Cinnamics

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. 

Claisen reaction Condensation of an aldehyde with another aldehyde or a ketone in the presence of sodium hydroxide with the elimination of water. Thus benzaldehyde and methanal give cinnamic aldehyde, PhCH CH-CHO. 

Perkin reaction A condensation between aromatic aldehydes and the sodium salts of fatty acids or their aromatic derivatives. The reaction between benzaldehyde and sodium ethanoate in the presence of ethanoic anhydride leads to sodium cinnamate... 

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-... 

For a further example of the Fischer-Speier method, see Ethyl cinnamate,... 

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... 

Ethyl cinnamate is a colourless liquid of b.p. 271° and 1-05 it possesses a pleasant and characteristic odour. 

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. 

Succinate, benzoate, phthalate and cinnamate give buff or brownish coloured precipitates of the basic ferric salts in the cold. Add dil. H2SO4. The basic ferric succinate dissolves giving a clear solution the other basic ferric salts also dissolve, but simultaneously a white precipitate of the free acid is also formed. 

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. 

As a general guide, however, it may be noted that the following have fairly easily recognisable odours methyl and ethyl formate methyl and ethyl acetate (apples) methyl and ethyl benzoate methyl salicylate (oil of winter-green) and ethyl salicylate methyl and ethyl cinnamate. (It is however usually impracticable to distinguish by odour alone between the methyl and ethyl esters of a particular acid.) Methyl and ethyl o. alate, and methyl and ethyl phthalate are almost odourless. Succinic and tartaric esters have faint odours. 

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

TEST Formic Acetic OxaJic Succinic Lactic Tartaric Citric Benzoic Salicylic Phthalic Cinnamic... 

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

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