W-Nitrocinnamic acid

A. tn-NUrocinnamic acid. In a 1-1. round-bottomed flask fitted with a reflux condenser are placed 151 g. (1 mole) of tw-nitro-benzaldehyde (Note 1), 115 g. (1.1 moles) of malonic acid, 250 ml. of 95% ethanol, and 25 ml. of pyridine. The mixture is heated on a steam bath under gentle reflux for 6-8 hours and cooled. The large masses of crystals are broken up with a spatula, and the reaction mixture is cooled in an ice bath. The solid is collected on a Buchner funnel, and the residue is washed with 100 ml. of cold ethanol and then with two 100-ml. portions of diethyl ether. The crude w-nitrocinnamic acid is suspended in 300 ml. of ethanol and digested on a steam plate for 2-3 hours. The mixture is cooled and filtered, and the solid is air-dried. The product, 144 155 g. (75-80%), is a light-yellow solid and melts at 200-201° (Note 2). 

In one run, the product was extracted from the reaction mixture with benzene, removed from the benzene by a sodium carbonate solution, and this solution in turn acidified to obtain the w-nitrocinnamic acid. Neither the product nor the yield was as satisfactory by this method. 

If acid is added to the solution of the ammonium salt, the precipitated w-nitrocinnamic acid carries down a considerable quantity of ammonium salts. 

The melting point of w-nitrocinnamic add is given in the literature as 195° and 196-197°. Beilstein describes it as yellow needles. Alcohol is mentioned as a good solvent for recrystallization but experience in this work showed that benzene is also satisfactory, a white w-nitrocinnamic acid being obtained from this solvent. 

After the last precipitation, the w-nitrocinnamic acid is washed with a little water and then sucked as dry as possible (Note 5). The product, which still contains considerable water, is dissolved in 250-300 cc. of boiling 95 per cent alcohol from which the nitrocinnamic acid crystallizes on cooling. The yield amounts to 47-49 g. (74-77 per cent of the theoretical amount). 

Decarboxylation Reactions. Taking advantage of its basic properties, quinoline is generally useful as a solvent for decarboxylation reactions. It is especially suitable because its relatively high boiling point facilitates the decarboxylation. Examples include the decarboxylation of 3-methyl-2-furoic acid (10) to 3-methylfuran (11) (eq 6), /w-nitrocinnamic acid (12) to m-nitrost)frene (13) (eq and a-phenylcinnamic acid (14) to cis-stilbene (15) (eq 8). Copper catalysts such as copper or copper chromite are used to effect the decarboxylations. 

This procedure has been used by the submitters and others to prepare the following cinnamic acids from substituted benzal-dehydes o-nitrocinnamic acid (70%),2 -nitrocinnamic acid (77%),2 w-cyanocinnamic acid (71%),3 o-chlorocinnamic acid (82%),4 m-chlorocinnamic acid (53%),4 -chlorocinnamic acid (73%),4 2,4-dichlorocinnamic acid (70%),4 3,4-dichlorocinnamic acid (81%),4 w-bromocinnamic acid (31%),4 -methoxycinnamic acid (60%),4 and 3,4-dimethoxycinnamic acid (77%).4... 

Hartman, I., and P. W. Robertson The Kinetics of Halogen Addition to Unsaturated Compounds. Part XX. Nitrocinnamic Acids. J. chem. Soc. (London) 1945, 891-... 

---