Synthesis and thermal decomposition of N,N-dialkoxyamides

N,N-dialkoxyamides 1c, a virtually unstudied member of the new class of anomeric amides, amides bearing two electronegative atoms at nitrogen, have been synthesised in useful yields directly from hydroxamic esters using phenyliodine(III)bis(trifluoroacetate) (PIFA). Infrared carbonyl stretch frequencies and carbonyl (13)C NMR properties have been reported, which support strong inhibition of amide resonance in these amides. Their thermal decomposition reactions in mesitylene at 155 °C proceed by homolysis to form alkoxyamidyl and alkoxyl free radicals in preference to HERON rearrangements to esters. The reactions follow first-order kinetics and for a series of N,N-dimethoxy-4-substituted benzamides, activation energies of 125-135 kJ mol(-1) have been determined together with weakly negative entropies of activation.     

Synthesis and structural diversity of barium (N,N-dimethylamino)diboranates

The reaction of a slurry of BaBr(2) in a minimal amount of tetrahydrofuran (THF) with 2 equiv of Na(H(3)BNMe(2)BH(3)) in diethyl ether followed by crystallization from diethyl ether at -20 °C yields crystals of Ba(H(3)BNMe(2)BH(3))(2)(Et(2)O)(2) (1). Drying 1 at room temperature under vacuum gives the partially desolvated analogue Ba(H(3)BNMe(2)BH(3))(2)(Et(2)O)(x) (1') as a free-flowing white solid, where the value of x varies from <0.1 to about 0.4 depending on whether desolvation is carried out with or without heating. The reaction of 1 or 1' with Lewis bases that bind more strongly to barium than diethyl ether results in the formation of new complexes Ba(H(3)BNMe(2)BH(3))(2)(L), where L = 1,2-dimethoxyethane (2), N,N,N',N'-tetramethylethylenediamine (3), 12-crown-4 (4), 18-crown-6 (5), N,N,N',N'-tetraethylethylenediamine (6), and N,N,N',N",N"-pentamethylethylenetriamine (7). Recrystallization of 4 and 5 from THF affords the related compounds Ba(H(3)BNMe(2)BH(3))(2)(12-crown-4)(THF)·THF (4') and Ba(H(3)BNMe(2)BH(3))(2)(18-crown-6)·2THF (5'). In addition, the reaction of BaBr(2) with 2 equiv of Na(H(3)BNMe(2)BH(3)) in the presence of diglyme yields Ba(H(3)BNMe(2)BH(3))(2)(diglyme)(2) (8), and the reaction of 1 with 15-crown-5 affords the diadduct [Ba(15-crown-5)(2)][H(3)BNMe(2)BH(3)](2) (9). Finally, the reaction of BaBr(2) with Na(H(3)BNMe(2)BH(3)) in THF, followed by the addition of 12-crown-4, affords the unusual salt [Na(12-crown-4)(2)][Ba(H(3)BNMe(2)BH(3))(3)(THF)(2)] (10). All of these complexes have been characterized by IR and (1)H and (11)B NMR spectroscopy, and the structures of compounds 1-3, 4', 5', and 6-10 have been determined by single-crystal X-ray diffraction. As the steric demand of the Lewis bases increases, the structure changes from polymers to dimers to monomers and then to charge-separated species. Despite the fact that several of the barium complexes are monomeric in the solid state, none is appreciably volatile up to 200 °C at 10(-2) Torr.     

Kinetics and mechanism of the thermal decomposition of methyl isocyanate

The kinetics of gas-phase decomposition of methyl isocyanate have been investigated in the range of 427–548°C. Two decomposition routes are followed; the predominant one is a radical-chain process giving CO, H₂, and HCN as major products, which has an order of 1.5 and an Arrhenius equation given by log k(L^1/2/mol^1/2·s) = (13.12 ± 0.06) ? (56,450 ± 1670) cal/mol/2.303 RT. The minor route is the bimolecular formation of N,N′-dimethylcarbodiimide and CO₂, which from the low activation parameters E_a = 31.6 kcal, A = 10^5.30 L^1/2/mol^1/2·s, and the reaction order of 1.57 appears to be heterogeneous.     

