SYNTHESIS OF AN AZO DYE revisited (1 or 2 credits) This lab you can revisit the fist experiment of this quarter and synthesize more azo dyes of your choice. The old procedure is given below followed by some suggested changes you could do in the experiment to enhance your yield. If you synthesized one dye you get 1 credit, 2 dyes 2 credits. Note: if you can isolate and highly purify you solid dye you can received up to 5 extra credit points. AZO DYE SYNTHESIS Azo dyes are synthesized via the following reaction. A primary amine (R- ) is converted to a diazonium salt and this is reacted with another aryl unit. X NaNO 2 + N N H 3 PO 4 acitv ated aromatic X=,, OR N N X primary amine diazonium salt azo dye Synthesis of your Dye(s): Choose two compounds from the list on the next page (note that we added p-bromoaniline as a possible amine). The first must be a primary amine ( ). This is the compound you will react with sodium nitrite in the first step of the reaction. The second compound you choose can be any of the activated aromatic listed in the second group of compounds. This compound will be used in the second step of the reaction when you add this to the diazonium salt that you generate in the first step. To Prepare for this lab: Review the lab from earlier this quarter. Also review possible modification section below. Prelab to be turned into your instructor before you begin. Pick your primary amine and activated aromatic and write the reaction equation for your dye reaction. Draw the most likely azo dye product. Also consider that you may have more than one product due to ortho, para substitution parameters--if you feel that you might produce more than one product you can draw all that you feel might be possible Create a reagent table for each reaction The table should include names of starting materials, MW, moles and grams to be used and theoretical yield of the dye. List all amines as toxins. You do not need to list the name of the dye or any melting \ boiling point information
PRIMARY AMINES: Choose one of the below for the first step of the reaction - SO 3 Na + HO 3 S Aniline 6-amino-2-naphthalene sulfonic acid, Sulfanic acid 4-amino-1-naphthalene sulfonic acid, sodium salt NH2 Cl O CH 3 4-aminoacetophenone Br p-bromoaniline SO 2 Sulfanilamide Chloroaniline 2-amino-1,5-naphthalene DIsulfonic acid, ACTIVATED AROMATICS: Choose one of the below for the second step of the reaction H 3 C CH N 3 Aniline 2-napthol Br p-bromoaniline NN-dimethylaniline O H HO 3 S 6-amino-2-naphthalene sulfonic acid, Cl O CH 3 4-aminoacetophenone O C Salicylic acid SO 2 Sulfanilamide SO 3 - Na + 4-amino-1-naphthalene sulfonic acid, sodium salt Sulfanic acid OCH 3 o-methoxy phenol vanillin OCH 3 2-amino-1,5-naphthalene DIsulfonic acid, Chloroaniline NO 2 HO p-nitrophenol
Part B: DYEING FABRIC In the last part of the experiment (part B) you will use your synthesized dye to color a special swatch of fabric. The swatch is woven such that it contains bands of some of the more common fibers used in making clothing. The fibers included are both natural fibers and synthetic. Here you will explore how the interaction of the dye with the fiber affects the color. The fibers contained in the swatch are shown below. Fabric type (starting a end with black thread) Acetate SEF Arnel (bright) Bleached cotton Creslan 61 Dacron 54 Dacron 64 Nylon 6.6 Orlon 75 Spun silk Polypropylene Viscose Wool
PROCEDURE #1 Part A. Synthesis of Azo Dye Step 1--Formation of the diazonium salt: Add 2.0 ml of water and 20 drops of 10% sulfuric acid (H 2 SO 4 ) to a 10 ml or 25 ml round bottom flask with spin bar. Cool the solution in an ice-water bath and stir. Add 1.0 mmole of the amine to be converted into a diazonium salt. Note: if your amine is a liquid, you can assume that one drop weighs about 0.03 g (30 mg). If the spin bar does not stir sufficiently, periodically stir with your spatula to break up clumps. Let the solution stir at 0 o C for 10 minutes. While the above solution is cooling, prepare a solution of 80 mg of sodium nitrite in 1 ml of water. Add the sodium nitrite solution dropwise to the reaction mixture (a color change may occur). Let this solution stir at 0 o C for 15 minutes. Step 2--Addition of the activated aromatic compound: Add 1.0 mmole of the aromatic amine or phenol to the diazonium salt solution. Stir at 0 o C for 15-20 minutes (There may be a color change). If the solid does not mix well by the spin bar action stir with your spatula. If necessary, periodically shake to help mixing. The solution will slowly turn color over time**. At the end of 15-20 minutes at 0 o C let