Acids cinnamic

Cinnamic acid melts at 134° it is soluble in 3,500 parts of water at 17° and in 100 parts at 100°. The yield is from 12 to 14 grams. 

Properties of Cinnamic Acid (Section 553).—(a) Test for the double bond in cinnamic acid.—Dissolve about 0.5 gram of the acid in carbon tetrachloride and add, drop by drop, a solution of bromine in the same solvent. If no reaction takes place in 1 minute, warm the solution gently. (Eq.) How does the rate at which this reaction proceeds compare with the rate with which ethylene and bromine react  

—(a) The rate at which bromine is added to a double bond is determined by the nature of the radicals linked to the carbon atoms joined by the double bond negative atoms or groups markedly retard the reaction. In the case of certain compounds which contain four negative groups, for 

Cinnamic acid is well known for its role as a phenolic compound that gives the oil cinnamon its characteristic odor and flavor. It is soluble in water or ethanol and in nature cinnamic acid derivatives are known to 

The reaction of cinnamic acid 279 with 18% oleum at 90 °C yields a mixture of the p-sulfonic acid (72%), the m-isomer (27%) and less than 1% of the o-isomer. In contrast, when cinnamic acid 279 was warmed with chlorosulfonic acid (four equivalents, 50-60 °C) for 3 hours apparently the only product was the p-sulfonyl chloride 280 (60%) (Equation 87). 

In cinnamic acid 279, the electron donation from the alkenic double bond (+M effect) apparently predominates over the electron-withdrawing (—1 effect) due to the carboxylic acid group which is transferred to the phenyl ring via the double bond. The latter effect probably accounts for the appreciable amount of the m-isomer isolated from the oleum sulfonation reaction. 

Coumarin. In a 250 ml. round-bottomed flask, provided with a small reflux condenser and a calcium chloride drying tube at the top, place 2 1 g. of salicylaldehyde, 2-0 ml. of anhydrous triethylamine and 5-0 ml. of acetic anhydride, and reflux the mixture gently for 12 hours. Steam distil the mixture from the reaction flask and discard the distillate. Render the residue in the flask basic to litmus with solid sodium bicarbonate, cool, filter the precipitated crude coumarin at the pump and wash it with a little cold water. Acidify the filtrate to Congo red with 1 1-hydrochloric acid, collect the precipitated o-acetoxycoumaric acid and recrystallise it from 70 per cent, isopropyl alcohol the yield is 0-40 g., m.p. 153-154°. 

Boil the crude coumarin with 200 ml. of water to which 0-2 g. of decolourising carbon is added, filter the hot solution, and concentrate it to a volume of 80 ml. Cool, collect the coumarin which separates, and recrystallise it from 40 per cent, aqueous methanol. The yield of coumarin, m.p. 68-69°, is 1 0 g. 

1 1-hydrochloric acid, collect the precipitated o-acetoxycoumaric acid and recrystaUise it from 70 per cent, isopropyl alcohol the yield is 0-40 g., m.p. 153-154°. 

of decolourising carbon heat the mixture to boiling, filter and acidify the filtrate immediately to Congo red with 1 1-hydrochloric acid. Cool. Collect the separated crystals by suction filtration and recrystallise from 60 per cent, ethanol. The yield of a-phenylcinnamic acid (1), m.p. 172-173°, is 55 g. 

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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. 

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. 

In general, condensation takes place at the a-carbon atom, leading to simple cinnamic acids or to their a-substituted derivatives. When possible, the anhydride corresponding to the sodium sail should be the condensing agent. 

Naphthalene, oxalic acid (hydrated), cinnamic acid, acetamide, benzamide, m-dinitrobenzene,/>-nitrophenol, toluene p-sulphon-... 

Cinnamic Acid. CeH5CH CH COOH. (Perkin s Reaction.)... 

Cinnamic acid is usually prepared by Perkin s reaction, benzaldehyde being heated with sodium acetate in the presence of acetic anhydride. It is probable that the benzaldehyde and the acetic anhydride combine under the catalytic action of the sodium acetate, and the product then readily loses water to give mono-benzylidene acetic anhydride (. ). The latter, when subsequently... 

