This invention relates to a denaturant formulation suitable for discouraging the ingestion of hydrocarbon liquids particularly paraffinic liquids such as lamp oil, white spirit, kerosene and other hydrocarbon solvents.
Liquid hydrocarbons are widely used for various technical purposes and are often available for household purposes, where unguarded use or storage may present risks to children and domestic animals who may confuse them with potable liquids. This is especially so in third world countries where near starving children will consume virtually any liquid in their desperation to quench a thirst. The inadvertent consumption of such liquids by vulnerable individuals is also a high risk because they are available as essentially colourless transparent liquids which are visually indistinguishable from water. The physiological damage arising from deliberate or inadvertent consumption of these liquids is serious and may be fatal. However, it is not practical to keep such substances permanently under secure conditions to avoid unauthorised access or uninformed intervention. Therefore it is desirable to denature the liquids in some way to render them undrinkable or at least to discourage ingestion thereof.
Aversive agents are known which impart a highly bitter taste to substances when mixed therewith. These cause such a bitter taste if an attempt is made to swallow the substance that the substance is rejected immediately, which usually avoids absorption or ingestion of amounts having any lasting harmful effect. Reference may be made to earlier patents including GB-A-955 309, for quaternary salts and compositions containing them, and GB-B-2 212 814 relating to aversive agents for liquid hydrocarbons.
Denatonium benzoate otherwise known as lignocaine benzyl benzoate is cited in the Guinness Book of Records as the most bitter substance known to man, and its preparation and properties are described in GB-A-955 309. It is available commercially under the Registered Trade Mark "BITREX". Other denatonium salts are known in the literature. Denatonium saccharide is a bittering agent analogous to denatonium benzoate and is described in US-A-4 652 577.
Liquid hydrocarbons of the type of concern here are predominantly organic liquids of an aliphatic character (alkanes) and mainly recognisable as of the liquid paraffin type but the invention is not restricted to a particular petroleum distillate fraction commonly called paraffin oil. The problem may be explained more generally by an understanding that aliphatic liquids are useful because of their relative chemical inertness. This, for example, makes white spirit useful as a diluent in enamel paints or as a cleaning liquid for removal of certain paints from surfaces without chemically attacking the surface. This predictable non-reactive character and stability, whilst providing desirable properties for marketing products based on such liquids, also presents a problem when seeking to include a denaturant or aversive agent therein. Thus the most preferred denaturant, denatonium benzoate, is extremely insoluble in apolar liquids. Therefore even though that denaturant would exhibit an acceptable level of aversive activity at concentrations as low as 10 ppm it has not proved possible to introduce it directly to liquid hydrocarbons and maintain a satisfactory level of concentration therein for a sufficient period of time even to satisfy a typical shelf life before eventual use. As cited in GB-B-2 212 814, the denaturant does not form a stable solution in kerosine or the like liquids and tends to migrate rapidly to the container walls.
This problem was addressed in GB-B-2 212 814, by introducing the desired denaturant, and at least one surfactant to the liquid hydrocarbon. This had the reported effect of permitting the desired aversion agent which has a high hydrophilic character but low lipophilic character to function in the desired manner without any inhibition of the rapid organoleptic reaction.
The need to introduce surfactants inevitably adds some expense to the product. Furthermore, there is now some doubt as to the effectiveness thereof with all target products, particularly with the higher levels of purity now achievable in comparison with the equivalent products routinely produced commercially over a decade ago. Presently there is tighter control on permissible levels of incidental aromatic contaminants in current commercial products, < 0.1% being achievable for some white oils of the n-paraffin type. It is postulated that the effectiveness of the previous proposal may have been enhanced by such incidental contaminants which facilitated the "solvation" of the small amounts of the preferred denaturant on account of its aromatic components.
Having researched this problem it is now proposed to adopt a different approach to achieving the objective of introducing a sufficient amount of hydrophilic denaturant or aversive agent into a liquid hydrocarbon of an essentially aliphatic character to deter ingestion of physiologically harmful amounts thereof .
The aforesaid objective is achievable as described hereinafter and defined in the appended claims by utilising a stabiliser in the form of a co-solvent which is at least miscible with the target hydrocarbon and has sufficient affinity with the selected aversion agent which is a denatonium salt, (preferably denatonium benzoate) to permit introduction of effective amounts thereof to the target hydrocarbon with satisfactory stability of the final formulation.
