Lecture 5 Chem 237 February 17 2015 Challenge Your challenge in this experiment is to isolate and identify a conjugated diene in Eucalyptus Oil Possible Conjugated Dienes in Eucalyptus Oil CH 3 CH3 H 3C CH3 CH 3 CH3 H 3C myrcene CH 3 H3 C allo ocimene CH3 terpinene H 3C CH 3 phellandrene What does conjugated mean Two double bonds separated by one single bond You will perform a Diels Alder reaction on eucalyptus oil with maleic anhydride to isolate the diene from the eucalyptus oil The melting point of the Diels Alder product will allow you to determine which diene is present in eucalyptus oil Outline of Experiment 3 This week Calculate the amount of maleic anhydride needed based on the weight of the diene from TAs Perform the Diels Alder reaction Crystallize the product Next week Recrystallize the product Take a melting point of product to identify product and the conjugated diene Look up adducts mp Obtain an IR spectrum of the product Two weeks Post Lab Report Due Diels Alder Cycloaddition General Reaction 1 3 Diene 4 e 4 2 cycloaddition Dienophile 2 e Cyclohexene Conformations of the Diene R R R R R R R R s trans R R R R s cis Although the s trans conformation is more stable the Diels Alder reaction can only proceed with the diene in the s cis conformation Diels Alder Reactions O Acyclic Cyclic O O O O O O O O s cis Diene O Maleic Anhydride Very Good Dienophile O Fused Bicyclic Product Bridged Tricyclic Product O Diels Alder Adduct Blue atoms from the diene component Red atoms from the dienophile component Black new bonds Really Good Diels Alder Reactions DIENE Electron Rich Can reach s cis conformation Unhindered Cyclic DIENOPHILE Electron Poor Unhindered What are you going to do this week Using w w of diene in eucalyptus oil to determine how much maleic anhydride you will use This number will come from your TA determine the fraction of diene in your 5 g sample Does it matter which diene it is for this calculation Set up your reaction and reflux for 45 60 minutes Crystallize product Recrystallize product Read your manual carefully However IR but NO NMR Organic Compound Drawing Available programs for drawing ChemDraw http computing scs illinois edu content chem draw ultra license available 2012 ChemDoodle http www chem illinois edu clcwebsite ChemDoodle html MarvinSketch http www chemaxon com products marvin marvinsketch gclid Cj0KEQiAjZGnBRCOuJOUo9Xd0sUBEiQAPbic N7ykXpQ1XJmYtEMI2nWz qRepLFiORMN1CC JZ QgEf4aApsf8P8HAQ Organic Compound Searching Compound searching SciFinder www library illinois edu chx sfchanges html Beilstein Through Reaxys http www library illinois edu chx reaxys html Both website search engines require a VPN connection or being on campus network Recrystallization What s the Point technique for purifying solids Why Should we Care One of the most important methods for purifying pharmaceuticals High purity but often low recovery Recrystallization Theory Theory is that the solvent should Not react with the compound Dissolve the compound at the solvent b p Not dissolve the compound at room temp Impurities should be soluble at all temps in part because they are minor components Usually the b p m p boiling point of solvent should be low enough to easily remove Recrystallization Concepts Crystals are formed by cooling supersaturated solution cool Equilibrium Xsolution Xsolid heat Crystal lattice is highly ordered Impurities are excluded with slow cooling Cooling too fast traps impurities Recrystallization crystallization Procedure for Recrystallization Soluble at high temps insoluble at low temps Like dissolves like polar compounds dissolve well in polar solvents nonpolar cmpds dissolve well in nonpolar solvents Try a small amt of sample and do some tests in several solvents or solvent mixtures In general but not always b p of solvent should be below m p of sample First weigh your sample Save a small amt of your sample Use minimal amount of hot solvent in order to make supersat d solution Procedure for Recrystallization cont Decolorize with Charcoal Charcoal binds many compounds non selectively Colored impurities that are usually present in very small amounts become bound to the charcoal Use small amounts of charcoal Your compound will also bind Don t add charcoal to boiling solution Cool first add and rewarm Filter Gravity filter the HOT solution do not use vacuum filtration Filtration removes insoluble impurities charcoal Crystallize Cool slowly seeding may be necessary Procedure for Recrystallization cont Obtain crystals from the mother liquor Use filtration break up clumps that may have impurities trapped Wash crystals Use minimum of COLD solvent avoid dissolving of your cmpd Dry crystals Air dry or place in desiccator Grind up large clumps to give larger surface area Second crop from filtrate Boil off some solvent to decrease volume Cool again and obtain more crystals Increases yield Determine purity and yield Melting point recovery crop 1 crop 2 DO NOT COMBINE 1st and 2nd crops SAVE SAMPLES FREQUENTLY DO A SOLVENT SURVEY In small test tubes take a few crystals and test solvents polarity Solvent Soluble Cold Soluble Hot pet ether no no cyclohexane no no carbon tet no no toluene no no diethyl ether no no chloroform no yes no EtOAc no yes yes CH2Cl2 yes acetone yes ethanol yes methanol yes water no solvent mixtures can be used no Crystals RECRYSTALLIZATION FLOW CHART IMPURE COMPOUND insoluble impurities soluble impurities dissolve in hot solvent hot gravity filtration FILTRATE compound soluble impurities cool to crystallize vacuum filtration CRYSTALS FIRST CROP pure compound wet with solvent INSOLUBLE IMPURITIES discard FILTRATE MOTHER LIQUOR compound and soluble impurities boil concentrate vacuum filtration CRYSTALS SECOND CROP less pure compound wet with solvent FILTRATE compound soluble impurities KEYS TO GOOD HOT GRAVITY FILTRATION