Chem 205 Final
Experiment 2 Techniques
1. Identification of solvent layers of two immiscible solvents 2. Partitioning of a compound between two immiscible solvents and determination of Kd. 3. Liquid-liquid extraction with aqueous acids/bases and organic solvents 4. Use of drying agents 5. Use of microscope techniques with centrifuge tubes
What is chromatography?
A technique used to separate mixtures of compounds for either analytical identification and quantification or for preparative purification.
Which of the following correctly orders the solubility, from greatest to least, of NaCl in solvents BF3, H2O, CH3(CH2)2OH
A) H20, CH3(CH2)2OH,BF3
Cfactor =
Ac / At
Ferrocene eluted from the column first, but it ended up as the higher of the two spots during TLC analysis. Explain
Column chromatography and TLC work in two different ways. In column chromatography yourmore nonpolarphase is going to elute out of the column first, in a TLC that is going to be what travels furthest due to the high affinity for the more non-polar mobile phasein both cases.
How do compounds move during column chromatography
Compounds with strong interactions to the adsorbant will move more slowly than those that have weaker interactions
Colored impurities typically come from two major sources, what are they?
Conjugated Systems and oxidation
a) you run TLC on a mixture of two unknown halogenated alkenes, but you see only one spot with an Rf of 0.91. The solvent used was ethyl acetate.
Considering the large Rf value and the fact that only one spot was formed, the solvent must have been too polar. This caused the solute to be attracted mostly to the mobile phase and not as much to the stationary phase, causing no separation. This problem could be fixed with using a less polar solvent like petroleum ether.
b) you run TLC mixture of two unknown halogenated alkenes, but you see only one spot with an Rf of 0.15. The solvent used was a mixture of petroleum ether and dicholoromethane
Considering the low Rf value and that only spot was formed, the solvent must have been not polar enough. This could be solved by using a more polar solvent such as ethyl acetate.
V%
Corrected Area / (sum of both corrected areas)
c)when you put your TLC plate in the developing chamber, the solvent in the chamber covered the spots on the TLC plate baseline
If the solvent is shown covering the spots on the baseline, then the solvent would have dissolved your solute. The only way to fix this is by preforming a new TLC plate and making sure your solvent is not filled too high, it should not touch the baseline.
o-hydroxyacetophenone has a melting point of 4-6C. P-hydroxyacetophenone has a melting point of 109-111C. Explain the basis for the sizable difference in melting points of these two compounds.
In o-hydroxyacetophenone, the OH and CO are in close proximity to each other, so there will be intramolecular hydrogen bonding in the molecule whereas in p-hydroxyacetophenone, the OH and CO are at opposite ends and therefore cannot form intramolecular hydrogen bonding. There is, however, intermolecular hydrogen bonding in the molecule, which forms a strong crystal lattice. Therefore, more energy is required to break the bonds in p than o-hydroxyacetophenone, which contributes to the high melting point of p-hydroxyacetophenone.
Why is it important to use only the minimal amount of hot solvent needed to achieve recrystallization?What would be the effect of using too much solvent while dissolving a solid for recrystallization?
It is important to use the minimal amount of hot solvent needed to achieve a recrystallization because having too much solvent (past the saturation point) will cause the crystals to take too long to recrystallize.
What is the partition coefficient?
Kd is the relative solubility that a compound has in two given solventsKd= C2/C1
Write the reaction between acetic acid and sodium bicarbonate? What drives this reaction forward?
NaHCO3(aq)+ CH3COOH (aq) ------> CH3COONa (aq) + H2O(l)+ CO2 (g gas evolution drives it foward
How hot should you make a hot plate?
Never use the heater dial above 4 (390) the top plate can crack
Can we use NaOH as a base in this lab?
No because the NaOH would deprotonate both the carboxylic acid and the phenol so both would reside in the aqueous layer and separation would not be feasible using NaOH as a base.
Do pasteur pipets have volume markings?
No, you should mark them
what is produced by condensation polymerization?
