Method for the preparation of diarylmethane dyes and triarylmethane dyes including isosulfan blue

Isosulfan Blue having a purity as measured by LC-MS that is greater than 95% and contains silver below the detectable limit as measured by Inductively Coupled Plasma Mass Spectrometry (ICP-MS), and optionally one or more of the following properties:

• contains a metal below the detectable limit as measured by Atomic Absorption spectrometry (flame or electrothermal), Inductively Coupled Plasma (ICP), or ICP Mass Spectrometry (ICP-MS);
• a purity as measured by HPLC that is greater than 99%;
• and
• a purity as measured by MS/MS that is greater than 98%.

A process of preparing a diarylmethane dye or a triarylmethane dye, comprising:

• oxidizing a compound of formula IIa or formula IIb in an electrochemical process in the presence of an aqueous solvent:
• wherein each R1, R2, R3 and R4 independently is a substituted or unsubstituted C1-C8 alkyl, a substituted or unsubstituted phenyl, or an unsubstituted C1-C4 alkylphenyl, wherein the substitution can be a halogen, a C1-C8 alkyl, an amino, a C1-C6-mono- or dialkylamino, a mono- or diphenylamino, hydroxyl, C1-C8alkoxy, or hydroxysulfonyl;
• each R5 and R6 are independently hydrogen or C1-C2 alkyl;
• Y is hydrogen, substituted or unsubstituted phenyl, or substituted or unsubstituted naphthyl;
• each R7 independently is a halogen, a C1-C8 alkyl, an amino, a C1-C6-mono- or dialkylamino, a mono- or diphenylamino, hydroxyl, C1-C8 alkoxy, or hydroxysulfonyl;
• and
• m is 1, 2, 3, or 4;
• the process is conducted using electrodes
• wherein the electrodes are
• platinum electrodes;
• or
• a platinum anode and a stainless steel cathode.