PROCESS FOR MANUFACTURING

METHYLENE BIS (THIOCYANATE) Field of the Invention

The present invention relates to a process for manufacturing freely-flowing, crystalline methylene bis(thiocyanate) which contains practically no insolubles (<0.1%) and is stable on storage.

Background of the Invention

Methylene bis(thiocyanate), known also as methylene dithiocyanate, is a pesticide used broadly to control bacteria, algae, and fungi in industrial water systems. Methylene bis(thiocyanate) (MBT) can be formulated for convenient use as a solution in many organic solvents or as an aqueous dispersion, and its excellent penetrating power makes it a preferred biocide in many applications, an example being wood and leather preservation.

The production of MBT is based on the reaction between a thiocyanate salt and a dihalomethane, which can provide the product in a good yield, but by which it is difficult to prevent the formation of undesired oligomers or polymers [US 3,524,872].

Xiao-ling et al. describe a catalytic synthesis of MBT comprising heating and reacting a stoichiometric mixture of sodium thiocyanate (NaSCN) and dibromomethane (DBM) in 10% ethanol/water, at 85°C, in the presence of a phase transfer catalyst [Yang Xiao-ling et al.: Technology & Development of Chemical Industry, 36(2) (2007) 7-9] according to the equation:

CH ₂ Br ₂ + 2 NaSCN → CH ₂ (SCN) ₂ + 2 NaBr.

Solid MBT is usually a lumpy, non -free -flowing powder, and contains impurities insoluble in methanol. CN 101906058 describes a method for preparing MBT from NaSCN and DBM under conditions similar to those employed by Xiao-ling et al., including the use of the same phase transfer catalyst (PTC), but the method further includes, in addition to the steps of reacting and crystallizing, also the steps of primary filtration, washing, treatment with water and with hot ethanol, comprising another hot filtration, crystallization and additional filtration step. The added steps aim at removing the undesired insoluble impurities from the product, but the method is obviously too complex. Moreover, it was found by the present inventors that the products obtained by the known methods may develop insolubles on storage, even if initially being quite pure and free from the insolubles. The presence of insolubles in the MBT product results in grave problems when employing the material, because said insolubles remain on the surface of the used equipment as a glue-like residue which is insoluble in any one of water, methanol, and acetone. The insolubles can even cause a blockage of the pipes. It is therefore an object of the invention to provide an economic process for manufacturing MBT product without methanol- insoluble and acetone -insoluble residues.

It is a further object of this invention to provide an MBT solid product which does not contain more than 0.1% residues insoluble in methanol or acetone.

It is a still further object of this invention to provide an MBT solid product which is stable on storage, and which does not contain more than 0.2% residues insoluble in methanol or acetone even after storage of at least three months at room temperature (RT).

It is another object of this invention to provide a process for manufacturing pure MBT which does not contain more than 0.05% residues insoluble in methanol or acetone after the production. It is still another object of this invention to provide a process for manufacturing pure MBT which does not contain more than 0.1% residues insoluble in methanol or acetone after storage of at least six months at RT.

It is also an object of this invention to provide a non -lumpy, crystalline MBT product comprising more than 99% MBT.

Other objects and advantages of the present invention will appear as the description proceeds.

