# Citric Acid (CAS 77-92-9) — Complete Guide to Properties and Applications **Category:** Organic Acid / Food Additive | **Formula:** C₆H₈O₇ | **MW:** 192.12 g/mol --- ## What Is Citric Acid? **Citric Acid (CAS 77-92-9)** is a organic acid / food additive with the molecular formula **C₆H₈O₇** and molecular weight **192.12 g/mol**. The IUPAC systematic name is **2-hydroxypropane-1,2,3-tricarboxylic acid**. It appears as a **white crystalline powder or granules**. ## Physical and Chemical Properties | Property | Value | Source | |----------|-------|--------| | CAS Number | 77-92-9 | | | Molecular Formula | C₆H₈O₇ | | | Molecular Weight | 192.12 g/mol | | | IUPAC Name | 2-hydroxypropane-1,2,3-tricarboxylic acid | | | Appearance | white crystalline powder or granules | | | Melting Point | 153–159 °C | | | Boiling Point | Decomposes above 175 °C | | | Density | 1.665 g/cm³ | | ## Green Chemistry Advantages ### Citric Acid as a Model Green Chemical Citric acid embodies twelve principles of green chemistry more comprehensively than almost any other commodity chemical. Its production, use, and environmental fate align with the philosophy of sustainable chemistry at every stage. **Principle 7 — Use of Renewable Feedstocks:** Citric acid is produced industrially through the fermentation of glucose, sucrose, or molasses by the filamentous fungus *Aspergillus niger*. The feedstock is entirely bio-based — corn starch hydrolysate, sugarcane molasses, or sugar beet juice — and does not consume petrochemical resources. Annual global production exceeds 2 million metric tons, all via fermentation, making citric acid one of the largest-volume products of industrial biotechnology. **Principle 3 — Less Hazardous Chemical Syntheses:** The fermentation process operates at near-ambient temperature (28–32 °C) and atmospheric pressure in aqueous media. The only stoichiometric inputs are the carbohydrate feedstock, oxygen (from air sparging), and inorganic nutrients (ammonium nitrate, magnesium sulfate, potassium phosphate). No organic solvents are used in the production or purification process, and the product is isolated by simple precipitation as calcium citrate, followed by acidification with sulfuric acid to regenerate citric acid and precipitate calcium sulfate (gypsum). **Principle 10 — Design for Degradation:** Citric acid is a central metabolite in the tricarboxylic acid (Krebs) cycle, the universal energy-harvesting pathway present in all aerobic organisms. When released into the environment, it is rapidly biodegraded to carbon dioxide and water through natural metabolic pathways. Its half-life in soil and surface water is measured in hours to days. It does not bioaccumulate, persist, or produce toxic transformation products — it is, quite literally, food for microorganisms. **Principle 4 — Designing Safer Chemicals:** The acute oral LD₅₀ of citric acid in rats is 3,000–5,000 mg/kg, classifying it as practically non-toxic (GHS Category 5 or unclassified). It is GRAS (Generally Recognized As Safe) by the US FDA for use in food with no upper limit other than current Good Manufacturing Practices. This safety profile enables its use as a direct food additive, pharmaceutical excipient, and personal care ingredient without the extensive toxicity testing required for synthetic alternatives. **Principle 1 — Prevention (Waste Reduction):** In its role as a descaling and cleaning agent, citric acid replaces strong mineral acids (hydrochloric, phosphoric, sulfamic) that generate corrosive waste streams. Citric acid cleaning generates biodegradable, non-toxic effluent. Its chelating ability (three carboxylate groups and one hydroxyl group provide hexadentate metal coordination) enables metal cleaning with lower acid concentrations than non-chelating mineral acids. ## Key Applications 1. **Food and Beverage Acidulant (Primary Market)**: Approximately 70% of global citric acid production is consumed by the food and beverage industry as an acidulant, flavor enhancer, and preservative. Its clean, tart taste profile makes it the preferred acid for soft drinks (cola, lemon-lime, fruit-flavored), candies, jams, jellies, and dairy products. It buffers at pH 3–6 through its three pKa values (3.13, 4.76, 6.40), providing sustained tartness and microbial stability. Citric acid also chelates trace metals (Fe, Cu) that catalyze oxidative rancidity and color degradation, extending product shelf life without synthetic antioxidants. 