Carbonyl sulphide insecticide

Details Carbonyl sulphide insecticide Carbonyl sulphide insecticide

1997-11-10

2001-03-20

Pak, John (Department: 1616)

Drug, bio-affecting and body treating compositions

Inorganic active ingredient containing

Elemental sulfur or compound thereof

C424S040000, C424S699000, C424SDIG001, C426S319000, C426S312000, C422S032000, C043S124000, C043S125000, C047SDIG001

Reexamination Certificate

active

06203824

ABSTRACT:

TECHNICAL FIELD
This invention concerns gaseous fumigants. More particularly, it concerns the gas carbonyl sulphide (COS), which has also been termed carbon oxysulphide, as a fumigant.
BACKGROUND OF THE INVENTION
Fumigants are widely used for the disinfestation, and protection against infestation, that is usually required to protect particulate materials (such as grain) and other stored produce (including durable and perishable foodstuff), porous bulk materials (for example, soil or timber) and spaces (typically, empty buildings). An ideal fumigant should be toxic to insects, mites, nematodes, bacteria, fungi and moulds. It should be effective in low concentrations. It should have a low absorbtion by materials in the fumigated region. It should have a low mammalian toxicity and leave either no residue or an inert residue. In addition, the ideal fumigant should present no difficulties as far as safe handling is concerned, and it should not adversely affect the commodity or space that is being fumigated.
No fumigant meets all of these “ideal” criteria. The two fumigants most commonly used in the fumigation of grain, other particulate materials, fruit and timber are phosphine and methyl bromide. Phosphine is the preferred fumigant for grain stores and the like because it is effective against grain pests and leaves little residue (which is essentially a harmless phosphate). However, phosphine is spontaneously combustible when its concentration exceeds a relatively low value.
Methyl bromide is more toxic to grain pests than phosphine when used for short periods of fumigation, but phosphine is more toxic to grain pests when long term fumigation is effected. Methyl bromide has a lower flammability than phosphine, but recent work has shown that methyl bromide depletes the ozone layer. Thus approval of methyl bromide as a fumigant is currently under review, following the Montreal protocol.
Other fumigants that have been used against grain pests include acrylonitrile, carbon disulphide, carbon tetrachloride, chloropicrin, ethylene dibromide, ethylene dichloride, ethylene oxide, hydrogen cyanide and sulphuryl fluoride. It will be noted that a halogen is present in the majority of these “conventional” fumigants, none of which has the “ideal” fumigant properties.
For many years, there has been a. constant seeking of new fumigants and there is no doubt that the quest for improved fumigants will continue.
DISCLOSURE OF THE PRESENT INVENTION
The prime object of the present invention is the provision of a new fumigant that has properties which make it a viable alternative to the conventional fumigants, particularly in the control of insects, mites and moulds.
This objective is achieved by the use of carbonyl sulphide as a fumigant.
Carbonyl sulphide is a well-known compound. It is a gas at STP (Standard Temperature and Pressure), with a boiling point of −50.2° C. It is colourless, flammable (but not as flammable as phosphine), and soluble in water. Its solubility in water is 1.4 grams per litre at 25° C., compared with the aqueous solubilities of 13.4 grams per litre and 2.2 grams per litre for, respectively, methyl bromide and carbon disulphide (phosphine has been reported to be “sparingly soluble” in water). When in aqueous solution, it slowly decomposes. Commercially, carbonyl sulphide is normally supplied in liquefied form in cylinders at about 160 p.s.i.g. However, it occurs naturally, being the major sulphur species in the atmosphere (where it occurs uniformly in the troposphere and lower troposphere at a concentration of 1.3 micrograms per cubic metre) and part of the natural sulphur flux in soils and marshes. Carbonyl sulphide is also formed from the anaerobic degradation of manure and compost and is present in most pyrolysis products and in oil refineries.
As a consequence of its role in the sulphur cycle, its presence in pyrolysis products and its use as a chemical feedstock, carbonyl sulphide has been widely studied, and its properties and uses are well known. However, an extensive review of the technical literature, and a Dialog computer-based evaluation search (conducted in the files of
CAB Abstracts
1972-1991
, Biosis Previews
1969-1991
, Life Sciences Collection
1978 to 1991
, Agricola
1970 to 1991
, Agris International
1974 to 1991
, EuroDean Directors of Agrochemical Products
and
Oceanic Abstracts
1964 to 1991), has revealed no use or contemplated use of carbonyl sulphide as a fumigant, and no reference to the insect toxicity of carbonyl sulphide. A separate manual search of
Chemical Abstracts
extended back to the year 1900, but found no reference to carbonyl sulphide as a fumigant.
It is known that carbonyl sulphide is a mammalian toxic gas. In the article by Robert J Ferm entitled “The Chemistry of Carbonyl Sulfide”, which was published in
Chemical Review
, volume 57, 1957, pages 621 to 637, three references are given in support of the statement at page 627 that:
“Cold blooded animals show more resistance to carbonyl sulfide than do warm-blooded animals. Mice and rabbits die quickly when they are exposed to air containing more than 0.3 per cent carbonyl sulfide.”
And in the current
Matheson Gas Products Catalogue
, in the section entitled “Carbonyl sulfide” (pages 115 to 117), it is stated that (page 115):
“Carbonyl sulphide acts principally upon the central nervous system, with death resulting mainly from respiratory paralysis. Rabbits showed some ill effects after exposure of one half hour to 1300 ppm. With mice, death occurred in ¾ minute when they were exposed to 8900 ppm, in 1½ minutes on exposure to 2900 ppm, and in 35 minutes on exposure to 1200 ppm. Sixteen minutes exposure to 900 ppm caused no perceptible effects.”
However, it is known that gaseous compounds which are lethal to humans and smaller mammals, and also to cold-blooded vertebrates, may not be toxic to insects, moulds, mites and the like. One example of such a mammalian toxic gas is carbon monoxide. Thus, simply because carbonyl sulphide has a measured toxicity to mammals, it would be incorrect to conclude that carbonyl sulphide will also kill insects, moulds, mites and the like.
The present inventors, therefore, were surprised to find that carbonyl sulphide is useful as a fumigant. However, the present inventors have now established that when carbonyl sulphide is used as a fumigant, it may be applied undiluted, in a manner which allows it to mix with the atmosphere within the system under treatment, or it may be applied in a mixture with an inert diluent gas. The diluent gas will be used when a more dilute form of the fumigant is to be dispensed, or as an inhibitor to reduce flammability of the carbonyl sulphide. The diluent gas will normally be air, although other suitable carrier gases may be used.
The present invention also encompasses a method of fumigation of particulate materials, commodities, timber, spaces and soils which comprises applying gaseous carbonyl sulphide thereto.
Further details will now be provided, by way of example only, in the following discussion of the properties of carbonyl sulphide as a fumigant, including examples which demonstrate such properties.
DISCUSSION OF THE INVENTION
The effectiveness of a fumigant is usually expressed as a “CT product”, which is the concentration×time product for a specified effectiveness (usually for LC
95
or LC
99
, which are the lethal concentrations—doses—for 95 per cent and 99 per cent, respectively, of the population against which the fumigant is directed), expressed in milligram hours per litre. Normally, the temperature at which the fumigant is used is also given, for, in general, the higher the temperature of treatment with a fumigant, the lower the dose or concentration that is necessary to achieve a required effectiveness.
The concentration×time products, expressed in the usually adopted terms of LD
90
, LD
95
or LD
99
(although strictly speaking these figures are L(C×T)
90
, L(C×T)
95
and L(C×T)
99
values), for eleven previously known fumigants that are still in use agai

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