CA1174594A - Aqueous fungicidal formulations and their preparation - Google Patents

Abstract

Title Aqueous Fungicidal Formulations and Their Preparation Abstract of the Disclosure A stable aqueous composition of maneb which includes a soluble zinc salt and formaldehyde.

Description

3~745~

Title Aqueous Fungicidal Formulations and Th~ir Preparation Back~oun~ of the~ Invention This invention relates to the preparation of ~table formulations of manganese(II) ethylenebis~
(dithiocarbamate) (maneb) and, more particularly, to the preparation of aqueous formulations of maneb having unexpectealy low concentrations of ethylene-thiourea (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 lS storage.
Although much work has been done which relates to improving the stability of maneb, there are no known references which teach the present invention, L. Donev IKhimiyai industriya (Sofia) 41, lO0-lOl (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 ~rom a ormaldehyde-treated reaction mixture.
~he maneb is precipitated in aqueous medium rom a '~

9~

water-soluble s~lt o~ ethylenebis~dithiocarbamic acid) and a water-~oluble manganese(II) salt. Formaldehyde is a~ded to th~ reaction mixture after preclpitation.
The reference does not ~iscuss ETU concentration.
~ S. Patent 2,974,156 teaches that hexa-~ethylenetetram~ne ~HMTA~ can be added to maneb ~o improve stability.
U.S. Patent 3,173,832 teaches that para-formaldehy~e can be addea to maneb to improve stability and that a soluble zinc salt can reduce phytotoxicity.
Althoug~ the prior art discloses various methods o~ formulating maneb to improve strength and/or stability of the product, no known references discuss the preparation of maneb having a low ETU
concentration, eit~er as 2 dry or an aqueous product.

Summary of the Inventlon The present invention is a process for preparing a unique aqueous composition of maneb having an unexpectedly low concentration of ethylenethiourea consisting essentially of maneb, 0.05 to 5.0% by weight of a soluble zinc salt ~on Zn basis) and 0.05 to 5.0% by weight formaldehyde.
The combination of zinc (soluble Zn2~) and formaldehyde in aqueous medium with maneb unexpectedly retards the buildup of ETU in maneb.
Detailed Description of the Invention The maneb used in pxeparing the co~positions of this invention can be dihydrate, anhydrous or partially dehydrated~ The dihydrate form of maneb is preferred because o~ it~ hi~her overall stability with -respect to decomposition to ETU and because it can be formulated in a~ueous mixtures dtrectly without having to dry it first.

~745~4 Maneb, which has been prepared according to the process disclosed in Canadian patent application Serial No. 334 102 filed 1979 August 20, 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) or 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). Alter-natively 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 dispersantsinclude 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 o~ the maneb reaation mixture, which may neaessitate other means ~e.g., aentrifugation) for satisfactory maneb recovery. Generally, the amount of disper$ant can range from about 0.1 to 10% of the reaction mixture.
* denotes trade mark 4S9~

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 S is used at all.
~ e maneb concentration in the compositions of this inYention can vary ~epending on the strength desire2. For example, maneb strength can vary from about 10 to 50~ by weight, with 25 to 40% by weight la 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 form~lated as an aqueous composition.
Although either formaldehyde or soluble zinc salts 15 might contri~ute toward producing low ETU concentrations in fresh aqueous mane~ compositions, storage studies show that a zinc salt, in the absence of formaldehyde, can actually increase ETU concentration. Even though formal~ehyae alone operates to minimize ETU levels, 20 the use of both a soluble zinc salt and formaldehyde in the composition can produce surprisingly low ETV levels in aqueous maneb.
The compositions of this invention will ordinarily contain about 0.05 - 5,0~ by weight of zinc 25 salt (based on Zn) and about 0.05 - 5.0~ by weight of formaldehyde. Prefera~ly, the compositions will contain about 0.1 to 2.5% by weight each ~f zinc salt and formaldehyde. Too much formaldehyde can create odor or phyto~oxicity problems and too much soluble zinc 30 salt in the composition can affect maneb stability.
~his invention is illustrated in a preferred embodiment in Table A and the exampl~s which ~ollow. The table and examples are not to be considered as limiting, but merely exemplary. ~he significant feature i8 the co~bined 35 action of formaldehyde and a soluble zinc salt in reducing ETU concentrations in aqueous maneb composi-tions.

