Posted by: Mark Foreman | January 30, 2012

Cheats stained by their crimes

Now I am sure that some of you are keen to know how aromatic compounds are useful to those chemical enginners who do not want to get involved in the production of drugs and super exotic chemicals. This brings me onto tax, now despite what one left wing friend says paying tax is not fun. I can not say that I enjoy paying tax to the state.

But we need to pay tax, always bear in mind the different between need, want and enjoyment. The reason we need to pay tax relates to something called the social contract, the idea is that the state will take care of many of our needs in return for us paying attention to the law, obeying the law and also helping to keep the state financed through tax.

My view is that the state exists to serve the needs of the people in society (it should never be the other way around), the state needs to provide services such as rescue / emergency services (to put out fires and rescue people), police (to protect us from criminals and help manage things like the transport network), schools / universities (to educate us and thus protect us from ignorance) and medical services (to repair us when we get sick or injured).

Sadly not everybody wants to pay their share, one common method for avoiding tax is to use duty free fuel in road vehicles. While duty free petrol is not normally a big problem, the bigger problem is with duty free diesel. In many places duty free diesel is sold for use on building sites or on farms. This diesel is typically red in colour, it contains a red dye to allow police officers and tax inspectors to quickly identify it. Another duty free (or low tax) fuel is heating oil and kerosene. Some very bad people are known to run their cars, taxis and trucks on this fuel and thus zip about on the public road without paying the same tax as those of us who choose to obey the law.

UK law on these fuels which have misuse potential is quite simple, all gas oil and light oil (these oils are very close to the diesel fuel for a truck or car) need to be marked with the ‘Euromarker’ dye (the UK legal term is the common ‘fiscal marker’), quinizarin and a dye named ‘solvent red’.

While all kerosene has to be marked with the ‘Euromarker’ and coumarin.

All four of these chemicals use aromatic systems to provide the right optical properties which allow the law breakers to be identified. The Euromarker is intended as a common marker dye which is used throughout the whole of the EU for low tax fuel, this is solvent yellow 124 (AKA SY124, Sudan 455 and Somalia Yellow. Its CAS number is 34432-92-3) which is added at siz grams per cubic meter. This is a dye which is similar to methyl orange which is a indicator used by many chemists.

The chemical name of the euromarker is 4-phenylazo-N-ethyl-N-[2-(1-(2-methylpropoxy)ethoxy)ethyl]-benzenamine, so we can have a go at drawing it. Lets start with the 4-Phenylazo-1-aminobenzene part of the compound.


Then lets add the ethyl group onto the amine nitrogen, this gives us the following molecule.

N-ethyl phenylazoaniline

The hard part of the molecule is the 2-(1-(2-methylpropoxy)ethoxy)ethyl bit. This might look like a nasty bit of nomenculture but it can be solved.

It is a 2-ethyl thing so we know it is -CH2-CH2-, we then add the ethoxy group to get CH3-CH2-O-CH2-CH2-. Next we need to add the 2-methylpropoxy part to the 2-ethyoxy group to make the whole of the side group which we now attach to the aromatic part of the molecule.

The euromarker dye

The euromarker dye is designed so that when the marked fuel is shaken with hydrochloric acid that one of the side groups on the amine will change from a hydrophobic group into a hydrophilic group and thus stain the acid red. This allows both the tax inspector to check the fuel and also does make it possible for the cheat to wash some of the dye out with acid. The reaction to change the side group is likely to have the following mechanism. I am sure that you should be able to add the curved arrows to finish it off.

How the side group in the euromarker changes

Now the change in side group will enable the dye to go into the water layer and stay there. If washing with acid was able to make duty free diesel look like road diesel then the goverment would be cheated with great ease. The way that the UK goverment get around this problem is to add additional dyes, it is typical in gas / light oil to use quinizarin ( also known as 1,4-Dihydroxyanthraquinone or solvent orange 86). Looking at the molecule it appear that it is an acidic dye, as a result a second treatment with strong alkali would be needed to remove this dye as well as the euromarker. As a result it increases the amount of work which the fuel washing criminal needs to do. Also it gives the tax man a second chance to catch the fuel cheat.


Lastly the cheap UK diesel contains a very lipophilic (hydrophobic) dye named Sudan IV, this is a weakly acidic dye but I suspect that as the molecule is so lipophilic that it will be difficult to extract the majority of the dye using sodium hydroxide. Thus the UK farm diesel is likely to be very hard to convert into a fuel which will be able to fool the tax inspectors, maybe it would be just more simple and cheaper to fill up at a legal diesel pump !


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