Citric acid
IUPAC name	2-hydroxypropane-1,2,3-tricarboxylic acid
Other names	3-hydroxypentanedioic acid-3-carboxylic acid Hydrogen citrate
Identifiers
CAS number	[77-92-9]
PubChem	311
Properties
Molecular formula	C6H8O7
Molar mass	192. IUPAC Nomenclature is a system of naming Chemical compounds and of describing the science of Chemistry in general CAS registry numbers are unique numerical identifiers for Chemical compounds Polymers biological sequences mixtures and Alloys They are also referred to PubChem is a Database of chemical Molecules The system is maintained by the National Center for Biotechnology Information (NCBI a component A chemical formula is a way of expressing information about the Atoms that constitute a particular Chemical compound, and how the relationship between those atoms changes Molar mass, symbol M, is the Mass of one mole of a substance ( Chemical element or Chemical compound) 123 g/mol (anhydrous) 210. 14 g/mol (monohydrate)
Appearance	crystalline white solid
Density	1. The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different 665 g/cm³
Melting point	153 °C
Boiling point	decomposes at 175 °C
Solubility in water	133 g/100 ml (20°C)
Acidity (pKa)	pKa1=3. The melting point of a solid is the temperature range at which it changes state from solid to Liquid. The Celsius Temperature scale was previously known as the centigrade scale. The boiling point of a liquid is the temperature at which the Vapor pressure of the liquid equals the environmental pressure surrounding the liquid Solubility is the characteristic Physical property referring to the ability of a given substance the Solute, to dissolve in a Solvent. Water is a common Chemical substance that is essential for the survival of all known forms of Life. 15 pKa2=4. 77 pKa3=6. 40
Hazards
Main hazards	skin and eye irritant
Flash point	?°C
Related compounds
Related compounds	sodium citrate, calcium citrate
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Citric acid is a weak organic acid. Occupational safety and health is a cross-disciplinary area concerned with protecting the Safety, Health and welfare of people engaged in The flash point of a flammable liquid is the lowest Temperature at which it can form an ignitable mixture in air Sodium citrate usually refers to Trisodium citrate, though it can refer to any of the sodium Salts of Citric acid: Monosodium citrate Calcium citrate is the Calcium salt of Citric acid. It is commonly used as a Food additive ( E333) usually as a Preservative In Chemistry, the standard state of a material is its state at 1 bar (100 Kilopascals exactly Organic chemistry is a discipline within Chemistry which involves the scientific study of the structure properties composition reactions, and preparation In Computer science, ACID ( Atomicity Consistency Isolation Durability) is a set of properties that guarantee that Database transactions are It is a natural preservative and is also used to add an acidic, or sour, taste to foods and soft drinks. A preservative is a natural or synthetic chemical that is added to products such as foods pharmaceuticals paints biological samples wood etc Soft drink is a beverage that does not contain Alcohol. Carbonated soft drinks are commonly known as soda soda pop pop, or In biochemistry, it is important as an intermediate in the citric acid cycle and therefore occurs in the metabolism of almost all living things. Biochemistry is the study of the chemical processes in living Organisms It deals with the Structure and function of cellular components such as The citric acid cycle, also known as the tricarboxylic acid cycle ( TCA cycle) or the Krebs cycle, (or rarely the Szent-Györgyi–Krebs cycle Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life. Life is a state that distinguishes Organisms from non-living objects such as non-life and dead organisms being manifested by growth through Metabolism It also serves as an environmentally benign cleaning agent and acts as an antioxidant. An antioxidant is a Molecule capable of slowing or preventing the oxidation of other molecules

Citric acid exists in a variety of fruits and vegetables, most notably citrus fruits. The term fruit has different meanings dependent on context and the term is not synonymous in Food preparation and Biology. Citrus is a common term and Genus of Flowering plants in the family Rutaceae, originating in tropical and subtropical southeast regions of Lemons and limes have particularly high concentrations of the acid; it can comprise as much as 8% of the dry weight of these fruits (1. The lemon ( Citrus × limon) is a hybrid in cultivated wild plants Lime is a term referring to a number of different fruits (generally Citruses, both Species and hybrids, which are typically round green to yellow 44 and 1. 38 grams per ounce of the juices, respectively^[1]). For other uses of the words gram or gramme see Gram (disambiguation. This article is about the unit of mass For the unit of force see Pound-force.

