Chemistry Crystallization Lab 3

Experiment 2 ■ Crystallization 4. Thymol is very stig.htly юluЫе in water мd very soluЫe in 1.0 М NaOH. Explain. � Уон Thymol СН-СНз 1 СН3 5. Altlюugh canna.Ьinol and methyl alcohol are Ъoth вlcohols, cannabinol is very sLlghtly soluЫc tn methyl alrohol at room temperature. Explain. EXPERIMENT 2 Crystallization Cryst•llwitirm Vacuum filtr11tion Melting point Finding а crystallization soltJt!.nt Mirture melting point CritiCAl-thinking applic,itimt 1Ъе purpose of this experiment is to introduce the technique of crystaШzation, the most rommon procedure used lo purify crude solids in the orgaл.ic taЬoratory. For а thorough discussion of crystallizat:ion, read Technique 11 Ьefore proceeding, as an understanding of this met.hod is assumed in t.his experiment. ln Experiment 2А, you wШ carry out а crystaШzation of impure sulfanilamide using 95% ethyl alcohol as the solvent. Sulfanilam.ide is one of the suJfa drugs, the first gene[atjon of antibiotics to Ье used in successfuHy treating many major dis­ eases, such as malaria, tuЬerculosiз, алd leprosy (see the essay "Sulfa Drugs," that precedes Experiment 49). 1л Бxperirnent 2Ai and in most of the experiments in this textЬook, you are told what solvent to use for the crystaШzation procedure. Some of the factors involved in selecting а crystaШzation solvent for sulfanilamide are discussed in Tech­ nique 11, Section 11.5. Тhе most impor1antronslderation [s the shape of the solubll­ ity curve for the soluЫlity vs. temperature data. As сап Ье seen in Technjque 11, 10 P.art On� ■ lntroduc:tion to Basic Laboratof}' Techniques Figure 11.2, the soluЬility curve for sulfanilamide in 95% ethyl alcohol indicales that ethyl alcohol is an ideal solvent for crystallizing sulfaлilamide. Тhе purity of the final material after crystallization will Ье determined Ьу find­ ing the melting point of your sample. You \-vill also weigh your sample and calcu­ Jate the percent.,ge recovery. It is impossiЬle to obtain а 100% recovery. This is true for several reasons: There \-ViН Ье some experimental loss, the original sample is not 100% sulfanilamide, and some su1fanilamide is soluЬle in the solvenl even at 0°С. Вecause of this last fact, some sulfllnilamide will remain dissolved in the mother liquor {the liquid remaining after crystallization has taken place). Sometimes it is worth isolating а second crop of crystals from the mother liquor, especially if you have pcrformed а synthesis requiring many hours of work and the amount of product is relatively small. This сап Ье accomplished Ьу heating the mother liquor to evaporate some of the solvent and then cooling the resuJtaлt sotution to induce а second crystalliza.tion. The purity of the second crop wШ not Ье as good as the first crop, ho,vever, because the concentration of the impurities wШ Ье greater in the mother liquor after some or the solvent has been evaporated. ln Experiment 2В, you will Ье given ап impure sa.mple of the organic com­ pound fluorene (see structure that follows). You will use ал experimental proce­ dure for determining which one of three possiЬle solvcnts is the most appropriate. The three soJvents will illustrate three vегу different юlubility behaviors: One of the solvents will Ье an appropriate solvent for crystallizing fluorene. ln а second solvent, Лuorene will Ье highly soluЫe, even at room temperature. Fluorene will Ье reLatively insoluЫe in the third solvent, even at the Ьoiling point of the solvent. Your task wil\ Ье to find the appropriate solvent for crystallization and then per­ form а crystal!ization on this samplc. AuoNne You should Ьс aware that not all crystallizations will look the same. Crystals have many different shapes and sizes, and the amouлt of mother liquor \'isiЬle at the end or t:he Cr')'Stallization may vary signjficantly. Тhс crystallizations or sulfa• nilamide and fluorene will appear significantly diff@rent, e\•en though the purity of the crystals in each case should Ье vегу good. 1n Experiment 2С� you ,vШ determine the ident:ity of an unkrюwn using the melt­ ing point technique. The mi.xture- melting point technique is introduced in this