Isomers cinnamic acids

CgHgO, PhCH = CHCOiH. Colourless crystals. Decarboxylales on prolonged heating. Oxidized by nitric acid to benzoic acid. Ordinary cinnamic acid is the trans-isomer, m.p. 135-136 C on irradiation with u.v. light it can be isomerized to the less stable cis-isomer, m.p. 42" C. 

Recall from Section 7 13 that a stereospecific reaction is one in which each stereoiso mer of a particular starting material yields a different stereoisomeric form of the reaction product In the ex amples shown the product from Diels-Alder cycloaddi tion of 1 3 butadiene to as cinnamic acid is a stereo isomer of the product from trans cinnamic acid Each product although chiral is formed as a racemic mixture... 

Physical and Chemical Properties. Cinnamic acid is generally encountered as the thermodynamically favored (E)-isomer. (H)-Cinnamic acid [140-10-3] is an off-white soHd having the properties outlined in Table 1 (6,7). 

For (Z)-cinnamic acid [102-94-3], three distinct polymorphic forms have been characteri2ed. The most stable form, referred to as aHocinnamic acid, has a melting point of 68°C, and the two metastable forms, isocinnamic acids, have melting points of 58°C and 42°C, respectively. (E)-Cinnamic acid can be converted to the (Z)-isomer photochemicaHy through kradiation of a solution with ultraviolet light. 

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). 

The couplings of vicinal protons in 1,2-disubstituted alkenes lie in the range 6-12 Hz for cis protons (dihedral angle 0°) and 12-17 Hz for trans protons (dihedral angle 180°), thus also following the Karplus-Conroy equation. Typical examples are the alkene proton AB systems of coumarin (16a, cis) and tra 5-cinnamic acid (16b), and of the cis-trans isomers 17a and b of ethyl isopente-nyl ether, in addition to those in problems 3, 4, 8, 11, 13 and 38. 

The synthesis of isoxazolines usually takes the most thermodynamically favorable course to yield solely the more stable isomer. However, cinnamic acids (38) give not only isoxazoline-4-carboxylic acids (39) but also, as a by-product, the less stable isoxazoline-5-carboxylic acids (40)" which on heating undergo retro-addition. ... 

But catalytic reduction of the same phenyl propionic acid gives cis cinnamic acid. Therefore by adding hydrogen under various conditions, one can obtain a desired isomer. The conversion of acetylene into olefinic compounds has been carried out not only for the sake of obtaining the adduct, but Michael studied the various addition reactions for the sake of obtaining a desired product cis or trans. For example, he found that the addition of bromine to acetylene-dicarboxylic acid leads predominantly to the formation of trans isomer. 

As the insertion of the carbon monoxide retains the configuration of the Pd-C bond, a modification of the procedure permits the conversion of /ra/w-cinnamic acid into the cis-isomer (Scheme 8.11) [5]. 

Conversion of frans-cinnamic acids into the c/s-isomers (Table 8.12)... 

Because the accuracy of the data for three of the diacyl peroxides is in question, we will attempt to derive enthalpies of formation for them from the reverse of equations 15 and 16. The enthalpy of reaction 15 for dibenzoyl peroxide, using enthalpy of formation values of unquestioned accurac)f, is —400.8 kJmor. This is the same as the ca —398 kJmol for the hquid non-aromatic diacyl peroxides discussed above. Using the solid phase enthalpy of reaction for dibenzoyl peroxide and the appropriate carboxylic acid enthalpies of formation, the calculated enthalpies of formation of bis(o-toluyl) peroxide and bis(p-toluyl) peroxide are —432.2 and —457.6 kJ moU, respectively. From the foregoing analysis, it would seem that the measured enthalpy of formation is accurate for the bis(p-toluyl) peroxide but is not for its isomer. The analysis for dicinnamoyl peroxide is complicated by there being two enthalpies of formation for frawi-cinnamic acid that differ by ca 12 kJmoU. One is from our archival source (—336.9 12 kJmoU ) and the other is a newer measurement (—325.3 kJmol ). The calculated enthalpies of formation of dicinnamoyl peroxide are thus —273.0 and —249.8 kJmoU. Both of these results are ca 80-100 kJmol less negative than the reported enthalpy of formation. 

Figure 6.6 HPLC chromatogram of the extract from Superior potato flesh (a) and of the same extract spiked with standards (b). Identification p.1, chlorogenic acid p.2, chlorogenic acid isomer p.3, caffeic acid p.4, p-coumaric acid p.5, ferulic acid p.6, t-cinnamic acid. Column, Inertsil ODS-3 V (5 p.m, 4.0 X 250 mm) flow rate, l.OmL/min column temperatures, 20°C mobile phase, acetonitrile 0.5% formic acid (gradient mode) detector, UV at 280 nm.