Suitable co-solvents for the purposes of the invention are C6-C20 aliphatic or alicyclic alkanols, including diols and diol mono-ethers, esters, and mixtures thereof having at least one available, i.e. underivatised, hydroxyl group. A preliminary screening test to confirm or determine suitability of a co-solvent from amongst these classes of solvents would include determining if the solvent under consideration is miscible with the hydrocarbon to be denatured and if it is also capable of dissolving the desired denaturant at a satisfactory level, say 0.1%. Preliminary work suggests that substituted alkanols would be acceptable.
Thus, according to the present invention, there is provided a method for rendering a liquid hydrocarbon unpalatable with an aversive agent having poor solubility in said liquid hydrocarbon, comprising selecting a stabiliser in the form of a co-solvent from C6-C20 aliphatic or alicyclic alkanols and diols, optionally substituted with ester, ether, ketonic, alicyclic and/or aromatic groups, and having at least one available, i.e. underivatised, hydroxyl group, singularly or as mixtures, said co-solvent being miscible with..the liquid hydrocarbon to be denatured and being a solvent in which the aversive agent is soluble, dissolving the aversive agent in the co-solvent and introducing an effective amount of the solution into the liquid hydrocarbon.
Preferred stabilisers include diols and diol mono-ethers, esters, and mixtures thereof particularly branched chain lower secondary alkanol esters of lower fatty acids, especially those formed using a secondary diol. An especially suitable co-solvent is 2,2,4-trimethylpentan-1,3-diol-monoisobutanoate (CAS-Nr. : 25265-77-4, C12H24O3), which proved to be uniquely suitable for the purpose of the invention.
Alkanols which have not been derivatised have also been observed to be useful for the purposes of the invention with varying degrees of stability. Thus whilst preliminary tests suggest that aliphatic or alicyclic alkanols, i.e. C2-C20 and above such as 1-butanol and isopropanol, would show varying degrees of stability, according to the invention one would select C6-C20 alkanols, such as 1-octanol, 1-hexadecanol, and mixtures thereof with esters such as 1-octanol/ethyl acetate 1:1 w/w which are now found to be effective in enabling introduction of the preferred aversive agent "BITREX®" at the desired level.
In accordance with the invention a base oil to be denatured is selected, a preferred denaturant such as the aversive agent denatonium benzoate is provided, a stabilising co-solvent therefor is selected from amongst alkanols and aliphatic esters of the aforesaid type, the denaturant is introduced to the co-solvent and dissolved therein e.g. by stirring or similar agitation, to provide a doping medium and thereafter an amount of said doping medium sufficient to have an aversive organoleptic effect is added to the base oil to denature same.
The preparatory work leading to the realisation of the present invention included study of many liquids considered to be potentially suitable for use as co-solvents for the purposes of the invention. The study lead to evaluation of a number of liquids of apparently generally similar chemical and physical properties.
The following Table I summarises the results of this evaluation stage, and in particular assesses the success in obtaining a clear stable formulation of the preferred denaturant (denatonium benzoate/ "BITREX"®) in a target commercial product to be denatured (lamp oil). Those combinations marked as "FAIL" were observed to exhibit turbidity and insufficient stability in the amount of denaturant introduced to the lamp oil. In each case, the only critical variation lay in the selection of the co-solvent. Apart from the attempted use of rape seed oil, it is assumed that the co-solvent is essentially a single chemical entity. The results clearly showed that use of 2,2,9-trimethylpentan-1,3-diol-monoisobutanoate is highly effective in achieving the objective of the invention.
The successful co-solvent in Table I is commercially available under the trade mark TEXANOL® from Eastman Chemical Company (USA).
As an illustrative example of procedure, one may prepare a 40ppm "BITREX®" doped lamp oil by simply stirring in a previously prepared 0.1% solution of "BITREX®" in the selected co-solvent TEXANOL® to a level of 4% (all amounts described herein are w/w). A similar procedure was found effective in denaturing, white spirit, dearomatised white spirit, and isoparaffin.
Similar tests were conducted using 0.1% Bitrex® in the co-solvents shown in Table II below.
The fact that it has proved possible to incorporate the preferred denaturing substance at levels effective in achieving an aversive effect in apolar liquid hydrocarbons which are essentially free of aromatic content even upon storage of the treated product without the need to use surfactants or the like additives is surprising and of significant commercial value.