Melt-thermolysis

Perhaps the most remarkable illustration of the ability of metals to activate alkynes comes from reactions in which complete scission of the carbon-carbon triple bond occurs. On the stoichiometric level these include examples in which carbyne complexes are produced from alkyne completes as in the melt-thermolysis of CpCo(PPh3)(RCsCR) [112] or from reactions of alkynes with unsaturated metal species (Scheme 4-34) [113]. The remarkable alkyne metathesis reaction (Scheme 4-35), which involves overall cleavage and regeneration of two o-and four rt-bonds, is conceptually related. A variety of functionalized alkynes can be tolerated as metathesis substrates [114] and especially effective catalysts for these reactions are Mo(VI)-and W(VI)-carbyne complexes. Metallacyclobutadienes 64, formed by the reaction of the alkyne with a metal-carbyne complex, appear to be central intermediates in these reactions and the equilibrium between metallacycle and alkyne/metal-carbyne is observable in some cases [115]. 

S7O crystallizes in orange monochnic crystals which are yellow at —80 °C and melt with decomposition at 55 °C. However, even at 25 °C S7O decomposes quantitatively within 24 h in diffuse daylight, more slowly in the dark, to SO2, polymeric sulfur and httle Sg. Thermolysis in a high vacuum at 60 °C produces S2O and elemental sulfur. Therefore, the El mass spectrum exhibits only ions originating from these decomposition products (SO, 830, S ). In CH2CI2 solution S7O decomposes at 20 °C within 3 h to SO2, polymeric sulfur and Sio the latter can be isolated in 7% yield based on the starting material 87 [62] ... 

The earliest work on silicon carbide fibers was done by Yajima and co-workers [3]. Yajima applied the Kumada [4] rearrangement to Burkhard s [5] dimethylpolysilane - an insoluble and infusible compound - (Eq. 1) and obtained by thermolysis at 400 - 450°C or by catalysis with polyborodiphenyl-siloxane at 350°C a melt spinnable and soluble polycarbosilane (Eq. 2). 

This indicates that the prebaking temperature higher than the melting point of the azide decomposes the azide (50%) and it totally decomposes upto 100 mJ/cm2 irradiation. It is possible that subsequent reactions of the nitrene, generated from the azide thermolysis and photolysis, with the styrene resin could be responsible for solubility modulation of this type resist (16). 

All the S-, Se-, and Te-(perfluoroalkyl)dibenzothiophenium, -selenophenium, and -tellurophenium salts synthesized above are stable crystalline materials at room temperature. Their melting or decomposition points (dec. p) are higher than 100°C. Nitro substituents decrease their stability [S-salt 17 mp 155°C > dinitro S-salt 39 dec. p 130-135°C]. The chalcogen stability increases in the order S < Se < Te [dec. p S-salt 39 130-135°C < Se-salt 40 198-200°C < Te-salt 41 275-280°C]. Thermolysis of S-salt 17 at 200 C gave trifluoromethyl triflate (50) and dibenzothiophene (51) in high yields (Eq. 12). Thermolysis of dinitro S-salt 39 at 140°C gave 50 and dinitrodiben-zothiophene 52 (Eq. 13). 

The synthesis of a range of benzoxazines (35) from 34 using AgBp4 in anhydrous ether has been described . Thermolysis of these in a melt resulted in a retro-Diels-Alder reaction with loss of formaldehyde giving the azaxylylenes (36), which undergo spontaneous electrocyclization to give the 2-aIkyl-41/-3,1-benzoxazines (37) in excellent yields (Scheme 5). 

Other additives such as waxes and polyethylene glycols melt at relatively low tem-peratnres and vaporize over a more narrow temperatnre range. Oxidation of the binder canses the temperature to increase more rapidly. For the thermolysis of polyethylene glycol (PEG) in air, decomposition occnrs by the mechanism of chain scission and oxidative degradation. 

The increase in the rate of decomposition under the influence of added Cr203 and K2Cr207 is shown on Figs. 171 and 172 respectively.lt has been found that an increase of the rate occurred only at temperatures near to the melting point of the samples. Guiochon [17] also found that cobalt salts increase the rate of thermolysis of ammonium nitrate. Other mineral salts (of manganese, nickel and copper) have a similar but much weaker action. A large number of salts of other metals are without any noticeable action. 

