Nitrate esters, from alcohols

Table XXVII. Nitrate Esters from Alcohols with JV-Nitrocollidinium Tctrafluoroborate...

Olah and co-workers ° conducted a comprehensive study into the use of N-nitropyridinium salts for nitration. Such salts are easily prepared from the slow addition of the appropriate heterocyclic base to an equimolar suspension of nitronium tetrafluoroborate in acetonitrile. Olah studied the effect on nitration of changing both the structure of the heterocyclic base and the counter ion. Three of these salts (20, 21, 22) illustrated above have been synthesized and used for the 0-nitration of alcohols with success. Transfer nitrations with Al-nitropyridinium salts are particularly useful for the preparation of nitrate esters from acid-sensitive alcohols and polyols because conditions are essentially neutral. 

An extremely mild method for the synthesis of nitrate esters from easily oxidized or acid-sensitive alcohols involves the decomposition of a nitratocarbonate (29). The nitratocar-bonate is prepared in situ from metathesis between a chloroformate (reaction between phosgene and an alcohol) and silver nitrate in acetonitrile in the presence of pyridine at room temperature. Under these conditions the nitratocarbonate readily decomposes to yield the corresponding nitrate ester and carbon dioxide. Few examples of these reactions are available in the literature and they are limited to a laboratory scale. 

Use of sensors to measure gas phase NO2 concentration, electrical conductivity of the reaction mass, and gas phase temperatures at several critical points in semi-continuous nitration reactors permits safe operation of nitration processes [10]. The use of non-aqueous titration analysis in the control of nitration processes in explosives manufacture is discussed [11]. Counter-intuitively, safety of spent acids from nitrate ester production is decreased by lowered nitric acid content. This is because the runaway reaction is oxidation of alcohols, kinetically easier than that of the dissolved nitrate esters from which the alcohols are reformed by hydrolysis [16]. 

There are many methods to reduce nitrate esters from ester groups to alcoholic hydroxyl groups, most likely to obtain the corresponding alcohols. The oldest, also the most common, reduction method is the reductive hydrolysis by alkali sulfide or alkali sulfhydrate, such as sodium sulfide, ammonium sulfide, or corresponding sulfhydrate [39]. Transesterification reaction would happen in the hydrolysis of nitrate esters by sulfuric acid to form sulfate esters [40]. 

Esters of nitro alcohols with primary alcohol groups can be prepared from the nitro alcohol and an organic acid, but nitro alcohols with secondary alcohol groups can be esterified only through the use of an acid chloride or anhydride. The nitrate esters of the nitro alcohols are obtained easily by treatment with nitric acid (qv). The resulting products have explosive properties but are not used commercially. 

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... 

Alcohols form esters from inorganic acids as shown above. Like all esterifications, these reactions are reversible that is, in the presence of water and the right conditions, they revert to the original alcohol and acid. Nitrate esters are mainly used as explosives, but some have found use as diesel fuel additives. Note the difference between a nitrate ester such as ethyl nitrate (C2H5ONO2) and an organic nitro compound such as nitroethane (C2H5NO2). 

Conversion of ketone 80 to the enol silane followed by addition of lithium aluminum hydride to the reaction mixture directly provides the allylic alcohol 81 [70]. Treatment of crude allylic alcohol 81 with tert-butyldimethylsilyl chloride followed by N-b ro m o s u cc i n i m i de furnishes the a-bromoketone 82 in 84 % yield over the two-step sequence from a.p-unsaturated ester 80. Finally, a one-pot Komblum oxidation [71] of a-bromoketone 82 is achieved by way of the nitrate ester to deliver the glyoxal 71. It is worth noting that the sequence to glyoxal 71 requires only a single chromatographic purification at the second to last step (Scheme 5.10). 

All bacteria where nitrate ester degradation has been characterized have very similar enzymes. The enzymes eatalyze the nicotinamide cofactor-dependent reductive eleavage of nitrate esters that produces alcohol and nitrite. Purification of the PETN reduetase from Enterobacter cloacae yielded a monomerie protein of around 40 kilo Daltons, which required NADPH as a co-faetor for aetivity. Similar enzymes were responsible for the nitrate ester-degrading activity in Agrobacterium radiobacter (Snape et al. 1997) - nitrate ester reductase - and in the strains of Pseudomonas fluorescens and Pseudomonas putida (Blehert et al. 1999) - xenobiotic reduetases . All utilize a non-covalently bound flavine mononucleotide as a redox eofactor. 

Feuer and co-workers ° conducted extensive studies into alkaline nitration with nitrate esters, exploring the effect of base, time, stoichiometry, concentration, solvent, and temperature on yields and purity. Reactions are generally successful when the substrate a-proton acidity is in the 18-25 p A a range. Alkoxide bases derived from simple primary and secondary aliphatic alcohols are generally not considered compatible in reactions using alkyl nitrates. Optimum conditions for many of these reactions use potassium tert-butoxide and amyl nitrate in THF at —30 °C, although in many cases potassium amide in liquid ammonia at —33 °C works equally well. 

