Carboxylic acid aromatic

AROMATIC CARBOXYLIC ACIDS Aromatic carboxylic acids may be prepared — 

By the oxidation of a side chain, provided the molecule contains no other groups (e.g., amino NH, and hydroxyl OH) which are affected by oxidising agaits, for example  

The last example illustrates nitration by means of fuming nitric acid with retention of the side chain. 

By the hydrolysis of nitriles. The nitrUes may be easily prepared either from amines by the Sandmeyer reaction (Section IV,66) or by the action of cuprous cyanide upon aryl halides (compare Section IV,163). Benzyl cyanide 

The hydrolysis of arylacetonitnles may be arrest at the arylacetamide stage by treatment with concentrated hydrochloric acid at about 40° thus benzyl cyanide yields phenylacetamide  

Aromatic compounds that have one or more carboxyl groups (-COOH) in their structure are called aromatic carboxylic acids. 

Aromatic carboxylic acids have boiling points higher than 100°C. They are colorless solid substances with a crystalline structure. They show similar properties to aliphatic carboxylic acids but they are only slightly soluble in water due to the benzene ring. They are more acidic than aliphatic carboxylic acids as the benzene ring increases their acidic character. 

By the malonic ester synthesis (compare Section 111,165), for example  

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Hofmann s amine synthesis can be applied to both aliphatic and aromatic carboxylic acid amides, benzamide, C HsCONH, thus giving aniline, C4H5NH,. 

Amino-aromatic carboxylic acids Unsaturated aromatic acid... 

Add dil. H2SO4 until the solution is acid to litmus. Cool, and scratch the sides of the vessel with a glass rod a white precipitate indicates an aromatic carboxylic acid or uric acid, or a solid phenol insoluble in water (e.g., i- or 2-naphthol). If a precipitate is obtained, filter off through a Buchner funnel, wash with water, recrystallise if necessary and identify. 

Note. Useful information can often be obtained by adding (i) dilute H,SO or (ii) dilute NaOH solution to an aqueous solution of the substance under investigation. A precipitate with (i) usually indicates an aromatic carboxylic acid from a metallic or from an ammonium salt. A precipitate or oil with (ii) usually indicates an aromatic amine from an amine salt. 

It should be noted that only representative substances are indicated in the above list. Substituted derivatives of the compounds in most classes may be encountered, e.g., nitrobenzoic acid in the aromatic carboxylic acids (p. 347). This acid will contain CH(0)N, but the salient properties are still those of a carboxylic acid, CH(0), Section 14, although the properties of an aromatic nitro-compound (e.g.y reduction to an amino-compound) will also be evident. 

Aromatic carboxylic acids are usually crystalline sohds, bum with a smoky flame, and are generally sparingly soluble in water. They may be detected and characterised as already described under Aliphatic Carboxylic Acids (Section 111,85). 

B3 the slow distillation of an aromatic carboxylic acid and acetic anhydride in the presence of a little phosphoric acid ... 

The melting points of some typical substituted aromatic amides are collected in Table IV,192. Other examples will be found in the appropriate columns of Tables IV,100A and B Primary and Secondary Aromatic Amines) and of Table IV,175 (Aromatic Carboxylic Acids). 

Sulfur Tetrafluoride and Aromatic Carboxylic Acids. Ben2otrifluorides also are prepared from aromatic carboxyhc acids and their derivatives with sulfur tetrafluoride (SF (106,107). Hydrogen fluoride is frequently used as a catalyst. Two equivalents of sulfur tetrafluoride are required ... 

Aromatic carboxylic acids can be purified by conversion to their sodium salts, recrystallisation from hot water, and reconversion to the free acids. 

Man-made mineral fibre Mixed hydrocarbons (C3 to CIO) m air Total hexavalent chromium compounds in air Aromatic carboxylic acid anhydndes m air... 

Both aliphatic and aromatic carboxylic acids are converted to their fluorides by FAR [78, 79, by the Ishikawa reagent [S/], and by fluoroaminosulfuranes such as DAST [128, 166] and its analogues [128]... 

