IE51587B1 - Aqueous fungicidal formulations and their preparation - Google Patents

Description

This invention relates to the preparation of stable formulations of manganese(IX) ethylenebis(dithiocarbamate)(maneb) and, more particularly, to the preparation of aqueous formulations of maneb having unexpectedly low concentrations of ethylenethiourea (ETU).

Maneb is a known important fungicide, but the compound is unstable and tends to decompose. Decomposition products, such as ethylenethiourea (ETU), appear in freshly made maneb and increase in concentration during periods of storage.

Although much work has been done yiich relates to improving the stability of maneb, there are no known references which teach the present invention.

L. Donev IKhimiyai industriya (Sofia) 41, 100-101 (1969), No. 3], for example, teaches a method of preparing maneb of increased dithiocarbamate content in which aqueous formaldehyde is added to a manganese(II) sulfate solution. Then a solution of ammonium ethylenebis(dithiocarbamate) (amobam) is added to precipitate the maneb. ETU concentration is not discussed.

U.S. Patent 3,856,836 discloses a maneb derived from a formaldehyde-treated reaction mixture. The maneb is precipitated in aqueous medium from a water-soluble salt of ethylenebis(dithiocarbamlc acid) and a water-soluble manganese (II) salt. Formaldehyde is added to the reaction mixture after precipitation. The reference does not discuss ETU concentration.

U.S. Patent 2,974,156 teaches that hexamethylenetetramine (HMTA) can be added to maneb to Improve stability.

U.S. Patent 3,173,832 teaches that paraformaldehyde can be added to maneb to Improve stability and that a soluble zinc salt can reduce phytotoxicity.

Although the prior art discloses various methods of formulating maneb to improve strength and/or stability of the product, no known references discuss the preparation of maneb having a low ETU concentration, either as a dry or an aqueous product.

According to the Invention there is provided a process for preparing a stabilized aqueous composition of maneb which comprises mixing or washing said maneb with aqueous formaldehyde and an aqueous solution of a soluble zinc salt, combined or in either order, and if necessary mixing the result with further water to obtain an aqueous composition comprising maneb and 0.05 to 5.0% by weight of the total composition of formaldehyde and 0.05 to 5% by weight of the total composition, calculated as Zn, of said soluble zinc salt. 2+ The combination of zinc (soluble Zn ) and formaldehyde in aqueous medium with maneb unexpectedly retards the buildup of ETU in maneb.

The maneb used in preparing the compositions of this invention can be dihydrate, anhydrous or partially dehydrated.

The dlhydrate form of maneb is preferred because of its higher overall stability with respect to decomposition to ETU and because it can be formulated in aqueous mixtures directly without having to dry it first.

Maneb, which has been preoared according to the process disclosed and claimed in our ΕΡ-Α-ΟΟΠ8533 to which the reader is referred for further information, is preferred because of its resistance to decomposition. According to that process, maneb can be prepared by reacting a soluble manganese(II) salt with the disodium (nabam) ox dipotassium salt of ethylenebis(dithiocarbamic acid) which has been treated with formaldehyde. As used herein, the term nabam is intended to include the potassium analog of disodium ethylenebis(dithiocarbamate). Alternatively, maneb can be precipitated by reacting ammonium ethylenebis(dithiocarbamate) (amobam) or plain nabam with an aqueous solution of a manganese(II) salt. Nabam is the preferred salt because it yields maneb of lower initial ETU content. It has been noted that nabam treated with formaldehyde produces maneb of a relatively large particle size. Thus, it is preferable to precipitate the maneb in the presence of a dispersant which will cause the maneb to form and remain as small particles and reduce or eliminate the need for grinding, etc., prior to formulation.

Suitable dispersants include some of the ligninsulfonate type, such as Polyfon®.H (a sodium lignosulfonate produced by Westvaco Chemical Division, N. Charleston, South Carolina). The amount of dispersant will ordinarily depend on the nature of the dispersant. Economic considerations suggest using no more dispersant than necessary for obtaining the desired maneb particle size. Using too much dispersant could slow filtration of the maneb reaction mixture, which may necessitate ..other means (e.g., centrifugation) for satisfactory maneb recovery. Generally, the amount of dispersant can range from about 0.1 to 10% of the reaction mixture.