Nylon - 10,6 by sebacoyl chloride and hexamethylene diamine
You run a TLC plate spotted with three compounds: naphthalene, o-tuluic acid, and fluroenol. Predict the relative Rf values
O-toluic acid is going to have the lowest Rf value because it is going to be the most polar compound of these three, causing it to have a higher affinity for another polar substance causing it to "cling on" to the stationary phase more. The compound with the highest Rf is going to be naphthalene, which is least polar, so it will have a higher affinity for the mobile phase than the other two compounds will. The middle most polar is going to be fluorenol so it will have a Rf in between o-toluic acid and naphthalene.
What are the advantages and disadvantages of using a centrifuge tube?
The advantage is it's conical in shape, so you can take the bottom aqueous phase out very reliably without taking the organic phase out. However, the centrifuge tubes are made from glass and water has a high affinity for glass. With this, it is very common to have a small drop of water stay in the tube and that is a problem because the organic solvent will get wet.Any water that is dissolved in the organic phase is a contaminant that needs to be removed.
What may be see before actual melting that can trick us in the melting point apparatus?
Sweating
True or false: The heat from your hand can increase the vapor pressure of some organic solvents.
TRUE
What is frequently used for micro-scale recrystallization?
The Craig Tube (10-100mg)
What is the best method of rinsing your crystals? What is the purpose of this?
The best method is with cold water and to move traces of impurities.
When doing a synthesis of an organic compound, most impurities are organic as well. What is the biggest problem one would encounter here? How can that problem be mitigated?
The biggest problem one may encounter is side products. These products would most likely be soluble and related to the compound of interest in order to fix this the two compounds need to be separated by gravity filtration.
What is crystal formation dependent on?
The concentration of the solute and temperature of the solvent and what solvent is used. A solute or compound that is very soluble is less likely to form crystals.
How does temperature and solubility play a role in recrystallization?
You want to have a low solubility at low temperatures and a high solubility at high temperatures
What are the 3 components separated by liquid-liquid extraction
a carboxylic acid, a phenol, and a neutral compound
what does the reaction between sodium bicarbonate and a carboxylic acid produce? What are the safety precautions to be taken when doing this reaction?
The reaction between sodium bicarbonate and carboxylic acid is going to produce carbonic acid which can spontaneously decompose into carbon dioxide and water. With this you are going to get a little pressure, so you want to be careful with closed vessels because if the pressure builds up it may bubble over.
In terms of extraction of the phenol, what is the purpose of adding hydrochloric acid if you just used a strong base?
The reason for adding HCl is so you can isolate the phenol. This causes a less water-soluble organic compound to be converted into a more water-soluble compound. This will form a precipitate and allow you to recover your phenol through filtration.
How should you hold your pasteur pipet?
Vertical or you may loose several drops
When recovering your phenol, what does one wash with? What does this remove? What is the true name of the product we are recovering here?
When recovering your phenol, you will wash it with MtBE. When you wash with MtBE this is going to create a layer to allow you to remove any of the neutral compound or contaminants that was extracted with the phenol. The true name of the phenol that we recovered in this experiment is called beta-naphthol.
What is the proper rate of heating?
1-2 degrees / min
Eugenol
a terpene and a phenol, or an aromatic hydroxyl compound. has a boiling point of 250 would likely decompose if distilled directly.
Liquid-liquid extraction can be used to separate The extraction can be performed using
a weak organic acid from a weak organic base an aqueous acid or an aqueous base along with an immiscible organic solvent such as ether.
Suppose you are trying to determine the melting point of a compound, and the following happens: a) the compound turns from white to brown before melting b)the compound slowly disappears from the capillary tube before melting
a) If the compound turns brown first that means it has decomposed before actually melting. You could either try melting it at a lower temperature, or report that it is too low to be determined in this particular lab. b) If the compound has disappeared its likely that it has sublimed and gone straight to the gas form, so melting it in a sealed capillary should work.
What are the chemicals needed for this extraction?
benzoic acid, MtBE, water and anhydrous sodium sulfate
How are TLC plates prepared
by mixing silica gel particles with compounds that act as an adhesive for binding the particles to the solid for support.
