Synthesis
Parker Indigo Ashbaugh Chem. 104B Section 09 11/05/2007
TA: Tim Black
Abstract: In this lab the synthesis of indigo was analyzed. It was found that a percent
yield of indigo from 2-nitrobenzaldehyde was 107% and the conversion of indigo to Indigo Carmine was 100%. It was also found that the indigo produced was Blue #2 Indigo Carmine through the use of spectrophotmetry. The lab resulted in error and values that were not very accurate.
I. Introduction In this lab the common dye known as indigo (C16H10N2O2) will be produced and analyzed. Indigos are commonly used in the dying of fabrics as well as in the medical field. They are characterized by their blue to violet color. In this lab indigo will be synthesized from the reaction of 2-nitrobenzaldehyde (C7H5NO3) with acetone (CH3COCH3) in a basic solution. During the duration of the reaction, the indigo rapidly precipitates out of solution and then is isolated using the vacuum filtration. The indigo produced is in an insoluble form and is not adequate for dyeing fabrics. Because of this the indigo must be reduced to leucoindigo, which is soluble in water and can therefore be used as a dye. The dye works by re-oxidizing the leucoindigo with the air which causes the dye to adhere to the fabric molecules. As the dye is allowed to re-oxidize the fabric begin to gain the characteristic blue color of indigos. In the lab the indigo was then converted into Indigo Carmine. This was done in order to test the absorbency and determine the chemical makeup of the indigo. The reason for the difference in indigo make up is that indigo will gain sulfonic acid groups, while still maintaining the blue color. The difference in the amount of time that the reaction is allowed to react will result in different quantities of indigo dye because of the sulfonic acid attaching to the indigo.
II. Experimental During the first step of making the indigo, all mass and volume measurements were double the amount listed in the lab manual, in order to make excess indigo for another unrelated experiment. In order to begin the synthesis of indigo 0.802 grams of 2nitrobenzaldehyde were dissolved with acetone in a 6 inch test tube and NaOH added slowly to start the reaction to form indigo. The test tube was swirled in order to mix the reactants further and allow more product or indigo to be form. A vacuum filtration system was set up in order to collect the precipitate indigo. After collection of the precipitate the indigo was dried and weighed to determine a percent yield. Next 0.169 grams of indigo solid was dissolved with NaOH in a hot water bath. The reaction was allowed to progress for 5 minutes. Then a solution of sodium stannite was prepared by adding 1.003 grams of sodium chloride to 10 mL of 1 M HCl and 20 mL 3 of M NaOH. This solution was then slowly added to the indigo solution in order to produce leucoindigo. Another portion of .105g of indigo solid was weighed and placed in a cleaned test tube. Twenty drops of concentrated 18 M H2SO4 were added and the test tube placed in a simmering water bath. After eighteen minutes the solution was poured into water and vacuum filtered to collect any unreacted indigo. The collected filtrate was then measured and diluted in order to perform a spectrophotometric analysis. This was used to determine the concentration of indigo in the final solution.
III. Raw Data and Observations Can be found attached to this lab IV. Calculations Can be found attached to this lab
V. Results Reaction % yield Indigo Synthesis 60% Indigo Carmine Conversion 100%
Fabric Type Dye color Spun Diacetate Deep Blue/ Violet Bleach Cotton Slightly darker blue/ Denim Spun Polyamide Lighter Blue/ Denim Spun Polyester Slightly faded Blue Spun Polyacrylic Faded blue Worsted Wool Spotted blue and white
The Dye was found to be Blue # 2 Indigo Carmine through the Absorbency test.
VI. Discussion During the experiment the indigo was synthesized and produced a % yield of 60% for regular indigo and 100% for Indigo Carmine. It was also found that the Indigo Carmine produced was Blue #2 during the spectrophotometry test. The dye produced was very effective in dyeing the different types of fabrics. The dye did take time to produce but it resulted in a very effective soluble dye. The data collected was obtained to the best of the abilities of the individual. Despite this several sources of error were present and resulted in data that was not very accurate. The first source deals with the fact that the percent yield for the indigo synthesis is over 100% which is not possible in the physical universe. The reason that this error occurred is because the indigo was not given adequate time to dry. This resulted in a high weight of the sample after filtration. A possible way to correct this source of error is to allow the sample to dry overnight to ensure that the sample is fully dry. The next source of error is that this experiment was not preformed analytically. This results in data that is not always accurate and makes several assumptions. There was also inherent error in the way the synthesis of indigo took place. The reaction was exothermic and produced a lot of heat. This in turn can cause the acetone to evaporate and thus stop the reaction early. The measurements and data provided to complete analysis of the lab was not adequate and resulted in many assumptions being made. Overall the lab was a lesson in the collection and analysis of data. The sources of error can be corrected only to a certain extent but error will always occur in the lab.