Separation of Acidic SubstancesAuthor: Dr. Robert D. Craig, Ph.D.
Separation of Acidic SubstancesAuthor: Dr. Robert D. Craig, Ph.D.• Application:• Acids and Bases are one the most  fundame...
Background• Aqueous (water based) solvents are very  polar. Organic solvents are much less polar  than aqueous solvents.
Such that
Background• The underlying principle behind acid  extractions begins with the fact that many  neutral organic compounds ar...
Background• . The ion typically has a high solubility in water  and a reduced solubility in the organic solvent.  This oft...
Get to the point Rob . .• Benzoic acid –not soluble in water• But the “sodium salt is”
Get to the point . . ..• In order to separate these compounds, we will  convert the water insoluble acid into a watersolub...
Subsequently . . .• Can use a strong acid to take the salt back to  organic layer soluble acid form
Background• One possible experiment begins with two  neutral organic compounds (benzoic acid and  2-naphthol) dissolved in...
Diethyl ether instead A base is added which will selectively react withone of the materials and convert it into itsconjuga...
Like dissolves like• The aqueous phase is removed along with the  conjugate base of the first compound. This  layer is lat...
Not MTBE• This process is repeated with the addition of a  stronger base to the MTBE which will react  with the second com...
Oil floats on water . . .
Acetanilde and Acetanilde and p-Tolic                Acid
Acetanilde and p-Tolic Acid
Some terminology• 1. Some terminology related to Acid-base  extractions:• Acid: In this experiment we are discussing  Bron...
Some Terminology• Base: In this experiment we are discussing  Bronsted-Lowry bases, hence a base is a  material that may g...
Some Terminolgy• Partitioning: The distribution of a substance or  ions between two immiscible liquids.• Extractioning: Di...
Some terminology• Equilibruium Constant (K): The numberical  value of the concentration of the products  divided by the co...
Want to discuss• For octanol and water-partition and  distribution
Two phase system, hydrophobic (top) and hydrophilic (bottom)    for measuring the partition coefficient of compounds
Some terminology• pKa: The negative log of the acid equilibrium  constant. pKa= - log Ka where the acid  equilibrium const...
Smaller -pKa the stronger the acid.• 2. Useful pKa information. (Do not memorize  pKa values)
Smaller-pKa the stronger the acid. .ACID (HA)                 pKa          CONJUGATE BASE (A-)Hydrochloric Acid (HCl)   pK...
smaller-pKa the stronger the acid. .• First, identify the acid and the base on both sides  of the arrow.• Compare the pKa ...
.which way??????• If the pKa of the acid on the left, HA1 is larger  (that is, the acid is weaker) than the pKa of the  ac...
.which way??????•HA1 + -A2 →•       -A1 + HA2
All possible reactions• 4. Below are ALL the possible reactions for the lab.  @@@@the handout@@@@@• Examine each reaction,...
Possible Reactions of Mixture with    Sodium Bicarbonate (NaHCO3• Goto handout now!!
Possible Reactions of Mixture with      Sodium Hydroxide (NaOH)• See handout-show pdf
Protonation of anions with        hydrochloric acid (HCl)• Show pdf
@@@@@@@@@@@@@• 5. Additional structures and information.• MTBE is Methyl t-Butyl Ether. This compound  is often added to g...
Diethyl ether-goto portal-Now Rob
SEPARATION OF BENZOIC ACID, 2-        NAPHTHOL, AND 1,4-        DIMETHOXYBENZENE• Skip to slide 44.
• 3. Predicting if a reaction will proceed in the  forward direction or not. To determine if any  acid-base reaction will ...
•   VID 11 FIRST••   VID 1•   VID 2•   VID 3••   LAB #3: SEPARATION OF BENZOIC ACID, 2-    NAPHTHOL, AND 1,4- DIMETHOXYBEN...
• 6. Aqueous solutions are very polar. Organic  solvents are less polar than aqueous.• Like materials like other materials...
• If a neutral organic compound dissolved in an  organic solvent is deprotonated and turned  into an ion, the solubility i...
IF a base is chosen which will selectively• deprotante one of a mixture of dissolved   organic compounds and turn only int...
Slide 44• 7. The two compounds are separated as ions  dissolved in water. It is desired to reform  and isolate benzoic aci...
• solubility in water. 2-Naphthol and benzoic  acid are not an exception. As neutral  compounds they have a low solubility...
• 8. Separatory funnels are specially designed  glassware for the separation of immiscible  liquids. They have a ground gl...
• Prelab.  *Before lab begins, read the following:  Zubrick’s Chapters on Extracting and Washing  (Ch 15 and 16).  Zubrick...
• *Draw a flow chart of the extraction  procedure.  *Make a table of physical constants and safety  information. Include o...
• http://www.oppapers.com/essays/Separation-Of-  A-Carboxylic-Acid-A/193808••  Grading.  Completion 5 pts  (includes lab a...