Properties

Citric acid crystal under polarized light, enlarged 200x

At room temperature, citric acid is a white crystalline powder. It can exist either in an anhydrous (water-free) form or as a monohydrate. As a general term a substance is said to be anhydrous if it contains no Water. Hydrate is a term used in Inorganic chemistry and Organic chemistry to indicate that a substance contains Water. The anhydrous form crystallizes from hot water, whereas the monohydrate forms when citric acid is crystallized from cold water. The monohydrate can be converted to the anhydrous form by heating it above 74 °C. Citric acid also dissolves in absolute (anhydrous) ethanol (76 parts of citric acid per 100 parts of ethanol) at 15 degrees Celsius.

In chemical structure, citric acid shares the properties of other carboxylic acids. Carboxylic acids are Organic acids characterized by the presence of a Carboxyl group, which has the formula -C(=OOH usually written -COOH or -CO2H When heated above 175 °C, it decomposes through the loss of carbon dioxide and water. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single Water ( H2[[oxygen O]] H OH) is the most abundant Molecule on Earth 's surface composing of about 70% of the Earth's surface as

Measurement

Citric acid has been used as an additive to soft drinks, beer, and seltzer, and occurs naturally in many juices. This causes a problem in measurement because the standard measuring technique for sugar is refractive index. The refractive index of sugar and citric acid is almost identical. For soft drinks and orange juice the best measure of sweetness is the sugar/acid ratio. Recently, the use of infrared sensors has allowed measurement of both Brix (sugar content) and acidity by detecting sugars and citric acid through their characteristic molecular vibrations; this gives an accurate assessment of a drink's sweetness. Degrees Brix (symbol °Bx is a measurement of the dissolved Sugar -to-water mass ratio of a liquid

History

Lemons, oranges and other citrus fruit contain high concentrations of citric acid.

The discovery of citric acid has been credited to the 8th century alchemist Jabir Ibn Hayyan (Geber). The 8th century is the period from 701 to 800 in accordance with the Julian calendar in the Christian / Common Era. Alchemy a part of the Occult Tradition is both a philosophy and a practice with an ultimately unknown aim involving the improvement of the alchemist as well as the making of For the 12th century astronomer see Jabir ibn Aflah. For the anonymous 14th century Spanish alchemist see Pseudo-Geber. Medieval scholars in Europe were aware of the acidic nature of lemon and lime juices; such knowledge is recorded in the 13th century encyclopedia Speculum Majus (The Great Mirror), compiled by Vincent of Beauvais. An encyclopedia (or '''encyclopædia''') is a comprehensive written Compendium that contains Information on either all branches of Knowledge The Dominican friar Vincent of Beauvais ( Vincentius Bellovacensis) (c Citric acid was first isolated in 1784 by the Swedish chemist Carl Wilhelm Scheele, who crystallized it from lemon juice. Year 1784 ( MDCCLXXXIV) was a Leap year starting on Thursday (link will display the full calendar of the Gregorian calendar (or a Leap year "Sverige" redirects here For other uses see Sweden (disambiguation and Sverige (disambiguation. Carl Wilhelm Scheele (9 December 1742 &ndash 21 May 1786 was a German - Swedish pharmaceutical chemist born in Stralsund, Western Pomerania, Industrial-scale citric acid production began in 1860, based on the Italian citrus fruit industry. Italy (Italia officially the Italian Republic, (Repubblica Italiana is located on the Italian Peninsula in Southern Europe, and on the two largest

