4-Halophenol

Halophenols without 2,6-disubstitution do not polymerize under oxidative displacement conditions. Oxidative side reactions at the ortho position may consume the initiator or intermpt the propagation step of the chain process. To prepare poly(phenylene oxide)s from unsubstituted 4-halophenols, it is necessary to employ the more drastic conditions of the Ullmaim ether synthesis. A cuprous chloride—pyridine complex in 1,4-dimethoxybenzene at 200°C converts the sodium salt of 4-bromophenol to poly(phenylene oxide) (1) ... 

Other halophenols are miticides, bactericides, and leather preservatives. Halophenols account for about 5% of phenol uses. 

Other salts, especially fluoride salts, (e.g., KF) can be used to perform nucleophilic substitution. As is well known, halides, and particularly the fluoride anions, are rather powerful Lewis bases and can exert a catalytic effect on aromatic nucleophilic substitutions in dipolar aprotic solvents. Phenols can be alkylated in the presence of KF (or CsF) absorbed on Celite64,65 or Et4NF.66 Taking advantage of this reaction, halophenols and dihalides with bisphenols have been successfully polymerized in sulfolane at 220-280°C by using KF as the base. 

Halophenols are easier to dispose of by extraction. Chlorophenyl esters are resistant to hydrogenation and are hence compatible with benzyloxycarbonyl. Benzotriazolyl esters are unique in that they exist in two different forms (see Section 7.17). They are too reactive for routine use but are often employed without isolation after their preparation, using a carbodiimide or other (see Section 7.20). An exception to this are the benzotriazolyl adducts of. V-lrilylamino acids that are amide oxides (see Section 7.17), which are stable to aqueous sodium hydroxide but undergo aminolysis normally. 

Brooks, S.J., Doyle, E.M., Hewage, C., Malthouse, J.P.G. and O Connor, K.E., Biotransformation of halophenols using crude cell extracts of Pseudomonas putida F6. Appl. Microbiol. Biotechnol., 2004, 64, 486. 

A convenient preparation of dihydrobenzofurans has been achieved from the appropriately functionalized ort/ o-halophenol derivatives. Treatment of the aryl iodide (5)-33 with (TMS)3SiH and EtsB in the presence of air at room temperature, gave the aryl radical which cyclized in a 5-exo-trig mode and provided the bicyclic derivatives 34/35 as a 29 1 mixture of diastereoisomers in favour of 34 (Reaction 7.40) [51]. 

Tetrachlorodibenzo-p-dioxin (TCDD) is believed to be a byproduct in chemical processing generated by a halophenol or chlorobenzene starting material. An intermediate reaction will occur at an elevated temperature (equal to or greater than 160°C), an alkaline condition, or in the presence of a free halogen. The end reaction results in either direct dioxin, intermediate dioxin, or predioxin formation that will ultimately form dibenzo-p-dioxins [10]. TCDD is suspected in wastewaters from pesticide manufacture that uses such raw materials as 2,4,5-trichlorophenol (2,4,5-T) and 1,2,4,5-tetra-chlorobenzene, which are characteristic of TCDD precursors. A TCDD level as high as 111 mg/L has been found in drums of waste from the production of the pesticide 2,4,5-T. 

In contrast to the high reactivity of meta- and para-substituted halophenols, ortho-halo-phenols give low yields, even after prolonged reaction times with the [Rh(COD)Cl]2/... 

Halogenated Aromatic Compounds Halogenated Cresols Halogenated Ethers and Epoxides Halogenated Phenolic Compounds Halophenols Chlorophenol Dichlorophenol Halophenols Pentachlorophenol PCP Tetrachlorophenol Trichlorophenol... 

Chlorobenzene Monochlorobenzene under Ring-Substituted Aromatics Chloroform Tiichloromethane under Saturated Alkyl HaUdes Chloromethane Methyl Chloride under Saturated Alkyl Halides Chlorophenol under Halophenols Chlorotoluene, 2 under Ring-Substituted Aromatics... 

Dichloromethyl, 1,1, Ether Methyl-dichloro-1,1 Ether under Dihalogenated and Polyhalogenated Ethers Dichlorophenol under Halophenols... 

Tetracblorobenzene under Ring-Substituted Aromatics Tetracbloroethane, 1,1,2,2 under Saturated Alkyl Halides Tetracbloroethene Percbloroethylene PCE under Unsaturated Alkyl Halides Tetracblorophenol under Halophenols... 

Cabovska B., Kreishman, G. R, Wassell, D. R, and Stalcup, A. M., GE and NMR studies of interactions between halophenols and ionic liquid or tetraalkylam-monium cations, J. Chromatogr. A, 1007,179-187,2003. 

Figure 16.3 Biodegradability of halophenols and polycyclic aromatic hydrocarbons [2].

King, G. M. (1988). Dehalogenation in marine sediments containing natural sources of halophenols. Applied and Environmental Microbiology, 54, 3097-185. 

The reaction is extremely rapid, being substantially complete in less than one minute at room temperature. A similar reaction occurs with 2.6-dimethyl-4-chlorophenol. Kurian and Price 53) also polymerized several other 2.6-disubstituted-4-halophenols (Table 3). Only low molecular weight polymers (as measured by intrinsic viscosity) appear to have been obtained. 

In a recent patent Stamatoff (76) has described the polymerization of unsymmetrically substituted halophenols in a manner similar to that described by Price, using as initiators peroxides or persulfates. 

It is reasonable to assume that the polymerization of halophenols as described by Price proceeds through similar intermediates. The formation of 2.6-dimethylbenzoquinone (67) as a byproduct could then reasonably result from hydrolysis of the intermediate (XXVII). This then would also explain the necessity of using large amounts ( 10 mole percent) of initiator in the polymerization since initiator would be used up in this reaction. 

The formation of 3-halophenols in the metabolism of chlorobenzene, bromobenzene, and fluorobenzene215 cannot be explained on the basis of arene oxides as intermediates. These metabolites may represent examples of a direct hydroxylation of the ring. Besides, the magnitude of the isotopic effects observed during the metabolic formation of such meta-substituted phenols... 

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