1 / 20

Two main types: Thin-Layer Chromatography (TLC) Column Chromatography (CC) Uses:

Chromatography. Chromatography is a technique in which compounds in a mixture are separated based on differing affinities between a mobile phase and a stationary phase. Two main types: Thin-Layer Chromatography (TLC) Column Chromatography (CC) Uses:

cricket
Download Presentation

Two main types: Thin-Layer Chromatography (TLC) Column Chromatography (CC) Uses:

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Chromatography Chromatography is a technique in which compounds in a mixture are separated based on differing affinities between a mobile phase and a stationary phase. • Two main types: • Thin-Layer Chromatography (TLC) • Column Chromatography (CC) • Uses: • To separate the components of a mixture - TLC & CC • To determine the purity of a compound - TLC • To see if two compounds are identical - TLC • To monitor the progress of a reaction - TLC • To follow a column chromatography separation - TLC

  2. Chromatography Basics • How it works: • Your sample is loaded onto the polar stationary phase • Polar compounds will adsorb onto the stationary phase to a greater extent than non-polar compounds • The mobile phase (eluting phase) helps “push” or elute the compounds either down a column (for CC) or up a plate (for TLC) • The main concept to consider in chromatography is polarity. Column chromatography TLC Bottle/Chamber

  3. Column Chromatography Sample load: Dissolved in a small amount of solvent Polar Stationary Phase: alumina or silica gel with your sample loaded onto it - can accommodate a larger amount of sample vs. TLC Mobile Phase: Organic solvent(s) of varying Polarity Fraction Collection: Small Erlenmeyer flask to collect fractions A Packed Column A running Column

  4. Column Size/silica amount

  5. Dry pack/flow rate Flow rate Dry packing

  6. Benzoic Acid synthesis/purification • Colorless crystalline solid and a simple aromatic carboxylic acid. • Benzoic acid was discovered in the sixteenth century • Extracted from Gum Benzoin or Gum benjamin (gum benzoin or gum benjamin (lubān jāwī) لبان جاوي

  7. Industrial Preparation of Benzoic Acid • 140,000 tons per year • As precursor for other compounds • Food preservative (inhibits the growth of mold, yeast and bacteria) • Medicinal (constituent of some ointment which is used for the treatment of fungal skin diseases)

  8. Laboratory Synthesis • Cheap and readily available • Practiced for its educational value • From Benzaldehyde, Toluene, Bromobenzene Cannizzaro reaction Oxidation reaction Grignard reaction

  9. Grignard Reaction • An organometallic reaction in which alkyl or aryl magnesium halides (Grignard reagents) add to a carbonyl group. • An important tool for the formation of  carbon-carbon bonds. • This reaction was discovered by the Frenchman, Victor Grignard -- Nobel Prize in 1912 Formation of Grignard Reagent X = halogen

  10. Halide Reactivities RX + Mg R-Mg-X RELATIVE RATES : R-I > R-Br > R-Cl FAST SLOW expensive, good compromise less reactive, but easy to prepare or buy not readily available

  11. Ethers stabilize the Grignard Complex

  12. Et Et .. O .. Et .. : O Et Ethers stabilize the Grignard Complex ether molecules coordinate into empty 3p orbitals on magnesium The Grignard Complex R Mg X

  13. We can view the Grignard as a hybrid reagent. RMgX is a source of a carbanion ( R:- ) Therefore we expect Grignard reagents to be both a strong base and good nucleophile.

  14. Grignard reagents are strong bases and react readily with any slightly acidic hydrogen. Any source of H+ will bring about this reaction: water acids alcohols amines alkynes carboxylic acids atmospheric moisture Any -O-H, -S-H, or -N-H bonds are sufficiently acidic to react.

  15. Reaction with Carbonyl Compounds • formaldehyde primary alcohols • other aldehydes secondary alcohols • ketones tertiary alcohols • carbon dioxide carboxylic acids

  16. Reaction With Carbon Dioxide O ether R-Mg-X + O=C=O R-C-O- MgX+ H3O+ R-COOH (s) 1) CO2 Mg ether 2) H3O+

  17. Grignard & CO2 to produce Benzoic Acid   

  18. Use as little heat as possible to avoid formation of Biphenyl • The Organic Ether layer contains Benzoic Acid, Biphenyl and Inorganic Salts.

  19. Hydrolysis and isolation of Benzoic Acid 6 M HCLAnhydrous EtherSeparatory Funnel (Shake Gently) Ether Layer Aqueous Layer Benzoic Acid Biphenyl Inorganic Salts (Discard) Add 5% NaOH Aqueous Layer (Repeat 3 Times) Soluble Benzoic Acid Salt(Trace of Ether) Biphenyl (Discard) Heat on Hot Plate in Hood to Drive off Ether Cool to Room TemperatureAdd 6 M HCl

  20. Crystallization/precuation/waste • Benzoic acid can be purified by recrystallization from water because of its high solubility in hot water and poor solubility in cold water. • Diethyl Ether is extremely flammable • Anhydrous diethyl ether (recap the container) • Unreacted magnesium chips (solid waste)

More Related