Nitromethane initiation

The theory of detonation has also been extended to study the process of initiation of reaction by the commonest means used in practice, namely, by the shock wave arising from another high explosive. Campbell, Davis and Travis have studied the initiation by plane shock waves of homogeneous explosives, particularly nitromethane. Initiation occurs at the boundary of the explosive after an induction period which is of the order of a microsecond and which depends markedly on initial temperature. During the induction period the shock wave has proceeded through the explosive and compressed it. The detonation initially in compressed explosive has a velocity some 10% above normal, but the detonation soon overtakes the... 

Homoallylic nitro compounds 845 are accessible by conversion of allylic alcohols to carbonates followed by their palladium-catalyzed solvolysis in nitromethane [618]. Ethoxycarbonylation of the alcohols 843 with ethyl chloroformate provides the corresponding allylic ethyl carbonates in high yields (99% in the case of 844). Exposure of these substrates to catalytic palladium(O) in nitromethane initiates a reaction sequence of ionization - decarboxylation - nitromethylation, which culminates in the formation of nitroalkenes 845. 

Figure 2.40 Experimental effective C-J pressures of 9404, Composition B, TNT, and nitromethane initiated by a plane-wave Baratol lens vs. distance of run. The infinite-medium C-J pressures are shown on the right-hand side of the figure for each explosive. The nitromethane is self-overdriven and the other explosives are underdriven.

The most powerful teclmique for studying VER in polyatomic molecules is the IR-Raman method. Initial IR-Raman studies of a few systems appeared more than 20 years ago [16], but recently the teclmique has taken on new life with newer ultrafast lasers such as Ti sapphire [39]. With more sensitive IR-Raman systems based on these lasers, it has become possible to monitor VER by probing virtually every vibration of a polyatomic molecule, as illustrated by recent studies of chlorofonn [40], acetonitrile [41, 42] (see example C3.5.6.6 below) and nitromethane [39, 43]. 

The concentration of nitromethane, CH3NO2, can be determined from the kinetics of its decomposition in basic solution. In the presence of excess base the reaction is pseudo-first-order in nitromethane. For a standard solution of 0.0100 M nitromethane, the concentration of nitromethane after 2.00 s was found to be 4.24 X 10 M. When a sample containing an unknown amount of nitromethane was analyzed, the concentration remaining after 2.00 s was found to be 5.35 X 10 M. What is the initial concentration of nitromethane in the sample ... 

Equation 13.6 can then be solved for the initial concentration of nitromethane. This is easiest to do using the exponential form of equation 13.6. 

The insensitivity of nitromethane to detonation by shock under normal conditions of handling has been demonstrated by a number of fljH-scale tests. Sensitivity to shock increases with temperature at 60° C, nitromethane can be detonated by a No. 8 blasting cap. Nitroethane can be initiated only when heated near its boiling point under heavy confinement neither it or the nitropropanes can be detonated in unconfined conditions. 

Methylene chloride is one of the more stable of the chlorinated hydrocarbon solvents. Its initial thermal degradation temperature is 120°C in dry air (1). This temperature decreases as the moisture content increases. The reaction produces mainly HCl with trace amounts of phosgene. Decomposition under these conditions can be inhibited by the addition of small quantities (0.0001—1.0%) of phenoHc compounds, eg, phenol, hydroquinone, -cresol, resorcinol, thymol, and 1-naphthol (2). Stabilization may also be effected by the addition of small amounts of amines (3) or a mixture of nitromethane and 1,4-dioxane. The latter diminishes attack on aluminum and inhibits kon-catalyzed reactions of methylene chloride (4). The addition of small amounts of epoxides can also inhibit aluminum reactions catalyzed by iron (5). On prolonged contact with water, methylene chloride hydrolyzes very slowly, forming HCl as the primary product. On prolonged heating with water in a sealed vessel at 140—170°C, methylene chloride yields formaldehyde and hydrochloric acid as shown by the following equation (6). 

A similar transformation results when trimethylsilyloxy-substituted allylic halides react with silver perchlorate in nitromethane. The resulting allylic cation gives cycloaddition reactions with dienes such as cyclopentadiene. The isolated products result from desilyla-tion of the initial adducts ... 

Nitromethane is reacted with formaldehyde to give tris(hydroxymethyl)nitromethane in an initial step. This Intermediate may be reduced by catalytic hydrogenation (U.S. Patent 2,174,242) or by electrolytic reduction (U.S. Patent 2,485,982),... 

Benzyl chloride can be converted into benzaldebyde by treatment with nitromethane and base. The reaction involves initial conversion of nilro-methane into its anion, followed by SN2 reaction of the anion with benzyl chloride and subsequent E2 reaction. Write the mechanism in detail, using curved arrows to indicate the electron flow in each step. 

Since the initially formed enol ester rearranges slowly to an imide,3 the yield depends on the rate at which the isoxazolium salt reacts, and that rate is increased by vigorous stirring. The reaction time for the activation step is approximately 8 minutes in nitromethane at 25° and approximately 1 hour in acetonitrile at 0°. In reactions performed with acetonitrile as the solvent, the checkers did not obtain complete solution. The reaction flask should be kept in a water bath to minimize heat transfer from the magnetic stirrer to the reaction mixture. 

