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4-Hydroxybenzaldehyde (CAS 123-08-0): A Buyer's and Chemist's Guide to Properties, Quality Control, Safe Handling and Sourcing
4-Hydroxybenzaldehyde (also called p-hydroxybenzaldehyde, 4-formylphenol or PHB) looks like an ordinary pale crystalline powder. Procurement and R&D teams still run into the same problems with it: published melting points disagree, a batch yellows in storage, and different suppliers' safety data sheets classify it differently.
1. What 4-Hydroxybenzaldehyde Is
The molecule is a benzene ring carrying an aldehyde group (–CHO) and a hydroxyl group (–OH) in the para position. Both groups are reactive, which is why the compound is useful. The aldehyde can be oxidized, reduced or condensed. The phenolic hydroxyl can be alkylated, acylated or deprotonated. Because the two groups sit opposite each other, products stay linear and symmetrical, a feature that matters in liquid-crystal intermediates and in drug scaffolds.
The same compound occurs in nature. It is a volatile found in foods such as grapes, tea and wine, and plant tissue cultures of vanilla orchid produce it enzymatically (see references 1 and 4).
| Parameter | Typical value |
|---|---|
| CAS number / EC number | 123-08-0 / 204-599-1 |
| Molecular formula / weight | C7H6O2 / 122.12 g/mol |
| Appearance | White to light yellow or light brown crystalline powder |
| Melting point (literature) | 112–116 °C |
| Boiling point | About 191 °C at 50 mmHg (reduced pressure) |
| Density | About 1.129 g/cm³ |
| Water solubility | About 13–14 g/L at 30 °C; freely soluble in ethanol, ether, acetone and ethyl acetate |
| pKa (phenolic OH) | About 7.6 at 25 °C |
| Flash point | About 174 °C |
| HS code (customs) | 2912.49 |
Data compiled from supplier and database records (references 1, 2 and 3). Values vary slightly by source and purity grade, so always confirm against the batch Certificate of Analysis.
2. Where It Is Used
Most demand comes from four areas:
| Sector | Role of 4-hydroxybenzaldehyde | Examples reported in the literature |
|---|---|---|
| Pharmaceuticals | Starting material or intermediate for active ingredients | Trimethoprim, amoxicillin (through p-hydroxyphenylglycine), cefadroxil, esmolol, bezafibrate |
| Flavors and fragrances | Precursor to other aroma chemicals | Anisaldehyde, vanillin, ethyl vanillin, raspberry ketone |
| Agrochemicals | Intermediate for halogenated benzonitrile herbicides | Bromoxynil |
| Materials and research | Building block for liquid-crystal intermediates, Schiff bases and enzyme-inhibitor studies | Tyrosinase inhibitor derivatives (reference 4) |
Sources: references 1, 3 and 4.
A useful link for buyers: methylating the hydroxyl group of 4-hydroxybenzaldehyde gives anisaldehyde. If your process chain runs from phenolic aldehyde to methoxy aromatics, you may be able to source both stages from one supplier. See our P-Anisaldehyde, 4-Methoxybenzyl alcohol and P-Anisic acid pages.
3. How It Is Made, and Why That Affects Quality
Several commercial routes exist. The classic one is the Reimer–Tiemann reaction, in which phenol reacts with chloroform in alkaline solution. It gives mostly the para isomer plus some salicylaldehyde (the ortho isomer). Other reported routes start from p-cresol or use direct formylation of phenol (reference 1).
What matters for you is the impurity profile each route leaves behind. The ortho isomer, unreacted phenol and 4-hydroxybenzoic acid (from over-oxidation) are the usual suspects. Pharmaceutical and fragrance users should ask which route produced the batch, because a trace impurity that is harmless in a pigment intermediate may be unacceptable in an API step.
4. Quality Control: What to Check on a Certificate of Analysis
Jinli lists two typical grades for this product. The values below come from our 4-Hydroxybenzaldehyde product page.
| Test | Grade A | Grade B | Why it matters |
|---|---|---|---|
| Appearance | Light yellow crystalline powder | White crystalline powder | Color is a quick indicator of oxidation history |
| Purity | 99% min | 99.5% min | Drives yield and downstream impurity load |
| Melting point | 114.5–117 °C | 115–117 °C | A broad or depressed range signals impurities |
| Water | 0.5% max | 0.3% max | Matters for moisture-sensitive reactions |
| Heavy metals | 10 max | 10 max | Important for pharma and food-contact end uses |
| Chloride | 100 ppm max | 100 ppm max | Residue from chlorinated routes; can poison catalysts |
Heavy-metal limits are normally expressed in ppm; confirm the unit on the batch COA.
