SC CHEM 333 - Chemical Extraction Pre-Lab (8 pages)

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Chemical Extraction Pre-Lab



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Organic Chemistry 333L section 03M Laboratory Pre Lab Chemical Extraction By Cameron Kahn 14 January 2019 TA James Collie 1 Objectives The chemical extraction lab experiments objective is to separate the components of a ternary mixture by a chemical extraction procedure CITATION Geo12 l 1033 This experiment calls for the recrystallization of each component and record the melting point and percent recovered Also find the exact mixture composition for each unknown and calculate the percent composition of each component Theory Over the centuries humans have carried out solid liquid extraction by brewing just about every common plant leaf fruit or root In the process they have isolated a number of extracts with pharmacological activity Many of these compounds were used for medicinal purposes For example Sertuner first extracted morphine from poppy seeds in 1805 Sertuner and several derivatives such as codeine are used as painkillers today Unfortunately other derivatives such as heroine have become drugs of abuse Figure 1 Morphine Codeine and Heroini While solid liquid extraction is the most common technique used to brew beverages and isolate natural products liquid liquid extraction is a very common method used in the organic laboratory Organic reactions often yield a number of by products some inorganic some organic Also since they do not go to 100 completion some starting material is also often present at the end of an organic reaction The real work in organic chemistry is not running the reaction but rather in what is appropriately called the work up of the reaction mixture that is the separation and purification of the desired product from the mixture of by products and residual starting material Liquid liquid extraction is often used as the initial step in the work up of a reaction meaning liquid liquid extraction is done before final purification of the product by recrystallization distillation or sublimation A concrete example will help make sense of this One of the synthetic reactions one will be carrying out is a Grignard reaction involving the addition of phenyl Grignard reagent with benzophenone to form triphenylmethanol 2 Figure 2 Phenylmagnesium Cloride Benzophenone Triphenylmethanolii The final reaction contains the product the reaction solvents ether and aqueous hydrochloric acid There may also be traces of benzophenone from the starting material Since water and ether are immiscible he she will have two separate layers one aqueous acid and the other organic ether Since ether is less dense than water it will comprise the top layer A novice might simply evaporate the water and ether to get rid of them The problem is that the inorganic by product MgCl2 would not evaporate and the crystals of it would be mixed with crystals of the organic product triphenylmethanol Ones knowledge of chemistry and application of the principle like dissolves like should help you to figure out that in the 2 phase ether water reaction mixture the ionic inorganic salts of magnesium should want to be in the aqueous phase or layer and the water insoluble organic product triphenyl methanol should want to be in the organic ether phase or layer Extraction uses the solubility differences of these molecules to selectively draw the product into the organic layer Although the two layers are immiscible they work together to separate and select the compounds one is attempting to isolate By simply separating these two layers one can separate the inorganic salts from the organic materials In almost all cases extraction can be used to separate or partition ionic or polar low molecular weight substances into an aqueous phase and less polar water insoluble substances into an immiscible liquid organic phase This phenomenon is governed by the distribution coefficient CITATION Pen13 l 1033 Mechanism O O H C NaHCO3 C O Benzoic Acid O Na Sodium Bicarbonate 3 Sodium Benzoate O O Na H NaOH 2 naphthol sodium hydroxide 2 naphthol salt Procedure REMINDER Close and cap all reagent and waste containers Start by setting up an ice bath Next obtain four large test tubes TT label them A B C D and record their weight Now obtain 1 00g of the ternary mixture and dissolve fully in 6 mL of ether Transfer the mixture to your separatory funnel In the same separatory funnel add 2 0 mL of NaHCO3 and shake swirl the solution Be sure to vent the solution frequently Remove the bottom layer in the separatory funnel and put into the TT A Next place TT A in an ice water bath Now add 2 0 mL of NaOH into the separatory funnel and agitate Remove the bottom layer in the separatory funnel and place into TT B Place TT B into the ice bath Next add 1 4 mL of H2O into the separatory funnel and agitate Remove the lower H2O level and discard Place the remaining liquid into TT C Test Tube A Aqueous solution of sodium salt of benzoic acid Add 1 4 mL of ether and gently agitate the two solutions together Next remove the upper either layer and discard Now add concentrated HCl using the drop wise procedure until precipitates form Cool TT A in an ice bath to complete the crystallization Use the suctions filter to wash any impurities and then let dry Obtain the mass of benzoic acid from the TT A Be sure to record the melting point and calculate percent composition Test Tube B Aqueous solution of sodium salt of 2 Naphthol Start by adding 1 4 mL of ether and agitate Now remove the upper ether layer and discard Add concentrated HCl using the drop wise procedure until precipitates form Let TT B Cool then filter and dry Next obtain the mass of 2 naphthol from TT B Record the melting point and calculate total percent recovery of the ternary mixture Test Tube C Naphthalene Add anhydrous MgSO4 4 micro scoops if not sure what a micro scoops is ask your TA Decant the liquid into TT D and discard MgSO4 hydrate in the proper container Next evaporate the ether completely from the TT D by means of a controlled steam bath Now obtain the mass of the naphthalene Record the melting point and calculate percent composition 4 Apparatus Stand Buchner Funnel Rubber Tubing Filter Flask Adapter Cap Filter Flask Figure 3 Suction Filtrationiii Figure 5 Separatory Funnelv Figure 4 Steam Bath in Useiv 5 Ring Stand Glass or Teflon Tap Reagent Table Name Structure Molecular Weight g mol Melting oC Boiling oC Density g mL 122 12 1224 249 1 32 128 17 81 218 1 14 144 17 122 286 74 12 116 3 34 6 7134 84 00 50 1413 5 165 120 36 1124 2 66 36 46 30 100 1 2 39 99 318 1390 2 13 C7H6O2 Benzoic


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