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18 votes

Mechanism of formation of 2-naphthol red dye (aka Sudan 1)

The most important thing to point out here is that your arrows are backwards. The diazonium is not the nucleophile. It is the electrophile. The diazonium ion has one lone pair. If it were a ...
Zhe's user avatar
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14 votes

Looking for a dye which emits around 680 nm

There are two dyes commonly used in biochemistry research with $\lambda_\mathrm{Ex}$ of around $\pu{650 nm}$. They are Alexa Fluor 647 from ThermoFisher and Cyanine5 (Cy5) from Lumiprobe. Two example ...
Mathew Mahindaratne's user avatar
11 votes

Anthracine blue composition

Springmühl indeed reported Anthracene Blue (orig. "Anthracenblau" (German)) from an intermediate with brutto-formula $\ce{C14H7O3}$. It seems like this method only worked well at a lab scale....
andselisk's user avatar
  • 37.5k
10 votes

Mechanism of formation of 2-naphthol red dye (aka Sudan 1)

The formation of para-red is an example of electrophilic aromatic substitution. The electrophile reacts with the ring carbon that is ortho to both the activating group ($\ce{-OH}$) and the other ...
Archer's user avatar
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7 votes

Do indigo and leuco-indigo have fully conjugated pi systems?

Let's just start with stating the very obvious: Figure 2.23 has more errors than there should be in an entire chapter. Indigo With the exception of bonds to hydrogen, all other bonds are nicely ...
Martin - マーチン's user avatar
6 votes

Has anyone added dyes to a mixture about to separated by chromatography in order to visualize where the desired product lies?

the idea is good for academic purposes and good for a lecture hall demo. One may also try a UV lamp, if your compound fluoresces in the column. Caution UV is very harmful for the eyes (protective ...
AChem's user avatar
  • 39.8k
5 votes

Strange green and gold coloured chemical

I worked for a time with squaraine dyes that were often greenish in the crystalline state, but ink-blue when in solution. However, I would suggest that you take an analytical approach to identifying ...
Michael Lautman's user avatar
4 votes

How to make equal density pool dye without diffusion

Whole milk with food coloring solved my problem. Whole milk has a specific gravity of 1.01, which allowed it to settle to the bottom around the main drains. The diffusion rate was extremely slow ...
SouthernYankee65's user avatar
4 votes

What replaced lead-based pigments?

Into the 70's the better white paints were tri-metal; lead, zinc and tin (oxides). Titanium oxide (rutile) replaced the lead and the zinc and tin adjusted. The titanium has excellent hiding power so ...
blacksmith37's user avatar
  • 3,719
3 votes

Indigo and the Environment: is it that bad?

For this process, sodium dithionite (Na2S2O4) has been considered as a best reducing agent in traditional and industrial dying but the reducing agent releases sodium sulphate, sulphite and ...
AChem's user avatar
  • 39.8k
2 votes

Does there exist a dye that will primarily bind with water in a water/oil emulsion?

You are asking for water-soluble dyes. Typical applications are dyeing methods in microscopy and food coloring. Water-soluble dyes for microscopy: e.g. Eosin Y, Methylene Blue, Ethyl Green. See also ...
IV_'s user avatar
  • 271
2 votes

Why does SYBR green emit more signal when bound to DNA?

In dyes such as this rotation about bonds that can be involved in the conjugated part of the molecule contribute to radiationless transitions causing the excited state to transfer its energy to a ...
porphyrin's user avatar
  • 30.3k
2 votes

Do indigo and leuco-indigo have fully conjugated pi systems?

Concerning this part of your question: I also want to ask about why leucoindigo isn't planar. According to Wikipedia, "In indigo white, the conjugation is interrupted because the molecule is ...
gilleain's user avatar
  • 1,725
2 votes

Why don't universal indicator solutions react with themselves?

In a solution containing multiple species that undergo acid/base chemistry, everything will react with everything (including water, which can act as acid or as base). Equilibrium is established ...
Karsten's user avatar
  • 39.8k
2 votes

Looking for a non-toxic, environmentally safe highly colored or intense dye

Many organic dyes which are fluorescent can be carcinogenic like the famous Rhodamine dyes. You can try a couple of tricks. One of best inks, at least for demonstrations, is the yellow highlighter's ...
AChem's user avatar
  • 39.8k
1 vote

Which compounds react positively in the aniline dye test?

First, the aniline is converted to a diazonium halide salt in the presence of acid and sodium nitrite, per this reference. Then, the diazonium salt reacts with the phenol to give an azo compound, per ...
Greg D's user avatar
  • 700

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