chem lab – Chemistry – Flashcards
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recrystallization
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Separation technique used to purify particles of interest from a mixture of solids. Mixture is dissolved in saturating amounts in warm solvent. As the solution cools, the pure substance crystallizes while impurities remain in solution.
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Sublimation
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is used in solids that have a vapor pressure below its melting point
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Sublimation
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heat solid, condensing vapor on a cold surface, 3, scraping off condensed solid.
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Camphor
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symmetrical which means it can change from solid to vapor upon heating.
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Sodium Bisulfite
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Sodium Bisulfite used as a reducing agent to remove excess HOCl (REDUCTION)
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Sodium bisulfate and hypochlorite
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HOCl + HSO3- --> HCl + HSO4-
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Overall reaction
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Isoborneol + NaOCL --> Camphor + NaCL + H2O
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Oxidation of isoborneol
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Exothermic, heat evolved can lead to formation of camphoric acid so ice bath is used
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Sodium Hypochlorite and Acetic Acid
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Hypochlorite NaOCl + HOAc --> HOCl
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Acetic acid
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facilitates oxidation by converting sodium hypochlorite to hypocholorous acid
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when sodium hypochlorite is present in excess
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a drop will oxidize iodide to iodine turning it dark
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Potassium Iodide and Sodium Hypochlorite
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2KI + NaOCl + H+ --> I2 + KCL + KOH
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Purity of camphor can be estimated from melting point
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large freezing point depression constant. Kf = 40 C, camphor = solvent, isoborneol = solute.
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Green synthesis of camphor
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under reflux, add enough sodium hypochlorite to keep oxidizing agents in excess.. reaction rate controlled by adding sodium hypochlorite from separatory addition funnel
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Green synthesis of camphor
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sublimation, vacuum filtration, reflux; temperature should be below 40 degrees celsius; extreme heat can lead to creation of camphoric acid
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mixed solvent recrystallization
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when a particular compound can only be recrystallized in a mixture of solvents. At high temperatures mixed solvents behave like an alcohol, but at low temperatures behaves like water
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mixed solvent recrystallization
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Thus one would use a mixed solvent to recrystallize compounds that are soluble in alcohol but insoluble in water. 2,4-dinitrophenylhydrazone only dissolves a little in either water or alcohol.
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mixed solvent recrystallization
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Minimum amount of hot ethanol is used to dissolve solid, hot water is added until solution becomes cloudy.
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thin layer chromatography
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procedure which is used to separate a mixture of substances into its individual components, based upon relative solubility
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The rate at which spot moves up
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The rate of the development solvent The rate of the spotted compound the higher the polarity the faster and further the spot is moved
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Rf value
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distance travelled by spot / distance travelled by solvent.
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Solvent used for TLC
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3:1 mixture of toluene and petroleum ether. Both these solvents are non polar.
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1,2-DNPH derivative
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a condensation reaction (combination of addition and elimination reaction)
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In presence of sulphuric acid
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the derivative melting point will be lower due to catalyzed isomerization reactions.
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what is used to wash away traces of sulphuric acid?
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sodium bicarbonate
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Techniques (Idenitifcation)
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Recrystallization from mixed solvent, nuclear magnetic resonance, Rf value, thin layer chromatography, Vacuum Filtration.
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synthesis of salicyclic acid
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exothermic reaction ; saponification; no oxidation or reduction (conversion of ester into carboxylic acid); reaction under reflux
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sodium salicylate
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a dianion carboxylate intermediate that acts as a weak base
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methyl salicylate and sodium hydroxide
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form a white precipitate
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addition of dilute sulphuric acid to dianion
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white/foamy precipitate
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balanced eqn for e1
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2C8H8O3 + 2NaOH --> 2NaC7H5O3 + 2CH4O
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e1 techniques
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Recrystallization, Vaccuum Filtration, Heating under Reflux
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Haloform oxidation
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methyl ketone to carboxylic acid. Oxidation reaction
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oxidation reaction
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addition of oxygen, loss of hydrogen, increase in oxidiation number or loss of electrons.
