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.
Methyl alcohol passed over heated copper is decomposed into formaldehyde and hydrogen (Sabatier and Senderens). This reaction has been used by Mannich and Geilmann3 for the detection of methyl alcohol in various liquids. The vapour of the liquid under examination is passed over pumice impregnated with reduced copper and heated to 280-300°. In the condensed product, the formaldehyde which results is detected by the violet coloration developed on treatment with morphine and strong sulphuric acid as already described.
1 Loc. cit.
2 Bull. Assoc. Chim. Sucr., 1907, 24, 1623; (Abst.) Analyst, 1907, 32, 333.
3 Arch. Pharm., 1916, 254, 50.
An aqueous solution containing 0.1 per cent. of methyl alcohol gives a condensate which develops the coloration very faintly after one hour. In twenty-four hours the colour becomes more distinct, though still faint. The method is stated to be useful for detecting methyl alcohol in blood or urine, a positive result being obtained from as little as 0 01 gram of the alcohol in 100 c.c. of either of these liquids. The blood or urine, however, must be fractionated to concentrate the methyl alcohol, and the fraction containing the latter must be boiled for some time with freshly ignited animal charcoal before being passed over the catalyst. Even with these precautions the catalyst gradually becomes poisoned.
In order to detect methyl alcohol in the presence of ethyl alcohol, the mixture is diluted, if necessary, to contain about 50 per cent. of water, and passed over the catalyst. Acetaldehyde is removed from the condensate by heating it in a vacuum, and the residual liquid tested for formaldehyde with morphine and sulphuric acid as before. If the original mixture contains less than 1 per cent. of methyl alcohol, the diluted solution should be repeatedly fractionated before the test is applied to the fraction in which the methyl alcohol has been concentrated. 0.5 Per cent. of methyl alcohol in brandy can be detected by this process.
The foregoing method is included here because it introduces a new principle, the dehydrogenation of methyl alcohol by heat instead of conversion of the alcohol into formaldehyde by the ordinary oxidation processes. It may be useful in special cases, but appears to be less sensitive, and is certainly more troublesome, than some of the other processes.
Conversion into nitromethane (P. N. Raikow 1). - Two hundred c.c. or other suitable quantity of the sample are acidified with phosphoric acid, and 10 c.c. distilled off. To this, contained in a small flask, 25 grams of powdered iodine are added, and then 4 grams of amorphous phosphorus; the flask is at once connected with a reflux condenser and the action allowed to proceed for twenty minutes. The condenser is then reversed, and 5 c.c. distilled off; this is mixed in a small flask with from 2 to 3 grams of silver nitrite and gently distilled, the distillate being collected in fractions of three or four drops in small test-tubes. A little strong ammonia solution is added to each fraction, followed by a small quantity of a strong solution of sodium nitroprusside.
1 Eighth Intern. Cong. Applied Chemistry, 1912, 25, 417.
If methyl alcohol is present, nitromethane is formed from it according to the well-known reactions: -
3CH3.OH + p +I3 = 3CH3I
CH3I + AgNO2 = CH3NO2
The nitromethane, when treated with ammonia and sodium nitroprusside as described, yields a blue colour, changing to green and finally to yellow. The test is not vitiated by acetone, which under similar conditions gives a colour similar to Hofmann's violet.
Instead of sodium nitroprusside, C. D. Manzoff employs vanillin in this test. To the first five drops of the distillate from the silver nitrite, five drops of ammonia solution and 0.01 gram of vanillin are added, and the mixture heated. A red colour, which disappears on cooling, shows the presence of nitromethane, and hence of methyl alcohol in the original liquid. Nitroethane under similar conditions gives only a slight yellow colour. It is claimed that this test will detect one part of nitromethane in 100,000 parts of nitroethane.1
Conversion into methyl 3: 5-dinitrobenzoate (Mulliken). - See the corresponding process for ethyl alcohol, p. 201. The directions given by Mulliken are: -
"Convert 4 drops of the alcohol into its 3: 5-dinitrobenzoate," as described in the case of ethyl alcohol.
"Boil the reaction-product with 12 c.c. of dilute ethyl alcohol (3:1). Cool, shake, allow to stand for a minute or two, and filter. Wash with 2 c.c. of strong cold alcohol. Recrystallise from 12 c.c. of boiling dilute alcohol (3: 1). Cool, shake, allow to stand for a minute or two, and filter. Wash the crystals with 2 c.c. of cold strong alcohol. Dry at a temperature not above 100° and determine the melting point.
"The crystalline methyl dinitrobenzoate obtained in this reaction melts at 107.5° (uncorr.)."
Conversion into 2:4-dinitroanisole (Blanksma). - This reaction corresponds with the one noted on p. 202 for ethyl alcohol. The sodium derivative of methyl alcohol is formed, and by its action on l-chloro-2: 4-dinitrobenzene the compound C6H3(NO2)2.O.CH3 is obtained, and identified by its melting-point, 86.9°.