Summary of the Invention

The invention provides a process for manufacturing methylene bis(thiocyanate) (MBT) comprising the steps of i) dissolving sodium thiocyanate (NaSCN) in aqueous alcohol, preferably methanol or ethanol, and adding dibromomethane (DBM), wherein at least about 100 g aqueous alcohol, preferably at least 107 g, and at least about 100 g DBM, preferably at least 103 g, is present per 100 g NaSCN, which mixture is heated from room temperature to about 75°C and kept at that temperature for a total of about 6 hours, preferably with reflux; ii) adding about 100 g hot water per 100 g of original NaSCN and heating for 3 more hours, while increasing the temperature by about 10°C; iii) adding to the reaction mixture between about 15 and 25 g undiluted alcohol, preferably methanol or ethanol, either after step ii or before it; iv) gradually cooling the mixture below 20°C and adding aqueous sodium bicarbonate to reach a pH of between 6.1 and 6.5; v) filtering, and washing the filtrate at a temperature of about 15°C; and vi) drying under a vacuum at a temperature of about 60°C; thereby obtaining a product containing at least 99% MBT, not more than 0.3% moisture, not more than 0.1% bromide, and not more than 0.1% residues insoluble in acetone. Preferably, the product does not contain more than 0.1% residues insoluble in acetone even after at least six months storage at RT. Said aqueous alcohol in step i) is preferably methanol or ethanol, for example 25- 45% methanol, such as 30-40% methanol, for example 35% methanol or ethanol in a slight mass excess over the mass of said NaSCN; for example, 35% methanol or ethanol is preferably added at a mass excess of from 5 to 15% over the mass of said NaSCN, such as 8- 10%. Said DBM is preferably incorporated into the mixture at a mass of from 0 to about 8% over said NaSCN. Said undiluted alcohol is added during step i) before heating the mixture to about 75°C, or during step iii) before cooling the mixture. Said washing in step v) preferably comprises washing with three portions of washing liquid of a total mass of about two masses of the initial NaSCN. In a preferred embodiment, the first portion of washing liquid comprises diluted alcohol, for example 20% aqueous methanol or ethanol, and the second and third portions comprise water.

In one aspect, the process for manufacturing MBT according to the invention comprises the steps of i) dissolving sodium thiocyanate (NaSCN) in aqueous methanol, and adding dibromomethane (DBM), wherein between 120 and 125 g of 45% methanol and between about 100 and 107 g DBM is present per 100 g NaSCN, which mixture is heated from room temperature to about 75°C over about 1 hour, and kept at that temperature, for a total of about 5 hours with reflux; ii) adding about 100 g hot water per 100 g of original NaSCN and heating for 3 more hours, while increasing the temperature by about 10°C; iii) gradually cooling the mixture below 20°C and adding sodium bicarbonate to reach a pH of between 6.0 and 6.5; v) filtering, and washing the filtrate at a temperature of about 15°C; and vi) drying under a vacuum at a temperature of about 60°C; thereby obtaining a product containing at least 99% MBT, not more than 0.2% moisture, not more than 0.1% bromide, and not more than 0.2% residues insoluble in acetone even after at least three months storage at RT.

In another aspect, the process for manufacturing MBT according to the invention comprises the steps of i) dissolving sodium thiocyanate (NaSCN) in aqueous methanol, and adding dibromomethane (DBM), wherein between 107 and 108 g of 35% methanol and between about 100 and 106 g DBM is present per 100 g NaSCN, which mixture is heated from room temperature to about 75°C over about 1 h, and kept at that temperature for 5 more hours with reflux; ii) adding about 100 g hot water per 100 g of original NaSCN and heating for 3 more hours, while increasing the temperature by about 10°C; iii) adding to the reaction mixture between about 15 and 25 g undiluted alcohol per 100 g original mass of NaSCN; iv) gradually cooling the mixture below 20°C and adding sodium bicarbonate to reach a pH of between 6.1 and 6.4; v) filtering, and washing the filtrate at a temperature of about 15°C; and vi) drying under a vacuum at a temperature of about 60°C; thereby obtaining a product containing at least 99.0% MBT, not more than 0.2% moisture, not more than 0.1% bromide, and not more than 0.2% residues insoluble in acetone, such as not more than 0.06% residues, even after at least six months storage at RT.

The invention provides a non-caking crystalline product containing at least 99.0% MBT, not more than 0.2% moisture, not more than 0.1% bromide, and not more than 0.2%, preferably not more than 0.03% residues insoluble in acetone even after at least three months of storage at RT.

In a preferred embodiment, a non-caking solid product of the invention contains at least 99.5% MBT, not more than 0.2% moisture, not more than 0.1% bromide, and not more than 0.2%, preferably not more than 0.06% residues insoluble in acetone even after at least six months of storage at RT.