Phase transition and thermal decomposition of silver isocyanate (AgNCO)

The thermal behavior of AgNCO (silver isocyanate) has been studied via thermal analysis, optical spectroscopy, X-ray powder diffraction and transmission electron microscopy. Upon quenching the high temperature polymorph (HT-AgNCO) to room temperature, a new modification has been obtained (q-AgNCO). Its crystal structure was solved from X-ray powder diffraction data and refined by the Rietveld method (Pmmn (no. 59), a = 3.579(3) Å, b = 5.777(4) Å, c = 5.807(2) Å, V = 120.08(3) Å³, Z = 2, T = 295 K). The structure consists of chains of Ag⁺ ions bridged by isocyanate units. HT-AgNCO exists between T = 135 °C and the melting/decomposition point and exhibits virtually free rotation of the complex anions. According to preliminary single-crystal studies, HT-AgNCO (C2/m, a = 5.87 Å, b = 3.51 Å, c = 5.81 Å, ß = 105.953°, Z = 2, T = 373 K) is structurally related to α-NaN₃. The crystal structures of both, HT-AgNCO and q-AgNCO have been compared with that of the room temperature modification (RT-AgNCO). The thermal behavior and the ionic conductivity of AgNCO are discussed with respect to the related compounds AgN₃ and KSCN. Decomposition of AgNCO proceeds in distinct steps, as seen from TGA, and results in the formation of nanoparticles of elemental silver and an amorphous polymer consisting of C, N and O, only.     

富硅硅化剂N,N-二甲胺基五甲基二硅烷的合成

富硅硅化剂Ｎ，Ｎ┐二甲胺基五甲基二硅烷的合成胡春野郭哲（中国科学院化学研究所北京１０００８０）Ｎ，Ｎ－二甲胺基五甲基二硅烷作为一种新型富硅硅化剂，最近在干法正片深紫外微电子刻蚀技术中显示出重要的应用前景［１］。由于该试剂没有商业产品，我们在实验室进行...     

Mechanism of thermal decomposition of N,N-dinitromethylamine

Conclusions The methylnitroamine radical does not tend to undergo intramolecular oxidation: Me.NNO₂ MeO+N₂O and breaks down by decomposition into MeN: and NO₂. In the presence of NO₂ MeNNO₂ and MeN: are efficiently oxidized to MeNO.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 794–797, April, 1989.     

Cyclic and polycyclic tellurium-tin and tellurium-lead compounds--synthesis, structures and thermal decomposition

The miscellaneously substituted silyltellanes tBu(2)PhSiTeSiMe(3) (1) and (Me(3)Si)(3)SiTeSiMe(3) were used to synthesize the cyclic tin(II) and lead(II) tellurolates [(tBu(2)PhSiTe)(4)M(2)] (M = Sn (2), Pb (3)), [tBu(2)PhSiTePbC(SiMe(3))(3)](2) (4) and the uncommon cluster compound [{(Me(3)Si)(3)SiTe}(4)Te(2)Sn(4)] (5).     

Synthesis,characterisation and thermal decomposition of double sulfate

Upon evaporation at room temperature of an aqueous mixture containing Al(III) sulfate and trishydroxymethyl-ammoniummethane sulfate in a molar ratio 1:2, double sulfate as crystalline product was obtained. The stoichiometry of the obtained compound was determined by means of elemental and TG analysis. For identification, IR-spectra and X-ray powder diffraction patterns were done. It was found that the general formula of the obtained compound is Al(HOCH₂)₃CNH₃(SO₄)₂·₆H₂O. as revealed by TG, DTG and DTA analysis, the dehydration of the AL-compound takes place in one step which points out that the six water molecules are bonded in the same way. The thermal decomposition of the anhydrous compound starts at about 260°C and is very complex. This process takes place in many steps which are not well resolved. The pathway of the thermal decomposition is also supposed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and thermal decomposition of haloalkoxy-sym-triazines

The reaction of 4,6-bis[alkyl(dialkyl)amino]- or (4-alkylamino-6-dialkylamino-sym-triazin-2-yl)trimethylammonium chlorides with ethylene chlorohydrin and the action of phosphorus pentachloride on 2--hydroxyethoxy-sym-triazines give 2--chloroethoxy derivatives of sym-triazine, which on heating are converted to imidazo[1,2-a]-sym-triazine derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 262–265, February, 1977.     

Synthesis and thermal decomposition of haloalkoxy-sym-triazines

Reaction of [2-methylthio-6-dialkylamino-sym-triazin-4-yl]trimethylammonium chlorides with ethylene chlorohydrin gave 2-methylthio-4-(2-chloroethoxy)-6-dialkylamino-sym-triazines, which are converted to 2-methylthio-3-(2-chloroethyl)-4-oxo-6-dialkylamino-3,4-dihydro-symtriazines when they are heated to 115–120°C and to the corresponding tetrahydrothiazolo-symtriazine derivatives when they are heated at 180–190°C.See [1] for communication II.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1420–1423, October, 1977.     