Ethyl Cinnamate. C H5CH CHCOOC2H5. Required Cinnamic acid, 20 g. rectified spirit, 20 ml. 

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... 

Coumarin is usually prepared by heating salicylaldehyde with acetic anhydride and sodium acetate (i.e., the Perkin cinnamic acid synthesis, p. 23 6), whereby the 0" hydroxy-cinnamic acid (I) undergoes cyclisation to coumarin. Coumarins having substituents in the benzene ring can often be similarly prepared. 

Anthranilic acid HaNCeH COOH Cinnamic acid CeHjCH.CHCOOH... 

Physical properties. All are colourless crystalline solids except formic acid, acetic acid (m.p. 18 when glacial) and lactic acid (m.p. 18°, usually a syrup). Formic acid (b.p. loo ") and acetic acid (b.p. 118 ) are the only members which are readily volatile lactic acid can be distilled only under reduced pressure. Formic and acetic acids have characteristic pungent odours cinnamic acid has a faint, pleasant and characteristic odour. 

Does not give Unsaturation Test with alkaline potassium permanganate (distinction from cinnamic acid, see below). 

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. 

Methyl, ethyl, n-propyl, isopropyl, n-hutyl, benzyl, cyclohexyl esters of formic, acetic, oxalic, succinic, tartaric, citric, benzoic, salicylic (and other substituted benzoic acids), phthalic and cinnamic acids phenyl esters of acetic, benzoic and salicylic acids. 

Monohydric alcohols, aldehydes (including chloral hydrate), ketones, cinnamic acid, amines (2-naphthylaminc is odourless), nitrophenols (resemble both phenol and nitro-compound),... 

Substances suitable for the estimation acetanilide, sucrose, glucose, cinnamic acid, diphenyl amine, salicylic acid, vanillin, />"bromoacetanilide, toluene p-sul phonamide. 

Determine the melting point of pure cinnamic acid (133°) and pure urea (133°). Intimately mix approximately equal weights (ca. 01 g.) of the two finely-powdered compounds and determine the melting point a considerable depression of melting point will be observed. Obtain an unknown substance from the demonstrator and, by means of a mixed melting point determination, discover whether it is identical with urea or cinnamic acid. 

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.). 

Use 01 g. of the platinum oxide catalyst and 11 4 g, of pure cinnamic acid dissolved in 100 ml. of absolute alcohol. The theoretical volume of hydrogen is absorbed after 7-8 hours. Filter off the platinum, and evaporate the filtrate on a water bath. The resulting oil solidifies on cooling to a colourless acid, m.p. 47-48° (11-2 g.). Upon recrystallisation from light petroleum, b.p. 60-80°, pure dihydrocinnamic acid, m.p. 48-49°, is obtained. 

It is interesting to note that altliough cis-lrans isomerism about the double bond is theoretically possible in cinnamic acid, the Perkin reaction gives rise only to the trans form, m.p. 133°, the cis form, m.p. 68° (termed aHo-cinnamic acid) being unstable and easily converted into the trails acid. 

The a-carbon atom of the phenylacetyl group is more susceptible to attack by the basic catalyst (triethylamine) than the acetyl group hence a-phenyl-cinnamic acid, but no cinnamic acid, is obtained. 

Sodium hydroxide solution cannot be used at this stage since it may produce benzoic acid by the Cannizzaro reaction (Section IV,123) from any unchanged benzaldehyde. If, however, the reaction mixture is diluted with 3-4 volumes of water, steam distilled to remove the unreacted benzaldehyde, the residue may then be rendered alkaline with sodium hydroxide solution. A few grams of decolourising carbon are added, the mixture boiled for several minutes, and filtered through a fluted filter paper. Upon acidifying carefully with concentrated hydrochloric acid, cinnamic acid is precipitated. This is collected, washed and purified as above. 

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) ... 

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