Final Study Flashcards
What are the name and chemical formulas for common drying agents?
Sodium Sulfate - Na2SO4 - Most common. Absorbs a large amount of water, less accuracy than Mg.
Magnesium Sulfate - MgSO4 - magnesium ion is a strong lewis acid
Calcium Chloride - Ca2Cl2 - absorbs methanol/ethanol too
Potassium Carbonate - K2CO3 - base, used for drying basic substances (e.g. amines)
Benzoic Acid lab: Why did we add Na2SO4 to a solution?
Organic solvents like ether always take up a small amount of water.
How do you figure out how much drying agent to add to solutions?
Add in small chunks until it starts ‘chunking’ (swirls when you mix it)
Caffeine Lab: What is important to remember about caffeine?
It sublimes (not evaporate)
Other flavenoids have
Caffeine Lab (Chicago House):
What did we do in this lab? (concise)
What did we do in this lab? (detailed)
What are the components to remember?
Concise: Start with caffeine and impurities > ionize impurities with sodium carbonate > Separate impurities from caffeine with DCM + H2O > Sublime caffeine to purify
Detailed: Extracted caffeine by:
Heat tea bag to hydrolize tannins into gallic acid
Squeeze as much out of tea bag as possible
Add sodium carbonate to deprotonate gallic acids and tannins
Add methylene chloride to grab caffeine + chlorophylls + trace alkaloids
Add drying agent (Na2SO4) to get water out
- Evaporate* to get DCM out
- Sublime* to purify completely
Get weight, MP, % rec
Caffeine lab: What is the main component of tea leaves? What is its solubility with water like?
Cellulose.
Insoluble in water.
Presents no problems in isolation procedure.
Caffeine: how did we separate it from the other flavinoids?
Has methyl groups all around it
These methyl groups can’t be deprotonated, so caffeine can’t be ionized
Took advantage of this with sodium carbonate (Na2SO4)
Caffeine lab: What is the class of compounds used to tan leather called?
What properties do they have in common?
What happens when they are hydrolyzed?
What can they precipitate?
Tannins.
Properties: Phenol groups with MW 500-3000.
Two classes - those that can be hydrolized and those that can’t
Hydrolized: Those that are hydrolyzed yield glucose, gallic acid
Precipitate: They precipitate alkaloids (e.g. caffeine!) and proteins from aqueous solutions
Caffeine lab: What happens when tannins are extracted into hot water?
Tannins are acidic, so:
They hydrolize to form free gallic acid
Caffeine lab: What is sodium carbonate?
What does it do in the caffeine lab?
It’s a base.
Converts tannins to water-soluble sodium salts
(So, it can deprotonate phenol groups)
More basic than bicarbonate, less basic than hydroxide
Caffeine lab: Is caffeine soluble in water?
What about DCM?
Why is this important?
Yes
BUT: way more soluble in DCM.
This means that tannin / gallic acid salts (made by sodium carbonate) go to H2O, most of caffeine to DCM.
Caffeine lab: Why is tea brown?
How is this important?
Flavonoid pigments, chloryphyls, and their oxidation products
Important because flavonoids are not soluble in methylene chloride
But chloryphylls are
Caffeine lab: You’ve added sodium carbonate to make tannins/gallic acid salts.
You’ve added DCM and H2O to separate.
What is in the DCM? What is in water?
How do you purify?
DCM: Nearly pure caffeine. Has some chlorophylls (crude caffeine).
Water: Tannins (salt), sodium carbonate, flavonoids?, gallic acid (salt)
Purify with sublimation
Caffeine lab: How do you purify the crude caffeine?
What is physically important to do?
Sublimate it.
You need reduced pressure
(At air pressure, it just decomposes)
Caffeine lab: What machine did we use to sublimate the caffeine? How does it work?
Caffeine lab: What is a carcinogen? What is a toxic compound?
What compound is suspected of being one?
What else is problematic about this compound?
Why is this relevant?
What is less toxic (but can’t extract caffeine as efficiently)?
Carcinogen: cancer-causing agent. Toxic: Chemical that can injure biological tissue.
