Benzocaine Setup
calcium chloride clamps absorb moister or water sticking out
Le Chatelier's Principle
drive a reaction to complete" if dynamic equilibrium is disturbed through changing conditions, the position of equilibrium moves to counteract the change
What are some ways to drive a reaction to completion?
1. by removing product or adding reactant
2. exothermic, remove heat
Why is an acid needed in fischer esterification?
acid is used as a catalyst, it pronates the carbonyl, giving it a plus charge so the nucleophile can attack it.
Why is the anhydride calcium chloride so important?
with anhydride calcium chloride, water will be sucked out and could no the lost as a product, with the loss of water the reaction moves forward (removing of a product)
What is the acid is the fisher esterification experiment?
concentrated sulfuric acid
What is the OH reagent used in the fisher esterification experiment?
alcohol
What is the use of the TLC in the fisher esterifcation experiment?
lets you known when to stop the reaction
What will be the difference in the NMR of the before and after products for the fischer esterification experiment?
the starting material will have a signal for the carbonyl and the a broad signal for the OH group, the product will have a C-O signal in the finger print region and a carbonyl signal that appears further downfield that the starting material carbonyl signa
What should you do if concentrated sulfuric acid comes in contact with your skin??
immediately flush the infected area with cold water and then 5% sodium bicarbonate solution
Why is necessary to adjust the pH to pH8 prior to extracting the aqueous mixture with diethyl ether in the fischer esterification experiment? What reagent is used to do this?
to ensure that all of the sulfuric acid is neutralized so that all of the acid can be removed from the product that forms and to neutralize any free hydrogens to maximum the percent yield and prevent the equilibrium reaction to proceed in reverse, 10% aqu
In the fisher esterification experiment, why is it unwise to use a strong base such as NaOH or KOH to adjust the pH?
sponification would occur, a strong base will convert the ester back to a carboxylic acid
List two major precautions to be taking during the fischer esterification experiment?
concentrated sulfuric acid is corrosive to the skin and eyes, sodium bicarbonate is toxic if ingested
Fischer esterification is completely reversible. The reaction con be forced to go forward by adjusting two things in the experimental procedure. Explain
1. removing products cause a shift in dynamic equilibrium towards the products in order to replace what is being removed
2. adding excess reagents causes a shift in dynamic equilibrium towards the product side to compensate, generating more product yield.
Why is it important to use absolute ethanol rather than 95% ethanol in Benzocaine synthesis using fischer?
95% ethanol has 5% water, water is a byproduct of fischer that caused the reaction to reverse, increase in water to the reaction causes the equilibrium to undergo the reverse reaction.
What is the limiting reagent in the fischer experiment?
the acid
what is the starting and ending materials of the fischer experiment?
aminobenzoic acid to benzocaine
What can grignard reagents be added to?
aldehydes, ketones, and esters
What type of solutions with grignard reactions occur in?
aprotic, they will die in ptotic
Carbonion
an anion in which carbon has an unshared pair of electrons and bears a negative charge
Why are grignard reagents usually prepared in ethers as solvents??
ethers are non - acidic, is the grignard were to be prepared in water on alcohol, it would protonate the highly basic carbon atom of the grignard and it would be destroyed, diethyl ether is easy to remove from the mixture because of its low boiling point.
What would happen if the grignard was exposed to atmospheric environment?
it would react with oxygen or carbon dioxide
Why is it important to add a portion of the bromobenzene first then drop wise once the reaction occurs?
a coupling reaction would occur between two aryl halides.