Surprisingly, when nabam is used without formaldehyde, the presence of a dispersant, even though satisfactory when used with formaldehyde, may cause formation of maneb particles which are larger than if no dispersant is used at all.

Hie maneb concentration in the compositions of this invention can vary depending on the strength desired. For example, maneb strength can vary from about 10 to 50% by weight, with 25 to 40% by weight being the preferred concentration for economic reasons.

The use of formaldehyde with a soluble zinc salt achieves an unexpectedly low concentration of ETU when maneb is formulated as an aqueous composition. Although either formaldehyde or soluble zinc salts might contribute toward producing low ETU concentrations in fresh aqueous maneb compositions, storage studies show that a zinc salt, in the absence of formaldehyde, can actually increase ETU concentration. Even though formaldehyde alone operates to minimize ETU levels, the use of both a soluble zinc salt and formaldehyde in the composition can produce surprisingly low ETU levels in aqueous maneb.

The compositions of this invention will ordinarily contain about 0.05 - 5.0% by weight of zinc salt (based on Zn) and about 0.05 - 5.0% by weight of formaldehyde. Preferably, the compositions will contain about 0.1 to 2.5% by weight each of zinc salt and formaldehyde. Too much formaldehyde can create odor or phytotoxicity problems and too much soluble zinc salt in the composition can affect maneb stability.

This invention is illustrated in a preferred embodiment in Table A and the examples which follow. The table and examples are not to be considered as limiting, but merely exemplary. The significant feature is the combined action of formaldehyde and a soluble zinc salt in reducing ETU concentrations in aqueous maneb compositions .

As will be apparent from the Examples hereinafter, the compositions of this invention may be prepared in various ways. Broadly, such processes comprise mixing said maneb in the presence of water with formaldehyde and a soluble zinc salt to obtain a composition comprising 0.05 to 5% by weight of formaldehyde and 0.05 and 5% by weight (based on Zn) of said soluble zinc salt.

Additional formulation ingredients, such as dispersants, anticorrosion agents, etc., as well as other fungicides, such as methyl 2-benzimidazole-carbamate (carbendazim) and 2-cyano-N- £(ethyIamino)-carbonyl] -2-(methoxyimino) acetamide ^Curzate (RTM)J, can be present as long as they do not cause ETO buildup in the formulation or react substantially with formaldehyde to the detriment of the formulation.

As used herein, the term mancozeb is intended to mean a complex of maneb and zinc resulting from reaction of maneb with a soluble zinc salt under wet conditions.

[^For a description of maneb and mancozeb, see Pesticide 2o Manual, 5th Edition, edited by H.Martin and C.R. Worthing, issued by the British Crop Protection Council, pages 328 and 329].

It will be understood that a proportion of mancozeb is formed when the maneb has been treated under wet condit25 ions with a soluble salt of zinc, but such mixtures are for convenients still referred to herein as maneb.

Table A Formaldehyde (CH2O)/Nabam + MnS04 \ Dispersant | Maneb Filter Cake| 1. Wash with water 2. Wash with (soluble) 3. Add into agueous Ca)* ch2o Maneb + Zn2+ + CHjO stabilized agueous composition The preparation of the composition may be accomplished several ways: • (b) Add the filter cake directly into agueous CH2O + Zn^+ (soluble); (c) Wash the filter cake with aqueous [CHjO + Zn2+ (soluble)] and then add to water; (d) Wash with aqueous CHjO and add to agueous Zr.2+ (soluble); (e) Wash with aqueous Zn2+ (soluble) and add to aqueous CH2O.

Any other suitable variation of the above procedures, e.g., wash with agueous Zr»2+ (soluble) and add to water simultaneously with CHjO, can be used.

