Of cinnamic acid

Its chief importance is as a source of cinnamic acid by condensation with sodium ethan-oate and ethanoic anhydride and as a source of triphenylmethane dyestuffs by condensation with pyrogallol, dimethylaniline, etc. It is also used in the manufacture of perfumes. 

Cinnamic acid can be readily esterified by the Fischer-Speier method without any risk of the addition of hydrogen chloride at the double bond. Proceed precisely as for the preparation of ethyl benzoate (p. 104), using 20 g. of cinnamic acid and 20 ml. of rectified spirit. When the crude product is poured into water, a sharp separation of the ester is not readily obtained, and hence the addition of about 10 ml. of carbon tetrachloride is particularly desirable. Finally distil off the carbon... 

Oxidation, (a) Unsaturation test. Dissolve about o-i g. of cinnamic acid or of a soluble cinnamate in about 5 ml. of 10% NajCOg solution. To the cold solution add 1% aqueous KMn04 drop by drop. Immediate decolorisation denotes unsaturation. (Note. Many easily oxidisable substances, e.g.y formic acid, acetaldehyde, etc.y also rapidly decolorise alkaline permanganate. Cinnamates, however, do not reduce Fehling s solution.)... 

Formation of bromostyrene. Dissolve 0-2 g. of cinnamic acid (or a cinnamate) in about 5 ml. of NagCOg solution. Add bromine-water drop by drop and note the rapid separation of bromostyrene, CjHjCHiCHBr, as a colourless oil, having a pleasant characteristic odour. 

It is instructive for the student to construct a rough melting point diagram (compare Section 1,13 and Fig. 1,12, 1) for mixtures of cinnamic acid and urea. Weigh out 1 00 g. each of the two finely powdered components, and divide each into ten approximately equal portions on a sheet of clean, smooth paper. Mix 4 portions of cinnamic acid (A) with 1 portion of urea B) intimately with the aid of a spatula on a glass slide, and determine the melting point (the temperature at which the mixture just becomes completely fluid is noted). Repeat the procedure for 3 parts of A and 2 parts oiB 2 parts of A and 3 parts of B and 1 part of A and 4 parts of B. Tabulate your results as follows —... 

Plot temperatures as ordinates, and, as abscissae, the percentage of urea from left to right (0-100 per cent.) and of cinnamic acid from right to left (0-100 per cent.). 

Ethyl cinnamate may also be prepared by the esterification of cinnamic acid. The pure compound boils at 127°/6 mm. 

Hydrocinnamic acid may also be prepared by the reduction of cinnamic acid with sodium and alcohol or with sodium amalgam or with hydrogen in the presence of Adams platinum oxide catalyst (Section 111,150) ... 

Cinnamic acid undergoes reactions that are typical of an aromatic carboxyhc acid. Using standard methodology, simple esters are easily prepared and salts are formed upon neutrali2ation with the appropriate base. Hydrogenation of cinnamic acid under mild conditions leads to 3-phenylpropanoic acid [501-52-0] whereas under forcing conditions, such as under high pressure in presence of a nickel catalyst, complete saturation to 3-cyclohexylpropanoic acid [701-97-3] is readily accompHshed (8). 

Selective oxidation of either the aromatic ring or the side chain can also be accompHshed. For example, epoxidation of the double bond of cinnamic acid is effected in excellent yield by treatment with potassium hydrogen persulfate (10). 

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. 

Esters of cinnamic acid are used more extensively than the acid itself, and can be converted to the acid by standard hydrolysis protocols. The Claisen condensation between benzaldehyde and the appropriate acetate ester provides a direct, high yield route to the simple esters. 

The principal constituent of storax is cinnamic acid and for laboratory purposes styrene is still most easily obtained in high purity but dry distillation of cinnamic acid and its salts under atmospheric pressure (Figure 16.1). 

It contains 30 per cent, of d-camphoi, 17 per eonc. of rf-cainphene. cineol, an eater of cinnamic acid, a Htsumterpene, a high hniling phetiol, and probably limonene. 

It is a very aromatic oil, useful in some bouquets, and is found naturally in storax and other balsamic substances. It is prepared by various methods, amongst them being the heating of cinnamic acid with lime to 200°. It is a colourless, highly refractive liquid having the following characters —... 

The add is obtained by the reduction of cinnamic acid by means of sodium amalgam. The acid is then esterified by the condensing action of a mineral acid in methyl alcohol solution. The ester is an oil of very sweet odour, and is very useful for flower bouquets. 

