Phenylacetic acid
| Names | |
|---|---|
| IUPAC name
Phenylethanoic acid
| |
| Preferred IUPAC name
Phenylethanoic acid | |
| Other names
2-Phenylacetic acid
Alpha tolylic acid Benzeneacetic acid PAA α-Toluic acid β-Phenylacetic acid | |
| Properties | |
| C8H8O2 C6H5CH2COOH | |
| Molar mass | 136.15 g/mol |
| Appearance | White solid |
| Odor | Honey-like |
| Density | 1.081 g/cm3 (25 °C) |
| Melting point | 76.7 °C (170.1 °F; 349.8 K) |
| Boiling point | 265.5 °C (509.9 °F; 538.6 K) |
| 1.50 g/100 ml (20 °C) 1.73 g/100 ml (25 °C) | |
| Solubility | Very soluble in acetone, carbon disulfide, diethyl ether, ethanol Slightly soluble in chloroform Insoluble in ligroin |
| Vapor pressure | 3.8·10-3 mmHg at 25 °C |
| Acidity (pKa) | 4.31 |
| Thermochemistry | |
| Hazards | |
| Safety data sheet | Sigma-Aldrich |
| Flash point | 132 °C (270 °F; 405 K) |
| Related compounds | |
| Related compounds
|
Benzoic acid Phenylpropanoic acid |
| Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
| Infobox references | |
Phenylacetic acid (PAA), also called benzeneacetic acid, 2-phenylacetic acid and β-phenylacetic acid, is an organic chemical compound, an aromatic carboxylic acid with the chemical formula C8H8O2 or C6H5CH2COOH.
Contents
Properties
Chemical
Phenylacetic acid reacts with bases to form their respective salts.
Heating a mixture of phenylacetic acid and acetic anhydride yields phenylacetone.
- C6H5CH2COOH + (CH3CO)2O → C6H5CH2COCH3
Other acetates, such as sodium, potassium and lead acetate can be used, giving different yields. A large excess of acetic anhydride must be used in this reaction, otherwise dibenzyl ketone will be formed[1]
Physical
Phenylacetic acid is a white solid, with a honey-like odor. It is slightly soluble in water, but more soluble in organic solvents.
Availability
Phenylacetic acid is sold by chemical suppliers, but due to its legal status as drug precursor (used in the production of P2P and amphetamine-class drugs), it cannot be purchased by the home chemist without a hard to acquire permit. Since it's classified as List I drug precursor in most countries, it's almost impossible to be acquired by the hobby chemist. In the United States it is classified as a DEA List I chemical.
In some countries, methyl phenylacetate is available for sale as artificial honey-like fragrance, for use in perfumes. The free acid can be obtained from its hydrolysis.
Preparation
There are several routes to PAA:
Hydrolysis of benzyl cyanide gives phenylacetic acid. Sulfuric acid is often used as catalyst, usually as 70% concentration, however concentrated hydrochloric acid can also be used.[2][3] This is the most common route to PAA.
Oxidation of phenethyl alcohol using acidified KMnO4 will yield phenylacetic acid.
- C6H5CH2CH2OH + [O] → C6H5CH2COOH
Another route, involves reacting benzylmagnesium chloride (obtained by reacting perfectly dry benzyl chloride with Grignard reagent-grade magnesium flakes) in a dry and inert reaction flask with dry carbon dioxide. This yields very pure phenylacetic acid, though this route is expensive.[4]
Mandelic acid can be reduced with HI and red phoshporus to phenylacetic acid.[5]
Phenylacetic acid can also be obtained from acetophenone, by reacting the ketone with boron trifluoride etherate and lead(IV) acetate in dry benzene. This produces methyl phenylacetate, which is hydrolyzed with NaOH and acidified with HCl to yield the free acid.[6]
Another method that starts from acetophenone involves a Willgerodt–Kindler reaction with sulfur and morpholine. The resulting product 4-(phenylthioacetyl)morpholine is obtained in 80% yield.[7] Hydrolysis of the substance with potassium hydroxide and workup provides phenylacetic acid.[8][9]
An interesting route involves the oxidation of ethylbenzene with sodium dichromate solution in an autoclave, at 275 °C for several hours. The yield of this reaction is given as 90%. While dangerous, this route is attractive since the reagents are cheap and easy to acquire.[10]
Phenylacetate esters, like methyl phenylacetate, will yield phenylacetic acid via simple ester hydrolysis.
Projects
- Preparation of diclofenac (Voltaren)
- Preparation of sodium phenylacetate (used in Ammonul, as treatment of urea cycle disorders)
- Preparation of methyl phenylacetate, which has an odor very similar to that of honey
- Preparation of phenylacetone
Handling
Safety
Phenylacetic is only mildly corrosive and has low toxicity, though it's irritant.
Storage
In closed airtight bottles, away from bases and light.
Disposal
No special disposal is required. Can be diluted in water and slowly poured down the drain.
References
- ↑ https://erowid.org/archive/rhodium/chemistry/phenylacetone.html#phenylacetic
- ↑ Perfumery Essent. Oil Record 14, 336 (1924)
- ↑ https://erowid.org/archive/rhodium/chemistry/phenylacetic.html
- ↑ https://pubs.acs.org/doi/10.1021/ja01341a031
- ↑ https://onlinelibrary.wiley.com/doi/10.1002/hlca.19390220174
- ↑ https://www.thieme-connect.com/products/ejournals/abstract/10.1055/s-1981-29358
- ↑ https://illumina-chemie.de/viewtopic.php?t=4511
- ↑ H. G. O. Becker et al., Organikum, 22nd edition 2004, p. 427
- ↑ H. G. O. Becker et al., Organikum, 24th edition 2014, p. 436-437
- ↑ https://pubs.acs.org/doi/10.1021/jo01048a006