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phase transfer catalyst
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compound (such as a quaternary ammonium halide) that is soluble in both water and organic solvents and helps reagents move between organic and aqueous phases
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First step of haloform
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base catalyzed halogenation enolate ions replace hydrogen ions with chlorine
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second step haloform
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nucleophilic acyl subsitution, hydroxide ion acts nucleophile and CCL3 is the leaving group
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acetone
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consumes excess of sodium hypochlorite
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reaction haloforom
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sodium hypochlorite must remain in excess to make sure that the conversion to 4-methoxybenzoic acid occurs.
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recrystallization solvent for haloform
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60% aqueous ethanol.
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IR spectrum for 4-methoxybenzoic acid
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Carboxylic acid FG - 2200-3300 cm-1 Carbonyl signal @ 1625-1750 C-O single bond at 1175-1275 Sp2 single C-H Bonds at 3027 aromatic C=C around 1527 O-H Bending = 1325-1425
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lycopene heavily unsaturated
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13 double bonds; highly attracted to alumina, more so than B-carotene. Addition of acetone makes it run down the clume faster.
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saturated sodium chloride
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used to separate organic and aqueous layers
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Tomato paste washed with
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1:1 ratio of acetone and petroleum ether. Acetone is water soluble and petroleum ether is very volatile. Then washed with extraction solvent (hexanes). Then washed with potassium carbonate in order to neutralize acids in the tomato paste.
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sodium sulfate
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anhydrous. removed by gravity filtration.
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iodine
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saturates some of the double bonds, breaking up conjugation and reducing absorption in the visible region of light.
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DMF used for sodium iodoethane
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as solvent (polar aportic) because it does not solvate the nucleophile strongly leaving it to attack the substrate. DMF accelerates the reactions of SN2 reactions.
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N-ethylsaccharin
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major product because it is more stable and thermodynamically favored
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O-ethylsaccharin
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kinetic product since oxygen is more electronegative than nitrogen the reaction forms faster and is favored at lower temperatures.
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Iodoethane expt.
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kept at 80 degrees to favour thermodynamic product. Water is added to solidify product as the product is not soluble in water.
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e 30
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solvent used for triphenylmethanol recrystallization was 2:1 mixture of hexanes and absolute ethanol.
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magnesium turning
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higher surface area --> reaction rate
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diethyl ether
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volatile
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calcium chloride
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was used to make sure that water did not enter
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iodine crystal
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precipitate reaction by removing magnesiums oxide coating
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formation of grignard reagant
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exothermic process solution was refluxed.. protected because it is solvated in diethyl ether
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the precipitate that formed
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magnesium salt of triphenylmethanol - pink
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water and HCL is drop wise added
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to convert triphenylmethanol salt to the alcohol and the acid dissolve magnesium
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after addition of water
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separation into two layers; yellow ether layer.
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yellow ether layer
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washed with sodium bicarbonate and then saturated sodium chloride
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anhydrous magnesium sulphate for e30
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used to dry, forms a yellow like product.
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hexanes
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removes biphenyl
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e30 recrystallization
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2:1 hexanes and absolute ethanol
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Triphenylmethanol
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acetic anhydride and fluoboric acid --> trityl fluoborate
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Fluoboric acid
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strong lewis acid, protonates the triphenylmethanol.Pushes reaction forward
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acetic anhyride
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removes water because water that is present in the fluoboric acid could prevent the reaction
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lycopene
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oxidizes slowly in presence of atmospheric acid which allows us to do UV VIS spectroscopy
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conversion from 13-cis to all trans
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catalyzed by iodine
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cis trans
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360 nm
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carotene colour
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yellow
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lycopene
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orange red
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1st eluant for lycopene
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hexanes, then 10% acetone in hexanes, more polar
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reflux
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process of boiling reactants while continually cooling the vapor and returning it back to the flask. used to heat mixutres for an extended period of time and at a a certain temperature.
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e1
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sulphuric acid used as catalyst
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Sodium hypochlorite
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NaClO + HC2H3O2 ? HClO + NaC2H3O2
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4-methoxyacetophenone
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low melting solid; insoluble in aqueous sodium hypochlorite sol'n
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3M HCL haloform
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needed to bring the pH down to 2 to protonate the anion and precipitate the reaction.