Detailed Description of the Invention

It has been found that methylene bis(thiocyanate) (MBT) can be obtained from NaSCN and DBM in a good yield and in a high purity, without PTC, in a process comprising the steps of i) mixing 103 g DBM and at least 107 g aqueous alcohol per 100 g of NaSCN, which mixture is heated from room temperature to about 75°C over 1 hour and kept at that temperature for about 5 hours with reflux, ii) adding about 100 g hot water per 100 g of original NaSCN and heating for 3 more hours, while eventually increasing the temperature by 10°C, hi) cooling the mixture below 20°C and neutralizing it with bicarbonate, iv) filtering and washing with at least 3 x 100 g water at a temperature of about 15°C, and v) drying under a vacuum at a temperature of about 60°C. The yield based on NaSCN is usually at least 80%, the purity of the product is usually at least 99%, and the amount of the residues insoluble in methanol (called shortly "insolubles") is not higher than 0.2%.

It was observed by the inventors that under the usual conditions as described above, usually two phases were obtained when the stirrer was stopped before the crystalhzation stage. If the alcohol content increased above a certain limit, for example by adding 20 g methanol per 100 g of original NaSCN, only a single phase was present; this apparently small difference seemed to be more favorable for the final product stability on storage. It was found that an addition of alcohol to the reaction mixture during the first three steps of the process, i), ii) or iii), lowers the amount of insolubles in the product on storage. Said alcohol is preferably ethanol or methanol in an amount of between 15 and 25 g per 100 g original NaSCN. In a preferred embodiment, said alcohol is added after step ii), shortly before the crystallization step. The amount of the insolubles is usually not higher than 0.2% after storing the product for three months at RT.

In an economic process, the invention provides an MBT product with a very low content of insolubles, which remains at acceptable levels during prolonged storage at RT. It was found that the mass ratio between the reactants and added alcohol during the process substantially affects the insolubles content in the final product and the stability of the product on storage. An insolubles content as low as 0.03%, even after 3 months storage, can be obtained in a process according to the invention. In an important embodiment of the invention, additional alcohol is incorporated into the reaction mixture, for example 20-25 g pure methanol per 100 g of initial NaSCN is added to the reaction mixture, preferably before cooling and crystallization. So, increasing the amount of alcohol in the mixture, particularly at certain stages, favorably affects the amount of insolubles eventually formed during storage, probably via affecting the amount of residual materials which may contribute to the formation of insolubles during the storage. However, increasing the amount of the added alcohol too much may have negative effects; it is supposed by the inventors that DBM does not react only with NaSCN but, in a parallel competing reaction, also with the alcohol, as corroborated by the decreasing pH resulting from the formed HBr. Therefore, without wishing to be limited by any particular theory, the inventors show (see Experimental) that the precise alcohol dose is very important for obtaining a product of good yield and the desired properties.

From HPLC analyses of the reaction mixtures, it was found that the selectivity of the reaction at the end of the cooking stage was 90-95 area%. It was concluded that it is important to carry out the crystallization in a homogeneous solution, and to carry out an effective wash after the filtration step. In one embodiment, the first wash may be performed with an aqueous alcohol of the same alcohol/water ratio as the mother liquor, for example 20%.

In a preferred embodiment of the process, the molar ratio of NaSCN/CH2Br2 is between 2.02 and 2.16, preferably between 2.02 and 2.08.

As mentioned above, increasing the amount of alcohol, such as methanol, per batch, and its addition in different stages of the process, improved the process due to, as supposed, the fact that the crystallization stage starts from a homogeneous solution. The MBT product obtained in all the experiments was analysed by HPLC and the purity was >98%. The yield of the process may slightly decrease due to the higher alcohol volume, probably due to partial dissolution of the product. The yield based on DBM ranged between about 80-85%, the yield based on NaSCN ranged between 76 and 84%. In a preferred embodiment of the invention, alcohol, preferably methanol or ethanol, is added to the reaction mixture partly at the beginning of the reaction and partly before starting the crystallization. During the reaction, the pH of the mixture was measured. A continuous drop in the pH values was observed with time, and at the end of the cooking stage at 86-88°C, the mixture was very acid, pH = 0.6-1.9. This phenomenon probably results from the above mentioned parallel reaction. In a process with minimal alcohol additions, the amount of the methanol and acetone insolubles in the fresh products was below 0.2%; this content increased during the storage at RT usually to about 0.6% within four months. In a preferred embodiment of the process, when additional alcohol was admixed to the mixture, the content of acetone insolubles increased during the three months from the initial value of as low as 0.02% to between about 0.03 and 0.3%. In another preferred embodiment of the process, when additional alcohol was admixed to the mixture, and the crystallized MBT was washed once with aqueous methanol, the content of acetone insolubles, even after three months of storage at RT, was less than 0.03%.

