جلسه دوم شناسایی الکلEN
|
ALCOHOLS sodum test |
|
|||
|
Several methods are available for the analysis of the hydroxyl group, the functional group present in alcohols. Sodium metal undergoes reaction with hydroxyl groups of many alcohols to liberate hydrogen gas and form the salt of the alcohol. The rate is highly variable and depends upon the alcohol structure. chemical properties 2ROH+2Na .... 2RONa+H2
physical properties To 0.25 mL or 0.25 g of the sample, add small thin slices of freshly cut sodium until no more will dissolve. Evolution of hydrogen gas indicates the presence of acidic hydrogen, such as a hydroxyl group in an alcohol, hydrogen attached to the nitrogen in a primary or secondary amine, or a hydrogen in a terminal alkyne. Cool the solution, and observe. Add an equal volume of ether. Another positive test is the formation of the solid salt. Prior to testing, dry liquid samples with calcium sulfate. Any residual water will undergo reaction with the sodium. This test may be applied to solid compounds or very viscous liquids by dissolving them in an inert solvent such as anhydrous ligroin or toluene. The order of reactivity of alcohols with sodium is known to decrease with increasing size of the alkyl portion of the molecule. This test is subject to many limitations, and the results should be interpreted with caution. This test is most useful with alcohols of intermediate molecular weight, such as those containing from three to eight carbon atoms. Lower alcohols are difficult to obtain in anhydrous condition. The presence of traces of moisture causes the test to be positive. Alcohols of high molecular weight undergo reaction slowly with sodium, and the evolution of hydrogen gas is often so slow as to make the test of little value. Metallic sodium, when cut in moist air, adsorbs water on its surface so that, when placed in a perfectly dry solvent such as benzene, it gives off hydrogen gas produced by the interaction of the metal with the adsorbed moisture.
sodum test video |
|
|||
|
Another method of detecting such active hydrogen is by adding acetyl chloride to the alcohol to form the ester, which is less dense than the aqueous layer. complication 2RNH2 + 2Na ..... 2RNH-Na+ + H2(g) 2R-C==C-H + 2Na .... 2R-C==C-Na+ + H2(g)
|
|
|||
|
ceric amonum test MSDS of ceric amonum
physical propertis
reagent ceric amonum hexa nitrat
complication lots of chemical material can be oxide and destroy the color of ceric amonum jones test |
|
|||
chemical properties
reagent |
|
|||
|
cro3
|
||||
(Hydrochloric AcidlZinc Chloride (Lucas Test
Substrates that easily give rise to cationic character at the carbon bearing the hydroxyl group undergo the Lucas test readily. Therefore, only secondary (2°) and tertiary (3°) alcohols form the alkyl halide, which appears as a second liquid layer, tertiary alcohols being the most reactive. Primary (1°) alcohols undergo reaction with the zinc chloride and hydrochloric acid either negligibly slowly or not at all.
chemical properties

To 0.2 mL or 0.2 g of the sample in a test tube add 2 mL of the Lucas reagent. Stopper the tube and shake; then allow the mixture to stand. Note the time required for the formation of the alkyl chloride, which appears as an insoluble layer or emulsion.
physical properties
mechanism

Lucas Reagent Dissolve 13.6 g (0.1 mole) of anhydrous zinc chloride in 10.5 g (0.1 mole) of concentrated hydrochloric acid, with cooling. Since the Lucas test depends on the appearance of the alkyl chloride as a second liquid phase, it is normally applicable only to alcohols that are soluble in the reagent. This limits the test in general to monofunctional alcohols lower than hexyl and certain polyfunctional molecules.
Tertiary alcohols react with concentrated hydrochloric acid so rapidly that the alkyl halide is visible within a few minutes at room temperature, first as a milky suspension and then as an oily layer. The acidity of the medium is increased by the addition of anhydrous zinc chloride, which is a strong Lewis acid, and, as a result, the reaction rate is increased. The high reactivity of tertiary alcohols is a consequence of the relatively great stability of the intermediate carbonation. Alkyl alcohol, although a primary alcohol, yields a carbonation that is relatively stable because its charge is distributed equally on the two terminal carbon atoms.

As a result, alkyl alcohol reacts rapidly with the Lucas reagent and the reaction is accompanied by the evolution of heat. Addition of ice water to the reaction results in the formation of the alkyl
chloride as a separate layer.
فیلم تست لوکاس و جونز در آدرس سایت زیر را مشاهده کنید.
http://s8.picofile.com/file/8275449384/a_b69d75i7hhjjm066nk0jj086k3052l41lm081243521_7931d.mp4.html
refference
identification of organic compound/ sheriner





































