Hydrocarbon markers

Abstract

 Provided is a compound for marking a hydrocarbon, the compound having one of the following structures, or a tautomeric form of one of the following structures:



wherein R¹ is a substituent that does not comprise an aromatic unit; n is 0, or is an integer of from 1-5; D is the electron donor substituent; HP is the further hydrophobic substituent; p is an integer of from 1-4; q is an integer of from 1-4; wherein p+q does not exceed 5; at least one D is an OH group; and at least one HP is a straight chain alkyl group; and provided that the compound is not the following:

Description

[0001] The present invention concerns marker compounds and compositions, in particular dye compounds and compositions. The invention further concerns the use of these compounds and compositions for marking hydrocarbon fuels. The invention is particularly advantageous, since the marker compounds and compositions are resistant to removal from hydrocarbons, and are also resistant to alteration or destruction to mask their marking effect. Thus, the present compounds are a significant improvement over conventional markers for identifying and marking rebated fuels or other hydrocarbons.

[0002] Azo dyes were the earliest discovered solvent dyes. Because of their low cost and good solubility in many solvents, they are still being widely used for many applications. One of the most important applications is the colouring of petroleum products, so that different kinds or grades of products can be distinguished.

[0003] Most territories around the world, particularly the more industrialised nations, levy tax on fuels, such as gasoline, diesel and kerosene. However, most tax regimes allow for different rates of taxation depending upon the use to which the fuel is to be put, and the individual or organisation using the fuel. For example, in many territories fuels for agricultural use (e.g. in agricultural vehicles, such as tractors, or in other machinery employed in farming) are rebated in order to promote agricultural activity in the territory. In other words, the tax on fuel to be put to such uses is less than the equivalent tax levied for private use, such as in private cars or other vehicles. In some territories, the tax rebate may be different for different fuels, or there may be several levels of tax on a single fuel, depending on its uses.

[0004] The structure of taxation described above has lead to a requirement to mark fuels that are taxed at a number of different levels. This is required in order that the authorities can identify or detect the fuel, and determine whether it is being used lawfully, or unlawfully. Clearly, it is important to be able to determine if a rebated fuel is being used in an illegal way, such as in a private vehicle. In the past, this has been achieved in a number of ways.

[0005] Initially, dyes were introduced into fuels that were to be subject to a tax rebate. The colour of the dye was selected to indicate the type of fuel and/or the level of rebate applied to that fuel. Further compounds were sometimes added to the fuels as markers, or as antioxidants to preserve the colour of the dyes. For example, in the UK a red dye (often termed "Red 24"), in conjunction with a quinizarin antioxidant, has been used for many years as a marker for rebated diesel:

[0006] A blue dye has similarly been applied to kerosene in the UK to distinguish kerosene rebated fuel from diesel rebated fuel.

[0007] Dyes and markers are not only added to rebated fuels, but may be added for other purposes. For example, in many territories dyes are added to any potentially flammable substance as a warning, for safety reasons. In the UK, a violet dye is often added to methylated spirits for this purpose.

[0008] A particular problem for rebated fuels is the requirement to ensure that the marker compound cannot be separated from the fuel, or rendered undetectable. If the dye or marker can be removed, or deactivated in some way, then a criminal organisation is able to buy the fuel at the rebated price and sell it on for a profit at a price below the full non-rebated price of the fuel. In many countries this has been an increasing problem as criminal gangs have found ever more sophisticated methods for processing rebated fuels to remove and/or mask dyes and markers.

[0009] Attempts have been made to counter these activities by introducing markers into fuels that are less visible to the naked eye or are colourless but which, for identifying rebated fuels, can be detected using standard laboratory techniques. For example, across Europe a so-called "Euromarker" has been required by law to be introduced into rebated fuels. This marker has a yellowish colour (also termed Solvent Yellow 124) that is not immediately evident to the naked eye when added in the required dilute concentration to fuels, but which can be detected very simply when necessary:

[0010] In Somsaluay et al. "Petroleum markers synthesised from n-alkylbenzene and aniline derivatives", Ind. Eng. Chem. Res., 2003, 42, pp 5054-5059, petroleum markers are reported. The markers are invisible at an effective usable level, but are designed to give visible colours on extraction, and are proposed for use as markers in commercial fuel oils. Diazo compounds have received particular attention in the study.

[0011] Published patent US 6,514,917 discloses colourless markers for petroleum products. The markers are indicated to be colourless in the fuel, but are designed to be extracted and then developed using a developing agent. The focus of this document is on diazo compounds having a disubstituted amine-type substituent.

[0012] US 5,905,043 discloses diazo-type tags for organic fluids. The tags comprise two diazo-type units linked together by an amide bond. The tags are designed to be extracted from the fluid with an alkaline aqueous extractant, and then detected.

[0013] US 5,827,332 discloses the use of specific azo dyes as pH dependent markers for hydrocarbons. The dyes are designed to be practically colourless in the hydrocarbon, but to exhibit strong colour when a protic acid developer is added in an alcoholic medium. The dyes employed are generally diazo compounds having a disubstituted amine-type substituent.

[0014] US 4,514,226 discloses monoazo pyridine colorants. These compounds are indicated to be useful for dyeing and printing polyester materials, as well as being suitable as colourants for organic solvents.

