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Qualche tipo di nitrometano aveva un colorante giallo come indicatore di sicurezza.
In caso di contaminazione avrebbe virato al blu ol al verde indicando pericolo di esplosione.
Ecco un estratto da un forum di "piccoli chimici" USA.
Angus Chemicals , a subsidiary of Dow Chemical Co. since June of 2000 is the only
domestic manufacturer of Nitromethane. Angus makes just one grade of 98.4% pure
Nitromethane in a plant in Sterlington Louisiana for industrial use , car racing , and a
small amount devoted to RC model use. Prospective resellers and manufacturers are
subject to review and are eligible to receive bulk shipments only if approved by Angus.
The Angus plant produces Nitroalkanes on an industrial scale by vapor phase nitration
of Propane under pressure at up to 475 ºC. The resulting mixture of nitroparaffins ,
unreacted feed stock , and waste by products ( water, hydrogen , nitric oxide and
carbon monoxide and dioxide ) are then separated by filtration , distillation , and
other chemical processes into individual product lines and by products. Accordingly
composition of the production yields 25 % Nitromethane , 10 % Nitroethane ,
40 % 2-Nitropropane , and 15 % Nitropropane. Commercial Nitromethane thereby
contains residual amounts of Nitroethane and Nitropropane isomers as impurities.
The product also has trace amounts of Formaldehyde , Acetaldehyde , Methanol and
Ethanol. Nitromethane itself is affected by photodecomposition , and breaks down
slowly on exposure to light. Nitromethane is chemically stable when kept in the dark
at room temperature sealed in brown bottles or cans. Some Nitromethane fuel is tinged
yellow because it has an indicator dye in it. VP Racing Fuel brand Nitromethane has
this yellow dye. The purpose of it is to alert you if it has been accidentally sensitized.
Sensitized nitro does not burn , it explodes. If it turns blue or green it is sensitized.
Chinese bulk manufacture of Nitromethane relies on the method of synthesis used for
obtaining reagent grade product directly from precursors Dimethylsulfate and NaNO2
in a water slurry. It is obtained in 57 % yield when 1 mol of Dimethylsulfate is added
to 1 mol NaNO2 in a saturated water solution and mixed cold until the first stage is
completed when a second mol of of Nitrite is added. The reaction is carried at or below
20 ºC to limit formation of coproducts , primarily methyl nitrite and an aqueous solution
of Na2SO4. The mixture is then distilled at reduced pressure. Nitromethane is initially
obtained over 96 % pure , the primary contaminant being water. This and other residual
by products are removed in a two stage batch distillation. The resulting product is then
greater than 99 % having less than 0.1 % water.
These processes are outlined in Vogels Practical Organic Chemistry 3rd Editon on
pages 302 & 303. The lower yield preparative method using Chloracetic acid and NaNO2
is given on page 307. The purest Nitromethane is obtained as the sole product of
the reaction of Methyl Iodide on Silver Nitrite.
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