Nitrates s. Nitric acid esters

Nitrates s. Nitric acid esters Nitration NCUH 17, 912 ... 

Hantzsch opposed the theory of N205 existing in the nitrating mixture HN03 + + H2S04 Due to the importance of the Hantzsch theory in the development of our views on the nature of the nitration process, we shall discuss it in detail. In a number of works Hantzsch [21-23] developed a theory based on Schafer s experiments [24] on the absorption spectrum in ultra-violet light. Schafer s chief observation was, that the spectrum of anhydrous nitric acid in a non-aqueous solvent (hexane, sulphuric acid, etc.) is analogous with the spectra of nitric acid esters,... 

The general mechanism of nitrating alcohols to form nitrate esters is described under Nitration in this Vol. Several specific remarks about PETN are contained in that article. The industrial nitration of PE differs from most nitrate esters in that it employs coned nitric acid rather than mixed acid. Nevertheless nitration via the nitronium ion mechanism, which is the preferred mechanism in mixed acid nitrations, is also feasible in coned nitric acid. However, Eremenko and co-workers claim that the nitrating agent in PE nitrations, in mixed acid, is unionized nitric acid (Refs 39 76). The present writer does not find Eremenko s arguments to be very convincing. In any case, commercial production of PETN employs nitric acid and not the mixed acids of Eremenko s studies... 

It is of some interest to apply Trouton s rule (entropy of vaporization at the boiling point is a constant) to the above data. Unfortunately, boiling points are known only for nitric acid and some of the aliphatic nitrates. Their Trouton constants (AH p/Tbp) are 20.2 and ca 22.8 entropy units, respectively. Thus they straddle the normal Trouton constant of 21 eu. This observation, coupled with the observed constancy of the specific heat of vaporization, suggests that intermolecular bonding in nitrate esters may be relatively weak, or at least consistent... 

Organic nitrates (and nitrites) are simple nitric and nitrous acid esters of alcohols. They differ in their volatility for example, isosorbide dinitrate is solid at room temperature, nitroglycerin is only moderately volatile, whereas amyl nitrate is extremely volatile. These compounds cause a rapid reduction in myocardial oxygen demand followed by rapid relief of symptoms. They are effective in stable and unstable angina, as well as Prinzmetal s or variant angina pectoris. 

The mixture of the (R)-HMPC and the (S)-acetate 4 from the enzymatic hydrolysis was esterified with methanesulfonyl choride and triethylamine to afford a mixture of the corresponding (R)-sulfonate 5a and the (S)-acetate 4. The (S)-acetate 4 was unaffected by the sulfonation conditions. The resultant mixture of two esters, 4 and 5a, was hydrolyzed in the presence of a small amount of calcium carbonate. The (R)-sulfonate 5a was converted into the (S)-HMPC 6 as a result of inversion of configuration. On the other hand, the (S)-acetate 4, was hydrolyzed with retention of configuration. Consequently, all of the racemic acetate J3, was converted with maximum efficiency to the desired (S)-HMPC 6, by the sequence enzymatic hydrolysis and sulfonation followed by inversion of the chiral center in (R)-HMPC without separation of the (S)-acetate Similar transformations could also be carried out via nitrate ester intermediate 5b obtained from the reaction of the (R)-HMPC with nitric acid and acetic anhydride. 

Will and Lenze s studies, published in 1898, reflect an increasing appreciation of this vital problem of adequate stabilization of the nitrate ester. They fractionated starch nitrates (produced by the inferior technique of initial dissolution in nitric acid) by means of acetone-alcohol, and the fraction insoluble in alcohol was purified by several boilings in alcohol. A maximum nitrogen content of 14.04% was reported. This figure is possible but, taking into account the analytical accuracy of the time, was probably an inaccurately high value. 

Phis particular problem wa.s studied by Camera, Zolti and Modena [3, 4). They identified some of the products of the action of nitrating acid on ethyl nitrate as a model for the behaviour of nitrate esters in acid solution. They came to the conclusion that the initial process consisted in hydrolysis of the ester. Tlie hydrolytic equilibrium was disturbed by oxidation of the alcohol by liberated nitric acid. In the instance of ethyl nitrate the freed ethanol was oxidized to acetaldehyde. Some other products were also formed. Nitric acid was reduced to... 

According to Fanner [38] the first stage of hydrolysis proceeds in accordance with the eqn. (1) (p. 7). Afterwards, the products react with one another to form nitrous acid or nitrites and the series of compounds ennumerated above. Fanner s hypothesis seems unsatisfactory when hydrolysis of nitric esters is carried out in a neutral medium since, for example, if ethyl alcohol is treated with an aqueous solution of potassium nitrate no oxidation of the ethyl alcohol occurs even if the mixture of compounds is boiled. 

A number of such compds were prepd and then converted to the corresponding nitric esters by Wolfram et al of Ohio State Univ while working under a US Ordnance Corps contract(Ref 5 6). They found that all the pentanitrates prepd by them could be detonated by gentle heat or by a hammer blow on steel. Thermal stability tests have shown that the aldonamide pentanitrates are more stable than aldonic acid pentanitrates or their methyl esters and that the esters were less stable than the corresponding acids. All of their purified nitrates underwent rapid decompn at their mp s, accompanied by violent bubbling and evolution of nitrogen oxides. No residue was visible after decompn... 

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