Cinnamic acid reduction

[Ritter]

Rhodium:

I found two reductions of cinnamic acid for you:

Nickel-Aluminum alloy in 10%NaOH at 90-100'C (80-95% yields)
Org. Synth. Col. Vol. 4  p 136
J. Chem. Soc. 1948, 999

Saturation via chromous sulfate:
JACS 1966, 88, 4964

[Rhodium]

Thank you. The Org. Syn. ref can also be found here:

http://www.orgsyn.org/orgsyn/prep.asp?prep=cv4p0136

beta-(o-Carboxyphenyl)propionic acid

In an open 1-l.wide-mouthed round-bottomed flask are placed 18 g. (0.094 mole) of o-carboxycinnamic acid and 550 ml. of 10% sodium hydroxide solution. The mixture is warmed to 90°C (Note on a steam bath and stirred mechanically. The steam bath is then removed while 54 g. (Note 9) of nickel-aluminum alloy (Raney catalyst) powder is added through the open neck of the flask in small portions (from the end of a spatula) at frequent intervals (Note 10). When addition of the alloy is complete (about 50 minutes), the mixture is stirred and maintained at 90-95°C for 1 hour by warming on a steam bath. Distilled water is added as needed to maintain the total volume at approximately 550 ml. The hot mixture is filtered with suction, and the metallic residue is washed with 50 ml. of hot 10% sodium hydroxide solution and two 50-ml. portions of hot water in such a manner that the solid is always covered with liquid (Note 11). The cooled filtrate and washings are added dropwise with mechanical stirring to 300 ml. of concentrated hydrochloric acid (sp. gr. 1.19) in an open 2-l. beaker at such a rate that the temperature does not exceed 80-85°C (Note 12). Separation of crystalline material begins almost immediately and is complete when the beaker contents have cooled to room temperature. The beta-(o-carboxyphenyl)propionic acid is separated by suction filtration, washed with water, and air-dried (Note 13). The yield is 16.8-17.3 g. (92-95%), m.p. 165.5-167°C (Note 14).

Notes:

8. It is advisable to insert a thermometer only at intervals since the alkaline mixture attacks glassware to an appreciable extent on prolonged contact.

9. Using less than 50 g. of the alloy results in the same yield of final product, which, however, contains small amounts of unchanged o-carboxycinnamic acid. Equally good results are obtained when proportionately smaller quantities of reactants are used.

10. If excessive foaming is encountered it may be controlled as required by the addition of a few drops of octyl alcohol.

11. The metallic residue may ignite if allowed to dry on the filter. Disposal can be carried out by dissolving the residue in dilute nitric acid. (Caution! Vigorous reaction.)

12. With this order of addition, aluminum salts remain in solution, thus simplifying the procedure. External cooling may be applied in order to save time.

13. Extraction of the filtrate with ether gives an additional 0.4-0.5 g. of the crude acid after removal of solvent by distillation. It may be purified by conventional means to give an additional 0.25-0.35 g. of the pure product.

14. beta-(o-Carboxyphenyl)propionic acid may be recrystallized from hot water (about 20 ml./g.), giving material m.p. 166.5-167.5°C.

[Rhodium]

3-(4-Nitrophenyl)propanoic acid

A suspension of 4-nitrocinnamic acid (13.5 g, 70 mmol) in H2O (100 mL) was treated with hydroxylamine sulfate (18.5 g, 113 mmol) and
hydroxylamine-o-sulfonic acid (43.5 g, 385 mmol) at 0°C. The pH was adjusted to 7.6 with 50% NaOH, and additional base was added as
needed over the next 6 hours to maintain a pH of 7.6. The mixture was then filtered, and the filtrate was acidified to pH 2 with 2N H2SO4.
The solids that formed were filtered, washed with H2O, and recrystallized from EtOH:H.sub.2 O (30 mL:150 mL) to give the title compound.

Ref: US Pat 6,046,355 (Example DD)

Just HOW does this work? Cinnamic acid that usually only can be reduced by H2/Pd, Na/Hg or electroreduction suddenly can be reduced by hydroxylamine derivatives?