In 1893, C. Wehmer discovered that Penicillium mold could produce citric acid from sugar. Penicillium (from Latin penicillus: paintbrush) is a Genus of Ascomyceteous Fungi that includes WikipediaManual_of_Style#National_varieties_of_English --> Molds (or Sugar is a class of edible Crystalline substances mainly Sucrose, Lactose, and Fructose. However, microbial production of citric acid did not become industrially important until World War I disrupted Italian citrus exports. World War I (abbreviated WWI; also known as the First World War, the Great War, and the War to End All In 1917, the American food chemist James Currie discovered that certain strains of the mold Aspergillus niger could be efficient citric acid producers, and Pfizer began industrial-level production using this technique two years later, followed by Citrique Belge in 1929. Year 1917 ( MCMXVII) was a Common year starting on Monday (link will display the full calendar of the Gregorian calendar (or a Common year The United States of America —commonly referred to as the Aspergillus niger is a Fungus and one of the most common species of the genus Aspergillus. Pfizer Incorporated ( is a major Pharmaceutical company, which ranks number one in the world in sales Citrique Belge or Citric Belge, located in Tienen is a Belgian biotech company and one of the biggest producers of Citric acid.

Production

In this production technique, which is still the major industrial route to citric acid used today, cultures of Aspergillus niger are fed on a sucrose or glucose-containing medium to produce citric acid. Aspergillus niger is a Fungus and one of the most common species of the genus Aspergillus. Solubility of Pure SucroseTemperature(Cg Glucose (Glc a Monosaccharide (or simple Sugar) also known as grape sugar, is an important Carbohydrate in Biology. The source of sugar is corn steep liquor,^[2] molasses, hydrolyzed corn starch or other inexpensive sugary solutions. Molasses or Treacle is a thick Syrup by-product from the processing of the Sugarcane or Sugar beet into Sugar. Cornstarch, or cornflour, is the Starch of the Maize grain commonly known as Corn. ^[3] After the mold is filtered out of the resulting solution, citric acid is isolated by precipitating it with lime (calcium hydroxide) to yield calcium citrate salt, from which citric acid is regenerated by treatment with sulfuric acid. Precipitation is the formation of a Solid in a Solution during a Chemical reaction. Calcium hydroxide, traditionally called slaked lime, hydrated lime, or pickling lime, is a Chemical compound with the chemical formula Sulfuric (or sulphuric acid, H 2 S[[oxygen O]]4 is a strong Mineral acid.

Krebs cycle

Main article: Citric acid cycle

Citric acid is one of a series of compounds involved in the physiological oxidation of fats, proteins, and carbohydrates to carbon dioxide and water. The citric acid cycle, also known as the tricarboxylic acid cycle ( TCA cycle) or the Krebs cycle, (or rarely the Szent-Györgyi–Krebs cycle A chemical compound is a substance consisting of two or more different elements chemically bonded together in a fixed proportion by Mass. Physiology (from Greek grc φύσις physis, "nature origin" and grc -λογία -logia) is the study of the mechanical physical Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state Fats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl Carbohydrates (from ' Hydrates of Carbon ' or saccharides ( Greek σάκχαρον meaning " Sugar " are the most

This series of chemical reactions is central to nearly all metabolic reactions, and is the source of two-thirds of the food-derived energy in higher organisms. Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life. A chemical reaction is a process that always results in the interconversion of Chemical substances The substance or substances initially involved in a chemical reaction are called In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός It was discovered by Sir Hans Adolf Krebs. Hans Adolf Krebs ( August 25, 1900 – November 22, 1981) was a German, later British Medical doctor and Krebs received the 1953 Nobel Prize in Physiology or Medicine for the discovery. The Nobel Prize in Physiology or Medicine (Nobelpriset i fysiologi eller medicin is awarded once a year by the Swedish Karolinska Institute. The series of reactions is known by various names, including the citric acid cycle, the Krebs cycle, and the tricarboxylic acid cycle (or TCA cycle).