How is the filter pipet made
by pushing a pea sized amount of loose cotton into the construction of the pipette using a metal wire
What does a change in the pH of the solvent do?
can change the solubility of an organic compound in a solvent
What happens when the aqueous layer is made acidic?
carboxylic acid precipitate forms
how are crystals and solvents separated in micro-scale recrystallization?
centrifugation
The filtrate from the hot gravity filtration should be
clear and colorless
cross - linked polymerization
creates slime that is formed with PVA and borax (sodium borate decahydrate)
For the distillation lab, what compounds were seperated?
cyclohexane/toluene (1:1)
How are the spots on the TLC plate analyzed
either directly if the compounds are colored or with the aid of an indicator (UV light or I2 if the compounds are colorless)
What did we dissolve our unknown OTC tablet in
ethyl acetate
how is the neutral compound isolated
evaporate MtBE solvent with gentle heating
How can you achieve a good separation?
even heating is required and a low rate of distillation
how is your phenol isolated
extracting the organic layer with 1.5mL 5% NaOH, back extracting with MtBE and then adding HCl
the ability to separate compounds in a sample using liquid-liquid extraction depends upon
how differently the compounds of the sample mixture partition themselves between the two immiscible solvents.
Organic solvents frequently employed for liquid-liquid extraction:
petroleum ether, ethyl acetate, methylene chloride, and toluene. diethyl ether is an effective solvent but MtBE is used b/c less of a fire hazard
What does an impurity do to a melting point?
lowers it and broadens the range
with simple distillation the more volatile component would be
more pure
Should you add charcoal to a boiling solution?
no, it will cause the solution to boil over
Column chromatography
preparative method for separating and isolating compounds from mixtures. the method is used for obtaining compounds from natural sources or for purifying products. (upside down version of TLC)
What is the filter-tip pipet mostly used for?
remove solids from very small amounts of liquid by leaving the solid behind (as opposed to trapping it)
How can one ensure all of your sample recovered is removed from the Craig tube for accurate percent recovery calculation?
rinse out the craig tube with acetone
Gradient elution scheme
start with a solvent of lower polarity, then switch to a solvent of higher polarity as the column is running.
How can you increase the water solubility of organic compounds having basic groups?
the addition of an aqueous acid.
The ability to separate two liquids depends on
the differences in boiling points of the two liquids as well as the rate of distillation, heat source, insulation of the column, and how efficient the column is, the type of column, the column packing and the process of packing a column
The more polar the solute
the greater the interaction or affinity that the solute will have for the adsorbent and the less distance the solute will travel along the TLC plate
What is recrystallization?
the process of purification that involves dissolution of a solid in a hot solvent, filtration of the heated solution or mixture, crystal formation, and the isolation of the crystalline compound.
retardation factor
the ratio of the distance traveled by the compound to that of the solvent front in a given time
What is the melting point range?
the span of temperature from the point at which the crystals first begin to liquefy to the point at which the entire sample is liquid.
What is the purpose of using a pre-warmed funnel during the hot gravity filtration?
to avoid the formation of crystals that can occur if the solution you are filtering cools down when it comes in contact with a room temp filter funnel
What is NaHCO3 used for ?
to neutralize HCl
what is a filter pipet mostly used for?
to remove an unwanted solid from a liquid
Condensation polymerization
two monomers react to form a larger unit while a small molecule like H2O or HCl is eliminated or lost.
Thin Layer Chromatography
uses a thin layer of adsorbent material (stationary phase) that is bound to a solid support (glass, plastic or aluminum sheet)
how is the filter-tip pipet created?
using a very small piece of cotton and dropping it into the large end of the pipet and pushing the cotton into the tip with metal wire
How can you isolate your solid in extraction?
vacuum filtration with a Hirsch funnel, washed with cold DI water
What is the mobile phase of this experiment?
petroleum ether and MtBE
What other compounds are we analyzing in this lab?