The product manufactured according to the invention typically contained less than 0.1% bromide. The product manufactured according to the invention typically contained less than 0.2% water.

The invention, in one embodiment, thus provides a superior methylene bis(thiocyanate) product, comprising at least 99% MBT, up to 0.3% moisture, less than 0.1% bromide, and less than 0.3% insolubles in acetone, more preferably less than 0.1%. In another embodiment, the invention provides a methylene bis(thiocyanate) product, comprising at least 99.5% MBT, up to 0.2% moisture, less than 0.05% bromide, and less than 0.2% insolubles in acetone, more preferably less than 0.1% insolubles in acetone.

In a preferred embodiment, the invention provides a stable methylene bis(thiocyanate) product, comprising at least 99% MBT, up to 0.3% moisture, less than 0.1% bromide, and less than 0.3% insolubles in acetone even after three months storage, more preferably less than 0.2% or less than 0.1% or less than 0.05% insolubles in acetone even after three months storage at RT. In other preferred embodiment, the invention provides a methylene bis(thiocyanate) product, comprising at least 99.0% MBT, up to 0.2% moisture, less than 0.05% bromide, and less than 0.2% or less than 0.1% or less than 0.05% insolubles in acetone even after three months storage at RT. In another preferred embodiment, the invention provides a methylene bis(thiocyanate) product, comprising at least 99.5% MBT, up to 0.2% moisture, less than 0.1% or less than 0.05% bromide, and less than 0.3% insolubles in acetone even after one year storage at RT.

In one aspect of the invention, the MBT product is a non-caking crystalline solid which has good flowability and can be easily handled in preparing compositions in organic solvents or in aqueous dispersions for use in controlling bacteria, algae, yeasts and fungi, as a microbiocide, microbiostat, fungicide, fungistat, algicide, or disinfectant. Applications comprise, for example, treating industrial water systems such as water cooling systems, paint manufacturing, metalworking cutting fluids, pulp and paper mills, leather processing, latex paints, wood pressure treatments, wood protection treatments - including applying as a wood preservative stain to combat wood rot in residential areas. The MBT product of the invention can be advantageously used in applications where dry dosing is needed, such as oil and gas drilling, mainly fracturing. The MBT crystalline product of the invention will advantageously be incorporated directly, or after dissolving, or after dispersing, into products such as adhesives, coatings, fuels, plastic products, resin emulsions, paints, paper products, and other industrial products.

The invention will be further described and illustrated by the following examples.

Examples

Example 1

Comparative procedure for the preparation of MBT (Run 39290-32)

Into a 0.5 L glass reactor equipped with a mechanical stirrer, condenser and thermocouple were introduced water (105 g) and methanol (56 g). Sodium thiocyanate (NaSCN, 150 g, 1.852 mol) was added at 27°C under stirring. After complete dissolution of the NaSCN, dibromomethane (CH2Br2, 149 g, 0.856 mol) was added. The reaction mixture was heated to reflux (74°C) and held at 74-75°C for 5 h, with stirring.

Hot water (150 g) was added and the reaction mixture was heated to 88°C over 1.5 h then the heating (Tr = 88°C) was continued for 1.5 hours. The reactor was cooled gradually and slowly in order to crystallize the MBT. The reaction mixture was neutralized with aq. 8% NaHCOe (32 g) to pH 6.1. The slurry obtained was filtered and washed with water in three batches (3 x 100 g>.

The wet product (104 g) was dried in an evaporator at 60°C and a vacuum of 30 mm Hg over 5 h. MBT (95 g) was obtained in a purity of 99.2% by HPLC, area%. The yield was -85%, based on DBM.

Example 2

Procedure for the preparation of MBT in ethanol as solvent (Run 3929Q- 40) Into a 0.5 L glass reactor equipped with a mechanical stirrer, condenser and thermocouple were introduced water (105 g) and ethanol (56 g). Sodium thiocyanate (NaSCN, 150 g, 1.852 mol) was added at 25°C under stirring. After complete dissolution of the NaSCN, dibromomethane (CH2Br2, 160 g, 0.92 mol) was added. The reaction mixture was heated to reflux (74°C) and held at 74-75°C for 5 h, with stirring.