Phenolic esters (1) of aliphatic and aromatic carboxylic acids, when treated with a Lewis acid as catalyst, do undergo a rearrangement reaction to yield ortho- and para-acylphenols 2 and 4 respectively. This Fries rearrangement reaction is an important method for the synthesis of hydroxyaryl ketones. 

C. Aromatic Carboxylic Acids (See the following derivatization procedures.)... 

METHYL GROUPS BY REDUCTION OF AROMATIC CARBOXYLIC ACIDS 83... 

Habid and Malek49 who studied the activity of metal derivatives in the catalyzed esterification of aromatic carboxylic acids with aliphatic glycols found a reaction order of 0.5 relative to the catalyst for Ti(OBu)4, tin(II) oxalate and lead(II) oxide. As we have already mentioned in connection with other examples, it appears that the activation enthalpies of the esterifications carried out in the presence of Ti, Sn and Pb derivatives are very close to those reported by Hartman et al.207,208 for the acid-catalyzed esterification of benzoic and substituted benzoic acids with cyclohexanol. These enthalpies also approach those reported by Matsuzaki and Mitani268 for the esterification of benzoic acids with 1,2-ethanediol in the absence of a catalyst. On the other hand, when activation entropies are considered, a difference exists between the esterification of benzoic acid with 1,2-ethanediol catalyzed by Ti, Sn and Pb derivatives and the non-catalyzed reaction268. Thus, activation enthalpies are nearly the same for metal ion-catalyzed and non-catalyzed reactions whereas the activation entropy of the metal ion-catalyzed reaction is much lower than that of the non-catalyzed reaction. 

The ionization of (E)-diazo methyl ethers is catalyzed by the general acid mechanism, as shown by Broxton and Stray (1980, 1982) using acetic acid and six other aliphatic and aromatic carboxylic acids. The observation of general acid catalysis is evidence that proton transfer occurs in the rate-determining part of the reaction (Scheme 6-5). The Bronsted a value is 0.32, which indicates that in the transition state the proton is still closer to the carboxylic acid than to the oxygen atom of the methanol to be formed. If the benzene ring of the diazo ether (Ar in Scheme 6-5) contains a carboxy group in the 2-position, intramolecular acid catalysis is observed (Broxton and McLeish, 1983). 

Summary qf kinetic results for the decomposition of metal salts of aromatic carboxylic acids [88,460,1109,1110]... 

Dimsyl anion 88 reacts with esters of aromatic carboxylic acids and aliphatic acids which do not have a readily transferable proton, to give /5-ketosulfoxides114,133,138-141. There are not many cases in which acyl chlorides were used142,143. However, the reaction... 

This procedure illustrates a general method for the preparation of aromatic carboxylic acids by oxidation of the corresponding alkylarenes.2 For example, 2-naphthoic acid (360 g., 93% yield m.p. 184-185°) was obtained from 2-methylnaphthalene (320 g., 2.25 moles), sodium dichromate (975 g., 3.26 moles, 45% excess), and water (1.81.). 

Oxidation, of acids to peroxy acids by hydrogen peroxide, 43, 96 of alkylarenes to aromatic carboxylic acids, 43, 80... 

Similarly, triphenylphosphine dichloride (TPPCI2) can activate aromatic carboxylic acids in pyridine through the formation of acyloxyphosphonium salts (Scheme 2.30).313 A side reaction between tire intermediate acyloxyphosphonium species and a second carboxyl endgroup leading to the formation of anhydrides has been reported.313 This chain-limiting reaction decreases tire molar mass, while the presence of anhydride linkages in tire chains adversely affects the thermal and hydrolytic stability of the final polyester. 

Thionyl chloride is another activating agent employed for reactions between aromatic carboxylic acids and phenols in pyridine solution. The mechanism suggested does not involve the formation of an acid chloride but assumes the existence of an intermediary mixed sulfinic anhydride which undergoes reaction with phenolic endgroups (Scheme 2.32).311... 

Decarboxylation reactions performed on activated or aromatic carboxylic acids, e.g., /1-keto acids, is a well-known synthetic transformation. However, the reaction has also been applied on other systems, e.g., N-carboxythiopyri-dones, N-acyloxyphthalimides and by thermolysis of peresters [104-106]. 

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