[0015] Published German patent application DE 28 53 479 A1 discloses diazo dyes comprising two outer phenyl moieties and one central naphthyl moiety. The dyes may be used as colourants for mineral oil products and organic solvents.

[0016] Published British patent application GB 2,018,241 discloses diazo dyes having one pyridyl moiety and one phenyl or naphthyl moiety. The compounds are indicated to be useful in the selective extraction of copper from aqueous solutions comprising impurities. One of the compounds tested is 2-(2'-pyridylazo)-4-nonylphenol:

[0017] However, the dyes and markers disclosed in the prior art are still not entirely satisfactory. It is still possible to remove or deactivate them if sophisticated chemical processes are employed. Indeed, many of the dyes are designed to be removed before detection takes place, so that unscrupulous parties may easily remove the marker, provided that they are aware of its presence. In recent years a number of criminals have been apprehended after illegally removing or deactivating dyes and markers from rebated fuel in the UK and across Europe. Therefore, there is still a requirement to produce improved markers and/or dyes for use in rebated fuels.

[0018] It is therefore an aim of this invention to solve the problems of the prior art set out above. It is a further aim of this invention to provide improved marker compounds for marking hydrocarbon fuels, such as rebated gasoline, diesel, paraffin and kerosene. It is a still further aim of this invention to provide methods for synthesising such markers, and to provide compositions comprising these markers, which can be added to hydrocarbons, but which are not easily removed from the hydrocarbons.

[0019] Accordingly, the present invention provides a compound for marking a hydrocarbon, the compound having one of the following structures, or a tautomeric form of one of the following structures:



wherein R¹ is a substituent that does not comprise an aromatic unit; n is 0, or is an integer of from 1-5; D is the electron donor substituent; HP is the further hydrophobic substituent; p is an integer of from 1-4; q is an integer of from 1-4; wherein p+q does not exceed 5; at least one D is an OH group; and at least one HP is a straight chain alkyl group; and provided that the compound is not the following:

[0020] In the context of the present invention, this formula is intended to include and/or extend to all tautomeric forms of the above compounds. Tautomeric forms are two or more forms of a compound in equilibrium. One form is converted to another by migration of a hydrogen atom. For example, in the case where there is an XH_n group ortho to the Ph group (where X is N, P, O or S and n=1 or 2) a different tautomeric form may be the most common form, rather than the form corresponding to the above formula:

[0021] In this example, the first form is termed the enol form whilst the second form is termed the keto form. The invention therefore extends also to the second possible tautomeric form (the keto form) as well as the first form (the enol form). The keto form has the general formula:

where n is an integer of 1 or 2, and X is N, P, O or S.

[0022] The marker compounds of the present invention are particularly advantageous, since they are suitable for adding to hydrocarbons to mark the hydrocarbons, but are difficult to remove. Without being bound by theory, it is believed that it is a combination of an electron donor group and a hydrophobic group on an aromatic group attached to a diazo unit that provides the compound with a resistance to removal from its lipophilic environment. The presence of a combination of at least one hydroxy group and at least one straight chain alkyl group ensures that the compounds are particularly effective. In addition, it further hinders removal of the markers if they are liquid at ambient temperature and pressure (the temperature and pressure at which the fuel is to be used, e.g. at atmospheric pressure from -30° to 50°C, preferably from 0° to 30°C). This is therefore also preferred.

[0023] In the context of the present invention an electron donor substituent may be any substituent that is capable of donating electrons to a delocalised aromatic system. Thus, the electron donor may be capable of donating electrons by virtue of the direction of the dipole moment of the group, such as with groups that interact with the aromatic system only through σ-bonds (e.g. alkyl groups). Alternatively, the electron donor may be capable of donating π-electrons into the aromatic system (e.g. halogen atoms, and groups attached through O and N atoms may donate lone pairs situated in orbitals having π character). Thus, the donor group attached to the aromatic system may in some cases be attached through an electronegative atom which withdraws electrons through the σ-bond interaction, provided that the overall interaction is electron withdrawing when the π-interaction is taken into account. Cl, Br, I, O and N are all more electronegative than carbon and usually have an electron withdrawing effect through a σ-bond interaction with carbon. However, these atoms are capable of donating lone pair electrons into an aromatic delocalised system, rendering many groups attached via these atoms electron donating overall, despite the σ-bond effect. Typically the groups employed in the present invention include hydroxy, alkoxy, amino and substituted (e.g. N-alkyl and N,N-dialkyl) amino groups. The present invention employs any of the above electron donating groups. A more detailed description of the preferred groups is given below.

[0024] The meaning of hydrophobic substituent in the context of the present invention is any substituent that renders the marker compound less soluble in water and/or more soluble in a hydrocarbon liquid, such as a hydrocarbon fuel. The substituents are generally lipophilic and are typically straight chain or branched alkyl groups, but are not limited to such groups. A more detailed description of the preferred groups is given below.

[0025] The electron donor substituent and the further hydrophobic substituent may themselves be substituted if desired. The type of substitution of these substituents is not especially limited, provided that the function of the marker compound is not impaired. Preferred substituents are the same as for R¹ discussed below.

[0026] At least one hydroxy group and at least one straight chain alkyl group must be present on one of the phenyl rings. It is preferred that the hydroxy group and the straight chain alkyl group are para to one another on the phenyl ring. It is also preferred that one of these groups (typically the hydroxy group) is ortho to the N₂ group on the ring.