~74~9~
Additional formulation ingre~ients, s.uch as dispersants, anticorrosion agents, etc., as well as other fungicides, such as methyl 2-benzimidazole-carbamate (car~endazim), and 2 cyano-N-~(et~ylamino)-S carbonyl]-2--~methoximino)acetamide (Curzate*), can be present as long as they do not cause ETU ~uildup in the formulation or react substantially with formaldehyde to the detriment of thP formulation.
As used he~e.in, the te~m '!mancQzebt' is intended to ~ean a complex of maneb and zinc resulting from reaction of maneb with.a soluble zinc salt under wet conditions. IFor a description o~ maneb and mancozeb~ see Pesticide Manual, ;th Edition, edited by H. Martin and C. R. Worthing, issued by the British Crop Protection Council, pages 328 and 32g.]
The term ~Imaneb~ is intended to include ', mancozeb when the maneb has been treated under wet conditions with a soluble salt of zinc.
* denotes: trade mark ~7~5~4 Table A

¦~ormaldehyde (CH2O)/Nabam + MnS04¦

Dispersant ~ /
Maneb Fi Lter Cake~

1. Wash with water

2. Wash with zn2f (.soluble) I ~ (a)*

3. Add into agueous ~ f ¦ Maneb + Zn2+ + CH2O¦ = stabilized aque-ous composition The preparation of the co~position may be accomplished several ways:
(a) As shown abo~e, marked with the asterisk.
20 (b) Add the filter cake directly into aqueous CH2O + Zn2~ ~soluble~;
(c) Wash the filter cake with aqueous ~CH2O + Zn2+
(soluble)~ and then add to water;
(d) Wash with aqueous CH2O and add to aqueous Zn2+
(soluble);
(e) Wash with aqueous Zn2~ (soluble) and add to aqueous CH2O.
Any other suitable variation o:E ~he above procedures, e.g., wash with aqueous Zn2~ (soluble) and add to water 30 simultaneously wlth ~H2O, can be used.
~ urther reduction in maneb particle size can be accomplished, if desired, by wet-milling. If desired, the conversion o~ maneb to zinebl during tOe ~illin5 pro:e~s can be avoided by adding 35 1 zineb - zinc ethylenebis(dithiocarbamate) :~7~594 zn2~ (solu~le) after the milling process.
Wet-milling is further described in U.S. Patent 3,157,486 A

5Exa~Dle 1 Ta~le s Formal~ehy~e/Nabam:
Dispersant Duri~g ~recipitation:
10Maneb Aqueous ¦ CH20/Nabam I MnS04~

Dispersant 1~ ~
~Water-washed M, Lneb Filter Cakel -- --ZnC12 Wash;
~dd into water with ~0: ~2% CH2O
¦Mancozeb Aqueous Suspension with CH~O
-- ~ .
P~M Agln~
ETU 1-2 1 day, r~om t~mperature (R.T.) 2 0 days, R . T .

In~o a flask containing a stirred ~2-blanketed solution o~ 15.2 g. of Polyfon ~ in 1160 ml. of water at 2Sn was simultaneously added during a 50-minute peri-od an aqueous solution o~ 723.2 g. of 23~ MnSO4 and ~ormaldehyde/nabam ~1115 g. of 23~ nabam and 40.6 g.
o~ 37% CH20 mixed and let stand at ambient temperature ~or 30 minutes beore beginning to use in reaction with MnSO4]. After 10 minutes, the maneb was ~iltered o~f, L5~

washed with water and with 1 kg. of 7% ZnC12. The filter cake was s~spended in aqueous formal~ehyde such that the ~aneb concentration (expressed as anhy~rous) was a~out ~5% 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 exarnple is usually ~eferred to as a "heel pr~cess".
~_ Example 2 Table C

Fonmaldehyde/Nabam;
Dispersant During Precipitation;
Maneb Aqueous ¦ CH2o/Nabam ~ Mn ~
¦Dispersant ___ IWater-washed Maneb Filter Ca ZnC12 Wash;
Put into water with ~ ~ 0.1% CH2O
. _ , Mancozeb Aqueous Suspension with CH20 PPr5 Aging ETU 4 2 days, R.T, 2 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.

9~

Exam~le 3 Table D
¦ C~20/Nabam + MnS04 ¦
. .
Beel Pr~cess ! 25 with Polyfon H, ~5%
~ , ~Water-washe2 Maneb ~ilter 3 .