Practical advice from incoming-inspection practice:
- Run melting point plus HPLC on each lot. Melting point is quick and cheap; HPLC identifies which impurity is present.
- Do not reject a lot only because it is faintly yellow. The literature describes the material as ranging from white to light brown, so purity and impurity data should decide acceptance, not color alone.
- Compare the melting point against the 112–116 °C literature range. A value far outside it points to a data error or a wrong material.
5. Safe Handling and Storage
Hazards. Supplier safety data sheets agree that the compound is an irritant but differ on severity. Several list skin irritation (H315), serious eye irritation (H319) and respiratory irritation (H335). At least one major supplier classifies it as causing serious eye damage (H318). Reported oral toxicity is low (rabbit LD50 about 2,250 mg/kg), but dust still deserves respect. Always follow the SDS that ships with your own lot (references 2, 3 and 5).
Protective measures. Wear safety goggles, chemical-resistant gloves and a lab coat. Weigh and transfer powder in a ventilated enclosure or fume hood to keep dust out of the breathing zone. If it contacts skin, wash with soap and water; for eyes, rinse with water for several minutes and seek medical advice if irritation persists.
Storage. Keep it in a tightly closed container below 30 °C, away from light and strong oxidizers. Data sheets flag the material as air-sensitive and hygroscopic (reference 1). The practical risk is slow oxidation of the aldehyde to 4-hydroxybenzoic acid and moisture pick-up, which shows up as darkening, caking and a lower assay. For long storage, use sealed liners and consider purging the headspace with nitrogen after each opening.
6. A Sourcing Checklist
Before you place an order, ask any supplier, including us, for the following:
| Item | What to ask for |
|---|---|
| Batch documents | COA with assay method, melting range, water and impurity data |
| Safety documents | Current SDS in your region's format |
| Quality systems | ISO 9001, ISO 14001 and ISO 45001 certificates |
| Process transparency | Synthesis route category and change-notification policy |
| Packaging | Liner type, net weight per drum, label language, custom options |
| Samples | A retained-sample policy so you can compare lots over time |
7. About the Manufacturer
Jiaxing Jinli Chemical Co., Ltd. was founded in 2002 and operates from the Jiaxing Port Area Chemical Park in Zhejiang, China. According to our company profile, the site covers 22,000 square meters with annual capacity of 19,000 tons, and the company holds ISO 9001, ISO 14001 and ISO 45001 certification. Jinli is recognized as a national high-tech enterprise and works with university research partners, as described on our Technology page. Our products ship to the USA, EU, Korea, Japan and Southeast Asia.
For a summary of functions, packaging and customer types, read our earlier article, 4-Hydroxybenzaldehyde: Functions, Applications, Features, Specifications, and Industry Overview. To browse related chemistry, visit the Intermediates Series or the Industry News archive.
8. Request a Quote or Technical Data
Price depends on grade, order quantity and packaging. To request a quotation, a COA or an SDS, contact our team through the Contact page:
- Hotline: 0086-573-85580888
- Sales: Tommy Guo, tommy@jinlichemical.com, +86-18606736623
- Address: Intersection of Pinghai Road and Binhai Avenue, Jiaxing Port Area Chemical Park, China
Frequently Asked Questions
Is 4-hydroxybenzaldehyde the same as salicylaldehyde?
No. Salicylaldehyde is the ortho isomer (2-hydroxybenzaldehyde) and is a liquid at room temperature. The 4- (para) isomer is a solid that melts around 115 °C.
Why has my sample turned yellow or brown?
Light, air and moisture cause gradual oxidation and discoloration. Check purity by HPLC and melting point before deciding whether the lot is still usable, and tighten your storage practice.
Can it be recrystallized?
Yes. Laboratory literature reports recrystallization from water (reference 1), which helps remove colored impurities in small-scale work. Validate the method for your own purity target.