[0027] The electron donor substituent is not especially limited. Preferably it is selected from Cl, Br, I, a hydroxy group, an ether group, a primary secondary or tertiary amine group, a thiol group, and a thioether group. Most preferably it comprises a hydroxy group or an alkoxy (alkyl ether) group.

[0028] The nature of the further hydrophobic substituent is also not especially limited. The further hydrophobic substituent is preferably selected from a primary secondary or tertiary alkyl group, an alicyclic group and a heterocyclic group. More preferably the further hydrophobic substituent is selected from a straight or branched chain higher hydrocarbon having from 6-40 carbon atoms. More preferably still, the further hydrophobic group comprises an alkyl group having from 6-20 carbon atoms, more preferably from 6-12 carbon atoms and most preferably from 6-9 carbon atoms. The further hydrophobic substituent thus may comprise straight chain alkyl groups selected from a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group and a dodecyl group, as well as the branched chain regioisomers of all of the above groups.

[0029] The group R¹ may be any substituent, provided that the function of the marker compound is not impaired. However R¹ does not comprise an aromatic unit such as a phenyl unit. Thus, R¹ may comprise any organic group and/or one or more atoms from any of groups IIIA, IVA, VA, VIA or VIIA of the Periodic Table, such as a B, Si, N, P, O, or S atom or a halogen atom (e.g. F, Cl, Br or I). When R¹ comprises an organic group, the organic group preferably comprises a hydrocarbon group. The hydrocarbon group may comprise a straight chain, a branched chain or a cyclic group. Independently, the hydrocarbon group may comprise an aliphatic group. Also independently, the hydrocarbon group may comprise a saturated or unsaturated group. When the hydrocarbon comprises an unsaturated group, it may comprise one or more alkene functionalities and/or one or more alkyne functionalities. When the hydrocarbon comprises a straight or branched chain group, it may comprise one or more primary, secondary and/or tertiary alkyl groups. When the hydrocarbon comprises a cyclic group it may comprise an aliphatic ring, a heterocyclic group, and/or fused ring derivatives of these groups. The number of carbon atoms in the hydrocarbon group is not especially limited, but preferably the hydrocarbon group comprises from 1-40 carbon (C) atoms. The hydrocarbon group may thus be a lower hydrocarbon (1-6 C atoms) or a higher hydrocarbon (7 C atoms or more, e.g. 7-40 C atoms). The number of atoms in the ring of the cyclic group is not especially limited, but preferably the ring of the cyclic group comprises from 3-10 atoms, such as 3, 4, 5, 6 or 7 atoms. The groups comprising heteroatoms described above in respect of R¹, as well as any of the other groups defined above in respect of R¹, may comprise one or more heteroatoms from any of groups IIIA, IVA, VA, VIA or VIIA of the Periodic Table, such as a B, Si, N, P, O, or S atom or a halogen atom (e.g. F, Cl, Br or I). Thus the substituent may comprise one or more of any of the common functional groups in organic chemistry, such as hydroxy groups, carboxylic acid groups, ester groups, ether groups, aldehyde groups, ketone groups, amine groups, amide groups, imine groups, thiol groups, thioether groups, sulphate groups, sulphonic acid groups, and phosphate groups etc. The substituent may also comprise derivatives of these groups, such as carboxylic acid anhydrides and carboxylic acid halides. In addition, any R¹ substituent may comprise a combination of two or more of the substituents and/or functional groups defined above.

[0030] In the above structure, it is particularly preferred that each R¹ comprises a hydroxy group, an amine group, a halogen, or an alkyl group having from 1-6 carbon atoms.

[0031] In the above structure, it is preferred that D is situated at the 2-, 3-, or 4-position on the phenyl ring relative to the N=N group. Further, it is also preferred that HP is situated at the 3-, 4-, or 5-position on the phenyl ring relative to the N=N group. It is particularly preferred that D is in the 2-position, and it is additionally also preferred that HP is para to D.

[0032] The most preferred compounds of the present invention have one of the following structures:



















wherein R¹ is a substituent as defined above; and n is 0 or is an integer of from 1-5. In these structures, it is especially preferred that n=0. The C₆ group not comprising the HP and D groups may be replaced by a C₅N group if desired, as follows:

[0033] Where the above compounds have a D group that comprises an H atom and is adjacent the N=N group, then tautomerism may occur, as discussed above. In these cases, the following compounds are preferred:







wherein R¹ is a substituent as defined above; and n is 0 or is an integer of from 1-5. In these structures, it is especially preferred that n=0. In these cases, the hydrogen atom is typically attached to an N, P, O or S atom, such as in an NH₂ group, a PH₂ group, an OH group or an SH group. Thus D preferably comprises or includes such a group. The C₆ group not comprising the HP and D groups may be replaced by a C₅N group if desired, as follows:

[0034] Specific examples of the above most preferred types of compound which may be used in the present invention include the following:



























wherein R¹ is a substituent as defined above; and n is 0 or is an integer of from 1-5. In these structures, it is especially preferred that n=0. The C₆ group not comprising the OH and C₉H₁₉ groups may be replaced by a C₅N group if desired, as follows:

[0035] The most preferred compound of the present invention is the following:

or its tautomer:

[0036] This compound has particularly marked advantages, as will be outlined below in a description of the specific embodiments and examples of the invention. In use in the present invention, the compound comprising the C₆ group not comprising the OH and C₉H₁₉ groups may be replaced by a C₅N group if desired, as follows:

[0037] The C₉H₁₉ group specified in the above compounds may be replaced by a C₆H₁₃ group, a C₇H₁₅ group, a C₈H₁₇ group or a C₁₀H₂₁ group, a C₁₁H₂₃ group or a C₁₂H₂₅ group if desired.

