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by: Carmela Kilback


Carmela Kilback
GPA 3.92

Scott Clary

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Scott Clary
Class Notes
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This 10 page Class Notes was uploaded by Carmela Kilback on Wednesday September 9, 2015. The Class Notes belongs to CHEM 242 at University of Washington taught by Scott Clary in Fall. Since its upload, it has received 8 views. For similar materials see /class/192544/chem-242-university-of-washington in Chemistry at University of Washington.




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Date Created: 09/09/15
SYNTHESIS OF AN AZO DYE FOR INCORPORATION INTO CYRSTALS In this lab you are going to synthesize an azo dye You may not have thought about it before but what is it about a dye that makes it colored Dyes are organic molecules that selectively absorb wavelengths of light within the visible range of the electromagnetic spectrum 400 800 nm The human eye responds to wavelengths within this range The white light we receive from the sun contains all the wavelengths within the visible range When an object absorbs a particular wavelength we see the wavelengths that are left over and the object appears colored Filtering orange light out of white light for example results in blue green cyan hue The hue resulting from the removal of a color from white light is the latter s complementary color Complementary Colors So now what determines what wavelength is absorbed The color in dyes is the consequence of the presence of a chromophore Chromophores in dyes are generally large systems of conjugated double bonds alternating double single bonds It is this delocalized electron system that absorbs the energy from the light For example if the electrons in the dye require only a small amount of energy to be rearranged into new energy state then the substance absorbs a low energy wavelength 7 The longer the wavelength the lower the energy E hch If you look at the Table above you will see that the longest wavelength is associated with the absorption of red light If the incident light is white and red light is absorbed then the light re ected is perceived as green the complementary color of red If a lot of energy is required for the electrons promoted to a higher energy state then it absorbs only a short wavelength light since short wavelengths correspond to high energy If it absorbs blue light then the light it re ects is perceived as yellow In general the more conjugation more double bonds you have in a dye the less energy it takes to excite the electrons But there is more to it than that While the chromophore is the colorproducing portion of the dye molecules there are other factors Dyes also contain auxochromes which are a group of atoms attached to a chromophore that modify the ability of that chromophore to absorb light In general auxochromes in uence the intensity of the dye but they can also provide a site by which the dye can chemically bond to the fabric Examples of chemical groups that are chromophores and auxochromes are shown below Chromophores Auxochromes Aryl group CH3 gtlt Double bonds OH NH NN Azo group 2 so339Na In this lab you are going to synthesize a dye that contains both aryl and azo functionality s see above To look at the impact of conjugation on the wavelength absorbed let s look at two commercially available azo dyes DO 00 HO HO N N N N CH3 CH3 CH3 N N Sudan 11 km 493 CH3 Sudan IV A 520 max Notice that Sudan IV has a more extensive system of conjugation and thus absorbs a longer lower energy wavelength Life would be simple if we could just look at conjugation but the color we see is also dependent on the auxochrome what the dye is bound to in the fabric the pH the list goes on As part of this lab you will look at the effect of a change in the pH on the color of the dye and sometimes it is very dramatic This is generally due to a change in the charge on the dye molecules or a change in the level of conjugation Adding or subtracting auxochromes can also effect the electron delocalization and thus change the color Therefore much of the work done in dyes can be considered as trial and error You just try something and see what color you get In essence this is what you are going to do in lab AZO DYE SYNTHESIS In this experiment you will use various organic amines to synthesize your azo dye Once the dye is synthesized you will observe the effect of pH on the color use your dye to color a variety of fabrics and you will try to incorporate your dye into a crystal of potassium dihydrogen phosphate KDP Azo dyes which were developed in the mid 1800s are one of the most common dye