Thermal decomposition of phenyl

Generation of phenylnitrcne by thermal decomposition of phenyl azide in the same solvent mixture, or by deoxygenation of nitrosobenzene with triethyl phosphite in the absence of the trifluoroethanol, fails to yield the 1//-azepine. The role of the alcohol in promoting l//-azepine formation is not understood. 

The thermal, and more importantly, the photolytic decomposition of aryl azides in the presence of nucleophiles, generally amines or alcohols, is the commonest method for preparing 3H-azepines. In fact, jV-phenyl-3//-azepin-2-amine (32, R = Ph), the first example of a 3//-azepine, was prepared by thermal decomposition of phenyl azide in aniline.32... 

Dichlorocarbene, generated by the action of 50 % potassium hydroxide on chloroform, adds to ethyl 1 W-azepine-l-carboxylate to furnish the all /rntu-trishomoazepine 12 in 35% yield280 (see Houben-Weyl, Vol. E 19b, p 1523). Subsequently, and as a result of a careful and detailed study of the addition of dichlorocarbene generated by the thermal decomposition of phenyl(trichloromethyl)mercury, it was deduced that carbene addition takes place sequentially in the order C4 —C5, C2—C3 and C6 — Cl. The intermediary mono- 10 and bis(dichlorocar-bene) 11 adducts have been isolated and characterized. 

The apparent activation energy for the thermal decomposition of phenyl benzyl ether was calculated to be 50 kcal/mole, since the first order rate constants were 1.39x10 at 320°C, 5.19xl0"4 at 340°C and 9.52x10" S at 350°C, respectively. 

TABLE IV EFFECT OF PHENOLS ON THE THERMAL DECOMPOSITION OF PHENYL BENZYL ETHER AT 320°C FOR 30 MIN (Phenyl benzyl ether 27 mmole, Tetralin 220 mmole, Additive 140 mmole)... 

Warbentin (19) has indicated how the radical thermochemistry involved can assist in assigning a mechanism for the thermal decomposition of phenyl oxalate. Exclusive initial fission of either the one C—C or the two C—O bonds would lead, via PhOCO or OCCO intermediates, to high C02 or high CO yields. In experiments lasting about 75 hours at 500°K. in diphenyl ether, comparable amounts of CO (13%) and C02 (9% ) are formed. The following steps, possibly concerted ... 

VEEL spectra of surface phenyl groups have been obtained by ultraviolet photolysis of phenyl chloride on Ag(lll) at 300 K (211) and by thermal decomposition of phenyl iodide on Cu(lll) (212). The spectra are similar, and the strengths of the absorptions from the out-of-plane yCH modes, at 740 and 725 cm-1 respectively, show that the phenyl group is also more near to parallel than to perpendicular to the metal surfaces, again probably because of a combination of cr- and 77-bonding. 

The thermal decomposition of phenyl(trihalomethyl)-mercury compounds, C6H5.Hg.CX3, in the presence of olefins yields the dihalo-cyclopropane virtually quantitatively. A typical example is expressed in equation (15). The initial rate of disappearance of the organometallic... 

Smith and Brown have pointed out, the interpretation of many of the decompositions in acidic media are subject to question due to the failure to differentiate clearly between acid-catalysed and thermally-induced reactions. Since it is known that thermal decomposition of phenyl azides occurs at appreciable rates at temperatures in the range of 140-170°, it is probable that the reactions investigated by... 

The convenience and potential of this method was immediately apparent and its disclosure was followed by numerous examples and extensions. The method was of particular interest because previous methods used to generate dichlorocarbene all required rigorous exclusion of moisture. Among these methods are treatment of chloroform with potassium -butoxide in pentane, pyrolysis of anhydrous sodium trichloroacetate, and the thermal decomposition of phenyl(bromodichloromethyl)-mercury. 

The thermal decomposition of thia2ol-2-yl-carbonyl peroxide in benzene, bromobenzene, or cumene affords thiazole together with good yields of 2-arylthiazoles but negligible amounts of esters. Thiazol-4-ylcarbonyl peroxide gives fair yields of 4-arylthiazoles, but the phenyl ester is also a major product in benzene, indicating reactions of both thiazol-4-yl radicals and thiazol-4-carbonyloxy radicals. Thiazole-5-carbonyl peroxide gives... 

Phenyl cations are formed by thermal decomposition of aryl diazonium ions. The cation is so extremely reactive that under some circumstances it can recrqrture the nitrogen... 

Phenyl radicals can be generated by the thermal decomposition of lead tctrabcnzoate, phenyl iodosobenzoate, and diphenyliodonium hydroxide,- - and by the electrolysis of benzoic acid.- These methods have been employed in the arylation of aromatic compounds, including heterocycles. A method of promise which has not been applied to the arylation of heterocycles is the formation of aryl radicals by the photolysis of aromatic iodides at 2537... 

