Phenols iodophenols

The emission yield from the horseradish peroxidase (HRP)-catalyzed luminol oxidations can be kicreased as much as a thousandfold upon addition of substituted phenols, eg, -iodophenol, -phenylphenol, or 6-hydroxybenzothiazole (119). Enhanced chemiluminescence, as this phenomenon is termed, has been the basis for several very sensitive immunometric assays that surpass the sensitivity of radioassay (120) techniques and has also been developed for detection of nucleic acid probes ia dot-slot. Southern, and Northern blot formats (121). 

A spore-forming strain of Desulfitobacterium chlororespirans was able to couple the dechlorination of 3-chloro-4-hydroxybenzoate to the oxidation of lactate to acetate, pyruvate, or formate (Sanford et al. 1996). Whereas 2,4,6-trichlorophenol and 2,4,6-tribro-mophenol supported growth with the production of 4-chlorophenol and 4-bromophenol, neither 2-bromophenol nor 2-iodophenol was able to do so. The membrane-bound dehalogenase contains cobalamin, iron, and acid-labile sulfur, and is apparently specific for ortho-substituted phenols (Krasotkina et al. 2001). 

CL reaction can be catalyzed by enzymes other than HRP (e.g., microperoxidase and catalase) and by other substances [hemoglobin, cytochrome c, Fe(III), and other metal complexes]. The presence of suitable molecules such as phenols (p-iodophenol), naphthols (l-bromo-2-naphthol), or amines (p-anisidine) increases the light production deriving from the HRP-catalyzed oxidation of luminol and produces glow-type kinetics [6, 7], The use of other enzymes, such as glucose-6-phosphate dehydrogenase [38-41], P-galactosidase [42], and xanthine oxidase [43-46], as CL labels has been reported. 

Although substituted phenols (e.g., para-iodophenol, para-phenylphenol, firefly luciferin, coumaric acid) are popular enhancers, in both luminol and acridan ester oxidation, enhancers with other functional groups [24], e.g., phe-nylboronic acids [25-28], phenothiazines [29], are also useful. As an example the structure of the phenothiazine enhancer used in the Supersignal substrate family is shown in Figure 6. 

In an alternative strategy functionalized phenols, such as iodophenol, were involved in palladium-catalyzed carbonylation of alkynes or allenes, producing coumarin or chromone derivatives (Scheme 23) [130-133]. After oxidative addition of the iodoarene to the Pd(0) catalyst the order of insertion of either CO or the unsaturated substrate mainly depends on the nature of the substrate. In fact, Alper et al. reported that CO insertion occurs prior to allene insertion leading to methylene- or vinyl-benzopyranone derivatives [130]. On the contrary, insertion of alkynes precedes insertion of CO, affording couma-rine derivatives, as reported by Larock et al. According to the authors, this unusual selectivity can be explained by the inability of the acyl palladium species to further react with the alkyne, hence the decarbonylation step occurs preferentially [131-133]. 

Problem 19.9 Devise practical laboratory syntheses of the following phenols from benzene or toluene and any inorganic or aliphatic compounds (a) m-iodophenol, (b) 3-chloro-4-methylphenol, (c) 2-bromo-4-methylphenol. 

It is reported that the palladium-catalysed intramolecular aromatization of 1,1 -dichloro-9/T-fluoren-9-yIidene (15) may lead to the formation of fullerene fragments.89 The amiulation reaction, under palladium catalysis, between iodoanflines and ketones may yield indole derivatives.90 There have also been studies of the palladium-catalysed carbonylation of o-iodophenols with allenes which may lead to l-benzopyran-4-one derivatives,91 of the intramolecular coupling of phenols with aryl halides,92 and of the intramolecular Heck aiylation of cyclic enamides.93... 

Removal rates greater than 90% were observed for all of the phenols studied. The decay kinetics for phenol p-methoxyphenol p-cresol p-fluo-rophenol p-chlorophenol p-bromophenol 4-hydroxyacetophenone a,a,a-trifluoro-p-cresol p-cyanophenol and p-iodophenol were found to be consistent with the Langmuir-Hinshelwood kinetic model. After employing all the substituents, little variation on the Langmuir-Hinshelwood kinetic parameters was observed. 

Hypoiodous acid is reported to be the sole iodine species capable of the iodination of phenols (Cofman, 1919). The iodophenol bed was over 90% efficient for trapping HOI (prepared by sparging from a dilute alkaline iodine solution) and less than 1% efficient for CH3I. Voilleque (1979) used this sampler to analyse effluents from Boiling Water Reactors and found 131I to be 11% particulate, 38% I2, 29% HOI and 22% organic. 