Compound: DCM
Problematic: It’s also an environmental pollutant
Relevance: Need to be careful with methylene chloride, dispose in halogenated waste
Other compound like DCM: Ethyl acetate.
Caffeine lab procedure: Why did we heat the water? What happens?
So tannins would be hydrolized.
They form gallic acid
Sublimation: What is sublimation?
What labs is it relevant to?
When would something sublime?
What: Compounds going directly into gas phase from solid
Labs: We sublimed in caffeine lab to purify caffeine
Dry ice was subliming in benzoic acid lab when we added it to the grignard
When: Sublimation would occur when melting point of a compound is above atmospheric pressure (so it turns to gas at a pressure lower than the melting point, when it’s still a solid)
Sublimation: What do you do in the lab to get sublimation to happen?
You make a vacuum.
The vacuum effectively makes air pressure (‘appiled pressure’) disappear, causing both the boiling temperature to decrease and the melting point to decrease.
If the applied pressure is lower than the melting point pressure, then the compound will sublime before it melts.
Caffeine lab: What is it called when there are drops in solution that look like vesicles between two solvents?
Where do you see it and why?
How do you prevent them?
What: Emulsion (drops of immiscible solvent B floating around in A)
Where: See after adding DCM while liquids are separating
Prevent:
Keep it still
Add NaCl (moves water)
Centrifuge it
Swirl in separatory funnel
Caffeine lab: What is in the mixture after adding both Na2CO3 and DCM?
Why do we centrifuge at this point?
Aqueous: Tannins (salt), Gallic Acid, Na+, carbonic acid (from NaCO3 protonating), flavonoids. H2O, Na2CO3,
DCM: Caffeine, chlorophylls (e.g. trace alkaloids)
Why centrifuge: To break emulsion between DCM/aq.
Caffeine lab: Why do we need to add DCM multiple times after centrifuging?
Based on the distribution coefficient, some caffeine will remain in the aqueous layer.
We add DCM multiple times to get more of it out efficiently.
Caffeine: We’ve extracted an organic layer with DCM and caffeine 3x.
Now what?
Need to get trace H2O out.
Add drying agent (Sodium Sulfate Na2SO4)
Caffeine lab: We have purified caffeine that has been dried out. What do we need to do now? How do we do it?
Get the DCM out by evaporating it.
Use rotovap to do this (lowers pressure to evaporate out liquid)
Caffeine lab: What were we purifying by subliming at the end?
What did we do to sublime?
Why does it work?
Getting trace alkaloids out.
We assembled sublimation apparatus with cold finger/vacuum and heated bottom of RBF
(?) Works because the alkaloids don’t sublime at low pressures?
Caffeine lab: What is a distribution coefficient (K)?
What: A ratio describing the distribution of concentrations of a solute in two solvents.
K=C2/C1
Where C1 and C2 are concentrations at equilibrium in g/l or mg/ml
Caffeine lab: What’s better, extracting with several small portions of a second solvent or one big portion of the first?
Why?
Several.
The distribution coefficient has a constant value (the solvent concentration per ml is the same if there’s 9mlA and 1ml B or if there’s 1ml A and 1ml B)
If the solute concentrations are X/Y, then taking out the first solvent will take out X.
??
Meta: You’re given 4 multiple choice questions and asked to explain why you chose one. What will this explanation need to include?
Discussion as to why the other 3 wouldn’t work
Separations: What compounds are water-soluble?
(e.g. what can you get from a water wash?)
Highly polar materials (strong acids/bases, salts)
Low molecular weight polar materials (alcohols, carboxylic acids, amines)
Organic compounds containing fewer than 5 carbons
Separations: What do acid extractions remove?
Basic impurities (organic amines)
They convert things to cationic salts so that you can water wash
Separations: What do base extractions (e.g. 1M NaHCO3 or dilute NaOH) do?
Convert acids e.g. carboxylic acid to anionic salts
Separations: How can you separate phenols from carboxylic acids?
Choose base carefully:
NaHCO3 converts carboxylic acids to salts, but not phenols
Separations: What is a neutralization reaction?