[0038] In general, disperse dyes and solvent dyes have in common the property of being water insoluble. The difference between those dyes is mainly in their use. Disperse dyes are usually used in dispersed form in aqueous medium for synthetic fibres such as polyester and nylon. The solvent dyes, on the other hand, are used to colour materials through their ability to dissolve in an organic solvent or other substance. The marker compounds of this invention are typically solvent dyes, but the invention is not limited to solvent dyes, and disperse dyes may be employed in some cases.

[0039] The present invention further provides a composition for marking a hydrocarbon, the composition comprising a marker compound as defined above and one or more of:

(a) a further dye, pigment, colour, or other marker compound; and

(b) an additive.

[0040] Thus, this composition is an additive composition adapted for addition to a hydrocarbon compound, such as a hydrocarbon fuel, to mark the compound. The nature of the composition is not especially limited, provided that it is capable of marking the compound.

[0041] Additives for inclusion in such compositions are well known in the art and are not especially limited.

[0042] The composition may optionally comprise further markers, if necessary, such as those required by law (e.g. the Euromarker), anti-theft dyes, and/or colouring to render the fuel the same colour as existing fuels comprising current markers. This is preferred in order that the present colour scheme for rebated fuels is not altered. For instance, in the UK, diesel may comprise a marker of the present invention, but in addition may comprise the dye used at present (Red 24) in order that users easily recognise the fuel according to its known colour. The composition may also comprise antioxidants, such as the quinizarin antioxidant employed in diesel in the UK at present. Other dyes, pigments and marker compounds that may be additionally incorporated into the composition include one or more of the following Approved Dyes in Table 1 and Approved anti-theft dyes in Table 2 below:

Table 1 -

Approved Dyes in various territories
Territory	Red Dyes	Blue Dyes	Yellow Dyes	Green Dyes
Austria	Solvent Red equivalent (Dyeguard Red C®)		Solvent Yellow 124
Belgium	Solvent Red equivalent (Dyeguard Red C®)		Solvent Yellow 124
Denmark		Solvent Blue 79	Solvent Yellow 124
Rep. Ireland	Solvent Red 19	Solvent Blue 79	Solvent Yellow 124
Finland	Solvent Red 19		Solvent Yellow 124
France	Solvent Red 24	Solvent Blue 35	Solvent Yellow 124
Germany	Solvent Red 19		Solvent Yellow 124
Greece			Solvent Yellow 124
Netherlands			Solvent Yellow 124
Italy	Solvent Red 161		Solvent Yellow 124	Solvent Green 33
Luxembourg			Solvent Yellow 124
Portugal	Solvent Red 19	Solvent Blue 35	Solvent Yellow 124
Spain	Solvent Red equivalent (Dyeguard Red C®)	Sudan Blue 79	Solvent Yellow 124
Sweden		Solvent Blue 35	Solvent Yellow 124
USA	Solvent Red 164
Hong Kong	Solvent Red 24

[0043] The anti-theft dyes of Table 2 are particularly preferable for use in the compositions of the present invention. The following Dye (Dye 6 in the Examples below) is particularly preferred for use in the present compositions:

[0044] The composition may further optionally comprise additives for aiding dissolution and/or miscibility of the composition with the hydrocarbon to be marked, or stabilising and/or fixing the resulting mixture. Such additives are well known in the art.

[0045] Further provided by this invention is a method for synthesising of a marker compound as defined above, which method comprises coupling an R¹_nPh-N₂⁺ moiety with an (D)p(HP)qPh moiety in a diazo coupling reaction, or coupling an (D)_p(HP)_q-N₂⁺ moiety with an R¹_nPh moiety in a diazo coupling reaction, wherein R¹, D, HP, n, p and q are as defined above. Thus, either moiety in the compound may be coupled to the other using a diazo coupling reaction. The reagents and conditions for performing such reactions are well known in the art. The mechanism of this reaction involves the reaction of the Ph-N₂⁺ electrophile with another aromatic group under base catalysed conditions. Further details of such reactions are provided in the Examples.

[0046] The invention also provides a marked hydrocarbon fuel comprising a marker compound or composition as defined above. Preferably, the hydrocarbon fuel is selected from a gasoline, a diesel, a paraffin and a kerosene fuel, although any type of fuel may be marked, if desired. More preferably, the hydrocarbon comprises a straight chain or branched chain alkane, alkene, or fatty acid having from 3-30 carbon atoms, or a mixture of the above. More preferably still, the hydrocarbon comprises an alkane having from 5-20 carbon atoms. Most preferably, the hydrocarbon comprises pentane, hexane, heptane, octane, nonane, decane, undecane and/or dodecane.

