Synthesis of Phenylacetic acid from Mandelic acid (small scale)

[WillD]

Reaction scheme:

Synthesis:
1. Mandelic acid (15,0 g) was dissolved in hypophosphorous acid 85% aq (15 ml).

2. Iodine (15 g) was added in a small portions, whilst heating at reflux for 1 hour.

3. The solution was poured over cold water and the crude product recrystallised from hot water to yield a colourless crystalline product 10 g.

 

[rabbitass]

Hello, I am very interested in this synthesis, at least where I am from it is very easy to get kg of L-mandelic acid, what I am having a hard time is getting the hypophosphorous acid, can I replace it with another acid that is easier for me to get?

 

[lalalander]

Hello, I am very interested in this synthesis, at least where I am from it is very easy to get kg of L-mandelic acid, what I am having a hard time is getting the hypophosphorous acid, can I replace it with another acid that is easier for me to get?

rabbitassI don't think so. If you can find red phosphorus, you can also use phosphoric acid. It is much, much easier to find than hypophosphoric acid. Of course, finding red phosphorus is still a problem.

 

[lalalander]

Hypophosphorus acid is a pain in the ass to find.

 

[WillD]

It is precisely hypo. It is hard to get, but it suits the best. Obtaining meth from ephedrine is similar.

 

[hacke8]

It is precisely hypo. It is hard to get, but it suits the best. Obtaining meth from ephedrine is similar.

WillDHello, Will Chemist, can you publish a thread for preparing P2P with phenylacetic acid? I haven't found it for a long time. Thank you.

 

[OrgUnikum]

Looks you guys are missing something here. Possible phosphorus based reagents for the reduction are:
- RP, red phosphorus with iodine
- H3PO2, hypophosphorous acid and iodine
- H3PO3, phosphorous acid and iodine
- H3PO4, orthophosphoric or just phosphoric acid and NaI or KI, sodium iodide or potassium iodide

Whereby H3PO2 and H3PO3 are preferred.
All of those form HI, hydroiodic acid, whats the actual reducing agent.

H3PO2 is made from sodium or calcium or potassium hypophosphite and HCl. Look for "electroless nickel plating" and you find it.
H3PO3 is used in hydroponics and vineyards
H3PO4 is all over the place as rust remover, descaler etc.

Iodine is made by oxidation of NaI or KI.
NaI or KI are used for water disinfection, look for "Preppers" and "Survivalists"

btw. PAA. phenylacetic acid has a very special and sticky smell which is not washed off easily, be warned. Or better: It stinks like hell and so will you when making it. And the smell will be with you for about a week no matter how often you shower.