Processes for the production of methyl dithiocarbazinate

Details Processes for the production of methyl dithiocarbazinate Processes for the production of methyl dithiocarbazinate

2002-04-18

2003-04-08

Shippen, Michael L. (Department: 1621)

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

Organic compounds

Esters having the thiocarboxylate group, -cx-, wherein the...

Reexamination Certificate

active

06545172

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to processes for the production of methyl dithiocarbazinate (MDTC). More particularly, in invention relates to processes for the production of methyl dithiocarbazinate which comprise the steps of providing a mixture comprising hydrazine, solvent, carbon disulfide and base; adding methyl bromide to form a reaction mixture; cooling the reaction mixture; and recovering methyl dithiocarbazinate. The present invention further relates to processes of recovering MDTC from a reaction mixture comprising the steps of filtering the reaction mixture to yield a solid MDTC retentate and a liquid filtrate; acidifying the filtrate; and adding methyl isobutylketone to the acidified filtrate.
BACKGROUND OF THE INVENTION
Methyl dithiocarbazinate may serve as a reactant or intermediate in the preparation of useful compounds. For example, Le, U.S. Pat. No. 4,696,938, discloses a process for preparing and using methyl hydrazinecarbodithioate as a reactant in the preparation of 6-aryl-pyridine thiosemicarbazones. Le teaches that methyl dithiocarbazinate is prepared by adding hydrazine hydrate to a cooled solution of potassium hydroxide in water and 2-propanol, adding pre-cooled carbon disulfide while maintaining the internal temperature below 10° C., stirring for a further one hour and adding cooled methyl iodide.
Mayes, U.S. Pat. No. 5,861,526, discloses a process for preparing MDTC by reacting carbon disulfide and hydrazine in the presence of a non-alcoholic solvent to form hydrazinium dithiocarbazinate and methylating said hydrazinium dithiocarbazinate with methyl bromide. Mayes teaches that the reaction of carbon disulfide and hydrazine is conducted in the presence of a non-alcoholic solvent to reduce dithiocarbazinate buildup, and that the molar ratio of solvent to carbon disulfide is from about 0.4:1 to about 3:1.
Wasleski et al., U.S. Pat. No. 5,877,339, disclose a process for preparing MDTC by reacting carbon disulfide and hydrazine in an aqueous medium in an effective ratio to form a hydrazinium dithiocarbazinate, and, without isolating the hydrazinium dithiocarbazinate, methylating the hydrazinium dithiocarbazinate in the same aqueous medium with methyl bromide. Wasleski et al. teach that the aqueous medium is selected from the group consisting of water and a mixture of water and an aprotic solvent, provided that when said aqueous medium is a mixture of water and an aprotic solvent, the aprotic solvent is used in a molar ratio of from about 0.15 to 1 mole per mole of carbon disulfide.
Jackman et al., U.S. Pat. No. 6,025,514, disclose a process for preparing MDTC by reacting carbon disulfide, hydrazine and an adjunct base in an aqueous reaction medium to form a dithiocarbazinate salt, and methylating the dithiocarbazinate salt with methyl bromide. Jackman et al. teach that the base is added in such a manner that the pH of the reaction mixture is maintained between about 8 and about 14; that the mole ratio of carbon disulfide to hydrazine to base falls in the range of (1 to 1.2):(1 to 1.2):(1 to 1.2); and that the aqueous reaction medium is selected from the group consisting of water and a mixture of water and a non-alcoholic hydrocarbon solvent.
Unfortunately, many prior art processes produce MDTC in unsatisfactory yield and purity, or require the use of relatively expensive alkylating agents, such as methyl iodide. Thus, there is a need in the art for a process for producing MDTC in high yield and purity, and which preferably employs methyl bromide as an alkylating agent. Further, there is a need for a process of recovering MDTC from a reaction mixture. Preferably the MDTC recovery process renders any resulting aqueous waste non-biotoxic and suitable for normal waste disposal.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to obviate problems of the prior art. It is a further object of the present invention to provide processes for the production of MDTC in high yield and/or high purity. It is yet an additional object of the invention to provide for methods for the recovery of MDTC from the reaction mixture, and processes of treating the aqueous waste formed during the production of MDTC. These and additional objects are provided by the processes of the invention.
According to one aspect of the invention there are provided processes for the production of MDTC comprising the steps of mixing hydrazine with a solvent to form a mixture; adding carbon disulfide to the mixture; adding a base to the mixture after the addition of carbon disulfide is started; adding methyl bromide to the mixture after the addition of the carbon disulfide and base is completed; keeping the resultant reaction mixture at a temperature of from about 5° C. to about 40° C. for a period of from about 30 minutes to about 2 hours; cooling the reaction mixture to a temperature of from about 0° C. to about 15° C., and maintaining the reaction mixture at that temperature range for a period of from about 15 minutes to about 2 hours; and recovering MDTC. The solvent may be selected from the group consisting of water and a mixture of water and a non-alcoholic hydrocarbon solvent.
According to another aspect of the invention there are provided methods of recovering MDTC comprising the steps of filtering the reaction mixture to yield a solid MDTC retentate and a liquid filtrate; acidifying the filtrate with a mineral acid; and adding methyl isobutylketone to the acidified filtrate.
According to one aspect of the invention there are provided processes for the production of MDTC comprising the steps of providing a mixture comprising hydrazine and solvent; adding carbon disulfide to the mixture; after the carbon disulfide addition is completed then adding base to the mixture; after the base addition is completed then adding methyl bromide to the mixture; keeping the reaction mixture at a temperature of from about 5° C. to about 40° C. for a period of from about 30 minutes to about 2 hours; cooling the reaction mixture to a temperature of from about 0° C. to about 15° C., and maintaining the reaction mixture at that temperature range for a period of from about 15 minutes to about 2 hours; and recovering methyl dithiocarbazinate from the reaction mixture.
According to another aspect of the invention there are provided processes for the production of MDTC comprising the steps providing a mixture comprising hydrazine, solvent, carbon disulfide and base; adding methyl bromide to the mixture thereby forming a reaction mixture; cooling the reaction mixture to a temperature of from about 0° C. to about 15° C., and maintaining the reaction mixture at that temperature range for a period of from about 15 minutes to about 2 hours; and recovering MDTC.
The processes of the invention of the invention are advantageous in that MDTC may be produced with high yield (from about 89% to about 91%) and/or high purity (about 95%). Additionally, the aqueous waste formed during the MDTC production can be rendered non-biotoxic.
These and additional aspects, objects and advantages of the invention are more fully described in the following detailed description.
DETAILED DESCRIPTION
The process for the preparation of MDTC using base, hydrazine, carbon disulfide and methyl bromide can be represented as set forth below:
As used herein, “base” refers to a basic compound other than the hydrazine reactant. The hydrazine is preferably hydrazine hydrate.
In one embodiment of the invention, methyl dithiocarbazinate is prepared by providing a mixture comprising hydrazine, solvent, carbon disulfide and base; adding methyl bromide, thereby forming a reaction mixture, keeping the reaction mixture at a temperature of from about 5° C. to about 40° C., preferably from about 20° C. to about 30° C., for a period of from about 30 minutes to about 3 hours, preferably from about 1 to about 2 hours; cooling the reaction mixture to a temperature of from about 0° C. to about 15° C., and maintaining the reaction mixture at that temperature range for a period of from about 15 minutes to about 2 hours,

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