Thermal cinnamic acid

Another potentially valuable method for the preparation of cinnamic acid involves treatment of benzaldehyde with ketene (12). The initially formed oligomer of P-hydroxy-P-phenylpropionic acid is thermally decomposed at 100—250°C in the presence of an acid or base catalyst. 

Research Focus Method of preparing 4-hydroxystyrene by de-carboxylation of 4-hydroxylcinnamic acid for use in preparing poly(4-glycidyloxystyrene). Originality While the thermal decarboxylation of cinnamic acid as a method of... 

Polymers with other pendant photosensitive moieties such as 0-furylacrylic ester (2) or / -styrylacrylic ester (5) are highly photosensitive and have even higher photosensitivity after the addition of photosensitizers. However, the thermal stability of these polymers is inferior to that of the polymer with pendant cinnamic esters (4). Polymers with pendant benzalacetophenone (5), styrylpyridinium (6), a-cyanocinnamic ester (7) or a-phenylmaleimide (8) have high photosensitivity but they can not be sensitized. In addition, the photosensitive moieties that are used in the syntheses of these polymers are not commercially available, in contrast to cinnamic acid. 

The bromination of cinnamic acid dissolved in carbon tetrachloride or other inert solvent.offers a convenient system for study. The dibromocinnamic acid produced remains in the carbon tetrachloride solution. The thermal reaction is so slow that it can barely be measured at room temperature and it is entirely negligible in comparison with the photochemical reaction at ordinary intensities. The quantum yield is so large that considerable reaction occurs even if the intensity of light is much reduced by the monochromator or other device for confining the light to a narrow range of frequencies. Furthermore, the reaction is easily and accurately followed by titration with sodium thiosulfate. Potassium iodide is added and the iodine liberated is a measure of the remaining bromine. 

As a preparative method the direct decarboxylation of olefinic acids is almost limited to the formation of styrenes and stilbenes from substituted cinnamic acids. Thermal decomposition of cinnamic acid gives styrene (41%). The yield is nearly quantitative if the reaction is carried out in quinoline at 220° in the presence of a copper catalyst. The yields of substituted styrenes where the aryl radical contains halo, methoxyl, aldehyde, cyano, and nitro groups are in the range of 30-76%. cis-Stilbene and cis-p-nitrostilbene are prepared in this way from the corresponding a-phenylcinnamic acids (65%). One aliphatic compound worthy of mention is 2-ethoxypropene, prepared by heating -ethoxycro-tonic acid at 165° (91% yield). The mechanism of acid-catalyzed decarboxylations of this type has been studied. Isomerization of the double bond from the a,/5- to the /5, y-position before decarboxylation very likely occurs in many instances. ... 

Figure 28 shows that substituted cinnamic acid derivatives have a relatively low absorption in the 310—320 nm region, so that they are relatively ineffective ultraviolet absorbers. Their main advantage is that they have no phenolic hydroxyl group which could be sensitive to alkali or heavy metal ions. The alkali sensitivity is a severe shortcoming for textile applications. On the other hand, with polyoxymethylene for instance, the thermal degradation can be catalysed by phenols, and with polyvinylchloride, side reactions can occur with metal stabilizers. 

After 8 hours of heating, anthocyanin solutions contain benzoic and cinnamic acids, dihy-droflavonols, catechins and a certain number of unidentified molecules. Furthermore, malvidin, the major component of wine coloring matter, has been found to be much more sensitive to thermal degradation than cyanidin (Table 6.4). The temperature factor should, therefore, be taken into account when wines are aging in barrels, vats or bottles, in order to protect their color. 

The inclusion complexes were obtained in the form of precipitates from aqueous solutions of trans-cinnamic acid and a- or 3-cyclodextrin, in 74 and 89 % yields, respectively. The acid in the complexes was determined by NMR in (CH3)2SO-d0 and the observed acid/cyclodextrin ratios were 0.5 (ot-cyclodextrin) and 1.0 (3-cyclodextrin). The X-ray powder diffraction patterns of these complexes showed that they were highly crystalline as depicted in Figure 1 and did not corresponded to those of the pure components, so should exist as inclusion complexes.9 The thermal stability of trans-cinnamic acid in the complexes was found to be higher than those of the acid itself and in its mixture with cyclodextrins, as well as reported by Uekama, et Therefore, the guest molecule should be... 