No Wash ~ nC12 Wash rManebFilter Cake¦¦~ancozeb Filter Cake~

Add ~ Add H2O ~ Add ~ Add H2O +
H20~ \ CH20 ~ \~CH20 ~Maneb ~ Maneb ~ancozeb¦
aqueousI aqueous ~gE~ aqueous l wit~ CH2O I
A' B, Cl D
I
ETU51 12 3 1 ~ 1 day., ppm . .
121 34 728 <33~ ~ 51 w~-*This figure is unusually high ~ecause of interference peaks encountered in the liquid chromatographi.c method used ~or ETU assay. The true ETU level could possibly b~ as low as zero 7 i~ all the inter~erence plus ETU is reported as ETU, the ETU level is ~till less than 33 pp~. Similar comments apply to other examples herein where a "~No." is reported ~or ETU eoncentration.

~7~59~

The same general proce~ure was followed as in Example l! except the filter caXes were split at various stages as indicated to show effects of the CH2O and ZnC12 as to their absence, separate use, and combined use. Initially, CH2O and ZnC12 separately, and especially CH2O and ZnC12 combined, help reduce ETU, whereas after 1 wee~ at 45, the combination of CH2O and ZnC12 is more favorable. The CH2O concentra-tion in samples B and D was a~out 2%, 1 0 ~
Example 4 Table_E
r ~lain Nabam + MnSO4¦
' - - -~eel Pr~cess! 25 No Dispersant \ , IWater-washea Mane~ Filter Cakel .. . _ .. . . .

No Wash ~ ZnC12 Wash ¦Maneb Filter Cake~ ¦Mancoæeb Filter Cakel Add 1 Add H2O ~ Add 1 Add H2O +
H20 / \ CH20 H2Y \ CH20 ~ J ~
Maneb ¦Man~ozeb¦
aqueous ~ laqueous I with CH~O I¦with CH7O¦

A 1 B, C l D
t -ETU57 12 31 ~ 1 day., pp~ R.T~
518 40 ~45 174~9~
The sam~les were ~repared generally as describe~ in Example 3, except that plain nabam (no CH20) was used to prepare the initial maneb precipitate in the absence of a dispersant. Again, the sample (D) wit~ ~oth CH20 and Zn2~ is more ~atisfactory.

. Example 5 Ta~le ~
~Plain Nabam + MnS04¦

Heel Process~ 25n with Polyfon~9 H, Q, 5%
1 5 \ ~ .
Water-washed Maneb Filter Cake¦

N~ Wa~nC12 Wash ¦Maneb Filter Cake1 ¦Mancozeb Filter Cake¦

Add ~ Add H20 + Add 1 Add H20 +
H20l~/ ~ CH~0 ~ \~CH20 ¦Maneb ¦ I Maneb ¦Mancozeb1l Mancozeb laqueous J aqueous laqueous I aqueous ll with C~20 II with CH20 A~ B, Cl D, ETU 112 4 113 ~ 2 day., 297 66 ~450 __ . .

e.
~:~7~L~ii9~

The. samples were ~ade generally as described in Example 4, except that dispersant was present during precipitation of maneb, A~ain ~ the sample (D) with both CH2O and Zn2~ is more satisfactory, S
Example 6 Table G
I CH20/Nabc m ~ MnSO~

~eel Proces 5 ~ 2 5 \ No Dispersant ¦ Water-washea Mc neb Filter Cak3 No Wa ~ nC12 Wash ¦Maneb F~ rCak~ ~Mancozeb ~Filter cakeJ

Add f ~ Add H2O ~ Add 1 Add H2O +
H20~ \ CH20 ~ \CH20 1 Maneb lManco zeb ¦ ¦ Ma=
aqueo ~ aqueous ~aqueous ¦¦aqueous ~ I with C~2O ~ Iwith CH~O
25 A~ B, Cl Dl ETU 27 5 2 1 r 2 day., ppm S_ R .'T, 1~2 24 ~4 ~16 ~ wk~

~ he ~ame general procedure was followed a~s in Example 3, eXcept that no dispersant was present durlng precipitation. The particle size of the maneb obtained in this example was ~ar greater than that obtained in Example 3. It is perhaps for this reason 1~7~Sg~

that in this example alone, t~e presence of Zn2+
(in absence of CH20, sample C) has helped hold down ETU concentration during the l-week, 4S
storage of the aqueous ~aneb as compared to sample A, -~L~7459~

