Quiz 1 - Melting Point 1. What is the rate of temperature increase used in a true melting point determination? 1-2 °C per minute, starting at 30 °C below expected 2. In determining the identity of an unknown thought to be urea, what percentage of urea and of unknown are combined before mixed melting point is done? 50/50 3. What are two characteristics of an impure substance’s melting point? -broad 3-7 degrees -depressed (10-20 degrees lower) 4. Why would the melting point result be erroneous if the rate is increased too rapidly? -sample and aluminum block are not at thermal equilibrium with thermometer -since thermometer is mercury, it will respond sooner than sample and block which will result in higher observed melting point 5. Which intermolecular force requires greatest energy to overcome to melt? -ion-ion Quiz 2 – Separation by Liquid-Liquid Extraction 1. Define Distribution Coefficient KD KD = [compound]organic [compound]aqueous 2. What acid and base extract was used Base = 3-nitroaniline Acid = benzoic acid 3. When using aqueous and ether extraction system, what solvent is drawn off through the stopcock? Water (water more dense than organic) 4. What variable will be adjusted to help separate the acid and base? pH of aqueous solvent will be altered in order to separate 5. What is the purpose of adding dilute HCl to organic mixture? It protonates the primary amine functional group on 3-nitroaniline and makes it preferentially soluble in the aqueous phase HCl is proton DONOR protonates primary amine, therefore, makes it preferentially soluble in aq. phase EXTRACTION: REMOVAL OF 1+ COMPOUNDS FROM A MIXTURE BY ITS PREFERENTIAL ASSOCIATION WITH ONE PHASE OVER ANOTHER – used in isolation of desired product from reaction mixture Liquid-liquid extraction involves 2 liquid phases that are immiscible – don’t dissolve in one another After reaction completed, reaction mixture often contains desired product, also by-products, left over starting material, catalysts Extraction can separate these based on preferential solubility in certain phase Inorganic salts, Organic ions = more soluble in AQUEOUS phase Neutral organic molecules = more soluble in ORGANIC phase KD = Partition Coefficient = Distribution Coefficient Way to quantify how much more (or less) soluble a compound is in an organic solvent than water The solubility (or concentration) in organic solvent divided by solubility (or concentration) in water KD = [compound]organic [compound]aqueous P can be calculated from result of an extraction experiment – if P is known, can be used to predict how efficient an extraction will be P = [X]ether = [X]aq (g need to recover/ mL X was dissolved in) ((g of X dissolved – need to recover) / mL of water shaken against) Predict how much X would be recovered by evaporation of the ether layer if same (amt) X were dissolved in (amt2) mL diethyl ether and shaken against (amt3) mL of water? P= (m/ mL shaken against) ((g of X dissolved – m) / mL X was dissolved in) WR = Wx (V1) n (PV2 + V1) WR = amount of solute that remains in solution unextracted W = amount solute V1 = amount of solvent the solute is initially dissolved in V2 = amount immiscible solvent used in extraction P = distribution coefficient n = number of extractions performed Quiz 3 – (ctd.) 1. What is the major component found in highest percentage in clove oil? Eugenol (70-90%) Eugenol acetate ( 2 – 17% ) Caryophyllene ( 5 – 12% ) 2. What process is being used to isolate clove oil and name 2 reasons why it is used Steam distillation a) avoid inconveniently high boiling point b) avoid thermal decomposition 3. What are the medical properties of clove oil? Anesthetic, anti-flatulent, analgesic 4. Constituents of essential oils can further be isolated by other techniques. List 3 techniques used in natural products isolating other than steam distillation -solvent extraction -expression -super critical CO2 extraction -column chromatography STEAM DISTILLATION: DISTILLATION PROCESS IN WHICH ORGANIC COMPOUNDS IMMISCIBLE IN WATER ARE CO-DISTILLED WITH WATER ARE CO -DISTILLED WITH WATER Since the mixture is being distilled & the components of mixture are immiscible, BP is < 100, lower than either of the compounds in their pure forms Why? Since the 2 compounds are immiscible, each of the compounds as it boils exerts it’s own vapour pressure on the system BOILS when TOTAL VAPOUR PRESSURE of system = EXTERNAL PRESSURE of atmosphere If organic compound is truly immiscible with water, mole ratio of water:organic in the vapour is proportional to the vapour pressure of each component STEAM DISTILLATION USEFUL b/c of temperature depression effect on BP ---> for distilling compounds with very high BPs below their normal BP --->some compounds decompose before their BP is reached b/c enables compounds to be separated based on whether the compounds are volatile with steam or not o requires compound to have appreciable vapour pressure Only oils present