What does PCC do to secondary and tertiary alcohols?
turns secondary alcohols into ketones and no reaction with tertiary alcohols
What is the purpose of adding sulfuric acid during work up after the grignard reaction?
pronate the charged oxygen making it into an alcohol
What is the purpose of adding sodium bicarbonate during work up after the grignard reaction?
neutralize the acid
Grignard reactions safety precautions
1. Diethyl ether is very flammable
2. be sure to cool the flask to room temperature before placing in the ice bath to avoid shattering
Grignard reagents are very reactive towards acids? why?
grignard reagents are very basic due to the carbon missing a pair of electrons, bearing a negative charge. When the reagent come in contact with an acid, it undergoes an acid base reaction because the acid protonates the very basic carbon of the grignard
One student used anhydrous ethanol rather than anhydrous ether, how will this impact her experiment?
ethanol has an acidic proton, the acidic proton will protonate the very basic carbon of the grignard reagent destroying it.
One student added the alky halide starting material at once, rather than drop wise as the specified in the protocol. How will this mistake impact the outcome of her experiment?
she will get a byreaction, it will be a coupling of alkyl halides, and biphenyl will form.
One student used the right solvent, all the right steps, but accidentally exposed his grignard to CO2 before the addition of the carbonyl containing reagent. How will this impact his outcome?
the electrophilic carbon of the grignard would attack the slightly electropositive carbon of co2
What is the purpose of the calcium chloride plugs during the grignard reaction experiment?
calcium chloride clamps absorb water and keep it from getting into the reaction. If water was to into the reaction, the grignard would react with water using an acid base reaction. The acid would pronate the basic carbon of the grignard ultimately destroy
Why does aniline not undergo para bromination in Br2/acetic acid reaction mixture?
Aniline is base reacting with an acid, making it an electron withdrawing group rather than an electron donating group therefore, it pushes meta.
How would you judge the end point of the reaction in the bromination of the aromatic compounds?
the starting colors of arenas are a brownish color, when the reaction is complete, the solutions turn clear
Safety precautions for the electrophilic aromatic substitution experiment?
1. Bromine is an extremely hazardous chemical
2. open flame must not be present due to the flammability of compounds line anisole and acetic acid
Why is NH2 on aniline more of a benzene ring activator than the amide in acetanilide?
the oxygen in acetanilide is electron withdrawing so it pulls from the nitrogen and consequently from the ring decreasing reactivity
Would the current experiment still make sense if a large excess of bromine is use while measuring the relative rate of the reaction?
No, the reaction would not reach an endpoint in a relative amount of time because the bromine would not be used up. Bromine always has to be used as the limiting reagent there would be no color change.
What would happen if a stronger acid catalyst to try and speed up the rate of the reaction in the experiment?
no, the acid would protonate the NH2 of the compound and make it an electron withdrawing group pushing the bromine meta rather than ortho/para
what are some limitations in the EAS experiment?
1. Human observations
2. no quantitative values
3. three compounds react so quickly
Diene
must have conjugated double bonds in cis confirmation
Dienophile
needs to be activated, meaning it carries an electron withdrawing group
What does it mean when a diene is held in a ring?
they react faster because they are held in reactive conformation all the tim, dienes in an open chain have some portion of the diene in the unreactive s-trans confirmation
Why do you have to crack the diene?
cyclopentadiene can not be purchased because it readily dimerizes at room temperature by a Dies Alder reaction to give dicyclopentadiene, which is commercially available. However, the equilibrium between the monomer and dimer can be established at the boi
What would happen if the reaction of maleic anhydride and cyclopentadiene was ran in water?
maleic anhydride is unstable in water and hydrolyzes to a dicarboxylic acid
Can naphthalene be used as a diene for a Diels Alder reaction?
no because the electrons of the diene are apart of an aromatic ring. if the dials alder were to occur the aromaticity of the ring would be lost, the loss of aromaticity would make the reaction unfavorable
Kevin prepared fresh cyclopentadiene by fractional distillation during summer weekend. He however had an emergency and had to leave the lab so he stored it. He never came back to the lab until the next Tuesday. He decided to use the same sample he had dis
1. At room temperature cyclopentadiene dimerizes back to its dimer, and its dimer is not a diene.
2. In the presence of water or moisture, the maleic anhydride ring opens and forms a dicarboxylic acid.
Soluble in water, turns red litmus paper blue
Amines
Soluble in water, turns blue litmus paper red
carboxylic acids
Soluble in water, does not affect red or blue litmus paper
neutral compounds (ketones aldehydes esters ethers amides alkenes alkynes nitro compounds alcohols
What makes a witting reaction occur?
the methyl groups bound to the PPh3 should be CH2, the ylide must be able to accept a double bond through resonance
When the ylide is unstablized, which conformation is favored?
