P-Methoxybenzoic acid

Results of the sulfur tetrafluoride fluorination of benzenecarboxylic acids strongly depend on the nature of a benzene ring substituent Benzoic, toluic, and particularly p-methoxybenzoic acids give poor yields of the respective benzotri-... 

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. 

Quinoxalinediamine (172) and p-methoxybenzoic acid gave 2-p-methoxy-phenyl-17/-imidazo[4,5-/]quinoxaline (174) [neat synthon (2 equiv), 210°C,... 

In order to extend the scope of the reaction, and with the aim of designing a greener approach to the above set of reactions, we preformed the acylation of the same substrates with different acylation agents, such as maleic anhydride, p-methoxybenzoic acid and acetic acid (Scheme 48.4). Table 48.3 shows the results for acylation of benzenesulfonamide. 

Maleic anhydride p-methoxybenzoic acid Acetic acid ... 

A specific case of the carbonium ion mechanism [Eq. (5)] with reasonable plausibility is decarboxylation of metal arenoates by classic electrophilic aromatic substitution [Eq. (12)]. This mechanism would be favored by electron-donating substituents and has been invoked to explain the relative ease of decarboxylation of p-methoxybenzoic acid in molten mercuric trifluoroacetate (77) as well as the very facile decarboxylation on reaction of polymethoxybenzoic acids with mercuric acetate (18) (see below). 

Methoxychlor-DDE and p,p-dimethoxybenzophenone were formed when methoxychlor in water was irradiated by UV light (Paris and Lewis, 1973). Compounds reported from the photolysis of methoxychlor in aqueous, alcoholic solutions were p,p-dimethoxybenzophenone, p-methoxybenzoic acid, and 4-methoxyphenol (Wolfe et al., 1976). However, when methoxychlor in milk was irradiated by UV light (A. = 220 and 330 nm), 4-methoxyphenol, methoxychlor-DDE, p,p-dimethoxybenzophenone, and l,l,4,4-tetrakis(p-methoxyphenyl)-l,2,3-butatriene were formed (Li and Bradley, 1969). 

Methidathion oxon, see Methldathion Methiocarb sulfone, see Methlocarb Methiocarb sulfoxide, see Methiocarb Methionine, see Thiram Methoxyacetaldehyde, see Alachlor Methoxyacetic acid, see 1,4-Dioxane p-Methoxybenzaldehyde, see Methoxychlor p-Methoxybenzoic acid, see Methoxychlor... 

One compound may exist in more than one liquid crystal form. The structure of cholestryl myristate changes from solid to smectic A at 71 °C, to chiral nematic at 79 °C, and finally to an isotropic liquid at 85 °C. Figure 16.10 shows the transitions in p-methoxybenzoic acid. Note that the order increases with increased pressure and lower temperature. Liquid crystal phases are more densely packed than the... 

Phase diagram for p-methoxybenzoic acid. Data from S. Chandrasekhar, S. Ramase-shan, A. S. Reshamwala, B. K. Sadashiva, R. Sashudahar, and V. Surendranath, Proc. Internal Liquid Crystal Conf. (1973) 117. 

One great advantage of the decarboxylative halogenation with O-acyl esters of A-hydroxy-2-thiopyridone is that the reaction does not require any heavy metal such as Ag or Hg, unlike the Hunsdiecker reaction [24, 25]. Moreover, decarboxylative bromination of p-methoxybenzoic acid can be also carried out in good yield, while it does not proceed with the Hunsdiecker reaction instead, electrophilic bromination on the aromatic ring occurs. 

Kambara and Nishimura studied the hydrogenation of the methyl esters of o-, m-, and p-methoxybenzoic acid over platinum group metals in f-butyl alcohol at 60°C and atmospheric hydrogen pressure.197 As seen from the results shown in Table 11.15, hydrogenolysis occurred most extensively over platinum and iridium and much less extensively over rhodium and ruthenium, especially with the meta and para isomers. It is noted that the ortho isomer was hydrogenolyzed as extensively as the meta isomer over platinum and iridium, and much more extensively than the meta and para isomers over rhodium and ruthenium. Over Pd-C the most extensively hydrogenolyzed was the meta isomer. One of the reasons for the extensive hydrogenolysis in the case of the ortho isomer can be attributed to the direct formation of methyl benzoate, which amounted to 17.1% over rhodium, 20.7% over ruthenium, and 16.6% over platinum,... 

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