[0047] The marked hydrocarbon fuel can be formed by simply adding and/or mixing a marker compound or composition as defined above with a hydrocarbon fuel as defined above. The quantity of marker used in the fuel is not especially limited, and can be selected depending on the individual marker and fuel compound selected. Preferably, the concentration of the marker compound employed is 0.05 mg/l or more, more preferably 0.5 mg/l or more, more preferably still 1 mg/l or more, 2 mg/l or more and most preferably from 0.1-100 mg/l.

[0048] The invention further provides use of a marker in a hydrocarbon fuel for marking the fuel, wherein the marker comprises a compound or composition as defined above.

[0049] The invention will now be described in more detail by way of example only, with reference to the following specific embodiments.

EXAMPLES

[0050] Ten hydrophobic dyes were prepared and stability tests were carried out with diesel solutions of the individual dyes, and mixtures comprising the dyes, against common decolouring agents.

Example 1 - Preparation of Dyes

Synthesis of Dye 1 (CI Solvent Orange 14 - CI stands for Colour Index (a dye categorising and labelling system from the Society of Dyers and Colourists)

[0051] Comparative Dye 1 was prepared by coupling 2-naphthol with diazotised aniline, according to the following protocol. Aniline (0.025 M, 2.33 g) and hydrochloric acid (35 %, 6 ml) were dissolved in water (10 ml) and cooled to <5°C using ice/water bath. Sodium nitrite (0.025 M, 1.75 g), dissolved in water (10 ml), was then added to the cooled aniline solution over 5 minutes and the aniline/sodium nitrite mixture solution was stirred for a further 30 minutes in an ice bath. Starch-iodide paper was used to ensure excess nitrite ion and, at the end of diazotisation, 10w/w% sulphamic acid aqueous solution was added to remove the excess nitrite ion.

[0052] 2-naphthol (0.025 M, 3.61 g) was dissolved in aqueous NaOH solution (80 ml, pH 12) together with acetone (20 ml) and the previously prepared diazonium solution was added to the 2-naphthol solution slowly, ensuring that the temperature was kept below 10°C using an ice-bath. The pH during the azo coupling reaction was kept above 7 by adding 1 M NaOH solution as required. As the coupling reaction progressed water-insoluble azo dye precipitated. The precipitated dye was filtered, washed with distilled water and dried at room temperature. The reaction is depicted in Scheme 1:

[0053] This dye has maximum absorbance (λ_max in diesel) at 470.2 nm; dyed diesel solution was prepared for testing using a dye concentration of 2 mg/l.

Synthesis of Dye 2 (CI Solvent Red 1)

[0054] Comparative Dye 2 was prepared by coupling 2-naphthol with diazotised o-anisidine (2-methoxyaniline, 0.025 M, 3.12 g). The synthesis procedure employed was the same as that for Dye 1 except o-anisidine was used instead of aniline. The reaction is depicted in Scheme 2:

[0055] This dye has maximum absorbance (λ_max in diesel) at 490.8 nm; dyed diesel solution was prepared for testing using a dye concentration of 3 mg/l.

Synthesis of Dye 3

[0056] Comparative Dye 3 was prepared by coupling Naphthol AS (0.025 M, 6.6 g) with diazotised o-anisidine (2-methoxyaniline, 0.025 M, 3.12 g). The synthesis procedure was the same as that for Dye 2 except Naphthol AS was used instead of 2-naphthol. The reaction is depicted in Scheme 3:

[0057] This dye has maximum absorbance (λ_max in diesel) at 508.3 nm; dyed diesel solution was prepared for testing using a dye concentration of 5 mg/l.

Synthesis of Dye 4

[0058] Comparative Dye 4 was prepared by coupling 5-amino-1-naphthol (0.025 M, 4.2 g) with diazotised aniline. The synthesis procedure was the same as that for Dye 1, except 5-amino-1-naphthol was used instead of 2-naphthol. The reaction is depicted in Scheme 4:

[0059] This dye has maximum absorbance (λ_max in diesel) at 495.1 nm; dyed diesel solution was prepared for testing using a dye concentration of 2.5 mg/l.

Synthesis of Dye 5

[0060] Comparative Dye 5 was prepared by reaction of 1,4-diaminoanthraquinone with benzyl chloride. 1,4-diaminoanthraquinone (0.01 M, 2.65 g) and benzyl chloride (0.022 M, 2.87 g) were dissolved in DMF (N,N-dimethylformamide, 100 ml) and the solution was refluxed for 12 hours. The product solution was then poured in to distilled water (300 ml) and the resulting dyes precipitated; filtration was improved by the addition of sodium chloride. The precipitated dye was filtered, washed with distilled water and dried at room temperature. The reaction is depicted in Scheme 5:

[0061] This dye has maximum absorbance (λ_max in diesel) at 568.9 nm; dyed diesel solution was prepared for testing using a dye concentration of 9 mg/l.

