Diphenyl ether, formation

Note There is a tendency to byproduct diphenyl ether formation in reactor R-101. However, a recycle of 100 pph of DPE in the feed to the reactor prevents any further formation of this substance. 

Photochemical syntheses have also been attempted for the preparation of in-dolocarbazoles. Thus when the N,N -diphenyl-p-phenylenediamines 188a-b underwent photocyclization in diethyl ether, formation of low yields of the products... 

The smooth intramolecular nucleophilic displacement of biphenyl carboxylic acids leading to benzocoumarins (See Section II.A.) inspired also investigation of the behavior of similar diphenyl ether, diphenyl sulfide and A-methyldiphenyl amine derivatives 458 under similar conditions. However, all these attempts to achieve cyclization to tricyclic compounds 459 were unsuccessful, probably due to the unfavorable stereochemistry for the formation of the required seven-mem-bered transition states and also to the presence of the deactivating bridge groups X (Eq. 42) [68JCS(C)1030]. 

Scheme 3. Mechanism of Copper Catalyzed Formation of PBDD from Polybrominated Diphenyl Ethers.

Regarding the degradation of PBDEs by white-rot fungi, the first evidence of their ability to degrade a PBDE compound corresponds to a study published by Hundt et al. [27], which studied the degradation of 4-bromo-BDE by Trametes versicolor. The degradation occurs initially by hydroxylation reaction with the possible formation of three different isomers of hydroxy-diphenyl ether followed... 

C. Rappe and R. Lindahl, "Formation of Polychlorinated Dibenzofurans (PCDFs) and Polychlorinated Dibenzo-p-Dioxins (PCDDs) from the Pyrolysis of Polychlorinated Diphenyl Ethers,"Chemosphere, 2, 351 (1980). 

These are produced by polycondensation of pyromellitic anhydride and p,p -diamino diphenyl ether. The reaction, is carried out in stages. To start with, the reaction is carried out in suitable solvents, like DMF, at around 50°C, when a polyaddition reaction occurs with the formation of polyamic acid as under ... 

Raychaudhuri and Basu investigated the formation of side products in the large-scale cyclization of diethyl /V-(3-chlorophenyl)aminomethy-lenemalonate (250) in diphenyl ether (70J1C25). As side products, 7-chloro-1-ethyl-l,4-dihydro-4-oxoquinoline-3-carboxylic acid (551), 7-chloro-4-ethoxyquinoline (552), and 7-chloro-l-ethyl-4(l//)-quinoline (553) could be isolated. These were probably formed from the primarily cyclized product, ethyl 7-chloro-4-hydroxyquinoline-3-carboxylate. The quantities of the side products depended on the reaction temperature during the cyclization, the duration of heating, and the purity of the starting N-(3-chlorophenyl)aminomethylenemalonate (250). 

Cruickshank et al. reported that the thermal cyclization of 5-benzofuran-ylaminomethylenemalonate (808) in boiling diphenyl ether for 30 min gave a 10 1 mixture of the linearly and angularly fused tricycles (809 and 810) in 75% yield, while in the case of 6-benzofuranylaminomethylenemalonate (811), only formation of the linear product (812) could be detected (70JMC1110). 

The triplet reaction of 2-nitrodibenzo[fc,primary amines (n-propylamine and benzylamine) was studied110 in polar and apolar solvents. In polar solvents, the irradiation results in the formation of two isomeric compounds, (alky-lamino)hydroxynitrodiphenyl ether andiV-(alkylamino)-2-nitrophenoxazine (equation 54). In apolar solvents, only the nitrophenoxazine is obtained. In polar solvents, the exciplex formed between the 2-n i trodi benzol h,e [ 1,4]dioxin triplet state and amines dissociates to the solvated radical ions, from which the diphenyl ether arises. 1-Nitrodibenzo[fr,e][l,4]dioxin is stable even on prolonged irradiation. 

Photolytic. In a methanolic solution irradiated with UV light >290 nm), dechlorination of 4-chlorophenyl phenyl ether resulted in the formation of diphenyl ether (Choudhry et al., 1977). Photolysis of an aqueous solution containing 10% acetonitrile with UV light (X = 230-400 nm) yielded 4-hydroxybiphenyl ether and chloride ion (Dulin et al., 1986). 

The enthalpy of formation of diphenyl ether (s) is —32.1 1.5 kJmoL from Reference 12. 

The synthesis of pyridoquinolines by the formation of one bond often requires harsh reaction conditions (heating under reflux in diphenyl ether, ca. 250-260 °C) but the product yield is generally good (70-80%). However, the heteroatom Diels-Aldet reaction provides perhaps the most practical method, with a wide range of substrate types tested. Because of the large number of reports in this area, optimized conditions can now be applied which offer excellent regioselectivity and yields (see, for example, Equation (35) and Table 6). 

The nitro groups in 3,5-dinitrodiaryl ethers may be readily replaced with the residues of mono-and bis-phenols. The simplest 3,5-dinitrodiaryl ether - 3,5-dinitrodiphenyl ether - was reacted with 4-aminophenol or 4-acetamidophenol with the formation of 3-nitro-5-[4-amino(amido)]-phenoxydiphenyl ether subsequent transformation of this product led to 3-amino-5-(4-aminophenoxy)-diphenyl ether [24] (Scheme 4.9). 

Reactions with methylphenylcyclopropenone (154) provided an opportunity to compare the reactivities of the two different C—CO bonds. The reaction of 2-aminopyridines with methylphenylcyclopropenone (154) proceeded more slowly than with the diphenyl analog (153). In ether, formation of the ds-2-oxopyrido[l,2-a]pyrimidines (158 R1 = Me) and/or the imidazo[l,2-c<]pyridines (162) was observed, indicating that the cycloaddition proceeds via cleavage of the PhC—CO bond. The methyl-substituted trans-2-oxopyrido[l,2-a]pyrimidine (160 R1 = Me) was only detected in the reaction mixture of 2-amino-3-methylpyridine, where the H NMR spectrum exhibited signals assigned to 160 (R1 = Me, R = 9-Me). The compound was not isolated. The imidazo[l,2-a]pyridines (162) readily hydrolyzed to the acids (163), work-up therefore leading mainly to isolation of the acids. 

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