Reaction in which there is no excess hydrogen or hydroxide ions (in case of reaction with water)
Acids and bases react quantitatively with each other
Separations: What is a distillation?
When do you use it?
Purifying a liquid by vaporizing, condensing, collecting distillate
Use on alcohols to evaporate
Use on anything with different boiling points
(Can also do rotary evap)
Separations: How can you purify substances? (Ways we learned)
Distillation - boiling point (liquids)
Crystallization - heat to dissolve, cool to precipitate (solids)
Column chromatography - polarity, size
Sublimation - Lower pressure, heat solid to vapor, cool for deposition
What does it mean to elute?
Extract one material from another by washing with a solvent
What is reflux?
What is it for?
Vaporizing, then condensing vapor to where it came from
It’s distilation, but the distillate goes back
Separations: What is backwashing?
Adding the insoluble solvent to solution to remove impurities
e.g. backwash an aqueous layer with an organic solvent to remove unwanted neutral material
Separations: What experimental techniques may be included in a separation scheme?
Acid-base extraction
Drying steps
Sublimation - caffeine. No solvent needs to be removed
Distillation - for liquids
Crystallization - for solids; use e.g. hot methanol
Alkyl Halides What did we do in the alkyl halides lab (general)
1) Fill a set of test tube bottles up with NaI/acetone
Add different halides to test for SN2 reactivity
2) Fill a set of test tube bottles up with AgNO3/ethanol
Add different halides to test for SN1 reactivity
Get observations
Alkyl halides: What is used as the SN2 solvent?
Why?
Acetone
It’s a nonpolar solvent
Alkyl Halides: Is Cl or I a better nucleophile in polar protic solvents? Why?
I.
Hydrogen bonding solvents form a shell of solvent around nucleophiles to reduce nucleophilicity.
As atoms get bigger, electrons are spread farther apart (less electronegative) so they’re more nucleophilic
Alkyl Halides: Why does a precipitate form in SN2?
How does that affect things?
What kind of solvent is it?
NaCl or NaBr is the byproduct of an SN2, and those are solids
This means that as the reaction occurs, reaction keeps getting driven by precipitation
Solvent: acetone (nonpolar)
Alkyl Halides: What did we use as the solvent for SN1?
What else was there and why?
Solvent: Ethanol, cations can attack it after dissociation
What else: AgNO3. Silver ion coordinates with halide ion to form a precipitate (AgCl or AgBr). Similar to NaCl or NaBr in SN2.
Competing Nucleophile lab (Northtown Woods)
What did we do in this lab? (concise)
What did we do in this lab? (detailed)
What are the components to remember?
Concise:
SN1: Heat up acidic halides + alcohols in reflux to react > separate > figure out how much product there is with GC
SN2: Put acidic halide + tertiary alcohol in tube > shake > separate > figure out how much product there is with GC
Detailed:
SN2: Assemble reflux to heat up without losing stuff
Put H2SO4/NH4X in RBF to make an acidic nucleophile mixture
Heat up the mixture so salts don’t precipitate out
Add alcohol and heat the shit out of it in reflux to get the reaction to happen
Separate
Stick in separatory flask w/ propane, water > NaHCO3 > dry
SN1: Stick H2SO4/NH4X in tube
Put tertiary alcohol in
Separate
Get GC
What is the IR frequency for a C-O stretch?
What are the frequencies for a C=C stretch?
C-O: 1050-1150 strong
C=C aromatic: 1400-1600
C=C alkene: 1620-1680
Competing Nucleophiles: What solvents did we use?
Why?
H2SO4/H2O + NH4Br + NH4Cl
Why: Acidic polar protic solution to protonate alcohols to make them leaving groups
NH4 as a spectator (?)
Competing Nucleophiles: Is the nucleophile involved in rate-determining step in SN1? SN2?
Why does this matter?
SN1: No. Rate-determining happens when cation is formed.
SN2: Yes. Nucleophile is present.