Hot water (150 g) was added and the reaction mixture was heated to 86°C over 1.0 h then the heating (Tr = 86-88°C) was continued for 2.0 hours. Ethanol (20 g) was added dropwise to the reaction mixture then the reactor was cooled gradually and slowly in order to crystallize the MBT. The reaction mixture was neutralized with aq. 9% NaHCOe (13 g) to pH 6.4. The slurry obtained was filtered and washed with water in three batches (3 x 100 g).

The wet product (119.6 g) was dried in an evaporator at 60°C and a vacuum of 30 mm Hg over 5 h. MBT (101.1 g) was obtained in a purity of >99.0% by HPLC, area%. The yield was 84.6%, based on DBM.

Example 3

Procedure for the preparation of MBT in methanol as solvent (Run 3929Q- 41}

Into a 0.5 L glass reactor equipped with a mechanical stirrer, condenser and thermocouple were introduced water (105 g) and methanol (56 g). Sodium thiocyanate (NaSCN, 150 g, 1.852 mol) was added at 25°C under stirring. After complete dissolution of the NaSCN, dibromomethane (CH2Br2, 160 g, 0.92 mol) was added. The reaction mixture was heated to reflux (74°C) and held at 74-75°C for 5 h, with stirring.

Hot water (150 g) was added and the reaction mixture was heated to 86°C over 1 h then the heating (Tr = 86-88°C) was continued for 2 hours. Methanol (30 g) was added dropwise to the reaction mixture then the reactor was cooled to 15°C gradually and slowly in order to crystallize the MBT. The slurry obtained was filtered and washed with water in three batches (3 x 100 g).

The wet product (110.6 g) was dried in an evaporator at 60°C and a vacuum of 30 mm Hg over 5 h. MBT (99.7 g) was obtained in a purity of >99% by HPLC, area%. The yield was 83.4%, based on DBM.

Example 4

Procedure for the preparation of MBT in methanol as solvent (Run 3929Q- 42)

Into a 0.5 L glass reactor equipped with a mechanical stirrer, condenser and thermocouple were introduced water (105 g) and methanol (56 g). Sodium thiocyanate (NaSCN, 150 g, 1.852 mol) was added at 20°C under stirring. After complete dissolution of the NaSCN, dibromomethane (CH2Br2, 155 g, 0.89 mol) was added. The reaction mixture was heated to reflux (74°C) and held at 74-75°C for 5 h, with stirring.

Hot water (150 g) was added and the reaction mixture was heated to 86°C over 1.0 h then the heating (Tr = 86-88°C) was continued for 2.0 hours.

Methanol (20 g) was added dropwise to the reaction mixture then the reactor was cooled gradually and slowly in order to crystallize the MBT. The reaction mixture was neutralized with aq. 9% NaHCOe (12 g) to pH 6.2. The slurry obtained was filtered and washed with water in three batches (3 x 100 g).

The wet product (115.7 g) was dried in an evaporator at 60°C and a vacuum of 30 mm Hg over 5 h. MBT (97.4 g) was obtained in a purity of >99.0% by HPLC, area%. The yield was 84.1%, based on DBM. Example 5

Procedure for the preparation of MBT in methanol as solvent (Run 3929Q- 43)

Into a 0.5 L glass reactor equipped with a mechanical stirrer, condenser and thermocouple were introduced water (105 g) and methanol (56 g). Sodium thiocyanate (NaSCN, 150 g, 1.852 mol) was added at 21°C under stirring. After complete dissolution of the NaSCN, dibromomethane (CH2Br2, 150 g, 0.86 mol) was added. The reaction mixture was heated to reflux (74°C) and held at 74-75°C for 5 h, with stirring.

Hot water (150 g) was added and the reaction mixture was heated to 86°C over 1.0 h then the heating (Tr = 86-88°C) was continued for 2.0 hours. Methanol (30 g) was added dropwise to the reaction mixture then the reactor was cooled gradually and slowly in order to crystallize the MBT. The reaction mixture was neutralized with aq. 9% NaHCOe (28 g) to pH 6.2. The slurry obtained was filtered and washed with water in three batches (3 x 100 g).

