Phenol ester mixture

Details Phenol ester mixture Phenol ester mixture

1994-04-18

2001-07-03

Clardy, S. Mark (Department: 1616)

Plant protecting and regulating compositions

Plant growth regulating compositions

Organic active compound containing

Reexamination Certificate

active

06255252

ABSTRACT:

This invention relates to a mixture of herbicidal esters of 3,5-dibromo-4-hydroxybenzonitrile and compositions containing it.
3,5-Dibromo-4-hydroxybenzonitrile (hereinafter referred to as ‘bromoxynil’) and bromoxynil n-octanoate, or 3,5-dibromo-4-n-octanoyloxybenzonitrile, (hereinafter referred to as ‘bromoxynil octanoate’) are well known herbicides which are widely used to control the growth of annual broad-leafed weeds. Bromoxynil octanoate is used extensively as a contact herbicide for the control of seedlings of broad-leafed weeds in cereal crops and to control perennial weeds in industrial and other non-crop situations.
Bromoxynil octanoate is a cream-coloured waxy solid, which when pure, melts at 45-46° C. The grade of bromoxynil octanoate used commercially as a herbicide is usually somewhat less pure and melts at 40-44° C. Bromoxynil octanoate is practically insoluble in water at 25° C. and, for use as a herbicide, it is usually formulated as a liquid concentrate comprising a solution in a suitable hydrocarbon oil, together with conventional additives, e.g. emulsifying agents, which concentrate is diluted with water to give spray fluids suitable for application to weeds. Commercially available liquid concentrates contain up to 240 g per liter of bromoxynil phenol equivalent. (By the term ‘phenol equivalent’is meant the 3,5-dibromo-4-hydroxybenzonitrile moiety content of the formulation).
The n-heptanoic ester of bromoxynil, 3,5-dibromo-4-n-heptanoyloxybenzonitrile (hereinafter referred to as ‘bromoxynil heptanoate’), a cream-coloured waxy solid melting at 39.0° C., possesses herbicidal properties similar to those of bromoxynil octanoate and may be formulated and used in a similar fashion, but bromoxynil heptanoate has not hitherto been widely used as a herbicide. Bromoxynil octanoate and bromoxynil heptanoate may be prepared by known processes, for example as described in British Patent Specification No 1067033, by the esterification of 3,5-dibromo-4-hydroxybenzonitrile with n-octanoic acid anhydride and n-heptanoic acid anhydride, respectively.
As a waxy solid at normal ambient temperature, bromoxynil octanoate is less convenient to handle and transport than would be the case if it were a liquid at the same temperature. Furthermore, when preparing herbicidal liquid concentrates, it is necessary to melt the bromoxynil octanoate in order to facilitate mixing with the hydrocarbon oil and, if desired, conventional additives. This need to melt the bromoxynil octanoate necessitates the use of valuable energy which would otherwise be avoided.
As a result of research and experimentation, it has been found that a substantially 1:1 molar ratio mixture of bromoxynil octanoate and bromoxynil heptanoate, i.e. a mixture comprising substantially 50 molar percent of bromoxynil octanoate and substantially 50 molar percent of bromoxynil heptanoate, possesses an unexpectedly lower melting point than bromoxynil octanoate alone or bromoxynil heptanoate alone, or mixtures thereof in other proportions, which lower melting point renders the aforesaid substantially 1:1 molar ratio mixture of bromoxynil octanoate and bromoxynil heptanoate particularly advantageous in terms of ease of transportation, handling and formulation into herbicidal liquid concentrates and in the reduction of energy input necessary in the preparation of herbicidal liquid concentrates.
The aforesaid substantially 1:1 ratio molar mixture of bromoxynil octanoate and bromoxynil heptanoate possesses herbicidal properties very similar to those of bromoxynil octanoate and formulations of the mixture may be used in the same manner and at the same rates of application as bromoxynil octanoate to control the growth of weeds.