Aspirin, caffeine, acetaminophen, ibuprofen
Experiment 3b Column Chromatography: Topics and techniques
1. Chromatographic separation of compounds based on polarity 2. Column techniques: filling, loading, running columns 3. Use of TLC to identify fraction components
Experiment 3a: Thin Layer Chromatography: Topics and Techniques
1. Chromatographic separation of compounds based on polarity. 2. TLC techniques: spotting, developing, visualizing, Rf calculation 3. Use of TLC to identify the components of an OTC pain killer
Experiment 4 Making Polymers: Topics and Techniques
1. Explore various types of polymerization reactions. Condensation reaction to form Nylon-10,6. Radical polymerization reactions Formation of a cross-linked polymer, the "slime" experiment
Experiment 6: resolution of enantiomers topics and techniques:
1. Formation of diasteriomers 2. Separation of enantiomers 3. Fractional crystallization 4. Determination of optical purity by measurement of optical rotation (polarimetry)
Experiment 1: Recrystallization topics and techniques
1. Macro-scale and microscope recrystallization2. Decolorization of hot solutions3. Filtration techniques4. Use of a craig tube and a centrifuge
Experiment 5a Simple and Fractional Distillaton Topics and Techniques
1. Methods, techniques and separation of liquids using the process of distillation 2. Gas chromatography, relative response factors and analysis 3. Monitoring the separation of distillate fractions by gas chromatography
Experiment 5b: steam distillation topics and techniques
1. method and technique of steam distillation 2. isolation of an essential oil, a natural product 3. microscope methods of distillation
Experiment 0: Topics and Techniques
1. use of pasteur, plastic, and filter pipets 2. approximating volumes by drop count 3. melting point and mixed melting point
What volumes of methyl tert-butyl ether and water used? Why?
2mL of MtBE is used and 3mL of water is used. Partition coefficients are based on concentration, which is an intensive property, therefor the volumes used will not affect your outcome. The 3mL of water and 2mL of MtBE will still allow for the partitioning of benzoic acid and will create two separate layers so you may separate your organic and aqueous phases.
What solvent is used for the TLC lab?
30:70 ethyl acetate: petroleum ether
For each of the following pairs, predict which compound will have the larger Rf value if both are run on SiO2 TLC plate in 10% acetone/hexane: 4 decagon or 4-decanol; xylene or benzoic acid; cycloheptane or cycloheptanone
4-decanone is going to have a higher Rf than 4-decanol. Due to the hydrogen bonding (a strong intermolecular force) in 4-decanol it is going to stick with the SiO2 more than 4-decanone, causing 4-decanone to travel further. Similarly, xylene will have a higher Rf value than benzoic acid because it is less polar and cycloheptane will have a higher Rf than cyclopentanone because cyclopentanone is more polar.
Your TA may have told you to use acetone to clean your glassware after you finished your experiment. Acetone is a very popular solvent for cleaning glassware. Given the properties of acetone listed in MtC, why do you think this is? Do you think acetone would make a good recrystallization solvent? Why or why not? Form a safety standpoint, what do you suppose would be a major concern when using acetone?
Acetone is a good solvent for glassware because it dissolves most contaminants on the glassware, and works with water. It also helps dry the glassware better than water does, which in this experiment was an aid to the recrystallization drying process. Acetone would not make a good solvent because its boiling point is too low, so it would evaporate off too quickly to be an effective solvent. The biggest safety concern with acetone would be its high flammability.
What solvents do we use to check the solubility of our polymers?
Acetone, toluene, and ethanol
How do you remove soluble colored impurities?
Add charcoal and then perform hot gravity filtration
What comprises the unknown mixture? What steps will be taken to identify each component?