The latter property is somewhat of a mixed blessing, however. Poly(imides) are only soluble, for the most part, in extreme solvents such as concentrated sulfuric acid, fuming nitric acid and m-cresol. This lack of solubility in common solvents and their high melt temperatures render poly(imides) virtually intractable. For this reason, processing of the poly(imides) directly is often avoided by utilizing the polyfamic acid) precursor (Scheme 54). The more processable poly(amic acid) can be cast from solution, for example, and the poly(imide) may be generated in the desired configuration by thermolysis at 300 °C. 

An efficient synthesis of thieno[2,3-c]pyridine starting from 4-vinylpyridine (275) has been described by Klemm and coworkers (Scheme 69) (68JHC883). Because 4-vinylpyridine and hydrogen sulfide under high-temperature conditions formed (259) only in very low yield, (275) was converted into benzyl pyridyl sulfide (276) prior to thermolysis. Thieno[2,3-c]pyridine is obtained as low-melting (m.p. 59-60 °C) yellow crystals. 

Thermolysis of 3,6-diphenyl-l,4-di(phenylsulfonyl)-l,4-dihydro-l,2,4,5-tetrazine (127) in boiling toluene gives benzenesulfonic anhydride (128), phenyl benzenethiosulfonate (129), small amounts of diphenyl disulfide (130), 3,6-diphenyl-l,2,4,5-tetrazine (51) and a rearrangement product, 3,6-diphenyl-l,2-di(phenylsulfonyl)-l,2-dihydro-l,2,4,5-tetrazine (79) (79BCJ483). 3,6-Disubstituted hexahydro-1,2,4,5-tetrazines (132) afforded aldehyde hydrazones (133) when heated at their melting point (63AG1204). 

Unlike the related Na3[M (CO)5], where M = V, Nb, and Ta, which undergoes thermolysis below O0C (vide infra), these materials possess remarkable thermal stabilities for metal carbonyls and briefly survive without melting at temperatures as high as 300°C. By comparison, K2[Fe(CO)4], another metal carbonyl salt of high thermal stability, has been reported to melt at 270-273°C with decomposition (20). The related K[Co(CO)4] melts at about 203°C with decomposition (21). 

We examined the thermal decomposition of a number of nitramines in dilute solution and in the melt phase. The nitramines included acyclic dialkyl mononitramines, where the dialkyls were methyl, ethyl, propyl and isopropyl cyclic mononitramines (N-nitro-pipeiidine and N-nitropyrrolidine) and cycle multifunctional nitramines (N-dinitropiperazhe l,3-dinitro-l,3-diazacyclo-pentane l,3-dinitro-l,3-diazacycbhexane RDX and HMX). For all nitramines, the predominant condensed-phase product was the nitrosamine though the amount formed depending on the nitramine and the phase of the thermolysis. The common trigger in the decompositions was N-N02 ho mo lysis, but the fate of the resultant amine radical depended on the phase. In solution the radical was stabilized sufficiently so that it resisted further decomposition and, instead, reacted with NO to form nitrosamine. In vapor or condensed phase, the amine radical underwent further reaction therefore,... 

When compounds V (R = ethyl, isopropyl, cyclopentyl, n-butyl, or tert-butyl) have been heated 30-50°C above their melting points, VIII and the corresponding olefins have been obtained by (3 elimination (87,94). The course of the reaction has been controlled by the use of the deuterium-labeled compound V (R = CD2Me). It has been shown that all of the deuterium occurred in the ethylene formed by thermolysis (94). When R is methyl or phenyl, the thermolysis of V results in formation of IX. The styryl derivatives of V (R = cis-CH=CHPh and trans-CH=CHPh) have also been synthesized from VI and the corresponding Grignard reagents (94). Interestingly, thermolysis of these deriva-... 

Ca, Sr, and Ba carboxylate, thiocarboxylate, thiocarboxylate-carboxylate, sulfito, and sulfonate compounds and their monodentate base adducts are white solids, many of which decompose on melting and are only soluble in protic solvents such as alcohols and water.I68-232-240 They are invariably oligomeric or polymeric in the solid state see, for example, Refs. 235, 239, and 240. On thermolysis, the nonfluorinated carboxylates degrade to the metal carbonates while their fluorinated congeners usually form the metal fluorides.212 222-262 269 The thiocarboxylates give mixtures of the metal oxides and sulfates on thermolysis in air.238-239 270 The methyl-thiocarbonate compound, Ca[(OCS)OMe]2(MeOH)3 2, is a dimer in the solid state, soluble in polar coordinating solvents and stable under reduced... 

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