Orgo 321L Final UMKC
ways to perform a workup...
1) filtration 2) extraction 3) chromotography
three basic types of extraction...
1) liquid/liquid 2) acid/base 3)solid/liquid
seven possible steps for recrystallization...
1- choose solvent 2- dissolve solute 3- decolorize 4- filter 5- crystallize 6- wash product 7- dry (remove solvent)
steam distillation benefits
1- reduced temperatures (org. compounds decompose at high temps.) 2- increased selectivity 3- good separation codistillation with water; allows distillation of relatively nonvolatile organic compounds without using vacuum systems; special kind of azeotropic distillation; especially useful for separating volatile organic compounds from nonvolatile inorganic salts -separate volatile compounds from complex mixtures
What makes a good solvent pair?
1. Dissolve the solute in the solvent you think is most soluble 2. Add the other solvent dropwise until cloudiness appears/persits 3. If cloudiness appears then add the 1st solvent again in small portions until the cloudiness disappears 4. Let the solution cool 5. Formation of crystals = good solvent pair (p.226-27)
How to choose a solvent for recrystallization
1. Place a small sample of the compound in a test tube and add 1-5mL of a trial solvent 2. Shake the tubes in order to see if solubility occurs 3. If no solubility occurs then heat the solvent to its boiling point 4. If complete solubility occurs, then cool to induce crystallization (pg. 226)
with a partition coefficient of less than......multiple extractions will be necessary
10
C-O stretch
1000-1300
never add more than......per gram solute
10mL solvent
there is a.......increase in acidity for ever pKa unit
10x
C-O
1150 - 1050 cm-1
C=C stretch
1660-1640
C=C
1680 - 1640 cm-1
C=O stretch
1700
organic chemists usually extract/wash......times
3
=C-H stretch
3100-3000
OH stretch
3200-3500
O-H
3600 - 3000 cm-1
How do we determine melting point range?
A digital melting-point apparatus, determined by strength of intermolecular forces bw its molecules (polarity assoc with greater intermol forces and higher melting pts)
Mobile phase
Adding ferrocene to our alumina, allowing it to drip, nonpolar solvents move through quicker and polar solvents are eluted off last.
good way to test for the presence of a halide...
Beilstein test (ex. for bromide using a copper wire and flame)
How a drying agent works
Binds to H2O within the solution causing clumps
if an alkyl, benzyl, or aromatic halide is reacted with magnesium using an anhydrous solvent (diethyl ether), a ....... is formed
Grignard reagent (organometallic reagent)
What happens if the compound is wet or impure?
If wet, the range will be too wide making results worthless
Drying
Remove from H2O
How do you increase extraction efficiency?
Salting out, the presence of salt in the water decreases the solubility of the orgo compound in the aqueous phase. - Increases distribution coefficient - Help separate homogenous solution
Know what to do if crystals don't form as expected
Seed crystals Scrape the glass sides
What does the Belstein Test show?
Shows presence of halogens if its burning greenish-blue
What are the two phases of Thin-Layer Chromatography?
Stationary phase Mobile phase
When is drying done?
When the drying agent remains powdery and no longer clumps together
Know what a solvent pair is and how to choose a good solvent pair
Work together to recrystallize a product
in lab 9, sulfuric acid acted as...
a catalyst
Catalyst
a chemical/compound which promotes/accelerates the reaction but is not consumed by it.
