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(1)
(0)Tip #1
A technique used in reaction and separation includes:heating under reflux (NOT just 'reflux')
distillation and fractional distillation
recrystallisation and filtration
chromatography
Tip #2
Techniques used in analysis:melting temperature and mixed melting temperature
elemental analysis (empirical formula)
relative molecular mass determination and mass spectra
other spectra: ultraviolet, infrared, nuclear magnetic resonance
chromatography
Tip #3
Safety will need to be considered: this must be with regard to specific hazards, not in vague terms like 'wear goggles and lab coat':volatility and flammability
volatility and toxicity by inhalation
toxicity by skin absorbtion
The scale of the preparation is significant - small quantities of a toxic material may present less of a hazard than large quantities of a merely harmful one.
Tip #4
Tip #5
Qualitative Analysis of Organic CompoundsThere is no definite set procedure that can be applied overall to organic qualitative analysis.
A. Preliminary Test
Note physical characteristics: solid, liquid, color, and odor. Compounds that are yellow to red in color are often highly conjugated. Amines often have a fish-like odor, while esters usually have a pleasant fruity or floral smell. Acids have a sharp, biting odor. Odors can illicit information about your unknown; it is wise to sniff them with caution. Some compounds can have corrosive vapors or make you feel nauseous.
B. Physical Constants
Determine the boiling point or melting point. Distillation is recommended in case of liquids. It serves the dual purpose of determining the boiling point as well as purifying the liquid for subsequent tests.
C. Solubility Tests
The solubility of the unknown in the following reagents provides very useful information. In general, about 1 mL of the solvent is used with approximately 0.1 g or 0.2 mL (2-3 drops) of the unknown compound.
Assistance in analyzing the results from your solubility tests can be found in the solubility flowchart.
D. Group Classification Tests
After analysis of the previous tests and the compound's IR spectrum, if needed, further information can be deduced by performing carefully selected functional group classification tests.
Tip #6
Tip #7
Selection of a particular route:There may be several routes to a compound. Some routes may not be possible or desirable because of
too many steps - the more steps there are the higher the yield has to be at each step. A yield of 80% is good per step: a four step reaction would give an overall yield of 41%, which would be made poorer by handling losses. Many reactions have much lower yields than 80%.
yields from equilibrium reactions can sometimes be improved by changing the conditions
the products from competing reactions may or may not be useful
competing reactions, giving other products which might be difficult or expensive to separate from the main product.
stereochemical problems: chiral starting materials may have their configuration inverted or the product mixture may be racemic;
non-availability of starting materials, or the expense of their synthesis.
Tip #8
The choice of reagents and conditions:The reagents and conditions to produce a given material in industry are often different from those used in the lab
many laboratory reactions give useless by-products which may be difficult or hazardous to dispose of in quantity.
Thus oxidation reactions in the laboratory would probably
(II) salts; industry would prefer to use air or oxygen and not have the salts to dispose of.
use acidified potassium dichromate producing chromium salts or potassium manganate giving manganese
Thus ethane-1 ,2-diol, used as anti-freeze and hydraulic fluid can be made by the action of potassium manganate in alkaline solution on ethene.
A sludge of manganese oxide also results. Industrially, ethene is oxidised to epoxyethane with air at 300oC and a silver catalyst, the epoxy compound then being hydrolysed. There are no products other than the diol. The manganese-containing product is waste; epoxyethane can be used for other things as well as conversion to ethan-1,2-diol.
