Preparation of Cinnamic Acids

1 g of benzaldehyde, 61 g of sodium acetate and 18 g of potassium carbonate were initially introduced into a 2 litre flask with stirrer, reflux condenser, thermometer and dropping funnel, and were heated to 160° C. Then 136 g of acetic anhydride were added dropwise at a constant rate within 80 minutes. The mixture was then heated under reflux for 6 hours and 40 minutes. A sample of 27.1 g of the reaction mixture thus obtained exhibited, as a 10% by weight solution in glacial acetic acid, a Hazen number of 350 (APHA). The volatile constituents were then removed by distillation (111 g). 700 mL. of water and 250 mL. of toluene were added to the residue. The aqueous phase was adjusted to pH 8, and then the phases were separated. Extraction was repeated twice more with 200 mL of toluene each time, and then the cinnamic acid was isolated from the aqueous phase by acidification. 96.6 g of cinnamic acid with a Hazen number of 200 (APHA), measured as a 10% by weight solution in glacial acetic acid, were obtained. The purity of the cinnamic acid was more than 99%. 

4 g of benzaldehyde, 182 g of sodium acetate and 47 g of potassium carbonate were initially introduced into a 2 litre four-necked flask with stirrer, thermometer, dropping funnel (500 mL.) with facility for passing N2 over, and distillation device, and were heated to 165° C. At a constant bottom temperature of 165° C., 385 mL. (408 g) of acetic anhydride were added dropwise at a constant rate within 260 min. After the addition of about 150 mL. of acetic anhydride, reflux at the top of the column started, and a distillate was removed under normal pressure and at an overhead temperature of 117° C. (maximum 118.5° C.). After the end of the addition of the acetic anhydride, removal of distillate was continued for as long as this was possible at a bottom temperature of 165° (about 15 min.). A sample from the reaction mixture had a Hazen 

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Another potentially valuable method for the preparation of cinnamic acid involves treatment of benzaldehyde with ketene (12). The initially formed oligomer of P-hydroxy-P-phenylpropionic acid is thermally decomposed at 100—250°C in the presence of an acid or base catalyst. 

The standard procedure is illustrated by the preparation of cinnamic acid and furylacrylic acid (Expt 6.138). The cinnamic acid obtained is the more stable ( )-isomer. It may be readily reduced to the saturated acid (3-phenylpropanoicacid) and two procedures are described. Catalytic hydrogenation is a convenient method, but the conjugated double bond may also be reduced with, for example, sodium amalgam in the presence of alkali. 

Fig. 10.48. A Knoevenagel reaction with a twist preparation of cinnamic acid.

There are a large number of variations on this general theme, in which both the source of the carbanion and the carbonyl recipient have been varied. The preparation of cinnamic acid and its ester from benzalde-hyde exemplify some of these reactions (Scheme 3.84). 

C) Preparation of Cinnamic Acid (Sm.). Arrange an eight-inch... 

Preparation of Cinnamic Acid from Benzylidene Acetone... 

Preparation of Cinnamic Acids from Styryl Ketones... 

Beattie, J., H. Production of Parsley, Leaflet No. 136 1937 USDA Beitzke, B. Handschuh, V. Blank, H.U. Process for the Preparation of Cinnamic Acids which are Optionally Substituted in the Nucleus 1986 US 4,613,692... 

Preparation of Cinnamic Acids and Related Aromatic Derivatives... 

This reaction is very useful for the preparation of cinnamic acid derivatives. 

A study has been made on the scope and mechanism of the preparation of cinnamic acid derivatives by reaction of saturated aliphatic acids with... 

The reaction is often used for the preparation of cinnamic acids in 74-77% yield (eq 32). 

J.1 Preparation of Cinnamic Acids and Related Aromatic Derivatives 1.12 Aliphatic Aldehydes and Ketones... 

Table 1 Preparation of Cinnamic Acids brom Substituted Benzaldehydes - ...

An alternative method for the classical Knoevenagel-type preparation of cinnamic acids has been reported this came to light during a study of the bromine-induced decarboxylation of substituted cinnamic acids. Cinnamic acid derivatives can also be prepared by the palladium-catalysed coupling of methyl acrylate with electron-rich aryl iodidessimilarly 5-arylpenta-2,4-dienoic acids (29) can be synthesized from penta-2,4-dienoic acid and bromo-aryls. A Stobbe-type condensation between aromatic aldehydes and methyl propylidenemalonate leads to the , -unsaturated acids (30), probably via a 5-lactone intermediate. ... 

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