Melting Point
temperature at which the solid phase is in equilibrium with the liquid phase
Pure Compound
sharp melting point, range is narrow (1-2 degrees)
Why does the presence of a soluble impurity in a sample has the effect of lowering and broadening the melting point range?
because the impurity disrupts the crystalline lattice of the sample so less energy is required to convert the solid phase into a liquid phase
What effects does insoluble impurity like sand and glass has on MP?
no effect
Errors of taking melting points:
1. improper amount of sample in capillary tube 2) mistaking sagging or shrinking sample as melting 3) presence of solvent cause crystals to “sweat”
Benzoic acid
122-123°C
Mandelic acid
120-122°C
An unknown compound was determined to be 74.97% C, 8.39% H, and no nitrogen. What is the empirical formula
100-74.97-8.39 = 16.64% O
# of C: 74.97/12 = 6.25/1.04 = 6
# of H: 8.39/1=8.39/1.04= 8
# of O: 16.64/16 = 1.04/1.04 = 1
EmF: C6H8O
Can IR spectroscopy be used to distinguish 2-pentanone from 2-hexanone? why or why not?
No because IR spectroscopy is used to distinguish functional groups presents on molecules. Both 2-p and 2-h contains the same functional group.
Acetophenetidin
analgesic and antipyretic (pain and fever relief)
p-acetamidophenol
Williamson ether synthesis
p-phenetidine
Amide synthesis
Recrystallization
solvent that will completely dissolve both desired compound and impurities when the solvent is hot; desire compound must be insoluble in the chosen solved at cold temperature and inorganic remains soluble when cooled
What do seed crystals do?
They serve as nucleation sites where more molecules of the desired compound deposit themselves in layers.
Explain the purpose of the hot gravity filtration. Why is it good to use the stemless funnel for this technique?
– Hot gravity filtration serves to remove any insoluble impurities that do not dissolve when the solution is brought to its boiling point.
– it is good to use the stemless funnel for this technique because this would minimize any contact between the hot solution and the funnel. If a funnel with stem is used the droplets of hot solution might get stuck on the stem inner surface and early crystallization of the solution might occur
ligroin
solvent derived from petroleum consisting of C7 and C8 hydrocarbon, non polar
Amide synthesis of acetophenetidin
p-phenetidine + acetic anhydride (solvent: Sodium acetate and hydrochloric acid)
Why is the sample of p-phenetidine reddish brown?
small amount of impurities caused by air oxidation of the amino functional group
how to remove reddish brown from p-phenetidine?
decolorizing carbon
Why should you not stir the crystals in the buchner funner?
this makes the filtration less efficient and does not adequately remove the solvent from the crystal
Williamson Ether Synthesis
1) p-acetamidophenol +sodium methoxide, methanol, and ethanol
2) 1st product (addition of sodium) + Bromoethane
Why does the williamson ether synthesis take two steps?
Because the hydrogen on the alcohol group of acetamidophenol would react with the bromoethane to create ethane and there would not be any reaction. The sodium acetate turns that alcohol group into a nucleophile that would attack the C of the bromoethane
Reflux condenser
Allows the reaction to be carried out at the boiling point of the solvent and yet it prevents loss of solvent or reagent due to evaporation. The vapors condense as they rise up the condenser and thus prevent them from escaping.
What was the best recrystallization solvent for the acetophenetidin?
Water because the solute is completely soluble at boiling point, but the crystals reappear when solution is placed in an ice bath.
Wooden applicator
helps with gentle boiling
Simple experiment that could be used to determine if the samples made through the two synthetic routes are identical:
If the sample made through two synthetic routes are identical, one can create a mixture from the same amount of two samples and the MP should be sharp and close to the recorded MP. If MP is lower than theoretical MP and has big range: samples are different from one another.
Why is HCl used instead of just DIW?
HCl is a much stronger acid which protonates the amine group of the p-phenetidin, which makes it more soluble in the solution
What is the purpose of the sodium acetate solution in the amide synthesis?
HCl protonates p-phenetidine and drives the reaction to the right but too much HCl would convert all of the compound to its conjugate acid and no reaction with acetic anhydride would occur. Sodium acetate creates a buffer within the reaction that would control HCl’s acidity.
