Aldehydes Perkin reaction

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... 

Perkin reaction. The condensation of an aromatic aldehyde with an acid anhydride in the presence of the sodium or potassium salt of the acid... 

Other reactions similar to the aldol addition include the Claisen and Perkin reactions. The Claisen reaction, carried out by combining an aromatic aldehyde and an ester in the presence of metallic sodium, is useful for obtaining a,P-unsaturated esters. 

The Perkin reaction, uti1i2ing an aromatic aldehyde, an acid anhydride, and a base such as an acid salt or amine, produces the corresponding a,P-unsaturated acid. 

Aldehydes and Ketones. Pyrrole aldehydes and ketones are somewhat less reactive than the corresponding benzenoid derivatives. The aldehydes do not undergo Cannizzaro or Perkin reactions but condense with a variety of compounds that contain active methylene groups. They also react with pyrroles under acidic conditions to form dipyrryhnethenes (26). The aldehydes can be reduced to the methyl or carbinol stmctures. The ketones undergo normal carbonyl reactions. 

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. 

A variant of the Perkin reaction is the Erlenmeyer-Plochl-azlactone synthesis By condensation of an aromatic aldehyde 1 with an N-acyl glycine 5 in the presence of sodium acetate and acetic anhydride, an azlactone 6 is obtained via the following mechanism ... 

The condensation of aromatic aldehydes with anhydrides is called the Perkin reaction When the anhydride has two a hydrogens (as shown), dehydration always occurs the P-hydroxy acid salt is never isolated. In some cases, anhydrides of the form (R2CHC0)20 have been used, and then the hydroxy compound is the product since dehydration cannot take place. The base in the Perkin reaction is nearly always the salt of the acid corresponding to the anhydride. Although the Na and K salts have been most frequently used, higher yields and shorter reaction times have been reported for the Cs salt. Besides aromatic aldehydes, their vinylogs ArCH=CHCHO also give the reaction. Otherwise, the reaction is not suitable for aliphatic aldehydes. ... 

Formylfuran behaves in a very similar manner to benzaldehyde and undergoes the usual reactions of an aromatic aldehyde, e.g. (i) the Cannizzaro reaction with cone, sodium hydroxide to give furan-2-ylmethanol and the sodium salt of furoic acid, (ii) the Perkin reaction with acetic anhydride and sodium acetate to yield an aldol product that dehydrates to 3-(furan-2-yl)propenoic acid, and (iii) a condensation with potassium cyanide in alcoholic solution to form furoin (under these conditions, benzaldehyde undergoes the benzoin condensation) (Scheme 6.32). 

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 of this aldehyde with phenylacetic acid gives a mixture of the benzothiophene 13 (57%) and the thiocoumarin 14 (40%). ... 

Aromatic aldehydes lake up keiene in the presence of potassium acetate in the manner of a Perkin reaction. The producl is a cinnamic acid ... 

The forward synthetic reaction is a base-catalysed condensation reaction between two carbonyl compounds, the aldol condensation leading to -hydroxy-aldehydes or / -hydroxyketones followed by dehydration. This sequence is one of the most important carbon-carbon bond forming reactions, and aldol-type condensation reactions are considered in a number of other sections of the text, for example, the Doebner reaction (Section 5.18.3, p. 805), the Knoevenagel reaction (Section 5.11.6, p. 681), the Perkin reaction (Section 6.12.3, p. 1036) and the Robinson annelation reaction (Section 7.2). 

The condensation product of dithiooxamide with benzaldehyde has been shown to be 2,5-diphenylthiazolo[5,4-d]thiazole (equation 75) (60JA2719). Its formation involves dehydration of the reactants and further dehydrogenation. The reaction is comparable in scope with condensations such as the Perkin reaction, and many 2,5-diarylthiazolo[5,4-c ]thiazoles have been prepared from a variety of aryl aldehydes. Condensation products were not obtained from simple aliphatic aldehydes (71JMC743). 

Enols or enolates from anhydrides are not used very often in aldol reactions other than in one important application, usually known as the Perkin reaction. An acid anhydride, such as acetic anhydride, is combined with a non-enolizable aldehyde and a weak base, usually the salt of the acid. This base is used so that nucleophilic attack on the anhydride does no hami, simply regenerating the anhydride. q... 

Selenophene-2-aldehyde takes part in the Hantzsch synthesis [Eq. (I)]108 and reacts readily with ammonia, aromatic amines and diamines,109 hippuric, barbituric, and malonic acids, malononitrile,70 and rhodanine.109 /3-(Selenien-2-yl)acrylic acid has been obtained from selenophene-2-aldehyde by the Perkin reaction and by Knoevenagel condensation with malonic acid.70 Esters of /9-(selenien-2-yl)acrylic acid are easily formed by condensation of the aldehyde... 

Classically, this separation of roles was accomplished by utilizing substrates that differed drastically in their ability to form enolate anions. In fact, the various name reactions mentioned above are distinguished not by basic differences in mechanism, but by the nature of the components preferentially utilized as substrates. For example, in the Perkin reaction, the condensation of an aromatic aldehyde with an aliphatic acid anhydride is based on the fact that the electrophilic component, e.g. benzaldehyde, lacks a-hydrogens and therefore is incapable of forming an enolate. At the same time the utilized electrophile, acetic anhydride, contains a carbonyl group with reduced propensity to interact with nucleophiles. Hence, it is incapable of undergoing self-condensa-... 

Perkin Synthesis of Coumarin.—Coumaric acid and coumarin may be synthesized by the Perkin reaction for synthesizing unsaturated aromatic acids (p. 698). These syntheses are of historical interest as the two compounds obtained were the first onesprepared by this reaction. Instead of taking a simple aromatic aldehyde it is only necessary to take a phenol aldehyde viz., salicylic aldehyde,... 

Perkin reaction Anhydride II II 0 0 Aromatic aldehyde usually follows Dehydration... 

The condensation of aromatic aldehydes with anhydrides is called the Perkin reaction When the anhydride has two a hydrogens (as shown), dehydration... 

The reaction of benzaldehyde with phenylacetic acid to produce a mixture of the a-carboxylic acid derivatives of Z- and -stilbene a form of aldol condensation known as the Perkin reaction, is effected by heating a mixture of the components with acetic anhydride and triethylamine. In the course of the reaction the phenylacetic acid is probably present both as anion and as the mixed anhydride resulting from equilibration with acetic anhydride. A reflux period of 5 h specified in an early procedure has been shortened by a factor of 10 by restriction of the amount of the volatile acetic anhydride, use of an excess of the less expensive, high-boiling aldehyde component, and use of a condenser that permits some evaporation and consequent elevation of the reflux temperature. 

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 ... 

Perkins Reaction. This involves the reaction between an aromatic aldehyde and a carboxylic acid having a-hydrogen. The reaction is catalyzed by acid anhydrides. 

Perkin reaction Condensation of aromatic aldehydes with the anhydrides of aliphatic carboxylic acids to afford a,P-unsaturated carboxylic acids. 338... 

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