Synthesis of a stereochemically defined 1,2-diazetine N,N'-dioxide and a study of its thermal decomposition

Diazetine dioxide 1a has been synthesized in a single step via oxidation of meso-2,3-diphenyl-1,2-ethanediamine with dimethyldioxirane, albeit in low yield (7%). Thermal decomposition of 1a afforded predominantly either trans-stilbene or diphenyl glyoxime depending on solvent, temperature, and the presence of an amine catalyst. Reaction in chloroform at 69 degrees C favored elimination of NO and formation of trans-stilbene. The stereospecific formation of trans-stilbene suggests a mechanism of decomposition in which C-N bond cleavage leads to a diradical intermediate stabilized by the phenyl group. Bond rotation followed by cleavage of the second C-N bond accounts for the trans-stilbene. At 25 degrees C in chloroform, while trans-stilbene was still the major product, some diphenyl glyoxime was also observed (4% yield). However, 1a as a solution in chloroform in the presence of Et3N, or 1a as a solution in DMSO-d6, afforded predominantly diphenyl glyoxime. These results are interpreted in terms of two closely competing reactions subject to the effects of entropic contributions.     

The thermal decomposition of N,N-dimethyl-3-oxa-glutaramic acid and the kinetics of its second-stage thermal decomposition reaction

N,N-dimethyl-3-oxa-glutaramic acid was purified and characterized by 1H-NMR, Fourier transform in-frared spectroscopy (FT-IR) and elemental analysis. The thermal decomposition of the title compound was studied by means of thermogravimetry differential thermogravimetry (TG-DTG) and FT-IR. The ki-netic parameters of its second-stage decomposition reaction were calculated and the decomposition mechanism was discussed. The kinetic model function in a differential form, apparent activation energy and pre-exponential constant of the reaction are 3/2 [(1-α) 1/3-1]-1, 203.75 kJ-mol-1 and 1017.95s-1, respec-tively. The values of ΔS≠, ΔH≠ andΔG≠ of the reaction are 94.28 J-mol-1-K-1, 203.75 kJ-mol-1 and 155.75 kJ-mol-1, respectively.     

The thermal decomposition of N,N-dimethyl-3-oxaglutaramic acid and the kinetics of its second-stage thermal decomposition reaction

N,N-dimethyl-3-oxa-glutaramic acid was purified and characterized by ¹H-NMR, Fourier transform infrared spectroscopy (FT-IR) and elemental analysis. The thermal decomposition of the title compound was studied by means of thermogravimetry differential thermogravimetry (TG-DTG) and FT-IR. The kinetic parameters of its second-stage decomposition reaction were calculated and the decomposition mechanism was discussed. The kinetic model function in a differential form, apparent activation energy and pre-exponential constant of the reaction are 3/2 [(1?α)^1/3?1]^?1, 203.75 kJ·mol^?1 and 10^17.95s^?1, respectively. The values of ΔS ^≠, ΔH ^≠ and ΔG ^≠ of the reaction are 94.28 J·mol^?1·K^?1, 203.75 kJ·mol^?1 and 155.75 kJ·mol^?1, respectively.     

Synthesis and thermal decomposition of barium peroxytitanate to barium titanate

Barium peroxytitanate, Ba₂[Ti₂(O₂)₄(OH)₄(H₂O)₄], was synthesized and its thermal decomposition in the temperature range from 298 to 1173 K was investigated. The intermediates at 423, 533, 773 and 873 K were identified by means of quantitative analysis, IR spectroscopy and X-ray diffraction analysis. On the basis of the data obtained, a scheme of its thermal decomposition was suggested.Isothermal treatment was carried out at 873 and 973 K for different periods. The optimum conditions of preparation of tetragonal barium titanate with high crystallinity were determined, i.e. annealing for 390 min at 873 K.

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Zusammenfassung Bariumperoxotitanat Ba₂[Ti₂(O₂)₄(OH)₄(H₂O)₄] wurde dargestellt und seine thermische Zersetzung im Temperaturbereich 298–1173 K untersucht. Die bei 423, 533, 773 und 873 vorliegenden Zwischenprodukte wurden durch quantitative Analyse, IR-Spektroskopie und Röntgenbeugung untersucht. Nach den Ergebnissen wurde ein Ablaufschema der thermischen Zersetzung vorgeschlagen. Isotherme Behandlung über unterschiedliche Zeiten bei 873 und 973 K ergaben als optimale Bedingungen für die Präparation von Bariumtitanat hoher Kristallinität 390 min bei 873 K.