Recently, there has been an increasing interest in the use of supercritical fluid extraction (SEE) with carbon dioxide (CO2) as a solvent. This process uses the properties of gases above their critical points to extract selective soluble components from a raw material. Carbon dioxide is an ideal solvent for the extraction of natural products because it is nontoxic, nonexplosive, readily available, and easy to remove from extracted products [3,6]. SFE has the abihty to use low temperatures, leading to less deterioration of the thermally labile components in the extract. In addition, SFE is typically carried out in the absence of air which also ensures minimal alteration of the active ingredients and preservation of the curative properties [46, 47]. SC CO2 is generally efficient in the purification and fractionation of hydrophobic compounds, such as flavonoids and cinnamic acid derivatives from plant matrixes [49]. 

PhenoHc acids are precursors of a number of simple phenols, which result from the activities of microorganisms or during thermal processes. The main products of thermal degradation of cinnamic acids are 4-vinyl phenols that arise as decarboxylation products. The subsequent reactions yield the corresponding 4-formyl phenols, 4-ethyl phenols, 4-(prop-2-en-l-yl) phenols, 4-acetyl phenols... 

The background and detailed mechanisms of decarboxylation are very extensive, and therefore this chapter will discuss some specihc pathways of decarboxylation. In addition, we have highlighted recent cases of decarboxylation relevant to hydroxy-cinnamic acids in wine, beer and camelina and attempted to reason if such strategies can be transferred for value addition to processing of rapeseed and canola. An update on the recent thermal decarboxylation to form canolol, a phenol of interest in rapeseed and canola processing, is discussed in the last part of this chapter. 

Hydroxyl-functionalized cinnamic acid derivatives such as p-coumaric acid (p-hydroxycinnamic acid), ferulic acid, and sinapinic acid are attractive monomers for syntheses of high-performance polyesters. The obtained polyesters are also expected to be biodegradable in the case of copolymerization with aliphatic hydroxy acids such as lactic acid. Tanaka et al reported the thermal polycondensation of p-coumaric acid at 550 °C without any catalyst under high pressure up to 80 kbar (in the solid state) in 1975. They obtained red or brownish-red hard solids insoluble in conventional organic solvents. Higashi and his co-workers synthesized copolyesters of p-coumaric acid and 4-hydroxybenzoic acid or their methoxy substitutions (ferulic acid, vanillic acid, or syringic acid) by polycondensation using hexachlorocyclotri(phosphazene) in pyridine in 1981. The obtained polymers that exhibited UV spectra different... 

It may be suspected that the genuinely topotactic (as secured by the molecular precision of the AFM [18]) photodimerization of 2-benzyl-5-benzyli-denecyclopentanone [118] might be a good candidate for a quantitative preparative photo dimerization to give the head-to-tail anti-[2+2] dimer. Early quantitative solid-state [2-1-2] photodimerizations (most of the published mechanistic interpretations of which can no longer be accepted) are listed in [110]. These deal with the anti dimerization of acenaphthylene-1,2-dicarboxylic anhydride, the head-to-head syn dimerization of acenaphthylene-1-carboxylic acid, the syn dimerization of 5,6-dichloroacenaphthylene, and the thermally reversible head-to-tail anti dimerization of seven ( )-2,6-di-f-butyl-4-(2-aryl-ethenyl)pyrylium-trifluoromethanesulfonates. All of these reactions proceed fully specific. On the other hand, quantitative photoconversions of a 1 1 mixed crystal of ethyl and propyl a-cyano-4-[2-(4-pyridyl)ethenyl]cinnamates gives mixtures of diesters with one (A>410 nm) or two cyclobutane rings (no cutoff filter). 

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