This acid, CgH. CH. CH COOH, has a sweet and powerful odour, and can be used to advantage in many rose odours. It is recommended especially for perfuming powders and sachets. It is a crystalline compound, melting at 47° and boiling at 280°. It can be obtained by the reduction of cinnamic acid by means of sodium. 

Eastman Organic Chemicals cinnamaldehyde gave satisfactory results. If colorless crystals are present in the neck of the bottle or on the walls above the liquid, the cinnamaldehyde is seriously contaminated with cinnamic acid and should be distilled before use. A small amount of cinnamic acid apparently does not affect the yield of phenylcyclopropane. 

The column consists of a glass tube of 13-14 mm. internal diameter, 24 cm. long from lower end to the side arm, which has an internal diameter of 7 mm. It is important that these dimensions be observed in order to avoid polymerization of the product. It has been found in checking that better results are obtained by making indentations in the tube at frequent intervals and at different angles these tend to reduce the number of cinnamic acid particles which are carried over with the vapor. A column of the Vigreux type would no doubt also be suitable. 

If the temperature of the escaping vapor rises above 130° appreciable amounts of cinnamic acid pass into the condenser and the yield falls materially. 

Phenylethylene should not be distilled under atmospheric pressure since the temperature (146°) required for the distillation causes a considerable loss by polymerization. The decomposition of cinnamic acid cannot be effected by distillation under diminished pressure, since the acid under these conditions distils below the temperature required for decomposition (approxi-natcly 300°). 

Fragmentation The esters of cinnamic acid follow the fragmentation of benzoates except there is a relatively abundant M - 1 peak. Prominent ions arc as follows ... 

The greater intensity of the band of the metabolite at 220 mis probably due to the presence of a second, superimposed chromophore which could also account for the shift of the minimum. On the other hand, the band near 300 m/u. has the expected intensity. Its broadness and displacement towards longer wavelength are probably due to the presence of a substituent on the double bond or benzenoid ring. That the assignment to a coumaroyl chromophore is essentially correct is evidenced by the fact that both M and the model compound underwent the same type of reaction on irradiation in the near-ultraviolet (Figure 4). The observed isosbestic points imply that the photoreaction is a simple one, such as A -> B or A = B, and is obviously the well-known light-induced trans- to c/r-isomerization (7) of cinnamic acid derivatives. 

As shown in Schemes 10-44 and 10-45, two products may be formed in a Meerwein reaction Scheme 10-44 shows a simple aryl-de-hydrogenation of cinnamic aldehyde, whereas Scheme 10-45 shows an aryl-de-hydrogenation combined with the addition of HC1 to the double bond of the methyl ester of cinnamic acid. No systematic studies have been made as to which of the two products will be formed in a given reaction, what experimental conditions will favor one or the other product, and what substituents or other structural characteristics of the alkene influence the ratio of the two types of product. The addition product can, in most cases, easily be converted... 

The rates of hydration of substituted phenylpropiolic acids give a rho of —4.77 when plotted against a, comparable to Ihe acid-catalyzed isomerization of czs-cinnamic acid, with a rho value of —4.3. The solvent deuterium isotope effects are 3.7-S.2 for the isomerization of cinnamic acids at... 

Simandi and Nagy studied the kinetics of the catalyzed hydrogenation of cinnamic acid (S) to dihydrocinnamic acid (SHj) under steady-state conditions 166). They concluded that the kinetically important reactions were the two successive transfers of hydrogen atoms, viz.. 

Sun worshipers and those who work outside can protect themselves from ultraviolet exposure with skin creams that contain UV-absorbing molecules. The UV-absorbing molecule in the first sunscreens was PABA, para-aminobenzoic acid. However, this compound may have toxic effects of its own. The UV-absorbing components of current sunscreens are derivatives of cinnamic acid and benzophenone. 

A number of carboxylic acids are found in nature and also present in metabolic pathways. Accordingly, if monobasic acids are smoothly decarboxylated, they are expected to provide us with new routes to supply useful materials for chemical industry without depending on petroleum. Actually, there are some already known examples. The representative examples are the decarboxylation of cinnamic acid derivatives (Table 8). ... 

The pure enzyme was tested for activity against several methylated phenolic and cinnamic acids (Table 2). The enzyme was active on methyl esters of cinnamic acids caffeio p-coumaric> ferulic, and is therefore termed a cinnamoyl esterase (CinnAE). 

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