Synthesis of Dye 6

[0062] Comparative Dye 6 is a commercially available dye from Hollidays (Yule Catto) in Huddersfield (UK). The commercial name of this dye is Sublaprint Blue 70038 (CI Solvent Blue 36). This dye has maximum absorbance (λ_max in diesel) at 596.7 nm and 644.6 nm; dyed diesel solution was prepared for testing using a dye concentration of 2 mg/l. The structure of Dye 6 is depicted in Scheme 6:

Synthesis of Dye 7

[0063] Dye 7 is a dye of the present invention, and was prepared by coupling nonylphenol (0.025 M, 5.75 g) with diazotised aniline. The synthesis procedure was the same as that for Dye 1, except nonylphenol was used instead of 2-naphthol. The resulting dye was of liquid form and separation was carried out using column separation method: there were clear two layers, dye and water/acetone mixture. The bottom part of the layers (water/acetone mixture) was drained. The resulting dye was dried over anhydrous Na₂SO₄ at room temperature. The reaction is depicted in Scheme 7:

[0064] This dye has maximum absorbance (λ_max in diesel) at 402.0 nm; dyed diesel solution was prepared for testing using a dye concentration of 4 mg/l.

Synthesis of Dye 8

[0065] Comparative Dye 8 was prepared by reaction of Rhodamine 6G (CI Basic Red 1) with sodium hydroxide. Rhodamine 6G (0.01 M, 4.8 g) and excess sodium hydroxide (0.08 M, 3.2 g) were dissolved in distilled water (100 ml) and this solution was heated up to 75°C. As the temperature was increased, the Rhodamine dye became insoluble in water and precipitated. After a further 30 minutes, the precipitated dye was filtered, washed with warm distilled water and dried in an oven (60°C) for 6 hours. The dried dye was then mixed with oleic acid (0.01 M, 3.1 g). The reaction is depicted in Scheme 8:

[0066] This dye has maximum absorbance (λ_max in diesel) at 531.6 nm; dyed diesel solution was prepared for testing using a dye concentration of 9 mg/l.

Synthesis of Dye 9

[0067] Comparative Dye 9 is Dyeguard Yellow 124 (CI Solvent Yellow 124), which will be added as the Euromarker throughout Europe. It is commercially available throughout Europe. This dye has maximum absorbance (λ_max in diesel) at 406.8 nm; dyed diesel solution was prepared for testing using a dye concentration of 5 mg/l. Its structure is depicted in Scheme 9:

Synthesis of Dye 10

[0068] Comparative Dye 10 is a mixture of CI Solvent Red 24 and quinizarin, which is the so-called 'Gas Oil Marker'. This dye is currently being used to mark rebated diesel in the UK. This dye has maximum absorbance (λ_max in diesel) at 517.2 nm; dyed diesel solution was prepared for testing using the concentration of 1 part concentrate solution/1000 part oil. The structures of Red 24 and quinizarin are depicted in Scheme 10:

Example 2 - Stability Tests of the Prepared Dyes

[0069] Stability tests for each dye were carried out using 10 ml of dyed diesel. Four of the most common and likely methods used to remove dyes were selected to assess resistance. These included hydrochloric acid (HCl 35 %, 0.5 ml), sodium hypochlorite (NaOCl at pH 12, 3 ml), sodium hydroxide (5M NaOH, 3 ml) and activated carbon (A.C.1 means after one filtration with A.C. and A.C.2 means after the second filtration with A.C.) Each test was carried out by mixing the above chemicals with dyed diesel and shaking for a while and left overnight. Filtration using activated carbon was carried out twice for each case. The absorbance of the dye solution was measured before and after the laundering process at the wavelength of maximum absorption of the dyes using a Perkin-Elmer Lambda 15 UV-Visible light spectrophotometer. The percentage loss of each dye under the applied methods was determined using the following equation:

[0070] The results of the test are depicted in Table 3 below. The tests results that proved to be satisfactory and demonstrated good resistance to loss of dye absorbance are shown in bold type. Negative values are indicative of a higher absorbance after the laundering process. Values over 100 are indicative of the solution having lower absorbance compared to undyed original diesel.

Table 3 -

Loss of Dye absorbance after Laundering Process
	Dye 1	Dye 2	Dye 3	Dye 4	Dye 5	Dye 6	Dye 7	Dye 8	Dye 9	Dye 10
HCl	0.8	9.5	5.9	96.8	95.4	98.5	-1.7	96.3	76.9	69.2
NaOC1	67.8	94.9	79.4	82.6	83.8	88.5	-12.8	91.7	-93.2	28.2
NaOH	-0.2	2.0	73.3	16.0	3.6	0.4	2.3	81.5	17.7	11.8
A.C.1	88.9	91.4	94.4	93.5	96.1	76.0	22.3	100.2	54.8	100
A.C.2	92.6	98.4	100.5	99.1	97.3	88.9	49.7	101.4	106.3	102.9

[0071] It can be seen from Table 3 that some of the azo dyes, such as Dyes 1, 2, 3 and 7 showed good resistance against hydrochloric acid, whereas Dyes 4, 9 and 10 did not. All of the anthraquinone dyes (Dye 5 and 6) showed very poor resistance (over 95 % dye destroyed) against hydrochloric acid, although these were better against sodium hydroxide. The rhodamine dye (Dye 8) showed the worst overall performance against all the removal agents employed.

[0072] Dye 9, which will be added throughout Europe as the 'Euromarker', showed relatively poor resistance (c.a. 77 % dye destroyed) against hydrochloric acid, although this dye solution increased to almost twice the absorbance following laundering with sodium hypochlorite. Filtration by activated carbon results resulted in more than half of Dye 9 being absorbed in the first filtration. After filtering twice, the original Dye 9 as well as some additives were totally removed.