2. **Pharmaceutical Excipient and Effervescent Formulations**: Citric acid combined with sodium bicarbonate forms the effervescent couple used in antacid tablets, vitamin C supplements, and analgesic formulations. Upon contact with water, the acid-base reaction generates carbon dioxide, which disperses the active ingredient and masks unpleasant tastes. Citric acid also serves as a buffering agent in ophthalmic solutions, injectable formulations, and oral syrups to maintain pH stability. Its calcium-chelating property is exploited in anticoagulant citrate dextrose (ACD) and citrate phosphate dextrose (CPD) solutions used for blood collection and storage, where citrate binds ionized calcium and inhibits the coagulation cascade. 3. **Green Descaling and Cleaning Agent**: Citric acid effectively dissolves calcium carbonate (limescale), rust (iron oxides), and soap scum through acid dissolution and chelation. A 5–10% aqueous solution heated to 60–80 °C removes boiler scale, coffee maker deposits, and bathroom mineral buildup. It is the active ingredient in 'green' descaling products for espresso machines, dishwashers, and washing machines. Unlike hydrochloric acid-based descalers, citric acid does not corrode stainless steel at typical use concentrations and its spent solutions are safe for septic systems. 4. **Crosslinking Agent in Biodegradable Polymers**: Citric acid serves as a non-toxic, bio-based crosslinker for polysaccharide and protein-based materials. The three carboxylic acid groups can form ester bonds with hydroxyl groups on cellulose, starch, chitosan, and poly(vinyl alcohol), creating crosslinked networks that improve mechanical strength, reduce water solubility, and impart antimicrobial properties. Citric acid-crosslinked starch films and coatings are being developed as biodegradable packaging alternatives to petroleum-derived plastics. The crosslinking reaction is thermally activated (120–150 °C) and does not require organic solvents or toxic catalysts. ## Frequently Asked Questions ### What is the CAS number of Citric Acid? The CAS Registry Number is **77-92-9**. This unique identifier is registered with the Chemical Abstracts Service and serves as the authoritative reference for chemical substance identification in scientific literature, regulatory filings, and commercial transactions. When ordering Citric Acid from any supplier, specifying the CAS number ensures you receive the correct compound regardless of naming variations. ### What is the molecular weight of Citric Acid? The molecular weight is **192.12 g/mol** based on the molecular formula **C₆H₈O₇**. This value is calculated from the standard atomic weights of the constituent elements and represents the mass of one mole of the compound. For synthetic planning, use this value to calculate molar equivalents and prepare solutions of known concentration. ### What is Citric Acid used for? Citric Acid is primarily used as a organic acid / food additive in organic synthesis and related chemical processes. The specific applications depend on the particular research or industrial context. For detailed application information, consult the product sections above or refer to the supplier's technical documentation and published synthetic protocols. ### How should Citric Acid be stored? Store Citric Acid in a cool, dry, well-ventilated area away from incompatible materials including strong oxidizing agents, strong acids, and sources of ignition. Keep the container tightly closed when not in use. Always consult the Safety Data Sheet (SDS) from your specific supplier for the most accurate and up-to-date storage recommendations, as conditions may vary by purity grade and formulation. ### Where can I buy Citric Acid? Citric Acid (CAS 77-92-9) is available from major chemical suppliers. Availability, pricing, and purity grades vary by supplier and region. Check the product sourcing section for CoreyChem availability or contact our sales team for sourcing assistance and bulk quotation. ### What is the purity of commercial Citric Acid? Commercial Citric Acid is typically available at ≥97% purity from major chemical suppliers. Higher purities (≥99%) may be available for specialized applications in pharmaceutical manufacturing and analytical standards. Always verify the specific purity grade and certificate of analysis (CoA) with your supplier before use in critical applications. ## Where to Buy **Citric Acid is available in the CoreyChem catalog.** [View Citric Acid (CAS 77-92-9) on CoreyChem →](https://careerchemical.com/product/77-92-9)