Figure 6.8 UV spectra of standard chlorogenic acid (a) trans-cinnamic acid (b) cafFeic acid (c) p-coumaric acid (d) and femlic acid (e). The spectra of peaks 1 (chlorogenic acid) (f), peak 2 (chlorogenic acid isomer) (g), and peak 3 (caffeic acid) (h) were determined with HPLC fractions isolated from extracts of Superior potato peel.

Dimethomorph. Dimethomorph (Figure 4.36) is effective against Oomycetes except Pythium spp. The compound, which is a cinnamic acid derivative, operates as a protectant but also has some curative activity that can be modified by means of formulation. Only the Z isomer is active but because of the rapid interconversion of isomers in the light, there is no practical advantage in its specific synthesis. 

For instance, head-head photodimers are predicted from the crystal structures of 9-cyanoanthracene and 9-anthraldehyde, but the head-tail isomer is produced. Craig and Sarti-Fantoni and later others found that photoreactions of 9-cyanoanthracene and 9-anthraldehyde take place at defect sites [96,215], Systematic photochemical and crystallographic studies by Schmidt and co-workers uncovered many cases of substituted anthracenes which behave in an unexpected fashion (Scheme 40) [216,217]. Examples shown in Scheme 40 clearly illustrate that, unlike cinnamic acid derivatives, the stereochemistry of the product dimer from anthracenes cannot be predicted on the basis of crystal packing. An example from the laboratories of Venkatesan is noteworthy in this context [218], Irradiation of crystals of 7-... 

Further support for the intermolecular route is provided by the isolation of the substituted trans-cinnamic acid, the normal Perkin product. This arises through elimination of carboxylic acid from the fully acylated species (393) rather than cyclization. For example, a considerable amount of 2-acetoxy-3-methoxycinnamic acid is formed from 3-methoxysalicylaldehyde, perhaps as a result of steric interference with cyclization so allowing the intermolecular process to predominate (39JPR(152)23). It should be noted that trans- 2-hydroxycinnamic acids do not cyclize under normal Perkin conditions, though the cis isomer does so quite readily. Isomerization of the trans acid has been effected by treatment with a trace of iodine in acetic anhydride or by UV irradiation. 

The effect of polar groups on the diimide reaction is sensitive to the configuration of the attached groups. For example, fumaric acid (trans) is ten times as reactive as maleic acid (els ) and the ratio of reactivities of the geometrical isomers of cinnamic acid, trans/cis. is 10 3 (ref. 21b). In comparison, cis- and trans-2-butene have almost identical reactivities. The difference may be explained by a change in the degree of advancement of the transition state towards the saturated product where the eclipsed conformation would result in a greater non-bonded repulsive interaction between the cis-substituents than the trans. 

This polymer was able to convert more than 50% of the tnmv-cinnamic acid in 8-truxinic acid (12), an isomer that is never formed with the catalyst in solution. This demonstrated how the cavity of the imprinted polymer could control the stereochemistry of the reaction in a direction which did not occur at all using the free catalyst in solution (Scheme 3) [9]. 

The standard procedure is illustrated by the preparation of cinnamic acid and furylacrylic acid (Expt 6.138). The cinnamic acid obtained is the more stable ( )-isomer. It may be readily reduced to the saturated acid (3-phenylpropanoicacid) and two procedures are described. Catalytic hydrogenation is a convenient method, but the conjugated double bond may also be reduced with, for example, sodium amalgam in the presence of alkali. 

Incorporation of [4-3H j3-14C]cinnamic acid into norpluviine caused 50% 3H loss, and the same loss was observed in the incorporation of the [3,5-2H2 4-3H j8-14C] isomer, in agreement with para-hydroxylation... 

Trans-cinnamic acid upon irradiation in solution yields the cis isomer with a quantum yield of 0.62. On the other hand, irradiation of the crystalline... 

Acetovanillone Vanillyl alcohol Vanilloylmethyl cetone p-Hydroxybenzaldehyde p-Hydroxybenzyl alcohol Vanillic acid p-Hydroxybenzoic acid Aliphatic acids Acetic acid Propanoic acid Isobutyric acid Butyric acid Isovaleric acid Valeric acid Hexanoic acid Heptanoic acid Octanoic acid 2-Heptenoic acid Nonanoic acid Dodecanoic acid Myristic acid Pentadecanoic acid Hexadecanoic acid 9-Hexadecanoic acid Heptadecanoic acid Stearic acid Oleic acid Linoleic acid Aromatic acids Benzoic acid Benzene propanoic acid Cinnamic acid (isomer 1) Cinnamic acid (isomer 2) Anisic acid Alcohols... 

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