NMR of acetylphenetidin
N – 8ppm
CH3 (acetyl group) – 2ppm
H(2) (closer to N)- 7.4 ppm
H(2) (closer to O)- 6.8-7ppm
CH2 (closest to O)-4 ppm
CH3 (closet to O) – 1.4 ppm
Hexane vs water
immiscible (Hexane top)
Methylene chloride vs water
immiscible (Water top)
Ethanol vs. water
miscible
ether and water
immiscible (ether top)
Why is phenol much more acidic than cyclohexanol
There more stable or the weaker the conjugate base, the more acidic the compound is. When losing a proton, phenol’s conjugate base has resonance stability from its double bond.
Could you separate 2,4-dinitrophenol (pH 3.96) from benzoic acid using extraction procedure IN THIS EXPERIMENT?
no since both are very close in acidity; cannot use reagents in this experiment to neutralize one and keep one (stronger acid) as a weak acid; both would be neutralized
What is extraction? What types are there?
Extraction is a technique that chemists use to remove selected components from a mixture. The different types are solid-liquid extraction and liquid-liquid extraction.
Why is carbon dioxide used as a solvent for solid-liquid extractions?
It offers a greener alternative to other solvents, it is readily available, nonflammable, nontoxic, and safe for the environment. Ease of removal of solvent at the end of procedure, and it is relatively quick.
What criteria must be met in order for a liquid-liquid extraction to be successful?
The two solvents that are chosen for the extraction must be immiscible. In addition, the compound to be extracted must have different affinities for the two solvents.
Treating NaOH vs NaHCO to the carboxylic-phenol mixture
NaOH is so strong that it would neutralized both strong acid such as carboxylic acid and weaker ones like phenol. On the other had NaHCO3 is weak enough that it can only react with strong carboxylic acid and remains unreacted with phenol
Carboxylate ions + HCl solution
this protonates carboxylate ions back into carboxylic acid compounds that forms solids when put in ice bath
If carboxylic compounds remain aqueous
use ETHER for back extraction
Phenol and Ether + BRINE
wash the organic layer – removing remaining water in solution
Anhydrous Magnesium Sulfate
The salt absorbs the water that is dissolved in the organic solvent.
What is present in the aqueous layer you drained? How do you neutralize it? How do you isolate it?
The carboxylate ion is present. In order to regenerate the carboxylic acid it must be added to HCl in an ice bath to induce crystallization. To isolate the crystals, vacuum filtration is performed.
What is present in the organic layer? What steps do you need to take to isolate the desired product?
The phenol is present. There may be some water present in the solution so it must be dried with brine and anhydrous magnesium sulfate until it no longer clumps together. The drying agent is then separated from the organic solution through gravity filtration. Once this is done, the ether must be evaporated under reduced pressure so that the pure phenol solid is left in the flask.
What is the difference between “extracting” and “washing”?
Extraction and washing can share very similar procedure but ultimately have different purposes. Extraction removes desire compounds/solutions from a mixture whereas washing filters out the impurities from the desired solution. Keep extraction and discard washed impurities.
Describe the practical reasons behind the direction of the flow of water through condenser:
Since the heated vapor from the distillation flask will travel from high to low, the water flows in the opposite direction in order to effectively cool the vapor which would liquify and flow down into the collection tube
Why is it important to soak the clover in water?
Since cloves are dried up, soaking them would allow water to penetrate into the cloves and more eugenol would be isolated.
Why is dichloromethane (CH2Cl2) added to the solution in the collection vessel? What process is this called?
To extract the eugenol from the water. This process is liquid-liquid extraction and the lower layer will be the dichloromethane along with the desired essential oil.
To dry the CH2Cl2:
brine and anhydrous magnesium sulfate
Major functional groups for eugenol
-OH group : 3517.6 (3600-3300)–10ppm
-OCH3 group: 2934 (3100-2700)–
Advantages and disadvantages of distillation vs. CO2 extraction:
with distillation, cloves are allowed to sit in water for full penetration which would be more advantageous because it would yield higher % of product. Extraction using CO2 reduces the chance of water remnant and impurities. CO2 extraction would produce better quality result; during the heating process of distillation, a lot of quality from the oil is evaporated
Is chlorophyll b more or less polar than chlorophyll a?