[0073] Dye 10, which is being used at present to mark rebated diesel in the UK, showed relatively poor resistance (c.a. 70 % dye destroyed) against hydrochloric acid. This dye had relatively good resistance (c.a. 30 % dye destroyed) against oxidative bleaching (NaOCl) when compared with the other dyes, although this dye was not as good as Dye 7. In particular, this dye was completely absorbed in the first filtration by activated carbon and clear diesel was obtained.

[0074] Dye 7 (a marker compound of the present invention) shows very good resistance against all laundering processes employed. It is the only dye displaying an acceptable performance across the full range of decolourants employed. The colour strength of Dye 7 was even improved after treatment with hydrochloric acid and sodium hypochlorite (by 1.7 % and 12.8 %, respectively). Dye 7 had also relatively good resistance against sodium hydroxide as did Dyes 1, 2, 5 and 6. The most surprising and advantageous result was that this dye showed uniquely positive results against activated carbon filtration. Only half of this dye was absorbed after twice filtration whereas the other dyes were completely absorbed under the same condition, except Dyes 1 and 6 (c.a. 93 % and 89 % absorbed, respectively). It can therefore be concluded that Dye 7 would be suitable for use as a new oil marker having good resistance against acid, oxidative bleaching and filtering processes.

Example 3 - Mixtures of dyes

[0075] It has already been shown that Dye 7 has good resistance, especially against activated carbon filtration, and thus dye mixtures containing this dye will have acceptable resistance to laundering. Accordingly fuels could be produced using Dye 7 that have various colours. To demonstrate this, five different mixtures were prepared and tested, and the colour strength of each dye in the dye mixtures was quantified by measuring absorbance at λ_max of each dye. It should be noted that mixtures of dyes have been termed 'colours' for the purposes of this comparison. The five different colours tested were as follows:

Colour 11

A mixture of Dye 6 (1 mg/l) and Dye 7 (2 mg/l).

Colour 12

A mixture of Dye 6 (1 mg/l) and Dye 10 (0.5 part concentrate/1000 part oil).

Colour 13

A mixture of Dye 6 (0.7 mg/l), Dye 7 (1.3 mg/l) and Dye 10 (0.5 part concentrate/1000 part oil).

Colour 14

A mixture of Dye 7 (4 mg/l), Dye 9 (5 mg/l) and Dye 10 (1 part concentrate/1000 part oil).

Colour 15

A mixture of Dye 6 (2 mg/l), Dye 7 (4 mg/l) and Dye 9 (5 mg/l).

Example 4 - Stability Tests of the Colours

[0076] The five colours were subjected to the same stability tests as the dyes were subjected to in Example 2. The results are set out below in Table 4.

Table 4 -

Loss of Absorption in Dye Mixtures after Laundering Processes
Colour	11		12		13			14		15
λmax/mn	402	644.6	517.2	644.6	402	517.2	644.6	402	517.2	402	644.6
HCl	-1.9	96.5	77.7	96.9	-0.5	71.3	95.3
NaOCl	-13.3	72.2	30.7	70.7	-12.9	34.4	74.7
NaOH	2.7	0.4	9.5	0.4	4.8	11.3	1.4
A.C. 1	38.4	73.1	97.2	79.9	55.5	94.4	75.2	45.5	95.0	47.8	82.2
A.C.2	69.6	93.1	102.8	94.9	82.8	105.6	93.4	65.6	99.7	66.9	93.8

[0077] It can be seen from Table 4 that, in general, performance of the dyes employed in mixtures was virtually the same as when tested separately. Dye 7 (λ_max at 402 nm) showed good resistance against all laundering processes employed, as before. Differences between Colours 11 and 15 are the concentration of the two dyes (Dyes 6 and 7) and the inclusion of Dye 9 in the case of Colour 15 (λ_max not shown in Table 4). When comparing filtration properties between two mixtures, similar results were obtained regardless of the dye concentration after the second filtration.

[0078] The portion of Dye 6 (at 644.4nm) also displayed some resistance to filtration, and Colours 11 and 15 had blue shade left after second filtration, although analysis showed that over 90% of dyes were absorbed and its performance was clearly inferior to Dye 7. Dye 10 (at 517.2nm) in Colours 12, 13 and 14 showed poor performances especially in the case of all filtering processes: no red shade was left after twice activated carbon filtration.

[0079] It can be therefore seen that a mixture of Dye 7 with other Dyes, such as Dye 6, Dye 9 and Dye 10 can be used to mark oil having good resistance against known laundering processes such as activated carbon filtering, and the fuel hue can be varied by using different concentrations of the two dyes or adding other dyes for various colours.

[0080] From the above test results, it is clear that the marker compounds of the present invention show good resistance against HCl, NaOCl, NaOH, and activated carbon, i.e. across a wide range of agents commonly employed to destroy or remove markers.

[0081] Conventional dyes show either a very poor resistance, or at best resistance to only one or two reagents. The Euromarker (Dyeguard Yellow 124, Dye 9) and UK Gas Oil Marker (Dye 10), show relatively poor resistance against hydrochloric acid; Dye 9 showed almost twice the absorbance after laundering with sodium hypochlorite. Filtration results show that after two filtration treatments, the original dyes as well as some their additives were completely absorbed by activated carbon with the important exception of Dye 7, a preferred marker of the present invention. Dye 7 (namely, Leeds Yellow) shows the best resistance against all the laundering processes employed. The colour strength of Dye 7 even improved after treatment with hydrochloric acid and sodium hypochlorite. This dye showed superior results compared with all the other dyes against activated carbon filtration. Only half of this dye was absorbed after twice filtering with activated carbon whereas Dyes 2, 3, 4, 5, 8, 9 and 10 were completely absorbed under the same conditions; Dyes 1 and 6 also showed some resistance to activated carbon filtration, and may also be used in the compositions of the present invention in conjunction with the present markers, such as Dye 7.

