I was referred to your website by the good people over at dharma trading and was hoping that you could help me out. I am a research assistant in a physiology lab and we recently found that we were running low on procion orange dye (reactive orange 14). Apparently Sigma does not carry it anymore, so I am trying to find another supplier but I am having a tough time trying to figure out what dyes out there correspond with the old Procion orange dye. I need it to correspond in more that color, I really need it to be chemically identical to Sigma's procion orange. Ivy, at Dharma Trading said that their orange #4 is a pure reactive orange and I was wondering if you had, or knew how to get either the structure or molecular weight of the compound. 

Reactive Orange 14 appears to be coded as Yellow MX-4R; different dye companies will change "MX" to their own preferred code, but so far, for reactive dyes only, most will use the same code that follows the dash. ("Reactive orange 14" is this dye's Colur Index name.) Unfortunately, this is on neither my list of pure unmixed Procion MX dyes nor my list of pure unmixed Procion H dyes. (Procion MX dyes are dichlorotriazines, while Procion H dyes are monochlorotriazines.) This means that you won't be able to buy this dye from an art dye retailer such as Dharma or ProChem, nor an arts and crafts supplier such as Blick. Classic Dye doesn't have it, according to their site, and neither does Standard Dye; these are two dye wholesalers in the US that I've dealt with or known others who have.

You cannot simply substitute reactive orange 4 for reactive orange 14, since they are different chemicals, though the reactive portion of the dye molecule is the same. Reactive Orange 4, which Dharma and other art dye suppliers sell, is coded as Orange MX-2R. You may be able to use a different dichlorotriazine dye in place of the one currently in your recipe, but the color is almost entirely irrelevant, since the important point is the reaction between dye and protein molecule. Different specific reactive dyes have different reactivities. I do not have any information of how quick to react the reactive orange 14 dye may be; there's a table of the relative reactivities of other dyes in the same class posted on the Dye Forum, which was excerpted from the book "Reactive Dyes in Biology", by Victor Ivanov, but unfortunately reactive orange 14 is not included in that table.

I was able to find the structure for your reactive orange 14, from the Comparative Toxicogenomics Database and from the Sigma Aldritch web site. Compare Sigma's representation of its structure, on the left, with that of reactive orange 4, on the right. You can see that reactive orange 14 is very unlike reactive orange 4. Reactive orange 4 contains two naphthalene groups that are not found in reactive orange 4. In fact, I already had a hand-drawn structure for reactive yellow MX-4R on my page of known Procion MX dye structures, but did not realize that it was the same dye until I compared the structures. The molecular weight of reactive orange 4 is 715.527, while that for reactive orange 14 is 631.39.

There is a US National Library of Medicine Medical Subject Headings (MeSH) entry for this dye listed in the Comparative Toxicogenomics Database, with a source article referenced as appearing in a 1987 issue of the journal Anal. Biochem., 163(2):385. Sometimes you can find a little more information on a dye by searching with its CAS Registry Number, which in this case is given as 12225-86-4. (Always put quotes around the number itself when searching, as otherwise it will be split at the dashes.) Searching with either the CAS number or the phrase "reactive orange 14" yields a number of possible sources, for example, Advance Scientific & Chemical, which sells it for $57.15 for 50 grams. You can probably get a pound or more of the same dye for that price from a textile dye supplier, but it might be slightly less pure. It would be nice to avoid having to do any additional purification of your own, if possible.

A web search for the Colour Index name of a dye, in this case the phrase "reactive orange 14", is often your best way to find a supplier, and in this case it does turn up a number of possible leads. The first one I happened to look at was Liberty Specialty Chemicals, which I don't know anything at all about, but they do have a US office, and they manufacture or sell reactive orange 14. It should be much easier to deal with a company that has an office in the US, rather than one with offices only in India or China (the two countries where it seems that most of this kind of dye is made). You could try calling them:

Be very specific that you want only reactive orange 14, not any similarly colored substitute; sometimes large dye companies will change a formula without making much notice of it, but a similarly-colored mixture of other dyes will be of no use to you at all. You may have to buy an entire kilogram of dye, or more; on the other hand, a kilogram of dye from most textile dye sources will probably cost less than a few grams of the same dye from Sigma.

I hope that you won't have to buy five kilograms as your minimum order size per color; that is the minimum amount you can order from Dystar, which is a major dye supplier and the owner of the 'Procion' trade name. I have purchased one-pound buckets from Standard Dye, which is as much as I like to deal with at a time.

You may want to look at the FAQ for my website, which has some information that is relevant for scientific use of these dyes. There is also some information on how dichlorotriazine dyes react with cellulose in my Hand Dyeing Q&A blog (the reactions with proteins are more complex); see I'm wondering if you could explain the chemistry behind why cotton can't be dyed at an acidic pH  and
Chemical Reaction for a Dichlorotriazine Dye with Cellulose.

I think you will be able to find some of the dye you need. Please let me know how it works out.

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Another drawing of Procion Yellow MX-4R (Colour Index
Reactive Orange 14), from the Comparative
Toxicogenomics Database.