Further reduction in maneb particle size can be accomplished, if desired, by wet-milling. If desired, the conversion of maneb to zineb1 during the milling process can be avoided by adding I zineb = zinc ethylenebis(dithiocarbamate) S1587 Zn2+ (soluble) Wet-milling is 3,157,486. after the milling process, further described in U.S. Patent Example 1 Table B Formaldehyde/Nabara: Dispersant During Precipitation: Maneb Aqueous CH2O/Nabam + MnSO^ Dispersant {Water-washed Maneb Filter Cake I ZnCl2 Wash; Add into water with ~2% CH2O _V _ Mancozeb Aqueous Suspension with CH2O PPM ETU 1-2 _Aging_ day, room temperature (R.T.) days, R.T.

Into a flask containing a stirred Nj-blanketed solution of 15.2 g. of Polyfon® H in 1160 ml. of water 2Q at 25’ was simultaneously added during a 50-minute period an aqueous solution of 723.2 g. of 23% MnSO^ and formaldehyde/nabam (1115 g. of 23% nabam and 40.6 g. of 37% CH2O mixed and let stand at ambient temperature for 30 minutes before beginning to use in reaction with MnSO^]. After 10 minutes, the maneb was filtered off, ε washed with water and with 1 kg. of 7% ZnCl2- The filter cake was suspended in aqueous formaldehyde such that the maneb concentration (expressed as anhydrous) was about 35% and the formaldehyde concentration was 2.2%. The zinc assay was 1.1% total and 0.9% soluble.

The ETU assays are noted above.

The method of adding reactants simultaneously to a common body of water as in this example is usually referred to as a heel process.

Example 2 Table C Formaldehyde/Nabam; Dispersant During Precipitation; _Maneb Aqueous_ j CHjO/Nabam + MnSO^' Dispersant ____,, _ - | Water-washed Maneb Filter Cake| ZnCl2 Wash; Put into water with ~0.1% CHjO _Ψ Mancozeb Aqueous Suspension with CHjOj PPM Aging ETU 4 2 days, R.T, 22 days, R.T.

The same general procedure was used as in Example 1. The final maneb mixture contained about 28% maneb (expressed as anhydrous), about 0.1% CH2O, and the zinc assay was 1.3%, total, and 1.0% soluble The ETU assays are noted above.

S1S87 Example 3 Table D ETU 51 ppm 121 728 <33* <1 day., R.T.

J+ 1 wk. L_45e *This figure is unusually high because of interference peaks encountered in the liquid chromatographic method used for ETU assay. The true ETU level could possibly be as low as zero; if all the interference plus ETU is reported as ETU, the ETU level is still less than 33 ppm. Similar comments apply to other examples herein where a The same general procedure was followed as in Example 1, except the filter cakes were split at various stages as indicated to show effects of the CHgO and ZnClj as to their absence, separate use, and combined use. Initially, CHgO and ZnClj separately, and especially CHgO and ZnCl^ combined, help reduce ETU, whereas after 1 week at 45s, the combination of CHgO and ZnCl2 is more favorable. The CHjO concentration in samples B and D was about 2%, Example 4 Table E Plain Nabam + MnSO^ | Heel Process, 25“ No Dispersant _V _ |Water-washed Maneb Filter Cake) No Wash /\ ZnClg Wash |Maneb Filter Cake] |Mancozeb Filter Cake] Add / s. Add H20 + Add / v Add H*O + H20 / \ CH2O h2% \ ch2o >> z Maneb aqueous Maneb aqueous with CH2O Mancozeb aqueous Mancozeb aqueous with CH,0 ETU ppm 518 I , Γΐ day., 1R.T. 1367 <8 *k· |_45s The samples were prepared generally as described in Example 3, except that plain nabam (no CHjO) was used to prepare the initial maneb precipitate in the absence of a dispersant. Again, the sample CD) with both CHjO and Zn^+ is more Satisfactory.