Chlorophyll b should be more polar than chlorophyll a because the former has a CHO group where the latter only has a CH3 group.
Which one is more polar? B-carotene vs. xanthophyll
xanthophyll would be more polar than B-carotene because of the -OH group at the ends of the molecules. B-carotene contains no oxygen and is quite non polar.
Ethyl acetate
polar solvent (-CO interaction)
Pencil for TLC plates?
the ink in the pen can tamper with the process; the ink would travel up the TLC plate with the solvent
Chromatography
techniques for separating, analyzing, and identifying compounds (column, thin layer, gas, high performance liquid)
Mobile phase
the eluent, the has or liquid phase in which the sample mixture is placed in
Stationary phase
a solid support that contains an adsorbent
If a component has a greater affinity for the stationary phase
travels more slowly
If a component has a greater affinity for the mobile phase
travels thought the stationary phase more quickly
Silica gel
has many sites for hydrogen bonding; polar compounds would interact with the silva and adsorb readily to the stationary phase
Rf value
distance from the origin to the center of the spot DIVIDED BY the distance form the origin to the solvent front; Polar compounds interacts more strongly with stationary phase and travel a shorter distance –> the more polar the compound, the smaller the Rf values
UV Light for TLC
UV lights activates a fluorescent indicator on the plates
Why is acetone used in chlorophyll extraction?
Acetone breaks down chlorophyll’s lipid bonds to a plant’s thylakoid structure and suspends the pigment in solution.
Why do we have to cover the test tube of acetone and spinach mixture with parafilm?
Acetone evaporates extremely quickly when interacting with air and all the solution would evaporate
What is the perfect composition of the eluent for the spinach lab?
50:50 hexane/ethyacetate
Why is a 50:50 ratio the best for this case?
Ethyl acetate is a polar compound while hexane is non polar; one compound interacts with the polar compounds of spinach while the other with the non polar compounds. The 50:50 ratio was enough to separate the polar and non polar compounds of the spinach, at the same time, the polar compounds also get to move up from the origin due to its interaction with the ethyl acetate. If only hexane was use, the chlorophyll a and b would remains at the origin and would not be separated form one another.
Why do we need to take pictures of TLC plates during lab?
because the compounds being separated will oxidize rapidly on exposure to air so it would fade away
Which pigment is the least polar which is the most?
B-carotene is the least polar and chlorophyll b is the most polar
What is the purpose of salicylamide?
an analgesic and antipyretic drug
Considering the directing effects of the substituents on salicylamide and predict the possible structures of the iodination products. Which do you think will be the major product?
-OH is an ELECTRON DONATING GROUP, the substituent would be directed to its para and ortho position. -NH2 is an ELECTRON WITHDRAWING GROUP and would direct the substituent to its meta position. The major projects has iodine at the ortho position to -OH and meta position to -NH2. (compare to the iodine group being para to the -OH)I think this would produce a higher % yield because the iodine group is being paced farther away from both functional groups which reduce the strain.
Electrophilic aromatic substitution
common reaction of benzene and its derivatives; two steps: 1) aromatic ring acts as a nucleophile and attack electrophile 2) aromatic ring is regenerated through the loss of proton
Charged intermediate species
stabilized by resonance
Why is iodine used instead of chlorine and bromine?
EAS with Cl2 and Br2 can occur in the presence of Lewis acid such as AlCl3, BUT iodine is the least reactive of the halogens
Green method for EAS:
iodination reactions using sodium iodine as the source of iodine and household bleach as an oxidizer (instead of nitric acid and I2)
What does absolute ethanol do to the salicylamide?
Dissolve the solid – use warmth of your hand to speed up dissolution
6% sodium hypochlorite solution (household bleach)
is an oxidizing agent that reacts with sodium iodine and turns it from a stable compound to a strong electrophile that would now react with the salicylamide in the electrophilic aromatic substitution
sodium thiosulfate
removes any residual iodine from the solution
1M hydrochloric acid
acidify the aqueous solution which drives the products to precipitates
IR Spectrum of Iodine at the ortho position to -OH
815.3cm-1
IR: -CO
1095.3
IR: -C=C
1621.6
IR: -NH2
3200-3300 (double peaks)
IR: -OH
3450.1
What is the directing effects of the substituents on salicylamide?
