Cinnamic acids Perkin reaction

Furfural condenses with acetic anhydride and potassiuiu acetate to give furylacrylic acid (compare Perkin reaction, Cinnamic Acid, Section IV, 124) ... 

Cinnamic Acid by Perkin s Reaction.—Cinnamic acid has the constitution assigned to it above as is proven by the following synthesis from benzaldehyde by condensation with sodium acetate in the presence of acetic anhydride. 

Cinnamic acid was prepared from benzaldehyde and acetyl chloride by Bertagnini. Cinnamic aldehyde was synthesised by Chiozza from benzaldehyde, acetaldehyde, and hydrochloric acid, and on oxidation forms cinnamic acid. Perkin synthesised cinnamic acid by the action of acetic anhydride and sodium acetate on benzaldehyde. He thought an explanation of the reaction on the lines of Fittig s hypothesis ... 

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... 

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... 

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. 

Chapter IV. a-Chloromethylnaphthalene (IV,23) benzylamine (Gabriel synthesis) (IV,39) i r.N -dialkylanilines (from amines and trialkyl orthophosphates) (IV,42) a-naphthaldehyde (Sommelet reaction) (IV,120) a-phenyl-cinnamic acid (Perkin reaction using triethylamine) (IV,124) p-nitrostyrene (IV,129) p-bromonaphthalene and p naphthoic acid (from 2 naphthylamine-1 -sulphonic acid) (IV,62 and IV,164) diphenic acid (from phenanthrene) (IV,165). 

Manufacture. The most widely employed method for the commercial synthesis of (H)-cinnamic acid uti1i2es ben2aldehyde, acetic anhydride, and anhydrous sodium or potassium acetate in a condensation reaction commonly referred to as the Perkin reaction (11). 

The cinnamic acid is readily prepared by heating benzaldehyde with acetic anhydride and sodium acetate (the Perkin Reaction) (Figure 16.2). 

Cinnamic Acid.—The reaction, which takes place when an aldehyde (aliphatic or aromatic) acts on the sodium salt of an aliphatic acid in presence of the anhychide, is known as Perkin s reaction, and has a ery wide application. Accoid-ing to the result of Fittig s researches on the properties of the unsaturated acids described below, the reaction occurs in two steps. The aldeh) de forms first an additive compound with the acid, the aldehyde caibon attaching itself to the n-carbon ii.e.i nevt the carbovyl) of the acid. A saturated hydiOKy-acid is formed, which is stable, if the a-carbon is attached to only one atom of hydrogen, as in the case of isobutync acid,... 

The aldol-like reaction of an aromatic aldehyde 1 with a carboxylic anhydride 2 is referred to as the Perkin reaction. As with the related Knoevenagel reaction, an o ,/3-unsaturated carboxylic acid is obtained as product the /3-aryl derivatives 3 are also known as cinnamic acids. 

The method constitutes a simple preparation of ethanol-in-soluble cinnamic acids, of a high degree of purity when compared with the Perkin reaction 6 or the usual procedure for the Doebner reaction,6 which uses a large excess of pyridine. A useful modification of this reaction is to warm the reactants on a steam plate in the absence of alcohol.7 8... 

When benzaldehyde is condensed with hippuric acid in the presence of acetic anhydride a Perkin s reaction takes place and benzoyl-a-amido-cinnamic acid is formed —... 

Hydrogenation of benzaldehyde yields benzyl alcohol, condensation with aliphatic aldehydes leads to additional fragrance substances or their unsaturated intermediates. Unsaturated araliphatic acids are obtained through the Perkin reaction, for example, the reaction with acetic anhydride to give cinnamic acid. 

Perkin Reaction (Perkin cinnamic acid synthesis) The Reaction ... 

Use of the Knoevenagel reaction (67OR(l5)204), in which a benzaldehyde reacts with an activated methylene compound in the presence of an amine, goes some way to overcoming the inherent difficulties of the Perkin synthesis of coumarins (see later). In order to obtain the coumarin rather than the usual cinnamic acid, a 2-hydroxy substituent must be present... 

Application of the Perkin cinnamic acid synthesis to salicylaldehydes provides a coumarin synthesis of some renown. The reaction itself has been reviewed <42OR(l)2l0) and some discussion of its value in coumarin synthesis is contained in other reviews (37CB(A)83, 45CRV(36)l). 

---