Unsaturated aromatic acids

Amino-aromatic carboxylic acids Unsaturated aromatic acid... 

The chemical properties of coumarin are those of the lactone of an a,P-unsaturated aromatic acid. 

Cinnamic Alcohol.—The latter alcohol yields an unsaturated aromatic acid known as cinnamic acid (p. 697), and the alcohol is thus known as cinnamic alcohol. Phenyl ethyl alcohol, CeHs—CH2—CH2 —OH, is a constituent of oil of rose and has the characteristic odor of roses. 

Perkin Synthesis of Coumarin.—Coumaric acid and coumarin may be synthesized by the Perkin reaction for synthesizing unsaturated aromatic acids (p. 698). These syntheses are of historical interest as the two compounds obtained were the first onesprepared by this reaction. Instead of taking a simple aromatic aldehyde it is only necessary to take a phenol aldehyde viz., salicylic aldehyde,... 

There are a few efficient methods for the stereoselective synthesis of vinyl halides, and this transformation remains a synthetic challenge. Research by S. Roy showed that the Hunsdiecker reaction can be made metal free and catalytic catalytic Hunsdiecker reaction) and can be used to prepare ( )-vinyl halides from aromatic a,p-unsaturated carboxylic acids. The unsaturated aromatic acids were mixed with catalytic amounts of TBATFA and the A/-halo-succinimide was added in portions over time at ambient temperature. The yields are good to excellent even for activated aromatic rings which do not undergo the classical Hunsdiecker reaction. The fastest halodecarboxylation occurs with NBS, but NCS and NIS are considerably slower. The nature of the applied solvents is absolutely critical, and DCE proved to be the best. This strategy was extended and applied in the form of a one-pot tandem Hunsdiecker reaction-Heck coupling to prepare aryl substituted (2 ,4 )-dienoic acids, esters, and amides. 

Cinnamic Acid, C6H5.CH = CH.COOH, is the most important member of the class of unsaturated aromatic acids. It occurs in oil of cinnamon, the balsams of Peru and Tolu, gum-benzoin, storax, and the leaves, of certain plants. The acid crystallizes from hot water, melts at 134°, and boils with partial decomposition at 300°. 

Data on salts of unsaturated aromatic acids are rather limited. One example is uranyl vinylbenzoate U02(VBA)2 [32]. 

Formation of carboxylic acids ami their derivatives. Aryl and alkenyl halides undergo Pd-catalyzed carbonylation under mild conditions, offering useful synthetic methods for carbonyl compounds. The facile CO insertion into aryl- or alkenylpalladium complexes, followed by the nucleophilic attack of alcohol or water affords esters or carboxylic acids. Aromatic and a,/ -unsaturated carboxylic acids or esters are prepared by the carbonylation of aryl and alkenyl halides in water or alcohols[30l-305]. 

These are highly purified petroleum products which have been fully refined by either acid treatment or hydrogenation to remove all unsaturates, aromatics, and coloring materials to meet JnitedSfates Pharmacopoeia (USP) requirements. 

Physical and Chemical Properties. The (F)- and (Z)-isomers of cinnamaldehyde are both known. (F)-Cinnamaldehyde [14371-10-9] is generally produced commercially and its properties are given in Table 2. Cinnamaldehyde undergoes reactions that are typical of an a,P-unsaturated aromatic aldehyde. Slow oxidation to cinnamic acid is observed upon exposure to air. This process can be accelerated in the presence of transition-metal catalysts such as cobalt acetate (28). Under more vigorous conditions with either nitric or chromic acid, cleavage at the double bond occurs to afford benzoic acid. Epoxidation of cinnamaldehyde via a conjugate addition mechanism is observed upon treatment with a salt of /-butyl hydroperoxide (29). 

This reaction was also extended to other aromatic aldehydes for the preparation of a,P unsaturated carboxyUc acids. Several mechanisms of the reaction have been proposed (45). The most accepted mechanism iavolves the reaction of the aldehyde with the enol form of the acid anhydride which is promoted by the presence of the sodium salt or of another base. The resulting reaction product is then dehydrated iato an unsaturated carboxyUc acid. 

The aldol-like reaction of an aromatic aldehyde 1 with a carboxylic anhydride 2 is referred to as the Perkin reaction. As with the related Knoevenagel reaction, an o ,/3-unsaturated carboxylic acid is obtained as product the /3-aryl derivatives 3 are also known as cinnamic acids. 

A surprising exception has been reported with evidence for a cleavage reaction in the case of divinyl sulphone. In non-aqueous and slightly acidic media, the behaviour of a., ji-unsaturated aromatic sulphones is also complex (see Table 7) since the cleavage and the saturation may compete. Strongly electrophilic double bonds undergo Michael additions in aprotic solvents by slowly protonated anions. Transfer of labile hydrogen may also lead to unactivated bases. It is noteworthy that in numerous cases (Table 6) the saturation is the preferred route. 