Claims

1. A compound for marking a hydrocarbon, the compound having one of the following structures, or a tautomeric form of one of the following structures:



wherein R¹ is a substituent that does not comprise an aromatic unit; n is 0, or is an integer of from 1-5; D is the electron donor substituent; HP is the further hydrophobic substituent; p is an integer of from 1-4; q is an integer of from 1-4; wherein p+q does not exceed 5; at least one D is an OH group; and at least one HP is a straight chain alkyl group; and provided that the compound is not the following:

2. A compound according to claim 1, wherein each R¹ comprises a hydroxy group, an amine group, a halogen or an alkyl group having from 1-6 carbon atoms.

3. A compound according to claim 1 or claim 2, wherein D is situated at the 2-, 3-, or 4-position on the phenyl ring relative to the N=N group.

4. A compound according to any of claims 1-3, wherein HP is situated at the 3-, 4-, or 5-position on the phenyl ring relative to the N=N group.

5. A compound according to any preceding claim, wherein the electron donor substituent is selected from Cl, Br, I, a hydroxy group, an ether group, a primary secondary or tertiary amine group, a thiol group, a CN group, an SCN group and a thioether group.

6. A compound according to any preceding claim, wherein the further hydrophobic substituent is selected from a primary secondary or tertiary alkyl group, an alicyclic group and a heterocyclic group.

7. A compound according to claim 6, wherein the further hydrophobic substituent is selected from a straight or branched chain higher hydrocarbon having from 6-40 carbon atoms.

8. A compound according to any preceding claim, having one of the following structures, or a tautomeric form of one of the following structures:



















wherein R¹ is a substituent as defined in claim 1 or claim 2; and n is 0 or is an integer of from 1-5.

9. A compound according to claim 8, having the following structure, or a tautomeric form of the following structure:

10. A composition for marking a hydrocarbon, the composition comprising a marker compound as defined in any of claims 1-9, and one or more further components selected from:

(a) a further dye, pigment, colour, and other marker compound; and

(b) an additive.

11. A composition according to claim 10, comprising a compound having the following structure, or a tautomeric form of the following structure:

12. A composition according to claim 11, comprising one or more further branched-chain regioisomers of the compound.

13. A composition for marking a hydrocarbon according to any of claims 10-12, wherein the further marker compound comprises the following compound:

14. A method for synthesising of a compound for marking a hydrocarbon as defined in any of claims 1-9, which method comprises coupling an R¹_nPh-N₂⁺ moiety with an (D)p(HP)qPh moiety in a diazo coupling reaction, or coupling an (D)_p(HP)_q-N₂⁺ moiety with an R¹_nPh moiety in a diazo coupling reaction, wherein R¹, D, HP, n, p and q are as defined in any of claims 1-9.

15. A marked hydrocarbon fuel comprising a marker compound or composition as defined in any of claims 1-13.

16. A marked hydrocarbon fuel according to claim 15, wherein the hydrocarbon fuel is selected from a gasoline, a diesel, a paraffin and a kerosene fuel.

17. A marked hydrocarbon fuel according to claim 15 or claim 16, wherein the hydrocarbon comprises a straight chain or branched chain alkane, alkene, or fatty acid having from 3-30 carbon atoms, or a mixture of the above.

18. A marked hydrocarbon fuel according to any of claims 15-17, wherein the hydrocarbon comprises an alkane having from 5-20 carbon atoms.

19. A marked hydrocarbon fuel according to claim 18, wherein the hydrocarbon comprises pentane, hexane, heptane, octane, nonane, decane, undecane and/or dodecane.

20. A method for forming a marked hydrocarbon fuel, comprising mixing a marker compound or composition as defined in any of claims 1-13 with a hydrocarbon fuel.

21. A method according to claim 20, wherein the hydrocarbon fuel is a fuel as defined in any of claims 16-19.

22. Use of a marker in a hydrocarbon fuel for marking the fuel, wherein the marker comprises a compound having one of the following structures, or a tautomeric form of one of the following structures:



wherein R¹ is a substituent that does not comprise an aromatic unit; n is 0, or is an integer of from 1-5; D is the electron donor substituent; HP is the further hydrophobic substituent; p is an integer of from 1-4; q is an integer of from 1-4; wherein p+q does not exceed 5; at least one D is an OH group; and at least one HP is a straight chain alkyl group.

23. Use according to claim 22, wherein the marker comprises a compound as defined in any of claims 1-9.

24. Use according to claim 22 or claim 23, wherein the hydrocarbon fuel is a fuel as defined in any of claims 16-19.

25. Use of a marker composition in a hydrocarbon fuel for marking the fuel, wherein the marker composition comprises a composition as defined in any of claims 10-13.

26. Use according to claim 25, wherein the hydrocarbon fuel is a fuel as defined in any of claims 16-19.