Example 7 Table H

Mane~ Dihydrate YS. Maneb Anhydrous For Mane~ ~ueous Suspensi~ns ¦Plain Nabam + MnS04 ¦

10 ¦ ~eer-W~sh~d I Dry to ¦Anhydrous 1 Maneb Filter Cake = 0% H 0 Maneb , Maneb Dihydrate + Water 2 (38p~ m ETU)~

L/
~1 H20 -+1 C~2 + I
~ ZnC12¦ 2 ETU 101 10 18 2 ~3 da., ppEn 306 9 324 2 ~ 510 wk., 1- 1H2~+
¦;~ rH2 ~1 CH20 +
~ ¦ZnCl~¦ ZnC12 __ E F G H

ETU 215 22 137 3 ~R.T.
pp~
400 25 1561 ~120 ~ 5o ~ 7~59~

In this example, ~aneb dihydrate was compared to anhydrous maneb in aquecus composition. In each case, the presence or absence of ZnCl2 and CH2O and their combination were examined, Pr~ssure built up ~uring the accelerated storage o~ samples F, G, a~d H, ~hough ETU levels were held down with CH2O and with CH2O/ZnCl2. Overa~l, stability is good for the samples made from maneb dihydrate.
.. . . . .. ..
Example 8 Table I

Maneb Aqueous From Amobam ¦Amobam + MnS04¦
_ Heel Process \ /
_ . __ _ _ Water-Washed Mane~ Filter Cake ZnCl2 Wash /
. . .
Mancozeb Filter Cake ~ Add H2O + CH2O

¦ Mancozeb Aqueous + CH2O~

~ e~L33Y~ 2n, ~otal 16 as-made ~,l9 25 a~ter l wk. at 45 ~mobam, as previously exemplified with nabam, can also provide low-ETU aqueous maneb when used in conjunction Wit}l Zn2' ~soluble) + CH2O. The levels of ~il745~

ETU obtained appear to be somewhat higher than those obtained when the maneb is deri~ed from nabam or CH20/nabam .

_

Claims (9)

WHAT IS CLAIMED IS:

1. In a process for preparing a stabilized aqueous composition of maneb by reacting a disodium, dipotassium, or diammonium salt of ethylenebis(di-thiocarbamic acid) with a water-soluble manganese(II) salt in aqueous medium to precipitate maneb, and re-covering the maneb, the improvement which comprises mixing the maneb in an aqueous medium with about 0.05-5.0% by weight of formaldehyde and about 0.05-5.0%
by weight (based on Zn) of a soluble zinc salt.

2. The process of Claim 1 including the additional step of treating the disodium or dipotassium salt of ethylenebis(dithiocarbamic acid) with formaldehyde prior to reaction with the water-soluble manganese(II) salt.

3. The process of Claim 1 in which the water-soluble manganese(II) salt is reacted with the disodium salt of ethylenebis(dithiocarbamic acid).

4. The process of Claim 1 in which the water-soluble manganese(II) salt is reacted with the diammonium salt of ethylenebis(dithiocarbamic acid).

5. A stabilized aqueous composition of maneb of low ethylenethiourea content having a maneb concentration of about 10 to 50% by weight which is prepared by the process which comprises reacting a disodium, dipotassium, or diammonium salt of ethylene-bis(dithiocarbamic acid) with a water soluble manganese (II). salt in aqueous medium to precipitate maneb, re-covering the maneb and then mixing the maneb in a aqueous medium with about 0.05-5.0% by weight of formaldehyde and about 0.05-5.0% by weight (based on Zn) of a soluble zinc salt.

6. The stabilized aqueous composition of Claim 5 in which the disodium salt of ethylenebis-(dithiocarbamic acid) is reacted with a water-soluble manganese(II) salt.

7. The stabilized aqueous composition of Claim 6 in which the disodium salt of ethylenebis-(dithiocarbamic acid) is treated with formaldehyde prior to reaction with the water-soluble manganese (II) salt.

8. The improvement of Claim 2 in which the salt of the ethylenebis(dithiocarbamic acid) and the manganese(II) salt are reacted in the presence of a dispersant.

9. The stabilized aqueous composition of Claim 7 in which maneb is precipitated in the presence of a dispersant.