The compounds implicated in allelopathy have been divided into chemical classes by recent reviewers (4, 20). They can be arbitrarily classed as (A) hydrocarbons, (B) organic acids and aldehydes, (C) aromatic acids, (D) simple unsaturated lactones,... 

The decarboxylation of carboxylic acid in the presence of a nucleophile is a classical reaction known as the Hunsdiecker reaction. Such reactions can be carried out sometimes in aqueous conditions. Man-ganese(II) acetate catalyzed the reaction of a, 3-unsaturated aromatic carboxylic acids with NBS (1 and 2 equiv) in MeCN/water to afford haloalkenes and a-(dibromomethyl)benzenemethanols, respectively (Eq. 9.15).32 Decarboxylation of free carboxylic acids catalyzed by Pd/C under hydrothermal water (250° C/4 MPa) gave the corresponding hydrocarbons (Eq. 9.16).33 Under the hydrothermal conditions of deuterium oxide, decarbonylative deuteration was observed to give fully deuterated hydrocarbons from carboxylic acids or aldehydes. 

Lipids from marine products have been studied less frequently. The detection of co-(o-alkylphenyl)alkanoic acids with 16,18 and 20 carbon atoms together with isoprenoid fatty acids (4,8,12-trimethyltetradecanoic acid and phytanic acid) and substantial quantities of bones from fish and molluscs has provided evidence for the processing of marine animal products in vessels [58 60]. C16, C18, and C20 co-(o-alkylphenyl)alkanoic acids are presumed to be formed during the heating of tri-unsaturated fatty acids (C16 3, C18 3 and C20 3), fatty acyl components of marine lipids, involving alkali isomerization, pericyclic (intermolecular Diels-Alder reaction) and aromatization reactions. 

Polyester polyols, 25 464 468 Polyester resin(s), 11 302 coating resins, 7 104-106 cyclopentadiene and dicyclopentadiene applications, 8 230 flammability of, 20 115-116 properties in powder coating, 7 43t standard test methods for, 20 11 It unreinforced, 10 187t weathering of, 20 116 Polyester resin-based powder coatings, organic titanium compounds in, 25 125 Polyester resin composites, 26 762-763 Polyester resin formulations ingredients of, 20 96t unsaturated, 15 511-512 Polyesters, 10 185-189, 497 12 655-656. See also Thermoplastic polyesters Unsaturated polyesters acid resistance of, 20 7-8 antioxidant applications, 3 121 aromatic ionic, 23 722 based on 1,4-cyclohexanedimethanol, 12 674-675... 

The phthalic anhydride based resins were the first developed useful unsaturated resins. Using phthalic anhydride offers resin producers the flexibility to substitute, mole-for-mole , maleic anhydride out of the formulation and therefore reduce the active double-bond sites. Consequently, the product becomes less brittle. Furthermore, aromatic acid components in the polymer backbone provided much better strength for the cured products. Phthalic anhydride is not a costly material and historically it is similarly priced to maleic anhydride. By... 

R = t-Bu, 81%) and r-butylbenzene (5%) (Scheme 119) [447]. Similarly, the Pd(II) complex catalyzes the electrosynthesis of aromatic carboxylic acids under CO2 atmosphere [448]. The electrocar-boxylation of vinyl triflates is performed with CO2 and a catalytic amount of PdCl2(PPh3)2 to give a,/ -unsaturated carboxylic acids [449]. 

Recently, Choudary et al. reported the first example of catalytic N-oxidation of tertiary amines by tungstate-exchanged Mg/Al LDHs in water [113], and the halodecarboxylation of Q ,/l-unsaturated aromatic carboxylic acids to /1-bromostyrenes has also been achieved for the first time, using a molybdate-exchanged Mg/Al LDH catalyst [114] this latter catalyst was active for selective oxidation [ 115,116]. 

The carboxylic group in carboxylic acids can be reduced to an aldehyde group, to an alcoholic group and even to a methyl group. Unsaturated acids and aromatic acids can be reduced at the multiple bonds or aromatic rings. 

A variety of dicarboxylic acids have been measured in air, including, for example, oxalic acid [(COOH)2], succinic acid [HOOCCH2CH2COOH], and malonic acid [HOOCCH2COOH], as well as larger straight-and branched-chain carboxylic acids unsaturated and aromatic acids such as phthalic acid are also observed in smaller concentrations (e.g., see Kawamura et al., 1996a, 1996b). Because of their lower vapor pressures, they are found predominantly in particles (see Chapter 9). 

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