Cumulative Review

organic synthesis

production of complex, organic molecules from simpler molecules

isolation

removing or separating the desired product from the mixture/solvent it’s in, done in the initial crystaliaxation and filtration

purification

removal of impurities from the desired product, done in the recrystallization step

amide

NH-C(=O)-CH3

amine

NH2

formation of acetaminophen

amine from p-aminophenol is acetylated by acetic anhydride to form an amide functional group of acetaminophen and acetic acid (by product)

how does recrystallization purify the crude solid

• crude solid dissolves by heating in a little solvent (supersaturated solution) → cooled to room temp → ice bath → crystals form

• most impurities remain dissolved in the cold solution when done slowly without disruption

precipitation

forming a solid (crystals)

rxn 1: synthesis of acetaminophen

• p-aminophenol + DI heated for increased solubility

• acetic anhydride added

• heat reaction, mix

• remove from heat, mix

• ice bath, don’t mix

step 2: isolation

• isolate crude via vacuum filtration

• use some DI to transfer solid to funnel

step 3: recrystallization

• mix crude with DI

• heat and mix, fully dissolve crude

• cool to room temp, undisturbed

• ice bath, undisturbed

• filter

saturation

solvent dissolved it’s maximum capacity of solute. this is when the heated solution cools to room temperature because no crystals form yet

supersaturation

solution contains more dissolved solute than usually possible at a given temp, causes crystallization.

solubility

how much solute can dissolve in a given solvent at a specific temperature

how to induce crystals to form if none do

scratch the glass rod to the bottom of the flask, introduced some glass particles and induces precipitation

what does fast recrystallization cause

traps impurities in the lattice. crystallization should be done at room temp, or initiated in ice and then continued at room temp.

compared to the pure solid, the crude solid will have.. (melting point)

lower melting point and a broader melting point range

why must DI used in product transfer be cold or room temperature

won’t dissolve the acetaminophen

PPE required in the chem lab

• lab safety goggles/shielded/close-fitted safety glasses

• footwear must be full coverage and slip resistant

• lab coats are not mandatory

general safety in the lab

• hair tied back

• no food or drink

preventing accidents and injury

• never leave experiment unattended

• keep sink and bench top clean

• wipe spills and bottle rings

• end of day clean up

• aisles and benches clear (bags in cubbies or under sink cabinets)

• hands away from face eyes body

first aid: chemicals on the skin

• go to nearest sink, eyewash, or shower and flush area with water

• inform TA or instructor

• go to health services for irritation or pain, know about the chemical

first aid: chemicals in the eye

• locate emergency eye wash closest to your station

• wash with flowing fresh water for at least 10 minutes

• someone inform instructor

• go to health services after flushing

first aid: cuts, abrasions, or burns

• rinse cut with water to remove chemicals

• run cold water on burns

• report to instructor or TA for treatment and dressing if needed

major injury or illness

call 911

minor injury or illness

health services or UW police

safety: fire and explosions

• know nearest fire exit, alarm, and extinguisher

• assemble apparatus for access to valves and switches

• keep back to clear exit in a fire

Fire or explosion somewhere else (alarm rings)

fire alarm sounds: turn off gas, electricity, water and leave through indicated exit

Fire or explosion in the lab

fire/explosion in the lab: evacuate, close doors, pull alarm and leave immediately

dealing with flammable liquids

• only get what’s immediately needed

• vapor of almost all organic solvent is flammable

• keep flames, sparks, and heating away from solvents

• prevent vapor by keeping lids closed

class A fire

combustible material (paper, wood, and most plastics)

class B fire

flammable/combustible liquid (gasoline, solvent, grease, oil)

class C fire

electrical equipment (appliances, wiring, circuit breakers, outlets)

where are fire extinguishers, what kind

hallway outside the lab; multipurpose dry chemical extinguisher (type abc)

how to use extinguisher

PASS

• pull pin

• aim low

• squeeze handle

• sweep slow and even at the base

when to use extinguisher

• everyone is leaving and 911 is dialled

• fire is small, localized, smoke/heat is controlled

• extinguisher matches the type of fire

• confidence

what to know before using a chemical

boiling point, flash point, vapor pressure, toxicity, explosive limits, incompatibilities and other precautions, found on safety data sheet (SDS)

what creates most of the danger in the lab

vapors. may be toxic, flammable, or both. handle in the hood

when handling chemicals…

keep hands (especially gloved) away from face eyes and skin

to sample a chemical by odor…

fan toward the nose after filling lungs with air

acid water rule

pour acids into water, never water into acid

rules with poruing from a bottle

• keep stopper out of contact with anything but air

• clean drips and spills off bottle

• re-cap/stopper immediately

what to do with excess chemicals

don’t return to stock bottle. give to another student or dispose in waste container

unlabeled chemicals

don’t use, report to TA or instructor. ensure all chemical are properly labeled at the work space

heating flammable liquids

gas or open flame can never be used. only use electric heating mantle, heating block, sand bath, or steam bath

how to neutralize acid/base

wash with lots of water. for big spills, spill kits are in the storeroom

what goes down the sink

nothing! everything in the waste containers

what to do with broken glass

clean with brush and dustpan or absorbent cotton held with tongs. never use paper towel, discard in the glass waste not garbage pails

what is not safe for vacuum suction

• cracked chipped or otherwise weakened

• thin-walled flat bottom flasks like erlenmeyer

• packing flasks on full suction

• disassembly with suction on

how to carry glass tubing and long glassware

vertically

rolling items should be placed…

on a right angle to the edge

when shouldn’t you use a pippete

if it has ragged edges or shortened ends. discard or send for repair, report to TA or instructor

cleaning electronics

dont immerse in water, use damp cloth if needed

general safe handling of electronics

don’t pour over electronics, keep cords away from water and liquid

emission

light released, high n → low n, produces bright spectral lines

absorption

light absorbed, low n → high n, produces dark spectral lines

λ

wavelength, distance between maxima of a wave in m

ṽ

wavenumber, reciprocal of the wavelength, usually given in cm^-1

fluorescent lamp emission spectra

has distinct lines of blue, teal, green, orange, red. mercury vapor is excited via electric discharge, allowing electron transitions and emission spectra

incandescent lamp emission spectra

continuous spectrum because the tungsten is heated until it glows, not caused from electron transitions but rather blackbody radiation