The wet product (108.0 g) was dried in an evaporator at 60°C and a vacuum of 30 mm Hg over 5 h. MBT (96.3 g) was obtained in a purity of >99.0% by HPLC, area%. The yield was 85.9%, based on DBM.

Example 6

Procedure for the preparation of MBT in methanol as solvent (Run 3929Q- 48)

Into a 0.5 L glass reactor equipped with a mechanical stirrer, condenser and thermocouple were introduced water (105 g) and methanol (56 g). Sodium thiocyanate (NaSCN, 150 g, 1.852 mol) was added at 22°C under stirring. After complete dissolution of the NaSCN, dibromomethane (CH2Br2, 150 g, 0.86 mol) was added. The reaction mixture was heated to reflux (74°C) and held at 74-75°C for 5 h, with stirring. Hot water (150 g) was added and the reaction mixture was heated to 83°C over 1.0 h then the heating (Tr = 83-86°C) was continued for 2.0 hours. Methanol (40 g) was added dropwise to the reaction mixture then the reactor was cooled gradually and slowly in order to crystallize the MBT. The reaction mixture was neutrahzed with aq. 9% NaHCOe (20 g) to pH 6.3. The slurry obtained was filtered and washed with water in three batches (3 x 100 g).

The wet product (104.2 g) was dried in an evaporator at 60°C and a vacuum of 30 mm Hg over 5 h. MBT (92.7 g) was obtained in a purity of >99.0% by HPLC, area%. The yield was 82.7%, based on DBM.

Example 7

Procedure for the preparation of MBT in methanol as solvent (Run 3929Q- 49)

Into a 0.5 L glass reactor equipped with a mechanical stirrer, condenser and thermocouple were introduced water (105 g) and methanol (56 g). Sodium thiocyanate (NaSCN, 150 g, 1.852 mol) was added at 22°C under stirring. After complete dissolution of the NaSCN, dibromomethane (CH2Br2, 155 g, 0.89 mol) was added. The reaction mixture was heated to reflux (74°C) and held at 74-75°C for 5 h, with stirring.

Hot water (150 g) was added and the reaction mixture was heated to 84°C over 1.0 h then the heating (Tr = 84-86°C) was continued for 2.0 hours. Methanol (35 g) was added dropwise to the reaction mixture then the reactor was cooled gradually and slowly in order to crystallize the MBT. The reaction mixture was neutrahzed with aq. 9% NaHCOe (25 g) to pH 6.3. The slurry obtained was filtered and washed with methanol/water 20^80 (100 g) and water in two batches (2 x 100 g).

The wet product (107.6 g) was dried in an evaporator at 60°C and a vacuum of 30 mm Hg over 5 h. MBT (91.8 g) was obtained in a purity of >99.0% by HPLC, area%. The yield was 79.3%, based on DBM. Table 1 summarizes all the experiments carried out.

Table 1 Preparation of MBT under various conditions

* In this experiment, EtOH was used instead of MeOH

** In this experiment, the first wash was with aqueous MeOH

Reaction mixtures were analyzed by HPLC after the addition of hot water (first row) and before crystallization (second row. The results are summarised in Table 2.

Table 2 HPLC analysis of reaction mixture

XI, X2 and X3 are impurities The results showed that the selectivity of the reaction at the end of the cooking stage was about 90-95 area%.

The solid product, stored at room temperature, was checked for the insolubles in acetone once a month. The content of insolubles is shown in Table 3.

The main differences in the reaction conditions and acetone insolubles (AIBs) after different periods of product storage

(a) : After four months

(b) : After six months

Stage 1 : After cooking stage at 86-88°C

Stage 2: After cooking stage at 74-75 °C

Stage 3: After introducing raw materials

Stage 4: First washing stage of the product

The content of insolubles in acetone was checked (10 g MBT in 50 g acetone) in samples prepared in the laboratory four months ago by the usual process (39290-32, 39290-36) and those prepared by the improved process one month and three months after their production in the laboratory (39290-40; 39290- 41; 39290-42; 39290-43; 39290-45; 39290-46; 39290-48; 39290-49). The results are summarised in Table 3.

While the invention has been described using some specific examples, many modifications and variations are possible. It is therefore understood that the invention is not intended to be limited in any way, other than by the scope of the appended claims.