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Fractional distillation
- - multiple distillations done in the same apparatus
- - multiple simple distillations in a single reaction vessel is accomplished by the extra surface area of te column
- -therefore longer column = better seperation
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How can the efficiency of distillation be increased?
- by using a longer column
- Adding a packing material to the column such as glass beads, glass helices or metal sponge
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Theoretical plates
measures the efficiency of a distillatin apparatus. 1 TP is equal to 1 simple distillation.
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chromatographic methods
allow for the separation of mixtures of molecules based on their differing physical properties. (bp, polarity, solubility, etc)
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Gas Chromatography
a technique used to separate molecules based on their differing boiling points.
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Give some examples of carrier gases
nitrogen, helium, argon
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retention time
the time that it takes for one component of the mixture to arrive at the detector from the point of injection.
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name some solvent pairs used for recrystallization of organic solids
- ethanol/water
- methanol/water
- ethyl acetate/hexanes
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how can you remove insoluble impurities in recrystallization?
by hot filtration
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Why are NMR instruments with larger magnets more desireable?
Because larger magnets give better resolution of NMR peaks based on larger energy separation of alpha and beta states.
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The inverted capillary technique of Siwoloboff
- The Thiele tube is heated gradually until a rapid stream of capillaray bubbles emerges from the capillary.
- This point is few degrees above the boiling point.
- The temperature is slowly decreased. The point at which it stops bubbling is the boiling point.
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boiling point of a liquid
the temperature at which the vapor pressure inside the capillary equals the external atmospheric pressure exerted on the top surface of the liquid in the boiler tube
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what is a limitation of the Siwoloboff method of boiling point determination?
Traces of volatile impurities will drop the boiling point significantly.
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What are hydrazones?
- one of the most valuable derivatives of aldehydes and ketones
- hydrazones are formed by reaction of the carbonyl compound with a hydrazine
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what is one issue with aldehydes and ketones with six or more carbon chains and how can you solve it?
- aldehydes and ketones with six or more carbon chains are not soluble in water.
- Ethanol or methanol can be added to increase the solubility of the long chanin carbonyl compound
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what is the purpose of trituration?
The purpose of trituration is to dissolve the impurities to purify the crude product
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Suppose you had an aldehyde as your unkown. How would you determine from the HNMR that your unknown is an aldehyde and not a ketone?
Aldehyde shows a peak at 9-10 ppm, whereas ketone shows a peak at 2.1 ppm.
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What was the role of xylenes in preparation of cyclohexene?
xylene was used to chase the product from the distillation apparatus in order to maximize the yield.
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What is saponification?
The conversion of an ester to a carboxylic acid via reaction with NaOH is called saponification
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What is more nucleophilic ammonia (H3N: ) or water (H2O: ) ?
H3N:
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In part C you are instructed to cool the ammonia solution to 0 degree C and slowly add the 3-nitrobenzoyl chloride to it. Explain the reason.
N: is a better nucleophile at lower temperatures than oxygen. Increasing temperature decreases this selectivity forming an increasing percentage of carboxylic acid.
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How did you remove the byproduct of biphenyl in the Grignard reaction?
by washing the crude products with hexanes, a nonpolar solvent.
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Why is it not possible to isolate any benzophenone that is an intermediate in the Grignard rxn?
Because benzophenone serves immediately as a second electrophile that undergoes another Grignard rxn.
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Can you think of a more efficient way of keeping the moisture out of the reaction vessel, than using a drying tube?
Run the rxn under an inert atmosphere (argon or nitrogen gas)
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Can you think of a different solvent that may be used to get rid of the biphenyl in the Grignard experiment?
A nonpolar organic solvent such as cyclohexane
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What is the IUPAC name for Orange II?
4-[(2-hydroxy-1-naphthalynyl)azo] benzene sulfonic acid monosodium salt
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What does in situ mean?
in the reaction mixture
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what was the purpose of adding sodium carbonate in the diazotization of sulfanilic acid?
To produce a free amine that can serve as a nucleophile
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Why is it important to keep the temperature low when you add make nitrous acid?
Because N2 is unstable (good leaving group). The solution must always be kept cold to prevent the water present from acting as a nucleophile producing phenols.
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