Molecular Structure and Properties of Hydrocarbons and Related Compounds

Abstract

March, 1958 MOLECULAR STRUCTURE AND PROPERTIES OF HYDROCARBONS 27 1ably results in a rather high concentration of N204 right near the burning surface. I n this way gemdinitropropane can concentrate Nz04 in the region in which it is most effective in suppressing reaction 5. Previous studies showed that gem-dinitropropane is formed in the reaction between 2-nitropropane and nitric acid a t about 160O.I Consequently, in the 2-nitropropane-nitric acid system gem-dinitropropane can be formed deep in the preheat zone and then decompose again right near the top of the preheat zone where the temperature is above 180". This means that the system 2-nitropropanenitric acid is somewhat unique in that one of the products of reaction 5 is a material which tends t o inhibit reaction 5. Thus the inhibiting effect of gemdinitropropane would be acting in the same direction as the shortening dwell-time for reactants in the preheat zone as consumption rate increases. This may be the reason why the change in slope in the upper part of the step is very sharp in the 2-nitropropane-nitric acid system as compared t o the other nitroparaffin systems. Table IV gives burning rate data for the system gem-dinitropropane-nitric acid and it can be seen that the consumption rate curve is linear and there is nothing unusual about the absolute value of the rates. If the above interpretation of the effect of N204 on the combustion of other nitroparaffin systems is correct, then addition of Nz04 to the gemdinitropropanenitric acid system should have no appreciable effect on the shape or absolute value of its consumption rate curve. The data in Table IV show this to be true. Both of these systems have a property of burning with and without flame. A comparison of rates in corresponding regions shows that the Nz04 does not alter the rate in either region. There is a discontinuity in the consumption rate curve a t the point of transition from flameless to flame combustion. However, this is a true discontinuity and has no relation to the low pressure step which has been shown to be a continuous phenomenon.2.3 I n view of the above and previous results, it appears that the proposed mechanism has been able to predict correctly several observable effects of chemical composition on the low pressure step, and has served as a good basis for correlating many phenomena observed in the combustion of nitric acid systems. Consequently, it continues to be an acceptable working hypothesis.Acknowledgment.-The author wishes to express his thanks to Mr. C. Stanifer and Mr. E. Dimitroff for their assistance in obtaining some of the consumption rate data.Empirical equations, involving only structural parameters, are presented for calculating the isomeric variation in the values of certain physical and thermodynamic properties of the paraffin hydrocarbons. Those properties are the molal volume, the molal refraction, the standard heat of formation, the standard heat of vaporization (all a t 25"), the normal boiling point and the boiling point a t 10 mm. As an example of the...

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