Biphenyl structures

Polychlorinated biphenyls structure, retention times, response factors, and octanol/water partition coefficients (log Kow)... 

Table 24.2 (continued) Polychlorinated Biphenyls Structure, Retention... 

The degradation products of GOG were (Vm), GC -Dimer, vanillin (II), and dehydrodivanillin (X). The reaction of GOG by laccase III, therefore, brings about the formation of biphenyl structures, the cleavage of C-C bond between a- and -carbons, and the cleavage of -0-4 ether linkages. The mode of these cleavages is similar to that of SOG. 

Table 24.2 Polychlorinated Biphenyls Structure, Retention Times, Response Factors, and Octanol/Water Partition Coefficients (log K J... 

Formation and Degradation of Biphenyl Structures During Alkaline Oxidation of Phenols with Oxygen... 

Our studies were concerned with the reactions occurring during mild oxidation. This paper deals with model experiments on one of the possible reaction sequences—namely, the formation of biphenyl structures and oxidative degradation. Numerous oxidation experiments with suitable lignin models were performed, and during these studies we determined the rate of oxygen consumption by the compounds dissolved in 0.27V NaOH at 70°C. A detailed description of our method is given under Experimental. 

Carbon-0-carbon coupling might, of course, also be considered in the case of lignin oxidation. Because there is no accurate method for determining biphenyl structures in lignins, the extent of such couplings could not be estimated. 

The isolation of 2,2 -dihydroxy-3,3 -dimethoxy-5,5 -dialkylbiphenyls from both neutral (IS) and alkaline hydrogenation supports Pew s proposal that the biphenyl structure is of considerable importance in lignin... 

Racemic l,ll-dimethyl-5,7-dihydrodibenzo[c,< ]thiepine A-oxide 24 and A,A-dioxide 25 and 10,12-dihydro-4/7,6/7-[2]benzothiepino[6,5,4- i/][2]benzothiepine 30, based on bridged biphenyl structures, were resolved into enantiomers by chromatography on swollen microcrystalline TAC <2000HCA479>. The first-eluted enantiomers were assigned to have the (A)-configuration by comparison of the experimental CD spectra with spectra calculated by the CNDO/S method (see also Sections 13.03.3.1 and 13.03.3.3). 

M. Franek, M.V. Pouzar and V. Kolar, Enzyme-immunoassays for polychlorinated biphenyls. Structural aspects of hapten-antibody binding, Anal. Chim. Acta, 347 (1997) 163-176. 

This unique phenomenon provides a powerful strategy in the molecular design of chiral catalysts that is, the requisite chirality can be served by the simple binaphthyl moiety, while an additional structural requirement for fine-tuning of reactivity and selectivity can be fulfilled by an easily modifiable achiral biphenyl structure. This certainly obviates the use of two chiral units, and should be appreciated in the synthesis of a variety of chiral catalysts with different steric and/or electronic properties. Actually, quaternary ammonium bromide possessing a sterically demanding substituent such as (S)-12b can be easily prepared, and benzylation with (S)-12b as catalyst gave 9 in 95% yield with 92% ee. Further, theenantioselectivity was enhanced to 95% ee with (S)-12c as a catalyst [12]. 

Very recently, Maruoka and co-workers described a new N-spiro quaternary ammonium bromide with two chiral biphenyl structures as easily modifiable subunits [37]. These phase-transfer catalysts with biphenyl subunits, containing methyl groups in the 6,6 -position for inducing chirality, and additionally bulky substituents in the 4-position, efficiently catalyzed the alkylation of protected glycinate with high enantioselectivity of up to 97% ee. The substrate range is broad, for example (substituted) benzyl bromide and allylic and propargylic bromides are tolerated [37]. 

Name 4,4 -Bis-(p-methoxybenzylidene amino)-3,3 -dichloro biphenyl Structure ... 

Biphenyl structures and a-carbonyl-p-aryl ether structures, which are both assumed to be present in native lignin with a higher abundance than coniferyl alcohol structures (22,23) and both considered to be important leucochromophores, were not observed among die products, presumably because they are not present in spruce lignin as end groups. Both these types of structures are very stable and unlikely to be structurally changed during mild acid hydrolysis (24). 

In a recent paper, the same authors showed that iron(III) chloride can mediate the oxidative coupling of substituted aryl ethers with an observed regioselectivity that depends on the substitution pattern [66] meta-substituted phenol ethers 77 led to polymers (Scheme 18a) whereas para-substituted phenol ether 79 gave predominantly biphenyl structures (Scheme 18b). ortho-Substituted phenol ether 81 provided a dimer with the Ar-Ar bond at a position para to one of the methoxy substituents (Scheme 18c). 

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