byproducts of the following structure VIII. ##STR3##
Diaminoalkylene compounds in which neither R.sup.1 nor R.sup.2 is hydrogen might react with carbon disulfide to give noncyclized products of the structure IX.
In addition to the possible byproducts described above, other structures are also possible.
However, the fact that the possible byproducts as well as the active ingredient itself are capable of releasing methyl isothiocyanate is of considerable importance. Consequently, the byproducts too could contribute to the activity in the granules.
The formation of the desired granules my be due to the fact that, on the one hand, byproducts of the structures assumed above are sufficient to disturb the "orderly" crystallization but, on the other hand, such compounds have sufficient similarity to the active ingredient itself, so that they form a disordered conglomerate with the crystals and hence the desired granule

REFERENCES:
patent: 2838389 (1958-06-01), Yoder
Chem Asbstr. 166783g, vol. 102 (1985).

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