This section is from the book "Alcohol, Its Production, Properties, Chemistry, And Industrial Applications", by Charles Simmonds. Also available from Amazon: Alcohol: Its Production, Properties, Chemistry, And Industrial Applications.
(1) If the alcohols are distilled with phosphorus and iodine, the corresponding iodides are formed: classes of alcohols is afforded by oxidation. Primary when oxidised yield first the corresponding aldehyde, two at hydrogen being removed from the group -CH1OH, leaving characteristic aldehyde group -CHO; then by further of this is converted into the carboxyl group,
3C2H5.OH + P + I3 = 3C2H5I + H3PO3.
The iodides, on heating with silver nitrite, are converted into the nitroso-derivatives: -
C2H5I + AgNO2 = C2H5NO2 + Agl,
Now the primary nitrocompounds, when mixed with potassium nitrite in strong potassium hydrate solution, give a deep red colour on the addition of strong sulphuric acid. The secondary nitrocompounds give a dark blue colour, and the tertiary yield no colour. Hence these reactions serve to distinguish the three classes of alcohols hydes, or ketones, but are decomposed, with the pro
(2) When the vapour of the alcohols is passed over finely-divided copper seated to 300°, primary alcohols are decomposed into hydrogen and aldehydes, secondary alcohols give hydrogen and ketones, and tertiary alcohols yield water and unsaturated hydrocarbons.1
The apparatus employed for this reaction consists of a hard glass tube about 28 inches long and \ an inch in diameter, containing a layer of finely divided copper 24 inches long. The copper is prepared from powdered copper oxide by reduction in a current of dry hydrogen at 300° To one end of the tube is attached a bent capillary, to the vertical part of which is fixed by means of a cork a piece of glass tubing about 3 inches long and J an inch in diameter. The other end of the hard glass tube is connected with a receiver, which is cooled by a mixture of ice and salt. A space of 4 or 5 inches next the capillary is kept free from copper, so that the alcohol may be vaporised before coming into contact with the finely-divided metal. To regulate the temperature, it is found convenient to use a cylindrical air-bath about 26 inches in length, with two small holes on the top about 12 inches apart, carrying two thermometers.
When the tube has attained a temperature of 300°, a small quantity (2 or 3 c.c.) of the alcohol to be examined is poured into the short, wide tube connected with the capillary, through which the liquid slowly flows into the heated tube and is vaporised. The vapour, which contains some unaltered alcohol, condenses in the cooled receiver. To a few drops of this distillate a solution of magenta, decolorised by sulphur dioxide, is added, when a red coloration indicates the presence of an aldehyde and shows that the alcohol is a primary one. If no red colour appears, a solution, containing 1 gram of semicarbazide and 1 gram of potassium acetate to 6 c.c. of water, is added to a second portion of the distillate. A white precipitate, formed at once, or only after some time, shows the presence of a ketone. Finally, an unsaturated hydrocarbon can be detected by its power of decolorising bromine. (3) Another general method for distinguishing between the three
1 Sabatier and Senderens, Bull. Soc. chim., 1905, 33, 263; and G. B. Neave, Analyst, 1909, 34, 346.
OH' the ch aracteristic group of organic acids. Secondary alcohols give k oxidation, two hydrogen atoms being removed from t
H OH with formation of the ketone group phenylydrazine sulphonic acid primary compounds give with phenylhydrazine sulphomc acid the OH-group has been replaced by an acid radical, in the second by a metal.
Tertiary alcohols when oxidised do not give the correspondir .
re present in the original alcohols.
As oxidising agents potassium chromate dichromate with sulphnric acid are employed; or potass; ate in add or in alkaline solution; or hydroger peroxide in acid solution according to circumstances.
(4) According to an observation of, L. Wacke,1primary alcohols may be distinguished from secondary and tertiary alcohols by the strong red coloration which the . , ...
Centinormal solutions of the alcohols are prepared, and 10 or 20 c.c. of each are diluted to 100 c.c. with water in a cylinder. A solution of phenylhydrazine sulhonic acid in dilute Bodium hydroxide is prepared, containing 0.4 gram of the acid per c.c.; this solution should be used quite fresh. One c.c. is added to each cylinder,followed immediately by 25 c.cof sodium hydroxide souution (33 per cent.), and the cylinders are shaken every fifteen minutes during the first two to three hours to develop the coloration.
The colours are best compared after seven to eight hours. A "blank" test with water is made at the same time. Only the primary alcohols show intense colorations, the others will be found to differ but little from the "blank."