section. REQUIRED READING SoluЬility Reviao: Technique 10 Nnv: Technique 8 Filtration, Sections 8.3 and 8.5 Technique9 Physical ConstantsofSolids: The MeJtjng Point Technique 11 Crystallization: Purification of Solids SUGGESТED WASТE DISPOSAL Dispose of all organic \vastes into the nonhalogenated organic \-vaste container. &pC!:riment 2А ■ Macroscale C i:ystaШzation Macroscale CrystallizaHon Тhis experiment assumes а famШarity with the generaJ macroscale crystallization procedure (see Techruque 11, Section 1 t.3). ln this experiment, step 2 in Figure 11.4 (removal of insoluЫe impurities) wШ not Ье required. Although the impure sample may have а slight color, it will also rюt Ье necessary to use а decolorizing age:nt (see Technique 11, Section 11.7). Leaving out these зteps makes the aystallization easier to perform. Furthermore, very few experiments in this textЬook requ:ire eit:her of these techniques. lf а fiJtration or decolorizing step is ever requirE:d, you may con­ sult Tecnnique 11, which descriЬes these procedures in detail. Pre-leb C.lculetiona 1, Calculate how much 95% ethyl alcohol will Ье required to dlssolve 0.75 g of sulfanilo1midc at 78°С. Use the graph in Technique 11, Figure 11.2, tomake thi9 calculation. Тhе reason for making: this c.alcu1ation is ю lhat you wШ know ahead of time the approxi­ mate amount of hot sclvent you wШ Ье adding. 2. Using the volwne of solvent calcul.ated in step 1, caJculate how much sulianilamide will rema[n dlssolved in thc mothcr liquor after the mixture is aюl«t to О"С. То dissolve the sulfanila.JJ'Ude in the minimum amount of hot (ЬоШng or aJmost ЬоШng} solvent, you must 1сеер the mixture at (or near) th.e ЬоШng point of 95% ethyl alcohol during the entire procedure. You will likely add more solvent than the amount you calculated, as some solvent will evaporate. Тhе amount of solvent is calculated only to indicate the app.to)(lmate amount of solvent required. You should folJow the proced.ure to determine the сопесt amount of solvent needed. PROCEDURE Pr1p1r1tlo■1. Weigh 0.75 g of impure sulfenilamide end trensfer this solid to а 25•ml Erlenmeyer flssk. 1 Note the color of the impure sulfanilamide. То а second Erlenmeyer flask:, add aЬout 15 ml of 95% ethyl alcohol and � Ьoiling stone. Hezit the solvent on е warm hot pla1e until the solvent is ЬОШng.1 Весаuзе 95% ethyl elcohol boils at а relativety lсн,,, temper&­ ture (78"С), it evapora1es quite rapidly. Settino the temperature of the hot plate too high wi11 result in too mud1 loss of solvent through eveporвtion. DJ1181vl11 tha Sull11i111Wtd1. Ввfоrв hвaring thв ffask conraining rhe sulfвnilamide, add enough hot solvent with а Pasteur pipet 10 barelv cover the crystzits. Then heat the tlesl: containing the sulfanilamlde until the solvent is Ьoiling. At flrst this may Ье difficult to see. OOC8use so little so1vent 1s present. .дdd another small ponion of solvent (eЬout 0.5 mL), con­ tinue to heat the flask. and swirl the flask frequently. You rNy swirl the flask while it is оп the hot p1ate or, fог more vigorous swirting, remove it frorn the hot plate fог а few seconds while you swirl it. When you have swir1ed the flask. for 10-15 seconds, check. to see if the sol1d hзs dissolved. lf it has not, add another portion of so1vent. Heet the flesk again with occas1ona1 swirllng until the solvent ЬOils. Тhen swirl the flask for 10-15 seconds, frequently returning 1 Тhе impu� sulfanilnmidc contains 5% fluoronone, а yeHow compound, as the impurity. 1То prevcnt bшnping in tlw Ьoili11g solv@nt, you may want to place Pasteur pipel in the flask. U!!e в 50-mL Aask so thal the Pasteurplpet does not ttp the Rask over. This is а conveiUent melhod Ьec.iiu.se а Pasteur plpet will also Ье used Ю transferthe solvent. 1!1 P.1rt One ■ lntroduction to Basic LaЬoratory Techniques the flask to the hot plate so thet the temperature of the mixturв does not drop. Continue repeating the process of adding solvent. heat1ng, and swirling untll all th e solid has dissotved completely. Note that it \s essentiel to add just erюugh solvent to dissolve the solid-neither too much nor too little. Вecause 95% ethyl alcohol is very v