Separation of acidic substances new
Separation of acidic substances new
Separation of acidic substances new
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Using acid base chemistry in the separation of substances can be a quite useful technique in organic chemistry. A basic extraction can be carried out by applying a hot solvent such as water to a dry substance like coffee. This will allow for the extraction of caffeine and flavor from the coffee beans. Acid base chemistry can be useful in separating neutral, basic, and acidic organic substances by controlling the pH of the aqueous layer. In acid base extraction a solvent such as ether is mixed with an aqueous solution of a different pH. This will aid in ionizing the intended compound and separate it from the mixture. Once the molecule is ionized it will precipitate out of the ether solvent and dissolve into the aqueous layer. The aqueous layer can then be removed and the pure substance can be obtained through crystallization.

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Separation of acidic substances new

  1. 1. Separation of Acidic SubstancesAuthor: Dr. Robert D. Craig, Ph.D.
  2. 2. Separation of Acidic SubstancesAuthor: Dr. Robert D. Craig, Ph.D.• Application:• Acids and Bases are one the most fundamental principles of chemistry. Acidity and basicity are involved in determining chemical reactivity, separation, solubility, and transport of molecules across membranes.
  3. 3. Background• Aqueous (water based) solvents are very polar. Organic solvents are much less polar than aqueous solvents.
  4. 4. Such that
  5. 5. Background• The underlying principle behind acid extractions begins with the fact that many neutral organic compounds are not soluble in water but are soluble in organic solvents. If a neutral organic compound is converted to an ion by reaction with a base, then the polarity of that compound is significantly increased.
  6. 6. Background• . The ion typically has a high solubility in water and a reduced solubility in the organic solvent. This often causes the ion to migrate to the aqueous phase from the organic phase.
  7. 7. Get to the point Rob . .• Benzoic acid –not soluble in water• But the “sodium salt is”
  8. 8. Get to the point . . ..• In order to separate these compounds, we will convert the water insoluble acid into a watersoluble salt:
  9. 9. Subsequently . . .• Can use a strong acid to take the salt back to organic layer soluble acid form
  10. 10. Background• One possible experiment begins with two neutral organic compounds (benzoic acid and 2-naphthol) dissolved in an organic solvent, MTBE (methyl t-butyl ether). ####This is changed (diethyl ether)
  11. 11. Diethyl ether instead A base is added which will selectively react withone of the materials and convert it into itsconjugate base (an ion). These ions have a highsolubility in water and a low solubility in ether,so they will migrate (partition) to the aqueousphase.
  12. 12. Like dissolves like• The aqueous phase is removed along with the conjugate base of the first compound. This layer is later acidified, protonating the conjugate base. The solubility of the neutral material in water is low, and the compound precipitates and is recovered by filtration.
  13. 13. Not MTBE• This process is repeated with the addition of a stronger base to the MTBE which will react with the second compound and that material will deprotonate, form an ion then partition to the aqueous phase.• Again the aqueous layer is removed, acidified and the precipitated neutral material is recovered.
  14. 14. Oil floats on water . . .
  15. 15. Acetanilde and Acetanilde and p-Tolic Acid
  16. 16. Acetanilde and p-Tolic Acid
  17. 17. Some terminology• 1. Some terminology related to Acid-base extractions:• Acid: In this experiment we are discussing Bronsted-Lowry acids, hence an acid is a material that may lose a proton and form a conjugate base. HA -> H+ + A-• The stronger the acid, the weaker the conjugate base.
  18. 18. Some Terminology• Base: In this experiment we are discussing Bronsted-Lowry bases, hence a base is a material that may gain a proton and form a conjugate acid. B- + H+ -> HB• The stronger the base, the weaker the conjugate acid.
  19. 19. Some Terminolgy• Partitioning: The distribution of a substance or ions between two immiscible liquids.• Extractioning: Dissolution and removal of one constituent of a mixture in a solvent.• Precipitation: If the concentration of a compound in a solvent is greater than the solubility of that compound, the compound will no longer remain dissolved and will form a new solid phase
  20. 20. Some terminology• Equilibruium Constant (K): The numberical value of the concentration of the products divided by the concentration of the reactants. If the value of K is smaller than one, the equilibrium lies in favor of the starting material. The reaction does not proceed greatly in the forward direction.• If the value of K
  21. 21. Want to discuss• For octanol and water-partition and distribution
  22. 22. Two phase system, hydrophobic (top) and hydrophilic (bottom) for measuring the partition coefficient of compounds
  23. 23. Some terminology• pKa: The negative log of the acid equilibrium constant. pKa= - log Ka where the acid equilibrium constant Ka is equal to:The smaller the pKa the stronger the acid
  24. 24. Smaller -pKa the stronger the acid.• 2. Useful pKa information. (Do not memorize pKa values)
  25. 25. Smaller-pKa the stronger the acid. .ACID (HA) pKa CONJUGATE BASE (A-)Hydrochloric Acid (HCl) pKa= -7.0 Chloride ion (Cl-)Benzoic acid (Ph-CO2H) pKa = 4.17 Benzoate ion (Ph-CO2-)Carbonic acid (H2CO3) pKa = 6.35 Bicarbonate ion(HCO3-)2-Naphthol pKa = 9.5 2-Naphthonate ionWater (H2O) pKa = 15.7 Hydroxide ion (HO-)
  26. 26. smaller-pKa the stronger the acid. .• First, identify the acid and the base on both sides of the arrow.• Compare the pKa of the acids. Determine if the stronger acid is on the right or the left of the arrow.• If the pKa of the acid on the left, HA1 is a smaller number (that is, the acid is stronger) than the pKa of the acid on the right, HA2 then the reaction will proceed in the forward direction
  27. 27. .which way??????• If the pKa of the acid on the left, HA1 is larger (that is, the acid is weaker) than the pKa of the acid on the right, HA2, then the reaction willnot proceed in the forward direction (but it willproceed in the reverse direction).