A huge number of ester and carbonate derivatives of polynitroaliphatic alcohol have been synthesized driven by the search for new explosives and energetic plasticizers and oxidizers for propellant and explosive formulations. Most of these are derived from 2-fluoro-2,2-dinitroethanol and 2,2,2-trinitroethanol ° and have excellent oxygen balances. Some examples are illustrated above (168-174) but more comprehensive lists can be found in numerous reviews. " " Direct esterification of polynitroaliphatic alcohols with nitric acid, mixed acid, or acetic anhydride-nitric acid has been used as a route to mixed polynitroaliphatic-nitrate ester explosives. ... 

Commercial 70 % nitric acid can be used for the 6>-nitration of low molecular weight alcohols like ethanol and 2-propanol. The nitrate ester products are isolated from the cautious distillation of a mixture of the alcohol and excess 70 % nitric acid. The presence of urea in these reactions is very important for the destruction of nitrous acid and its omission can lead to very violent fume-off. However, this method is not recommended on safety grounds. Using temperatures above ambient for the O-nitration of alcohols, with either nitric acid or mixed acid, is dangerous and greatly increases the risk of explosion. 

The Henry condensation of nitroform and terminal dinitromethyl compounds with formaldehyde and other aldehydes, followed by nitration of the resulting alcohol functionality, has been used to synthesize numerous explosives. The nitrate esters (104), (105), (106) " and (107)155 ij yg ijggjj synthesized from the action of absolute nitric acid on the parent alcohols. In a similar manner, NMHP (109) is synthesized from the condensation of TNHP (108) with formaldehyde, followed by O-nitration with absolute nitric acid. ... 

Solutions of dinitrogen pentoxide in anhydrous nitric acid are unlikely to find wide use for the industrial synthesis of nitrate esters - synthesis from the parent alcohol is relatively straightforward and so this reagent, which is more expensive than mixed acid, holds few advantages. 

Chemical Properties NG reacts chemically as a nitrate ester, saponifiable to glycerol by alka-lies (preferably with peroxide present), and hydrolyzed by nitric acid to glycerol. In general, side products tend (d be produced resulting from cleavage of the C—C bonds and oxidation of the alcohol functions... 

Pentryl, or 2,4,6-trinitrophenyInitraminoethyI nitrate, is another explosive which is derived from ethylene. It is a nitric ester, an aromatic nitro compound, and a nitroamine. The substance was described in 1925 by Moran54 who prepared it by the action of mixed acid on 2,4-dinitrophenylethanolamine (large orange-yellow crystals from alcohol, m.p. 92°) procured by the interaction of dinitrochlorobenzene with ethanolamine. von Herz later prepared pentryl by the nitration of 0-hydroxyethylaniline, a material which is more commonly called phenylethanolamine and is now available commercially in this country, and was granted... 

We said esters are condensation products between carboxylic acids and alcohols, but this definition is really too restrictive. In the most general sense, an ester is the condensation product between an alcohol and an acid, not just a carboxylic acid. We saw an example of a nitrate ester earlier in the structure of nitroglycerin. In biochemistry, phosphate esters are one of the most important classes of esters. A phosphate ester is derived from an alcohol and phosphoric acid (H3P04). Again, the acid and alcohol are condensed (under special reaction conditions) to give the ester and a molecule of water. This is shown in Figure 11.53. Phosphate esters form the backbone of DNA and RNA. 

Nitrate esters are formed from alcohols and nitric acid. 

In evaluating the energetics of oxidizers, it is apparent that the perchlorate salts are more desirable than nitrate salts. Therefore one would expect that attempts would be made to incorporate the perchlorate group into binder structures. The study of perchlorate esters was not pursued when it was found that simple model compounds obtained from alcohols and perchloric acid were excessively shock sensitive. However, when the C104 group existed in ionic or salt-like form, these materials were found to be far less sensitive. Bell Aerosystems Corp., in conjunction with the Food Machinery Corp. prepared the polyethylene hydrazine perchlorates. 

An alternate procedure involves the precipitation of mixed copper and chromium hydroxides from a solution of chromium nitrate and copper nitrate by the addition of an sodium bicarbonate and then heating the precipitate to 300°-500°C.30 In this procedure, the copperchromium ratio can be varied over a wide range. A ratio between four and eight was optimum for use in the hydrogenation of esters to alcohols (Eqn. 13.6).30 A related Zn-CrO catalyst prepared by the decomposition of precipitated zinc-copper hydroxides was effective in the hydrogenation of unsaturated esters to unsaturated alcohols (Eqn. 13.7). 0 The presence of a small amount of alumina increased catalyst activity and selectivity. Some of these catalysts, however, tend to become colloidal on use so they can present separation problems. O... 

Three kinds of nitrate esters arc distinguished primary, secondary and tertiary deriving from primary, secondary and tertiary alcohols respectively ... 

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