Major product gives the less strained position of Iodine that followings the directing effect of both substituent: meta to NH2 and ortho to OH
Interpret NMR:
H between I -NH2: 8.15 ppm (singlet)
H closer to I (between I and O): 7.7 ppm (doublet)
H closer to O (between I and O): 6.75ppm (doublet)
How would the Rf values change if a more polar solvent (like ethyl acetate) were used?
When a more polar solvent is used instead of non polar one like ligroin, it will interact more with the polar molecules and less with the non polar molecules causing a less dramatic separation. Rf values would be higher.
Why is it important not to dilute the initial sample before it has been loaded onto the chromatography column?
The more concentrated sample would produce a more significant or finer separation between polar and non polar compounds. Diluting the sample would cause a blurry separation between complex compounds instead of a fine separation
Which compound would elute first from the column: unreacted ferrocene, acetylferrocene, or diacetylferrocene? Why?
Non-polar or least polar compound elute first and therefore unreacted ferrocene elute first because it has no polar group. Acetylferrocene elute seconds because it only has 1 polar C=O group compared to diacetylferrocene which would elute last with 2 polar C=O groups.
Reaction of acetic an hydride
acetic anhydride reacts with phosphoric acid to form asylum ion which is an electrophile that can be used to add into an aromatic ring
Why is ferrocene called the super aromatic molecule?
it is about 10^5 times more reactive than benzene in electrophilic aromatic substitution because it consists of an iron atom sandwiched between two cyclopentadienyl anion
3M sodium hydroxide
neutralize the solution
TLC of acetylferrocene: eluent
methylene chloride
Why can you not introduce water into the chromatography column?
Water is very polar and should not be in the mix of the chromatography column. If water is present, it would interact with the acetylferrocene and diacetylferrocene and the whole solution would travel down together with no separation
Why cant you allow the volume of solvent to go below the top of the adsorbent?
because the drop would dry out and channels can form in the packing material which leads to inappropriate, poor separation.
What is the goal of pipets full of ligroin after addition of crude sample of acetylferrocene?
To load the sample onto the top of the column
How to elute ferrocene?
use ligroin
More polar solvent that is used to elute acetylferrocene
70:30 ligroin:ethyl acetate
Solvent for diacetyl ferrocene:
pure ethyl acetate
Comparing TLC plates: did chromatography serve to purify the sample?
the column chromatography served its purpose of separating and purifying samples. with the crude sample there are ferrocene, acetylferrocene and diacetylferrocene all present in the product. After purifying through the chromatography column, only acetylferrocene was collect.
Use knowledge of the mechanism and theory of electrophilic aromatic substitution to explain the formation of the diacetylferrocene isomer:
1,1′-diacetylferrocene would be the isomer present. If 1,2 and 1,3-diacetylferrocene were to be formed, both C2 and C3 would have to be able to accept the acetyl group which means those position has to be nucleophilic. However if looked at the resonance structure of those positions, those carbon has the tendency to be positively charged which means they are electrophilic and would not be able to accept acetyl group. Therefore acetyl group at C1 an C1′ is the best option
What is the purpose of crushing magnesium turnings?
Helps expose fresh metal surface by removing some magnesium oxide on the exterior.
How does iodine help facilitate the reaction of the magnesium turnings?
Cleaning the surface of the magnesium metal.
What takes place during a Grignard reaction?
First bromobenzene reacts with magnesium to form phenyl magnesium bromide. Then by adding the electrophile, the PMB would nucleophilically attack the compound.
Why must the apparatus be flame dried prior to the beginning the reaction?
Grignard reagents are sensitive to water. If water is introduced into the mix, the benzene will become unreactive because it would take an H from H2O.
Why must bromobenzene be mixed with anhydrous diethyl ether during formation of the Grignard reagent?
Grignard reagents are sensitive to water so if diethyl either containing more water is used it will interfere with the formation of the Grignard reagent.
Why is the reaction mixture added to hydrosulfuric acid and ice?
– ice prior to hydrosulfuric acid to complete the precipitates before it is dissolved by the acid to.
