Subambient temperatures

Monoisocyanates undergo anionic homopolymerization at subambient temperatures to yield nylon-1 polymers (polyamides) (63). 

Another chemical route is by decomposition of solid adducts of ozone with triaryl and other phosphites at subambient temperatures ... 

Many HPLC instruments are already furnished with temperature controls for the column. Unified chromatography requires a much wider temperature range than is currently practiced in HPLC. Until better defined by experience, a temperature range from about —60 to about 350°C seems reasonable as a specification. Since this is well in the range of a GC oven with subambient temperature capability, no new technology is required. 

Palladium, platinum, and Raney nickel 7,126) all have been used successfully under mild conditions for hydrogenation of the azido function. In especially sensitive molecules, subambient temperature may prove advantageous. Reduction of methyl 3, 5-dihydroxy-4 -methoxy-7-(3-azido-3-carboxypropoxy)flavanone (32) in aqueous alkali proved capricious, The major product (33) was contaminated by several other products when reagents were mixed and hydrogenated at room temperature or above, but by the... 

Temperature can also be used to optimize enantioselectivity in SFC. The selectivity of most CSPs increases as temperature decreases. For this reason, most chiral separations in SFC are performed at ambient or subambient temperatures [50, 74]. Subambient temperatures are particularly useful for compounds having low conformational stability [75]. Stringham and Blackwell explored the concept of entropically driven separations [76]. As temperature increased, enantioselectivity decreased until the enantiomers co-eluted at the isoelution temperature. Further increases in temperature resulted in reversal of elution order of the enantiomers. The temperature limitations of the CSP should be considered before working at elevated temperatures. 

A solution of 2-bromo-4-chloro-5-phenyl-2,3-dihydro-1-benzothiepin (1.02 g, 2.84 mmol) in THF (3 mL) was added in one portion to a solution of DBN (0.52 g, 4.2 mmol) in THF (3 mL) at rt. After stirring for 2h, the red mixture, containing some precipitate, was poured into 10% aq HC1 (20 mL) and the aqueous solution was extracted with CHCl, (2x15 mL). The combined extracts were washed with H20, dried (MgS04) and carefully concentrated in vacuo at subambient temperature. The yellow oil, which solidified on cooling, was chromatographed [alumina (Merck 71707,25 g), hexane] to give colorless crystals yield 0.58 g (76%) mp 87-88 °C. 

The success of spectral identification depends on the appropriate reference spectra for comparison. IR measurement of eluates that are at slightly subambient temperature is advantageous considering that the large databases of condensed-state spectra may be searched. Spectra measured by matrix-isolation GC-FTIR have characteristically narrow bandwidths compared with the spectra of samples in the condensed phase near ambient temperature or in the gas phase. In addition, the relative intensities of bands in the spectra of matrix-isolated samples often change compared with either gas- or condensed-phase spectra [195]. GC-FTIR spectra obtained by direct deposition match well with the corresponding reference spectra in standard phase... 

V. Bohm, Effect of subambient temperature on RP-HPLC of / -carotene isomers. Chromatographia 50 (1999) 282-286. 

Lou, D.-W., Saito, Y., Zarzycki, P. K., Ogawa, M., and Jrrmo, K. (2006b). Isocratic separation of ginsenosides by high-performance liquid chromatography on a diol column at subambient temperatures. Ancd. Bioanal. Chem. 385, 96-104. 

Sander, L.C. and Wise, S.A., Subambient temperature modification of selectivity in reversed-phase liquid chromatography, Ana/. Chem., 61, 1749, 1989. 

Solutions of acetyl nitrate at subambient temperature can react with alkenes to yield a mixture of nitro and nitrate ester products. Cyclohexene forms a mixture of 2-nitrocyclohexanol nitrate, 2-nitrocyclohexanol acetate, 2-nitrocyclohexene and 3-nitrocyclohexene. This illustrates one of the problems of allylic and homoallylic alcohol 0-nitration with this reagent. 

Canfield and Rohrback ° reported on the reaction of some electron-deficient difluo-roaminoalkenes with dinitrogen pentoxide in chloroform at subambient temperatures. Contrary to previous work that the /3-nitro-nitrate ester should be the main product, the corresponding vtc-dinitrate esters were isolated from these reactions l,4-bis(iV,iV-difiuoroamino)-2,3-butanediol dinitrate (55), 3,4-bis(iV,iV-difluoroamino)-l,2-butanediol dinitrate (56) and 3-(iV,iV-difluoroamino)-1,2-propanediol dinitrate (57) were isolated in 30 %, 27 %, and 55 % yields respectively, from the parent alkenes. 

Eremenko and co-workers used nitryl fluoride for the deamination of amines at subambient temperatures in acetonitrile. The same reaction occurs with primary nitramines and their alkali metal salts bis-nitramines react to give the corresponding bis-nitrate esters. 

Cyclopropane is reported to react with dinitrogen pentoxide in methylene chloride at subambient temperature to yield 3-nitro-l-propanol nitrate. ... 

Trinitrophloroglucinol has been synthesized via the nitrosation of phloroglucinol followed by nitric acid oxidation. The direct nitration of phloroglucinol must be conducted at subambient temperature to avoid excessive oxidation, and even then, the yield rarely exceeds 70... 

Nielsen and co-workers studied the oxidation of arylhydroxylamines and their O-methyl derivatives with ozone in inert solvents at subambient temperature. 1,2,3,5-Tetranitrobenzene (54) is formed in quantitative yield from the oxidation of both N-hydroxy-2,4,6-trinitroaniline... 

