Print version Print setup

Reduction of benzpthalide to 2-(2-phenylethyl) benzoic acid; 2-(2-phenylethyl) benzoic acid

SyntheticPage 929
Submitted Jul 02, 2020, published Jul 06, 2020
Ramesha Ramakrishna (
A contribution from ramesha

			Reaction Scheme: Reduction of benzpthalide to 2-(2-phenylethyl) benzoic acid

Chemicals Used

1. Benzpthalide, commercial, min 99% (one can also buy from Aldrich)

2. Ni-Al alloy (50:50), Commercial.

3. Toluene, commercial, 99%

4. Sodium hydroxide -Commercial, min 99%

5. Hydrochloric acid, commercial, about 35%

6. Acetic acid, commercial, > 98%



Preparation of 2-(2-Phenylethyl)benzoicacid from Benzpthalide

To a stirred a solution of sodium hydroxide (20 g, 0.5 mole) in water (500 mL), benzpthalide (105 g, 0.47 mole) was added all at once and heated to about 95-98°C. After stirring for 30-35 min, benzpthalide is completely soluble in water. The aqueous solution was cooled to about 40°C and pH adjusted to about 7.5-8 with acetic acid (about 3-5 mL required). Once pH is adjusted, Nickel-aluminium alloy (60 g) was added small portions at 50-60°C over a period of 4 hours. After complete addition of Ni-Al alloy, the reaction mixture was heated and stirred at 95-98°C and maintained at the same temperature for 8 h, then cooled to room temperature. Raney Nickel thus formed was filtered and washed with 100 mL hot water twice (Note: This process gives highly active pyrophoric Raney Nickel, this can be disposed of in water). The aqueous layer thus obtained is acidified with conc. HCl (200 mL). The white precipitate thus obtained was filtered and washed with water. The product can be dried at 80-90 °C for 6 h to get almost white 2-(2-phenylethyl)benzoic acid . The product thus obtained is practically pure by NMR. (Yield: 98-100g, Yield: 93%).


Author's Comments

1. Ni-Aluminium (50:50) alloy should not be added all at once. This might lead to run away reaction.

2. Frothing is observed if the pH is above 8. Therefore, at least 50% empty space is required in the reaction flask.



Melting point: 128-132 oC.

1H NMR (400 MHz, CDCl3): δ 8.10 (q, J = 8.0 Hz, 1H), 7.49-7.45 (m, 1H), 7.33-7.16 (m, 7H), 3.33 ( t, J = 8.0 Hz, 2H), 2.94 (t, J = 8.0 Hz, 2H)

13C NMR (100 MHz, CDCl3): δ 37.6, 38.6, 126.4, 126.7, 128.6, 128.8, 129.0,132.0, 132.3, 133.5, 142.4, 145.3, 173.9.


Lead Reference

Lead reference:

1. Metz, G. Synthesis 1972, 612.

2. Kollonitsch, J.I.; Mertel, H.E.; Verdi, V.F. J. Org. Chem. 1962, 27, 3362.

3. A. R. Ramesha.; Anjan K. Roy, Synthetic Communication, 2001, 31(16), 2419-2422.


Other References


Supplementary Information

Synthesis of Phenyl ethyl benzoic acid NMR.docx

This page has been viewed approximately 334 times since records began.

Get structure file (.cdx, .sk2, .mol)

Keywords: Alkanes, alkenes, benzoic acid, benzpthalide, carboxylic acids, Ni-Al alloy, reduction

Post new comment
Loading ...