The author of 《Commercial dyes synthesized under solvent-free or aqueous-only conditions》 were Soydaner, Umut; Ozturk, Gozde Ipek; Taralp, Alpay. And the article was published in Preprints of Extended Abstracts presented at the ACS National Meeting in 2004. Safety of 2-Hydroxy-2-(4-propoxyphenyl)acetic acid The author mentioned the following in the article:
In this work, the literature synthesis of C.I. Disperse Red 356 from 4-propoxymandelic acid was revised to exclude the use of H2SO4 and PhCl. P-toluenesulfonic acid was used as the catalyst. In addition to this study using 2-Hydroxy-2-(4-propoxyphenyl)acetic acid, there are many other studies that have used 2-Hydroxy-2-(4-propoxyphenyl)acetic acid(cas: 79694-16-9Safety of 2-Hydroxy-2-(4-propoxyphenyl)acetic acid) was used in this study.
2-Hydroxy-2-(4-propoxyphenyl)acetic acid(cas: 79694-16-9) belongs to ethers. Ethers lack the hydroxyl groups of alcohols. Safety of 2-Hydroxy-2-(4-propoxyphenyl)acetic acid Without the strongly polarized O―H bond, ether molecules cannot engage in hydrogen bonding with each other.
Referemce:
Ether – Wikipedia,
Ether | (C2H5)2O – PubChem