– The double bond with Oxygen (benzophene) reacts with the hydosulfuric acid and it is protonated by an addition of hydrogen creating an alcohol
After all of the ether has evaporated, what can we do to purify the organic solid?
Recrystallization using ethanol. The desired compound is soluble in ethanol at boiling point and is insoluble in ethanol when it cools.
When the reaction mixture is added to the separatory funnel with diethyl ether what happens? Where is the desired compound?
An aqueous layer forms (bottom) and an organic layer forms (top). The desired compound is dissolved in the organic layer (like dissolves like).
Why aldehydes and ketone add only one equivalent of Grignard reagent, but esters added two equivalent
While for aldehydes and ketones, after the first Grignard reaction, there is nothing left to react, for esters, after the first reaction the compound becomes a keno or aldehyde and can drive further Grignard reaction
Common bi product o the Grignard Reaction lab is biphenyl which is generated through a coupling reaction of phenyl magnesium bromide with unreacted bromobenzene. Which part of the workup remove this byproduct?
Since the compound is very non polar due to the lack of O group, it can only be remove through a workup step using a non polar substance. By adding the cold ligroin, the biphenyl would be removed which followed the ligroin down the Buchner funnel.
OH (IR)
3374
Phenyl (IR)
600-800 (ring torsion)
C=C (IR)
1500
C-H (IR)
3000
C-O (IR)
1200
presence of benzene rings (IR)
small stretches from 1500-2000
why is it important that the glassware and reagent used in a Grignard reaction are completely dry?
Grignard reagent is extremely sensitive and reactive with water. Since it is a strong nucleophile it would react with water first and will not be able to produce the desirable reaction and product
What is the reaction what would happen if phenyl magnesium bromide reacts with water
Phenyl magnesium bromide + h2o –> benzene + hydroxyl magnesium bromide
Why is isolating neutral p-aminobenzoic acid in step 3 difficult?
PARA is difficult to isolate because it has so many resonance that the compound can have many charges on it at different pH. Isoelectric point is where the compound carries not net charges, containing equal amount of (+) and (-) that neutralize each other. It is where it is easiest to gain precipitates and therefore its is very unstable and sensitive to pH.
Reducing the number of steps in synthesis:
increase % yield
Ginkgo biloba
most widely used herbal remedies, treating various ailments including asthma, macular degeneration, cardiovascular disease, vertigo, and memory loss and dementia associated with Alzheimer’s disease
If the p-toluidine in water+HCl is excessively dark,what would you do?
decline with charcoal before proceed
What is the reaction of the first step? (Protection)
P-toluidine + acetic anhydride (NaOAc, HCl aq) –> N-acetyl-p-toluidine
How do you test for the completion of reaction with magnesium sulfate, n-acetyl-p-toluidine, and potassium permanganate?
via halo test: dip the stirring rod into the mixture then touch the tip to a piece of filter paper –> purple halo = incomplete; light pink/clear halo = complete
Oxidation reaction
needs to boil gentle: too little heat will keep the reaction from occurring at a good time, too much heat will cause excessive frothing and possible boo over
Why cant you let the Celite dry out?
this will cause cracks in the filter bed and result in insufficient filtration
why must the solution of KMnO4 be hot when filtering using the Celite bed?
this would minimize crystallization of product in the filter –> precipitate should form when being acidified
For step 3- why do you need to scratch the wall of the flask?
the precipitates needs a nucleation site that can be stimulated by glass particles.
mechanism of Step three (Deprotection)
At the isoelectric pt. the desirable precipitate will form, more acidic = salt precipitates (NH3+), more basic = no precipitate
1) add 3M NH4OH solution –> decrease pH to isoelectric pt
2) Adjust pH of the filtrate until it is just basic
3) adjust pH again with glacial acetic acid
C=O (IR)
1663
NH2 (IR)
double peaks at ~3000+
why don’t we simply oxidize p-toluidine with KMnO4 to make p-aminobenzoic acid? wouldn’t that be faster? what unwanted reactions may occur?
we cant oxidize p-touluidine with KMnO4 because the NH2 must first be protected or else it would be oxidized also. the side product would have been a R-NOO-
Why don’t we do the esterification step prior to the deprotection step?
if esterification occur prior to deprotection then both functional would would be deprotected and we would have to report esterification.
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