An acid, phenol, and neutral compound comprises the unknown mixture. In order to identify the acid, you are going to take your 150 mg of unknown and add 3 mL of MTBE along with 5% sodium carbonate to separate your acid from the phenol and neutral. Once separated you will draw out the bottom layer containing your acid and transfer it into a separate centrifuge tube. With the acid you want to add 10% HCl until it becomes acidic on pH paper and you should begin to see precipitate form. With this you are going to filter your acid solution, and wash with cold water to make sure all your substance is accounted for. Next you will want to dry your solid and discover the mass and melting point. If your melting point reveals your substance can be more than one possible unknown, you should perform a mixed melting point and will be able to determine which is you substance by whichever mixed melting point does to cause the melting point to change. For your mixture of neutral and phenol you will extract with NaOH and once they are separated you will treat your phenol as you did the acid to determine your substance. For your neutral you will wash it with water you can extract any contaminants. Then you want to dry over sodium sulfate and make sure to rinse the sodium sulfate with MtBE so you get all your substance. Next you want to evaporate the MtBE so you only have your neutral substance. Once your neutral layer is isolated and dry you will be able to take the mass and melting point as you did for your phenol and acids accounted for. Next you will want to dry your solid and discover the mass and melting point. If your melting point reveals your substance can be more than one possible unknown, you should perform a mixed melting point and will be able to determine which is you substance by whichever mixed melting point does to cause the melting point to change. For your mixture of neutral and phenol you will extract with NaOH and once they are separated you will treat your phenol as you did the acid to determine your substance. For your neutral you will wash it with water you can extract any contaminants. Then you want to dry over sodium sulfate and make sure to rinse the sodium sulfate with MtBE so you get all your substance. Next you want to evaporate the MtBE so you only have your neutral substance. Once your neutral layer is isolated and dry you will be able to take the mass and melting point as you did for your phenol and acid
Benzyl alcohol has a boiling point of 205C. It has solubility characteristics that would seem to make it a good choice for use as a recrystallization solvent for fluorenol (mp 153-155C) but in fact benzyl alcohol is a poor choice of solvent for this recrystallization. Why do you think this is?
Benzyl alcohol wouldn't be a good solvent for fluorenol because its boiling point is much higher than fluorenol's melting point, when you try to boil the benzyl alcohol solvent off, the fluorenol will already be melted, so we wouldn't be able to reform crystals unless the solvent's boiling point was lower than the fluorenol's melting point.
What do you use for suction filtration? (macro)
Buchner funnel
What do you use for extraction of your oil?
CH2Cl2 (dicholoromethane)
Differences between chain addition and condensation polymerization?
Chain addition usually involves a vinyl-type monomer. Chain addition polymers have simple hydrocarbon backbone and any functional group is pendant to the parent chain. Where as condensation polymerization, the functional group is part of the polymer backbone. And the empirical formal of a chain addition polymer is identical to that of the monomer.
What will you be separating in column chromatography
Ferrocene (not polar) and acetylferrocene (polar)
Why does ferrocene elute from the column first? Why was the solvent changed in the middle of the column procedure
Ferrocene Eluded from the column first because it is more non-polar acetyl ferrocene. This caused ferrocene to bemore attracted to the mobile phase which was more non-polar than the polar stationary phase. The solvent was changed in the middle of the column procedure because acetylferrocene needed a more polar mobile phase in order to elute from the column, hence why MtBE was used.
How does liquid-liquid extraction work?
First the component mixture is dissolved in a solvent and a second solvent that is immiscible with the first solvent is added (diethyl ether and water) then the contents are mixed and separated into 2 layers.
What does glycerol do in this experiment?
Prevents leaks
Arrange the following solvents in order of increasing polarity: ethyl acetate- dichloromethane- isopropanol- ethanol- toluene- heptane
Heptane < toluene < dichloromethane < ethyl acetate < n-propanol < ethanol
What is liquid-liquid extraction?
Liquid liquid extraction is a method used for the separation of compounds comprising of sample mixture using two immiscible solvents.
What compounds are we analyzing in this lab?
Ortho-hydroxyacetophenone and para-hydroxyacetophenone
What is the most common stationary phase (adsorbent)?
Silica gel and alumina
What does the sodium bicarbonate extract out of your mixture? What are our products to be and where are they located in your extraction system?
Sodium bicarbonate extracts carboxylate saltout of your mixture. This is going to allow you to separate the acid from the phenol and neutral substances. Your products will be your carboxylic acid on the bottom of your two layers that form and then a mixture of your phenol and neutral substances will be on the top layer that forms.
