Combinatorial Synthesis of Azo Dyes

The effects of reagent diversification of dye formation were examined by combining different diazonium salts with different aromatic coupling reagents in order to observe the dye on fabric and the maximum wavelength produced. The structure of the diazonium ion has little effect on the dye produced because no matter which position the SO3H group is attached at, the bond always forms at the nitrogen. The structure of the aromatic coupling reagent affects the active position (α, β, or γ) in which the bond forms between the diazonium ion and the coupling reagent. The SO3H group attached to each diazonium ion is electron withdrawing and the OH group attached to each coupling reagent is electron donating. The color observed on the dyed fabric strips depends on conjugated double bonds, as in the aromatic rings of the structures. This is what absorbs energy from light. The wavelength depends on how much energy is required to reach the new energy state; therefore, lower energy results in longer wavelength. More conjugation in the structure of the dye compliments less energy required to move electrons. The intensity of color on the fabric is dependent upon the functional groups that are attached to the structures. The polarity of the groups, such as an oxygen or nitrogen, has a partial charge. Partial charges are responsible for stronger chemical bonds between the dye and the fabric—thus, more color intensity. Wool and nylon work best because their structures contain both oxygen and nitrogen. The partial charges on their oxygen and nitrogen atoms allow the opportunity for a stronger bond to the partial charges on the dye structures. For the reaction of naphthalen-2-ol with 4-, 3-, and 2- aminobenzene sulfonic acid, the λmax values were 580, 768, and 756 nm, respectively. The dye colors were shades of orange and red, and the fabric strips were various shades of orange (some white if the dye didn’t bond to the fabric). According to the visible light spectrum, these values coordinate with colors ranging from light orange to dark red. The reaction of naphthalen-1-ol with the aminobenzene sulfonic acids produced λmax values of 469, 478, and 480 nm. The dye colors were shades of red, and the fabric strips were different shades of brown and red.  The values represent energy used to move electrons in the conjugated system of the aromatic coupling reagent. The reaction of 2-hydroxybenzoic acid with the aminobenzene sulfonic acids gave λmax values of 400, 400, and 401 nm. The dye colors were yellow, and the fabric strips were related colors of yellow. Although these values do not coordinate with the yellow color in the visible light spectrum, they do represent a larger amount of energy required to promote electrons to a higher energy state because the structure of the aromatic coupling reagent contained less conjugation than the other coupling reagents in this lab. For the reaction of 8-anilino-1-naphthalenesulfonic acid with the amminobenzene sulfonic acids, the λmax values were 357, 498, and 479 nm. The dye colors were pick and red, and the fabric strips were shades of maroon, gray, pink, and tan. These low values correspond to the low wavelength violet region of the visible light spectrum.

In this experiment, combinatorial chemistry was examined through the synthesis of dyes formed from diazonium salts and coupling reagents. Because wavelength is based upon energy required to move electrons in the structures, structures with more conjugation possessed a more visible λmax and a lower energy requirement. The difference in colors on the fabric strip were affected by functional groups attached to the structures that affected intensity of color and were also responsible for chemical bonds formed to specific fabrics. When a single diazonium salt was reacted with 4 different coupling reagents, the result was 4 completely different dyes. When the same coupling reagent was reacted with three different diazonium salts, the result was three similar fabric strips—all the same color with different shades of that one color depending on the fabric. Therefore, the structure of the coupling reagents affected the product dye more than the structure of the diazonium ions with reference to dye colors on the fabric strips.

Electrophilic Aromatic Substitution

Conclusion:

In this experiment, two EAS reactions were performed and analyzed. The nitration of methyl benzoate formed the meta-nitration product 3-nitro methyl benzoate, according to NMR data. The Alkylation of m-xylene formed the 1,3,5-trisubstituted product, according to out-of-plane bending IR peaks.

Discussion:

In this experiment, two Electrophilic Aromatic Substitution (EAS) Reactions were performed and analyzed. The first EAS reaction was the nitration of methyl benzoate. The final recrystallized product weight was 0.307 g. The molecular weight was 182.16 g/mol. This calculated a theoretical yield of 0.4008 g and a percent yield of 76.6%. The melting point range was 79-80 deg C. The HNMR provided resulted in a meta-nitration product—3-nitro methylbenzoate. In this reaction, an excess of nitric acid and sulfuric acid were used; therefore, the major product was only mono-nitrated because the mono-nitration is strongly electron withdrawing. Excess sulfuric acid protonated the excess nitric acid to yield the nitronium cation. The nitronium cation was the nitrating electrophile. Excess sulfuric acid also pushed the equilibrium to the right in order to yield the nitronium cation. The second EAS reaction was the alkylation of m-xylene. The product molecular weight was 162.257 g/mol. This accumulated 0.206 g formed, or 0.00127 moles. Since the limiting reagent was 2-chloro-2-methylpropane, the theoretical yield was 0.73 g, which was used to calculate the percent yield as 28.2%. During the experiment, after 1ml of sat. sodium bicarb. was added, another ml was accidently added before the sat. sodium chloride; therefore, an extra extraction was done and accounts for much of the low percent. Also, while distilling the m-xylene, the temperature reached 200 deg C, or slightly above, probably causing some of the product to be distilled as well. There were 4 significant IR peaks that were taken into consideration. Peaks 691.7 and 768.5 cm-1 represented m-xylene starting material in the product; therefore, the reaction had to be heated to distill the m-xylene. Peaks 705.9 and 846.3 cm-1 were the C-H out-of-plane bending peaks that represented the substitution in the product; therefore, the product can be concluded as 1,3,5-trisubstituted. The expected substitution product would be 1,2,3-trisubstituted. Steric effect controlled the reaction outcome. The 1,2,3-trisubstituted product is a kinetic product and 1,3,5-trisubstituted is a thermodynamic product. The 1,2,4-trisubstituted product could have been obtained by using chloroethane instead of t-butyl chloride. The HNMR provided contains values for the aromatic proton peaks. These values were used to calculate coupling constants. The splitting patterns and oupling constants (J_ortho and J_meta) determined the position of the nitro group as meta.