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Indigo Synthesis

Author: Carolina Morales

Group #1

Lab Partners: Jennifer Capeloto, Samantha Hoffman and Adriana Garibay

Instructor: Saehan Park

Chem. 152, Section 43

Date Work Performed: February 10, 2010

Date Work Submitted: February 24, 2010


The percent yield of the color Indigo that is the color of blue jeans for the three trials was determined to be 13.50%, 15.30% and 14.80%. A series of experiments were performed to a cloth dye comparison. The absorbance of Disulfonic Acid in the experimental trial was 608nm with an absorbance of 1.037 with Beer’s law the epsilon value was determined to be 22416.67m-1c-1. The percent yield of the second indigo Carmine experiment was determined to be 7.55%, 8.06%, 6.91%, 5.10% and 4.72%.


This is a two week experiment involving transformation of matter where we will investigate the synthesis of the dye indigo, which will be made, isolated by the process of vacuum filtration and then evaluated. Indigo is the name given to an organic molecule with an intense blue color. It has been used to dye cotton and wool fabric, it is commonly known as the source of the color in blue jeans. The synthesis of new chemicals involves different processes. For example, first reactions are performed that generates new chemicals, and then the products are isolated from the other materials present, purified and characterized. The last step involves measurement of the chemical and physical properties to confirm their identity and purity. There are many different ways to make Indigo, using chemical equation, 2C7H5NO3 + 2C3H6 → C16H10N2O2 + 2CH3CO2H + 2H2O, the organic molecules are dissolved in water, a NaOH solution is then added to start the reaction, because Indigo is insoluble in water it precipitates as fast as it forms. The product will be collected by filtration and then will be quantified. By the process of Filtration is when the solid will be separated from the liquid leaving us with Indigo in solid state. Indigo insolubility in water makes it easily to isolate as well as it makes a good dye. In the second week Leucoindigo will be produced by a process called vat dyeing. In this process the indigo is first converted to the water-soluble leucoindigo using an appropriate reducing agent known as Sodium Stannite Reagent. Leucoindigo is a colorless molecule that is insoluble in water. The dye cloth of Indigo will be reduced to leucoindigo with an a reagent and dissolved water, where the cloth dye will be dipped in the solution and then the cloth should be able to dry completely because the oxygen in the air will oxidize the leucoindigo to indigo. This is known for the dye to become “Fixed” in the cloth as the color appears. Although Indigo is insoluble in water, it can be reacted with sulfuric acid to produce water-soluble forms that retain the characteristic of intense blue color, and it will be placed in a concentrated solution of sulfuric acid, the indigo will add two, three or four sulfonic acid (HS3-) units that the number will depend on the strength of the acid, temperature could possible affect the outcome. This is the process where Indigo will be transformed into Indigo Carmine. Where 18MH2SO4 will be dissolved with solid indigo and heated to promote the reaction and then adding water which will dilute the sulfuric acid and the un-reacted indigo will precipitate out. The wavelength will be useful to find the concentration (in Mol/L) using beer-lamber law[pic]., and finding the epsilon value of this reaction. Indigo disulfonic acid is a mixture that contains two units of sulfonic acid, trisulfonic acid contains three units, and tetrasulfonic acid contains four units. We will be able to find each one in this experiment that will be producing a new Indigo sulfuric acid reaction. Percent yield will used to Indigo Carmine by dividing the experimental yield of indigo carmine by the yield theoretically obtained from the moles of indigo used....
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