The substantially 1:1 molar ratio mixture of bromoxynil octanoate and bromoxynil heptanoate according to the present invention may be prepared by mixing the appropriate amounts of bromoxynil octanoate and bromoxynil heptanoate or by reacting bromoxynil with a substantially 1:1 molar ratio mixture of suitable reactive derivatives of n-octanoic acid and n-heptanoic acid, for example a substantially 1:1 molar ratio mixture of n-octanoic acid anhydride and n-heptanoic acid anhydride or a substantially 1:1 molar ratio mixture of n-octanoyl chloride and n-heptanoyl chloride.
By the term ‘substantially 1:1 molar ratio mixture’ as used in the present specification in respect of mixtures of bromoxynil octanoate and bromoxynil heptanoate and mixtures of suitable reactive derivatives of n-octanoic acid and n-heptanoic acid, is meant mixtures wherein the molar ratio of bromoxynil octanoate to bromoxynil heptanoate and reactive derivative of n-octanoic acid to reactive derivative of n-heptanoic acid, is from 1:1.5 to 1.5:1, preferably 1:1.02 to 1.02:1, and more especially 1:1.
The unexpectedly low melting point of the substantially 1:1 molar ratio mixture of bromoxynil octanoate and bromoxynil heptanoate in comparison with bromoxynil octanoate alone or bromoxynil heptanoate alone or mixtures thereof in other proportions has been demonstrated in the following experiment:
Experiment 1
Mixtures of bromoxynil octanoate and bromoxynil heptanoate in the molar ratios indicated in the following Table I were prepared by mixing appropriate amounts of the two esters. Each mixture was then melted and the molten mass was stirred to render it homogenous. The molten mass was then rapidly cooled to −10° C. by external cooling. A sample of the crystals from the solid frozen mass thus obtained was placed in a capillary tube which was then placed in a stirred water bath. The temperature of the water bath was raised at a rate of 0.5° C. per minute and the temperature at which a meniscus first appeared in the tube was recorded as the melting point of the mixture in question.
The results obtained are given in the following Table I.
TABLE I
Molar percentage
Molar percentage
of Bromoxynil
of Bromoxynil
octanoate in
heptanoate in
Melting
mixture
mixture
point (° C.)
100
0
44.5
88.1
11.9
41.5
78.1
21.9
38.5
69.7
30.3
35.0
57.4
42.6
30.0
48.8
51.2
22.0
38.1
61.9
28.0
26.9
73.1
33.0
17.7
82.3
34.0
9.4
90.6
37.0
0
100
39.0
As already mentioned, bromoxynil octanoate is commercially available as a liquid concentrate comprising a solution of up to 240 g per liter of bromoxynil phenol equivalent in a suitable hydrocarbon oil, together with conventional additives, e.g. emulsifying agents. For reasons of convenience and economy, liquid concentrates containing the maximum amount of bromoxynil octanoate are preferred. Such liquid concentrates are frequently distributed and marketed during the winter months involving transportation and storage at relatively low temperature. With commercially available formulations comprising 240 g per liter of bromoxynil octanoate in a suitable hydrocarbon oil, crystallisation may begin to occur at temperatures as high as −7° C. The occurrence of crystallisation in such bromoxynil octanoate liquid formulations presents a serious problem since the formulations are thereby rendered less effective or even completely unusable and the crystals are, in practice, extremely difficult to re-dissolve. It is, therefore, usually necessary to take special precautions in transport and storage to avoid permitting the temperature of the liquid formulations to fall to a level at which crystallisation occurs.
The substantially 1:1 molar ratio mixture of bromoxynil octanoate and bromoxynil heptanoate provided according to the present invention provides the further unexpected advantage of possessing significantly greater solubility in hydrocarbon oils than bromoxynil octanoate alone, bromoxynil heptanoate alone or mixtures of bromoxynil octanoate and bromoxynil heptanoate in other molar ratios, thereby permitting liquid formulations to be prepared comprising a solution of a substantially 1:1 molar ratio mixture of bromoxynil octanoate and bromoxynil heptanoate in a suitable hydrocarbon oil, e.g. mineral oils and more especially mineral oils having a flash point higher than 34° C. Suitable mineral oils include, in particular, mineral o

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