Toluene Thermal decomposition

Impurity atoms do perturb the character of the toluene thermal decomposition on the flat surfaces. At carbon or sulfur coverage levels of 20% or higher on Ni(100), where an ordered c(2x2) low energy difraction pattern was obtained and where the impurity atoms reside over four-fold sites, the differentiation between aliphatic and aromatic C-H bond cleavage rates was lost. Under these conditions, only a single hydrogen desorption maximum was observed. 

Thermodynamic parameters have been obtained from kinetic HNMR spectroscopic studies of the thermal decomposition of ethyl 2,7-di-to7-butyl-5-methylthiepin-4-carboxylaten and two 1-benzothiepin compounds.12 The activation parameters for sulfur extrusion are AH = 93.7 kJ mol - 1 and AS = — 112.6 J Kmol-1 (in [2H18]Decalin) for the thiepin derivative,11 and AH = 75.3 and 87.9 kJ mol1 and AS = —100.4 and —104.6J Kmol-1 (in [2Hs]toluene) for the benzothiepin compounds.12 The large negative activation entropy values are consistent with a high degree of order in the anticipated thianorcaradiene transition state of the sulfur extrusion reaction. 

The determination of A V is illustrated by data for the thermal decomposition of di-ferf-butyl peroxide.10 The rate constants at 120 °C in toluene are as follows ... 

A plot of the logarithm of the rate constant for the thermal decomposition of di-rm-butyl peroxide with pressure. The data, from Ref. 10, refer to a temperature of 120 °C in toluene. 

Thermal decomposition of 1-methyl-A -phospholen in toluene at 356-444 °C yielded butadiene as the primary product. The activation parameters are in agreement with a mechanism involving ring opening to a biradical followed by fragmentation into butadiene, phosphorus, and methyl radicals. ... 

Starting materials other than sulphonyl azides have been used as possible sources of sulphonyl nitrenes. The decomposition of the triethyl-ammonium salt of iV- -nitrobenzenesulphonoxybenzenesulphonamide (26) in methanol, ethanol, and aniline gave products derived from a Lossen-type rearrangement 20> (Scheme 3). It was felt that the rearrangement did not involve a free sulphonyl nitrene since, when the decomposition was carried out in toluene-methylene chloride or in benzene, no products (benzenesulphonamides) of substitution of the aromatic solvent nucleus were found (as are usually found with sulphonyl nitrenes from the thermal decomposition of the corresponding azides). On the other... 

It has been suggested however that isotacticity derives from polymerization occurring on colloidal particles formed by thermal decomposition of the catalysts. As stated previously, in the presence of the monomer even the allyl compounds are stable at 65°C and none of the thermal decomposition products (black to yellow solids) could be detected. As a check on these results a polymerization of propylene was carried out with Zr (benzyl) 4 in toluene at 0°C in a sealed tube. The reaction was very slow and analytical quantities of polymer could be obtained only after 312 hr. NMR analysis showed peaks assignable to isotactic sequences, and these were much stronger than the peaks assignable to syndiotactic diads. It was concluded... 

The first example we address is taken from a paper by Bawn and Mellish, published some 50 years ago [323]. It reports kinetic studies of the thermal decomposition of benzoyl peroxide in several solvents (reaction 15.5), over the temperature range of 49-76 °C. Here, we analyze the data obtained in toluene over the temperature range of 49.0-70.3 °C. 

The thermolysis of a variety of 1,2,4-trioxanes in methanol has been followed by mass spectrometry and provided evidence of the corresponding products. A smdy of the thermal decomposition of 3,6-diphenyl-1,2,4,5-tetroxane in toluene and methanol revealed a significant solvent effect that supported a homolytic stepwise mechanism instead of a concerted process. ... 

A number of reports on the thermal decomposition of peroxides have been published. The thermal decompositions of f-butyl peroxyacetate and f-butyl peroxypivalate, of HCOH and a kinetic study of the acid-induced decomposition of di-f-butyl peroxide in n-heptane at high temperatures and pressures have been reported. Thermolysis of substituted f-butyl (2-phenylprop-2-yl) peroxides gave acetophenone as the major product, formed via fragmentation of intermediate alkoxy radicals RCH2C(Ph)(Me)0. A study of the thermolysis mechanism of di-f-butyl and di-f-amyl peroxide by ESR and spin-trapping techniques has been reported. The di-f-amyloxy radical has been trapped for the first time. jS-Scission reaction is much faster in di-f-amyloxyl radicals than in r-butoxyl radicals. The radicals derived from di-f-butyl peroxide are more reactive towards hydrogen abstraction from toluene than those derived from di-f-amyl peroxide. 

The dichloro compound can be converted to the bicyclic molecule 6 on treatment with MeaSiNSNSiMea (Figure 6). Related bicyclic compounds with fluorine (or Ph and F) substituents on phosphorus have previously been obtained from the reaction of PF5 (or PhPF ) with MeaSiNSNSiMea (I8, IS) The thermal decomposition of 6 in toluene at ca. 900C for 3h regenerates the six-mem-bered ring (l). 

