Azo Dyes and Colored Smoke

Today I synthesized 3,4'-dicarboxy, 4-hydroxyazobenzene.


By louf11 at 2011-08-28

It was made by coupling salicylic acid and para-aminobenzoic acid. No procedure in literature was followed. The synthesis was made on a 1/15 mol scale.

The purpose for synthesizing this azo dye was to make colored smoke with it. This did not turn out well.

Reagents:


By louf11 at 2011-08-28

Hydrochloric acid- technical, hardware store grade
PABA- relatively pure- extracted from a nutritional supplement
Salicylic acid- reagent grade, from Elemental Scientific
Sodium nitrite- Reagent grade, from Mallinckrodt
KI-Starch paper- Pure, from an old chemistry set

Procedure:

A basic solution of para-aminobenzoic acid (9.13 g) was made by adding granulated PABA to a solution of sodium hydroxide. All dissolved. Approximately 100 mL of 31.45% hydrochloric acid, a large excess, was then added. This gave a very fine acidic suspension of PABA, which would allow a quick reaction with nitrous acid.


By louf11 at 2011-08-28

The suspension was cooled in a NaCl salted ice bath. Ice cubes were added to the beaker. The temperature was -4C. An aqueous solution containing 5 grams sodium nitrite (4.6 grams required) was added slowly, keeping the temperature below 0C.

The NaNO2 solution was added until the solution turned potassium iodide-starch paper blue. Granular urea was added until the KI-starch paper was no longer blue. Urea reacts with excess nitrous acid generating gaseous products.

9.2 grams of salicylic acid was dropped in the beaker.


By louf11 at 2011-08-28

The salicylic acid seemed to dissolve to an extent. A saturated solution of sodium hydroxide, NaOH, was added.


By louf11 at 2011-08-28

By louf11 at 2011-08-28

The solution turned dark brown, and began boiling (due to adding the NaOH too quickly).

The goopy mixture was filtered, and the filtrate was clear.


By louf11 at 2011-08-28

The filter cake was dried in the oven for about half an hour.


By louf11 at 2011-08-28

The weight of the slightly moist powder was 19 grams, which would be a 100% yield (except for the moisture).

The powder will be recrystallized from ethanol tomorrow.


By louf11 at 2011-08-28

The dye is water and alcohol soluble, and depending on the concentration, gives solutions whose color can be anywhere between yellow, orange, or brown.


The dry powder was mixed with sodium chlorate, sodium bicarbonate, and sugar. The mix was ignited, but the smoke was pure white, not orange-brown as hoped.


By louf11 at 2011-08-28
This is a picture of the pyrotechnic mixture.

Does anybody know how to make colored smoke with azo dyes? I have searched the forum, but found nothing.

There is a youtube video by Chemx01 which shows smoke coloring of Para Red, so it definitely possible.

Is it possible that this dye simply doesn't color smoke? Could smoke coloring be somewhat of a physical property?

Thanks!


Oh, and one more thing... 250th post! AWWW YEAH!








[Edited on 28-8-2011 by redox]

Quote: Originally posted by redox

Today I synthesized 3,4'-dicarboxy, 4-hydroxyazobenzene. Does anybody know how to make colored smoke with azo dyes? I have searched the forum, but found nothing. There is a youtube video by Chemx01 which shows smoke coloring of Para Red, so it definitely possible. Is it possible that this dye simply doesn't color smoke? Could smoke coloring be somewhat of a physical property? Thanks!

What Ukl Sap currently uses for red smoke

Quote: Originally posted by redox

Thanks Wizard, I'll check out those links. Thus, I still don't know why it won't color smoke.

Quote: Originally posted by The WiZard is In

If the ratio of — oxidizer - sugar - smoke dye is off it may burn too hot - too cold for good effect.

Yeah, it looks like I'll have to experiment with the right ratio of components.

An update:

The dye was recrystalized from ethanol, yeilding 4.02 grams of a brown powder.

Cotton samples and pieces of paper towels were immersed in the supernatant liquid, which contained about 5 grams of contaminants and dye. The samples were dried, giving a very pleasant orange-brown stain.

Since I have found no common name for the dye, 3,4'-dicarboxy, 4-hydroxyazobenzene, I have named it "Carboxy Brown."


By louf11 at 2011-08-29

The dyeing solution, which is distinctly orange


By louf11 at 2011-08-29

A picture showing two dyed samples and the dry powder


By louf11 at 2011-08-29

A glass vial with a dyed sample, which will be a gift to a friend


I still cannot make the colored smoke.

[Edited on 29-8-2011 by redox]

Quote: Originally posted by redox

A glass vial with a dyed sample, which will be a gift to a friend I still cannot make the colored smoke.

The putative product is a known compound. SciFinder gives 32 references (output attached bellow), lists a number of commercial sources and gives the mp of 223 °C. It is referred by a trivial or by partially rational names such as benzalazine, salicylazobenzoic acid, [(carboxyphenyl)azo]salicylic acid. It was investigated and claimed to be useful for the treatment of gastrointestinal illnesses. I would tend to believe that it is only a prodrug for 5-aminosalicylic acid.

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