Organic Chemistry Lab Final

what solvents were used in extraction

diethyl ether, dichloromethane, and ethyl acetate

top layer?

organic

bottom layer?

aqueous

method for identifying top and bottom layer?

add drop of water to separatory funnel. Bottom layer is aqueous if water passes through top to bottom layer.

charged bases prefer

aqueous layer

neutral bases prefer

organic layer

adding base converts acidic organic molecules into

charged versions, making them dissolve in the aqueous layer

where do neutral molecules stay

in the organic layer

how to select appropriate recrystallization solvent?

trial and error

#1 characteristic of a good recrystallization solvent

dissolves compound when solution is hot but NOT when cold

#2 characteristic of a good recrystallization solvent

noninflammable, nontoxic, very volatile, inexpensive

#3 characteristic of a good recrystallization solvent

either NOT dissolve impurities OR dissolve them very well

#4 characteristic of a good recrystallization solvent

NOT react with solute

Recrystallization lab solvents

water for benzoic acid and 95% ethanol for naphthalene

Recrystallization step #1 and why

choosing the appropriate solvent because purification of the compound depends on how it behaves in solvent

Recrystallization Step #2 and why

Dissolving the compound to separate it from impurities

Recrystallization step #3 and why

decolorizing the solution to remove colored impurities

Recrystallization step #4 and why

gravity filtration to remove insoluble and colored impurities

Recrystallization step #5 and why

crystallizing the compound to isolate the purified compound

Recrystallization step #6 and why

collecting and washing the crystals to separate from solvent and remove remaining impurities

Recrystallization step #7 and why

drying the compound to obtain the final purified product

what solvents are commonly used in recrystallization

water, ethanol, acetone, hexane, ethyl acetate, toluene

Melting point step #1

place small sample into capillary tube

melting point step #2

drop capillary tube (closed side down) down a long glass tube several times to pack the sample

melting point step #3

place capillary tube in mel-temp apparatus with a thermometer and heat it

melting point step #4

record melting point range from when it first starts to melt to when it is fully melted

meniscus point

meniscus becomes clearly visible

first drop or onset point

start of the melt

clear point

substance is completely liquid

impurities …. the melting point

lower

impurities … the melting point range

broaden

simple distillation separates liquids with …. boiling points

very different

simple distillation separates liquids from …

non volatile impurities

fractional distillation is more … than simple

efficient

fractional distillation is

multiple simple distillations

fractional distillation separates liquids with … boiling points

similar

why is one distillation method chosen over another

depends on closeness of boiling points

purpose of packing beads in fractional distillation

to increase surface area where vapor can condense and re-evaporate

water inlet

right side

water outlet

left side

retention time gc

time between injection and the peak or to the detector

lower boiling point …

shorter retention time

higher boiling point

longer retention time

similar polarity to stationary phase …

longer retention time

different polarity to stationary phase

shorter retention time

first gc elution

cyclohexane

second gc elution

toluene

Rf=

distance traveled by compound/distance traveled by solvent front

non polar molecules travel

further

polar molecules

get stuck

which compound travels further on tlc plate

methyl benzoate

percent yield =

actual yield/theoretical yield times 100

g=

mol times g/mol

mol=

grams/molar mass

silver nitrate test

1 drop of alkyl halide to 2ml of 0.1M silver nitrate in 95% ethanol if no rxn warm beaker and add drops of 1M nitric acid if there is precipitate

sodium iodide test

place 1ml alkyl halide and 2 drops of chloro-compound in a test tube and warm in beaker of water at 50 degrees C for 6 minutes and cool to room temperature and record precipitate

silver nitrate test observations

cloudiness removes Cl-

sodium iodide observations

no precipitate because tertiary alkyl halides are too sterically hindered for SN2 reaction

silver nitrate compound formed

white precipitate

sodium iodide compound formed

no reaction

baeyer test

detects unsaturation by oxidation

silver nitrate test theory

tests for SN1 reactions

why wash with NaHCO3 sodium bicarbonate

to neutralize and remove acetic acid in the organic layer

why wash with sodium bisulfite NaHSO3 

to remove any remaining hypochlorite (bleach)

why wash with NaCl

to remove water and separate the layers

purpose of extracting twice with diethyl ether

to pull out the remaining product from the first extraction to increase product

purpose of checking with starch strips

to see if there is any oxidizing agent (bleach) hypochlorite left in the mixture