materials They contain the basic structure of ArNNAr Their color is due to the high level of conjugation that extends through NN double bond to the aryl unit Axo dyes are synthesized via the following reaction A primary amine RNHZ is converted to a diazonium salt see Solomons 7 ed section 207 and this is reacted with another aryl unit 0X acitvated aromatic XX X NH OH OR NH2 NaNOg 2 NEV N H3PO4 primary amine diazonium salt azo dye The aromatic ring can be substituted with different functional groups auxochromes and these substituents due to their conjugation with the azo system will effect the color of the dye see Solomons 7th ed section 209 for more details In this experiment you will be assigned which dye to synthesize from the various amines and activated aryl compounds shown on the next page Different combinations will lead to different colors Synthesis of your Dye You will choose two compounds from the list on the next page The first must be a primary amine NHZ 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 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 rst step NH2 NH NH2 O S Q 3 3 803H 2 6amino2naphthalenesulfonic acid aniline 3031 1 mw 241 1 2amino15naphthalenedisulfonic acid mw 303 NH2 303 NH2 803 NH2 803H 6 6 amino 1 naphthalene 7 803quot SOSH 5 sulfonic acid mw 223 3Amino15naphthalene 8amino15naphthalenedisulfonic acid dISUIfomc aCId dISOdlum salt mono sodium salt NH2 NH NH2 2 DNHZ H3CNCH3 039 11 Q 10 pchloroaniline 12 13 9 OOCHs W 127 SOZNHz NNdimethyaniine SO3 4 Aminoacetophenone sulfanilamide mw 121 mw 135 mw 172 suldfanilic alcid so Ium sa mw 231 OH CHO H HN 18 162napthol 17 CH3 5 033 15 mw 144 OH 2napththol6 sulfonic acid sodium salt Vanmin mw 152 mw 246 diphenylamine mw 169 SOSH c NH2 so 20 ochloroaniline NH2 mw127 4aminonaphthalene sulfonic aicd MW 223 Warning Amines are in general toxic compounds avoid skin contact NH chOQ 4 OCH3 35dimethoxy aniline mw 153 NCH32 I NN Dimethyl 1naphthylamine mw 171 OH NH2 sogH 14 303 8amino1naphthol 57disulfonic acid monosodium salt mw 341 NO ACCEOH 39033 19 30339 1nitroso 2 naphthol 36 disulfonic acid disodium salt mw 377 DYEING CRYSTALS Researchers have shown that molecules in solution 7 even molecules that are very different from the crystal molecules and ions 7 can arrange themselves on a growing crystal surface so that they make speci c non covalent bonds If these interactions are strong enough and crystal growth is fast enough the crystal can actually grow around and entomb the impurity However this only works for molecules with particular structures that match structural features of the growing crystals In part B of this lab we will attempt to grow dyed crystals of KHZPO4 potassium dihydrogen phosphate with azo dye that you have synthesized These dyes will tend to selectively stain the pyramid faces called 101 in crystallographic language See below 101 100 DYEING FABRIC In the last part of the experiment part C 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 effects the color The fibers contained in the swatch are shown below PROCEDURE Part A Synthesis of Azo Dye Step 1 F011nati0n 0f the diazonium salt Add 2 mL of water and 10 drops of phosphoric acid to a 5 mL conical vial with spin vane Cool the solution in an icewater bath and stir Add 01 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 0015 g 15 mg If the spin vane does not stir sufficiently periodically stir with your spatula to break up clumps Let the solution stir at 00 C for 10 minutes While the above solution is cooling prepare a solution of 20 mg of sodium nitrite in 1 mL of water Add approx 7 drops of the sodium nitrite solution to the conical vial a color change may occur Let this solution stir at 00 C for 10 minutes After 10 minutes test the reaction solution for excess sodium nitrite using starchIodide paper If the paper immediately shows a dark blueblack spot then this means that all of the amine has been converted to the diazonium salt If the paper does not turn black then add another 34 drops of sodium nitrite solution and let stir for another 5 minutes After 5 minutes of stirring proceed onto step 2 or if the starch Iodide paper turns black where you will add the aromatic compound you chose for the second component of your dye Dip a micro capillary it into the reaction vial and then touch the capillary onto a piece of Starch Iodide paper and let the solution bleed onto it Step 2 Additi0n 0f the activated aromatic compound Add 01 mmole of the aromatic amine or phenol to the diazonium salt solution Stir at 00 C for 5 minutes there may be a color change If the solid does not mix well by the spin vane action stir with your spatula or periodically cap the vial and shake for 10 