In general, acyl azides are too unstable to survive at the temperatures required for addition to acetylenes, although benzoyl azide adds readily to ynamines in toluene. Ethoxycarbonyl azide also gives triazoles in good yield with ynamines. The azide adds to propargylic alcohols in boiling ethanol, and to acetylene at 100° under pressure. Addition to phenylacetylene and to electron-deficient acetylenes has been carried out at 130°. Oxazoles are also formed at this temperature by competing thermal decomposition of the azide, and addition of ethoxycarbonylnitrene to the acetylenes. The triazole obtained from phenylacetylene is 2-ethoxycarbonyl-4-phenyltriazole the two 1-ethoxycarbonyltriazoles can be isolated if the addition is carried out at 50° over several weeks. Since the IH- to -triazole isomerization takes place readily in these systems, a IH-structure cannot be assumed for a triazole formed by addition of these azides. 

Thermal decomposition of allylbenzene ozonide (58) at 37°C in the liquid phase gave toluene, bibenzyl, phenylacetaldehyde, formic acid, (benzyloxymethyl)formate, and benzyl formate as products. In chlorinated solvents, benzyl chloride is also formed and in the presence of a radical quench such as 1-butanethiol, the product distribution changes. Electron spin resonance (ESR) signals are observed in the presence of spin traps, adding to the evidence that suggests radicals are involved in the decomposition mechanism (Scheme 9) <89JA5839>. 

A recent oommtiruo tion by Gritter and Wallace discloses initiation of a study of the free-radical chemistry of epoxides Under the influence of U t-butoxy radicals, formed by thermal decomposition of di-lerf-butyl peroxide, propylene oxide is believed to yield an epoxy radical as shown in Eq. (3). The latter undergoes Isomerization to CHsCOCH - and further reaction with unreaoted propylene oxide or other available substrates, such as 1-octene, toluene, oyolohexene, and ethanol,fl7a as shown in Eq. (3). 

When the more reactive sulfonyl isothiocyanates are used as 1,3-dipolarophiles 4-alkyl-5-sulfonylimino-A2-l,2,3,4-thiatriazolines are readily prepared at room temperature by reaction with alkyl azides.64,65 The thiatriazolines are obtained in 50-75% yield. Their structures are deduced from NMR, IR, and mass spectral data and degradation experiments. Thus thermal decomposition at moderate temperature (45°-80°) in inert solvents (dry toluene, CC14, acetone) furnished the corresponding carbodiimides [Eq. (22)]. These were identified by their... 

The greater part of the tetraazadiene-metal complexes are extremely stable to thermal decomposition as well as to further reaction with 02 and H20. For example, Co(/j5-Cp)(Ph2N4) is stable in air and can be sublimed at 180°C/1 mmHg.181 The Ni(R2N4)2 complexes can be refluxed in toluene for days in air without appreciable decomposition.176 In particular this stability is striking when compared with the extreme sensitivity of the corresponding Ni(RN=CHCH=NR)2 complexes (see Section 13.5.3.4.3.vi). 

Using the normal addition procedure (02 diffusion into a 75/25 benzene/THF solution of poly(styryl)lithium) the 37% dimer fraction analyzed for 19% alkyl radical dimer and 18% macroperoxide after LiAlH4 reduction. The yield of macroperoxide was also confirmed by thermal decomposition experiments in refluxing toluene, followed again by size exclusion chromatography analysis of the dimer fraction. The amount of hydroperoxide could be deduced from the difference between the amounts of total peroxide (determined by iodometric titration) versus the amount of macroperoxide determined by LiAlH4 reduction. 

Thermal decomposition of 29 in refluxing benzene or toluene or azo-bis-isobutyronitrile (AIBN) initiated radical chain reactions employing either Bu,SnH or f-BuSH as chain propagating agents also can be used. 

Products which can be ascribed to the intermediate formation of radicals have long been observed in carbene reactions. In the gas phase these products could arise by homolytic decomposition of excited primary products before collisional deactivation rather than from radicals generated in the course of insertion. This is not so in solution. It is found that, in the thermal decomposition of diphenyldiazomethane (Bethell et al., 1965) or photolysis of diphenylketene (Nozaki et al., 1966) in toluene solution, the product of insertion of diphenylmethylene into the benzylic carbon-hydrogen bonds, 1,1,2-triphenylethane, is accompanied by substantial amounts of 1,1,2,2-tetraphenylethane and bibenzyl. This is a strong indication that discrete diphenylmethyl and benzyl radicals are formed, and, taken in conjunction with EPR (Section IIB) and other evidence (Etter et al., 1959) that diphenylmethylene is a ground-state triplet, would support the view that equation (20) is an adequate representation of triplet insertion. 

Activation by silicon of a P-C-H bond to an intramolecular carbene insertion reaction is exemplified by the silicon-directed Bamford-Stevens reaction.68 For example, thermal decomposition of P-trimethylsilyl /V-aziridinyl imines 72 in toluene (Scheme 8) [with or without Rh2(OAc)4 catalyst] results in the formation of allylic silanes 73 as major or exclusive products by the preferential insertion of the carbene intermediate into the C-H bond P to the silicon substituent. 

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