Some interesting results have been obtained by Akand and Wyatt56 for the effect of added non-electrolytes upon the rates of nitration of benzenesulphonic acid and benzoic acid (as benzoic acidium ion in this medium) by nitric acid in sulphuric acid. Division of the rate coefficients obtained in the presence of nonelectrolyte by the concentration of benzenesulphonic acid gave rate coefficients which were, however, dependent upon the sulphonic acid concentration e.g. k2 was 0.183 at 0.075 molal, 0.078 at 0.25 molal and 0.166 at 0.75 molal (at 25 °C). With a constant concentration of non-electrolyte (sulphonic acid +, for example, 2, 4, 6-trinitrotoluene) the rate coefficients were then independent of the initial concentration of sulphonic acid and only dependent upon the total concentration of non-electrolyte. For nitration of benzoic acid a very much smaller effect was observed nitromethane and sulphuryl chloride had a similar effect upon the rate of nitration of benzenesulphonic acid. No explanation was offered for the phenomenon. 

The reaction mixture heats to 60-80° during the addition of nitromethane. The mixture may require external heating to maintain this temperature. The initial yellowish color begins to turn red-brown and gradually deepens as ammonia gas is liberated. 

Reinhoudt et al. [174] reported the self-assembly of an AB2 type of monomer 83 with two Pd centers. Labile coordinating ligand, acetonitrile, when removed by heating from a solution of nitromethane in vacuo initiated an intramolecular coordination of benzylnitrile group with the tridentate Pd-centers leading to a hyperbranched structure. Coordination of the benzylnitrile group was moni-... 

Addition of bases or acids to nitromethane renders it susceptible to initiation by a detonator. These include aniline, diaminoethane, iminobispropylamine, morpholine, methylamine, ammonium hydroxide, potassium hydroxide, sodium carbonate, and formic, nitric, sulfuric or phosphoric acids. 

Presence of, for example, 5% of methylammonium acetate and 5% of methanol sensitises nitromethane to shock-initiation. 

Dining preparations to initiate the explosion of nitromethane sensitised by addition of 20% of the diamine, accidental contact of the liquid mixture with the solid tetryT detonator caused ignition of the latter. 

Contact with metal oxides increases the sensitivity of nitromethane, nitroethane and 1-nitropropane to heat (and of nitromethane to detonation). Twenty-four oxides were examined in a simple quantitative test, and a mechanism was proposed. Cobalt, nickel, chromium, lead and silver oxides were the most effective in lowering ignition temperatures [1]. At 39 bar initial pressure, the catalytic decomposition by chromium or iron oxides becomes explosive at above 245° C [2],... 

In 1950 an alternative to the Sanger procedure for identifying N-terminal amino acids was reported by Edman—reaction with phenyl-isothiocyanate to give a phenylthiocarbamide labeled peptide. When this was heated in anhydrous HC1 in nitromethane, phenylthiohy-dantoin was split off, releasing the free a-NH2 group of the amino acid in position 2 in the sequence. While initially the FDNB method was probably the more popular, the quantitative precision which could be obtained by the Edman degradation has been successfully adapted to the automatic analysis of peptides in sequenators. 

HNO, (10%, 16 ml, 25 mmol) and TBA-AuCl4 or TBA-AuBr4 (0.25 mmol) are added to the dialkyl sulphide (5 mmol) in nitromethane (8 ml). The initially colourless solution is stirred until a yellow colour persists. Aqueous Na2S20, (sat. soln. 10 ml) is then added (for basic substrates, Na,CO, is also added to make the mixture alkaline). The mixture is extracted with CH2Cl2 (2 x 25 ml) and the dried (Na2S04) extracts are evaporated to yield the sulphoxides. 

Unstable chemicals are subject to spontaneous reactions. Situations where unstable chemicals may be present include the catalytic effect of containers, materials stored in the same area with the chemical that could initiate a dangerous reaction, presence of inhibitors, and effects of sunlight or temperature change. Examples include acetaldehyde, ethylene oxide, hydrogen cyanide, nitromethane, organic peroxides, styrene, and vinyl chloride. 

The catalytic activity of a lanthanum (R)-BINOL complex tethered either on silica (62a) or MCM-41 (62b) was evaluated for the enantioselective nitroaldol reaction of cyclohexanecarboxaldehyde (Se), hexanal (Sf), iso-butyraldehyde (Sg) and hydro-cinnamaldehyde (Sh) with nitromethane inTHF (Scheme 12.22) [166]. The silica-anchored lanthanum catalyst 62a gave 55-76% e.e. and yields up to 87%, while the PMS-immobilized catalyst 62b revealed slightly higher e.e.s (57-84%) for the same aldehydes. The homogeneous counterparts showed similar catalytic performance, albeit within a shorter reaction time. The increased enantioselectivity observed for the MCM-41 hybrid catalyst 62b was explained by transformations inside the channels, which is also reflected by lower yields due to hindered diffusion. The recyclability of the immobilized catalysts 62b was checked with hydrocin-namaldehyde (Ph). It was found that the reused catalyst gave nearly the same enantioselectivities after the fourth catalytic run, although the time period for achieving similar conversion increased from initially 30 to 42 h. 

The addition of nitromethane (56% yield/168h 87% ee) or methyl a-cyanoacetate (94% yield/52h 82% ee) as alternative CH-acidic methylene compounds required increased reaction temperatures (60 to 80 °C) to furnish the adducts 7 and 8. As exemplarily depicted in Scheme 6.69 for benzylic alcohol thiourea 12 catalyzes the transformation of the obtained malononitrile Michael products to the respective carboxyhc acid derivatives (89% yield/88h). This method of derivatization also described for methanol (87% yield/24h rt), benzyl amine (77% yield/3h rt), and N,0-dimethylhydroxyamine (75% yield/20h 60°C) as nucleophiles was reported to be feasible as a one-pot strategy without isolation of the initially formed Michael adduct [222]. 

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