Dihydro-2/7- 74 and -4//-l,2-oxazines and thiazines 75 are interrelated by prototropy, being enamines and imines, respectively. In the case of oxazines, the imine form 75 is favored, and there are several well established examples of this system, including the parent heterocycle 75 (X = O) [84MI2]. No tautomeric equilibrium between the 2H and 4H forms has been observed under normal conditions in solution or in the solid state. However, the formation of intermediate 2H isomers 77 was proposed both for the conversion of 3-phenyl-5,6-dihydro-4//-l,2-oxazine 76 (R = Ph, r = R = H) into 2-phenylpyrrole(89TL3471) under strong basic conditions and for thermal decomposition of cyclopentene-fused 1,2-oxazine 76... 

Lithiochloromethyl phenyl sulfoxide 99 was found to react with aryl or alkyl halides in the presence of one equivalent of hexamethylphosphoramide to afford alkylated products 100 in high yields135. Thermal decomposition of these products in the presence of a catalytic amount of hydroquinone in xylene gave the corresponding vinyl compounds 101. 

The H and 13C CIDNP studies have shown that not only the sulfone 14, but also the sulfmic ester 15, is generated as cage products from the phenyl/p-toluenesulfonyl radical pair during the thermal decomposition of phenylazo aryl sulfone (13)54 (Scheme 2). The cross-termination of arenesulfonyl and triethylgermyl radicals was found to occur exclusively via the formation of germyl sulfinate, ArS(0)0GeEt333. 

Dimethyl-I,l -biphenyl has been prepared by a wide variety of procedures, but few of these are of any practical synthetic utility Classical radical biarjl syntheses such as the Gomberg reaction or the thermal decomposition of diaroyl peroxides give complex mixtures of products m which 4,4 dimethyl-l.l -biphenyl is a minor constituent A radical process maj also be involved in the formation of 4,4 dimethyl-1, l -biphenyl (13%) by treatment of 4-bromotoluene with hydrazine hydrate 5 4,4 -Dimethyl-l,l -biphenyl has been obtained in moderate to good yield (68-89%) by treatment of either dichlorobis(4-methyl phenyl)tellurium or l,l -tellurobis(4-methylbenzene) with degassed Raney nickel in 2 methoxyethyl ether 6... 

Since the benzene emission in the thermal decomposition of benzoyl peroxide results from radical transfer by the phenyl component of a benzoyloxy-phenyl radical pair, phenyl benzoate produced by radical combination within the same pair should appear in absorption. A weak transient absorption has been tentatively ascribed to the ester (Lehnig and Fischer, 1970) but the complexity of the spectrum and short relaxation time (Fischer, personal communication) makes unambiguous assignment difficult. Using 4-chlorobenzoyl peroxide in hexachloro-acetone as solvent, however, the simpler spectrum of 4-chlorophenyl 4-chlorobenzoate is clearly seen as enhanced absorption, together with... 

Komendantov et al. found that thermal decomposition of methyl diazoacetate in the presence of benzonitrile yielded two products.<73JOU431> One is the expected 2-phenyl-5-methoxyoxazole 4 in about 35% yield and the other product was methyl 3-phenyl-2//-azirine-2-carboxylate 5 in around 1% yield (Scheme 4). 

The rates of radical-forming thermal decomposition of four families of free radical initiators can be predicted from a sum of transition state and reactant state effects. The four families of initiators are trarw-symmetric bisalkyl diazenes,trans-phenyl, alkyl diazenes, peresters and hydrocarbons (carbon-carbon bond homolysis). Transition state effects are calculated by the HMD pi- delocalization energies of the alkyl radicals formed in the reactions. Reactant state effects are estimated from standard steric parameters. For each family of initiators, linear energy relationships have been created for calculating the rates at which members of the family decompose at given temperatures. These numerical relationships should be useful for predicting rates of decomposition for potential new initiators for the free radical polymerization of vinyl monomers under extraordinary conditions. 

The wide utility of aryl diazonium ions as synthetic intermediates results from the excellence of N2 as a leaving group. There are several general mechanisms by which substitution can occur. One involves unimolecular thermal decomposition of the diazonium ion, followed by capture of the resulting aryl cation by a nucleophile. The phenyl cation is very unstable (see Part A, Section 3.4.1.1) and therefore highly unselective.86 Either the solvent or an anion can act as the nucleophile. 

Recently, Traynelis and his coworkers 221 have reported the thermal decomposition of some substituted benzo[6]thiepins (Table 2). A slight increase in the stability of the thiepin ring by phenyl, benzyl, methyl, chloro, and bromo substituent was... 

The high temperatures reached in the GS/MW process have been used to achieve the thermal decomposition of O-alkylcarbamates (Scheme 7.6) [15, 16]. The latter are prepared from corresponding alcohols and phenyl isocyanate in the presence of stannous octanoate [49]. 

The procedure given here is essentially that described previously by the submitters2 and is based on the early work of Knoevenagel.8 2-Phenylindazole has been prepared by reduction of N-(o-nitrobenzyl)aniline with tin and hydrochloric acid,4 by reduction of N-(o-nitrobenzyl) -N-nitrosoaniline with tin and hydrochloric acid,5 by dehydration of 2-(phenylazo)benzyl alcohol,6 by elimination of acetic acid from 2-(phenylazo)benzyl acetate,7 by dehydrogenation of 3,3a,4,5,6,7-hexahydro-2-phenyl-indazole with sulfur,8 and by thermal decomposition of o-azido-benzalaniline.9... 

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