What is the drying agent? (extraction)
Sodium sulfate (organic phase)
When a pipette is first filled with a volatile organic solvent, what happens that makes the pipette leak immediately? How do you keep your data accurate and not let any leak occur?
The pipette is going to leak immediately because the vapor pressure of the volatile solvent is coming in contact with the air already in the pipette. In order to avoid this draw the solvent in and out of the pipe it a few times so it does not drip then obtain your sample.
What is the point of using fluted filter paper? What is one of the most important rules to remember when making fluted filter paper?
The point is in order to increase the surface area for an increased rate of filtration.
What is the purpose of using sodium sulfate in part a: the partition coefficient of benzoic acid? How can you ensure you are collecting all of your sample from the sodium sulfate?
The purpose of using sodium sulfate is to remove any water that may have dissolved in the organic phase, leaving the organic phase moisture free. In order to ensure you are collecting all your sample from the sodium sulfate you should rinse the sodium sulfate with a small amount of MtBE, this way you are not losing any benzoic acid.
What is the purpose of washing the aromatic phenol with sodium hydroxide?
The purpose of washing the aromatic phenol with sodium hydroxide is so the phenol and the neutral substances will separate.
What is the reason we use methyl tert-butyl ether (MTBE)? What type of functional group is this solvent classified under? Comment on the high volatility of these compounds.
The reason we use MtBE is because it is safer than diethyl ether. This is because while MtBE is still flammable it is not as flammable as diethyl ether. MtBE is classified under the dialkyl ethers functional group. The high volatility of these compounds means that they easily vaporize/ evaporate.
What is the importance of the use of an Erlenmeyer flask in macro scale recrystallization?
This flask allows the water vapor to condense and drip down the sides so solvent is not evaporated and lost
What is the purpose of using a small beaker to collect your filtered solution in macro-scale recrystallization?
This makes it easier to collect your crystals (would be much harder from and erlenmeyer flask).
What can the melting point be used for?
To establish the qualitative purity and possible identity of a compound.
Why is NaOH added to the solution?
To neutralize the HCl released each time a new amide bond is formed
Explain how each of the following contaminants is removed during the recrystallization process a) sand (inorganic contaminant) b) colored organic contaminants c) a very soluble contaminant
a) Sand is removed from the solution by the filtration; the fluted filter paper will catch the grains of sand that didn't dissolve in the boiled solution. b) Colored organic compounds are removed from the solution by the addition of charcoal powder, which will filter out those contaminants when the hot gravity filtration is performed. c) a very soluble contaminant is removed when the solution is boiled; the contaminant will be boiled off so that only the desired compound remains for recrystallization.
Given the procedures described for using Pasteur pipets from Part A of Experiment 0, and literature densities if needed, explain how you would a) add about 0.8mL of chloroform to a vial b) add about 1.2 grams of methanol to a vial c) c) determine the volume and mass of 38 drops of methylene chloride
a) You would use the set number of drops from a pipet that you found was needed for 1mL and use that value to discover the number of drops needed for .8mL b) You would use the density of methanol to find the number of mL in 1.2 grams and with this you could use the standard drops from the pipet as described in part a. c) In order to get the volume, you could drop 38 drops into a graduated cylinder and from here you could use the density to obtain the mass.
what is polystyrene soluble in
acetone and toluene
Corrected Area=
area / cfactor
There are likely to be blank in your unknown that will not dissolve in the hot solvent, and how can this be removed?
insoluble impurities and by hot gravity filtration
Is melting point intensive or extensive?
intensive
What is radical, or chain addition polymerization? whats the initiator?
involves the use of an initiator that forms a reactive species. In our polystyrene synthesis the initiator is benzoyl peroxide, a compound that generates radicals when heated to an appropriate temp. These radicals then react with the styrene monomer to begin the chain addition process.
While TLC relies on capillary forces for moving the solvent, in column chromatography an eluent
is allowed to percolate through the column by gravity
Spotting
when a drop of solution containing a sample for separation is placed at one end of the plate.
