Ter Meer reaction

The Ter Meer reaction provides a convenient route to terminal m-dinitroaliphatic (15) compounds via the displacement of halogen from terminal Q -halonitroalkanes (11) with nitrite anion 

The Ter Meer reaction has been used for the synthesis of the potassium salt of dinitromethane 

Both 1,1-dinitroethane (26) and 1,1-dinitropropane, and their methylol derivatives, 2,2-dinitropropanol (25) and 2,2-dinitro-l-butanol respectively, have been synthesized via the Ter Meer reaction. - The formal and acetal of 2,2-dinitropropanol in the form of a 1 1 eutectic is an energetic plasticizer and so the synthesis of 2,2-dinitropropanol has been the subject of much investigation. On a pilot plant scale 2,2-dinitropropanol (25) is synthesized in 60 % overall yield from nitroethane (22). Thus, treatment of 1 -chloronitroethane (23) with potassium nitrite 

The Ter Meer reaction has been used to synthesize a,a, u, u-tetranitroalkanes from the corresponding a, ty-dihalo-a, ty-dinitroalkanes. Thus, treatment of l,4-dibromo-l,4-dinitrobutane (28) under the Ter Meer conditions yields the dinitronate salt of 1,1,4,4-tetranitrobutane (29) acidification of the latter yields 1,1,4,4-tetranitrobutane (30).  

The Ter Meer reaction has not been widely exploited for the synthesis of m-dinitroaliphatic compounds. This is partly because the Kaplan-Shechter oxidative nitration (Section 1.7) is more convenient, but also because of some more serious limitations. The first is the inability to synthesize internal em-dinitroaliphatic compounds functionality which shows high chemical stability and is found in many cyclic and caged energetic materials. Secondly, the em-nitronitronate salts formed in the Ter Meer reactions often need to be isolated to improve the yield and purity of the product. Dry em-nitronitronate salts are hazardous to handle and those from nitroalkanes like 1,1,4,4-tetranitrobutane are primary explosives which can explode even when wet. Even so, it is common to use conditions that lead to the precipitation of gem-nitronitronate salts from solution, a process that both drives the reaction to completion and also provides isolation and purification of the product salt by simple filtration. Purification of em-nitronitronate salts by filtration from the reaction liquors, followed by washing with methanol or ethanol to remove occluded impurities, has been used, although these salts should never be allowed to completely dry. 

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The ter Meer reaction consists of the production of 1,1-dinitro compounds from 1-halo-l-nitroalkanes. The reaction proceeds under the action of alkali metal nitrites in basic medium (Scheme 4.34). 

Recent research into the ter Meer reaction (Shugalei and Tselinskii 1994) has demonstrated that it actually chooses the chain ion-radical mechanism. Chain branching is attributed to air oxygen, after transformation into the superoxide ion (O2 see Section 1.7.1). The whole process of substitution in the aqueous-alkaline buffer medium is expressed by a 14-step sequence summed in Scheme 4.36. 

In a moderately alkaline medium, the ter Meer reaction proceeds through a considerable induction period the kinetic curves are S-shaped. Peroxide compounds and UV irradiation accelerate the process (Bazanov et al. 1978). Radical traps inhibit the reaction (as discussed earlier). This indicates the radical nature of the process. The rate of formation of active radical centers obeys the second-order equation in the total concentration of chloronitroethane introduced into the reaction. In nonionized substrate and anion conjugated with it, the reaction is a first-order one. The rate of the whole reaction is independent of the nitrite concentration. 

The chain ion-radical mechanism of ter Meer reaction has been supported by a thorough kinetic analysis. The reaction is well-described by a standard equation of chain-radical processes (with square-law chain termination) (Shugalei et al. 1981). This mechanism also explains the nature of side products—aldehydes (see steps 13 and 14) as well as vicinal dinitroethylenes. Scheme 4.37 explains formation of vic-dinitroethylenes. 

The data on kinetics of parallel reactions permitted Shugalei et al. (1981) calculating the rate constants of competing pathways, which are essentially the constants of the conversion selectivity. The analysis of the constants allowed the authors to formulate the optimal conditions of ter Meer reaction s synthesis of 1,1-dinitroalkanes. 

They suggested conducting the reaction at concentrations of the initial reagents, 1-halo-l-nitro-alkane and sodium nitrite, exceeding 1 mol Then, because of the low solubility of molecular oxygen in water (approximately 10 mol L ), the presence of oxygen does not affect the yield of the target product. An increase in the concentration of nitrite ion promotes ter Meer reaction. 

The revealed mechanism of ter Meer reaction is well-founded. It helps us to understand the peculiarities of nucleophilic substitution reactions having the chain ion-radical mechanism and involving the interaction of radicals with anions at the chain propagation steps. It also demonstrates how the knowledge of kinetics and mechanism can be used to find new ways of initiating and optimizing the reactions important for technical practice. The ter Meer reaction turns out to be a reaction having one name and mechanism. This differs from, say, aromatic nitration, which has one name bnt different mechanisms. 

The choice of base used in the Ter Meer reaction is important for two reasons. First, studies have found that strong bases, such as alkali metal hydroxides, inhibit the reaction and promote side-reactions, whereas the weaker alkali metal carbonates generally give higher yields.Secondly, if the m-nitronitronate salt needs to be purified by filtration it should be sparingly soluble in the reaction solvent and both the reaction solvent and the counterion of the gm-nitronitronate salt affect this solubility. Use of the potassium salt is advantageous for aqueous systems where the em-nitronitronate salts are usually only sparingly soluble, whereas the sodium salt can be used for nonaqueous reactions. 

Good yields of internal gem-dinitroalkanes are attainable, whereas the Ter Meer reaction fails for the synthesis of this class of compounds. 

Oxidative nitration is a one step process from nitroalkane to gem- dinitroalkane, whereas the Ter Meer reaction requires two steps (initial halogenation followed by halide displacement with nitrite anion). 

The chain ion radical mechanism of the ter Meer reaction has been supported by a thor-... 

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