5 components of chromatographic system

stationary phase, chromatography bed, mobile phase, delivery system, detector

stationary phase

a solid, gel, or immobilized liquid. in this experiment, its the cation exchange resin

chromatographic bed

column (glass or metal) or sheet (glass, plastic, paper\0 used to support the stationary phase. in this experiment, glass column.

mobile phase

solvent (liquid or gas) carrying the sample through the stationary phase. in this experiment, DI water

delivery system

force moving the mobile phase through the stationary phase like gravity and pressure

detector

method of identifying/quantifying substances as they elute

elute

action of substances leaving the stationary phase

eluate

sample leaving the column

eluent

sample loaded onto the column

binding affinity

attraction an ion has to the resin; Cu 2+ has a greater binding affinity, allowing it to replace H+ in the resin

hard water and ion exchange

Ca 2+ and Mg 2+ replace Na+-saturated resin. Since they have 2+ charges but Na+ is 1 charge, 1 Cu 2+ takes up 2 binding sites. the resin can be reused by flushing with an excess of salt solution

what is the pH of the eluate at the start of the experiemnt

neutral (same as DI, around 5.5-6)

how to use the chromatography column

remove parafilm, drain DI in waste beaker, load sample, collect sample in Erlenmeyer flask, add DI to push all H+

volume of rinse water in chromatography

equivalent or slightly more than the volume of the resin bed; DI acts like a plunger

what happens if you don’t add enough rinse to the resin

desired product (H+) remains in the bed

what happens if you add too much rinse to the resin

nothing; generally too much isn’t an issue

what should the pH of the eluate be after the experiment

neutral (same as DI)

reactions of copper: filtrate

substance passing through a filter; liquid in the glass of the Buchner funnel

reactions of copper: decant

carefully pour off liquid from a mixture; copper solid at the end is decanted from the Zn HCl mixture

reactions of copper: supernatant

liquid sitting on top of a solid or heavier liquid; solution above black CuO and solution above copper solid at the end

reactions of copper: gelatinous

jelly-like and thick; used to describe the Cu(OH)2 solution before heating and decomposing into CuO

reactions of copper: coagulate

to clump together or thicken; mixing of the CuO with heating is done to achieve this

reactions of copper: bumping

violent boiling and bubbling of a liquid; stirring the Cu(OH)2 while heating is done to prevent this

reaction 1: copper metal to copper (II) nitrate

nitric acid is added to almost completely pure copper wire → water, brown NO2 gas and blue copper 2 nitrate produced

what is excess in the reaction of copper and nitric acid

nitric acid; doesn’t need to be an exact measurement

reaction 2: copper (II) nitrate to copper (II) hydroxide

add DI water to the cupper nitrate/acid solution (one exception of acid to water rule), add NaOH to Cu(NO3)2 → gelatinous Cu(OH)2 and check the pH >10

reaction 3: copper (II) hydroxide to copper (II) oxide

copper (II) hydroxide decomposes into copper oxide and water by heating with Bunsen burner

filtration step of CuO

small portions of DI are used to quantitatively transfer all CuO from the beaker to the buchner funnel. each rinse is swirled and used to rinse the solid on the filter paper to remove NaNO3 and NaOH

reaction 4: copper (II) oxide to copper (II) sulphate

• dilute H2SO4 is used to rinse the filter paper containing CuO back into the container it was heated from

• dropper used to draw acid up and continue rinse of funnel

• DI used to rinse acid

• solution swirled to dissolve CuO

what should you do if the CuO isnt dissolving in the H2SO4

check with TA, more acid might be needed or slight heating

rxn 5: copper (II) sulphate to metallic copper

• single displacement by Zn solid occurs to obtain finely divided solid copper. H2 gas fizzing occurs in side rxn, thus snorkel exhaust vent is used

• swirl until blue color disappears

what side reaction occurs to produce H2 gas when Zn is added to the Cu (II) sulphate

Zinc reacts with acid to form H2 gas

rxn 6: removing excess zinc

• add HCl to copper, zinc aqueous solution

• swirl to speed reaction, H2 gas produced

• all zinc is gone when H2 bubbles stop, no silver

isolating drying and weighing the copper

• settle the copper, decant the supernatant

• wash twice with DI, decant into a clean beaker

• transfer to evaporating dish with as much DI needed, decant, heat with a cool flame

• when a little water left stop heating and cool until comfortably warm

• weigh

common mistakes

• wrong container

• not stirring Cu(OH)2 while heating

• adding the wrong acid to CuO

• loss of product during filtration

• loss of product during decanting

what happen when copper is reacted with HNO3 in a erlenmeyer instead of beaker

it’ll take much longer as gas can’t escape as freely

what happens when Cu (II) OH not stirred while heating

vigorous bumping

what happen if wrong acid is added to CuO

• HCl → bright green, wrong

• HNO3 → bubbling and fuming like rxn 1, wrong

• H2SO4 → bright blue, correct!

what causes product to be lost when filtering

• small filter paper, creased/folded/teared paper, dry paper can cause CuO to be drawn into filtrate

• needs to be filtered again