seconds At the end of 5 minutes let the solution stir at room temperature for 30 minutes If necessary periodically shake to help mixing The solution will slowly turn color over time If time permits you may want to let the reaction stir longer in order to insure getting a more concentrated color Step 3 Dye color dependence on pH While you are waiting for the completion of step 2 prepare 2 test tubes as described below In test tube 1 add 2 mL of6 M NaOH check the pH to make sure it s basic In test tube 2 add 2 mL of distilled water this will be acidic once you add your solution After stirring at room temperature add 1 mL of the reaction mixture to test tubes 1 and 2 Note the colors Place one drop from each test tube on a piece of filter paper and note the color Place 3 drops of your most colored solution 1 or 2 in a vial with cap and add 1 drop of glycerol Cap and save this solution for analysis in the Electrophoresis lab next week Part B Incorporation of Dye into crystals of potassium dihydrogen phosphate KDP In this section you will make 2 different crystallization solutions One will contain the dye you synthesized and the second will contain the dye Chicago Sky Blue or Amaranth Red your choice The Chicago sky blue and Amaranth red dyes are known to incorporate into KDP but for your dye it is unknown whether it will incorporate Crystallization is an Art Crystal growth is effected by an array of subtle factors concentration of the solution amount of heat used to dissolve rate of cooling rate of evaporation and stillness of the crystal solution all can make a critical difference in the shape and beauty of the crystals you grow For this lab it is important that you get your KDP to dissolve by heating at low temperature It is also important that once you have dissolved your KDP and have added the solution to the crystallizing dish that you do not move itit is important that the solution remains still and to be on the safe side still your mind as well I Incorporation of your dye Label your crystallizing dish with your name and lab section Place the crystallization dish in the area marked for your section Your TA will show you where this is Eventually you will pour your crystallization solution into this dish Once this has been done it cannot be moved Preset the heat knob of your stirring hot plate to level 2 and let it warm up Weigh 17 grams of potassium dihydrogen phosphate KDP and transfer into a 250 mL beaker Add 50 mL of distilled water and a magnetic stirrer Cover the beaker with a watch glass and place the beaker on a hot plate Stir the solution with the heat set at 2 for 2 minutes then turn down to low and continue stirring until all solid has dissolved if the KDP does not dissolve after 10 minutes you may turn up the heat a little bit Once the KDP has dissolved add 1 mL of the solution prepared in test tube 1 or 2 Choose the color that pleases you the most Stir this solution for 1 minute be ready to do the next step immediately after the minute stir While the solution is still warm carefully pour it but not the stir bar into the crystallizing dish that you have placed in the designated area Immediately after pouring cover the dish with a watch glass Once poured be careful not to move the solution You will recover the crystals during the next lab meeting II Incorporation of Chicago sky blue or Amaranth red Dye In a 250 mL beaker labeled with your name and lab section dissolve KDP in the same manner as described above Once dissolved add 3 mL of Chicago Sky blue dye solution or 4 mL of Amaranth Red instead of your dye Once the dye has mixed for one minute cover the solution with a watch glass and quickly and carefully place this solution in the space designated for your lab section Part C Dying of Fabric Choose a solution from test tube 1 or 2 above that is of a preferable color Dilute this dye solution with 1015 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 1015 minutes cover with a watch glass to avoid evaporation If you want to increase the concentration of your dye you may add the remains of the original reaction vial 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 Warning Be careful not to touch your dye solution or the cloth without glove Your azo dye may be toxic andor a skin irritant Dye Synthesis RepOIt Form NAME Data and Results l15 pts Outline the synthesis of your dye Show the two reactants you chose and the structure of the nal product 2 5 pts Denote the color seen in each of the three test tubes Test tube Color 1 1M NaOH 2 distilled water 3 5 pts Did you see incorporation of your dye into a crystal What was the color of the incorporated dye


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