Solute
a compound which is dissolved in another compound and present in a lesser amount
Filtration
a process by which one material is separated from another based on differences in particle size
Extraction Efficiency
a series of extractions using small volumes of solvents is more efficient than a single large-volume extraction
Aliquot
a small amount of a liquid, which is either added to or taken from a solution
Emulsion
a suspension of insoluble droplets of one liquid in another liquid; when formed, the entire mixture has a milky appearance, often with no clear separation between the immiscible layers, or there may be a third milky layer between the aqueous and organic phases
Grignard reagent reacted with ketone or aldehyde forms....
alcohol
why is hexane a good solvent
aliphatic hydrocarbon; dissolves hydrophobic compounds
what reaction was favored in lab 10
anti-elimination (E2, one step)
extraction can be referred to as the...
aqueous workup
why is toluene a god solvent
aromatic solvent; contains benzene ring
Theoretical Yield
based off the moles of limiting reactant
if there is a halide present, the Beilstein test will produce a ... flame
blue-green (copper bromide) green (copper chloride) blue (copper iodide)
boiling chips/sticks are used to avoid...
bumping/superheating; boiling out all at once
another way to look at the Grignard reagent is to consider it as a....
carbanion
Superheating
caused by bumping/a temperature gradient in the liquid - lower temperatures near the surface and higher temperatures at the bottom of the liquid near the heat source; can lead to loss of product and a potentially dangerous situation if the superheated liquid spatters out of the container and causes burns
purpose of the wash with saturated sodium bicarbonate
causes benzoic acid to transfer to aqueous layer
what is used to decolorize a compound in recrystallization
charcoal
positive test for the presence of an alkene in iodide solution if purple color becomes .... (lab 9)
clear/light pink
most organic compounds are...
colorless
process of "oiling out" is due to...
compound's insolubility; melting point is lower than that of solvent; compound is cooled too quickly
indicator of reflux
condensation
Aqueous
contains water
aqueous
contains water
(lab 9) cyclohexanol -> dehydration (under acidic conditions) ->?
cyclohexene
positive test for the presence of an alkene in potassium permanganate solution suspension forms from purple to .... (lab 9)
dark brown suspension in clear to light brown solution
IR
determine which functional groups are present based on light
once a solid is isolated at the end of a reaction...
dissolve it with the smallest amt. solvent possible
Vacuum Distillation
distillation at reduced pressure; takes advantage of the fact that the boiling point of a liquid is a function of the pressure under which the liquid is contained; less efficient; only way to distill compounds with boiling points > 200℃
Codistillation
distillation performed on mixtures in which the two compounds are not miscible.
partition coefficient is the same as...
distribution coefficient
How to calculate mmoles
don't worry about it
Understand Molarity (M)
don't worry about it
Salting Out (Brine)
done by adding a saturated solution of Na2SO4 to the aqueous layer; the presence of a salt in the water layer decreases the solubility of the organic compound in the aqueous phase, causing the distribution coefficient to increase and allowing more of the organic compound to be transferred from the aqueous phase to the organic phase; can help to also separate a homogeneous solution of water and a water-soluble organic compound into two phases
elimination reactions form...
double bonds
NMR gives information about...
environment and overall structure
preparation of our Grignard reagent in lab 6 was...
exothermic
CaSO4 (Drierite)
fast and efficient drying agent but low capacity
aromatic solvents would...in water
float (have benzene rings, less dense than water)
water is a .... leaving group
good
Na2SO4
good for predrying; hydrate is unstable above 32 degrees C, clumping, dries slow
Silica gel
good general drying agent but somewhat expensive, dries medium
MgSO4
good general drying agent, clumping, dries quick
most chlorinated solvents have densities...than water
greater than (float when used as a solvent in extraction)
formation of a Grignard reagent can be identified by the use of...
half arrows (free radicals) forming R-Mg-X
select solvents for recrystallization which...
have similar structures to the solute
Reflux
heating a solvent/compound to its boiling point. It is evident from the condensation of that liquid on the walls of the container
Weight of water per gram organic material
how much organic material can be dissolved in it - don't worry about it
Beilstein Test
if there is the halide present, there flame will appear to be blue-green due to the presence of copper bromide
Organic Layer
immiscible; organic; generally is on top
enolate is formed...
in a deprotonation step where hydroxide pulls off a proton on the alpha carbon to yield a resonance-stabilized enolate
solubility of the solute should be at its maximum...