  28. 28. .which way??????•HA1 + -A2 →• -A1 + HA2
  29. 29. All possible reactions• 4. Below are ALL the possible reactions for the lab. @@@@the handout@@@@@• Examine each reaction, assign acid and base to each compound, determine if the reactionwill proceed in the forwarddirection or not.Place an X across each arrow which will not proceed inthe forwarddirection. Only write the reactions that WILL proceed inyour lab notebook.
  30. 30. Possible Reactions of Mixture with Sodium Bicarbonate (NaHCO3• Goto handout now!!
  31. 31. Possible Reactions of Mixture with Sodium Hydroxide (NaOH)• See handout-show pdf
  32. 32. Protonation of anions with hydrochloric acid (HCl)• Show pdf
  33. 33. @@@@@@@@@@@@@• 5. Additional structures and information.• MTBE is Methyl t-Butyl Ether. This compound is often added to gasoline to increase the oxygen content and improve the burn efficiency. MTBE has a density of 0.7404 g/mL and is less than that of water (density 1.00g/mL) hence MTBE floats on top of water.
  34. 34. Diethyl ether-goto portal-Now Rob
  35. 35. SEPARATION OF BENZOIC ACID, 2- NAPHTHOL, AND 1,4- DIMETHOXYBENZENE• Skip to slide 44.
  36. 36. • 3. Predicting if a reaction will proceed in the forward direction or not. To determine if any acid-base reaction will succeed, as shown,• HA1 + -A2 → -A1 + HA2
  37. 37. • VID 11 FIRST•• VID 1• VID 2• VID 3•• LAB #3: SEPARATION OF BENZOIC ACID, 2- NAPHTHOL, AND 1,4- DIMETHOXYBENZENE
  38. 38. • 6. Aqueous solutions are very polar. Organic solvents are less polar than aqueous.• Like materials like other materials like themselves. Ions are very polar.• Typically ions have a higher solubility in water than organic solvents. Most neutral organic compounds have limited solubility in water but an increased solubility in organic solvents.
  39. 39. • If a neutral organic compound dissolved in an organic solvent is deprotonated and turned into an ion, the solubility in the organic solvent will be decreased and the ion will want to move or partition into an available aqueous solvent.
  40. 40. IF a base is chosen which will selectively• deprotante one of a mixture of dissolved organic compounds and turn only into an ion,• then mixtures of compounds can be separated. This concept is why this separation• experiment is possible.
  41. 41. Slide 44• 7. The two compounds are separated as ions dissolved in water. It is desired to reform and isolate benzoic acid and 2-naphthol as pure solids. In order to do this, a very strong acid is added to the aqueous solutions, this will reprotonate the ions and turn them back into neutral organic molecules. Most neutral organic compounds have a low
  42. 42. • solubility in water. 2-Naphthol and benzoic acid are not an exception. As neutral compounds they have a low solubility in the water, and hence will precipitate as a solid. The solid is isolated by vacuum filtration. A melting point will be taken to assess the purity of these materials
  43. 43. • 8. Separatory funnels are specially designed glassware for the separation of immiscible liquids. They have a ground glass access port at the top and a stopcock at the bottom. This is the most expensive piece of glassware in your drawers. A new sep funnel costs approximately $110.00. Handle with care
  44. 44. • Prelab. *Before lab begins, read the following: Zubrick’s Chapters on Extracting and Washing (Ch 15 and 16). Zubrick’s Chapter on Drying Agents (Ch 10). *Draw the balanced acid-base reactions including the structures of benzoic acid, 2- naphthol, and 1,4-dimethoxybenzene and the products.
  45. 45. • *Draw a flow chart of the extraction procedure. *Make a table of physical constants and safety information. Include only relevant data for this experiment.
  46. 46. • http://www.oppapers.com/essays/Separation-Of- A-Carboxylic-Acid-A/193808•• Grading. Completion 5 pts (includes lab and a report turned in on time) Prelab 3 pts Experimental 2 pts Results 5 pts Conclusion 5 pts
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