Why it matters: It means SN1 reactions will have the same concentrations of product as in reactant, SN2 reactions will have more of the stronger nucleophile
Competing Nucleophiles: You heat up your reaction with a secondary alcohol. What do you need to watch out for in terms of mechanisms?
Elimination.
It means that weird products can get formed, because alkenes will attack H-X to form cations
Competing nucleophiles: What property of molecules is most important for determining retention times?
Boiling point
Competing nucleophiles: Why did we heat the primary/secondary substrate but cool the tertiary?
Cool tertiary: Acids stick protons on to tertiary alcohols really fast (and this is the rate-limiting step)
ALSO: if you heat it, you get elimination!
Heat primary: To get reaction done in an hour
If you’re asked to get theoretical yield, what do you need to do? What do you need?
Figure out limiting reagent
Figure out grams
Only give % if you’re asked for % yield!
4-Methylcyclohexane (Dad’s house)
What did we do in this lab? (concise)
What did we do in this lab? (detailed)
What are the components to remember?
Concise:
Detailed:
Give methylcyclohexanol a proton source (H2SO4/H3PO4) and heat it
Distill alkene product as it forms
Purify alkene product
Get % yield
IR
4-methylcyclohexene: What are the differences between sulfuric acid and phosphoric in this reaction? Why would you use one or the other?
Sulfuric: Causes charring, but makes reaction go faster
Phosphoric acid: no charring, better choice, but slower
4-methylcyclohexene: How do you drive equilibrium forward in this reaction?
What other compounds are in the product solution with this method?
Distill the methylcyclohexene as it’s formed with H2O (Reaction done with distillation apparatus)
Other products: Some phosphoric acid codistills (remove by washing with NaCl); some water
4-methylcyclohexene: Why does bromine decolorize the product?
Why does KMnO4?
Bromine: Reacts with double bonds and gets decolorized
KMnO4: Reacts with double bonds to make MnO2 (brown)
4-methylcyclohexene: Why do we wash with the NaCl?
Draw water from the organic layer
Draw phosphoric acid from the organic layer
C4/C5 Acetate Ester
What did we do in this lab? (concise)
What did we do in this lab? (detailed)
What are the components to remember?
Concise: Made an ester from acidic unknown l/acetic acid > purified > IR/GC/NMR to figure out alcohol
Detailed:
Put together a reflux with a drying tube
Stick alcohol + acetic acid H2SO4 + heat in RBF
wait
Take out everything but CH3COOR with H2O
Take out H2SO4 as Na2SO4, CH3COOH as CH3COONa with NaHCO3
Take out ROH with NaCl wash
Dry out H2O with Na2SO4
Distill ester to purify (remove the side-products still there)
% yield / IR/GC/NMR
What is density defined as?
Mass per unit volume (g/ml)
Used to convert weight of a liquid to corresponding volume and vice/versa
Acetate Ester: What’s one way to completely remove methanol from an organic phase?
Salt wash (NaCl)
Benzoic Acid
What did we do in this lab? (concise)
What did we do in this lab? (detailed)
What are the components to remember?
Concise: Make a benzylic Grignard > turn it into a benzylic magnesium carbonyl with CO2 > add acid to make it calm down
Detailed:
Get % yield, IR, MP
Benzoic Acid: How can a grignard make a secondary alcohol? Tertiary?
Secondary: react w/ aldehyde
Tertiary: react w/ ketone
Benzoic Acid: What does Grignard + ester form?
Tertiary alcohols
But it reacts with ester twice
Benzoic Acid: What’s are the biggest impurities? How do they get made?
Benzene (anything with a proton is present somewhere)
Biphenyl (No idea but it involves two rings attaching and radicals)
C4/C5 Acetate: How did we get data about what alcohol we used?
Benzoic Acid
What did we do in this lab? (concise)
What did we do in this lab? (detailed)
What are the components to remember?
Concise: Made a Grignard, turned it into a carboxylic acid with CO2, separate
Detailed: Set up incredibly dry apparatus (CaCl2 to get water in air)
Make ether by heating up Mg and PhBr in ether
Make carboxylic derivative with CO2
Hydrolize with HCl
Separate