in the hot solvent; minimum in cold solvent
Anhydrous
insoluble in the organic phase and can be removed by filtration; formed by anhydrous drying agents reacting with water
Extraction
isolating and purifying the products of organic chemical reactions
Azeotrope
it is a mixture of two or more liquids, which boils at a constant boiling point
partition coefficient: compound A solubility is 6g/100mL in diethyl ether and 3g/100mL in water k = ?
k = (6g/100mL)/(3g/100mL) = 2
Partition Coefficient
k = g compound per mL organic solvent / g compound per mL water; pg. 144
most aliphatic compounds (hexanes) have densities.......than water
less than
most ethers have densities......than water
less than
Bumping
liquids heated in laboratory glassware tend to boil by forming large bubbles of superheated vapor; can be prevented by the addition of a boiling stick or stone/chip (porous material)
if a compound is not dry (contains some solvent) the melting point will be...
low and broad
good way to determine if you have your product....
melting point of product versus starting materials
you need to use two solvents that are......in recrystallization
miscible
aldehyde
molecule with an R-HC=O
with a product not completely dried, the melting point will be...
much less than expected
if a compound is heated too quickly the melting point will be...
narrow, sharp, and close to the true value
binder (in analgesic tablets)
neutral substance; not soluble in water or common org. solvents; holds together
Organic
non-aqueous (does not contain water), usually hydrophobic.
organic
non-aqueous; usually hydrophobic
NMR stands for
nuclear magnetic resonance spectroscopy
Simple Distillation
only two or three vaporizations and condensations occur; used (1) as the last step in the purification of a liquid compound and (2) for removal of a low boiling solvent from an organic compound with a high boiling point separate two or more liquids with boiling points less than 150°C at 1 atmosphere (but no more than 25°C difference btwn.)
caffeine is a.....
organic base
things to consider when choosing solvent for extraction...
polarity and density
SN2 reaction
primary or secondary carbocation charged nucleophile
Bronsted base
proton (H+) acceptor
Bronsted acid
proton (H+) donor
azeotropes behave like...
pure compounds
recrystallization is used to...
purify a solid
K2CO3
reacts with acidic compounds, dries quick
CaCl2
reacts with many organic compounds like alcohols and carbonyl compounds to form solid complexes, dries slow
pH Paper
red = acid, blue = basic
partition coefficient
relationship btwn solubility ratios of two different layers for a compound soluble in both solvents
Titration
repeated washing of a solid with a solvent
trituration
repeated washing of solid with solvent
SN1 reaction
secondary or tertiary carbocation neutral nucleophile
Buchner funnel
see page 45 in book
filter flask
see page 45 in book
vacuum adapter
see page 46 in book
distillation
separation of liquids by vaporization and subsequent condensation of vapors into separate container
Boiling Stick
short pieces of wooden applicator sticks; should not be used in reaction mixtures, with any solvent that might react with wood, or in a solution containing an acid
Boiling Stones/Chips
small pieces of carborundum, a chemically inert compound of carbon and silicon
Limiting Reactant
smallest amount of moles used
k (partition coefficient) = ?
solubility of solution A in solution ÷ solubility of solution A in water
workup
steps performed at end of rxn to isolate/purify product
aspirin is a....
strong organic acid
Solvent
the compound which is present in the excess; is capable of dissolving a solute but not reacting with it
if you see only one point listed for the melting point range it is likely...
