Chemical Properties
Phenylacetic Acid occurs in Japanese peppermint
oil, in neroli oil, and in traces in rose oils. It is a volatile aroma constituent
of many foods (e.g., honey). It forms colorless crystals (mp 78°C) that have a
honey odor.
The common route to phenylacetic acid is conversion of benzyl chloride into
benzyl cyanide by reaction with sodium cyanide, followed by hydrolysis. Because of its intense odor, phenylacetic acid is added to perfumes in small quantities
for rounding off blossom odors. Addition to fruit aromas imparts a sweet
honey note.
Chemical Properties
Phenylacetic acid has a sweet, animal, honey-like odor in dilute solution. The odor is persistent and disagreeable in
concentrated solution. It has a sweet, honey-like flavor at high levels. At low levels, it is a sweetener.
Chemical Properties
white crystals with a honey-like odour
Occurrence
Reported found among the constituents of a few essential oils: tobacco, Rosa centifolia, Bulgarian rose, orange
flowers absolute, neroli and Mentha arvensis of Japanese origin; also reported present among the volatile constituents of cocoa. Also
reported found in guava, papaya, raspberry, strawberry, cooked potato, tomato, peppermint oil, pepper, rye bread, cheddar cheese,
Swiss cheese, Gruyere cheese, boiled mutton, beer, cognac, cider, sherry, grape wines, white wine, sake, cocoa, tea, honey soy protein,
passion fruit, starfruit, mango, mushroom, malt, wort, roasted chicory root, naranjilla fruit, choke berry, sea buckthorn and
Chinese quince.
Definition
ChEBI: A monocarboxylic acid that is toluene in which one of the hydrogens of the methyl group has been replaced by a carboxy group.
Preparation
By the treatment of benzyl cyanide with dilute sulfuric acid and other processes.
Aroma threshold values
Detection: 1 ppm
Taste threshold values
Taste characteristics at 30 ppm: sweet, floral, chocolate, honey and tobacco.
Flammability and Explosibility
Nonflammable
Synthesis
10% of a solution of 125 g benzyl chloride in 250 ml of
sodium-distilled diethyl ether is added to 24 g magnesium turnings under
100 ml
ether, and a small iodine crystal is added. after start of the grignard
reaction the rest of the benzyl chloride is added with stirring to
maintain gentle
boiling (if the reaction becomes too vigorous, useless
1,2-diphenylethane is formed) and the mixture is heated and stirred
until most magnesium is dissolved.
The grignard reagent solution is poured on 1 kg water-free, crushed dry
ice (solid CO2) and stirred for 2 hrs. 200 ml warm ether is added and
the mixture
is heated in a water-bath until the internal temperature reaches 25°C.
200 ml 32% hydrochloric acid is added, and the heterogenous mixture
stirred until
any inorganic precipate is dissolved. after filtering, the organic layer
is separated, washed with cold water, and dried over 20 g anhydrous
sodium sulfate.
The ether is distilled off, and the rest is recrystallized from water,
to yield 75% - about 100g - phenylacetic acid, mp 76-77°C.
Metabolism
Phenylacetic acid is conjugated in man and the chimpanzee, but probably in no other species, with glutamine. In most other animals, except the hen, it behaves like benzoic acid, forming glycine and glucuronic acid conjugates. In the hen, it conjugates with ornithine, forming phenacetornithuric acid. Phenacetylglutamine and its addition compound with urea were isolated from human urine alter the administration of phenylacetic acid (Williams, 1959).
Purification Methods
Crystallise the acid from pet ether (b 40-60o), isopropyl alcohol, 50% aqueous EtOH or hot water (m 77.8-78.2o). Dry it in vacuo. It can be distilled under a vacuum. [Beilstein 9 II 294, 9 III 2169.]