Tertiary alkylamines react with dinitrogen pentoxide in carbon tetrachloride at subambient temperature to give tertiary alkylnitramine nitrate salts (Equation 5.10). ... 

The choice of reagent determines whether a nitrosamine undergoes conversion to a nitramine by either nitrolysis or oxidation. An example is given for the conversion of 1,3,5-trinitroso-1,3,5-triazacyclohexane (109) to l,3,5-trinitro-l,3,5-triazacyclohexane (3) (RDX) - the use of 30 % hydrogen peroxide in 99 % nitric acid at subambient temperature goes via oxidation of the nitrosamine functionality, whereas dinitrogen pentoxide in pure nitric acid makes use of a nitrolysis pathway via C-N bond cleavage. 

Millar and Philbin have explored the nitrodesilylation of silylamines with dinitrogen pen-toxide for the synthesis of nitramines and their derivatives. These reactions, which involve nitra-tive Si-N heteroatom cleavage, are conducted in methylene chloride at subambient temperature. Trimethylsilylamines give high yields of nitramine product and reactions are clean (Table 5.8). 

The condensation of ethylenedinitramine (2) with paraformaldehyde in the presence of sulfuric acid at subambient temperature yields lV,Al -dinitroimidazolidine (88). ... 

The presence of HMX as an impurity in RDX is not a problem when the product is used as an explosive. However, the need for an analytical sample of RDX makes other more indirect methods feasible. One such method involves the oxidation of 1,3,5-trinitroso-1,3,5-triazacyclohexane (109) ( R-salt ) with a mixture of hydrogen peroxide in nitric acid at subambient temperature and yields analytical pure RDX (74%) free from HMX." The same conversion has been reported in 32 % yield with three equivalents of a 25 % solution of dinitrogen pentoxide in absolute nitric acid. l,3,5-Trinitroso-l,3,5-triazacyclohexane (109) is conveniently prepared from the reaction of hexamine with nitrous acid at high acidity. ... 

Li and co-workers recognised the potential of cyclic IV-nitroureas as energetic materials and reported the synthesis of 2,4,6,8-tetranitro-2,4,6,8-tetraazabicyclo[3.3.0]octane-3-one (109) (K-55) from the nitration of 2,4,6,8-tetraazabicyclo[3.3.0]octane-3-one dihydrochloride (108) with absolute nitric acid in acetic anhydride at room temperature the latter obtained from the condensation of lV,lVL(iiformyl-4,5-dihydroxyimidazolidine (107) with urea in aqueous hydrochloric acid. Pagoria and co-workers " " reported the synthesis of 2,4,6-trinitro-2,4,6,8-tetraazabicyclo[3.3.0]octane-3-one (110) (HK-55) in 72% yield from the nitration of (108) with 90 % nitric acid in acetic anhydride at subambient temperature (Table 5.3). HK-55 has a relatively high density (1.905 g/cm ) coupled with a low sensitivity to shock. 

Alkyl lV,lV-dinitramines (154) have been prepared from the reaction of the tetraalkylam-monium salts (155) of primary nitramines with nitryl fluoride in acetonitrile at subambient temperature. The same reaction with the primary nitramine or its alkali metal salts yields the corresponding nitrate ester. Treatment of the ammonium, potassium, or lithium salts of primary nitramines (156) with a solution of nitronium tetrafluoroborate in acetonitrile at subambient temperature yield alkyl iV,iV-dinitramines. ° The same reactions in ether or ester solvents enables the free nitramine to be used. The nitrolysis of A-alkylnitramides (157) and N,N-diacylamines with nitronium tetrafluoroborate in acetonitrile, and the nitration of aliphatic isocyanates with nitronium tetrafluoroborate and nitric acid in acetonitrile, also yield alkyl A,A-dinitramines (154). 

Initial nitration of pyrazole derivatives with nitric acid in acetic or trifluoroacetic anhydrides leads to A-nitropyrazoles, which rearrange to the C-nitrated product on stirring in concentrated sulfuric acid at subambient temperature. This N -> C nitro group rearrangement often occurs in situ when pyrazoles are nitrated with mixed acid. 

C-Nitration of 1,2,3-triazole and 1,2,4-triazole rings can be achieved with either mixed acid or solutions of nitric acid in acetic anhydride. V-Nitration is usually achieved with nitric acid in acetic anhydride at ambient to subambient temperatures. Thermal rearrangement of the N-nitro product to the more stable C-nitro product often occurs at higher nitration temperature. 

Treatment of the ammonium salt of 3,5-dinitro-1,2,4-triazole (113) with hydrazine hydrate leads to selective reduction of one of the nitro groups to yield 3-amino-5-nitro-1,2,4-triazole (ANTA) (114), a high performance explosive (calculated VOD 8460 m/s) possessing thermal stability (m.p. 238 °C) and an extremely low sensitivity to impact. ANTA (114) is also synthesized from the nitration of 3-acetyl-l,2,4-triazole with anhydrous nitric acid in acetic anhydride at subambient temperature followed by hydrolysis of the acetyl functionality. The ammonium salt of 3,5-dinitro-l,2,4-triazole (113) is itself a useful explosive which forms a eutectic with ammonium nitrate. ... 

The 1,2-nitramine-nitrate Tris-X (189) (VOD 8700 m/s, m.p. 69 °C)has been synthesized from the reaction of 2,4,6-tris(aziridino)-l,3,5-triazine (188) with dinitrogen pentoxide in chloroform or methylene chloride at subambient temperature (Section 5.8.1). °... 

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