the high end of the range
Filtrate
the material that passes through the filter and remains in the receiving flask. It is sometimes referred to as the mother liquor
chemical shift
the place on the chart at which a nucleus absorbs
Partial Pressure
the pressure of each gas in a mixture
Vaporization
the process of turning a liquid into vapor
Condensation
the process of turning a vapor into a liquid
KMnO4
the product will turn from purple to greenish/brown with a suspension
Iodine
the product will turn from purple to pink if an alkene is present
aromatic examples
those with benzene rings; toluene, benzene
purpose of sodium sulfate in extractions
to "dry" the aqueous portion still remaining with the organic layer
Protonation
to add a proton (H+) usually as in an acid base reaction
Deprotonation
to remove a proton (H+ ) as in an acid/base reaction. In this experiment, water is acting as the base
Miscible
two or more compounds, which dissolve in one another to form a homogenous solution are said to be miscible
exceptions: cyanide (CN-) and azide (N3-)
use substitution only
KOH
used to dry amines, dries fast
fractional distillation
used when the different components of the mixture have boiling point ranges less than 25°C btwn. - Process of repeated vaporizations and condensations that allow you to separate liquid components of a mix by exploiting the vapor pressure differences
what acted as the base in lab 9
water
when in doubt, and performing extraction, you can add......to determine which is the aqueous layer
water (whichever it joins is the aqueous)
why is water a good solvent
water contains networks of hydrogen bonds
Aqueous Layer
water; generally is less dense and is the bottom layer
acetaminophen is a.....
weak organic acid
Recrystallization
when a crystalline material (solute) dissolves in a hot solvent and then returns to a solid in a cooled solvent by crystallizing; success depends on the increasing solubility of the crystals in hot solvent and their decreased solubility when the solution cools, thereby causing the compound to recrystallize; impurities in the original crystalline material are usually present at a lower concentration than in the substance bring purified, thus as the mixture cools, the impurities tend to remain in solution while the highly concentrated product crystallizes
calculate the amt. of water required for distillation of a given amt. of organic material
wt. water per g of organic material = (18*pressure of water)/[MW organic material* (760-pressure of water)]
when drying is done
you can tell drying is done with drying agent remains powdery and moves freely in the mixture while the flask is gently swirled
if the material goes into your solvent at room temperature...
you cannot recover it
Percent Yield (pages 24-25)
% yield = (actual / theoretical) x 100
What to do if you do not get product from recrystallization
- Add 1 or 2 seed crystals - Scratch bottom of flask vigorously - If neither of those work try boiling off some of the excess solvent in the hood and cool the solution again
Main factors in choosing a drying agent
- Capacity for removing H2O - Efficiency - Speed of removing H2O - Chemical inertness
Types of distillation
- Fractional - Simple - Steam - Vacuum
Common drying agents
- MgSO4 - CaCl2 - Silica gel - Na2SO4 - K2CO3 - CaSO4
Solvent pair
- Used when a single solvent will not work - Pair of miscible solvents (very soluble in one another)
Common sources of lost product
- Weighing crystals when wet - Adding too much solvent
Aqueous layer
Contains H2O
Immiscible
Describes what we wash extractions with when getting an aqueous and organic layer (We wash with immiscible liquids)
Melting point range
From when the first drop of liquid starts to when the compound is completely liquified
Organic layer
Non-aqueous (does not contain H2O), usually hydrophobic
What information can TLC plates give us?
Number of components, if two compounds are the same or not, how polar or nonpolar a compound is, and purity
How to use a drying agent
Placing sodium sulfate in the orgo layer to dry the leftover aqueous layer - Scooping solid into test tube until the sodium sulfate until it stops clumping and is powdery and floats
Density
Ratio between mass and volume per unit of volume
Rf
Ratio of distance each compound has traveled relative to the distance that the solvent has traveled *Calculate* You divide the distance from the middle of the compound that traveled by the total distance between the origin of the compound and the solvent line on top
carbonyl group
C=O
Hydrate
Insoluble in the organic phase and can be removed by filtration
Know how to choose a solvent for recrystallization
Like dissolves like
Stationary phase
The phase that does not move in chromatography, typically polar (alumina)
TLC plate how polar vs nonpolar marks move
The polar compounds move slower on the TLC plate, while the nonpolar compounds move quicker and are closer to the solvent line
Boiling point
The temperature at which the vapor pressure of the liquid is equal to the external pressure applied to the surface of the liquid.
Choice of solvent for TLC
Volatile solvent that will evaporate easily at room temp in order to create gas to make the TLC plate results -Anhydrous acetone or ethyl acetate