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-Ba₂[Ti(O₂)₄(OH)₄(H₂O)₄] — 298–1173 . , , 423, 533, 773 873 . . 873 973 . 873 390 .

     

Synthesis and thermal decomposition of cobalt-containing oligosilanes

Oligo(phenylcobaltcarbonylsilane) was prepared from oligo(phenylsilane) and dicobalt octacarbonyl. The reaction proceeds with elimination of H₂ and CO and insertion of cobalt carbonyl fragments into the silicone backbone of oligosilane. Oligosilane containing cobalt carbonyl groups in side organic substituents was obtained from oligolmethyl(phenylethynyl)Isilane and CO₂(CO)₈. The reaction of 1,2-bis(phenylethyny1)tetramethyldisilane with Co₂(CO)₈ proceeds with the sequential attachment of cobalt carbonyl fragments to ethynyl groups to form disilane derivatives [²-CCPhCo₂(CO)₆] Thermal decomposition of cobalt-containing oligosilanes affords a mixture of paramagnets and ferromagnets.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 10, pp. 2561–2567, October, 1996.     

Synthesis of 2'-O-[2-[(N,N-dimethylamino)oxy]ethyl] modified nucleosides and oligonucleotides.

A versatile synthetic route has been developed for the synthesis of 2'-O-[2-[(N,N-dimethylamino)oxy]ethyl] (abbreviated as 2'-O-DMAOE) modified purine and pyrimidine nucleosides and their corresponding nucleoside phosphoramidites and solid supports. To synthesize 2'-O-DMAOE purine nucleosides, the key intermediate B (Scheme 1) was obtained from the 2'-O-allyl purine nucleosides (13a and 15) via oxidative cleavage of the carbon-carbon bond to the corresponding aldehydes followed by reduction. To synthesize pyrimidine nucleosides, opening the 2,2'-anhydro-5-methyluridine 5 with the borate ester of ethylene glycol gave the key intermediate B. The 2'-O-(2-hydroxyethyl) nucleosides were converted, in excellent yield, by a regioselective Mitsunobu reaction, to the corresponding 2'-O-[2-[(1,3-dihydro-1,3-dioxo-2H-isoindol-2-yl)oxy]ethyl] nucleosides (18, 19, and 20). These compounds were subsequently deprotected and converted into the 2'-O-[2-[(methyleneamino)oxy]ethyl] derivatives (22, 23, and 24). Reduction and a second reductive amination with formaldehyde yielded the corresponding 2'-O-[2-[(N,N-dimethylamino)oxy]ethyl] nucleosides (25, 26, and 27). These nucleosides were converted to their 3'-O-phosphoramidites and controlled-pore glass solid supports in excellent overall yield. Using these monomers, modified oligonucleotides containing pyrimidine and purine bases were synthesized with phosphodiester, phosphorothioate, and both linkages (phosphorothioate and phosphodiester) present in the same oligonucleotide as a chimera in high yields. The oligonucleotides were characterized by HPLC, capillary gel electrophoresis, and ESMS. The effect of this modification on the affinity of the oligonucleotides for complementary RNA and on nuclease stability was evaluated. The 2'-O-DMAOE modification enhanced the binding affinity of the oligonucleotides for the complementary RNA (and not for DNA). The modified oligonucleotides that possessed the phosphodiester backbone demonstrated excellent resistance to nuclease with t(1/2) > 24 h.     

Synthesis, characterization and kinetics of thermal decomposition of dimeric peroxycarbamates

Several dimeric peroxycarbamates (PCs) have been synthesized by using cycloaliphatic and aromatic diisocyanates with mono- and di-hydroperoxides. The reactions were carried out under suitable conditions either in the presence of T-12 (dibutyltin dilaurate) as catalyst or in the absence of this catalyst. The products were characterized by IR-spectra and molecular weight measurements from isocyanate and peroxygen analyses. Thermal decomposition kinetics of these PCs were studied in THF solution at 80, 90 and 100 °C; the reactions were found to be first-order and decomposition rate constants (k_d) were found. Activation energies and frequency factors for the decomposition were calculated. Activation energies were found to be in the range 67-121 kJ mol⁻¹ and frequency factors were of the order of 10¹¹-10¹⁵ s⁻¹ depending on the structure of the PC. The results for the PCs agree well with literature values.