Example 5 Table F 112 4 11 3/2 day., 1R.T. ppm 297 66 1460 <12+ 1 145° The samples were made generally as described in Example 4, except that dispersant was present during precipitation of maneb. Again, the sample (D) with both CHjO and Zn2+ is more satisfactory, Example 6 Table G 2 1 /2 day,, ]_R.T. 152 24 94 <16 ETU ppm The same general procedure was followed as in Example 3, except that no dispersant was present during precipitation. The particle size of the maneb obtained in this example was far greater than that obtained in Example 3. It is perhaps for this reason 2+ that in this example alone, the presence of Zn (in absence of CH2O, sample C) has helped hold down ETU concentration during the 1-week, 45° storage of the aqueous maneb as compared to sample A Example 7 Table K Maneb Dihydrate vs. Maneb Anhydrous For Maneb Aqueous Suspensions E F G H ETU 215 22 137 3 ppm 1+ 1 v 400 25 1561 <120 ^450 In this example, maneb dihydrate was compared to anhydrous maneb in aqueous composition. In each case, the presence or absence of ZnClj and CI^O and their combination were examined. Pressure built up during the accelerated storage of samples F, G, and H, though ETU levels were held down with CHjO and with CHjO/ZnClj. Overall, stability is good for the samples made from maneb dihydrate.

Example 8 Table I Maneb Aqueous From Amobam ppm ETU_ % Zn, Total as-made 0.19 after 1 wk. at 45° Amobam, as previously exemplified with nabam, can also provide low-ETU aqueous maneb when used in conjunction with Zn2A (soluble) + CH^O. The levels of ETU obtained appear to be somewhat higher than those obtained when the maneb is derived from nabam or CH2O/nabam.

Claims (10)

1. A process for preparing a stabilized aqueous composition of maneb which comprises mixing or washing said maneb with aqueous formaldehyde and an aqueous solut5 ion of a soluble zinc salt, combined or in either order, and if necessary mixing the result with further water to obtain an aqueous composition comprising maneb and 0.05 to 5.0% by weight of the total composition of formaldehyde and 0.05 to 5% by weight of the total composition, 10 calculated as Zn, of said soluble zinc salt.

2. A process according to claim 1 wherein from 0.1 to 2.5% by weight each of zinc and formaldehyde are present in said composition.

3. A process according to claims 1 or 2 wherein the 15 resultant stabilized composition contains 10 to 50% by weight of maneb.

4. A process according to claim 3 wherein said composition contains 25 to 40% by weight of maneb. 5. Formaldehyde and 0.05 to 5.0% by weight (based on Zn) of a soluble zinc salt. 16. A composition according to claim 15 comprising 25 to 40% by weight of maneb and 0.1 to 2.5% by weight each of formaldehyde and zinc.

5. A process according to claim 1, substantially as 20 described herein.

6. A process according to claim 1 wherein said maneb has been made by a process which comprises reacting a disodium, dipotassium, or diammonium salt of ethylenebis (dithiocarbaroic acid) with a water-soluble manganese 07/ ¢¢7 1 }i> W0iw·' e ii^neb, aiid recovering the maneb.

7. A process according to claim 6 wherein the disodium 5 or dipotasslum salt of ethylenebls(dithiocarbamic acid) is treated with formaldehyde prior to reaction with the water-soluble manganese (II) salt.

8. A process according to claim 6 or 7 in which the water-soluble manganese (II) salt is reacted with the di10 sodium salt of ethylenebis(dithiocarbamic acid).

9. A process according to claim 6 in which the water soluble manganese (II) salt is reacted with the diammonium salt of ethylenebis(dithiocarbamic acid). 10. A process according to any of claims 6 to 9 in 15 which maneb is precipitated in the presence of a dispersant. 11. A process as claimed in any of the preceding claims wherein the maneb in said stabilized composition is substantially in the dihydrate form. 12. A process according to claim 6, substantially as 20 described herein. 13. A process substantially as described herein with reference to any one of the Examples. 14. An aqueous composition of maneb prepared by the process of any of claims 1 to 13. 15. A composition according to claim 14 comprising 10 to 50% by weight of maneb, 0.05 to 5.0% by weight of

10. 17. A composition according to claim 14, substantially as hereinbefore described.