Para-chlorobenzoic acid

Case 2 - The Hyde Park Landfill site, located in an industrial complex in the extreme northwest corner of Niagara, New York, was used from 1953 to 1975 as a disposal site for an estimated 80,000 tons of chemical waste, including chlorinated hydrocarbons. A compacted clay cover was installed in 1978 over the landfill and a tile leachate collection system was installed in 1979. Hazardous compounds such as ortho-, meta- and para-chlorobenzoic acid toluene ortho- and meta-chlorotoluene 3,4-dichlorotoluene and 2,6-dichlorotoluene were detected in the leachate (Irvine et al., 1984). Since 1979, the existing leachate treatment system has used activated carbon as the technology for removing organic carbon. Although... 

Osol, A., Kilpatrick, M. (1933) The salting-out and salting-in of weak acids. I. The activity coefficients of the molecules of ortho, meta, and para chlorobenzoic acids in aqueous salt solutions. J. Am. Chem. Soc. 55, 4430-4440. 

A further interesting application of BEA zeolite is illustrated by the direct benzoylation of arenes with BACs. The synthetic method is the subject of a patent and shows very interesting properties by the eco-efficient point of view. As an example, a mixture of toluene, para-chlorobenzoic acid, and a little BEA (previously calcined at 400°C) pressurized with nitrogen to 2 x 10 Pa, heated to 200°C, and stirred for 4 h gives 4-chloro-4 -methylbenzophenone with 84% yield (Scheme 4.11). 

It is also important to determine the point in a reaction sequence at which a substituent should be chemically modified. In the synthesis of para-chlorobenzoic acid from toluene, the methyl group is oxidized after it directs the chloro substituent to the para position. (orf/zo-Chlorobenzoic acid is also formed in this reaction.)... 

It is often possible in these cases to predict the correct isomer. In many cases, the groups already on the ring reinforce each other. Thus, 1,3-dimethylbenzene is substituted at the 4 position (ortho to one group and para to the other), but not at the 5 position (meta to both). Likewise the incoming group in p-chlorobenzoic acid goes to the position ortho to the chloro and meta to the carboxyl group. 

The reactivity of aromatically bound halogen is increased by nitro-groups in the ortho- and para-positions likewise the chlorine in o-chlorobenzoic acid is rather loosely held. 

Mercaptobenzoic acids (ortho, meta and para isomers) were prepared in fair to good yields from the reaction of the chlorobenzoic acids with elemental sulfur and molten NaOH-KOH (1 1 molar ratio) at 270 "C for 3 min. Both 2- and 4-chloropyridine gave the mercaptopyridines by an analogous procedure.198 Use of selenium instead of sulfur gave poor yields and mixtures of isomeric products. 

Nitration of p-chlorobenzoic acid gives the desired product, because the directing effects of the chlorine (ortho, para) and the carboxyl (meta) groups reinforce each other. 

In recent years some studies were performed using submerged membrane modules coupled to photocatalytic systems for the removal of organic pollutants such as fulvic acid [84], bisphenol-A [85], para-chlorobenzoate [86]. 

Aqueous sodium xylenesulfonate has been used to extract fragrances, such as 2-phenylethanol, as a mild replacement for the usual steam distillation.249 The alcohol was recovered by dilution with additional water. The hydrotrope could be reused after concentration of the aqueous phase. A mixture of ortho- and para- c h 1 o r o b e n z o i c acids was separated by dissolving the ortho isomer in water containing sodium 2-butoxyethyl sulfate.250 The o chlorobenzoic acid was recovered by diluting the extract with more water to precipitate it. Base-catalyzed condensations (8.38) have been carried out with the aid of sodium 2-butoxyethylsul-fate or sodium p loluenesulfonale as hydrotropes.251... 

The relation between the constant of the para acid and that of the ortho or meta acid varies with the nature of the substituent. While p-nitrobenzoic acid is a slightly stronger acid than m-nitro-benzoic acid, the constant of p-chlorobenzoic acid is only about one-half that of the meta acid. The case of p-hydroxybenzoic acid is a striking one while o-hydroxybenzoic acid and m-hy-droxybenzoic acid are more highly ionized than benzoic acid, the constant of the para acid is less than half that of benzoic acid. A satisfactory explanation of such facts as these would, no doubt, materially advance organic chemistry. The effect of a phenyl radical on a carboxyl group in a side-chain, is shown by the constants for phenylacetic acid, hydrocinnamic acid, and cinnamic acid. 

The Hammett eqnation is the best known and most widely stndied of the various linear free energy relations for correlating reaction rate and equilibrium constant data. This equation was first proposed to correlate the rate constants and equilibrium constants for the side chain reactions of para- and me/a-substituted benzene derivatives. Hammett (37-39) noted that for a large number of reactions of these compounds plots of log k (or log K) for one reaction versus log k (or log K) for a second reaction of the corresponding member of a series of such derivatives was reasonably linear. Figure 7.5 is a plot of this type involving the ionization constants for phenylacetic acid derivatives and for benzoic acid derivatives. The point labeled p-C has for its ordinate log for p-chlorophenyl acetic acid and for its abscissa log for p-chlorobenzoic acid. 

The acidic product generated in the reaction is assumed to be 4-chlorobenzoic acid. This material also is a para-substituted aromatic compound thus, the spectrum of this compound (Fig. 6.17) possesses a macro frequency train (a), similar to those of the aldehyde and alcohol. In addition, this benzoic acid derivative exhibits an extended aromatic acid macro group frequency train (b).The macro frequencies are as follows ... 

Figure 8.3 (a) The layered structure of aromatic acid salts. The cleavage plane exposes the apolar side of the molecules. The polar parts, with the acid moieties and M cations, are bnried. The cleavage plane properties (e.g., hydrophobicity) and unit-cell parameters can be modulated to some extent by the nature (f-butyl, chlorine, etc.) and also by the position (ortho, meta, or para) of the substituent X. Reproduced from Reference [11] with permission of Pergamon Press, (b) Combined diffraction pattern of poly(ethylene terephthalate) and the sodium salt of p-chlorobenzoic acid. The salt reflections are sharp spots the PET reflections are more arced. The contact plane of PET is (100) the chain axis is vertical. 

A concerted elimination-cyclization mechansim, involving a sulfenyl halide in a 1,3-butadiene-1-thio system, is the most probable mechanism for the formation of benzo[6 Jthiophenes from cinnamic acids or 4-aryl-2-butanones by treatment with thionyl chloride. The reactions shown in Scheme 5 have been carefully worked out, and the intermediates isolated (75JOC3037). The unique aspect of this synthesis is the reduction of the sulfinyl chloride (a) by thionyl chloride to form the sulfenyl chloride (b). The intermediate (b) was isolated and converted in pyridine to the 3-chlorobenzo[6]thiophene-2-carbonyl chloride in 36% yield (73TL125). The reaction is probably initiated by a sulfenyl ion attack on the aromatic ring, since it is promoted by electron-releasing groups para to the site of ring closure. For example, when X in (36) was N02, a 23% yield of (37), a mixture of 5-and 7-nitro derivatives, was obtained, but when X in (36) was OMe, a 54% yield of (37) was obtained, contaminated with some 3,4-dichloro-5-methoxybenzo[6]thiophene-2-carboxylic acid. 

The effect of para-substituents on the rate of exchange of benzoic acid was examined by Bender etal. (1956). Small differences were found in the rates of exchange of m- and p-chlorobenzoic, -anisic, p-toluic, mesitoic and benzoic acids in acid solution (see Table 7). No simple correlation between rates and electronic effects of the substituents could be found. 

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