Expert: Dr. Henry Boyter, Jr. - 11/27/2005

Question
The methyl violets are aniline dyes which consist basically of three aniline molecules conjugated at the center and with varying degrees of methylation of the amine groups.

Structures of the common ones are at this link:
http://en.wikipedia.org/wiki/Methyl_violet

I want to know what is the “theoretically ideal” solvent for these molecules (we don't necessarily know which of the three configurations it is).
From experimentation I already know that they are soluble in water, in glacial acetic acid, and in ethoxyethanol > ethanol > methanol. I guess I "discovered" that the higher alcohols are better than methanol, otherwise these are just “textbook” examples of common solvents and these findings are already widely known. What I am really asking is, given the choice of any solvent or combination of solvents which can be prepared as liquids at room temperature, what would you choose from the point of view of solubility theory? Would aniline itself be a good choice? Are there some generalizations which can be made about the solubility of the methyl violets by looking at the structures and the functional groups ?

The purpose of the question is related to an art restoration project involving aniline dyes used in the 19th century. Your profile on AllExperts suggests a lot of experience with textiles so I will also raise a related secondary question. Several aniline dyes are to be removed from cellulose fibers by washing so I wonder also about the nature of these dyes' bonding to cellulosic fibers and how they can be encouraged to dissociate themselves. (This is related to but somewhat different from the concept of their solubility per se).

First I ask the opinion of an expert from the point of view of theory (all practical considerations aside), and then secondarily I can consider whether this could be translated into a feasible practical method.

Thank you !  

Answer
There are several questions that you need to answer first.  I'm also going to refer you to Charles Sweeny at CDS Lab to better help you with dyes and their properties (570-725-3411).

As far as a solvent, water is the obvious choice, BUT that depends on what you want to do with it. Are you trying to save a fabric or ID the dye?  If IDing the dye, a more organic solvent may be needed for the analysis that will be used.  If you are going to do new dyeings, water is the only choice.

Is your restoration to strip and redye, just redye, recreate, or to clean.  It gets to be a very complicated process depending on your goal.  If stripping, do you want to destroy the dye and/or prep for redyeing?  You may want to talk to the American Textile History Museum concerning restoration (978-441-0400).

Lastly, why do you think you have aniline dyes?  There are different types also, do you know the type (acid, direct, etc)?