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346 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

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It is carried out at 480-530°C at a pressure of 15 atm in the presence of a Cr 2 O 3 +

+ MoO 3 catalyst, on a Al 2 O 3 or MgO carrier. The yield obtained amounts to 72%

of the theoretical.

Crude toluene obtained by this method contains 3-5% olefins, so it must be

purified by refining with sulphuric acid, followed by washing with water and dis-

tillation.

Toluene for nitration must be of high purity, in fact almost chemically pure.

The boiling range of the product should be 109-111°C, with at least 95% distilling

within a range of 1°C. The specific gravity should be 0.870±0.002 at 15°C.

Only an insignificant amount of unsaturated aliphatic hydrocarbons is admis-

sible in toluene for nitration. They may be detected by shaking a sample with concen-

trated sulphuric acid. If the toluene is pure, the sulphuric acid separates very quickly

as a colourless or slightly yellow (“straw yellow”) lower layer. If unsaturated hydro-

carbons are present in significant quantities a stable emulsion is often formed,

and the sulphuric acid turns brown or even black. Such a product cannot be used

for nitration.

Nowadays an infra-red spectrophotometric technique is usually applied in testing

toluene for purity (Gore and Patberg [2]).

It should be noted that toluene purity cannot be assessed by the ultra-violet

technique, since strong bands produced by toluene (as about 262 mμ) mask those

that may be produced by olefins.

Toluene obtained from petroleum should contain no more than 4% of paraffinic

hydrocarbons. The content of the latter is determined by sulphonation of the toluene

with concentrated sulphuric acid or with 20% oleum. Sulphonated aromatic com-

pounds are washed out with water to leave the paraffin hydrocarbon which is not

affected by oleum.

If the toluene contains a higher proportion of paraffinic hydrocarbons it can

still be nitrated, provided the mononitration product is subjected to distillation

(preferably with steam) to remove saturated hydrocarbons. According to Desseigne,
Gladel, Guillemin and Sousselier [3], toluene containing 30-40% of saturated

hydrocarbons can be treated in this way to obtain nitrotoluene suitable for further

nitration.
The U.S.S.R. specification (OST 464) for nitration grade toluene requires the

following properties (Table 81):