Z ( hydrogens in cis)
When the ylide is stabilized, which conformation is favored?
E (hydrogens in trans)
When does E conformations occur?
when there is a resonance stabilized group directly attached to the carbon atom of the phophonium ylide.
____ ylide has a higher melting point than ____ ylide
E/Z
____ ylide has a higher boiling point than ____ ylide
E/Z
why is a ylide stabilized or unstablized?
stabilized ylide are stabilized by resonance and will bond to E confirmations to stabilize, unstablized ylides have a clear partial positive and partial negative charge and will bond to Z confirmations to stabilize
Why are ylides acid sensitive?
ylides have a carbonation that wants to stabilize itself, in a witting reaction it attacks the carbonyl of another compound but if an acid is present, it will pick up the hydrogen and neutralize itself
Name four bases that could be used in the witting reaction?
NaH
CH3CH2Li
NaNH2
NaOEt
Why do wittig reactions react very slowly or not at all with esters?
esters prevent the four member ring intermediate from forming which is necessary for a Wittig reaction
Why does a wittig not react with an alcohol or carboxylic acid?
the ylide pick up the proton on the alcohol, and the acidic proton on the acid
What is the by product of the Wittig reaction?
triphenylphosphine oxide, it is removed during extraction. Stilbenes are insoluble in water while the byproduct is not, when 10ml of water was added, triphenylphosphine oxide was transferred to the aqueous layer while the stilbenes were not
What will be the major product in this experiment?
cis, trans intemediate has too much steric hinderance from the phenyl groups which makes it unstable
What was the purpose of the sodium bisulfate wash after the Wittig reaction?
to remove unreacted benzaldehyde by converting it to salt and to be drained with the aqueous layer
How does an enolate form?
the base picks up the alpha carbon to form the base
Compare and contrast Wittig to Adol Condensation
compare
- both run in a basic environment
- both use a nucleophilic carbon
- attack occurs on the carbonyl
different
- witting has ylides aldol has enolates
- two different mechanisms
- in the witting the carbonyl is completely absent, in aldol an insatur
why do acids not work in aldol condensation?
the alpha proton is much more acidic and would not occur in basic conditions and the enolate would not form
why can't benzaldehyde undergo aldol condensation with itself?
it does not have an alpha proton to give up
what groups react slower with aldol condensation
edg
why does aldol condensation produce a cis isomer?
cis isomer creates too much steric hinderance in the product which makes it unstable
insoluble in water, soluble in NaOH, NaHCO3 soluble
carboxylic acids
insoluble in water, soluble in NaOH, NaHCO3 insoluble
phenols
insoluble in water, insoluble in NaOH, HCl soluble
Amines
insoluble in water, insoluble in NaOH, HCl insoluble, H2SO4 soluble
neutral compounds
insoluble in water, insoluble in NaOH, HCl insoluble, H2SO4 insoluble
alkanes, alkyl halides, and aromatics
what test can be used to distinguish between and ketone and an aldehyde?
Tollen's Test, aldehyde will produce a silver mirror and ketone will not react
What test can be used to distinguish between an alcohol/ester/carboxylic acid and ketone/aldehyde
2,4 DNP, precipitate forms when a ketone or aldehyde is present
What test can be used to distinguish between an alcohol and a ketone?
Jones Test, alcohols will turn a blue green color, and ketones will not react