Methoxybenzoic acid complexes

An example of a reaction series in which large deviations are shown by — R para-substituents is provided by the rate constants for the solvolysis of substituted t-cumyl chlorides, ArCMe2Cl54. This reaction follows an SN1 mechanism, with intermediate formation of the cation ArCMe2 +. A —R para-substituent such as OMe may stabilize the activated complex, which resembles the carbocation-chloride ion pair, through delocalization involving structure 21. Such delocalization will clearly be more pronounced than in the species involved in the ionization of p-methoxybenzoic acid, which has a reaction center of feeble + R type (22). The effective a value for p-OMe in the solvolysis of t-cumyl chloride is thus — 0.78, compared with the value of — 0.27 based on the ionization of benzoic acids. 

N-arylation has been used as the first step in several syntheses of complex molecules. The Ullmann-type reaction of 2-iodo-3-methoxybenzoic acid with l-methylpiperazine-2,5-dione forms the basis of Kishi s total synthesis of dehydrogliotoxin (81T2045) (Scheme 12). 

Let us now look at a more complex spin system, in which we have two different coupling constants to the same proton. In the trisubstituted aromatic 3-amino-4-methoxybenzoic acid shown in Figure 4.18, we have an AMX spin system and this leads to a 1,3- (or meta) coupled doublet for at 6 7.26, a 1,2- (or ortho) coupled doublet for at 5 6.85 and a... 

The photoelectro-Fenton method [98] complements the photo-Fenton and electro-Fenton reactions. In the latter, a potential is applied between two electrodes immersed in a solution containing Fenton reagent and the target compound. The recent study of the herbicide 2,4,5-T, performed in an undivided cell with a Pt anode and an 02-diffusion cathode, showed that the photo-electrochemical process was more powerful than the electro-Fenton process, which can yield only about 60-65% of decontamination. The electro-Fenton method provides complete destruction of all reaction intermediates, except oxalic acid, which, as already mentioned, forms stable complexes with Fe3+ that remain in the solution. The fast photodecarboxylation of such Fe(III)-oxalate complexes by UV fight explains the highest oxidative ability of the photoelectro-Fenton treatment, which allows a fast and total mineralization of highly concentrated acidic aqueous solutions of 2,4,5-T at low current and temperature. A similar behavior was found for the herbicide 3,6-dichloro-2-methoxybenzoic acid [99]. 

Another representative system is the induction of mesomorphism by the self-assembly of nonmesogenic H-bonding components. Complexation of 4-methoxybenzoic acid (2, n = ) and 4,4 -bipyridine (4) results in the formation of novel hydrogen-bonded mesogen 5 [ 2 (n = l)/4] (Fig. 4). A nematic phase is observed for 5 between 153 and 163 °C [31, 32]. 

To get a complex set of substituents by direct derivatization of benzotriazole is not feasible. In such situations, it is better to have all the substituents in place first and later construct the heterocyclic ring. High reactivity of anilines and their well-developed chemistry makes them good stating materials. In an example shown in Scheme 215, acetanilide 1288 is nitrated to afford nitro derivative 1289 in 73% yield. Catalytic reduction of the nitro group provides methyl 4-acetylamino-3-amino-5-chloro-2-methoxybenzoate 1290 in 96% yield. Nitrosation of compound 1290 in diluted sulfuric acid leads to intermediate 1291, which without separation is heated to be converted to 7-chloro-4-methoxy-l//-benzotriazole-5-carboxylic acid 1292, isolated in 64% yield <2002CPB941>. 

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