Ortho-carboxylate group

The reverse reaction is an intramolecular acidolysis of amide group by the o-carboxyhc acid to reform anhydride and amine. This unique feature is the result of an ortho neighboring effect. In contrast, the acylation of an amine with ben2oic anhydride is an irreversible reaction under the same reaction conditions. The poly(amic acid) stmcture (8) can be considered as a class of polyamides. Aromatic polyamides that lack ortho carboxylic groups are very... 

This would mean that in DMSO and other aprotic solvents a proton is transferred from the amino group to the ortho-carboxylate group. 

Poly(amic acids) in which the ortho-carboxylic group has been chemically modified to either an ester- or amide moiety have been known for many years. However, their commercial significance was non-existent until very recent applications involving dielectric insulators [48] and photosensitive polyimide precursors [49, 50]. As with many synthetic pathways, there are generally several ways to arrive at the same goal. Similarly, the preparation of derivatized poly(amic acids) can be divided into two general categories ... 

S-Arylthioglycolic acids possessing an ortho carboxyl group (77 R = R = H) are cyclized by acetic anhydride or base to the corresponding thioindoxyl-2-carboxylic acids (78 R = H) (method c), which often lose carbon dioxide spontaneously to give the thio-indoxyls (Table V).315 S>-(o-Cyanophenyl)thioglycolic acids give similar products on treatment with alkali (method d) (Table V).315... 

Almost all phenol compounds in aqueous alkaline solution display a marked bathochromic shift and usually (but not always) an increase in absorption (symbol 7i) comparison with solution in methanol, as result of ionisation. Salicylic acid [1105] is an exception the influence of the free ortho-carboxyl group predominates. Salicylic acid esters [703] display the alkali shift again. Ortho-diphenols are unstable in alkaline solution and can therefore hardly be measured. 

Mixed backbones covering a phenolic hydroxy group as well as an ortho-carboxylic group as found, for example, in salicylic acid were likewise used by Selent and Borner [44] for the construction of cyclic mixed anhydrides ( acylphosphites ) (Figure 2.17). 

Table 19 3 lists the ionization constants of some substituted benzoic acids The largest effects are observed when strongly electron withdrawing substituents are ortho to the carboxyl group An o nitro substituent for example increases the acidity of benzoic acid 100 fold Substituent effects are small at positions meta and para to the carboxyl group In those cases the values are clustered m the range 3 5-4 5... 

Synthetic phenol capacity in the United States was reported to be ca 1.6 x 10 t/yr in 1989 (206), almost completely based on the cumene process (see Cumene Phenol). Some synthetic phenol [108-95-2] is made from toluene by a process developed by The Dow Chemical Company (2,299—301). Toluene [108-88-3] is oxidized to benzoic acid in a conventional LPO process. Liquid-phase oxidative decarboxylation with a copper-containing catalyst gives phenol in high yield (2,299—304). The phenoHc hydroxyl group is located ortho to the position previously occupied by the carboxyl group of benzoic acid (2,299,301,305). This provides a means to produce meta-substituted phenols otherwise difficult to make (2,306). VPOs for the oxidative decarboxylation of benzoic acid have also been reported (2,307—309). Although the mechanism appears to be similar to the LPO scheme (309), the VPO reaction is reported not to work for toluic acids (310). 

Reactions of the Carboxyl Groups. Carboxyl groups in the ortho position spontaneously form a strainless ftve-membered ring when heated to give anhydrides as shown for (8). Salts and esters (4) are readily formed as shown for (4) and (5), respectively. 

Phtha/k anhydride is the most important type of dibasic acid derivative ki alkyd preparation because of its low cost and the excellent overall properties it imparts to the reski. The anhydride stmcture allows a fast esterification to form half-esters at relatively low reaction temperatures without hberatkig water, thereby avoiding the danger of excessive foaming ki the reactor. However, skice the two carboxyl groups of phthaUc anhydride are ki the ortho position to each other on the benzene ring, cycHc stmctures may and do occur ki the reski molecules. 

Decarboxylation of sahcyhc acid takes place with slow heating because of the presence of the electronic configuration of the carboxyl group ortho to the hydroxyl group, but does not occur in the other isomers of hydroxyben2oic acid. On rapid heating, sahcyhc acid sublimes because of its low vapor pressure. This property allows commercial separation from the other isomers as a means of purification analogous to distillation. The differences ia the vapor pressures are shown ia Table 4. 

A hydroxyl group is situated ortho to a carboxyl group which as a bidentate ligand is terminally metallized on the fiber when aftertreated with dichromate. An example is Alizarine Yellow GG [584-42-9] (50) (Cl Mordant Yellow 1 Cl 14025). Cr(III) has a coordination number of six, and therefore normally two dye molecules of the sahcyhc type are chelated to the metal ion. 

The hydroxyl group of the resulting phenol is situated immediately adjacent to where the carboxyl group was previously located. This same Hquid-phase copper oxidation process chemistry has been suggested for the production of cresols by the oxidation of toluic acids. y -Cresol would be formed by the oxidation of either ortho or para toluic acids a mixture of 0- and -cresols would be produced from y -toluic acid (6). A process involving the vapor-phase catalytic oxidation of benzoic acid to phenol has been proposed, but no plants have ever been built utilizing this technology (27). 

Substitutions that displace electrons toward the carboxyl group of aromatic acids diminish the rate of the reaction (16). The substitution of fluoromethoxy or ethoxy groups in the ortho position has an accelerating action, whereas iodo, bromo, nitro, or methyl groups produce retardation. The influence of groups in the meta and para positions is not nearly so marked (17). 

When a positively charged substituent such as the trimethylam-monio group is anywhere on the ring, but most effectively when it is ortho to the leaving group, it can favorably affect the entropy of activation with anionic nucleophiles and accelerate reaction. A recent example of reagent-substituent interaction is the electrophilic substitution of 2-carboxybiphenyl, nitration (non-polar solvent) of which occurs only at the 2 -position and not the 4 -position and has been postulated to be due to the interaction of the nitronium ion with the carboxyl group. 

Sodium pyrazolate and 3,5-dimethylpyrazolate, [( " -cod)Rh(/A-Cl)]2, carbon monoxide, 3-(diphenylphosphino)benzoic acid, or (2-formylphenyl)diphenyl-phosphine give rise to complexes 120 (R = H, Me) and 121 (R = H, Me) [94JOM(469)213]. However, 2-(diphenylphosphino)benzoic acid (the carboxyl group in the ortho position) leads to formation of the mononuclear complexes 122. The products appear to be catalysts for hydroformylation reactions [93MI2]. 

Carboxylic acids, particularly aromatic acids with a methyl group ortho to the carboxyl group Aliphatic ethers with one alkyl group containing more than eight carbons... 

Aromatic acids with methyl groups ortho to the carboxyl groups... 

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