Uses

In 2007 world wide annual production stands at approximatley 1700. 000 MT/y. More than 50% of this volume is being produced in China. More than 50% is being used as acidulent in beverages and some 20% in other food applications. 20% is being used for detergent applications and 10% for other non food related applications like cosmetics and chemical industry.

Food additive

As a food additive, citric acid is used as a flavouring and preservative in food and beverages, especially soft drinks. Food additives are substances added to food to preserve flavour or improve its taste and appearance Alternate meanings Seasoning (cast iron; Seasoning (wood; Seasoning (slave Seasoning is the process of imparting or improving Food is any substance usually composed primarily of Carbohydrates Fats water and/or Proteins that can be eaten or drunk by an A drink, or beverage, is a Liquid specifically prepared for Human consumption It is denoted by E number E330. E numbers are number codes for Food additives and are usually found on Food labels throughout the European Union. Citrate salts of various metals are used to deliver those minerals in a biologically available form in many dietary supplements. The M acro E xpansion T emplate A ttribute L anguage complements TAL, providing macros which allow the reuse of code across The buffering properties of citrates are used to control pH in household cleaners and pharmaceuticals. For an aqueous solution composed of both a weak acid or base and its conjugate see Buffer solution. pH is the measure of the acidity or alkalinity of a Solution. In the United States the purity requirements for citric acid as a food additive is defined by the Food Chemical Codex (FCC), which is published by the United States Pharmacopoeia (USP). The United States Pharmacopeia is an official public standards–setting authority for all prescription and over–the–counter medicines and other health care products manufactured

Water softening

Citric acid's ability to chelate metals makes it useful in soaps and laundry detergents. Chelation is the binding or complexation of a bi- or multidentate Ligand. SOAP (see below for name and origins is a protocol for exchanging XML -based messages over Computer networks normally using A detergent (as a noun is a material intended to assist Cleaning. By chelating the metals in hard water, it lets these cleaners produce foam and work better without need for water softening. Hard water is the type of Water that has high Mineral content (in contrast with Soft water) In a similar manner, citric acid is used to regenerate the ion exchange materials used in water softeners by stripping off the accumulated metal ions as citrate complexes. Ion exchange is an exchange of Ions between two Electrolytes or between an electrolyte Solution and a complex. A water softener reduces the dissolved Calcium, Magnesium, and to some degree Manganese and Ferrous iron ion concentration in Hard water

Others

Citric acid is used in the biotechnology and pharmaceutical industry to passivate high purity process piping (in lieu of using nitric acid). Passivation is the process of making a material "passive" in relation to another material prior to using the materials together Nitric acid ( H[[nitrate NO3]] also known as Aqua fortis and spirit of nitre, is a highly corrosive and Nitric acid is considered hazardous to dispose once used for this purpose, while citric acid is not.

Citric acid is the active ingredient in some bathroom and kitchen cleaning solutions. A solution with a 6% concentration of citric acid will remove hard water stains from glass without scrubbing. In industry it is used to dissolve rust from steel. ^[4]

Citric acid is commonly used as a buffer to increase the solubility of brown heroin. Heroin ( INN: diacetylmorphine, BAN: diamorphine) is a semi-synthetic opioid synthesized from Morphine, a derivative Single-use citric acid sachets have been used as an inducement to get heroin users to exchange their dirty needles for clean needles in an attempt to decrease the spread of AIDS and hepatitis^[5]. Hepatitis (plural hepatitides) implies injury to the Liver characterized by the presence of Inflammatory cells in the tissue of Other acidifiers used for brown heroin are ascorbic acid, acetic acid, and lactic acid; in their absence, a drug user will often substitute lemon juice or vinegar. This article deals with the molecular aspects of ascorbic acid Acetic acid, also known as ethanoic acid, is an organic chemical compound, giving Vinegar its sour taste Lactic acid ( IUPAC Systematic name: 2-hydroxypropanoic acid) also known as milk acid, is a Chemical compound that plays a role Vinegar is an acidic liquid processed from the Fermentation of Ethanol in a process that yields its key ingredient Acetic acid (also called ethanoic acid

Citric acid is one of the chemicals required for the synthesis of HMTD, a highly heat-, friction-, and shock-sensitive explosive similar to acetone peroxide. Hexamethylene triperoxide diamine ( HMTD) is a High explosive Acetone peroxide ( triacetone triperoxide, peroxyacetone, TATP, TCAP) is an Organic peroxide and a primary High Purchases of large quantities of citric acid may rouse suspicion of potential terrorist activity.

