Combinatorial Synthesis of Azo Dyes
Paul Guinn and Zachary Nichols
6 February 2024
Reaction Scheme
Procedure
First, a hot water bath was made in a 250mL beaker. Next, 2.8mmol of 8-anilio-1-napthalenesulfonic acid ammonium salt was added to 5mL of .25M sodium carbonate in a test tube. This
was gently heated in hot water until all solids had dissolved. Next, 2.8mmol of sodium nitrite
was added to the test tube, as it was moved to an ice water bath.
Separately, 3g of crushed ice were added to a 25mL Erlenmeyer flask followed by 0.5mL of
concentrated HCl using a burette.
Next, the contents of the initial reaction solution were added to ice/acid solution dropwise, while
being swirled to mix periodically. After all of the initial reaction solution was added, the flask
was placed in an ice-water bath and allowed to sit.
In a separate small test tube, 2.8mmol of orthanilic acid were combined with 2.0mL of 2.5M
sodium hydroxide. This test tube was gently heated in a hot water bath until all solids had
dissolved, before it was transferred to sit in an ice-water bath for 5 minutes.
This cooled orthanilic acid solution was then added dropwise to the Erlenmeyer flask containing
the diazonium salt with thorough mixing. This mixture was allowed to react in the ice bath for 10
minutes before being removed from the bath, dried, and heated on the hot plate. The solution was
heated until all solids had dissolved. 1g of NaCl was added at that point, and heating continued
until all solids had dissolved once again.
The flask was removed from the hot plate and set on a bench to cool at room temperature until it
was cool to the touch. The flask was then transferred to an ice-water bath to continue to cool and
to crystalize the azo dye.
This mixture in the Erlenmeyer flask was then vacuum filtrated and rinsed with NaCl solution.
The filtrate was collected.
Having not obtained solid, 2mL of vacuum filtrate was mixed with 20mL of DI water in a 100mL
beaker. A strip of fabric was then inserted into the azo dye solution and allowed to soak for 5
minutes. The fabric was removed from the solution and rinsed thoroughly with tap water, before
being patted dry to allow for observation of the dye’s true color. Hazardous waste was disposed
of in hazardous waste containers.
Theoretical Yield
Balanced Chemical Equation:
1 8-anilio-1-napthalene-sulfonic acid ammonium salt + 1 orthanilic acid →1 azo dye compound
Moles of 8-anilio-1-napthalene-sulfonic acid ammonium salt: 0.0028
Moles of orthanilic acid: 0.00279
Limiting reagent: orthanilic acid
Theoretical yield calculation:
0.00279 𝑚𝑜𝑙 𝑜𝑟𝑡ℎ𝑎𝑛𝑖𝑙𝑖𝑐 𝑎𝑐𝑖𝑑 ×
1 𝑚𝑜𝑙 𝑎𝑧𝑜 𝑑𝑦𝑒
= 0.00279 𝑚𝑜𝑙 𝑎𝑧𝑜 𝑑𝑦𝑒
1 𝑚𝑜𝑙 𝑜𝑟𝑡ℎ𝑎𝑛𝑖𝑙𝑖𝑐 𝑎𝑐𝑖𝑑
The theoretical yield of this reaction is 0.00279 moles.
Reagent Solubility
Sodium carbonate is added to the aminobenzenesulfonic acid because it is not readily soluble in
acidic solutions. Thus, the basic sodium carbonate allows the aminobenzenesulfonic acid to
readily dissolve by deprotonating it.
Likewise, sodium hydroxide is added to the aromatic coupling reagent because it is acidic and
not readily soluble in acidic solutions. Thus, the basic sodium hydroxide allows the aromatic
coupling reagent to readily dissolve by deprotonating it.
Fabric Dyeing Analysis
The multi-fabric strip was thoroughly colored by our dye solution. It came out orange, with a
light coloring on the filament acetate, lighter coloring on the bleached cotton, the darkest
coloring on the spun polyamide, the lightest coloring on the dyeable polyester and spun
polyacrylic, with medium coloring on the silk and worsted wool, and similarly light coloring on
the spun viscose to that observed on bleached cotton.
All azo dyes seemed to work well across the spun polyamide, spun silk, and worsted wool
groups. Dyeing effect was minimal on other fabrics for the dyes synthesized from salicylic acid,
which could be due to the smaller size of this reactant’s product’s pi system, leading to less
conjugation and therefore less, lighter coloration
Azo dyes synthesized from 2-naphthol seemed to work to some extent across all fabrics,
excluding polyester and polyacrylic. This likely has to do with the electron-donating OH
attached to the pi system in each of these dye products.
Azo dyes synthesized from 8-anilio-1-napthalenesulfonic acid ammonium salt seemed to work
well across to some extent across all fabrics, excluding polyester and polyacrylic. They also
produced the deepest color. This likely has to do with the electron-withdrawing SO 3H group,
with the greatest dyeing effect when the group is ortho to the N=N bond of the product, and
lesser though similar dyeing effects when the group is meta or para to the N=N bond.
All of the products seemed to have a yellow-dyeing effect, excluding those from the 8-anilio-1napthalenesulfonic acid ammonium salt, of which two had a red dyeing effect, and one that
created an orange dyeing effect. This makes sense, as these products were the largest pi systems,
giving them a higher λmax than the other similarly-sized pi systems, leading to the stark color
difference.
The polyester fiber and the polyacrylic fibers both were dyed less intensely than the other fibers,
including the other synthetic polymers. Both of these molecules possess an oxygen-carbon
double bond in their structures and, due to not being able to form H-bonds like the amides and
alcohols can, are less soluble in H-bonding substances than molecules that can for H-bonds.
WHile polyacrilic can potentiall form H-bonds, the electrons in the system are concentrated
along the oxygen-carbon double bond. Notably, all of the possible dye products have groups that
are capable of forming H-bonds and, because of this, will have an easier time inserting
themselves into the fibers that can form H-bonds well. This reason would also explain the
filament acetate being less dyed, as it also has an oxygen-carbon double bond but has some Hbonding capability, which is hindered due to its massive structure.
Discussion
Given that our and our class’s results conform to our understanding of conjugation, diazonium
salts, and color, we assess that this was a successful experiment. Since our product dyed the
fabric orange, we expect its λmax to be in the range of complementary blue, which is 430-
490nm. The color we see is the complementary color of the light absorbed by the pi system, and
blue complements orange.
Lab Notebook