the solution stir at room temperature for 20 minutes. **If your activated aromatic is an amine the color formation may not be sufficient due to protonation of the amine at low ph of the solution. To remedy this slowly add a solution of 150 mg of sodium acetate dissolved in 1.0 ml water (make sure this solution is cooled to 0 o C before adding). If the ph is still too low and color has not improved slowly add 1 M Na dropwise until the solution becomes neutral (or just basic). You may see a strong color change with the addition of base. If time permits you may want to let the reaction stir longer in order to insure completion of the reaction. Step 3. Dye color dependence on ph When step 2 is complete you want to analyze the color of your dye depending on the ph of the solution. Measure the ph of your solution and note the color. Take about 5 drops of the solution and place it in a test tube and add either 1 ml of 1M Na or 1 ml 1 M HCl to change the ph from either acidic to basis or visa versa. There may be a dramatic color change. Step 4. TLC Prepare a TLC chromatography chamber using 95% methylene chloride, 5% methanol and 2-3 drops of acetic acid as a solvent system Obtain a TLC plate (silica gel) and spot your dye reaction mixture, 1 cm from the bottom of the plate (you and your partner can use the same TLC plate). The reaction mixture should be concentrated enough that you need spot only once and make the smallest spot possible. Develop the plate until the solvent level rises to about 1-2 cm from the top. Step 5. Isolation of the solid dye. Take about ¼ of the dye mixture (1-2 ml) and set it aside for part B (dyeing fabric). To the remainder of the solution cool your dye mixture on ice to precipitate (this may take a while). Once solid has formed filter the solution. Wash the filtered solid with ice water. (NOTE --see next paragraph if you didn t get any solid). Scrape the isolated solid onto a watch glass and let it dry until next period or attempt to recrystallize using water, ethanol or acetone as solvent. You may have to experiment around a bit to find the best system. You could also try a mixed solvent crystallization (see section 11.10 pg 667 of PLKE) using ethanol and water.
If you didn t isolate a solid from in the previous step, pour the colored solution into a beaker. Let the beaker stand uncovered in your drawer. Solid dye will crystallize over time. SAVE THE SOLID DYE THAT FORMS!--Later in the quarter we will try to create paint from your solid dye by incorporating it into either Gum Arabic or Linseed oil. PROCEDURE #2 Part A. Synthesis of Azo Dye Step 1--Formation of the diazonium salt: Add 2.0 ml of water and 20 drops of 10% sulfuric acid (H 2 SO 4 ) to a 10 ml round bottom flask with spin bar. Add 1.0 mmole of the amine to be converted into a diazonium salt. Note: if your amine is a liquid, you can assume that one drop weighs about 0.03 g (30 mg). If the amine does not dissolve gently heat the mixture until it does. Once dissolved cool the solution in an ice-water bath and let the solution stir at 0 o C for 10 minutes. Upon cooling the amine may or may not precipitate but in either case proceed to step #2 While the above solution is cooling, prepare a solution of 80 mg of sodium nitrite in 1 ml of water. Add the sodium nitrite solution dropwise to the reaction mixture. A color change may occur and the solution may become clear or remain as a suspension. Let this solution/suspension stir at 0 o C for 10-15 minutes. Step 2--Addition of the activated aromatic compound If your activated aromatic is an amine dissolve 1.0 mmole of the amine in 2.0 ml of acetic acid in a 25 ml round bottoms flask with spin bar. If you activated aromatic is a phenol dissolve the phenol in 2.0 ml of 1 M Na in a 25 ml round bottoms flask with spin bar Cool the activated aromatic solution to 0 o C. Once cooled, add the diazonium salt solution/suspension prepared in step 1, in small portions to your activated aromatic solution. Continue to stir at 0 o C during the addition. There may be a color change at this point**. Once all of the diazonium salt solution has been added let the solution stir at room temperature for 20 minutes. **If your activated aromatic is an amine the color formation may not be sufficient due to protonation of the amine at low ph of the solution. To remedy this slowly add a solution of 150 mg of sodium acetate dissolved in 1.0 ml water. If the ph is still too low and color has not improved slowly add 1 M Na dropwise until the solution becomes neutral (or just basic). You may see a strong color change with the addition of base. If