Orgo 2 Chm Lab Final

______ of a pure compound is a narrow range

Melting point

How many degrees at most is the melting point range

1-2 degrees

What will impurity in a sample do to the melting point

lower and broaden the range

what’s the explanation behind the impurity of a sample lowering and broadening a melting point

it introduces a freezing point depression since the impurity disrupts the crystalline lattice of the sample and less energy is needed to melt the sample

what will NOT affect meltin gpoint range

an insoluble impurity

Which melting point is 122-123 C

Benzoic Acid

what will impurity in a benzoic acid cause

119-121- making it broader and lower

What is the initial melting point range

• when you see the first drop pf liquid in the capillary

What is the final melting point range

when the entire sample in the capillary is liquid

What is the MP of a pure substance:

the temperature at which the solid phase is in equilibrium with the liquid phase

what can MP help identify

a compound and assess its purity , but it cannot be used alone for identification

Why is MP a unique property , but cant be used as a sole identifier

because while it can identify compounds, other compounds may have a similar makeup and cannot be used alone to identify it because other compounds could have similar MPs

What are inaccurate MPs mainly due to

poor heat transfer

What are things that can impact poor heat transfer

• must be finely powdered

• not the proper amount ( 1-2 mm tall)

• packed firms

• capillary action

What is a common error when measuring melting point

mistaking the sagging or shrinking of the crystals as melting (solvent can case the crystals to sweat before actually melting)

What is IR used for

identifying functional groups of the compound that are present

where do you find the OH bond

3400-3700

where do you find the C=O bond

1730

what do qualitative tests do in IR

utilize the differences reactivities of various functional groups with reagents that give a color change, precipitate, or other visible signs of reaction

other than qualitative tests how can IR identify compounds

making derivatives of compounds to identify the original unknown

What is an example of IR forming derivatives

aldehydes and ketones can be reacted with 2,4-dinitrophenylhydrazine to form 2,4-dinitrophenylhydrazone (2,4 DNP) derivatives that have sharp MP range

what happens to the reddish, brown color when alkene or alkyne is present with bromine

it will disappear

what does IR NOT do

it does NOT identify the actual molecule , it just determines if the functional group is present or not

What gives us info about structure and bonding in a molecule

NMR

what are the different ways in NMR that gives us info about structure and bonding in a molecule

• chemical shift/signal

• splitting patterns

• integration

what does a chemical shift tell

the types of protons present

what does a splitting pattern tell

neighboring protons

what does integration tell

how many protons in that peak

what is one way to determine the molecular formula of a compound

obtain the elemental analysis of the compound via empirical formula

for the synthesis of acetophenetidin explain the rxn

p-phenetidine and acetic anyhydride reacting with NaOac,HCl to form acetophenetidin

in the beginning what is important to note about p-phenetidine

its water insoluable

what is added to p-phenetidine to remove its impurities

activating carbon

what does the HCl do to the p-phenetidine once impurities have been removed

• HCL protonates the p-phenetidine

what does the HCl protonating the p-phenetidine do

it makes it easier to use in the reaction and make it water soluble

What is a WEAK BASE that deprotonates the newly formed NH3 to an amine for acylation

NaHCO3

what happens after NaHCO3 deprotonates the salt to an amine

nucleophilic acyl substitution takes place

what happens with a nucleophilic acyl substitution

an acyl group is attached to form an amide

An amine + acid anhydride yields

amide product

What removes insoluble components like ACTIVATED CARBON from a solution of desired compound

hot gravity filtration

why do we want to keep our compound HOT during gravity filtration

it keeps the compound stable or else it will crystallize and get caught in filter paper

what is one tool that MUST be used during gravity filtration

STEMLESS FUNNEL

why is it so important we use a stemless funnel during gravity filtration

we don’t want any of the compound to get stuck or recrystallize in the stem

what technique is being described here:

hot plate, beaker, STEMLESS FUNNEL

gravity filtration

what type of filtration removes organic impurities

vacuum filtration

what is the purpose of using a trap in vacuum filtration

to catch any overflowing filtrate before it can enter the house vacuum system

what do we do during vacuum filtration when there is some product remaining in the reaction flask

use some of the reaction solvent to transfer the remaining product into the buchner funnel

when we use some of the reaction solvent to transfer the remaining product into the buchner funnel which temperature of the solvent is preferred

COLD

what procedure purifies organic solids

recrystallization

What are the rules when doing recrystallization

• completely dissolve the compound when hot, but not when cold

• organic impurities must remain soluble when the solution is cooled

• solvent should be moderately volatile so that it can be easily removed

a rule of recrystallization is: organic impurities must remain soluble when the solution is cooled —- what do you do if there are insoluble impurities

remove via hot gravity filtration

a rule of recrystallization is: organic impurities must remain soluble when the solution is cooled —-why is it a problem if they do not stay soluble

no purification will be achieved since the impurities will crystallize with the pure material and the compound will become insoluble and crystalize visibly when cooled

What is the first step of recrystallization

heat the solution (saturated) SLOWLY so the crystal packs correctly

What is the second step of recrystallization

cool to room temperature then place in ice bath to maximize crystallization

During recrystallization what is the significance of the more well ordered a crystal lattice is

the better the packaging is within a crystal which allows for a narrow range for MP and to be very pure

during recrystallization during the cooling process, small pure seed crystals of the desired compound are formed, what is the significance of it

seed crystals serve as nucleation sites where more molecules of the desired compound deposit themselves in layers