Citric acid can be added to ice cream to keep fat globules separate, and can be added to recipes in place of fresh lemon juice as well. Citric acid is used along with sodium bicarbonate in a wide range of effervescent formulae, both for ingestion (e. Sodium bicarbonate or sodium hydrogen carbonate is the Chemical compound with the formula NaHCO3 g. , powders and tablets) and for personal care (e. g. , bath salts, bath bombs, and cleaning of grease). The term bath salts refers to a range of water-soluble usually inorganic solid products designed to be added to a bath either to improve cleaning provide a medical improvement A bath bomb, one form of bath fizzie is a bolus which when placed in bath water dissolves partly or completely and effervesces also in some cases adding scent color and/or other properties Petroleum ( L petroleum, from Greek πετρέλαιον, lit

Citric acid is commonly employed in wine production as a substitute or improver where fruits containing little or no natural acidity are used. Citric acid aids fermentation and is used in preference to other acids, for example tartaric acid, due to its stability, pleasant flavour and ability to impart brilliance to the finish wine.

When applied to hair, citric acid opens up the outer layer, also known as the cuticle. Hair is a keratinised protein filament that grows through the epidermis from follicles deep within the Dermis. While the cuticle is open, it allows for a deeper penetration into the hair shaft. It can be used in shampoo to wash out wax and coloring from the hair. Shampoo is a Hair care product used for the removal of oils, dirt skin particles Dandruff, environmental pollutants and other contaminant particles that It is notably used in the product "Sun-in" for bleaching, but is generally not recommended due to the amount of damage it causes.

Citric acid is also used as a stop bath in photography. Stop bath is the second of three chemical baths usually used in processing traditional black-and-white Photographic films plates and paper. Photography (fә'tɒgrәfi or fә'tɑːgrәfi (from Greek φωτο and γραφία is the process and Art of recording pictures by means of capturing The developer is normally alkaline, so a mild acid will neutralize it, increasing the effectiveness of the stop bath when compared to plain water. ^[6]

Citric acid is used as one of the active ingredients in the production of anti-viral tissues. ^[7]

The concentrations of citric acid in citrus fruits such as oranges and grapefruits is approximately . 005 mol/L. The concentration of citric acid is higher for others, approximately . 030 mol/L, in citrus fruits such as lemons and limes. These values will vary depending on the circumstances in which the fruit was grown.

Safety

Citric acid is recognized as safe for use in food by all major national and international food regulatory agencies. It is naturally present in almost all forms of life, and excess citric acid is readily metabolized and eliminated from the body.

Contact with dry citric acid or with concentrated solutions can result in skin and eye irritation, so protective clothing should be worn when handling these materials.

Excessive consumption is capable of eroding the tooth enamel. Tooth enamel is the hardest and most highly mineralized substance of the body and with Dentin, Cementum, and dental pulp is one of the four major

Close contact to the eyes can cause a slight burning sensation, and may cause loss of sight.

Sometimes a high concentration of citric acid can damage hair, since it opens hair cuticles. It can strip the hair of needed minerals and bleach it.

See also

• Citric acid intolerance
• Citric acid cycle
• The closely related acids isocitric acid, aconitic acid, and propane-1,2,3-tricarboxylic acid (tricarballylic acid, carballylic acid)

References

• Citric Acid MSDS Sheet

External links

• CID 311 from PubChem
• Citric acid analysis - free spreadsheet for titration of acids and pH calculation
• Applications of Citric Acid