Cinnam-aldehyde anhydride

Which of the two is the cis form and which the trans form has not been determined. A third cinnamic acid, viz., iso-cinnamic acid, is also known, but the constitution of it has not been established. Cinnamic acid is found in nature in the resin storax both as the free acid and as the cinnamic alcohol ester, styrin. It is also found in Peru and Tolu balsams as the free acid and as the benzyl alcohol ester, the benzoic acid ester of benzyl alcohol being present also. Thus benzyl alcohol, benzoic acid, cinnamic alcohol and cinnamic acid are all constituents of esters present in these plant resins. Allo-cinnamic acid, the geometric isomer, is obtained from coca leaves from which the alkaloid cocaine is also obtained (p. 896). When cinnamic acid is heated with lime it loses carbon dioxide and yields the unsaturated side-chain hydrocarbon st3rrene, or phenyl ethylene, CeHs—CH = CH2. On reduction it yields first cinnamic aldehyde, found in oil of cinnamon (p. 842) and then cinnamic alcohol. Both cinnamic acid and allo-cinnamic acid yield anhydrides. 

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... 

Reactions. Heating an aqueous solution of malonic acid above 70°C results in its decomposition to acetic acid and carbon dioxide. Malonic acid is a useful tool for synthesizing a-unsaturated carboxyUc acids because of its abiUty to undergo decarboxylation and condensation with aldehydes or ketones at the methylene group. Cinnamic acids are formed from the reaction of malonic acid and benzaldehyde derivatives (1). If aUphatic aldehydes are used acryhc acids result (2). Similarly this facile decarboxylation combined with the condensation with an activated double bond yields a-substituted acetic acid derivatives. For example, 4-thiazohdine acetic acids (2) are readily prepared from 2,5-dihydro-l,3-thiazoles (3). A further feature of malonic acid is that it does not form an anhydride when heated with phosphorous pentoxide [1314-56-3] but rather carbon suboxide [504-64-3] [0=C=C=0], a toxic gas that reacts with water to reform malonic 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. 

In this reaction the carbanion (103) is obtained by removal of an ot-H atom from a molecule of an acid anhydride (104), the anion of the corresponding acid acting as the necessary base the carbonyl acceptor is pretty well confined to aromatic aldehydes. The products are a/J-unsaturated acids, e.g. 3-phenylpropenoic(cinnamic) acid (105) from PhCHO/excess (MeC0)20/MeC02e at 140° ... 

A. 0.02 M substituted benzaldehyde, 27 g acetic anhydride, 12 g fused K acetate in 250 ml round bottom flask with air condenser and CaCI2 tube. Heat on oil bath at 160° one hour and then at 175c for four hours. Pour into water (neutralize with Na carbonate and steam distill to recover unreacted aldehyde), cool, acidify and filter to get about 60% yield substituted cinnamic acid (I). 

Cinnamic acid synthesis from aryl aldehyde and acetic anhydride. 

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. 

The Perkin synthesis of cinnamic acids is considered to involve reaction of the enolate anion derived from the acid anhydride with the aldehyde, giving rise to the alkoxide (391). Intramolecular acylation follows and the resulting /3-acyloxy derivative undergoes elimination to the unsaturated acid (Scheme 125). 

Malonic acid itself can react with aldehydes in the presence of piperidine by way of a Knoevenagel condensation. A decarboxylation occurs after the condensation, and this decarboxylation cannot be avoided. Figure 13.55 shows how the overall reaction can be employed for the synthesis of cinnamic or sorbic acid. This reaction sequence occurs under much milder conditions than the Perkin synthesis of cinnamic acids. (The Perkin synthesis consists of the condensation of aromatic aldehydes with acetic acid anhydride in the presence of sodium acetate.)... 

The reaction is usually carried out be heating equimolar quantities of the aldehyde and salt with excess of the anhydride for 8 hours at 170-180°. Lower temperatures are often employed when potassium acetate or trialkylamines are used as condensing agents. Continuous removal of acetic acid during the reaction was found to have no effect on the yield of cinnamic acid. Substitution of diacetimide for acetic anhydride gives cinnamide (77%). ... 

This condensation is essentially an aldol-type reaction of an aldehyde with the methylene group of an anhydride. The sodium salt may be replaced by other basic catalysts such as potassium carbonate oi tertiary amines. If the acid residue in the anhydride is not the same as that in the sodium salt, an equilibrium between these substances may occur before condensation. Thus, a mixture of acetic anhydride and sodium butyrate or a mixture of butyric anhydride and sodium acetate gives cinnamic acid and a-ethylcinnamic acid in the same ratio. ... 

In the Perkin reaction, acetic anhydride condenses with an aromatic aldehyde to yield a cinnamic acid. The reaction takes place by a mixed carbonyl condensation of the anhydride with the aldehyde to yield an a,/l-unsaturated intermediate that undergoes hydrolysis to yield the cinnamic acid. What is the structure of the unsaturated intermediate ... 

It follows from this that the sodium salt used always takes part in the reaction. In the experiment it is of course necessary that the fusion is not carried out at so high a temperature as in the above example, but only at the heat of the water-bath at higher temperatures the sodium salt of proprionic add and acetic anhydride decompose into sodium acetate and proprionic anhydride, so that cinnamic add is obtained, and therefore, apparently, the anhydride reacts with the aldehyde-... 

The Perkin reaction involves the condensation of a carboxylic acid anhydride and an aldehyde in the presence of a weak base, often the sodium or potassium salt of the acid or triethylamine, to give unsaturated carboxylic acids (equation 1). The first example of this reaction was described by Perkin in 1868 and involves a synthesis of coumarin by heating the sodium salt of salicylaldehyde with acetic anhydride (equation 2). The reaction is generally applicable only to aromatic aldehydes and is particularly useful for the preparation of substituted cinnamic acids, as illustrated by equation (3). ... 

The Perkin reaction,1 which is normally applicable only to aromatic aldehydes, is usually effected by heating a mixture of the aldehyde, an acid anhydride, and a weak base to form cinnamic acids.2... 

Substituted cinnamic acids are obtained by condensing higher aliphatic anhydrides with aromatic aldehydes in the presence of the alkali salts of the corresponding aliphatic acid. 

Cinnamic acid is manufactured by the so-called Perkin synthesis, which has been applied to the preparation of a large number of unsaturated acids. When benzoic aldehyde is heated with anhydrous sodium acetate in the presence of acetic anhydride, condensation takes place as the result of the loss of water CeHs.CHO + CHg.COONa = CeHB.CHrCH.COONa + H2O A similar condensation takes place between benzoic aldehyde and homologues of acetic acid. The hydrogen atoms which are eliminated from the salt of the fatty acid are those in the a-posi-tion —... 

The simplest synthesis of coumarins is a special case of the Perkin condensation i.e. the condensation of an aromatic aldehyde with an anhydride. ortho-Hydroxy-trans-cinnamic acids cannot be intermediates since they do not isomerise under the conditions of the reaction nor can O-acetylsalicylaldehyde be the immediate precursor of the coumarin, since it is not cyclised by sodium acetate on its own. ... 

The interaction between benzaldehyde (aromatic aldehyde) and acetic anhydride (an aliphatic anhydride capable of providing an active methylene moiety) in the presence of a basic catalyst, such as acetate ion and a hydronium ion yields an a, p-unsaturated carboxylic acid, cinnamic acid, and a mole of acetic acid. 

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