How do you collect crystals in recrystallization

vacuum filtration

how do you get rid of any impurities for vacuum filtration for recrystallization

rinse with a small amount of cold solvent

During recrystallization how do you yield a second crop of crystal

filtrate that can go through the recrystallization process again

what is a synthetic compound that acts as an analgesic (pain reliever) and antipyretic ( fever reducer)

• can be carcinogenic when ingested over a long period of time

• can be synthesized via williamson ether synthesis ( ether linkage) OR amide synthesis (amide bond)

Acetophenetidin (4-ethoxyacetanilide)

what is the starting material in the synthesis of acetophenetidin

p-phenetidine (colorless liquid)

why does the p-phenetidine have a reddish brown color when starting the aceto experiment

• bc it has a small amount of impurities caused by air oxidation of the amino functional group in the compound

How do you get the p-phen out of the vial in the beginning o the experiment

via a pipette

what is the first step in the aceto synthesis experiment

adding the p TO the HCl in a beaker

what is the second step in the aceto synthesis experiment

heat solution and then add activated carbon while stirring

what do we do in the aceto experiment after we heat the solution and add activated carbon

gravity filter to remove colored impurities ( use folded filter paper)

in step 4 of the aceto synthesis experiment you obtain a control pH and cause a nucleophilic attack , what causes what

• sodium acetate is the control pH

• acid anyhydride administers the nuclephilic attack

in the aceto synthesis experiment- we obtain NaOAc ( our pH control) and acid anyhydride for the nucleic attack after we gravity filter, what is the next step in this process

add NaOAc first, then stir once and then addAc2O then het hot plate again for few minutes

After we add NaOAc and Ac20 in the acteo experiment what do we do

Ice bath and then vacuum filtration

Why dont you stir crystals in the funnel

it makes the filtration less efficient and does not adequately remove the solvent from the crystals

what happens if no crystals form at room temperature

scratch the flask

After an ice bath in the aceto lab and vacuum filtration , what do we follow up with

allow filtration for 5 min then dry on the watch glass

when weighing, why dont you substitute filter paper for weighing paper

bc filter paper is porous and some of the solid chemicals will get stuck on it

how do you transfer solids

using a spatula or scoopula and not pouring from the bottle or fingers

when a liquid is heated above its boiling point in a smooth container

superheating

what happens during superheating

• rapid vaporization, causing the liquid to bump and expel from the container

• also occurs when rough surface like a teabag hits the liquid

what can you use before heating to avoid bumping

magnetic stir bar and boiling stick

what is the best solvent for acetic anyhydride

water because soluble with heat but will crystallize in ice, it is also the most polar

what is the least polar solvent for acetic anyhydride

hexane

what are two miscible solvents

water and ethanol

what lab is used to remove selected components from a mixture and usually based on solubility differences or chemical reactivity

extraction lab

the more acidic proton can be deprotonated by ______

weak bases

what is a weak base that deprotonate acidic protons

NaHCO3- sodium bicarbonate

what happens with a less acidic proton and deprotonation

cant be deprotonated by a weak base and needs a strong base to deprotonate

what are strong bases that can be used with a less acidic proton and to properly deprotonate

KOH, NaOH, OH or hydroxide

in extraction, how is the layer for aqueous and organic material situated

the aqueous layer is more on the bottom and organic layer on the top

what can be found in the aqueous layer of the extraction lab

salt

what can be found in the organic layer after drying with MgSO4 and before focusing on the aqueous layer of the extraction lab

phenol, ether, and carboxylic acid

when handling the components of both the aqueous and organic layer how do we pour it out

• pour out the aqueous layer in the bottom into a flask

• pour the org solution in the top to avoid going out the contaminated bottom

What do you dry ether with t get rid of water in the extraction experiment

MgSO4

How much MgSO4 is needed int he extraction experiment

small amount- only until it is no longer clumped

during the extraction experiment- organic solvents will absorb some water during mixing ,so we want to remove it before org solvent is evaporated.. what do we do

before the MgSO4, wash the organic layer with brine to remove the majority of dissolved water, once it is dry the water is removed

We have to use this technique to get rid of MgSO4 in the extraction experiment because MgSO4 will leave solids in the liquid product

vacuum filtration

what is the liquid product in the extraction experiment that we pour into the round bottom flask

phenol+ether

if we were to collect the product in the aqueous solution how would we obtain it

neutralize with dilute acid and collect product via vacuum filtering

between carboxylic acid and phenol which is more acidic

carboxylic acid

true or false both carboxylic acid and phenol BOTH dissolve inorganic solvent but in water its insoluble

true

since COOH is insoluble in water we use NaHCO3 which will_____

deprotonate it and creates carboxylate ions

once COOH deprotonates into carboxylate ions they must be neutralized.. how do we do that

adjusting the pH of the aqueous layer with HCl until the solution registers as acidic with pH paper

• if precipitate forms we vacuum filtrate

• if precipitate does not form compounds must extracted from the water using a fresh portion of organic solvent aka back extraction

in the extraction experiment what does HCl do

it protonated the salt (carboxylate ions) in the rxn to a carboxylic acid - neutralization

what is used in the solvent of a solid liquid extraction

CO2