What is the solubility of 4-Phenylbutyric Acid in water?

It doesn't trend on Twitter. It won't make the evening news. But in labs from Boston to Beijing, CAS 1821-12-1—better known as 4-phenylbutyric acid (4-PBA)—is quietly rewriting medical playbooks and enabling chemistry that ends up in your medicine cabinet, your clothes, and maybe one day your dialysis-free future.

 What is it?
A simple aromatic fatty acid: ten carbons, two oxygens, one gentle phenyl ring.
• Appearance: fluffy white needles
• Melting point: 49–51 °C—low enough to melt on a hot bench, high enough to stay solid during shipping
• Solubility: 5.3 g L⁻¹ in water at 40 °C, infinite in hope
• LogP: ~2.7—lipophilic enough to cross membranes, hydrophilic enough to play nice in blood

The Nephrologist's Secret Weapon
Kidneys fail when stressed-out tubules commit apoptosis via unfolded-protein hell in the endoplasmic reticulum.
4-PBA acts like a chemical chaperone: it stabilizes misfolded proteins, dials down the ER-stress alarm (PERK, IRE1α), and cuts renal cell death by up to 60 % in ischemia-reperfusion models. Translation: less fibrosis, less dialysis, more life.

The Medicinal-Chemist's Swiss-Army Side-Chain
Need a GABA-mimetic? Extend the chain.
Need an HDAC inhibitor? Hang a hydroxamate off the acid.
Need a brain-penetrant neuroprotectant? The phenyl ring taxis it across the BBB.
Over 120 PubMed syntheses cite 4-PBA as the launchpad for anti-inflammatory, antiepileptic, and even anti-COVID-19 small molecules.

 The Dye-Chemist's Forgotten Feedstock
Azo dyes don't grow on trees. Diazotize, couple, and—boom—sun-fast yellows and medical imaging contrast agents emerge from that same innocuous jar.

🌍 Green Credentials
• Readily biodegradable (OECD 301D: 78 % in 28 days)
• No PFAS, no heavy metals, no SVOC nightmares
• Bulk synthesis from benzyl chloride + malonic ester—98 % atom economy if you recycle your ethanol

⚠️ Handle with (Normal) Care
• Non-hazardous under GHS
• Dust mask + goggles suffice
• Store at RT, keep dry, and it will outlast your PhD

So the next time you're inventorying shelves and see that plain white bottle with the understated label "1821-12-1", give it a nod. Inside is a molecule that protects organs, inspires patents, and colors the world—all without ever asking for credit. Because real heroes don't always glitter. Sometimes they just crystallize.