Iodophenol was first obtained as a by-product of the action of iodine on salicylic acid in alkaline solution or by heating iodo-salicylic acid.1 It has also been obtained by the action of iodine on phenol in alkaline solution2 or in the presence of mercuric oxide,3 or by the action of iodine monochloride.4 It is best prepared by the diazotization of -aminophenol and replacement of the diazonium group by iodine 5 although it has also been obtained from />-iodoaniline by diazotization and replacement of the diazonium group by hydroxyl.6... 

The regioselectivity in certain aromatic chlorinations by hypochlorite is also pH-depen-dent. The ortho/para ratio in phenol chlorination increased from 0.64 at pH = 4 to 4.3 at pH = 10794. Selective 4-chlorination of phthalic acid is obtained in aqueous sodium hypochlorite solution795. Iodination of phenols in aqueous systems is also pH-dependent and the ortho iodophenol yield grows at stronger basic media796,797. 

A laboratory synthesis of phenylated phenols has been developed by N. Kharasch and co-workers. They first introduced iodine in the 2-, 4- and/or 6-positions of phenol and then photolysed the iodophenols in the presence of benzene. Phenylated phenols in yields of 60-75% were found 57). 

Fig. 1.31. Reversed-phase gradient-elution scparalion of a mixture of phenols using binary linear gradients of methanol in water and of acetonitrile in water and a ternary gradient of methanol and acetonitrile in water optimised to attain improved. separation of the pairs of compounds 2 and 3, 8 and 9. Column LiChro.sorb RP-CI8. 5 pm, 300 x 4 mm i.d.. flow rate I ml/mtn detection UV, 254 nm. Sample compounds 4-cyanophenol (/). 2-methoxyphenol (2), 4-fluorophenol (i), 3-fluorophenol (4). m-cresol (5), 4-chlorophenol (6), 4-iodophenol (7), 2-phenylphenol (8) and 3-/err.-bulylphenol (9).

Phenol is a reducing agent and is capable of reacting with ferric salts in neutral to acidic solutions to form a greenish-colored complex. Phenol decolorizes dilute iodine solutions, forming hydrogen iodide and iodophenol stronger solutions of iodine react with phenol to form the insoluble 2,4,6-triiodo-phenol. 

V(Ce, X) populations are close to their values in the corresponding halobenzene however, there is a small electron transfer towards this basin for X = F, whereas the iodine atom undergoes an opposite effect. With respect to phenol, the regioselectivity of the electrophilic substitution is softened because as the OH and X = F, Cl, Br groups are both ortho-para directors, they contribute in opposite directions. As all the positional indices of CeHsI are positive, they are enhanced in the trans orf/io-iodophenol. The additive rule works satisfactorily for all positions as the largest discrepancy between estimated and calculated value does not exceed 0.002. 

The 3-X-phenols (X=C1, Br, I) protonated at the C4 and Cg positions are nearly isoenergetic their PAs are equal to 815 and 811 kJmol in 3-chlorophenol, 818 and 815 kJmoG in 3-bromophenol, and 823 and 820 kJmol in 3-iodophenol, whereas the C2-protonated species lie slightly higher in energy due to a steric repulsion with the OH group. 

In the case of 3-X-phenols, the X-protonated structures are local minima, but they are consistently above the high-energy ipio-protonated phenols, except for 3-iodophenol in which an ipio-protonation is less favourable by 13 kImol than an I-protonation. The calculated PAs for the X-protonated 3-halophenols are the following 613 kImoC for 3-fluorophenol, 676 kJmol for 3-chlorophenol, 680 kImoC for 3-Br-phenol and 704 kImoC for 3-iodophenol, using the same level of theory. 

The enhanced chemiluminescense obtained with the horseradish peroxidase-H202-luminol (139) system was applied to the development of a CLD biosensor for p-iodophenol, coumaric acid (26), 2-naphthol and hydrogen peroxide. The enzyme was immobilized by microencapsulation in a sol-gel matrix. LOD for the phenolic compounds were 0.83 p,M, 15 nM and 48 nM, respectively. A remote version of the enhanced biosensor was designed by directly immobilizing the enzyme on the tip of an optical fiber. This model was used for H2O2 assay. LOD was 52.2 p,M, with RSD 4.7% (w = 4) °. A bioluminescent response was obtained for phenols with pA a > 7 in the presence of a recombinant Escherichia coli strain, DPD2540, containing a fabA luxCDABE fusion this behavior may have analytical applications. 

---