time permits you may want to let the reaction stir longer in order to insure completion of the reaction. Step 3. Dye color dependence on ph When step 2 is complete you want to analyze the color of your dye depending on the ph of the solution Measure the ph of your solution and note the color. Take about 5 drops of the solution and place it in a test tube and add either 2 ml of 1M Na or 2 ml 1 M HCl to change the ph from either acidic to basis or visa versa. There may be a dramatic color change. Step 4. TLC Prepare a TLC chromatography chamber using 95% methylene chloride, 5% methanol and 2-3 drops of acetic acid as a solvent system Obtain a TLC plate (silica gel) and spot your dye reaction mixture, 1 cm from the bottom of the plate (you and your partner can use the same TLC plate). The reaction mixture should be concentrated enough that you need
spot only once and make the smallest spot possible. Develop the plate until the solvent level rises to about 1-2 cm from the top. Step 5. Isolation of the solid dye. Take about ¼ of the dye mixture (1-2 ml) and set it aside for part B (dyeing fabric). To the remainder of the solution add 0.5 grams of sodium chloride and cool your dye mixture on ice to precipitate (this may take a while). Once solid has formed filter the solution. Wash the filtered solid with ice water. (NOTE --see next paragraph if you didn t get any solid). Scrape the isolated solid onto a watch glass and let it dry until next period or attempt to recrystallize using water, ethanol or acetone as solvent. You may have to experiment around a bit to find the best system. You could also try a mixed solvent crystallization (see section 11.10 pg 667 of PLKE) using ethanol and water. If you didn t isolate a solid from in the previous step, pour the colored solution into a beaker. Let the beaker stand uncovered in your drawer. Solid dye will crystallize over time. SAVE THE SOLID DYE THAT FORMS!--Later in the quarter we will try to create paint from your solid dye by incorporating it into either Gum Arabic or Linseed oil. Part B Dying of Fabric (this is the same for both procedure #1 and #2) Take the dye solution saved from step #5 in part A. Dilute this dye solution with 15-20 ml of distilled water. Obtain a piece of multibanded fabric and submerge the fabric into the dye solution and gently heat on a hot plate for 10-15 minutes (cover with a watch glass to avoid evaporation). Once you are done heating, rinse with water and leave the cloth in your drawer. In some cases the dye color and intensity will change once the fabric has dried out. Possible Modifications: 1.Isolating the dye early, before it decomposes. Many of the dyes seem to get worse the longer they reaction. Try stopping the reaction at a good color by perhaps cooling it on a dry ice bath (see 2 below) and then quickly filtering. 2.Isolation of the solid dye. If you dye doesn t precipitate by cooling, add sodium chloride (0.3-0.6 grams) to the solution & cool. This may salt out your dye product. Also try cooling the solution in an ice bath with sodium choride added this will lower the temp by about 10 C. You could also try a dry ice bath for cooling (dry ice in acetone to get -78 C! 3. Recrystallization of your Dye: Try and get extra pure dye by recyrstallizing it using water, ethanol or acetone as solvent. You may have to experiment around a bit to find the best system. You could also try a mixed solvent crystallization (see section 11.10 pg 667 of PLKE) using ethanol and water. Getting pure dye product you will receive 1-3 extra credit points. 4. Solvent effect of color: Once you have isolated a solid dye, dissolved it in different solvents (acetone, methanol, water, methylene chloride) and note the color variation. 5. Anything else you can think of do.
Chemistry 252 Experiment :Azo dye revisted Spring 2010 REPORT GUIDE Report Due: check out day. Worth: 1 or 2 credit Turn in one report for each dye synthesized NAME Attach you multfabric cloth and turn in you dye in a vial (label with your name and structure) 1 a.outline the synthesis of your dye. Show the two reactants you chose and the structure of the final organic product under acidic conditions. (note: If you have both ortho and para products you only need to show one of them) b. Sketch the TLC plate and note the colors of each spot, Rf values and the solvent system. Also include a TLC of any purified dye you produced. 2.Part A Denote the color for each ph condition. Acidic conditions (ph < 7) Basic conditions (ph > 7) Color 3. What changes did you do how did they work out?(you can add more details on the back of this page.)