on surfaces of plant material are able to vaporize with steam Oily compounds present on surface of plant material are able to vaporize with steam -must diffuse out to the surface, as an oil-in-water mixture, to be distilled ---as oil diffuses out, water must diffuse in to replace the oils (hydrodiffusion) to accelerate release of volatile oils, - soak the plant material in water crush the plant material Hydrodiffusion is important in determining composition of essential oils recovered from plant material The more soluble the oil is in water, the more easily it will diffuse out of the plant tissue to the surface. With cloves, steam distillation from the whole spice produces essential oil that’s mostly eugenol with crushed cloves, produces significantly less eugenol Further purification: - (eugenol – phenol) extraction with base Quiz 4 – Preparation of Cyclohexanol 1. __addition/hydration___ reaction breaks pi bond and adds a single hydroxyl 2. Technique used to isolate cyclohexanol? Steam distillation 3. What is an azeotrope a mixture of 2 or 3 compounds which, when distilled, exhibit a fixed melting point, like that of a pure compound (cyclohexanol, water, small amount of cyclohexene) 4. What is the effect of adding NaCl and why? Higher yield of product ‘salt out’ the alcohol Used in extractions Adding enough salt to the aqueous phase to make it a saturated solution Salt helps to remove the organic compound from the aqueous phase by reducing the solubility of the organic compound in water, forcing a transfer of the organic compound out of the aqueous phase and into the organic phase This step is followed by the separation of the organic phase from the aqueous phase Diethyl ether is added as a precaution against mechanical lloss After separation, organic layer is dried prior to distillation Drying agents: - Anhydrous potassium carbonate is used because it will neutralize any trace of acid that may have been carried through the work up procedure as well as absorb water In the final distillation, a trace of acid would cause dehydration of the cyclohexanol DISTILLATION Used for: removing a solvent Purifying a liquid Separating the components of a liquid mixture Liquid is vaporized by boiling Hot vapour condenses back into a liquid, called distillate/condensate Collected into receiving flask Highest-boiling components remain in distillation flask as a residue Appendix A2 – Distillation Appendix B2 – Refractive Index REFRACTIVE INDEX nD Physical property – can be used to determine identity and purity of a liquid compound Refraction – bending of a ray of light as it passes obliquely from one medium to another of different density Occurs because light travels more slowly through a more dense substance; called a liquid Refractive index useful property because the degree of refraction depends on the structure of compound Determined using refractometer Index is very sensitive to temperature Water can be used to calibrate the refractometer Adjustment calculation**** Quiz 5 – (ctd.) 1. Explain distillation technique 1. Remove solvent, purify liquid or separate components of a liquid mixture 2. Liquid mixture is vaporized by boiling 3. Hot vapour rises up to distillation head is forced to travel at a right angle through a cold condenser which causes vapour to condense back into a liquid and drip out the end of the condenser tube 4. A mixture of liquids would be separated by the lowest boiling compound boiling off first, followed by next low boiling point and so on 2. Why is diethyl ether used to rinse distillate into separatory funnel? Used to reduce mechanical loss of cyclohexanol Cyclohexanol is viscous and needs to be dissolved in ether to transfer as much as possible and therefore increase the yield 3. What 2 compounds need to be removed in the forerun when crude distillate is distilled the second time Diethyl ether and unreacted cyclohexene Quiz 6 – Multistep Synthesis 1. What are the functional groups in methyl salicylate Ester and phenolic hydroxyl group 2. Methyl salicylate can be hydrolyzed using either acid or base Here we’re using NaOH (base) 3. What is the purpose of adding dilute sulfuric acid to the mixture after reflux To protonate sodium salt of salicylic acid which converts it to a free acid 4. What are 2 purposes of reflux a) Supply heat to the reaction at boiling point of solvent b) Keep solvent from being lost to the atmosphere 5. What are 2 techniques used to purify then test the purity of a compound Recrystallization and melting point determination Quiz 7 – (ctd.) 1. Why can’t salicylic acid be directly ingested 2. Why are reflux reactants not necessary Acetic anhydride is sufficiently reactive 3. What functional group on salicylic acid is involved in substitution reaction with acetic anhydride Phenolic hydroxyl group 4. What compounds are going to be present in mother liquor after first vacuum filtration -unreacted salicylic acid -sulfuric acid -acetic acid
