Lecture 5 Chem 237 February 17, 2015Challenge: Your challenge in this experiment is to isolate and identify a conjugated diene in Eucalyptus OilPossible Conjugated Dienes in Eucalyptus Oil What does conjugated mean? 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. CH3H3CCH3H3CCH3CH3CH3H3C CH3CH3H3C CH3β-myrcene allo-ocimeneα-phellandreneα-terpineneTwo double bonds separated by one single bondOutline of Experiment 3 This week • Calculate the amount of maleic anhydride needed based on the weight % of the diene (from TAs) Next week • Perform the Diels Alder reaction • Crystallize the product Two weeks: Post-Lab Report Due • “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.Diels-Alder Cycloaddition 1,3-Diene(4πe—)Dienophile(2πe—)Cyclohexene[4+2]cycloadditionConformations of the Diene:RRRRRRRRRRRRs-ciss-transAlthough the s-trans conformation is more stable, the Diels-Alder reaction can only proceed with the diene in the s-cis conformation.General Reaction‡Diels Alder Reactions OOOOOO++OOOOOOs-cisDieneMaleic AnhydrideVery Good DienophileDiels Alder AdductAcyclicCyclicFused BicyclicProductBridged TricyclicProductBlue- atoms from the diene componentRed – atoms from the dienophile componentBlack – new bondsReally Good Diels Alder Reactions DIENE• Electron Rich• Can reach s-cis conformation• Unhindered• Cyclic DIENOPHILE• Electron Poor• UnhinderedWhat 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 NMROrganic 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=Cj0KEQiAjZGnBRCOuJOUo9Xd0sUBEiQAPbicN7ykXpQ1XJmYtEMI2nWz_qRepLFiORMN1CC_JZQgEf4aApsf8P8HAQ)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 networkRecrystallization ✔ 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 recoveryRecrystallization Theory 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 Theory is that the solvent should:Recrystallization Concepts Crystals are formed by cooling supersaturated solution Equilibrium: coolheatXsolutionXsolidCrystal lattice is highly ordered Impurities are excluded with slow cooling. Cooling too fast traps impurities. Recrystallization ≠ crystallizationProcedure 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 Use minimal amount of hot solvent in order to make supersat’d solution. First weigh your sample!! Save a small amt of your sampleProcedure 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! Filter Cool slowly; seeding may be necessary Gravity filter the HOT solution (do not use vacuum filtration) Filtration removes insoluble impurities + charcoal Crystallize Don’t add charcoal to boiling solution! Cool first, add and rewarm.Procedure for Recrystallization (cont.) Obtain crystals from the mother liquor Use filtration, break up clumps that may have impurities trapped Use minimum of COLD solvent (avoid dissolving of your cmpd) Air dry or place in desiccator; Grind up large clumps to give larger surface area Second crop from filtrate Melting point, % recovery (crop 1 + crop 2), DO NOT COMBINE 1st and 2nd crops SAVE SAMPLES! Boil off some solvent to decrease volume Determine purity and yield Wash crystals Dry crystals Cool again and obtain more crystals. Increases yieldFREQUENTLY DO A SOLVENT SURVEY In small test tubes take a few crystals and test solvents: Solvent Soluble Cold? Soluble Hot? Crystals? 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 no polarity(solvent mixtures can be used)RECRYSTALLIZATION FLOW CHART IMPURE COMPOUNDinsoluble impuritiessoluble impuritiesdissolve in hot solventhot gravity filtrationINSOLUBLE IMPURITIES discardFILTRATEcompoundsoluble impuritiescool to crystallizevacuum filtrationCRYSTALS (FIRST CROP)pure compound(wet with solvent)FILTRATE (MOTHER LIQUOR)compound and soluble impuritiesboil - concentratevacuum filtrationFILTRATEcompoundsoluble impuritiesCRYSTALS (SECOND CROP)less pure compound(wet with solvent)KEYS TO GOOD HOT GRAVITY