Sodium Benzoate
Properties
| State | Solid at room temperature |
| Color | White crystalline powder |
| Solubility | Soluble in water (62.7 g/100 mL at 25 °C) |
| Melting Point | Decomposes above 300 °C |
About Sodium Benzoate
Sodium benzoate is the sodium salt of benzoic acid, formula NaC7H5O2 with a molar mass of 144.103 g/mol. It is the food preservative that keeps your bottle of soy sauce, your jar of pickles, and your supermarket fruit juice from fermenting on the shelf. It works because at pH below about 4.5 the equilibrium tips back toward undissociated benzoic acid (pKa 4.20), which is membrane-permeable. Once benzoic acid crosses into a yeast or mold cell, it dissociates against the higher cytoplasmic pH, dumping a proton load that the cell cannot easily pump back out and stalling glycolysis at the phosphofructokinase step. Above pH 4.5 you get mostly the charged benzoate anion, which doesn't cross membranes well — that is why sodium benzoate is useless in high-pH foods like cured meats, which use sorbate or nitrite instead. Industrial production is straightforward: bubble benzoic acid into NaOH or Na2CO3 solution and crystallize. The compound is on the FDA GRAS list at up to 0.1 percent in finished foods. Coca-Cola and Pepsi reformulated the diet variants of several drinks in the mid-2000s after FDA testing flagged benzene formation in trace amounts when ascorbate and benzoate sat together in sun-warmed bottles.
Where you'll encounter it
If you've ever read the ingredient label on a bottle of Sprite, a jar of Branston pickle, or Heinz Ketchup, you've already met E211. Beyond the supermarket, sodium benzoate is what cardiologists give intravenously as part of the ammonia-scavenging cocktail (Ammonul, with sodium phenylacetate) for newborns in hyperammonemic crisis from urea cycle disorders — the benzoate conjugates with glycine to form hippurate, which the kidneys excrete and carries one nitrogen equivalent out per molecule. In pyrotechnics, finely milled sodium benzoate mixed with potassium perchlorate is the signature whistle composition: as the column burns down, alternating fast and slow combustion oscillates pressure in the tube to produce the rising whistle of consumer fireworks. Mechanics see it as a corrosion inhibitor in aqueous engine coolants for cast iron blocks. Cosmetic chemists use it at 0.5 percent in shampoo and conditioner along with potassium sorbate as a paraben-free preservative system.
Common Uses
- Antimicrobial preservative (E211) in carbonated soft drinks, juice, jams
- Fungistatic in pickles, sauces, and acidic salad dressings below pH 4.5
- Hippurate-pathway nitrogen scavenger in IV treatment of urea cycle disorders
- Whistle-fuel composition with potassium perchlorate in pyrotechnic devices
- Corrosion inhibitor for ferrous metals in aqueous engine coolant blends
- Preservative in shampoos and water-based cosmetics at 0.5 percent
- Plasticizer additive and nucleating agent in polyolefin processing
- Tablet lubricant and antimicrobial in oral pharmaceutical formulations
Safety Information
GRAS at food-grade concentrations, with a permitted use level in finished foods set under 21 CFR 184.1733. GHS: H319 (causes serious eye irritation), no other classifications. No occupational exposure limit has been set. JECFA has assigned an acceptable daily intake. The well-documented hazard is in-bottle benzene formation: ascorbic acid plus benzoate ion plus trace transition metal catalyst (iron, copper) plus heat or UV produces parts-per-billion benzene through a hydroxyl-radical-mediated decarboxylation. FDA sampling in 2006 found 4 of 200 beverages above the drinking-water limit for benzene, prompting reformulation of Diet Pepsi Wild Cherry and several others. Pseudoallergic reactions in aspirin-sensitive asthmatics are documented but rare. Standard PPE (gloves, dust mask) is sufficient for bulk handling.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals. We deliberately do not publish occupational exposure limits or other regulatory thresholds: those values are revised over time and differ between jurisdictions, so the only correct source is the current SDS and the regulations that apply where you work.